Intoxication, inflammaging, and injury: my journey through leukocyte biology

Abstract

Senior author E.J.K. writes: As a scientist, teacher, research mentor, and mom, I asked myself, “what is my legacy?” Legacies usually have numbers associated with them. When asked this question in the past, I summed my accomplishments in terms of who, not what. First and foremost, I have my daughter, Cathy, and then scores of spectacular lab trainees (N > 130), many of whom have contributed to the tally of “lab babies.” At present, 79 lab babies (Cathy, of course, being lab baby 1; there is also 1 lab “grandchild”). Together, we are the “Kovacs Empire.” Watching the trainees develop into clinicians/scientists/parents and more has been among the greatest joys of my career, and seeing their kids grow up is an added bonus. Of course, other numbers could be thrown into the mix. For example, I have published >300 papers and have been funded by the US National Institutes of Health for >29 consecutive years (along with multiple local, national, other federal funding agencies) and, importantly, have helped launch the careers of many mentees from my lab and elsewhere. The “Kovacs Babies in the Empire” email list is broad and gives me an excuse to check in with the group relatively frequently. The other part of my “legacy,” of course, is the money I have earned. Sorry to the lab members and readers who expect a cut of this: it all goes to Cathy.

1. Preface (by E.J.K.): The journey begins.

I was born in New York City (NYC) and grew up with two amazing parents (Barbara and George) and a brother (Peter), who is 13 months my senior. What drove me to become a scientist, a teacher, and a mentor? To answer that I need to go back to before I was born. My mother was an artist (born in Brooklyn, NY, to parents from Poland and Ukraine), and my father was a lamp manufacturer (born in Vienna, Austria, to Austrian parents and sent at age 11 to England by his mother via the Kindertransport on the first train from Vienna after Kristallnacht). My parents met in NYC when they were in college. Shortly after their marriage, my mother received a Fulbright scholarship to study art in Vienna, Austria, and they were off globetrotting. Returning to NYC the following year, they settled in Manhattan. Years after they passed away, my brother told me our parents had considered relocating to Denver, partly to escape my mother’s parents, who, although they were refugees themselves, wanted my mother to marry an American and not a refugee. They changed their tune when Peter and I were born and when my father’s lamp business, called George Kovacs, started making money.

I grew up on 93rd Street near Lexington Avenue (technically, the “upper east side” of Manhattan, but not the posh part). Peter briefly attended the local public elementary school in East Harlem. On the third day of school, 1 of his little classmates showed Peter his knife; on the fourth day, Peter was enrolled in a private school on the upper west side (Columbia Grammar and Preparatory School). Being 1 year behind my brother in a small private school created some challenges for me. I had many of his former teachers, and two of them asked why I was not as good as my brother. (This foreshadows my self-inflicted sibling competition and lifelong imposter syndrome.)

Peter is/was brilliant in almost everything academic, and he loved politics and economics. In high school, he read The New York Times, while I lied about where I was spending the weekend and hitchhiked across New England with friends. Peter had straight As and perfect SAT scores. I was better at sports and excelled in misbehaving. I liked art, math, and science classes (mostly because Peter did not). In high school, I followed in my mother’s footsteps as an artist and sculpted life-size statues of children commandeering the school’s art classroom. I won art awards, sold some of my works, and started a business, called “Liz Kovacs Creations,” which may or may not still be on the books as a company in NYC.

In high school, I played volleyball, basketball, and field hockey—alas, no soccer; at that time, soccer was only for boys. I also volunteered at my neighborhood hospital, Mount Sinai Medical Center, and, after a year of being a “candy striper” (the only hospital opportunity for a 15-year-old girl), I was able to work my way up to volunteering in labs. Because of my interest in science, when applying to college I asked my high school biology teacher, Jules Alexander, for a letter of recommendation. Years later, I found out that he wrote something like “great artist, mediocre scientist.” He and others suggested that with my dual interest in art and science, I should consider careers in art restoration or plastic surgery. As you know, I chose neither. Peter went to Brown University in Providence, RI, and I elected to attend Reed College in Portland, OR (~3,000 miles from home in NYC). I chose Reed for multiple reasons, including not thinking I was Ivy League material (imposter syndrome, again) and as a way to get as far away from my brother as possible.

Starting my first semester at Reed, without a declared major, I was given an Art History professor as my faculty advisor. As a freshman, my worst subjects in college were the sciences. I got a C in introductory chemistry, and I did surprisingly well in humanities. I tried to manage both art and science coursework during my freshman year. After enrolling in and dropping a sculpture class, because we were asked to sculpt out of corrugated cardboard and I wanted to use more sophisticated media, like clay, wood, and stone, I quickly learned that I could not be an art major at a liberal arts college. Because I took Advanced Placement (AP) biology in high school, I skipped introductory college biology and, as a freshman, I began my biology training taking upper-level classes. My first biology class was upper-class cell physiology, that Reed was intellectually intimidating is an understatement. Everyone was in the top 5% to 10% of their high school classes, or so they said. Most of the time, I felt stupid.

One of the few things that helped preserve my sanity at Reed was playing soccer. As a freshman, I joined the men’s soccer club. There was no women’s team. By my second year, I found enough women interested in playing soccer and started a women’s soccer club, which I named the Reed Lemmings (foreshadowing something?). That year, I also began working on graduating from college in 3 years. At that time, only about 75% of “Reedies” graduated in 4 years, mostly because they took a year off during college to work, travel, or do something amazing, very few (~1%) were “allowed” to graduate in 3 years. With AP credits and summer school classes, I wanted to try. Doing so would enable me to obtain a Bachelor of Arts (BA) degree approximately 4 weeks before my brother got his BA (from Brown). (Remember: “It’s not a competition, but it is.”) Reed College requires students to write a thesis, and I chose the field of neuroscience, long before it was trendy. By far, my favorite undergraduate class was “Neural Basis of Behavior” taught by Dr. Dell Rhodes. I worked over the summer in the lab of Dr. Dorothy Krieger in Endocrinology at Mount Sinai Hospital in NYC, studying circadian rhythms, which involved collecting blood from rats every 4 hours for 48 hours. I continue research for my undergraduate thesis with Dr. Vaughn Critchlow at the University of Oregon Health Sciences Center. In the Critchlow lab, I performed survival brain surgery on rats, ran radio-immune assays, and conducted neuroanatomic analysis in a project designed to determine whether the medial forebrain bundle was responsible for maintaining circadian rhythms. At the conclusion of the work, when brains were analyzed, we found that the brain lesions were incomplete, hence, the research was inconclusive. As a result, I gave up neuroscience for over 2 decades.

After Reed, I spent a year back in NYC at Columbia University. I took graduate courses, taught undergraduate introductory biology at Barnard College, and played a lot of soccer for multiple women’s teams, including the Budweiser Eagles. It was during that year that I fell in love with teaching and wanted to escape from NYC (again). The following year, I matriculated into the Graduate Cell Biology Program at the University of Vermont (UVM), in Burlington, VT.

Because my Graduate Record Examination scores were less than stellar, I was not given a full scholarship but rather was awarded only tuition remission (with no stipend for living expenses). To make ends meet, sort of, I was hired by the UVM athletics department as the assistant coach to the women’s varsity soccer team. The job “paid” $75/week and covered most of my room and board, allowing me to live in an unheated attic bedroom of a house and to leave the lab at 3 PM to “play/coach” soccer five afternoons/week. I was charged with training the team’s three want-to-be goalkeepers. Note that I had never played goalie. (More imposter syndrome?) Anyway, compared with NYC, living in Burlington was magical, until I found out how cold it could get in the winter.

The following year, I was given a teaching fellowship, which paid slightly better than coaching soccer, and I jumped on the opportunity because it allowed me to teach undergraduate biology classes. I continued playing soccer for the Eagles, and they covered my commuting costs from Burlington to New York. We played in soccer tournaments up and down the East Coast, including against teams from other countries and in huge arenas, like the Meadowlands in New Jersey, where we were the opening act before a match in which Pelé played. That year, I was chosen to represent NYC in the Empire State Games. During one of those matches, an opponent’s slide tackle tore my posterior cruciate ligament, mangled my medial meniscus, and chipped a bone, ending my thoughts about being professional soccer player. I have had 9 knee operations, including, decades later, 2 knee replacements.

Back in graduate school in Vermont after the first operation, my knee needed to be in the whirlpool every day for several weeks. At the time, immunology was in its infancy, relative to today. The “textbooks” were tiny portable paperback books. Because the immunology books were smaller than my massive biochemistry and physiology text, I read the immunology books while soaking my knee in the whirlpool. That helped me earn an A⁺ in immunology in the first half of the semester. Later, when my knee had healed enough to give up the whirlpool, my immunology reading was reduced and grades tanked. I got a C in immunology. At that time, immunology was almost exclusively T cells and B cells. Because of my disappointing grade in the class and the lymphocyte focus, I have always thought of myself as a cell biologist who happens to work with immune cells. If innate immunity had been part of the curriculum, in those days, I might have done much better in the course.

My doctor of philosophy (PhD) research was on lung fibrosis and the role of alveolar macrophages in a rat model. That experience triggered my love of the macrophage (my favorite cell), which resided in my favorite inflatable organ, the lung (Fig. 1). Some people have a favorite molecule, some love a cell type, others an organ, or a disease. For me, it was anything related to monocytes/macrophages and innate immunity, long before the term was popularized. Feeling fatalistic, I chose to defend my dissertation on the Ides of March in 1984, 4 years after starting graduate school.

Figure 1.

E.J.K. and her inflatable lungs at an SLB meeting (circa 2015).

When looking for postdoctoral fellowships, I circled the United States exploring options at about a dozen universities and research centers. My first interview was at the National Cancer Institute in the laboratory of Dr. Joost J. (Joe) Oppenheim at the Frederick Cancer Research Center in the Biological Response Modifiers Program. (The NIH loves abbreviations!) The group had just relocated from Bethesda to Frederick, MD, on the campus of Fort Detrick. Because I thought if I worked at the NIH, it should be in Bethesda, I treated this as a “practice interview.” I was surprised to see how enthusiastic and dynamic the group was. Unlike several of my other job talks, the audience members actually listened to my research presentation, asked questions, and even offered me reagents (antibodies) to test in my model. I was hooked. Importantly, Joe Oppenheim told me with whom I should work (and whom I should avoid). Howard Young, PhD, was highest on the “should” list. Howard, a molecular biologist, had joined the Biological Response Modifiers Program the prior year after working as the head of technical services at a biotech company. Joe thought that I could teach Howard some immunology and he would teach me molecular biology. I guess Joe did not look at my immunology grade.

Prior to accepting the postdoctoral position, I invited Joe (whom I then called Dr. Oppenheim) to visit the UVM and give a seminar. Seminars were on Mondays, and because it was over the winter, I boldly asked Joe if he wanted to come up over the weekend before the seminar and bring family members, stay at my house, and go skiing. I do not know what I was thinking. Anyway, to my surprise, he took me up on this and brought his 13-year-old daughter. Not only did we spend a day skiing, Joe and his daughter stayed with me, Joe paid for my lift ticket, and he changed the flat tire on my car on the way to the mountains. While driving from Burlington to the mountains, I asked him to tell me about himself, because I needed to introduce him when he gave his lecture the following day. I expected him to tell me where he went to college, medical school, and so forth. Instead, he described his childhood in Holland. During the 2-hour drive, he told me about being a hidden child with his younger brother during World War II, and much more. It was not until later that I told him about my father’s experience as a Kindertransport child sent from Austria to England.

As suggested by Joe, I worked with Howard Young and mastered the molecular biology methods of the day, including RNA isolation, Northern blot analysis, cloning genes, plasmid preps, DNA isolation, and ³²P labeling. While Howard loved interferon-γ and T lymphocytes, I wanted to work on macrophages and sought help from a macrophage collaborator, Dr. Luigi Varesio. I collaborated with anyone who needed help with molecular biology experiments and, as a result, was quite prolific. One of the first of the 21 papers I published as a postdoctoral fellow was on DNA methylation of the interleukin-1β (IL-1β) gene and mRNA expression¹—and it was published in the Journal of Leukocyte Biology (JLB). (Note that with this work I studied epigenetics long before it was trendy.)

About a year into my postdoctoral training, I was told that if I wanted to stay for a second year, I needed a job offer to prove my worth, so at age 28, I began hunting for a faculty position. I had given a couple of lectures at a local community college, Hood College, allowing me to think/hallucinate that I was ready to take on a full teaching load along with my research. I interviewed for faculty jobs at multiple universities and found that Loyola University Chicago’s (LUC) Department of Anatomy (as it was called back then) was looking for a tenure-track assistant professor to teach histology to medical students. I had never taken histology and thought that with the colorful histologic images and my background in art, it would be easy to teach. I was wrong and stayed barely a chapter ahead of the students. (Note: To continue our sibling rivalry, my brother kept reminding me “those who can do and those who can’t teach.”).

When I started as a beginning assistant professor, during the last millennium, my job was probably not that different from what it would be like today: teach a lot, do research, and be a mentor to the next generation of scientists. What was somewhat unexpected, and definitely unplanned, was also becoming a mom and, 14 months into my faculty appointment, I gave birth to Cathy. Although there is never a good time in a woman’s career to have kids, Cathy came into the world while I was launching my lab and about 1 month after I broke up with her father. If it were not for pictures and very supportive parents and friends, I probably would not remember much about her first year of life. In those days, LUC had no maternity-leave policy, and I was back at work full time 4 weeks after having a cesarean section delivery. I put a playpen bed and a swing in my office and stacked it with diapers and onesies. I did not ask permission; I just brought my kid to work for 6 months, until she got a slot in the day care. When I had to teach, I would either take her with me or one of the graduate students or staff would babysit, often in my office. When I went to conferences out of town, I either brought her with me (she went to Europe four times before she turned 2 years old) or my mother would fly in from NYC to stay with her. Later, I hired graduate and medical students to babysit or left Cathy with close friends.

Several years after I started my lab at LUC, an internationally renowned burn surgeon-scientist, Richard Gamelli, MD, moved his lab from UVM to LUC to create a research institute conducting shock and trauma research. The Burn and Shock Trauma Institute (BSTI) was founded and, when the group moved into a newly built research building, I joined them (who could pass on new lab space?). A few years later, after my burn research program matured, Dr. Gamelli formally “kidnapped” me and moved my NIH grants from the Department of Cell Biology, Neurobiology, and Anatomy (renamed) to the Department of Surgery. I discuss more about my research trajectory later; for now, note that John Clancy gave me a job and Richard Gamelli gave me a career.

In 2015, I was able to escape from a Chicago winter and do a “skibattical” at the University of Colorado in tropical Denver. This was more of a mental health break after my mother passed away in NYC. I was in Colorado for 92 days, skied for 26 of those days, and learned about clinical research (from hanging out with collaborators Drs. Ellen Burnham and Marc Moss, in the Department of Medicine). After 6 weeks in Colorado, I started asking department chairs in Colorado and elsewhere to hire me. I did not look for jobs the usual way, hunting for posted positions. I chose to pick a few places where I might want to live and work and sent my curriculum vitae (CV) and a cover letter. One such introductory email was quickly typed on my phone from the Keystone Ski Resort parking lot and I attached my CV. It worked, and ~10 years ago, I moved to Colorado with 3 members of my lab. The rest is history.

In summary, after coming to the realization that a professional soccer career was off the table, I obtained a PhD in Cell Biology (in 4.5 years) followed by 2 years of postdoctoral training at the National Cancer Institute’s Biological Response Modifiers Program in Frederick, MD, before accepting the first of my two (yes, only two) academic positions at LUC on April 1st, 1987. Because my birthday is on April 5th and I was wanting a position as tenure-track assistant professor before turning 30, I was thrilled to have been able to achieve that at the age of 29.9836 years.

My second faculty appointment started 29 years later, to the day, at the University of Colorado on April 1st, 2016. For those of you who, like me, have imposter syndrome, starting new jobs on April Fool’s Day is very appropriate.

2. The Society for Leukocyte Biology and life lessons from Liz

For those who are old enough to remember, the Society of Leukocyte Biology (SLB) used to be called the Reticuloendothelial Society, and JLB was the Journal of the Reticuloendothelial Society. In graduate school (during the last millennium), I published my first “first authored” paper on macrophages-derived factors in acute lung injury² in the JLB, shortly after the journal name transitioned. In my naïveté, I thought it was a bad thing to have my paper in this “new journal.” Little did I know the influence that the Journal and SLB would have on me and my career.

I joined SLB when I was a postdoctoral researcher (postdoc) at the NIH. I am sure it was Joe Oppenheim who told me about the Society and he “voluntold” me to get involved by showing up at meetings and opening my mouth. Joe had two rules for his postdocs: (i) you had to ask a question at a session at every conference and (ii) you had to bring slides with you even if not scheduled to give a podium presentation. You never knew if someone might be unable to make it to the conference, and those who had slides with them might suddenly have the opportunity to give an oral presentation. (Note that in those days, “slides” meant actual Kodachrome slides. This was long before digital presentations [ie PowerPoint] became the norm). Perhaps through connections like being part of “Team Oppenheim” I got an early seat at the table and served on just about every SLB committee, beginning in the 1990s as a junior council member. A decade later I was again on the council, prior to being elected president, serving as program chair, and becoming a life-long groupie. Along the way I learned that accomplishing things is personally rewarding but also that if you want to achieve your goals, you must promote yourself. (Note that Joe Oppenheim told me “if you don’t brag about your accomplishments, who will?” I suggest repeating this out loud at least once a day until it sinks in.)

SLB has been my professional home. I was given leadership opportunities and brought trainees to meetings to give them the opportunities I was afforded. To me, SLB meetings are like a college homecoming or reunion—a chance to see colleagues and friends over the years while also developing scientific relationships and collaborations. Additionally, it is a society through which I have recruited multiple trainees (graduate students → postdocs) and even a couple of tenure-track assistant professors. Because I attended most SLB meetings from the 1990s onward, when a scheduling conflict kept me away, a number of my SLB colleagues reached out to see if I was al-right. That, to me, says a lot about what makes SLB special: it is not simply a scientific society; it is a community.

Mentoring the next generation of scientists is important to me, and SLB has provided countless opportunities to contribute to that mission. I participated in and/or co-organized scores of SLB educational and career development activities, including, a “Grant Writing Workshop”³ and “Street Smarts of Science for Students.”⁴ Both of these workshops were written up as publications in Nature Immunology as communications. I was also a panel member or speaker in multiple sessions for the Committee on Women and Diversity and gave presentations on “Best Practices for Job Talks in Academia” and “Finding Mentors.”

Among the other life lessons I learned early in my career is that everyone has something to teach and we all learn from each other. Part of that is pushing the agenda of being on a first-name basis with everyone, what I like to call “lower-archy” (the opposite of hierarchy). Those who know me well are aware I prefer being called Liz, not Dr. Kovacs (or Elizabeth). (Note that the only person who has to call me Dr. Kovacs is my brother.)

When I started my career in academia, there were far more men than women in leadership. Sad to say, that ratio has not changed much. In any case, as a young woman assistant professor, who had to pick up her toddler from day care on time or face a $1/minute late fee, I needed to learn to say “no” to things. Serving on numerous committees at my university, possibly to show another female face, because I was competent, or both, I had to learn to limit these other activities. To accomplish this, I put and, still have, a sticky note on my wall between my computer screen and my telephone that simply says “NO!!” Although “NO!!” did not necessarily mean I would not say yes, it just reminded me to take a moment or a day to think about it and not automatically agree to be on a committee or take on a task without having time to think it over.

Lastly, two other important lessons I learned over the course of my career are (i) to be open to new research ideas opportunities and (ii) to consider working on something of interest to your boss. The latter might encourage them to toss some funding in your direction (more on this later). This is clearly a situation for another of my personal mottos: “If you don’t ask, you won’t get.” I asked. And I got not only $6,000 but also a career.

3. On to research

In the following 3 subsections, I describe embarking on projects focused on alcohol intoxication, burn injury, and aging and their intersection. Then my coauthors and I describe subsequent research in my lab.

3.1.1. Project 1. Alcohol intoxication and burn injury research and how it started.

At LUC in the BSTI, I was in the ladies’ room chatting with a research nurse, Vicky McGill, who was writing a paper on inflammatory mediators in burn patients, some of whom were intoxicated at the time of injury. Instead of making small talk about the weather or local sports teams, I asked what kinds of patients there were in the Burn Intensive Care Unit (ICU). She said that young adult burn patients who drank before they sustained their injuries had a worse prognosis than comparably injured nondrinkers. That conversation led me to explore alcohol and burn injury, and Dr. Richard Gamelli (the BSTI boss) gave me a small amount of funding, just $6,000, to develop a mouse model of alcohol intoxication and burn injury. That small grant turned into nearly 3 decades of continuous NIH funding. Thus, it was serendipity and a moment of curiosity that changed the course of my career—clearly one of the better returns on investment: starting with $6,000 and bringing in more than 29 years of NIH R-level funding.

3.1.2. Project 2. “Inflammaging” and burn injury research and how it started.

About a year later, in the same women’s bathroom in BSTI, I ran into the same research nurse and was told that older burn patients do not do as well as young adult burn victims. My response was “duh,” and I embarked on aging and burn injury research. That work has been funded by NIH for 23 years.

3.1.3. Project 3. Alcohol and Aging Research and How it Started.

My interest in combing research in aging and alcohol was sparked when I observed the assisted-living establishment in which my mother lived on the upper west side of Manhattan. The facility had a mediocre, nearly empty gym (despite the amazing view of Hudson River and the George Washington Bridge) and a well-attended, dynamic happy hour. I knew alcohol suppressed immunity, increasing susceptibility to infections, and is metabolized more slowly in older individuals, including those taking medications for their age-related comorbidities. My mother was never a drinker; however, I worried about all the other grandparents who might miss out on the important family event, graduation, or wedding because they might contract a respiratory infection. This drove me to begin to explore the effects of alcohol exposure on lung, in the absence of burn injury, and on other favorite organs in the context of infectious challenges. When a grant reviewer accused me of being “a below-the-neck researcher,” it pushed me to examine neuroinflammation and cognitive impairment in older inebriated individuals.

3.2. From curiosity to discovery

What began with a series of unexpected conversations and observations evolved into 3 decades of NIH-funded research that reshaped understanding of trauma, aging, alcohol biology, and immunology. Across these studies, the Kovacs laboratory defined how diverse physiological stressors alter innate immunity, barrier function, and inflammatory signaling, while integrating clinical observations with mechanistic studies in experimental models. Together, this work revealed a unifying scientific theme: how physiological stressors disrupt immune homeostasis and drive systemic inflammation across multiple organ systems. The sections that follow trace the evolution of these discoveries, from alcohol-associated burn injury to aging, intestinal barrier biology, and gut-organ communication.

4. Project 1. Alcohol Intoxication and Burn Injury and How It Is Going

4.1. Alcohol intoxication worsens outcomes after burn injury

A major focus of the Kovacs research program has been defining how acute alcohol intoxication alters the host response to burn injury. Clinical studies in the late 1990s established that a substantial proportion of burn patients are intoxicated at the time of injury and experience significantly worse outcomes than nonintoxicated patients with comparable burns. At that time, despite reports that as many as 50% of burn patients presented with alcohol intoxication, little was known about how alcohol altered recovery after burn trauma.⁵ Subsequent studies from the Kovacs laboratory demonstrated that acute alcohol intoxication at the time of injury is associated with increased infection and mortality risk and further showed that most alcohol-positive burn patients were episodic rather than chronic drinkers, emphasizing the clinical importance of acute intoxication in burn trauma.^6,7 Clinical investigations demonstrated that acute alcohol intoxication at the time of burn injury is associated with increased injury severity, worse clinical outcomes, and heightened systemic inflammatory responses characterized by altered circulating cytokine profiles.^8,9 These clinical observations led to development of a murine model of acute ethanol exposure followed by burn injury that became the foundation for more than 2 decades of mechanistic studies. Using this model, the Kovacs laboratory systematically defined how alcohol alters immune function, disrupts intestinal barrier integrity, and promotes systemic inflammation and multiorgan injury after burn trauma.

4.2. Alcohol reshapes postburn immune responses

Early investigations established that acute ethanol exposure profoundly alters both innate and adaptive immune responses after burn injury.^10,11 Ethanol exposure before burn injury suppressed delayed-type hypersensitivity responses, reduced splenic T-cell proliferation, increased susceptibility to bacterial infection, and ultimately increased mortality compared with burn injury alone.^12–14 These studies provided some of the earliest evidence that acute alcohol intoxication directly compromises postburn host defense rather than simply increasing injury severity.

Subsequent mechanistic studies demonstrated that alcohol not only impairs lymphocyte function but also alters macrophage activity, increasing IL-6 production and further suppressing T-cell responses following the combined insult.^13,15–18 Together, these studies established that alcohol produces a complex immune phenotype characterized by impaired antimicrobial defense occurring alongside persistent inflammatory activation. This work changed the understanding of alcohol-associated burn injury by demonstrating that increased susceptibility to infection results from dysregulated immunity rather than generalized immunosuppression alone.

4.3. Alcohol amplifies pulmonary inflammation after burn injury

Pulmonary complications, including acute respiratory distress syndrome (ARDS), are a major cause of morbidity and mortality after severe burn injury, even in the absence of smoke inhalation,¹⁹ and alcohol intoxication substantially increases postburn complications.^5,6,8 Building on clinical observations, the Kovacs laboratory examined how alcohol intoxication alters inflammatory responses in the lung after burn injury. Early studies demonstrated that ethanol exposure before burn injury significantly increased pulmonary neutrophil accumulation, inflammatory cytokine production, and tissue edema compared with burn injury alone.^20,21 Histological analyses further showed that neutrophil infiltration begins within hours of injury and remains elevated for at least 24 h, indicating that alcohol both accelerates and prolongs pulmonary inflammation. Subsequent studies further demonstrated that alcohol-induced alterations in alveolar macrophage phenotype contribute to sustained pulmonary inflammation, impaired innate immune function, and the development of respiratory dysfunction after burn injury.^18,22,23

Mechanistic studies identified leukocyte-endothelial interactions as important mediators of this exaggerated response. Using intercellular adhesion molecule-1 deficient (ICAM-1–deficient) mice, the Kovacs laboratory demonstrated that loss of ICAM-1 reduced pulmonary neutrophil recruitment, inflammatory cytokine production, and lung injury after ethanol and burn injury, establishing endothelial activation as a critical component of alcohol-induced pulmonary inflammation.²⁴ Similarly, studies using Toll-like receptor–deficient (TLR-deficient) mice identified TLR4, but not TLR2, as a central regulator of pulmonary cytokine production and neutrophil recruitment after the combined insult.²⁵ Building on earlier studies, subsequent work showed that the presence of alcohol at the time of burn injury, rather than the pattern of prior alcohol exposure, is sufficient to worsen pulmonary inflammation, and later studies identified induction of the antimicrobial peptides cathelin-related antimicrobial peptide and S100 calcium-binding protein A8 (S100A8) as important components of the post-burn pulmonary inflammatory response.^26,27 Together, these studies demonstrated that alcohol enhances pulmonary inflammation through coordinated activation of endothelial adhesion pathways and innate immune signaling.

Importantly, this exaggerated inflammatory response did not improve host defense. Despite increased leukocyte recruitment, mice exposed to ethanol before burn injury had impaired bacterial clearance and significantly greater mortality following intratracheal Pseudomonas aeruginosa infection.²⁸ These findings reinforced a recurring theme throughout the Kovacs laboratory’s work: excessive inflammation and impaired antimicrobial immunity coexist after alcohol intoxication and burn injury.

4.4. The intestine as a driver of systemic inflammation after alcohol and burn injury

One of the most influential contributions from the Kovacs laboratory was demonstrating that the intestine is a central regulator of systemic inflammation after alcohol and burn injury. Independently, both insults impair intestinal barrier integrity. We reported that the combined injury markedly increased epithelial barrier dysfunction, bacterial translocation, and dissemination of gut-derived inflammatory mediators.^29–31 These findings shifted the intestine from being viewed as a passive target of injury to an active driver of multiorgan postburn inflammation.

Subsequent studies expanded this model by demonstrating that alcohol and burn injury also disrupt the intestinal microbiome. Clinical studies identified significant alterations in the fecal microbiota of burn patients both with and without recent alcohol exposure,^32,33 and preclinical mouse models demonstrated reduced microbial diversity together with increased epithelial apoptosis, disruption of tight junction proteins, and expansion of potentially pathogenic bacteria.^34–36 The Kovacs lab also demonstrated that acute ethanol intoxication exacerbates burn-induced neuroinflammation, and this is associated with disruption of blood-brain barrier integrity and greater dysbiosis of the gut microbiome, implicating the gut-brain axis as a key driver of postburn neurologic complications.³⁷ Collectively, these findings established intestinal barrier dysfunction and microbial dysbiosis as complementary mechanisms driving sustained systemic inflammation.

Mechanistic studies further demonstrated that preservation of intestinal barrier integrity reduces both gut and distal organ injury. Pharmacologic inhibition of myosin light-chain kinase preserved expression of the tight junction proteins zonula occludens-1 and occludin, and reduced bacterial translocation to mesenteric lymph nodes, attenuated intestinal inflammation, and protected against hepatic injury after ethanol and burn injury.³⁸ Furthermore, intestinal overexpression of the antimicrobial peptide regenerating islet-derived protein 3-γ (REG3γ) reversed intestinal barrier dysfunction, reduced bacterial translocation and, attenuated hepatic inflammation following ethanol intoxication and burn injury, identifying REG3γ as a novel therapeutic target.³⁹ Likewise, modulation of IL-6 signaling and reduction of intestinal bacterial burden decreased pulmonary inflammation and improved barrier function, providing proof-of-concept that interventions targeting the intestine can modify the systemic response to burn injury.^40,41

Taken together, these investigations transformed alcohol-associated burn injury from an organ-specific disorder into a systems-level disease driven by dysregulated immunity and loss of intestinal barrier homeostasis. By linking intestinal barrier dysfunction, microbial dysbiosis, bacterial translocation, and gut-derived inflammatory signaling with pulmonary and hepatic injury, the Kovacs laboratory established a gut-centered framework for understanding multiorgan dysfunction after alcohol and burn injury.^{29–31,38,40,41}

4.5. Therapeutic strategies to improve outcomes after alcohol and burn injury

In parallel with defining the mechanisms underlying alcohol-exacerbated burn injury, the Kovacs laboratory evaluated several therapeutic approaches to limit postburn inflammation and immune dysfunction. Early studies demonstrated that modulation of corticosterone and sex hormone signaling, including 17β estradiol treatment, improved immune function after burn injury.^15,42 Subsequent work identified IL-6 and IL-4 as key therapeutic targets, with cytokine blockade reducing inflammation and improving outcomes after ethanol and burn injury, and later studies further demonstrated the benefits of combining IL-6 inhibition with phosphoinositide 3-kinase inhibition or antibiotic therapy.^16,29,43 More recently, mesenchymal stem cell therapy was shown to attenuate pulmonary and hepatic inflammation, highlighting the potential of regenerative approaches to improve recovery after alcohol and burn injury.⁴⁴

5. Project 2. “Inflammaging” and burn injury and how it is going

The studies described in the preceding section established that burn injury and alcohol converge on common mechanisms of innate immune dysfunction, intestinal barrier dysfunction, microbial dysbiosis, and chronic systemic inflammation. The Kovacs laboratory elected to explore how advanced age altered the physiological response to burn injury and whether inflammation played a role. This work stemmed from reading about “inflammaging,” a term coined by Claudio Fransceschi as an evolutionary perspective on aging and immunosenescence.⁴⁵ Since then, extensive clinical and experimental evidence has revealed that healthy aged individuals are in an elevated basal inflammatory state, which can slow the immune system’s response to invading pathogens. Advanced age is among the strongest independent predictors of poor outcome after burn injury, with older patients experiencing increased mortality, delayed wound healing, infection, and multiple-organ dysfunction compared with younger adults.^19,46 Although these differences have long been recognized, the biological mechanisms remained poorly understood. The Kovacs laboratory demonstrated that advanced age reshapes the host response to burn rather than simply reducing physiological reserve,^46–49 establishing the mechanistic foundation for understanding why older adults experience disproportionately poor outcomes after burn injury. Clinical studies by our lab confirmed that these altered inflammatory responses correlate with poorer outcomes after burn and inhalation injury in older patients.⁵⁰

5.1. Advanced age reprograms postburn inflammatory and immune responses

A major contribution of Dr. Kovacs’ research program has been defining how aging medicates innate immune responses. Early studies demonstrated that macrophages from aged animals exhibit impaired cytokine production, reduced responsiveness to pathogen-associated stimuli, diminished phagocytic capacity, and defective bacterial clearance compared with cells from young animals.^51–54 Mechanistic investigations identified impaired TLR signaling and altered mitogen-activated protein kinase activation as important contributors to these defects.^55–57 Similar abnormalities were observed in pulmonary macrophages and Kupffer cells following systemic inflammatory challenge.^58–61 Collectively, these studies established that aging produces a dysregulated immune phenotype characterized by persistent inflammatory activation despite impaired host defense.

In further studies, our laboratory examined mechanisms by which advanced age alters immune responses after burn injury. Compared with young animals, aged mice exhibit reduced survival, impaired cell-mediated immunity, and heightened systemic IL-6 responses.⁴⁷ Rather than mounting a regulated inflammatory response, immune cells from older mice exhibit impaired pathogen sensing together with persistent inflammatory activation, contributing to delayed resolution of inflammation and increased susceptibility to secondary complications. Adaptive immunity is similarly impaired. Burn injury suppresses T-cell proliferation and shifts helper T-cell responses away from protective cell-mediated immunity in aged animals, reducing delayed-type hypersensitivity responses and altering cytokine production within secondary lymphoid tissues.^62–64 Additional studies demonstrated that 17β-estradiol treatment partially restored immune function after burn injury, highlighting complex interactions among aging, endocrine signaling, and immune regulation.^65–68 Together, these investigations established age-associated alteration in immune responses, as well as inflammaging, a major determinant of burn outcome, and provided the foundation for subsequent studies of the inflammatory response in multiple organs after burn injury.

5.2. Hepatic responses and systemic inflammation after burn injury in aged individuals

The liver also exhibits significant age-related alterations after burn injury. Earlier studies demonstrated oxidative injury during liver aging that may predispose hepatocytes to dysfunction after trauma.⁶⁹ Subsequent investigations revealed complex interactions among aging, IL-6 signaling, and the hepatic acute-phase response, including altered acute-phase protein production in aged IL-6–deficient mice and persistently elevated systemic IL-6 levels despite reduced macrophage production.^59,70 Burn injury also causes heightened hepatocyte apoptosis and mitochondrial dysfunction in aged mice.^71–75

5.3. The intestine and microbiome drive systemic inflammation in the aged burn host

Because the gut was a driver of inflammation in studies on ethanol intoxication and burn injury,^38,40,41 the Kovacs laboratory went on to explore whether advanced age amplifies intestinal dysfunction after burn injury. Although burn injury disrupts intestinal barrier integrity in both young and aged hosts, these defects are substantially greater in aged animals, resulting in increased intestinal permeability, bacterial translocation, and heightened systemic inflammation.⁷⁶ Elevated intestinal epithelial cell death in the ileum, together with increased expression of the damage-associated molecular pattern molecules S100A8 and S100A9, further perpetuate barrier dysfunction in aged, injured mice relative to comparably injured younger animals.^76,77 More recent work extended these findings by demonstrating that aging also impairs the regenerative capacity of the colonic intestinal epithelium following burn injury.⁷⁸ Aged burn-injured mice exhibit increased cellular senescence, reduced epithelial proliferation and stem cell-associated markers, enhanced apoptosis, and diminished antimicrobial peptide expression, suggesting that defective epithelial repair contributes to persistent barrier dysfunction after burn injury.⁷⁸

Advanced age also impairs intestinal antimicrobial peptide responses and exacerbates burn-induced microbiome dysbiosis in mice.⁷⁹ Aged burn-injured mice have reduced bacterial diversity, altered microbial community structure, and diminished postburn induction of antimicrobial peptides, including REG3 family proteins— changes that likely contribute to increased bacterial translocation.^77,79 Not surprisingly, clinical studies performed by the Kovacs group reveal that age and burn size influence the magnitude of dysbiosis along with correlations between microbial composition, short-chain fatty acid metabolites, and outcomes.⁸⁰ These observations support a central role for the gut and its microbial contents in regulating systemic inflammation after burn injury.^80–83

5.4. Pulmonary complications after aging and burn injury

The lungs are particularly vulnerable in aged burn victims, with remote injury triggering exaggerated inflammatory responses even in the absence of smoke inhalation injury.^84,85 C-X-C motif chemokine receptor 2 (CXCR2) and its ligands play central roles in age-related pulmonary pathology.^84,85 CXCR2 inhibition prevents age-associated increases in pulmonary inflammation after burn injury, identifying this pathway as a therapeutic target.⁸⁴ Combined dysregulation of neutrophil CXCR2 expression and pulmonary endothelial ICAM-1 levels promotes age-related inflammation.⁸⁵ Studies using lipopolysaccharide administration also revealed that advanced age exacerbates pulmonary inflammatory responses independent of burn injury.⁵⁸ The observed neutrophilic inflammation contributes to acute lung injury and may predispose elderly burn patients to ARDS.⁶¹ Subsequent studies further demonstrated that age-related intestinal dysbiosis is accompanied by enrichment of gut-associated bacterial taxa within the lung and increased susceptibility to Streptococcus pneumoniae infection, providing direct evidence that alterations in the intestinal microbiome influence pulmonary host defense through the gut-lung axis.⁸⁶ Although these findings were not generated in a burn model, they suggest that age-associated alterations in gut-lung axis may also contribute to the heightened pulmonary complications observed after burn injury in advanced age, when intestinal barrier dysfunction and dysbiosis are common.

Alveolar macrophages from aged mice also exhibit altered phenotypes and functional responses after burn injury.⁸⁷ These cells exhibit increased expression of inflammatory mediators while demonstrating impaired phagocytic capacity and bacterial clearance.⁸⁷ Transcriptional profiles reveal upregulation of genes associated with inflammaging and cellular senescence.⁸⁷ These alterations compromise pulmonary host defense and may contribute to the increased incidence of pneumonia observed in elderly burn patients.^88,89

5.5. Neuroinflammation and the gut-brain axis after burn injury

Given that multiorgan responses after burn injury in aged individuals are elevated and older burn patients suffer from delirium and cognitive impairment,^90,91 recent studies in the Kovacs lab focused on neuroinflammation. Cutaneous burn injury induces neuroinflammation and reactive astrocyte activation specifically in the hippocampus of aged mice, whereas young mice remain unaffected.⁹² Expression of inflammatory mediators, including C-C motif chemokine ligand 2 and tumor necrosis factor-α, increases significantly in brains of aged burn-injured mice.⁹² Immunofluorescence analysis reveals increased glial fibrillary acidic protein–positive astrocytes within hippocampal regions associated with neurotoxicity and cognitive decline.⁹² Aged mice also show reduced phosphorylated cAMP response element-binding protein (pCREB) staining in the dentate gyrus.⁹² This decrease in pCREB, combined with burn-induced neuroinflammation, likely contributes to cognitive dysfunction and delirium frequently observed in elderly burn patients. More recently, clinical studies by Dr. Kovacs’ lab have identified circulating biomarkers of central nervous system injury in burn patients, providing translational evidence that burn injury is associated with neurological dysfunction and supporting experimental findings implicating neuroinflammation as an important component of the systemic response to burn injury while highlighting the need for future studies to determine whether these biomarkers differ by age.⁹³

The connection between intestinal dysfunction and neuroinflammation represents a critical pathway in the pathophysiology after burn injury in the aged. Remote burn injury induces colonic lymphoid aggregate expansion and dysbiosis that correlates with neuroinflammation.⁹⁴ Increased intestinal permeability allows translocation of bacteria and bacterial products to mesenteric lymph nodes and to the central circulation, where they have access to the blood-brain barrier, possibly triggering neuroinflammation.^77,92 The correlation between fecal microbiome alterations and neuroinflammatory markers indicates that dysbiosis contributes to cognitive complications through gut-brain communication.^82,94

5.6. A systems-level framework for aging and burn injury

Collectively, these studies demonstrated that advanced age amplifies burn-induced immune dysfunction through coordinated effects on innate immunity, intestinal barrier integrity, microbial homeostasis, and communication among the gut, lung, liver, and brain.⁷⁷ This body of work established important conceptual frameworks for understanding aging and innate immunity,^51,52,95 animal models of systemic injury,⁴⁶ tissue-resident macrophage biology,^88,89,96 intestinal immunity and dysbiosis of the gut microbiome,^79,81 and gut-mediated multiorgan dysfunction after burn injury.⁷⁷ Similar to what was observed with ethanol exposure and bur injury, rather than viewing organ failures as independent events, these studies established an integrated systems-level model in which intestinal barrier dysfunction and microbial dysbiosis propagate inflammatory responses across multiple organs, providing the conceptual foundation for subsequent investigations into aging and alcohol.

6. Project 3. Aging and alcohol intoxication and how it is going

As life expectancy increases, understanding factors that affect healthy aging has become increasingly important. Lifestyle factors, including alcohol consumption, are increasingly recognized as contributors to age-related disease, and alcohol misuse among older adults continues to increase.^97,98 Older individuals are also more susceptible to the adverse effects of alcohol because age-associated physiological changes alter alcohol metabolism and tissue responses. Both aging and alcohol misuse independently exert profound effects on inflammatory homeostasis, and their convergence, as highlighted by Dr. Kovacs’ research program, amplifies these disruptions.^{34,39,83,99–102} As noted, in flammaging is associated with a chronic, low-grade inflammatory state, characterized by elevated levels of circulating cytokines, impaired resolution pathways, and dysregulated innate immune responses.⁴⁵ In parallel, alcohol misuse disrupts epithelial barriers, alters innate immune function, and promotes translocation of microbial products, leading to chronic systemic inflammation.¹⁰⁰ Collectively, these processes create a synergistic inflammatory environment that increases susceptibility to tissue injury and multiorgan dysfunction. Therefore, understanding the unique risks that alcohol poses to older adults became the focus of an additional line of research in the Kovacs lab. Following the discoveries in alcohol-associated trauma and aging described in the preceding sections, the laboratory researchers next sought to define the mechanisms through which aging increases susceptibility to alcohol-induced tissue injury.

6.1. Aging and alcohol converge on intestinal dysfunction

A major conceptual advance from the Kovacs laboratory was recognizing that the intestinal epithelium and microbiome are not simply bystanders but upstream drivers of postburn inflammation in combination with age and alcohol exposure. Extending this paradigm to aging and alcohol, moderate ethanol exposure produced substantially greater intestinal barrier dysfunction, inflammatory responses, and hepatic inflammation in aged mice than in young animals.¹⁰³ Importantly, gut-protective transcriptional responses that were activated in young animals were markedly blunted with aging, suggesting that impaired epithelial adaptation is a defining feature of alcohol susceptibility during advanced age. Concurrently, research findings by the Kovacs laboratory elevated the intestinal epithelium and microbiome from bystanders to upstream drivers of inflammaging during alcohol exposure in advanced age. Murine studies demonstrated that alcohol-induced barrier dysfunction is accompanied by alterations in microbial homeostasis that promote the translocation of gut-derived inflammatory mediators capable of activating tissue-resident macrophages and amplifying systemic inflammation.³⁴ Moderate ethanol exposure also suppresses antimicrobial peptides, including REG3β and REG3γ, in aged mice, while promoting age-dependent alterations in the intestinal microbiome.³⁴ These microbial changes correlated with intestinal and hepatic inflammatory gene expression, supporting the concept that impaired epithelial defense, microbial dysbiosis, and barrier dysfunction cooperate to amplify systemic inflammation during aging.³⁴ Together, these processes lower the threshold for inflammatory activation, creating a permissive environment for persistent gut-derived immune stimulation and exaggerated tissue injury.

6.2. Gut-organ communication amplifies inflammaging

Expanding on the gut-centered paradigm, the Kovacs laboratory demonstrated that the consequences of intestinal dysfunction extend well beyond the gastrointestinal tract. Rather than functioning as isolated organs, the intestine, liver, lung, and brain communicate through gut-derived microbial products, inflammatory mediators, and tissue-resident macrophages that amplify inflammatory signaling throughout the body.¹⁰⁰ Studies from the laboratory identified Kupffer cells, alveolar macrophages, and microglia as important downstream effectors linking the gut-liver, gut-lung, and gut-brain axes during aging and alcohol exposure.^83,101,103 Complementing these observations, multi-omics analyses demonstrated that aging alters hepatic responses to alcohol exposure, revealing coordinated transcriptional and metabolic changes that distinguish aged from young mice.¹⁰⁴ These findings further support the concept that advanced age reshapes tissue responses to ethanol and provide molecular insight into mechanisms linking alcohol exposure with age-related liver dysfunction.

Further work revealed that binge ethanol exposure produced exaggerated neuroinflammation and impaired contextual memory in aged mice compared with young animals.¹⁰¹ Mechanistic studies further demonstrated that activation of NF-κB and inflammasome signaling contributes to enhanced microglial activation and inflammatory responses in the aged brain after alcohol exposure.¹⁰² These findings extend the concept of inflammaging to the central nervous system and identify alcohol as a potentially important modifiable risk factor for age-related cognitive decline.¹⁰²

7. Concluding perspectives

In summary, Dr. Kovacs’s research program has transformed the understanding of how physiological stressors, including alcohol intoxication, burn injury, and aging, reshape innate immunity and systemic inflammation. Beginning with seminal studies defining immune dysfunction after ethanol intoxication and burn injury, the laboratory demonstrated that excessive inflammation and impaired antimicrobial defense coexist after injury and identified mechanisms responsible for increased susceptibility to infection and organ dysfunction. Subsequent investigations established that aging fundamentally alters the host response to injury and, together with alcohol exposure, converges on shared mechanisms of intestinal barrier dysfunction, microbial dysbiosis, and chronic inflammation that drive multiorgan injury. Across these distinct models, the Kovacs laboratory consistently identified the intestinal barrier and microbiome as central regulators of systemic inflammation, establishing a unifying framework in which gut-derived signals coordinate immune dysfunction through the gut-liver, gut-lung, and gut-brain axes.

Collectively, this body of work has unified previously distinct areas of investigation by demonstrating that burn injury, alcohol exposure, and aging converge on common mechanisms of intestinal barrier dysfunction, microbial dysbiosis, and macrophage dysregulation, amplifying inflammation across the lung, liver, and brain and contributing to systemic immune dysfunction and multiorgan injury (Figure 2). Through the integration of clinical observations with mechanistic studies, Dr. Kovacs’s laboratory established the intestine as a central regulator of systemic inflammation and defined how tissue-resident innate immune cells coordinate inflammatory responses across the gut-liver, gut-lung, and gut-brain axes. These discoveries have provided a conceptual framework that continues to shape investigations of inflammation and organ injury while identifying preservation of intestinal barrier integrity, maintenance of microbial homeostasis, and restoration of immune resilience as promising therapeutic strategies for improving outcomes in vulnerable patient populations. By revealing the shared mechanisms linking local tissue injury, immune dysregulation, and systemic inflammation, Dr. Kovacs’s research has established a lasting framework for understanding host responses to injury and aging that continues to influence basic discovery, translational research, and clinical practice.

Figure 2.

Overview of macrophage-mediated integration of systemic and gut-derived signals driving multiorgan inflammation after alcohol intoxication, aging, and burn injury. Alcohol intoxication, age-associated inflammaging, and burn injury, independently and in combination, trigger systemic inflammation, accumulation of damage-associated molecular patterns (DAMPs), dysfunction of the intestinal epithelial barrier, and dysbiosis of the gut microbiome, which lead to translocation of microbial products and metabolites. These signals converge on macrophages to activate dysregulated TLR, mitogen-activated protein kinase (MAPK) (p38/c-Jun N-terminal kinase [JNK]), and inflammasome pathways, increasing proinflammatory cytokines, including IL-6, TNF-α, and IL-1β, while impairing phagocytic activity. Activated tissue-resident macrophages amplify inflammation in distal organs, including the lung (alveolar macrophages), liver (Kupffer cells), and brain (microglia), contributing to acute lung injury and ARDS, hepatic injury, and neuroinflammation. Collectively, these pathways promote an overexuberant systemic proinflammatory response leading to aberrant immune responses, impaired host defense, increased susceptibility to infection, and multiorgan dysfunction. Created in BioRender. Mcmahan, R. (2026) https://BioRender.com/ij2dcvf.

Key Concepts.

1. Intoxication and advanced age heighten inflammatory responses after burn trauma.

2. Activation of proinflammatory pathways leads to immune dysregulation and tissue damage resulting in organ failure.

3. Burns are more than skin deep, and the gut plays a critical role in mediating systemic and organ-specific inflammation after burn trauma.

Open questions.

1. How do second hits, including intoxication and infection, modulate systemic responses to burn injury?

2. What are the multiorgan responses to burn injury and are there organ-specific therapeutic agents that can limit excessive tissue damage and accelerate repair?

3. Which microbial products, metabolites, and immune mediators are responsible for communication between the intestine and distant organs?

4. Can circulating biomarkers of intestinal injury, neuroinflammation, or immune dysfunction identify patients most likely to develop organ failure?

Data availability

This is a review of the literature and no novel datasets are presented; therefore, no data are stored or available to share.