Table 1.

Summary of human epidemiologic and in vitro studies of arsenic exposure and altered immune response during pregnancy and/or early life

Author	Year	Country	Population	Study design	Immune focus	As level	Primary outcomes	Main results
Heaney et al.	2015	Bangladesh	Pregnant women	Nested case-control study	Humoral immunity	Median 61.6 and 65.6 ppb Σurinary arsenic in the non-seroconverting and seroconverting groups, respectively during the first trimester	Authors assessed the urinary arsenic species, HEV-specific serum IgG, and serum cytokines in enrolled women in the first and third trimester as well as 3 months postpartum.	The authors found that the odds ratio of maternal HEV seroconversion was 2.17 per IQR increase in urinary inorganic arsenic plus methylated species (ppb). Serum IL-2 concentration was also found to be positively correlated with increasing maternal urinary arsenic concentration in both seroconverters and non-seroconverters.
Ser et al.	2014	Bangladesh	Pregnant women	Prospective cohort study in pregnant women	Humoral immunity	3.1–1356 ppb range in urine	The authors measured total maternal serum IgG as well as cord blood total IgG along with maternal urinary arsenic species.	Increasing arsenic exposure results in a greater concentration of maternal serum IgG, but not cord blood IgG.
Kile et al.	2014	Bangladesh	Pregnant women	Prospective cohort study in pregnant women	Humoral and cell-mediated immunity	<1–1400 ppb range in drinking water	Authors assessed drinking water arsenic at enrollment along with self-reported symptoms at four visits during pregnancy and after birth.	When analyzing all symptoms together, women in the highest quartile of arsenic exposure were more likely to experience any symptoms than women in the lowest quartile. Notably, women in the second quartile (0.9–2 ppb arsenic) were protected against symptoms (95% CI 0.44–0.88). When looking at individual symptoms alone, women in the highest arsenic exposure quartile were significantly more likely to experience nausea/vomiting and abdominal cramping than women in the lowest quartile. Risk of cold/flu/respiratory infection was the same across quartiles.
Saha et al.	2013	Bangladesh	Children	Prospective cohort in children 2–5 years of age	Humoral and cell-mediated immunity	Low (mean 6.6 ppb) and high (mean 291.8 ppb) arsenic in urine	The authors measured urinary arsenic species and serum C3 and C4 concentrations. Cholera-specific, diphtheria-specific, tetanus-specific, and measles-specific antibodies were also measured, and the cholera antibody vibriocidal activity was assessed.	Diphtheria and tetanus-specific IgG were higher in the high arsenic-exposed group when compared to the low arsenic-exposed children as well as serum concentrations of C3 and C4. No differences were noted in the vibriocidal activity of the postimmunization antibodies of high-arsenic vs. low-arsenic-exposed children nor a difference between measles-specific igG levels.
Farzan et al.	2013	USA	Pregnant women and infants	Prospective cohort study in pregnant women in New Hampshire	Humoral and cell-mediated immunity	0.01–67.5 ppb range in drinking water; 0.45-58.3 ppb range in urine	Relative risk of respiratory or other infection in infants was calculated in relation to a onefold increase in maternal urinary arsenic on a natural logarithmic scale.	Risk of lower respiratory tract infections was significantly positively associated with increasing maternal arsenic exposure.
Rahman et al.	2011	Bangladesh	Pregnant women and infants	Prospective cohort study in pregnant women and their newborns	Humoral and cell-mediated immunity	1–1211 ppb range in urine	The authors assessed urinary arsenic levels in pregnant women at GW8 and GW30 along with infant morbidity and mortality by 7-day recall during monthly postnatal follow-up visits.	Risk of lower respiratory tract infection, severe lower respiratory tract infection, and diarrheal illness in the first year of life increased by 69, 54, and 20% when comparing infants in the highest quintile of maternal urinary arsenic with those in the first quintile. Risks for lower respiratory tract infections were more pronounced when based on late gestation maternal urinary arsenic, while risk of diarrheal illness was more pronounced when based on early gestational urinary arsenic.
Raquib et al.	2009	Bangladesh	Pregnant women and infants	Prospective cohort study in pregnant women and their newborns	Humoral and cell-mediated immunity	1–2020 ppb range in urine	The authors assessed urinary arsenic levels in pregnant women at GW8 and GW30 along with infant thymic index and lactoferrin and IL-7 in breastmilk at 12 months postpartum. Additionally, the authors looked at maternal diarrheal disease and fever as well as infant acute respiratory infection.	The authors found that increasing maternal urinary arsenic concentration was inversely correlated with infant thymic index and lactoferrin and IL-7 in breastmilk, as well as positively associated with maternal morbidities and acute respiratory illnesses in male infants only.
Kile et al.	2014	Bangladesh	Infant cord blood	Prospective cohort study in pregnant women	Cell-mediated immunity	<1–510 ppb range in drinking water	Whole cord blood DNA methylation was measured along with drinking water arsenic.	Maternal arsenic exposure was associated with differential cord blood DNA methylation at various CpG sites. Increased methylation was found at CpG sites within genes such at the TNFR superfamily member 10b and CD151. Additionally, increased maternal arsenic was associated with a decreased percentage of CD4+ and an increase in percentage of CD8+ in the cord blood.
Nadeau et al.	2014	USA	Pregnant women and infants	Prospective cohort study in pregnant women in New Hampshire	Cell-mediated immunity	5.7 ± 10.8 ppb (mean ± SD) in drinking water	Authors measured maternal urinary arsenic concentration along with drinking water arsenic concentration. They further measured cord blood leukocyte populations by flow cytometry, cord blood T cell proliferation, and cord blood mononuclear cell gene expression.	Authors found that increasing maternal arsenic exposure was positively correlated with placental IL-1β expression (a potent pro-inflammatory cytokine), cord blood T cell proliferative capacity, and changes in cord blood naïve T cell subsets.
Bailey et al.	2014	Mexico	Pregnant women and infants	Cross-sectional study of pregnant women and their newborns	Cell-mediated immunity	<0.456–236 ppb range in drinking water	Maternal drinking water and urinary arsenic species were determined within 4 weeks of delivery. Fetal cord blood was assessed for proteomic composition.	Proteomic analysis revealed 111 developmental and immune response proteins that were significantly altered (either in an activated or repressed state) with relation to maternal urinary arsenic species. Activator status in male newborns was associated with lower average urinary arsenic, DMA in urine, and neonatal head circumference than repressor males. Pathway analysis revealed TNF as a potential regulator of this urinary arsenic-cord blood proteome relationship.
Ahmed et al.	2014	Bangladesh	Children	Prospective cohort study of children	Cell-mediated immunity	12–1228 μg/L urine range, adjusted by specific gravity	Prenatal and early life arsenic exposure was determined utilizing urinary arsenic species from pregnant mothers and children at 4.5 years of age.	The highest quartile of childhood urinary arsenic concentration was associated with a significantly lower plasma IL-2 concentration when compared with all lower quartiles.
Burchiel et al.	2014	USA	Healthy adult donors	In vitro	Cell-mediated immunity	0, 0.1, 1, 10, 100 nM As3+ or MMA3+	Proliferative ability of PBMCs from healthy individuals was assessed after exposure to As3+ or MMA3+.	Authors uncovered differential susceptibility of PBMCs to low-dose arsenic exposure revealed by reduced proliferative capacity when stimulated with anti-CD3 antibody in vitro. Additionally, arsenic-exposed PBMCs from “susceptible” individuals exhibited altered CD4 subset populations.
Ahmed et al.	2012	Bangladesh	Pregnant women and infants	Prospective cohort study in pregnant women and their newborns	Cell-mediated immunity	17-481 ppb (5-95 percentile) range at gestational week 8 or 14 in urine	Authors measured maternal urinary, placental, and cord blood arsenic as well as assessing cord blood oxidative stress markers and cord blood PBMC gene expression and sjTREC concentration.	Arsenic concentrations (from all sources) were found to be positively correlated with cord blood oxidative stress and inversely related to expression of several antioxidant genes in cord blood mononuclear cells and sjTREC concentration.
Smith et al.	2011	Chile	Adults	Retrospective cohort study of adults	Cell-mediated immunity	∼10–870 ppb range depending on the time period	Authors utilized historical data on arsenic concentrations in municipal water supplies in Antofagasta, Chile, since the 1950s as well as death certificates over this period of time.	The authors found a significant association between periods of high arsenic exposure through municipal drinking water and tuberculosis mortality, using a 5-year latency period.
Luna et al.	2010	Mexico	Children	Cross-sectional study of children	Cell-mediated immunity	12.3–1411 μg/g of creatinine in urine	Arsenic exposure was determined through analysis of urine. Nitric oxide and superoxide anion production from PBMCs and isolated peripheral blood monocytes was determined before and after ex vivo stimulation.	Authors identified significant positive associations between inorganic arsenic species in urine and basal levels of nitric oxide in PBMCs and monocytes as well as an association between urinary DMA and basal superoxide anion levels in PBMCs. Authors also noted that superoxide anion production in stimulated monocytes was positively correlated with all species of urinary arsenic.
Vega et al.	1999	Mexico	Healthy adult donors	In vitro	Cell-mediated immunity	0, 0.01, 0.1, 1 μM	Authors assessed proliferative ability and IL-2 secretion of primary human PBMCs via stimulation with phytohemagglutinin at various arsenic concentrations. They also looked at IL-2 mRNA concentration, intracellular IL-2 concentration, and electron microscopy of arsenic-exposed cells.	The authors found that increasing arsenic concentrations were inversely correlated with proliferative ability of PBMCs as well as their ability to secrete IL-2, up to 1 μM, at which dose, a few individuals’ PBMCs produced more IL-2. Additionally, the authors found that IL-2 mRNA was unaffected by increasing arsenic dose, while intracellular IL-2 increased slightly, perhaps because of a lack of secretion. Electron microscopy revealed severe morphological changes in PBLs treated with 0.01 μM sodium arsenite.
Vega et al.	2004	Mexico	Healthy adult donors	In vitro	Cell-mediated immunity	0, 0.01, 0.1, 1 μM	Authors assessed proliferative ability and IL-2 secretion of primary human PBMCs via stimulation with phytohemagglutinin at various arsenic concentrations. They also performed flow cytometry on stimulated cells.	The authors confirmed earlier findings that increasing doses of arsenic suppress PBMC proliferation, particularly in cells from female donors (except for a small increase in proliferation of cells over control from female donors at the lowest dose, 1.3 ppb). Flow cytometry of stimulated cells revealed that CD4+ T cell populations were severely decreased in cells from female donors at 130 ppb, while CD8+ T cells remained unaffected. This assay also revealed that activated T cells are more susceptible to arsenic toxicity than resting T cells.
Smith et al.	2013	Bangladesh	Children	Retrospective cohort study of children	Asthma and spirometry	0–1512 ppb	Arsenic in drinking water sources throughout pregnancy and early life were assessed through a combination of recall questionnaires and historical arsenic data collected from all local tube wells. Children’s lifetime morbidity information was assessed via questionnaire.	Authors found that children in the highest in utero arsenic exposure category had significantly elevated OR of asthma, wheezing while not having a cold, and shortness of breath when walking fast or on flat ground.