Immunodeficiency secondary to anti-cytokine autoantibodies

Abstract

Purpose of review

Anti-cytokine autoantibodies are an important and emerging mechanism of disease pathogenesis. We will review the clinical and laboratory features of syndromes in which immunodeficiency is caused by or associated with neutralizing anti-cytokine autoantibodies.

Recent findings

A growing number of patients have been described who demonstrate unique infectious phenotypes associated with neutralizing autoantibodies that target a particular cytokine known to participate in host defense against the offending organism.

Examples include

anti-granulocyte macrophage-colony stimulating factor (GM-CSF) autoantibodies and pulmonary alveolar proteinosis; anti-interferon(IFN)-γ autoantibodies and disseminated nontuberculous mycobacteria(NTM); anti-(interleukin)IL-6 autoantibodies and severe staphylococcal skin infection; anti-IL-17A, antiIL-17F or anti-IL-22 autoantibodies in patients with mucocutaneous candidiasis in the setting of both the autoimmune polyendocrinopathy, candidiasis, ectodermal dystrophy (APECED) syndrome and in cases of thymoma.

Summary

Anti-cytokine autoantibodies have manifestations that are diverse, ranging from asymptomatic to life-threatening. These emerging and fascinating causes of acquired immunodeficiency may explain some previously idiopathic syndromes.

Introduction

Anti-cytokine autoantibodies are increasing as important mechanisms of disease pathogenesis. Their manifestations are diverse but they are often caused by a single polyclonal anti-cytokine IgG autoantibody. Examples include pulmonary alveolar proteinosis (PAP), due to anti-granulocyte macrophage colony stimulating factor (GM-CSF) autoantibodies; disseminated nontuberculous mycobacterial (NTM) disease due to anti-interferon(IFN)-γ autoantibodies; and pure red-cell aplasia (PRCA) due to anti-erythropoietin (EPO) autoantibodies. Anti-EPO antibodies do not result in immunodeficiency, but anti-IFN-γ autoantibodies may cause severe immunodeficiency. Although anti-GM-CSF autoantibodies, when causing disease, primarily result in severe and chronic lung disease due to PAP, case reports indicate that some patients with PAP have unusual pulmonary and extrapulmonary infections, correlated with in vitro evidence that their antibodies cause both macrophage and granulocyte dysfunction[1,2]. Finally, other diseases such as autoimmune polyendocrinopathy, candidiasis, ectodermal dystrophy (APECED) syndrome and thymoma [3**,4**] demonstrate high-titer neutralizing autoantibodies against multiple cytokines that may be acting in concert to impair host defense, although their direct role in disease causation remains to be definitively established.

While primary congenital immunodeficiencies tend to present early in life, anti-cytokine autoantibody syndromes tend to present in adulthood as a milder phenocopy of the congenital form, effecting a natural history that may wax and wane, depending on dynamic processes such as antibody titer or avidity. Given the accumulation of reports of new pathologic autoantibodies such as anti-osteoprotegerin autoantibodies associated with severe osteoporosis[5*] in some patients with celiac disease [5] and anti-IL-17 or anti-IL-22 autoantibodies associated with some chronic mucocutaneous candidiasis(CMC)[3,4] and practically boundless number of both endogenous soluble factors and clinical manifestations, there are likely to be many important anti-cytokine autoantibodies awaiting identification.

Text of Review

We will describe recent reports of anti-cytokine autoantibodies with particular focus on those that cause immunodeficiency (table 1) [6-22]. These reports identify individuals with an inappropriate production of specific (or possibly multiple) high-titer, neutralizing autoantibodies which, by blocking a given cytokine signalling pathway, can explain a particular clinical syndrome. Using other recent examples of anticytokine autoantibodies (which may or may not be associated with infectious complications) we hope to illustrate not only the complexity of anti-cytokine autoantibody phenomena but also how a better understanding of them lends itself to developing new treatments and gaining a deeper understanding of infection and inflammation (figure 1).

Table 1.

Clinical and biological evidence for contribution of anticytokine autoantibodies to disease pathogenesis

Cytokine target	Biological rational in vivo	Supporting evidence in vitro	Supporting evidence in vivo	Comments
G-CSFa	G-CSF critical for differentiation and  expansion of neutrophils; autoantibodies  associated with neutropenia in Felty’s  syndrome [6]c	IgG fraction of some of the patients with  anti-G-CSF autoantibodies inhibited cell  survival and proliferation in a G-CSF/ILb-3  dependent cell line [6]	Neutropenia	Associated with patients with  Felty’s syndrome and systemic lupus erythematosus
GM-CSFc	GM-CSF critical for differentiation of  monocytes to alveolar macrophages which  play important role in metabolism of surfactant.  Hallmark of PAPd is accumulation of surfactant  (reviewed by [2]	Serum from patients with PAP inhibits growth  of GM-CSF dependent cell line; identified as  neutralizing IgG autoantibody present in  bronchoalveolar lavage fluid and serum	BAL fluid contains large foamy  macrophages or monocyte-like  macrophages and elevated  levels of surfactant proteins	Pulmonary and extra-pulmonary infections with Nocardia,  Aspergillus, Proteus, Cryptococcosis  and disseminated Histoplasmosis  reported. Many of these reports are  prior to known cause of PAP  (anti-GM-CSF autoantibodies)
IL-6	IL-6 signaling mediated by STATe-3 [7] and  defects in STAT-3 result in severe  staphylococcal skin infections; autoantibodies to  IL-6 associated with recurrent staphylococcal skin infection [8]	Neutralizing IL-6 autoantibodies prevented  STAT-3 phosphorylation and production of  C-reactive protein (CRP) mRNA in Hep3B  cell line [8]	Severe staphylococcal skin infection with  undetectable CRP during episodes of  severe infection with other markets of  systemic inflammation (fever, elevated  neutrophil count) [8]	Only one case reported to date
IL-17	Genetic diseases which resulting in susceptibility  to Candida demonstrate impaired Th17  function [9,10,11*,12*]	Anti-IL-17A autoantibodies in APECED patients  inhibited IL-17A-induced IL-6 production  in human fibroblasts; no in-vitro assessment  of biological activity of IL-17F antibodies	Patients with APECED syndrome and  two patients with thymoma and fCMC  demonstrated neutralizing autoantibodies  to IL-17A and/or IL-17F [3**,4**]	Some patients with these  autoantibodies do not have CMC;  others without these autoantibodies  do have CMC
IL-22	IL-22, coexpressed in Th17 cells [13], plays a  role in mucosal immunity [14*,15]	No assessment of biological activity of IL-22  autoantibodies	Patients with APECED syndrome and two  patients with thymoma and CMC  demonstrated neutralizing autoantibodies  to IL-22 [3**,4**]	Some patients with these  autoantibodies do not have CMC; others without these autoantibodies  do have CMC
IFNg-γ	IFN-γ is critical for monocyte activation and  host control of mycobacterial infections;  defects in this pathway result in severe  opportunistic infection with nontuberculous  mycobacteria (NTM) [16]	Autoantibodies block IFN-γ-stimulated STAT-1  phosphorylation as well as IL-12 and TNF-α  production by monocytes	High-titer highly neutralizing IgG anti-IFN-γ  autoantibodies identified in patients with  severe disseminated NTM infection and  no other evidence of immunodeficiency  [17–21,22*]	11 of 14 reported cases of Asian  descent

^aGranulocyte-colony stimulating factor.

^bIL, interleukin.

^cGM-CSF, granulocyte macrophage-colony stimulating factor.

^dPAP, pulmonary alveolar proteinosis.

^eSTAT, signal transducer and activator of transcription.

^fCMC, chronic mucocutaneous candidiasis.

^gIFN, Interferon.

Figure 1.

Examples of currently known anti-cytokine autoantibodies syndromes.

Anti-interferon-γ autoantibodies and disseminated nontuberculous mycobacterial infection

IFNγ is elaborated predominantly by activated T helper 1(T_H1) cells and is central to host defense against mycobacteria and other intracellular pathogens. It signals via the IFN-γ receptor (IFN-γR), located primarily on monocytes and leads to phosphorylation and activation of downstream signaling molecules such as signal transducer and activator of transcription (STAT)1. STAT1 becomes phosphorylated and homodimerizes then translocates to the nucleus and initiates transcription of IFN-γ responsive genes that facilitate macrophage differentiation and elaboration of inflammatory mediators including TNF-α and IL-12. Susceptibility to tuberculosis (MTB) and nontuberculous mycobacterial (NTM) infection as well as listeriosis, salmonellosis, histoplasmosis, coccidioidomycosis, melioidosis, and penicilliosis has been demonstrated in patients with IFN-γR deficiency (reviewed by Dorman et al.[16]). Other defects impacting the same metabolic pathway have similar susceptibilities, including STAT1, IL-12p40, IL-12Rb1, and NEMO[16]. The first cases of immunodeficiency caused by autoantibodies to IFN-γ were described in 2004[17,18].

There are now 14 HIV-negative adults reported with severe opportunistic infections in conjunction with high-titer neutralizing autoantibodies to IFN-γ[17-22*]. In vitro, anti-IFN-γ autoantibodies block downstream mediators of IFN-γ including STAT1 phosphorylation, TNF-α and IL-12 production, and IFN-γ responsive gene expression, suggesting that these autoantibodies interfere with the natural inflammatory response to infection with mycobacteria. Clinically, all patients had at least one NTM infection and 5 were infected with multiple mycobacterial species. The most common organisms were M. avium complex (MAC) (11 infections) followed by rapid-growing mycobacteria (6 infections). Of the 14 reported cases, 11 were Asian suggesting possible genetic associations. Outcomes ranged from fatal infection to complete recovery.

Immunodeficiency caused by anti-IFN-γ autoantibodies is probably under-appreciated. Case series from Thailand and Taiwan have described HIV-negative patients with disseminated NTM[23,24], many of whom have high titer autoantibodies to IFN-γ (unpublished data).

Autoantibodies to granulocyte-macrophage colony-stimulating factor (GM-CSF)

The GM-CSF receptor is on many cell lineages, including neutrophils, macrophage precursors, dendritic cells, and megakaryocytes, where it mediates proliferation, differentiation, and immune activation. In both humans and mice GM-CSF influences terminal differentiation of monocytes to alveolar macrophages and augments innate immunity, largely through GM-CSF stimulation of the transcription factor PU.1[25-27].

GM-CSF and its receptor play critical roles in the pathogenesis of PAP. There are 3 distinct forms of PAP, each demonstrating abnormalities of surfactant metabolism that result in accumulation of acellular periodic acid-Schiff (PAS) positive proteinaceous material in pulmonary alveoli and development of large foamy, monocyte-like alveolar macrophages (reviewed by Trapnell et al.[2]). Primary PAP, the most severe form, results from mutations in the GM-CSF receptor and generally leads to respiratory failure and death shortly after birth[28]. Secondary PAP is often related to hematologic malignancies, iatrogenic immunosuppression or inhaled toxins, and results from qualitative or quantitative deficiency of alveolar macrophages[29]. The acquired form of PAP, first described in 1958 [30], was termed “idiopathic” PAP until anti-GM-CSF autoantibodies were identified as the cause nearly 40 years later[31,32].

Anti-GM-CSF autoantibodies in patients with PAP contribute to a range of defects in alveolar macrophage function including chemotaxis, adhesion, phagocytosis, microbicidal activity, and phagolysosome fusion[33,34]. Evidence from GM-CSF receptor-deficient mice suggests that GM-CSF induces PU.1, a gene critical to both surfactant homeostasis and TLR signaling [27], which potentially explains both surfactant accumulation and infection susceptibility seen in PAP. Defects have also been shown in neutrophil phagocytosis, adhesion, oxidative burst and bacterial killing from both PAP patient blood and from GM-CSF^−/− mouse bone marrow [1]. Anti-GM-CSF autoantibodies have been found not only in bronchoalveolar lavage material but also in the serum of patients with PAP[35], implying that the immune defects associated with this disease may extend beyond the lung. The reports of respiratory infections and extrapulmonary infections in PAP appear to exceed the expected hazards of underlying lung disease. The preponderance of infections in PAP for which neutrophils and macrophages are important mediators of host defense suggests an immune consequence for these anti-GM-CSF autoantibodies. Selected reports include pulmonary and CNS Nocardia[30,36-38], nocardia septic arthritis[39] and perinephric abscess[40]; disseminated histoplasmosis[41]; and disseminated cryptococcus[30,42]. Although some cases have been reported with pulmonary MAC, [43] none of these infections were treated with antimycobacterials and outcomes did not differ from those without infection. Unfortunately, the majority of these reports remain limited to case series and are further confounded by diagnostic heterogeneity, since most appeared prior to the knowledge that autoantibodies to GM-CSF were etiologic in the pathogenesis of PAP.

Anti-IL-17A, anti-IL-17F, or anti-IL-22 autoantibodies and chronic mucocutaneous candidiasis

Chronic mucocutaneous candidiasis (CMC) may complicate a multitude of disorders ranging from patients with congenital immunodeficiency to human immunodeficiency virus (HIV) to hematologic malignancy. CMC has recently been associated with anti-IL-17A, anti-IL-17F or anti-IL-22 autoantibodies in patients with the autoimmune polyendocrinopathy, candidasis, ectodermal dystrophy (APECED) syndrome[3,4]. APECED is a rare, autosomal recessive disorder caused by mutations in the autoimmune regulator (AIRE) gene that is characterized by a classic triad of CMC, hypoparathyroidism, and Addison’s disease (reviewed by Perheentupa[44]). Although CMC in APECED has long been an enigma, CMC in other immunodeficiency syndromes has elucidated pathways which may be important to control these opportunists. Accordingly, STAT3 deficient hyper IgE (Job’s) syndrome[9,10], dectin-1 deficiency [11*], CARD9 deficiency [12*], and to a lesser extent IL-12 receptor beta 1 deficiency[9] all have CMC and varying degrees of Th17 impairment, implicating this pathway in mucosal defense against Candida. Thus, the identification of anti-IL-17 anti-IL-17A, IL-17F or IL-22 autoantibodies in the vast majority of nearly 200 APECED indicates a novel group of pathogenic anti-cytokine autoantibodies that explain CMC in APECED.

Puel et al. evaluated 33 APECED patients and identified anti-IL17 autoantibodies in all 33 APECED patients tested, 29 of whom had CMC; healthy controls had neither those autoantibodies nor CMC [4]. They confirmed function of the anti-IL-17A antibody by inhibiting IL-6 production from IL-17 responsive fibroblasts. In another report, Kisand et al. examined 162 APECED patients and found anti-IL-17 A, IL-17F, and IL-22 autoantibodies in up to 90% of cases, also strongly associated with CMC [3]. They also identified anti-IL-17 and anti-IL-22 autoantibodies in two patients with thymoma and CMC, but none of 33 thymoma patients without CMC. Both groups report a few instances of autoantibodies without CMC, and there are many instances of CMC outside of APECED without autoantibodies. Furthermore, isolated PBMC of patients with CMC demonstrated significantly decreased IL-17-F and IL-22, with a trend towards decreased IL-17A production when stimulated with SEB or heat-killed Candida compared with controls [3]. Together, these data suggest that autoantibodies to IL-17 and IL-22 do not fully explain CMC. Nevertheless, the new work highlighting the roles of autoantibodies to IL-17 and IL-22 in CMC in APECED are a strong start towards developing new insight into the relationship between anti-cytokine autoantibodies and CMC.

APECED offers an enticing opportunity to study anti-cytokine autoantibodies because it is a fully penetrant Mendelian disorder with an identified gene defect. The defective gene in APECED, AIRE, promotes thymic expression of tissue-specific genes and permits intrathymic destruction of autoreactive T cells, thereby promoting survival of only self-tolerant T cells[45]. Autoantibodies in APECED were first described in a series of 76 APECED patients who all had neutralizing IgG autoantibodies to IFNα[46]. Although clearly biologically active in vitro, the physiologic consequences of these anti-IFNα autoantibodies are unclear. However, other autoantibodies in APECED are clearly pathologic, such as those to glutamic acid decarboxylase, thyroid peroxidase, 21-hydroxylase and now perhaps anti-IL-17A, IL-17F and IL-22. APECED embodies an exciting convergence of three fascinating and interrelated topics: CMC, immunodeficiency, and the origins of anti-cytokine autoantibodies.

Thymoma, autoantibodies and immunodeficiency

The thymus plays a critical role in T cell development, including negative selection of autoreactive T cells. Disruption of this process is seen with thymoma, an epithelial neoplasm of the thymic cortex, and likely explains the link between thymoma and autoimmunity. Pathogenic autoantibodies are common in thymoma, most often in the form of myasthenia gravis caused by anti-acetylcholine receptor antibodies. Also described are a wide range of anti-cytokine autoantibodies, most commonly including IL-12 p35 and p40 subunits and type I interferons, but also other neutralizing anti-cytokine autoantibodies including those to IL-1α, IL-17A, IL-22 [47]. Lack of AIRE expression has been shown in thymoma tissue[48,49] suggesting that beyond APECED, AIRE may play a role in other autoimmune conditions and, in particular, contribute to the development of anti-cytokine autoantibodies, which are striking features of both APECED and thymoma (figure 2).

Figure 2.

Relationship between overlapping genetics and phenotype identified in certain anti-cytokine autoantibody-associated syndromes.

While it is clear that a many anti-cytokine autoantibodies are elaborated in thymoma patients, no specific syndrome of immunodeficiency had been etiologically linked with these autoantibodies. Recently, we reported 17 patients with thymic neoplasm who were profiled for immunologic status, opportunistic infections and the presence of anti-cytokine autoantibodies [47*]. Five of 17 thymoma patients had opportunistic infections, all of whom had at least 3 anti-cytokine autoantibodies (range 3-11 of 39 cytokines screened). Interestingly, none of these patients met criteria for Good’s syndrome, (thymoma, hypogammaglobulinemia and variable lymphopenia [50]). Infections ranged from CMC (3 patients), all with either IL-17A and/or IL-22 autoantibodies, confirming the previous report of these antibodies in thymoma with CMC [3], disseminated cryptococcosis (1 patient), sinopulmonary M. avium and Scedosporium apiospermum (1 patient), and disseminated varicella (2 patients). The patient with the most opportunistic infections (CMC, M. avium and S. apiospermum) also had the most anti-cytokine autoantibodies (11 or 39 screened). Although pulmonary alveolar proteinosis, and mycobacterial disease from anti-IFN-γ autoantibodies [19,20] demonstrate a clear relationship between a single autoantibody and a specific syndrome, the spectrum of infections identified in thymic neoplasm suggests that combinations of different autoantibodies may contribute to unique patterns of susceptibility. Since patients with opportunistic infections had higher numbers of autoantibodies, it is plausible that combinations of autoantibodies may have additive or synergistic effects.

Autoantibodies to interleukin-6

IL-6 is produced by a multitude of cells including lymphocytes, macrophages, and hepatocytes and is involved in both acute and chronic inflammation. In particular, IL-6 regulates the acute phase response in the liver, inducing production of C-reactive protein and other inflammatory markers. One case of neutralizing anti-IL-6 autoantibodies has been described in a Haitian boy who had two episodes of severe staphylococcal cellulitis and subcutaneous abcesses that complicated skin lesions initially caused by chickenpox and then mosquito bites[9]. Hyper-IgE syndrome, characterized by recurrent staphylococcal skin abscesses, is due to mutations in STAT3, the critical signal transduction molecule for IL-6 and IL-10 responses [7]. Undetectable C-reactive protein in the patient’s blood, despite severe infection, further suggested an impaired response to IL-6[51]. His infections resolved without any apparent change in his anti-IL-6 autoantibody titers.

Autoantibodies to granulocyte colony-stimulating factor (G-CSF) in autoimmune disease

Granulocyte colony-stimulating factor is produced by bone marrow stromal cells at a low basal rate that can dramatically increase with physiologic stress, such as bacterial infection, or low absolute neutrophil counts[52]. It acts primarily on myeloid cells to accelerate maturation rate, increase neutrophil turnout from the bone marrow, and decrease constitutive neutrophil apoptosis. Beyond an important role in innate immunity, neutrophils may contribute to tissue destruction and inflammation seen in some autoimmune diseases [53].

Anti-G-CSF autoantibodies were identified in patients with Felty’s syndrome (FS) (the clinical triad of rheumatoid arthritis, splenomegaly and neutropenia) and patients with SLE but not in patients with rheumatoid arthritis alone[6]. Eleven/16 patients studied with FS had anti-G-CSF autoantibodies; some patients with SLE had anti-G-CSF autoantibodies with either neutropenia or normal neutrophil levels. Three of 9 anti-G-CSF-containing plasmas tested inhibited G-CSF stimulated cell proliferation while the others did not, suggesting that there are different mechanisms of neutropenia in these patients or that the G-CSF autoantibodies are not the cause of the neutropenia. Although patients with FS may develop infections as a consequence of neutropenia[54,55], the authors did not evaluate the contribution of G-CSF autoantibodies to infection susceptibility.

Conclusion

Autoantibodies to cytokines can have severe consequences, as seen with autoantibodies to IFN-γ, GM-CSF or EPO. In PAP, the identification of anti-GM-CSF autoantibodies came over 40 years after the initial description of the syndrome suggesting that currently “idiopathic” diseases may someday be explained by neutralizing or agonizing autoantibodies.

Identification of anti-cytokine autoantibodies is critical because it will have important implications for the treatment of those diseases, with strategies to reduce autoantibody levels[56*], overcome the autoantibodies or induce tolerance with pharmacologic dosing of the inhibited cytokine[2,9], or use agents that bypass the cytokine which is inhibited. For example, a new approach the treatment of pure red-cell aplasia (anti-erythropoietin autoantibodies) is to bypass the autoantibody with a EPO receptor synthetic peptide agonist (hematide-Affymax) that does not share homology with the EPO ligand[57**]. In a series of patients treated with this agent, thirteen of the 14 patients studied had improvement in hemoglobin levels. Others have reported efforts to reduce autoantibody titers using plasmapheresis and cyclophosphamide [56] or rituximab [58*].

Autoantibodies to receptors, as seen in diseases such as myasthenia gravis or Grave’s disease, suggest that immunodeficiency could be caused by anti-cytokine receptor autoantibodies. Autoantibodies may be inhibitory or stimulatory, may inhibit inflammatory or anti-inflammatory molecules, or may act in concert with other autoantibodies, providing countless possibilities for disease. The emerging role of anticytokine autoantibodies in disease pathogenesis offers a fascinating window onto the biology of immunity, inflammation and infection.