Anthony K. Shum

Protein microarray analysis reveals BAFF-binding autoantibodies in systemic lupus erythematosus

Autoantibodies against cytokines, chemokines, and growth factors inhibit normal immunity and are implicated in inflammatory autoimmune disease and diseases of immune deficiency. In an effort to evaluate serum from autoimmune and immunodeficient patients for Abs against cytokines, chemokines, and growth factors in a high-throughput and unbiased manner, we constructed a multiplex protein microarray for detection of serum factor-binding Abs and used the microarray to detect autoantibody targets in SLE. We designed a nitrocellulose-surface microarray containing human cytokines, chemokines, and other circulating proteins and demonstrated that the array permitted specific detection of serum factor-binding probes. We used the arrays to detect previously described autoantibodies against cytokines in samples from individuals with autoimmune polyendocrine syndrome type 1 and chronic mycobacterial infection. Serum profiling from individuals with SLE revealed that among several targets, elevated IgG autoantibody reactivity to B cell-activating factor (BAFF) was associated with SLE compared with control samples. BAFF reactivity correlated with the severity of disease-associated features, including IFN-α-driven SLE pathology. Our results showed that serum factor protein microarrays facilitate detection of autoantibody reactivity to serum factors in human samples and that BAFF-reactive autoantibodies may be associated with an elevated inflammatory disease state within the spectrum of SLE.

Effector Mechanisms of the Autoimmune Syndrome in the Murine Model of Autoimmune Polyglandular Syndrome Type 1

Mutations in the Aire gene result in a clinical phenomenon known as Autoimmune Polyglandular Syndrome (APS) Type I, which classically manifests as a triad of adrenal insufficiency, hypoparathyroidism, and chronic mucocutaneous infections. In addition to this triad, a number of other autoimmune diseases have been observed in APS1 patients including Sjögren’s syndrome, vitiligo, alopecia, uveitis, and others. Aire-deficient mice, the animal model for APS1, have highlighted the role of the thymus in the disease process and demonstrated a failure in central tolerance in aire-deficient mice. However, autoantibodies have been observed against multiple organs in both mice and humans, making it unclear what the specific role of B and T cells are in the pathogenesis of disease. Using the aire-deficient mouse as a preclinical model for APS1, we have investigated the relative contribution of specific lymphocyte populations, with the goal of identifying the cell populations which may be targeted for rational therapeutic design. In this study, we show that T cells are indispensable to the breakdown of self-tolerance, in contrast to B cells which play a more limited role in autoimmunity. Th1 polarized CD4+ T cells, in particular, are major contributors to the autoimmune response. With this knowledge, we go on to use therapies targeted at T cells to investigate their ability to modulate disease in vivo. Depletion of CD4+ T cells using a neutralizing Ab ameliorated the disease process. Thus, therapies targeted specifically at the CD4+ T cell subset may help control autoimmune disease in patients with APS1.

Identification of an Autoantigen Demonstrates a Link Between Interstitial Lung Disease and a Defect in Central Tolerance

A defect in immune tolerance to self-antigens may underlie the lung damage that accompanies many autoimmune diseases. Autoimmune diseases are intractable and varied, appearing in many guises. Patients with lupus, for example, experience destructive immune reactions that affect the heart, other organs, and the joints. This generalized attack is in stark contrast to the very selective autoimmune destruction of insulin-producing β islet cells in type I diabetes or the antibodies to the acetylcholine receptor that characterize myasthenia gravis. Why are there generalized immune responses in some diseases and very specific reactions in others? Shum et al. have exploited a mutant mouse defective in AIRE, a transcription factor that controls expression of many self-antigens in the thymus. As immune T cells pass through, these self-antigens in the thymus trigger the deletion of cells that react with them, preventing these autoreactive T cells from entering the circulation. Thus, when AIRE is absent or mutated, T cells directed at self-antigens are not deleted and escape into the circulation where they can trigger autoimmunity. This is not only true in mice: Patients with a genetic disease called autoimmune polyglandular syndrome type 1 (APS1) have defective AIRE and suffer from autoimmune disease. One organ that often deteriorates in autoimmune diseases is the lung, which can develop severe fibrosis, preventing effective breathing and oxygen exchange. To investigate the basis of this interstitial lung disease and other similar problems that arise sporadically, Shum et al. explored how lung damage occurs in AIRE-deficient mice and in a patient with APS1. The diseased lungs from both mice and human were infiltrated with T helper 1 CD4+ cells, with smaller numbers of other immune cells. Further work showed that one of the main targets of these cells in mice was, unexpectedly, a protein called vomeromodulin, which the authors determined is expressed in the thymus under AIRE control. Indeed, activated T cells to vomeromodulin cause lung-specific disease when given to immunodeficient mice. In the patient with the same genetic defect as the mice, the lung antigen was not vomeromodulin but was a similar protein called LPLUNC1 (long palate, lung, and nasal epithelium carcinoma–associated protein), located adjacent to the human version of vomeromodulin, which is a pseudogene. This multifaceted study offers several benefits. The lung-specific autoimmune disease seen in the AIRE-deficient mouse closely resembles human interstitial lung disease and can provide a tractable way to understand its progression and develop treatments. This clear example showing how a failure in establishing tolerance to self-antigens can produce an organ-specific disease points to similar mechanisms as possible causes of other autoimmune problems. Finally, the new results elevate vomeromodulin—and its human cousin LPLUNC1—from an interesting secretion product of the nasal epithelium to an autoimmune target in a serious disease, increasing our understanding of how to combat these illnesses. Interstitial lung disease (ILD) is a common manifestation of systemic autoimmunity characterized by progressive inflammation or scarring of the lungs. Patients who develop these complications can exhibit significantly impaired gas exchange that may result in hypoxemia, pulmonary hypertension, and even death. Unfortunately, little is understood about how these diseases arise, including the role of specific defects in immune tolerance. Another key question is whether autoimmune responses targeting the lung parenchyma are critical to ILD pathogenesis, including that of isolated idiopathic forms. We show that a specific defect in central tolerance brought about by mutations in the autoimmune regulator gene (Aire) leads to an autoreactive T cell response to a lung antigen named vomeromodulin and the development of ILD. We found that a human patient and mice with defects in Aire develop similar lung pathology, demonstrating that the AIRE-deficient model of autoimmunity is a suitable translational system in which to unravel fundamental mechanisms of ILD pathogenesis.

BPIFB1 IS A LUNG-SPECIFIC AUTOANTIGEN ASSOCIATED WITH INTERSTITIAL LUNG DISEASE

Autoimmunity targeting the lung-specific antigen BPIFB1 may be important to the pathogenesis of interstitial lung disease. Seeing the Forest by Examining the Trees Sometimes looking at something too closely obscures the big picture. However, when the big picture is too big, a reductionist approach may be best. Interstitial lung disease (ILD) is a complex and heterogeneous disorder, frequently associated with autoimmune syndromes. However, due in part to this heterogeneity, it remains unclear whether autoimmunity directly contributes to ILD. Now, Shum et al. attack this question by example—connecting one form of autoimmune disease, autoimmune polyglandular syndrome type 1 (APS1), with clinical ILD. The authors screened patients with APS1 and found autoantibodies to a lung-specific protein—BPIFB1—associated with the development of ILD in APS1 patients. They then extended these findings to non-APS1–associated ILD and found that 12 to 15% of patients also had these autoantibodies. The authors then examined a potential pathogenic mechanism of these autoantibodies in a mouse model of APS1, finding that similar autoantibodies and development of ILD resulted from a defect in thymic tolerance. Indeed, autoimmune targeting of BPIFB1 could cause ILD in mice without the autoimmune defect. These results suggest not only that ILD may be an autoimmune disorder in APS1 patients but also that autoimmunity may also contribute to pathology in a broader swath of ILD patients. Interstitial lung disease (ILD) is a complex and heterogeneous disorder that is often associated with autoimmune syndromes. Despite the connection between ILD and autoimmunity, it remains unclear whether ILD can develop from an autoimmune response that specifically targets the lung parenchyma. We examined a severe form of autoimmune disease, autoimmune polyglandular syndrome type 1 (APS1), and established a strong link between an autoimmune response to the lung-specific protein BPIFB1 (bactericidal/permeability-increasing fold-containing B1) and clinical ILD. Screening of a large cohort of APS1 patients revealed autoantibodies to BPIFB1 in 9.6% of APS1 subjects overall and in 100% of APS1 subjects with ILD. Further investigation of ILD outside the APS1 disorder revealed BPIFB1 autoantibodies present in 14.6% of patients with connective tissue disease–associated ILD and in 12.0% of patients with idiopathic ILD. The animal model for APS1, Aire−/− mice, harbors autoantibodies to a similar lung antigen (BPIFB9); these autoantibodies are a marker for ILD. We found that a defect in thymic tolerance was responsible for the production of BPIFB9 autoantibodies and the development of ILD. We also found that immunoreactivity targeting BPIFB1 independent of a defect in Aire also led to ILD, consistent with our discovery of BPIFB1 autoantibodies in non-APS1 patients. Overall, our results demonstrate that autoimmunity targeting the lung-specific antigen BPIFB1 may contribute to the pathogenesis of ILD in patients with APS1 and in subsets of patients with non-APS1 ILD, demonstrating the role of lung-specific autoimmunity in the genesis of ILD.

Defective Autoimmune Regulator-Dependent Central Tolerance to Myelin Protein Zero Is Linked to Autoimmune Peripheral Neuropathy

Chronic inflammatory demyelinating polyneuropathy is a debilitating autoimmune disease characterized by peripheral nerve demyelination and dysfunction. How the autoimmune response is initiated, identity of provoking Ags, and pathogenic effector mechanisms are not well defined. The autoimmune regulator (Aire) plays a critical role in central tolerance by promoting thymic expression of self-Ags and deletion of self-reactive T cells. In this study, we used mice with hypomorphic Aire function and two patients with Aire mutations to define how Aire deficiency results in spontaneous autoimmune peripheral neuropathy. Autoimmunity against peripheral nerves in both mice and humans targets myelin protein zero, an Ag for which expression is Aire-regulated in the thymus. Consistent with a defect in thymic tolerance, CD4+ T cells are sufficient to transfer disease in mice and produce IFN-γ in infiltrated peripheral nerves. Our findings suggest that defective Aire-mediated central tolerance to myelin protein zero initiates an autoimmune Th1 effector response toward peripheral nerves.

Transglutaminase 4 as a prostate autoantigen in male subfertility

TGM4 is a male-specific autoantigen for prostatitis associated with autoimmune polyendocrine syndrome type 1. AIREing out autoimmunity Patients with autoimmune polyendocrine syndrome type 1(APS1) experience dysfunction in multiple endocrine glands due to mutations in the AIRE gene, which helps promote immune tolerance. These patients frequently are infertile; female infertility can be explained by autoimmune ovarian failure, but the causes of male infertility have remained unclear. Now, Landegren et al. report that the prostatic secretory molecule tranglutaminase 4 (TGM4) is a male-specific autoantigen in APS1 patients that could contribute to subfertility. They found autoantibodies to TGM4 in APS1 patients beginning at puberty, and confirmed in AIRE-deficient mice that TGM4 autoantibodies lead to a destructive prostatitis. These data could help explain infertility in male APS1 patients. Autoimmune polyendocrine syndrome type 1 (APS1), a monogenic disorder caused by AIRE gene mutations, features multiple autoimmune disease components. Infertility is common in both males and females with APS1. Although female infertility can be explained by autoimmune ovarian failure, the mechanisms underlying male infertility have remained poorly understood. We performed a proteome-wide autoantibody screen in APS1 patient sera to assess the autoimmune response against the male reproductive organs. By screening human protein arrays with male and female patient sera and by selecting for gender-imbalanced autoantibody signals, we identified transglutaminase 4 (TGM4) as a male-specific autoantigen. Notably, TGM4 is a prostatic secretory molecule with critical role in male reproduction. TGM4 autoantibodies were detected in most of the adult male APS1 patients but were absent in all the young males. Consecutive serum samples further revealed that TGM4 autoantibodies first presented during pubertal age and subsequent to prostate maturation. We assessed the animal model for APS1, the Aire-deficient mouse, and found spontaneous development of TGM4 autoantibodies specifically in males. Aire-deficient mice failed to present TGM4 in the thymus, consistent with a defect in central tolerance for TGM4. In the mouse, we further link TGM4 immunity with a destructive prostatitis and compromised secretion of TGM4. Collectively, our findings in APS1 patients and Aire-deficient mice reveal prostate autoimmunity as a major manifestation of APS1 with potential role in male subfertility.

Type I interferon pathway activation in COPA syndrome

Mutations of the COPA gene cause an immune dysregulatory disease characterised by polyarticular arthritis and progressive interstitial lung disease with pulmonary haemorrhages. We report the case of a young girl that presented at age 3 with polyarticular arthritis, chronic cough and high titer rheumatoid factor. Radiologic imaging showed interstitial lung disease with tree-in-a-bud nodules and air-filled cysts. Targeted genetic analysis of COPA gene showed the reported c.698G>A mutation. The patient was lost to follow up for 3years during which therapy was discontinued with the development of joint damage and deformities. Analysis of peripheral blood showed activation of type 1 interferon pathway, which was also confirmed in 4 previously reported COPA patients. Our observations underline the importance of early treatment in COPA disease to avoid loss of joint function. Furthermore, our results suggest a role for type 1 interferon in disease pathogenesis opening the possibility for targeted therapeutic approaches.

Rare variants, autoimmune disease, and arthritis

Purpose of reviewWe review select studies of newly discovered rare variants in autoimmune diseases with a focus on newly described monogenic disorders, rheumatoid arthritis, and systemic lupus erythematosus. Recent findingsTwo new monogenic syndromes of inflammatory arthritis were discovered using whole exome sequencing: the coatomer subunit alpha syndrome because of rare mutations in coatomer subunit alpha and haploinsufficiency of A20 resulting from rare mutations in TNFAIP3. Targeted exon sequencing identified rare variants in IL2RA and IL2RB associated with rheumatoid arthritis. Rare variants in TREX1 and other genes associated with monogenic interferonopathies are also associated with systemic lupus erythematosus. SummaryRare genetic variants contribute to the heritability of autoimmunity and provide key insight into both novel and previously implicated immunological pathways that are disrupted in autoimmune diseases.

T cell types that take your breath away

A new T helper cell signature in asthma patients highlights the potential impact of a personalized approach to asthma care (Choy et al., this issue). A new T helper cell signature in asthma patients highlights the potential impact of a personalized approach to asthma care (Choy et al., this issue).

Analysis of pulmonary features and treatment approaches in the COPA syndrome

The COPA syndrome is a monogenic, autoimmune lung and joint disorder first identified in 2015. This study sought to define the main pulmonary features of the COPA syndrome in an international cohort of patients, analyse patient responses to treatment and highlight when genetic testing should be considered. We established a cohort of subjects (N=14) with COPA syndrome seen at multiple centres including the University of California, San Francisco, CA, USA. All subjects had one of the previously established mutations in the COPA gene, and had clinically apparent lung disease and arthritis. We analysed cohort characteristics using descriptive statistics. All subjects manifested symptoms before the age of 12 years, had a family history of disease, and developed diffuse parenchymal lung disease and arthritis. 50% had diffuse alveolar haemorrhage. The most common pulmonary findings included cysts on chest computed tomography and evidence of follicular bronchiolitis on lung biopsy. All subjects were positive for anti-neutrophil cytoplasmic antibody, anti-nuclear antibody or both and 71% of subjects had rheumatoid factor positivity. All subjects received immunosuppressive therapy. COPA syndrome is an autoimmune disorder defined by diffuse parenchymal lung disease and arthritis. We analysed an international cohort of subjects with genetically confirmed COPA syndrome and found that common pulmonary features included cysts, follicular bronchiolitis and diffuse alveolar haemorrhage. Common extrapulmonary features included early age of onset, family history of disease, autoantibody positivity and arthritis. Longitudinal data demonstrated improvement on chest radiology but an overall decline in pulmonary function despite chronic treatment. When to consider COPA syndrome, a Mendelian disorder with lung disease and arthritis, plus a review of treatments used http://ow.ly/hWv130k21vT