Pathogenic Role Of Autoantibodies Research Articles

Single-cell analysis of refractory anti-SRP necrotizing myopathy treated with anti-BCMA CAR-T cell therapy

Immune-mediated necrotizing myopathy (IMNM) is an autoimmune disorder associated with the presence of autoantibodies, characterized by severe clinical presentation with rapidly progressive muscular weakness and elevated levels of creatine kinase, while traditional pharmacological approaches possess varying and often limited effects. Considering the pathogenic role of autoantibodies, chimeric antigen receptor (CAR)-T cells targeting B cell maturation antigen (BCMA) have emerged as a promising therapeutic strategy. We reported here a patient with anti-signal recognition particle IMNM refractory to multiple available therapies, who was treated with BCMA-targeting CAR-T cells, exhibited favorable safety profiles, sustained reduction in pathogenic autoantibodies, and persistent clinical improvements over 18 mo. Longitudinal single-cell RNA, B cell receptor, T cell receptor sequencing analysis presented the normalization of immune microenvironment after CAR-T cell infusion, including reconstitution of B cell lineages, replacement of T cell subclusters, and suppression of overactivated immune cells. Analysis on characteristics of CAR-T cells in IMNM demonstrated a more active expansion of CD8+ CAR-T cells, with a dynamic phenotype shifting pattern similar in CD4+ and CD8+ CAR-T cells. A comparison of CD8+ CAR-T cells in patients with IMNM and those with malignancies collected at different timepoints revealed a more NK-like phenotype with enhanced tendency of cell death and neuroinflammation and inhibited proliferating ability of CD8+ CAR-T cells in IMNM while neuroinflammation might be the distinct characteristics. Further studies are warranted to define the molecular features of CAR-T cells in autoimmunity and to seek higher efficiency and longer persistence of CAR-T cells in treating autoimmune disorders.

Pathogenic role of autoantibodies at the ependyma in autoimmune disorders of the central nervous system.

Ependymal cells make up the epithelial monolayer that lines the brain ventricles and the spinal cord central canal that are filled with cerebrospinal fluid. The ependyma has several functions, including regulating solute exchange between the cerebrospinal fluid and parenchyma, controlling microcirculation of cerebrospinal fluid via coordinated ciliary beating, and acting as a partial barrier. Dysregulation of these functions can lead to waste clearance impairment, cerebrospinal fluid accumulation, hydrocephalus, and more. A role for ependymal cells in a variety of neurological disorders has been proposed, including in neuromyelitis optica and multiple sclerosis, two autoimmune demyelinating diseases of the central nervous system, where periventricular damage is common. What is not known is the mechanisms behind how ependymal cells become dysregulated in these diseases. In neuromyelitis optica, it is well established that autoantibodies directed against Aquaporin-4 are drivers of disease, and it has been shown recently that these autoantibodies can drive ependymal cell dysregulation. We propose a similar mechanism is at play in multiple sclerosis, where autoantibodies targeting a glial cell protein called GlialCAM on ependymal cells are contributing to disease. GlialCAM shares high molecular similarities with the Epstein-Barr virus (EBV) protein EBNA1. EBV has recently been shown to be necessary for multiple sclerosis initiation, yet how EBV mediates pathogenesis, especially in the periventricular area, remains elusive. In this perspective article, we discuss how ependymal cells could be targeted by antibody-related autoimmune mechanisms in autoimmune demyelinating diseases and how this is implicated in ventricular/periventricular pathology.

Le malattie autoinfiammatorie: aspetti patogenetici e clinici (Prima parte)

Autoinflammatory diseases (AIDs) are a family of rare medical entities, characterized by sterile systemic inflammatory episodes caused by exaggerated activation of the innate immune system, for which the pathogenic role of autoantibodies, B or T cells is less relevant. During the past 20 years, a growing number of monogenic inflammatory diseases have been described and their respective responsible genes identified. Proteins encoded by these genes are involved in the regulatory pathways of inflammation and they are mostly expressed in cells of the innate immune system. Since symptoms can overlap within this rapidly expanding disease category, accurate genetic diagnosis is extremely important to start early targeted treatment and to prevent clinically significant or life-threatening complications. On the other hand, detection of more and more genetic variants makes interpretation of results more complicated, and often a genetic diagnosis is not achieved. Thus, the clinical picture represents the starting point for establishing an effective therapy when genetic data are not sufficient or inconclusive. Biologic agents blocking cytokines action have proved to be dramatically effective in a lot of patients.

Identification of monoclonal antibodies against human renal glomerular endothelial cells in lupus nephritis that induce endothelial interferon-alpha production

BackgroundThe pathogenesis of lupus nephritis (LN) remains not fully understood. In this study, we aimed to explore the pathogenic roles of autoantibodies against human renal glomerular endothelial cells (HRGEC) in LN patients.MethodsThe serum levels of anti-HRGEC antibodies in systemic lupus erythematosus (SLE) patients without LN and LN patients were determined by cell-based enzyme-linked immunosorbent assay (ELISA). Monoclonal IgG anti-HRGEC antibodies were subsequently generated from LN patients. The binding activities of these monoclonal antibodies to HRGEC, their cross-reactivity with double-stranded DNA (dsDNA), and the ability to activate HRGEC were further evaluated.ResultsLN patients had higher serum levels of IgG anti-HRGEC antibodies than SLE patients without LN and healthy controls. Four monoclonal IgG anti-HRGEC antibodies (LN1–4) were obtained; LN1 and LN2 were IgG3 while LN3 and LN4 were IgG1. Among these monoclonal antibodies, LN1–3 were cross-reactive with dsDNA. The functional assays showed that compared with IgG1/IgG3 isotype controls, LN3 had an effect on HRGEC to enhance interleukin (IL)-6 production, LN4 could enhance IL-8 and monocyte chemoattractant protein (MCP)-1 production, and LN1–3 possessed the ability to induce interferon (IFN)-α production by HRGEC. Moreover, the removal of DNA on the HRGEC surface by DNAse 1 did not interpose the binding of LN1–3 to HRGEC and the effects of LN1–3 on IFN-α induction by HRGEC.ConclusionsSome IgG anti-HRGEC antibodies in LN patients had the ability to enhance endothelial proinflammatory cytokine (IL-6, IL-8, and MCP-1) production, and some could induce the DNA-independent production of IFN-α by HRGEC.

Pathogenic Roles of Autoantibodies and Aberrant Epigenetic Regulation of Immune and Connective Tissue Cells in the Tissue Fibrosis of Patients with Systemic Sclerosis.

Systemic sclerosis (SSc) is a multi-system autoimmune disease with tissue fibrosis prominent in the skin and lung. In this review, we briefly describe the autoimmune features (mainly autoantibody production and cytokine profiles) and the potential pathogenic contributors including genetic/epigenetic predisposition, and environmental factors. We look in detail at the cellular and molecular bases underlying tissue-fibrosis which include trans-differentiation of fibroblasts (FBs) to myofibroblasts (MFBs). We also state comprehensively the pro-inflammatory and pro-fibrotic cytokines relevant to MFB trans-differentiation, vasculopathy-associated autoantibodies, and fibrosis-regulating microRNAs in SSc. It is conceivable that tissue fibrosis is mainly mediated by an excessive production of TGF-β, the master regulator, from the skewed Th2 cells, macrophages, fibroblasts, myofibroblasts, and keratinocytes. After binding with TGF-β receptors on MFB, the downstream Wnt/β-catenin triggers canonical Smad 2/3 and non-canonical Smad 4 signaling pathways to transcribe collagen genes. Subsequently, excessive collagen fiber synthesis and accumulation as well as tissue fibrosis ensue. In the later part of this review, we discuss limited data relevant to the role of long non-coding RNAs (lncRNAs) in tissue-fibrosis in SSc. It is expected that these lncRNAs may become the useful biomarkers and therapeutic targets for SSc in the future. The prospective investigations in the development of novel epigenetic modifiers are also suggested.

The pathogenic role of autoantibodies in recurrent pregnancy loss.

In the present manuscript, we review the recent research investigating the pathogenic association between most studied autoantibodies and recurrent pregnancy loss. Pregnancy loss represents a common obstetric complication occurring in about 15%-25% of all clinically recognized pregnancies. The recurrence of pregnancy loss identifies a distinct clinical entity, that is recurrent pregnancy loss (RPL), affecting about 2%-4% of couples. Several factors, including age, chromosomal abnormalities, uterine anomalies, thrombophilic disorders, endocrinopathies, hormonal and metabolic disorders, infections, sperm quality, and lifestyle issues, are involved in RPL. The role of autoantibodies in RPL is only partially determined. In some cases (antiphospholipid antibodies [aPL]), their involvement is well established. In other cases (anti-thyroid autoantibodies, antinuclear, anti-transglutaminase, and anti-endomysial antibodies), it is still debated, despite multiple, although not fully conclusive, evidences strongly suggest a possible involvement in RPL. Further extensive research is needed to definitively confirm or exclude their actual role.

Pathogenic roles of autoantibodies in systemic sclerosis: Current understandings in pathogenesis

The potential pathogenic role for autoantibodies in systemic sclerosis has captivated researchers for the past 40 years. This review answers the question whether there is yet sufficient knowledge to conclude that certain serum autoantibodies associated with systemic sclerosis contribute to its pathogenesis. Definitions for pathogenic, pathogenetic and functional autoantibodies are formulated, and the need to differentiate these autoantibodies from natural autoantibodies is emphasized. In addition, seven criteria for the identification of pathogenic autoantibodies are proposed. Experimental evidence is reviewed relevant to the classic systemic sclerosis antinuclear autoantibodies, anti-topoisomerase I and anticentromere, and to functional autoantibodies to endothelin 1 type A receptor, angiotensin II type 1 receptor, muscarinic receptor 3, platelet-derived growth factor receptor, chemokine receptors CXCR3 and CXCR4, estrogen receptor α, and CD22. Pathogenic evidence is also reviewed for anti-matrix metalloproteinases 1 and 3, anti-fibrillin 1, anti-IFI16, anti-eIF2B, anti-ICAM-1, and anti-RuvBL1/RuvBL2 autoantibodies. For each autoantibody, objective evidence for a pathogenic role is scored qualitatively according to the seven pathogenicity criteria. It is concluded that anti-topoisomerase I is the single autoantibody specificity with the most evidence in favor of a pathogenic role in systemic sclerosis, followed by anticentromere. However, these autoantibodies have not been demonstrated yet to fulfill completely the seven proposed criteria for pathogenicity. Their contributory roles to the pathogenesis of systemic sclerosis remain possible but not yet conclusively demonstrated. With respect to functional autoantibodies and other autoantibodies, only a few criteria for pathogenicity are fulfilled. Their common presence in healthy and disease controls suggests that major subsets of these immunoglobulins are natural autoantibodies. While some of these autoantibodies may be pathogenetic in systemic sclerosis, establishing that they are truly pathogenic is a work in progress. Experimental data are difficult to interpret because high serum autoantibody levels may be due to polyclonal B-cell activation. Other limitations in experimental design are the use of total serum immunoglobulin G rather than affinity-purified autoantibodies, the confounding effect of other systemic sclerosis autoantibodies present in total immunoglobulin G and the lack of longitudinal studies to determine if autoantibody titers fluctuate with systemic sclerosis activity and severity. These intriguing new specificities expand the spectrum of autoantibodies observed in systemic sclerosis. Continuing elucidation of their potential mechanistic roles raises hope of a better understanding of systemic sclerosis pathogenesis leading to improved therapies.

Heterogeneity but individual constancy of epitopes, isotypes and avidity of factor H autoantibodies in atypical hemolytic uremic syndrome.

Factor H (FH) autoantibodies are present in 6-10% of atypical hemolytic uremic syndrome (aHUS) patients, most of whom have homozygous deficiency of the FH-related protein FHR-1. Although the pathogenic role of the autoantibodies is established, little is known about their molecular characteristics and changes over time. Here, we describe the specificity and other immunological features of anti-FH autoantibodies in the Spanish and Hungarian aHUS cohorts. A total of 19 patients were included and serial samples of 14 of them were available. FH autoantibodies from FHR-1 deficient patients (n=13) mainly recognized FH, its SCR19-20 fragment and FHR-1, but autoantibody specificity in patients who are homo- or heterozygous for the CFHR1 gene (n=6) was heterogeneous. No significant changes apart from total antibody titer were observed during follow-up in each patient. Fine epitope mapping with recombinant FH SCR19-20 containing single amino acid mutations showed significantly reduced binding in 6 out of 14 patients. In most cases, autoantibody binding to residues 1183-1189 and 1210-1215 was impaired, revealing a major common autoantibody epitope. Avidities showed variations between patients, but in most cases the avidity index did not change upon time. Most autoantibodies were IgG3, and all but three presented only with kappa or with lambda light chains. Although the pathogenic role of anti-FH autoantibodies in aHUS is well established, this study shows autoantibody heterogeneity among patients, but no significant variation in their characteristics over time in each patient. The presence of a single light chain in 16 out of 19 patients and the limited number of recognized epitopes suggest a restricted autoantibody response in most patients.

Evidence on the pathogenic role of auto-antibodies in acute cardiovascular diseases

Atherothrombosis is the major determinant of acute ischaemic cardiovascular events, such as myocardial infarction and stroke. Inflammatory processes have been linked to all phases of atherogenesis In particular, the identification of autoimmunity mediators in the complex microenvironment of chronic inflammation has become the focus of attention in both early and advanced atherogenic processes. Auto-antibodies against self-molecules or new epitopes generated by oxidative processes infiltrate atherosclerotic plaques and were shown to modulate the activity of immune cells by binding various types of receptors. However, despite mounting evidence for a pathophysiological role of autoantibodies in atherothrombosis, the clinical relevance for circulating autoantibodies in cardiovascular outcomes is still debated. This review aims at illustrating the mechanisms by which different types of autoantibodies might either promote or repress atherothrombosis and to discuss the clinical studies assessing the role of auto-antibodies as prognostic biomarkers of plaque vulnerability.

TRAP ping the cellular mechanisms of lupus

<i>TRAP</i> ping the cellular mechanisms of lupus

Study of the relationship between Tourette syndrome and autoimmunity

Tourette syndrome is a chronic childhood-onset neuropsychiatric disorder,immune abnormality in Tourette syndrome may play a role in some susceptible children. Some researches suggest that bacterial infections produce antineuronal autoantibodies that can recognize and attack the central nervous system and cause dysfunction. And five criteria can be used experimentally to establish a pathogenic role for autoantibodies in neurologic disorders . Key words: Tourette syndrome; Autoimmunity; Antineuronal autoantibodies; Lymphocyte subgroup

Anti-neutrophil autoantibodies in tissue damage in systemic lupus erythematosus (135.31)

Abstract Systemic lupus erythematosus (SLE) is a complex autoimmune disease in which abnormal immune responses attack multiple organs, leading to life-threatening complications. Although the pathogenic role of autoantibodies in SLE has been well established, the most disease-relevant reactivity of autoantibodies and their use as disease progression biomarkers are not fully understood. Using a single-cell PCR approach, we generated a large panel of recombinant antibodies from B cells of SLE patients. We found that a high frequency of SLE-derived antibodies (~ 20%) bind to and activate neutrophils as assayed by degranulation, oxidative burst, calcium influx, and tyrosine phosphorylation. One of the antibodies, S4Ab4, also induces neutrophil extracellular trap (NET) formation and increases cell death to human vein endothelial cells. Using mass spectrometry, we found that S4Ab4 reacts with two neutrophil proteins: lactoferrin and nucleotide-binding oligomerization domains 27 (NOD27). While lactoferrin is a known neutrophil autoantigen, NOD27, a family member of NOD-like pattern recognition receptors, might be a novel autoantigen in SLE. Furthermore, S4Ab4 antibody can cause proteinuria and kidney and lung manifestations when administered into NZB/W F1 lupus-prone mice. Our results show that SLE-derived autoantibodies can directly bind to and activate neutrophils. These anti-neutrophil autoantibodies may play important roles in the disease progression and tissue damage in SLE.

TNF blocker drugs modulate human TNF-α-converting enzyme pro-domain shedding induced by autoantibodies

Novel biologic therapies targeted against specific components of the immune system, including blockade of TNF-α have revolutionized therapeutic approaches to inflammatory conditions and systemic inhibitors of TNF-α have been approved for the treatment of a wide variety of autoimmune diseases . No studies aimed to elucidate the effects of anti-TNF-α blockers on tumour necrosis factor-α convertase (TACE) expression and activation have yet been published. TACE is the principal protease involved in the activation of pro-TNF-α and is a target for anti-TNF-α therapy. Here we focused on regulation of TACE expression in human salivary gland epithelial cells (SGEC) treated by anti-Ro/SSA autoantibodies (autoAbs), characterizing primary Sjögren's syndrome and on the effect of anti-Ro/SSA autoAbs on TACE pro-domain shedding and activation. To test the hypothesis that anti-TNF-α blocker drugs affect TACE expression, we used Adalimumab and Etanercept to block TNF-α and evaluate the effects of these biological agents on post-translational regulation of TACE. Anti-Ro/SSA autoAbs determines TACE pro-domain shedding suggesting that TACE activity is necessary for the release of TNF-α observed in anti-Ro/SSA autoAbs-stimulated cells. The comparative efficacy analysis of the regulation of TACE activity by Adalimumab and Etanercept revealed that Adalimumab appear to be significantly more efficacious than Etanercept in preventing TACE activation caused by anti-Ro/SSA autoAbs. It is intriguing to consider that regulation of TACE may participate in the pathogenic role of autoantibodies and the modulation of TACE expression by TNF-α antagonists might contribute to the beneficial effect of these drugs in inflammatory and autoimmune diseases.

Functional studies indicate a direct pathogenic role of autoantibodies in atypical haemolytic uraemic syndrome by inhibiting factor H cell protective activity

Functional studies indicate a direct pathogenic role of autoantibodies in atypical haemolytic uraemic syndrome by inhibiting factor H cell protective activity

Diagnostik der Autoimmunerkrankungen

Autoantibodies play a key role in diagnostic laboratories as markers of autoimmune diseases. In addition to their role as markers they mediate diverse effects in vivo. Autoantibodies with protective effect have been described. Natural protective IgM autoantibodies against tumour-antigens of malignant cells or their precursors may contribute to increased survival rates of carcinoma patients. In a mouse model of systemic lupus erythematosus it has been shown that anti-dsDNA IgM autoantibodies protect from glomerular damage. In contrast, a direct pathogenic role of autoantibodies has been well established e.g. in myasthenia gravis or in Goodpasture syndrome. Similarly autoantibodies against SSA Ro52 are detrimental in neonatal lupus erythematosus with congenital heart block. Moreover, putatively protective autoantibodies may become pathogenic during the course of the disease such as the onconeuronal autoantibodies whose pathogenicity depends on their compartmentalisation. In patients with paraneoplastic syndromes tumour cells express proteins that are also naturally present in the brain. Anti-tumour autoantibodies which temporarily suppress tumour growth can provoke an autoimmune attack on neurons once having crossed the blood-brain barrier and cause specific neurological symptoms. Only a restricted number of autoantibodies are useful follow-up markers for the effectiveness of treatment in autoimmune diseases. Certain autoantibodies hold prognostic value and appear years or even decades before the diagnosis of disease such as the antimitochondrial antibodies in primary biliary cirrhosis or anti-citrullinated protein (CCP)-antibodies in rheumatoid arthritis. It is crucial to know whether the autoantibodies in question recognise linear or conformational epitopes in order to choose the appropriate detection methods. Indirect immunofluorescence microscopy remains a very useful tool for confirmation of results of commercially available immunoassays and for detection of special and rare autoantibodies that otherwise often remain undetected. Standardisation of autoimmune diagnostics is still underway and requires joint efforts by laboratories, clinicians and industry.

Pathogenic role of auto-antibodies against complement components in systemic lupus erythematosus

Pathogenic role of auto-antibodies against complement components in systemic lupus erythematosus

Characterization of human monoclonal autoantibody Fab fragments against oxidized LDL

Oxidized low-density lipoprotein (oxLDL) is a key autoantigen in atherosclerosis. The genetic structures and pathogenic roles of autoantibodies against this protein remain to be established. In this study, we cloned several monoclonal IgG autoantibody Fab fragments specific for oxLDL from peripheral blood lymphocytes of atherosclerosis patients, using phage display technology. The sequences of their variable regions were determined at the cDNA level. The closest germline counterparts for the heavy chains belonged to the V H3 or V H1 family. The sequences and lengths of complementarity-determining regions (CDR)3-V H were diverse, and frequent mutations of positively charged amino acids (particularly arginine) over entire V H and V L sequences were observed. It is proposed that anti-oxLDL autoantibody formation is driven by antigens. Among the Fabs, P2-8 and P3-175 bound to both MDA-LDL and Cu-oxLDL, and inhibited the uptake of oxLDL by macrophages, suggesting the epitope(s) recognized by the Fabs is a part of ligands on oxLDL that is involved in uptake by macrophage scavenger receptor. These human autoantibody Fabs require detailed investigation to ascertain their potential as agents for clinical applications.

The exploration of joint-specific immunoreactions on immunoglobulins G of anti-glucose-6-phosphate isomerase antibody-positive patients with rheumatoid arthritis

The pathogenic role of autoantibodies in rheumatoid arthritis (RA) remains elusive. Anti-glucose-6-phosphate isomerase (GPI) antibodies (Abs) are candidates for arthritogenic Abs because they directly induce arthritis in mice. High titers of anti-GPI Abs are found in some RA patients with severe forms. The aim of this study was to analyze the role of IgG, including anti-GPI Abs, in the joints of RA patients. Synovial tissue was obtained from 6 patients with RA (3 anti-GPI Abs- positive and 3 anti-GPI Abs- negative) and compared histologically and immunohistochemically for IgG and C3 deposition. IgG fractions were separated from the sera of anti-GPI Abs-positive RA patients and healthy subjects, and injected into the metacarpophalangeal joints of 4 cynomolgus monkeys. On day 16, the joints were harvested and examined histologically and immunohistochemically. The expression of the C5a receptor (C5aR) molecule in the synovium was quantified by real-time PCR using cDNA from the monkeys' joints. The synovia of anti-GPI Abs-positive RA patients showed diffuse infiltration of cells, including mast cells, and strong deposition of IgG and C3. In monkeys, IgG from RA patients, including anti-GPI Abs, resulted in recruitment of granulocytes and mononuclear cells, strong deposition of IgG on the articular surface, and overexpression of C5aR, but no joint swelling. No infiltrated cells or IgG deposition were observed in monkeys injected with IgGs from healthy subjects. Our results suggest that IgG fraction from RA patients, including that of anti-GPI Abs, may play a role in the synovitis of RA, although the pathogenesis of human anti-GPI Abs is still uncertain.

Autoimmunity, polyclonal B-cell activation and infection.

It is widely believed that autoimmunity is an integral part of the immune system, and that genetic, immunologic, hormonal, environmental and other factors contribute to the pathogenesis of autoimmune disease. Thus, autoimmune disease may represent an abnormal expression of immune functions instead of loss of tolerance to self, and it can be organ specific or systemic in its manifestations. We review the various factors that contribute to the development of autoimmune disease; we also review the mechanisms of polyclonal B-cell activation, with emphasis on the role of infectious agents. We consider systemic lupus erythematosus in humans and in experimental animals as prototypic autoimmune disease, and we summarize data to indicate that polyclonal B-cell activation is central to the pathogenesis of systemic autoimmune disease. The effect of polyclonal B-cell activation, brought about by injections of a B-cell activator-lipopolysaccharide from Gram-negative bacteria-is sufficient to cause autoimmune disease in an immunologically normal host. In fact, autoimmune disease can be arrested if excessive polyclonal B-cell activation is suppressed; alternatively, autoimmune disease can be exacerbated if polyclonal B-cell activation is enhanced. We explore the mechanism of tissue injury when autoimmune disease is induced or exacerbated, and we consider the pathogenic roles of autoantibodies, immune complexes, complement, the blood cell carrier system, and the mononuclear phagocyte system. Although polyclonal B-cell activation may be the mechanism whereby various factors can cause or exacerbate systemic autoimmune disease, polyclonal B-cell activation may cause autoimmune disease on its own.

Diabetes, autoimmunity, and arteriosclerosis

Autoantibodies are believed to play a pathogenic role in a variety of clinical conditions. While the direct or indirect pathogenic role of autoantibodies has been well established in conditions such as autoimmune hemolytic anemia, systemic lupus erythematosus, rheumatoid arthritis, myasthenia gravis, etc., their precise significance in many of the diseases in which they are detected remains the object of controversy. Also, many questions remain unanswered concerning the factors that trigger their production. Many theories have been proposed to explain the origin of autoimmune responses; for example, it has been postulated that immune responses directed against host antigens could result from genetic predisposition, exaggerated random B cell activity, cross-reactivity between host and foreign antigens, or modification of host proteins as a consequence of infection, inflammation, drug administration, etc. Theories such as those invoking the release of previously sequestered antigens or the persistence of a forbidden clone have lost popularity since considerable data have accumulated suggesting that, at best, those theories could only apply to a very limited number of situations. It is also becoming increasingly more obvious that autoimmunity manifestations are seen in such disparate conditions that no single theory may be expected to satisfactorily explain the emergence of all types of autoimmunity. Diabetes mellitus (DM) is a typical example of a disease in which autoantibodies have been detected but in which a considerable degree of uncertainty remains as to their precise role. In type I (insulin-dependent) DM, anti-islet cell antibodies (ICA) have been observed in almost all newly diagnosed patients and have been suggested as being involved in the pathogenesis of islet ceil damage. Many of these patients develop islet cell antibodies, usually of the IgG2 and/or IgG4 subclasses, months or years before the appearance of clinical symptoms. At the time of diagnosis ICA are detected in as many as 90% of type I diabetic patients, but they diminish in frequency to 5-10% in patients with long-standing DM (1). There is also evidence that certain HLA class I and class II serotypes are unusually frequent in patients with type I DM; many patients are positive for DR-3 and DR-4 (MHC class II antigens). It has been speculated that the MHC class II genes coding for these highly represented specificities may be linked to immune response genes and may account for the increased risk of developing diabetes in individuals who express them. In type II (noninsulin dependent) diabetic patients, the coexistence of DR3/DR4 heterozygosity and ICA positivity is associated with significant impairment of l3 cell function, suggesting that both genetic and immune