Autoimmune disease and molecular mimicry: an hypothesis

Pharmacological support to anti-arthritic prospective of physostigmine: a new approach

Rheumatoid arthritis (RA) is a slowly progressing inflammatory autoimmune disease. Several features are involved in the RA pathogenesis in addition to environmental and genetic factors. Previously it has been reported that acetyl cholinesterase (AChE) activity is enhanced in old age and may contribute in the progression of RA. The current experimental work was projected to assess the activity of physostigmine (a cholinesterase inhibitor) for treatment of RA. In vitro and in vivo approaches were used for such evaluation. However, enzyme linked immunosorbent assays (ELISA) was performed to determine the concentrations of Prostaglandins E2 (PGE2) and tumor necrosis factor-α in arthritic rats after treatment with physostigmine. Moreover, anti-oxidant assays were employed to calculate the level of super oxide dismutase (SOD) and catalase peroxidase (CAT) in tissue of treated animals. The results claimed the dose dependent protective and stabilizing effect of physostigmine on denaturation of albumin (egg and bovine serum) protein and human red blood cell membrane, respectively, through in vitro studies. Furthermore, the physostigmine (10 and 20 mg/kg) significantly (p < 0.001) reduced the swelling of paw after induction of arthritis with formaldehyde or complete Freund's adjuvant (CFA) as compared to arthritic control animals. Moreover, significant (p < 0.001) reduction in the levels of inflammatory markers (PGE2 and TNF-α) at doses of 10 and 20 mg/kg of physostigmine has been observed in ELISA test. Likewise, there was a prominent rise in levels of SOD and CAT in animals treated with physostigmine. These findings pharmacologically conclude the anti-arthritic effect of physostigmine.

Association Between Medication Use and Bullous Pemphigoid: A Systematic Review and Meta-analysis

Importance

The association between the use of medications and the development of bullous pemphigoid (BP) is unclear.

Objective

To assess the associations between previous exposure to certain medications and BP.

Data Sources

For this systematic review and meta-analysis, PubMed, the Cochrane Central Register of Controlled Trials, and Embase were searched for relevant studies from inception to February 20, 2020.

Study Selection

Case-control or cohort studies and randomized clinical trials that examined the odds or risk of BP in patients with previous medication use were included. No geographic or language limitations were imposed.

Data Extraction and Synthesis

The Meta-analysis of Observational Studies in Epidemiology (MOOSE) guideline was followed. The Newcastle-Ottawa Scale was used to evaluate the risk of bias of included observational studies; Cochrane Collaboration's tool was used for randomized clinical trials. Aggregate data were used to conduct a random-effects model meta-analysis if the included studies were sufficiently homogenous. Subgroup analyses were performed for use of various medications of the same category.

Main Outcomes and Measures

Odds ratio (OR), hazard ratio, and risk ratio of bullous pemphigoid in association with medication use.

Results

This meta-analysis included 13 case-control studies, 1 cohort study, and 1 randomized clinical trial with a total of 285 884 participants. The meta-analysis of case-control studies showed a significant association of BP with previous use of aldosterone antagonists (pooled OR, 1.75; 95% CI, 1.28-2.40), dipeptidyl peptidase 4 inhibitors (pooled OR, 1.92; 95% CI, 1.55-2.38), anticholinergics (pooled OR, 3.12; 95% CI, 1.54-6.33), and dopaminergic medications (pooled OR, 2.03; 95% CI, 1.34-3.05). One cohort study found an increased risk of BP among patients receiving dipeptidyl peptidase 4 inhibitors (hazard ratio, 2.38; 95% CI, 1.16-4.88; P = .02). One trial found a higher occurrence of BP in patients with diabetes receiving linagliptin (0.2% in diabetes group vs 0% in the placebo group).

Conclusions and Relevance

The findings of this systematic review and meta-analysis suggest that aldosterone antagonists, dipeptidyl peptidase 4 inhibitors, anticholinergics, and dopaminergic medications are associated with BP. These medications should be judiciously prescribed, particularly in high-risk patients who are elderly and have disabling neurologic disorders.

Fixed drug eruptions, bullous drug eruptions, and lichenoid drug eruptions

Drug reactions are among the most common reasons for inpatient dermatology consultation. These reactions are important to identify because discontinuation of the offending agent may lead to disease remission. With the rising use of immunomodulatory and targeted therapeutics in cancer care and the increased incidence in associated reactions to these drugs, the need for accurate identification and treatment of such eruptions has led to the development of the "oncodermatology" subspecialty of dermatology. Immunobullous drug reactions are a dermatologic urgency, with patients often losing a significant proportion of their epithelial barrier; early diagnosis is critical in these cases to prevent complications and worsening disease. Lichenoid drug reactions have myriad causes and can take several months to occur, often leading to difficulties identifying the offending drug. Fixed drug eruptions can often mimic other systemic eruptions, such as immunobullous disease and Stevens-Johnson syndrome, and must be differentiated from them for effective therapy to be initiated. We review the clinical features, pathogenesis, and treatment of immunobullous, fixed, and lichenoid drug reactions with attention to key clinical features and differential diagnosis.

The pathogenesis of bullous skin diseases

Bullous skin diseases are a group of dermatoses characterized by blisters and bullae in the skin and mucous membranes. The etiology and pathogenesis of bullous skin diseases are not completely clear. The most common are pemphigus and bullous pemphigoid (BP). Autoantibodies play critical roles in their pathogenesis. Abnormalities in the adhesion between keratinocytes in patients with pemphigus leads to acantholysis and formation of intra-epidermal blisters. Anti-desmoglein autoantibodies are present both in the circulation and skin lesions of patients with pemphigus. The deficient adhesion of keratinocytes to the basement membrane in BP patients gives rise to subepidermal blisters. Autoantibodies against the components of hemidesmosome can be detected in BP patients. Many novel therapeutics based on knowledge of the pathogenesis have emerged in recent years.

Drug-induced pemphigoid: a review of the literature

Bullous pemphigoid is an acquired autoimmune disease that is characterized by subepidermal blistering and affects mainly the elderly. The pathogenesis of the condition has not yet been fully elucidated, but it is widely accepted that a strong correlation with various medications may exist. In reality, more than 50 different drugs have been associated with the appearance of bullous pemphigoid and as new therapies emerge, this number is very likely to increase. A number of pathogenetic mechanisms have been proposed in the past. It is true that a delicate immunological balance is disturbed in all patients with the disease. The variable effects that may be exhibited by the use of biological drugs could shed some light in this complex immunological behaviour. At the same time, drug-induced bullous pemphigoid is difficult to differentially diagnose from its idiopathic counterpart, as the clinical picture and histopathological findings in both conditions may only have subtle differences. Patients who present with bullous pemphigoid and receive multiple regimens should always be suspected of suffering from the drug-induced variant of the condition. This possibility must be considered, as after the withdrawal of the suspect medication most patients respond rapidly to treatment and do not experience relapses.

Immunogenetics of drug-induced skin blistering disorders. Part I: Perspective

The overall immunopathogenesis relevant to a large series of disorders caused by a drug or its associated hyperimmune condition is discussed based upon the examination of the genetics of severe drug-induced bullous skin problems (sporadic idiosyncratic adverse events, including Stevens-Johnson syndrome and toxic epidermal necrolysis). An overarching pharmacogenetic schema is proposed. Immune cognition and early-effector processes are focused upon and a challenging synthesis around systems evolution is explained by a variety of projective analogies. Etiology, human leukocyte antigen-B, immune stability, dysregulation, pharmacomimicry, viruses and an aggressive ethnically differentiated 'karmic' response are discussed.

The contribution of gammadelta T cells to the pathogenesis of EAE and MS

Gammadelta T cells are a multifaceted group of cells which have both innate and adaptive characteristics and functions. Although they are most commonly known for their response to mycobacterium and their locations at mucosal sites, their roles in autoimmunity are still unclear. gammadelta T cells have been seen in the CSF and lesions of Multiple Sclerosis patients and although their function is not entirely understood, it is clear these cells may have roles in regulating autoimmune inflammation in the CNS. Recent studies have focused on the role of gammadelta T cells in MS and EAE as both pathogenic and protective, their functions within the CNS, the types of subsets and a possible role in Th17 inflammation. In this review we will examine the data acquired from both human patients and the murine models of MS, experimental autoimmune encephalomyelitis (EAE), in order to gain a clear picture of how gammadelta T cells influence pathogenesis of EAE and MS.

Role of antibody paratope conformational flexibility in the manifestation of molecular mimicry

Molecular mimicry is a recurrent theme in host defense processes. The correlation of functional mimicry with the structural features of the antibody paratope has been investigated, addressing the consequences of mimicry in host immune mechanisms. Two anti-mannopyranoside antibodies, 1H7 and 2D10, representing the possible extremes of the recognition spectrum with regard to peptide-carbohydrate mimicry were examined. Crystallographic and molecular dynamics simulation analyses established correlation between the antibody flexibility and the manifestation of mimicry. It was evident that monoclonal antibody (mAb) 1H7, which has a narrow specificity in favor of the immunizing antigen, exhibited structural invariance. On the other hand, the antigen-combining site of 2D10, the mimicry-recognizing antibody, showed substantial divergence in the complementarity determining region loops. The docking of mannopyranoside within the antibody paratope revealed multiple modes of binding of the carbohydrate antigen in mAb 2D10 vis à vis single docking mode in mAb 1H7, which overlapped with the common monosaccharide binding site defined in anti-carbohydrate antibodies. The presence of additional antigen binding modes is perhaps reflective of the utilization of conformational flexibility in molecular mimicry. A relatively broader recognition repertoire--attributable to paratope flexibility--may facilitate the recognition of altered antigens of invading pathogens while the antibodies with narrow recognition specificity maintain the fidelity of the response.

Paratope plasticity in diverse modes facilitates molecular mimicry in antibody response

The immune response against methyl-alpha-D-mannopyranoside mimicking 12-mer peptide (DVFYPYPYASGS) was analyzed at the molecular level towards understanding the equivalence of these otherwise disparate Ags. The Ab 7C4 recognized the immunizing peptide and its mimicking carbohydrate Ag with comparable affinities. Thermodynamic analyses of the binding interactions of both molecules suggested that the mAb 7C4 paratope lacks substantial conformational flexibility, an obvious possibility for facilitating binding to chemically dissimilar Ags. Favorable changes in entropy during binding indicated the importance of hydrophobic interactions in recognition of the mimicking carbohydrate Ag. Indeed, the topology of the Ag-combining site was dominated by a cluster of aromatic residues, contributed primarily by the specificity defining CDR H3. Epitope-mapping analysis demonstrated the critical role of three aromatic residues of the 12-mer in binding to the Ab. Our studies delineate a mechanism by which mimicry is manifested in the absence of either structural similarity of the epitopes or conformational flexibility in the paratope. An alternate mode of recognition of dissimilar yet mimicking Ags by the anti-peptide Ab involves plasticity associated with aromatic/hydrophobic and van der Waals interactions. Thus, antigenic mimicry may be a consequence of paratope-specific modulations rather than being dependent only on the properties of the epitope. Such modulations may have evolved toward minimizing the consequences of antigenic variation by invading pathogens.

Disease-specific cross-reactivity between mimicking peptides of heat shock protein of Mycobacterium gordonae and dominant epitope of E2 subunit of pyruvate dehydrogenase is common in Spanish but not British patients with primary biliary cirrhosis

Previous studies on Spanish patients with Primary Biliary Cirrhosis (PBC) have shown extensive, disease-specific cross-reactivity between the 65-kDa heat shock protein (hsp65) of Mycobacterium gordonae and pyruvate dehydrogenase complex-E2 (PDC-E2), the major target of anti-mitochondrial antibody (AMA). Studies on a British population were unable to substantiate these findings. Having found that there is an excellent and almost unique match between the PDC-E2 autoepitope and a sequence in mycobacterial hsp65s, we tested the corresponding peptides by ELISA for cross-reactivity using sera from 90 PBC patients, 40 Spanish and 50 British, and 84 pathological controls. Reactivity to the MYCGO hsp65(90-104)/human PDC-E2(212-226)pair was present in 19 (47.5%) Spanish PBC patients and in 2 (4%) of the 50 British. Reactivity was not seen in any of the controls. Simultaneous reactivity to mimics was due to cross-reactivity as confirmed by inhibition studies. Three dimensional modelling predicts mycobacterial hsp65(90-104)to be exposed on the surface of the protein. The affinity of anti-hsp65(90-104)antibody was higher than that of anti-PDC-E2(212-226). Hsp65(90-104)is a target of disease-specific cross-reactivity to PDC-E2(212-226). The geographical confinement of this phenomenon is probably the result of complex genetic, environmental and immunological interaction.

Peptides from common viral and bacterial pathogens can efficiently activate diabetogenic T-cells

Cross-reactivity between an autoantigen and unknown microbial epitopes has been proposed as a molecular mechanism involved in the development of insulin-dependent diabetes (type 1 diabetes). Type 1 diabetes is an autoimmune disease that occurs in humans and the nonobese diabetic (NOD) mouse. BDC2.5 is an islet-specific CD4+ T-cell clone derived from the NOD mouse whose natural target antigen is unknown. A biometrical analysis of screening data from BDC2.5 T-cells and a positional scanning synthetic combinatorial library (PS-SCL) was used to analyze and rank all peptides in public viral and bacterial protein databases and identify potential molecular mimic sequences with predicted reactivity. Selected sequences were synthesized and tested for stimulatory activity with BDC2.5 T-cells. Active peptides were identified, and some of them were also able to stimulate spontaneously activated T-cells derived from young, pre-diabetic NOD mice, indicating that the reactivity of the BDC2.5 T-cell is directed at numerous mouse peptides. Our results provide evidence for their possible role as T-cell ligands involved in the activation of diabetogenic T-cells.

Association between the primary biliary cirrhosis specific anti-sp100 antibodies and recurrent urinary tract infection

BACKGROUND AND AIMS

Recurrent urinary tract infections (rUTI) have been suggested to be involved in the induction of anti-mitochondrial antibodies (AMA), the serological hallmark of primary biliary cirrhosis (PBC), in view of the presence of AMA in rUTI women without liver disease and conversely of a high prevalence of rUTI in women with PBC. This prompted us to investigate whether PBC-specific anti-nuclear antibodies (ANA) to sp100, gp210 and lamin B receptor (LBR) antigens may also be related to rUTI.

METHODS AND SUBJECTS

PBC-specific ANA reactivities were investigated in 20 women with rUTI but without liver disease, some of whom were AMA-seropositive; 40 women with PBC, with or without rUTI; and 104 pathological and 23 healthy controls.

RESULTS

Among the women with rUTI but without liver disease, 8 (80%) of 10 AMA-positive women reacted with sp100 compared with none of the 10 AMA-negative women. Among the PBC patients, 14 (74%) of 19 with rUTI and 1 (4.8%) of the 21 without rUTI reacted with sp100. None of the rUTI women without liver disease reacted with gp210 or LBR. None of 127 pathological and healthy controls had PBC-specific ANA reactivity.

CONCLUSIONS

Anti-sp100 reactivity strongly correlates with AMA seropositivity in rUTI women, with or without evidence of primary biliary cirrhosis. These findings provide additional support to the notion that E. coli infection is involved in the induction of PBC-specific autoimmunity. Additional factors must be involved in the progression to overt autoimmune disease.

Autoantibodies to the transcriptional factor SOX13 in primary biliary cirrhosis compared with other diseases

The molecule SOX13 was initially identified as an autoantigen (ICA12) in Type 1 diabetes. SOX13 is a member of the SOX family of transcriptional regulatory proteins that contain a high mobility group (HMG) motif with structural similarity to HMG proteins 1 and 2. Antibodies to HMG 1 and 2 occur in autoimmune diseases of the liver and in ulcerative colitis. We measured the occurrence and levels of anti-SOX13 by radioimmunoprecipitation in primary biliary cirrhosis (PBC) and other diseases, and compared frequencies with anti-HMG measured by ELISA. Anti-SOX13 was detected in 18% of patients with PBC, 13% with autoimmune hepatitis, 18% with Type 1 diabetes, at lower frequencies in other conditions including the multisystem autoimmune diseases, systemic lupus erythematosus and rheumatoid arthritis, and in 1% of normal sera. Anti-HMG1 and anti-HMG2 occurred at frequencies of 30% and 35% respectively in PBC. Serum levels of anti-SOX13 and anti-HMG correlated significantly for PBC although not for Type 1 diabetes. Anti-SOX13 in PBC may occur merely as an immune response to products of damage to parenchymal tissue, or may be illustrative of a general proclivity of transcriptional regulatory proteins to elicit autoimmune responses.

Molecular mimicry in type 1 diabetes mellitus revisited: T-cell clones to GAD65 peptides with sequence homology to Coxsackie or proinsulin peptides do not crossreact with homologous counterpart

Type 1 diabetes mellitus is a T-cell mediated autoimmune disease in which the insulin-producing pancreatic beta cells are selectively destroyed. Molecular mimicry and T-cell crossreactivity to beta-cell autoantigens and environmental agents with sequence similarities have been a proposed mechanism underlying the pathogenesis of type 1 diabetes, but actual crossreactivity has not yet been demonstrated. We isolated and investigated T cells reactive to GAD65 peptides and homologous peptides of the Coxsackie virus protein P2C and proinsulin from recent onset type 1 diabetes patients, and tested their fine specificity and cytokine production profile. Six T-cell lines specific for GAD65 peptides (amino acids 491-530) with homology to proinsulin (B20-C14) were isolated from six newly diagnosed patients with type 1 diabetes, but none of the stable T-cell lines crossreacted to the homologous proinsulin peptides. Similarly, none of four T-cell lines reactive to GAD65 peptides (amino acids 247-280) with sequence homology to Coxsackie P2C (amino acids 30-50) crossreacted to the homologous viral peptide. Two T-cell lines corecognized a GAD65 peptide and a Coxsackie P2C peptide. However, the antigen-specific T-cell clones from these T-cell lines were reacting either with the GAD65 peptide or the Coxsackie P2C peptide using different restriction elements without crossreacting to the homologous peptide. Our data demonstrate that homologous peptides previously proposed to serve as targets for crossreactivity indeed are immunogenic. Yet, T-cell clones did not crossreact with linear sequence homologies, despite strong T-cell responses to individual peptides.

Do immune complexes formed with autoantibodies have a role in the maintenance of immune homeostasis through interaction with FC receptors

Natural autoantibodies play an important regulatory role in the maintenance of immune homeostasis. They act as a first line of defense against environmental pathogens like toxins, bacteria and erythrocytes. In humans they are mainly produced by CD5+ B cells that are under the control of a regulatory T cell population. Fc-gamma receptors are involved in antigen recognition and signal transduction and tuning, and some of the members of the FcR family have structural similarity to MHC molecules; they may interact with multiple Ig ligands and with non-Ig ligands. We discuss the interactions between immune-complexes formed with natural autoantibodies and Fc-gamma receptors and suggest that such interactions may affect self-recognition in the thymus and regulate immune homeostasis.

Recognising antibacterial hypersensitivity in children

Adverse reactions to antibacterial agents are not uncommon in children. They are classified as 'immediate' or 'nonimmediate' according to the time interval between drug administration and onset. Immediate reactions occur within 1 hour and are manifested by urticaria and/or angioedema, bronchospasm and anaphylactic shock; immunological reactions are mediated by IgE antibodies. The main nonimmediate reactions (occuring after more than 1 hour) are maculopapular rash, urticaria and serum sickness; T lymphocytes may participate in maculopapular rash. Clinical assessment of such reactions is complex. The patient's history is fundamental; the allergological examination includes in vivo and in vitro tests selected on the basis of the clinical features and the phase of reaction. In the late phase, prick and intradermal tests are sensitive in evaluating beta-lactam allergy. Together with delayed-reading intradermal testing, patch testing seems to be useful in diagnosing maculopapular reactions to systemically administered aminopenicillins. Determination of specific IgE levels is the most common in vitro method for diagnosing immediate reactions. In the acute phase, serum tryptase and urinary N-methylhistamine assays are reliable in diagnosing type I pathogenic mechanisms in immediate reactions. Unfortunately, there are few in vitro tests for evaluating other reactions, and most are not fully validated. In selected cases, provocation tests should be performed.

Crossreactive recognition of viral, self, and bacterial peptide ligands by human class I-restricted cytotoxic T lymphocyte clonotypes: implications for molecular mimicry in autoimmune disease

The immunodominant, CD8(+) cytotoxic T lymphocyte (CTL) response to the HLA-B8-restricted peptide, RAKFKQLL, located in the Epstein-Barr virus immediate-early antigen, BZLF1, is characterized by a diverse T cell receptor (TCR) repertoire. Here, we show that this diversity can be partitioned on the basis of crossreactive cytotoxicity patterns involving the recognition of a self peptide-RSKFRQIV-located in a serine/threonine kinase and a bacterial peptide-RRKYKQII-located in Staphylococcus aureus replication initiation protein. Thus CTL clones that recognized the viral, self, and bacterial peptides expressed a highly restricted alphabeta TCR phenotype. The CTL clones that recognized viral and self peptides were more oligoclonal, whereas clones that strictly recognized the viral peptide displayed a diverse TCR profile. Interestingly, the self and bacterial peptides equally were substantially less effective than the cognate viral peptide in sensitizing target cell lysis, and also resulted only in a weak reactivation of memory CTLs in limiting dilution assays, whereas the cognate peptide was highly immunogenic. The described crossreactions show that human antiviral, CD8(+) CTL responses can be shaped by peptide ligands derived from autoantigens and environmental bacterial antigens, thereby providing a firm structural basis for molecular mimicry involving class I-restricted CTLs in the pathogenesis of autoimmune disease.

Identification of mimicry peptides based on sequential motifs of epitopes derived from 65-kDa glutamic acid decarboxylase

Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease with a predominantly non-hereditary etiology that results in a destruction of pancreatic beta cells by autoaggressive T lymphocytes. Neither the mechanism of initial stimulation of these T cells nor the nature of the environmental factors implicated in the disease have so far been identified. However, both issues are taken into account by the hypothesis of initial T cell activation by viral or bacterial mimicry peptides with sequence similarities to pancreatic self antigens. We determined sequential epitope motifs to search for mimicry peptides stimulating T cell lines specific for two epitopes derived from the IDDM autoantigen 65-kDa glutamic acid decarboxylase (GAD65). These were GAD65 (88-99), presented by HLA-DRB1*0101, and GAD65 (248-257), presented by HLA-DRB5*0101. T cell stimulation by peptides with substitutions in HLA anchor or T cell contact positions was analyzed to establish degenerate epitope motifs for database searching. Out of 28 tested candidate mimicry peptides derived from bacterial, viral and human proteins, 3 stimulated T cell lines and a T cell clone specific for epitope GAD65 (248-257). Our results demonstrate that mono- and polyclonal GAD65-specific T cells from IDDM patients can be stimulated by viral and bacterial peptides with little apparent sequence homology with autoantigenic epitopes. Moreover, in a synopsis with related published studies, our findings suggest that simple degenerate search motifs comprising principal T cell contacts plus HLA class II binding motifs may suffice to identify most mimicry peptides.

Combined analysis of GAD65 and ICA512(IA-2) autoantibodies in organ and non-organ-specific autoimmune diseases confers high specificity for insulin-dependent diabetes mellitus

There is evidence that insulin-dependent diabetes mellitus (IDDM) may develop in association with other non-beta-cell-specific autoimmune diseases. We aimed to assess whether autoantibodies to the islet cell antigens glutamic acid decarboxylase (Mr 65,000 isoform) (GAD65) and ICA512(IA-2), present alone or in combination, are limited to IDDM or also occur in other organ- or non-organ-specific autoimmune disorders. We determined the frequency of these autoantibodies by radioimmunoassay in 199 sera from patients with autoimmune thyroid diseases (AITD), rheumatoid arthritis (RA), systemic lupus erythematosus (SLE) and primary biliary cirrhosis (PBC), and compared the results with those from 507 newly diagnosed patients with IDDM and 280 healthy controls. ICA512(IA-2) autoantibodies were detected exclusively in AITD with concurrent IDDM, but not in other autoimmune diseases without IDDM, whereas GAD65 autoantibodies exceeded the limit of normal in 67.7% (21 of 31) of patients with AITD who also had IDDM and in 5.5% (three of 55) of patients with PBC. The frequency of either GAD65 and/or ICA512(IA-2) autoantibodies was significantly higher in patients with AITD who also had IDDM (27 of 31, 87.1%) than in those with AITD alone (one of 53, 1.9%; P<10(-6)), but was not significantly different from those patients with newly diagnosed IDDM (418 of 507, 82.4%). Neither patients with organ- or non-organ-specific autoimmune diseases without IDDM nor healthy controls had autoantibodies against both GAD65 and ICA512(IA-2). Despite the fact that one of the two autoantibodies was occasionally detected in patients with non-beta-cell-specific autoimmune diseases without IDDM, combined determination of GAD65 and ICA512(IA-2) autoantibodies specifically identified IDDM in the majority of patients with AITD. In conclusion, because of the strong association of IDDM with AITD, testing for multiple islet autoanti-bodies could be useful as a predictive marker for risk of progression to IDDM onset amongst patients with autoimmune thyroid disorders.

Molecular mimicry and the pathogenesis of insulin-dependent diabetes mellitus: still just an attractive hypothesis

An abundant body of literature suggests that the cellular immune system plays a key role in the autoimmune destruction of insulin-secreting pancreatic beta cells that results in insulin-dependent diabetes mellitus (IDDM). For years, studies have supported the concept that molecular mimicry, a process of antigenic crossreactivity resulting from similarity in amino acid sequence or structure, could be one pathway whereby this disease is induced or its natural history modulated. However, the transfer of this 'hypothesis' to that of a proven mechanism underlying this clinical disorder has been slow and never fully achieved. This article reviews the theoretical basis for molecular mimicry in autoimmune disease and the evidence supporting its role in the pathogenesis of IDDM.

Antibodies against a peptide sequence located in the linker region of the HMG-1/2 box domains in sera from patients with juvenile rheumatoid arthritis

OBJECTIVE

To extend our work on the mapping of B cell epitopes on nucleosomal high mobility group (HMG) proteins in the sera of patients with juvenile rheumatoid arthritis (JRA).

METHODS

Seventy-seven pauciarticular-onset JRA serum samples from antinuclear antibody (ANA)-positive patients and 42 polyarticular-onset JRA patient sera found to react with HMG-2 by immunoblotting were used in this study. To identify B cell epitopes on HMG-2, recombinant HMG-2 protein fragments were used in enzyme-linked immunosorbent assay (ELISA) and in competition ELISA experiments with a set of overlapping synthetic peptides. Fine epitope mapping was achieved by oligopeptide synthesis, followed by immunoblotting.

RESULTS

Pauciarticular, but not polyarticular, JRA patient sera were found to recognize a lysine-rich major epitope (KKGKKKDP), which is located in the linker region of the HMG box domains of the HMG-2 nonhistone chromosomal protein. No significant immunoreactions were observed in sera from ANA-negative JRA patients and in sera from children with nonrheumatic diseases, indicating that this epitope seems to be specific for pauciarticular-onset JRA.

CONCLUSION

In addition to our previous finding that JRA sera will react with a defined epitope on HMG-17, pauciarticular JRA patient sera were also found to recognize a defined epitope on the HMG-2 protein, thus suggesting the importance of this epitope in the etiology of JRA.

Topological analysis of the functional mimicry between a peptide and a carbohydrate moiety

The shared surface topology of two chemically dissimilar but functionally equivalent molecular structures has been analyzed. A carbohydrate moiety (alpha-D-mannopyranoside) and a peptide molecule (DVFYPYPYASGS) bind to concanavalin A at a common binding site. The cross-reactivity of the polyclonal antibodies (pAbs) was used for understanding the topological relationship between these two independent ligands. The anti-alpha-D-mannopyranoside pAbs recognized various peptide ligands of concanavalin A, and the anti-DVFYPYPYASGS pAbs recognized the carbohydrate ligands, providing direct evidence of molecular mimicry. On the basis of differential binding of various rationally designed peptide analogs to the anti-alpha-D-mannopyranoside pAbs, it was possible to identify different peptide residues critical for the mimicry. The comparison of circular dichroism profiles of the designed analogs suggests that the carbohydrate mimicking conformation of the peptide ligand incorporates a polyproline type II structural fold. The concanavalin A binding activity of these analogs was found to have a direct correlation with the topological relationship between peptide and carbohydrate ligands.

Insulin-dependent diabetes mellitus: the hypothesis of molecular mimicry between islet cell antigens and microorganisms

Insulin-dependent diabetes mellitus (IDDM) in humans and the non-obese diabetic mouse is a polygenic disease, resulting from an autoimmune destruction of the insulin-secreting pancreatic beta cells. At least in NOD mice, the process is mediated through a T helper 1-cell-mediated cytotoxicity pathway. Although there is much circumstantial evidence to suggest that IDDM is environmentally induced, recent studies support the possibility that the inductive event involves cross-reactive immune responses to antigenic epitopes acting as molecular mimics between microbial proteins and autoantigens expressed by pancreatic insulin-secreting beta cells. The following article reviews the evidence for this concept.

A common structural motif in immunopotentiating peptides with sequences present in human autoantigens. Elicitation of a response mediated by monocytes and Th1 cells

We have found a common structural motif in human autoantigens, heat shock proteins and viral proteins. Peptides modelled after sequences present in those molecules were synthesized and immunomodulating properties tested. They share a core of 15 amino acid residues and a common pattern ('2-6-11' motif) characterized by requirements at fixed positions with respect to a Pro (position 6); an apolar residue or a Lys at position 2; and a Glu, Asp or Lys at position 11. Any of these peptides, when added to cultures of lymphomononuclear cells, caused the activation of monocytes manifested by a release of IL-1 alpha, IL-1 beta and TNF alpha. A release of INF gamma and IL-2 took also place; this release was abolished by anti-DR antibodies. Neither IL-4 nor IL-5 could be detected. This suggests a presentation by APCs and the appearance of cells with a Th1 phenotype. Monocytes and Th1 cells freshly obtained from 12 patients of Graves' disease, 8 of Hashimoto's disease and 8 of primary biliary cirrhosis exhibited activation features similar to those found in cells from healthy subjects incubated in the presence of peptides with a "2-6-11' motif and representing fragments of autoantigens. Their immunopotentiating properties suggest their involvement in the initiation or progression of the autoimmune response mediated by activated monocytes and Th1 cells.

Mechanisms of drug reactions: the metabolic track

Hypersensitivity syndrome (HSR) describes a drug-induced symptom complex consisting of fever, rash, and internal organ involvement. Although these reactions are rare, they are very important because of their severity and unpredictability. The metabolic conversion of drugs to chemically-reactive products is now established as a prerequisite for many idiosyncratic drug reactions. In the setting of HSR, an imbalance in the rates of formation of reactive metabolites and of enzymatic detoxification can lead to accumulation of these byproducts. Reactive metabolites could act as haptens eliciting an immune response, covalently bind target proteins causing cell death, or interact with nucleic acids leading to mutations. The lymphocyte toxicity assay (LTA) provides an in vitro assessment of host susceptibility to reactive metabolites of a given drug. It has validated the clinical finding of increased risk of HSR in first degree relatives of patients. It is hoped that the LTA will be used to predict host susceptibility before drug exposure. Ultimately it is hoped that the genetic defects that lead to drug reactions will be identified. This would improve drug development safety and allow primary prevention of serious reactions.

[Immunopathological mechanisms of human immunodeficiency virus infection]

Human immunodeficiency virus (HIV) infection usually elicits an early, strong and efficient immune response, despite which the virus can persist in the organism by using a complex strategy. It escapes immune surveillance through direct and indirect effects on cells of the immune system; by modifying its biological properties; and by antigenic drift as a result of the immune response selective pressure. The immune response to the virus could also lead to detrimental immunopathological mechanisms. In particular, any immune stimulation may increase the viral load, and specific immunisation may lead to enhancement of infection. However, reports that some "at risk" non HIV-infected individuals present markers of cell-mediated immunity to the virus, and occurrence of "long-term survivors" strongly suggests that the immune response to HIV may sometimes be protective. Understanding the immunological mechanisms involved in this infection is thus essential.

Induction of T cell responses to a self-antigen following allotransplantation

T cell tolerance to self-antigens is established through the recognition by immature T cells of dominant self-peptides presented in association with self-MHC molecules in the developing thymus (negative selection). The self-peptide Dd 61-80 is dominant in syngeneic BALB/c mice (H2d). T cell tolerance to Dd 61-80 in this mouse strain resulted in the absence of T cell proliferation following in vivo priming with Dd 61-80 peptide. Here, we show that transplantation of BALB/c mice with allogeneic B10.A (H2a) splenocytes led to an autoimmune T cell response toward the dominant self-peptide Dd 61-80. No T cell responses to Dd 61-80 peptide were observed after transplantation of C57BL/6 (H2b) splenocytes into BALB/c recipients. In addition, we provide evidence indicating that the breakdown of tolerance to Dd 61-80 self-peptide resulted from the presentation of the donor crossreactive peptide Kk 61-80 at the surface of recipient antigen-presenting cells. Taken together, our results suggest that following allotransplantation, T cell responses to donor antigens could spread to crossreactive determinants on self-proteins, thus perpetuating and amplifying the rejection process and presumably initiating tissue-specific autoimmune disorders.

Molecular mimicry in the MHC: hidden clues to autoimmunity?

The term 'molecular mimicry' has been used to describe a spectrum of antigenic crossreactivities thought to underlie autoimmune disease. For T-cell crossreactivities to occur, appropriate T-cell clones must be available. Here, Harold Baum, Huw Davies and Mark Peakman speculate that an important source of self-peptides that govern thymic selection of such clones are MHC molecules themselves.

Autoimmune diseases: nuclear autoantigens can be found at the cell-surface

The pathogenesis of autoimmune diseases is only partially understood. In particular, the question remains why many nuclear proteins have been identified as autoantigens. One possible mechanism for an autoimmune response to nuclear proteins involves their exposure to the immune system. In this report we discuss currently available data on the exposure of nuclear proteins by expression at the cell-surface. Although the pathways of surface expression remain unclear, the presence of nuclear proteins at the cell-surface might reflect a pathological reaction leading to an exposure of epitopes, e.g. to self-reactive B-cells. It is suggested that cell-surface expression of intracellular proteins can contribute to the generation of autoimmune diseases.

Sequence of the highly conserved gene encoding the human 54kDa subunit of signal recognition particle

The complete sequence of the human gene encoding the 54kDa subunit of the signal recognition particle has been isolated from a cDNA library. Degenerate oligonucleotides based on the 5' and 3' coding region of the canine gene and a mammalian codon usage table, were used to amplify the sequence using PCR. The nucleotide sequence of the human gene shows that the human sequence shares a 95.8% nucleotide sequence homology and 100% amino acid sequence homology to it's canine counterpart. The sequence has been given the accession number X86373 in the EMBL database.

Binding of human IgM from a rheumatoid factor to IgG of 12 animal species

The binding of IgM from a rheumatoid factor (RF-IgM) to IgG from 12 animal species was analyzed by an ELISA system. The RF-IgM bound various animal IgG with dissimilar affinities. The binding of RF-IgM to animal IgG was inhibited by addition of protein A, which binds some animal IgG by recognizing the junctional site on CH2-CH3 domains in the Fc region. As previously reported, no significant correlation was observed between the binding of RF-IgM to IgG and the content of galactose-free oligosaccharides, which is increased in IgG of rheumatoid arthritis patients or autoimmune mice. We suggest that the crucial epitope of IgG for RF-IgM binding is not the oligosaccharide structure generated specifically in IgG of autoimmune diseases but that RF-IgM may recognize a certain protein conformation of a region in IgG near the binding site of protein A.

Cross-recognition by T cells of an epitope shared by two unrelated mycobacterial antigens

The molecular mimicry represented by cross-recognition of determinants shared by unrelated antigens by antibodies or T cells is of broad immunological interest. In this study, we analyzed the cross-recognition by CD4+ T cells of a peptide epitope shared by two mycobacterial proteins of diverse sequence, represented by the 19-kDa antigen of Mycobacterium tuberculosis and the 28-kDa antigen of Mycobacterium leprae. This epitope was immunodominant with respect to the 19-kDa antigen, but cryptic in relation to the 28-kDa antigen. The cross-reactive epitope cores were identified by Pepscan window analysis and found to be eight residues long in both antigens (residues 69-76 and 127-134). Alignment of these octameric sequences revealed two identical and five conservatively related amino acids. Within the epitope core, two residues (73Asn and 76Ile) were identified as critical for recognition on the basis of inhibition of the cross-reactive T cell proliferative response using singly substituted analog peptides. These results suggest that T cell cross-reactive epitopes can exist in proteins with apparently not more than random levels of sequence homology. Their potential for unsuspected cross-sensitization may play a role in the maintenance of T cell memory, in the pathogenesis of autoimmune diseases and possibly in a wide range of host immune responses to infectious pathogens.

Molecular and immunological characterization of hr44, a human ocular component immunologically cross-reactive with antigen Ov39 of Onchocerca volvulus

Structural similarities between host self-antigens and infectious organisms may be involved in the expression of autoimmune reactivity and development of autoimmune disease. The unique eye pathology associated with Onchocerca volvulus infection, particularly the development of posterior segment lesions, may be promoted by such autoreactive responses. Ov39 is a parasite-derived antigen that has been shown previously to be antigenically cross-reactive with a 44,000-M(r) host ocular component. A clone, designated hr44, was isolated from a cDNA library of human retina by immunoscreen using serum to Ov39. A monoclonal antibody raised to Ov39 also reacted with hr44 and gave evidence for a shared conformational epitope. The primary structure analysis showed that identities between the antigens are limited and confined to small peptides. The cross-reactivity between the antigens appears to involve T cells, since Ov39-specific T cells can be stimulated by hr44, a neural-specific antigen. Based on secondary structure prediction, hr44 has the typical features of a membrane-associated type I antigen with an amino-terminal extracellular domain. mAbs and antisera localized the antigen in the optic nerve, neural retina, retinal pigment epithelium, as well as the epithelial layers of ciliary body and iris.

Mitochondrial antigens, molecular mimicry and autoimmune disease

The immune system is normally tolerant to mitochondrial self-antigens, but responsive against bacteria. Low-titre anti-mitochondrial antibodies (AMA) might be involved in this discrimination. Tolerance is broken in diseases characterised by high titre AMA. Some of these AMA, against cardiolipin, cross-react with DNA. The best studied AMA are those characterising primary biliary cirrhosis (PBC). These are directed against E2 subunits of the oxo-acid dehydrogenase complexes, and also against subunits E1 alpha, E1 beta and X of the pyruvate dehydrogenase complex. AMA of PBC patients also react with bacterial E2s. Reactivities are primarily peptide-specific but with cross-reactivity between mitochondrial and microbial antigens and between E2s of respective complexes. Immunodominant epitopes, for anti E2 AMA, include the conserved sequence flanking the site of lipoyl attachment. It is proposed that the initial stimulus for antibody production is chronic urinary tract infection. AMA themselves are not pathogenic, but CD4+ T-cells would be primed, recognising the lipoyl domain epitope in association with class II HLA. Inappropriate expression of class II antigens on bile duct epithelia, (as found in PBC), might lead to presentation of a particular fragment of HLA-DR alpha, known to be a major MHC presented self-peptide in the mouse. That sequence strongly mimics the lipoyl domain and might be recognised by primed T-cells, initiating the autoimmune cascade. In the mouse, a peptide of ND1 of Complex I is presented in association with class I MHC. Cells exhibiting somatic mutation of such a peptide might thus be subject to attack by CD8+ T-cells. If such peptides were presented by class II HLA, autoimmune diseases might arise, related to mimicry between such peptides and microbial sequences and/or self-antigens. These considerations might apply in Leber's disease and in age-related pathology.

Autoimmune mechanisms in the pathogenesis of paraneoplastic nervous system disease

There is compelling circumstantial evidence that humoral autoimmune response may be involved in the generation of paraneoplastic neurologic syndromes (PNS). However, still it is unproven whether the autoantibody is pathogenic or represents an epiphenomenon to the actual disease process. Paraneoplastic antibodies have been identified in patients with PNS which react with similar antigenic epitopes in tumor and neurons. However, the antigens identified by the paraneoplastic antibodies are primarily intracellular in location, questioning the pathogenetic role of the antibody. The molecular events of antigen processing and presentation, T-cell receptor restriction, polyclonal B-cell proliferation, cellular immunity, and the role of cytokines in mediation of neuronal injury must be further defined in order to elucidate the role of autoimmunity in the pathogenesis of these disorders.

In vitro analysis of metabolic predisposition to drug hypersensitivity reactions

Idiosyncratic hypersensitivity reactions may account for up to 25% of all adverse reactions, and pose a constant problem to physicians because of their unpredictable nature, potentially fatal outcome and resemblance to other disease processes. Current understanding of how drug allergy arises is based largely on the hapten hypothesis: since most drugs are not chemically reactive per se, they must be activated metabolically to reactive species which may become immunogenic through interactions with cellular macromolecules. The role of drug metabolism is thus pivotal to the hapten hypothesis both in activation of the parent compound and detoxification of the reactive species. Although conjugation reactions may occasionally produce potential immunogens (for example, the generation of acylglucuronides from non-steroidal anti-inflammatory drugs such as diclofenac), bioactivation is catalysed most frequently by cytochrome P450 (P450) enzymes. The multifactorial nature of hypersensitivity reactions, particularly the role of often unidentified, reactive drug metabolites in antigen generation, has hampered the routine diagnosis of these disorders by classical immunological methods designed to detect circulating antibodies or sensitized T cells. Similarly, species differences in drug metabolism and immune system regulation have largely precluded the establishment of appropriate animal models with which to examine the immunopathological mechanisms of these toxicities. However, the combined use of in vitro toxicity assays incorporating human tissues and in vivo phenotyping (or, ultimately, in vitro genotyping) methods for drug detoxification pathways may provide the metabolic basis for hypersensitivity reactions to several drugs. This brief review highlights recent efforts to unravel the bases for hypersensitivity reactions to these therapeutic agents (which include anticonvulsants and sulphonamides) using drug metabolism and immunochemical approaches. In particular, examples are provided which illustrate breakthroughs in the identification of the chemical nature of the reactive metabolites which become bound to cellular macromolecules, the enzyme systems responsible for their generation and (possibly) detoxification, and the target proteins implicated in the subsequent immune response.

Autoimmune myocarditis induced in mice by cardiac C-protein. Cloning of complementary DNA encoding murine cardiac C-protein and partial characterization of the antigenic peptides

Autoimmune myocarditis is considered to play a major role in the pathogenesis of dilated cardiomyopathy. A new autoimmune myocarditis model was attained by repeated immunization using murine cardiac C-protein with the immunological adjuvant, Klebsiella pneumoniae O3 lipopolysaccharide. For further analysis of a pathological epitope, the cDNA encoding C-protein was isolated; a fusion protein encoded by part of this cDNA induced myocarditis in SMA mice as well as in three other strains: DBA/1J (H-2q), O20/A (H-2pz1), and SJL (H-2s). The nucleotide sequence and its deduced amino acid analysis revealed that this protein had immunoglobulin-like and fibronectin-like repeats. This study provides a new animal model of autoimmune myocarditis which may shed light on the pathogenesis of dilated cardiomyopathy.

CMV-induced class II antigen expression in various rat organs

Cytomegalovirus (CMV) is thought to trigger acute or chronic allograft rejection by inducing the expression of MHC class II antigens in the graft. This induction may be mediated by gamma-interferon or directly by CMV. In this study, we have investigated which structures in the rat kidney, liver, and heart are responsive to CMV-induced class II expression in vivo. Rats were infected with rat CMV, the organs were harvested during the acute phase of infection, and the virus was demonstrated by culture from each organ. Direct CMV antigen detection was performed on frozen sections to demonstrate the detailed localization of CMV in the organs. In the kidney, CMV antigens were found in the vascular endothelium, in tubular cells, and scattered in the glomeruli. In the liver, the vascular structures and parenchyma contained CMV antigens. In the heart, CMV antigens were seen only in the capillary endothelium. Class II antigen expression was demonstrated by a monoclonal antibody and immunoperoxidase techniques. The induction of class II molecules was recorded in exactly the same cellular structures as those in which CMV antigens were detected.

Autoantibodies from patients with primary biliary cirrhosis recognize a restricted region within the cytoplasmic tail of nuclear pore membrane glycoprotein Gp210

Patients with primary biliary cirrhosis (PBC) frequently have autoantibodies against a 210-kD integral glycoprotein of the nuclear envelope pore membrane. This protein, termed gp210, has a 1,783-amino acid amino-terminal domain located in the perinuclear space, a 20-amino acid transmembrane segment, and a 58-amino acid cytoplasmic carboxy-terminal tail. We now demonstrate that autoantibodies from 25 patients with PBC that recognize gp210 react with the cytoplasmic carboxy-terminal tail while none react with unmodified linear epitopes in the amino-terminal domain. The epitope(s) recognized by autoantibodies from all 25 patients is contained within a stretch of 15 amino acids. The recognized amino acid sequence is homologous to the protein products of the Escherichia coli mutY gene and Salmonella typhimurium mutB gene with an exact identity of six consecutive amino acids, suggesting that anti-gp210 antibodies may arise by molecular mimicry of bacterial antigenic determinants.