Auto-anti-idiotype: a basis for autoimmunity and a strategy for anti-receptor antibodies

Synergistic Activation of Toll-Like and NOD Receptors by Complementary Antigens as Facilitators of Autoimmune Disease: Review, Model and Novel Predictions

Persistent activation of toll-like receptors (TLR) and nucleotide-binding oligomerization domain-containing proteins (NOD) in the innate immune system is one necessary driver of autoimmune disease (AD), but its mechanism remains obscure. This study compares and contrasts TLR and NOD activation profiles for four AD (autoimmune myocarditis, myasthenia gravis, multiple sclerosis and rheumatoid arthritis) and their animal models. The failure of current AD theories to explain the disparate TLR/NOD profiles in AD is reviewed and a novel model is presented that explains innate immune support of persistent chronic inflammation in terms of unique combinations of complementary AD-specific antigens stimulating synergistic TLRs and/or NODs. The potential explanatory power of the model is explored through testable, novel predictions concerning TLR- and NOD-related AD animal models and therapies.

Longitudinal studies of patients with ANCA vasculitis demonstrate concurrent reactivity to complementary PR3 protein segments cPR3m and cPR3C and with no reactivity to cPR3N

Antibodies recognizing the complement of the middle of PR3 (cPR3m) occur in ∼30% of PR3-anti-neutrophil cytoplasmic autoantibodies (ANCA)-vasculitis patients and immunization of animals with a peptide complementary to the middle of PR3 (cPR3m) induces not only anti-complementary PR3 antibodies, but also anti-PR3 antibodies derived through an anti-idiotypic response. PR3 epitopes recognized by patient ANCA, however, are not restricted to the middle of PR3. This prompted us to test for antibodies that react with proteins complementary to the terminal regions of PR3 (cPR3C and cPR3N) in PR3-ANCA patients. Anti-cPR3C reactivity was detected in 28% of patients but anti-cPR3N reactivity in only 15%. Ranked anti-cPR3C and anti-cPR3m reactivity correlated in the cohort, whereas there was no significant relationship between cPR3C and cPR3N reactivity. Serial samples from 3 patients' revealed that anti-cPR3C and anti-cPR3m reactivity followed a similar pattern over time. Serial samples from a fourth patient demonstrated an anti-cPR3N response without concurrent cPR3m or cPR3C reactivity. Epitope determination by mass spectrometry identified a 13-amino acid sequence on cPR3C that contained a common binding site recognized by antibodies from three patients. This peptide sequence contains a "PHQ" motif which was reported to be the basis for cross-reactivity of anti-cPR3m antibodies with plasminogen. Why these antibodies are detected in only ∼30% of the patients remains unclear. The data reveal that it is not due to lack of inclusion of flanking regions of complementary PR3 during screening. Instead, quite unexpectedly, the data demonstrate that patients' antibodies react with a restricted epitope that exists in both cPR3m and cPR3C.

Antibodies with dual reactivity to plasminogen and complementary PR3 in PR3-ANCA vasculitis

Patients with inflammatory vascular disease caused by anti-neutrophil cytoplasmic autoantibodies (ANCA) can harbor antibodies not only to the autoantigen proteinase 3 (PR3) but also to complementary PR3 (cPR3(105-201)), a recombinant protein translated from the antisense strand of PR3 cDNA. The purpose of this study was to identify potential endogenous targets of anti-cPR3(105-201) antibodies. Patients' plasmapheresis material was tested for the presence of antigens reactive with affinity-purified rabbit and chicken anti-cPR3(105-201) polyclonal antibodies. Antigen-containing fractions were tested with patients' anti-cPR3(105-201) affinity-purified IgG, and putative protein targets were sequenced by mass spectrometry. Unexpectedly, plasminogen was identified as a target of anti-cPR3(105-201). Reactivity of affinity-purified antibodies from two patients was lost when plasminogen was converted to plasmin, indicating restricted specificity. Antiplasminogen antibodies from five patients bound plasminogen at a surface-exposed loop structure within the protease domain. This loop contains an amino acid motif that is also found in a portion of recombinant cPR3(105-201); site-directed mutagenesis of this sequence decreased antibody reactivity by 30%. Functionally, antiplasminogen antibodies delayed the conversion of plasminogen to plasmin and increased the dissolution time of fibrin clots. Serologically, antiplasminogen antibody levels were higher in PR3-ANCA patients (n = 72) than healthy control subjects (n = 63), myeloperoxidase-ANCA patients (n = 34), and patients with idiopathic thrombosis (n = 57; P = 0.001). Of the patients with PR3-ANCA, nine had documented deep venous thrombosis events, five of whom were positive for antiplasminogen antibodies. In summary, capitalizing on interactions with complementary proteins, specifically complementary PR3, this study identified plasminogen as a previously undescribed autoantigen in PR3-ANCA vasculitis.

ANCA patients have T cells responsive to complementary PR-3 antigen

Some patients with proteinase 3 specific anti-neutrophil cytoplasmic autoantibodies (PR3-ANCA) also have antibodies that react to complementary-PR3 (cPR3), a protein encoded by the antisense RNA of the PR3 gene. To study whether patients with anti-cPR3 antibodies have cPR3-responsive memory T cells we selected conditions that allowed cultivation of memory cells but not naïve cells. About half of the patients were found to have CD4+TH1 memory cells responsive to the cPR3(138-169)-peptide; while only a third of the patients had HI-PR3 protein responsive T cells. A significant number of T cells from patients responded to cPR3(138-169) peptide and to HI-PR3 protein by proliferation and/or secretion of IFN-gamma, compared to healthy controls while there was no response to scrambled peptide. Cells responsive to cPR3(138-169)-peptide were not detected in MPO-ANCA patients suggesting that this response is specific. The HLADRB1(*) 15 allele was significantly overrepresented in our patient group and is predicted to bind cPR3(138-169) peptide with high affinity. Regression analysis showed a significant likelihood that anti-cPR3 antibodies and cPR3-specific T cells coexist in individuals, consistent with an immunological history of encounter with a PR3-complementary protein. We suggest that the presence of cells reacting to potential complementary protein pairs might provide an alternative mechanism for auto-immune diseases.

Myocarditis

Viruses are the most common cause of myocarditis in economically advanced countries.

Enteroviruses and adenoviruses are the most common etiologic agents.

Viral myocarditis is a triphasic process. Phase 1 is the period of active viral replication in the myocardium during which the symptoms of myocardial damage range from none to cardiogenic shock. If the disease process continues, it enters phase 2, which is characterized by autoimmunity triggered by viral and myocardial proteins. Heart failure often appears for the first time in phase 2. Phase 3, dilated cardiomyopathy, is the end result in some patients. Diagnostic procedures and treatment should be tailored to the phase of disease.

Viral myocarditis is a significant cause of dilated cardiomyopathy, as proved by the frequent presence of viral genomic material in the myocardium, and by improvement in ventricular function by immunomodulatory therapy.

Myocarditis of any etiology usually presents with heart failure, but the second most common presentation is ventricular arrhythmia. As a result, myocarditis is one of the most common causes of sudden death in young people and others without preexisting structural heart disease.

Myocarditis can be definitively diagnosed by endomyocardial biopsy. However, it is clear that existing criteria for the histologic diagnosis need to be refined, and that a variety of molecular markers in the myocardium and the circulation can be used to establish the diagnosis.

Treatment of myocarditis has been generally disappointing. Accurate staging of the disease will undoubtedly improve treatment in the future. It is clear that immunosuppression and immunomodulation are effective in some patients, especially during phase 2, but may not be as useful in phases 1 and 3. Since myocarditis is often selflimited, bridging and recovery therapy with circulatory assistance may be effective. Prevention by immunization or receptor blocking strategies is under development.

Giant cell myocarditis is an unusually fulminant form of the disease that progresses rapidly to heart failure or sudden death. Rapid onset of disease in young people, especially those with other autoimmune manifestations, accompanied by heart failure or ventricular arrhythmias, suggests giant cell myocarditis.

Peripartum cardiomyopathy in economically developed countries is usually the result of myocarditis.

New insights that link microbes with the generation of antineutrophil cytoplasmic autoantibodies: the theory of autoantigen complementarity

PURPOSE OF REVIEW

Reviewed are recent discoveries that provide insights into novel mechanisms involved in the aetiology and pathology of anti-neutrophil cytoplasmic autoantibodies (ANCA) disease.

RECENT FINDINGS

Gene expression profiles of circulating leukocytes from anti-neutrophil cytoplasmic autoantibody immunogenesis patients revealed high levels of proteinase 3 (PR3) and myeloperoxidase (MPO) mRNA. Combined with reports of increased expression of these proteins, it appears that increased antigen availability is a pathologic component of anti-neutrophil cytoplasmic autoantibody immunogenesis disease, which might be equally as important as the presence of anti-MPO or anti-PR3 autoantibodies. Genetic predisposition to develop anti-neutrophil cytoplasmic autoantibody immunogenesis disease may include a polymorphism in the promoter region of the PR3 gene. Signalling pathways affected by anti-neutrophil cytoplasmic autoantibody immunogenesis binding to neutrophils involve the p21 pathway. Lastly, a topic discussed at length in this review is the seminal observation that PR3-ANCA patients harbour antibodies reactive with a protein produced from PR3-antisense RNA, whose amino acid sequence has homologies with proteins from many microbes and viruses. Delineated in the Theory of Autoantigen Complementarity, it is proposed that the initiator of an autoimmune response is not the autoantigen, but instead is a protein that is 'antisense' or complementary to the autoantigen (e.g. from bacteria or PR3).

SUMMARY

The progress in research efforts in the past year, including the identification of complementary proteins as a potential cause of anti-neutrophil cytoplasmic autoantibody immunogenesis, should highly impact future approaches therapeutic intervention.

Autoantigen complementarity: a new theory implicating complementary proteins as initiators of autoimmune disease

Autoimmune diseases affect approximately 1 in 21 persons in the United States. Treatment often requires long-term cytotoxic therapy. How and why these deleterious diseases occur is unclear. A serendipitous finding in our laboratory using serum from patients with autoimmune vasculitis led us to develop the theory of autoantigen complementarity, a novel concept that may elucidate the etiological and pathogenetic mechanisms underlying autoimmune disease in general. The theory proposes that the inciting immunogen that elicits a cascade of immunological events is not the self-antigen (the autoantigen) or its mimic but rather a protein that is complementary in surface structure to the autoantigen; that is, a protein homologous or identical to the amino acid sequence of translated antisense RNA from the noncoding strand of the autoantigen gene. The cascade begins when this complementary protein initiates the production of antibodies that in turn elicit an anti-antibody or anti-idiotypic response. These anti-idiotypic antibodies can now react with the autoantigen. Strikingly, homology search of complementary proteins yields microbial and fungal proteins, thus indicating that invading micro-organisms can deliver the inciting immunogen. Curiously, approximately 50% of our patients transcribe the complementary protein's antisense RNA. If it transpires that these aberrant RNAs are translated, the complementary protein would be produced by the individual. Here we review published research investigating complementary proteins, anti-idiotypic immune responses, and antisense transcripts, all of which support complementary proteins as initiators of autoimmune disease. In addition, we provide possible microbial and/or fungal organisms that may incite some of the most studied autoimmune diseases. Lastly, we propose mechanisms by which cell-mediated autoimmunity can be triggered by autoantigen complementarity. Based on our data and the contributions of the researchers described in this review, identification of proteins complementary to autoantigens is likely to be informative in most autoimmune diseases. This vein of study is in the early phases; however, we expect "autoantigen complementarity" is an underlying mechanism in many autoimmune diseases.

Induction of auto-anti-idiotypic antibodies specific for antibodies to matrix and envelope glycoprotein from pigs experimentally infected with porcine reproductive and respiratory syndrome virus

Auto-anti-idiotypic antibodies (Aab-2s) specific for antibodies against envelope glycoprotein GP5 were previously identified in 10 of 12 pigs experimentally infected with porcine reproductive and respiratory syndrome virus (PRRSV). In this study, we report in addition the induction of Aab-2s specific for antibodies against matrix (M) and envelope glycoprotein GP5 antigens in 38 of 47 pigs experimentally infected with PRRSV. Two sets of Aab-2s were induced in the sera, one at 21 days post-infection (DPI) and peaked on 35 DPI and another at 49 DPI and peaked on 77 DPI. The Aab-2s induced at an early stage were from non-virus carrier pigs as defined when they were euthanized on and after 77 DPI. In contrast, the Aab-2s induced at a later stage were from virus carrier pigs. These Aab-2s possessed the characteristics of internal image Ab-2s and recognized shared idiotypes on swine and murine antibodies to the GP5 and M antigens of PRRSV. This study further demonstrates that, during the antibody responses to PRRSV infection, Aab-2s specific for both anti-M and anti-GP5 antibodies were induced. More importantly, the early and late Aab-2s possessed different idiotype-binding specificities. By detecting and characterizing these Aab-2s, it may be possible to identify whether pigs infected with PRRSV will clear the virus or become virus carriers.

Identification and characterization of auto-anti-idiotypic antibodies specific for antibodies against porcine reproductive and respiratory syndrome virus envelope glycoprotein (GP5)

Auto-anti-idiotypic antibodies (Aab-2s) were detected from pigs experimentally infected with porcine reproductive and respiratory syndrome virus (PRRSV). The Aab-2s were specific against the idiotypic antibodies (Ab-1s) to the envelope glycoprotein GP5 of PRRSV and were detected from serum samples collected between 21 and 98 days post-infection (DPI). Serological characterization indicated that the Aab-2s recognized the idiotype located within or near the antigen-combining sites of the anti-GP5 antibodies, which was shared by both mouse MAb anti-GP5 and swine polyclonal antibodies. The fact that the Aab-2 inhibited the anti-GP5 antibodies from binding to PRRSV and that they were detected at different time periods in pigs that cleared the infection prior to 98 DPI versus pigs in which virus was detected at 98 DPI suggests that Aab-2 antibodies may play a role in immunity to PRRSV infection.

Identification of the monomeric G-protein, Rhes, as an efaroxan-regulated protein in the pancreatic beta-cell

Efaroxan induces membrane depolarization by interaction with the pore forming subunit of the ATP-sensitive potassium channel, Kir6.2. However, this effect is not responsible for its full secretory activity. In this study we have used an anti-idiotypic approach to generate antibodies that recognize additional proteins that may be regulated by efaroxan in pancreatic beta-cells. Using these antisera in an expression cloning strategy we have identified a monomeric GTP-binding protein, Rhes, as a potential target for regulation by imidazoline ligands. Rhes is shown to be expressed in beta-cells and its expression is regulated by efaroxan under conditions when a structurally related molecule, KU14R, is ineffective. The results reveal that beta-cells express Rhes and suggest that changes in the expression of this molecule may regulate the sensitivity of beta-cells to imidazoline secretagogues.

Anti-idiotypic antibodies to delineate epitope specificity of anti-amiloride antibodies

Amiloride and related compounds have found widespread use as cation transport inhibitors. We have previously raised a series of polyclonal anti-amiloride antibodies using different amiloride-protein conjugates as immunogens, where amiloride was coupled to protein either through its guanidino moiety or through its 5-aminopyrazinyl moiety. The anti-amiloride antibodies recognized distinct sites on amiloride, and the site of attachment of amiloride to carrier protein was a critical factor in determining which part of the amiloride molecule was recognized by the anti-amiloride antibody. The specificity of binding of amiloride analogues to these polyclonal anti-amiloride antibodies mimicked the specificity of binding of amiloride analogues to selected isoforms of the epithelial Na+ channel or the Na+/H+ exchanger, suggesting that antigen binding site of these antibodies might be similar in structure to amiloride binding sites on selected Na+ transport proteins. We previously generated monoclonal anti-idiotypic antibodies RA2.4 and RA6.3 by an auto-anti-idiotypic approach, using amiloride coupled to albumin through the guanidinium moiety (amiloride-A1). We have now raised a series of monoclonal anti-idiotypic antibodies, T6, T26, T40, and T181, using amiloride coupled to keyhole limpet hemocyanin through the 5-aminopyrazinyl moiety (amiloride-A5) as an immunogen with the same auto-anti-idiotypic approach. These monoclonal anti-idiotypic antibodies recognized both polyclonal anti-amiloride-A1 and anti-amiloride-A5 antibodies, suggesting that idiotype-anti-idiotype interaction was not epitope restricted.(ABSTRACT TRUNCATED AT 250 WORDS)

Antigen mimicry in autoimmune disease sharing of amino acid residues critical for pathogenic T cell activation

A nonamer peptide from murine nicotinic acetylcholine receptor delta chain (ACR delta), which shared four amino acid residues with a nonamer peptide of murine ovarian zona pellucida glycoprotein ZP3, induced murine autoimmune oophoritis and IgG autoantibody to the zona pellucida. Crossreaction between the ACR delta and ZP3 peptides was established by the response of a ZP3 peptide-specific, oophoritogenic T cell clone to both peptides in association with IA (alpha k beta b). By substituting the ZP3 peptides with a single alanine, four amino acids within the ZP3 peptide were found to be important for ovarian autoimmune disease, autoantibody response, and stimulation of the ZP3-specific T cell clone. Substitution with conservative amino acids of three residues also ablated activity, whereas the fourth, a phenylalanine, was replaceable by tyrosine without loss of activity. Of the four critical amino acids, three were shared between the ZP3 peptide and the ACR delta peptide. Moreover, polyalanine peptides with the four critical ZP3 amino acids or the four amino acids common to the ZP3 and ACR delta peptides induced immune response to ZP3 and elicited severe ovarian autoimmune disease. Thus, organ-specific autoimmune disease can occur through immune response against unrelated self (or foreign) peptides that share with a self-peptide sufficient common amino acid residues critical for activation of pathogenic, autoreactive T cells.

Monoclonal IgM antibodies from cytomegalovirus-infected mice recognize the GlcNAc-containing receptor determinant of murine CMV as well as neutralizing anti-CMV IgG antibodies

This study examines monoclonal antibodies derived from mice at different time points after infection with attenuated murine cytomegalovirus (MCMV). The antibodies obtained from mice at 3 weeks p.i. were of IgG type (designated V-antibodies) and several could neutralize the virus. Those obtained at 5 weeks p.i. were of the IgM class (designated R-antibodies), bound to uninfected (MEF, mouse embryo fibroblast) cells, and thereby blocked MCMV plaque formation. In ELISA, the IgM monoclonals (R-antibodies) bound to GalB1-3GlcNAc and GalB1-4GlcNAc, the receptor determinants for MCMV. Similarly, these GlcNAc-containing residues blocked the binding of purified IgM monoclonal antibodies (MAbs) to MEF. The R- and V-series of antibodies showed mutual binding activities; for example, IgM MAb R-2D8 bound specifically to four (V-8C4, V-1C7, V-8C7, V-9C5) of six neutralizing IgG MAbs in ELISA. The same neutralizing IgG MAbs bound to antireceptor IgM antibodies in an immunoblot assay. This suggests that the IgM monoclonals directed against the known cell surface receptor determinant are anti-idiotypic antibodies against neutralizing antiviral IgG antibodies. The neutralizing antiviral IgG MAbs bound to 60- and 66-kDa MCMV polypeptides on Western blots, suggesting that these viral polypeptides may be important in MCMV binding to this receptor. The R-series might represent anti-idiotype antibodies capable of down-regulating antiviral V-antibodies and may also represent a mechanism for the induction of IgM autoantibodies directed at cell surface glycolipids present in autoimmune CMV-associated neuropathies.

Antiidiotypic antibodies against anti-cGMP polyclonal antibodies

Affinity-purified polyclonal anti-cGMP antibodies were obtained from rabbit serum after immunization by succinyl derivative of cGMP coupled to bovine serum albumin. These antibodies were used to raise antiidiotypic antibodies in rats. Putative antiidiotypic serum inhibited the binding of [3H]cGMP to affinity-purified anti-cGMP antibodies. The influence of immunoglobulins isolated from antiidiotypic serum on the ion conductance of rod outer segment plasma membrane fragments from frog retina was studied in patch-clamp experiments. These immunoglobulins increased the conductance of ion channels acting like a natural agonist (cGMP). Preimmune immunoglobulins did not act. The data obtained suggest that antiidiotypic antibodies interact with regulatory cGMP-binding sites of the plasma membrane channels.

Distinct epitopes on amiloride. II. Variably restricted epitopes defined by monoclonal anti-amiloride antibodies

Specific regions of amiloride appear to participate in binding to receptors on amiloride-sensitive transport proteins. Previous studies characterizing epitopes on amiloride recognized by anti-amiloride antibodies have demonstrated that antibodies recognize specific domains on amiloride and that these epitopes are determined, in part, by the site on amiloride used to couple to carrier protein. The 3,5-diaminopyrazinyl and guanidinocarbonyl moieties were identified as distinct epitopes. Since Na(+)-selective transport proteins are sensitive to changes of the halide on the amiloride molecule, additional monoclonal anti-amiloride antibodies were raised to determine whether the C-6 halo group of amiloride could be identified as an important site for drug-antibody binding. The epitopes recognized by a series of three monoclonal antibodies raised against amiloride coupled to rabbit serum albumin through its C-5 NH2-group were defined. Two antibodies recognize extensive regions on the amiloride molecule, including both the acylguanidino and pyrazinyl groups. In addition, both antibodies are sensitive to changes in the C-6 halo group on amiloride. A third antibody was relatively insensitive to changes in the halide in the C-6 position of the pyrazine ring of amiloride and recognized a more restricted epitope on amiloride.

Antiidiotypic antibodies interacting with cGMP-dependent channels of frog retinal rod outer segments

Antiidiotypic approach was used to obtain antibodies interacting with cGMP-binding site of the cGMP-activated channel of the photoreceptor cell. Monoclonal anti-BrcGMP antibodies having characteristics of binding of agonist and its analogs close to those for a natural receptor have been obtained. These antibodies were used to raise polyclonal antiidiotypic antibodies capable of interacting with a natural cGMP-receptor. Application of immunoglobulins, isolated from antiidiotypic serum, to inside-out fragments of the rod plasma membrane led to an irreversible increase of the conductance of cGMP-dependent channels.

Monoclonal antibodies to the pituitary growth-hormone receptor by the anti-idiotypic approach. Production and initial characterization

We obtained 10/192 and 3/384 antibody-secreting hybrids after immunization of Balb/c mice with either human growth hormone or affinity-purified rabbit anti-(human growth hormone) respectively. Radiolabelled rabbit anti-(human growth hormone) antibodies, but not human growth hormone, were specifically bound by supernatants from the 13 hybrids. The binding was completely inhibited by human-growth-hormone serum binding protein. However, anti-(human growth hormone antibodies) were detected in the sera of all the mice immunized with human growth hormone. In an independent fusion, which was carried out after immunization with fewer doses of human growth hormone, anti-(human growth hormone) antibodies were also obtained. Five hybrids, where the starting antigen was human growth hormone, were selected for ascites production, and the corresponding monoclonal antibodies were partially purified and characterized with respect to their immunoglobulin isotype and their interaction with human-growth-hormone receptors. These antibodies were found to enhance the binding of radioiodinated human growth hormone to human-growth-hormone serum binding protein from human and rabbit plasma by 40%. Scatchard analysis of the effect of one of the monoclonal antibodies showed that this enhancement was due to an increased number of binding sites. All of the partially purified antibodies but one (F12) inhibited the binding of human growth hormone to rat but not rabbit, liver microsomes to various extents, as well as to H-4-II-E rat hepatoma cells. Monoclonal antibody F12 enhanced the binding of radiolabelled human growth hormone to rat liver microsomes and H-4-II-E hepatoma cells. This enhancement was found to be due to an increase in the number of binding sites.

Distinct epitopes on amiloride

Most Na(+)-selective transport proteins are inhibited by the drug amiloride. Studies using amiloride analogues suggest that specific regions of amiloride might participate in binding to receptors on these transport proteins. To determine whether certain domains of this drug are recognized as distinct epitopes, amiloride was coupled to albumin through either its C-5 NH2-group on the pyrazine ring or through a terminal NH2-group of the guanidino moiety, and antibodies were raised against these amiloride-albumin conjugates. Studies of antibody binding to amiloride analogues identified the 3,5-diaminopyrazinyl, the guanidinocarbonyl, and the C-6 halo moieties as distinct epitopes, although the antibodies required the presence of both the 3,5-diaminopyrazinyl as well as the guanidinocarbonyl moiety for binding.

Some thoughts on the structural basis of internal imagery

Apparently, anti-idiotypic antibodies can mimic (almost?) any molecule in an organism or in its environment. If the molecule is a polypeptide, must the variable region of the antibody contain peptide sequences homologous or identical to sequences in the polypeptide it is mimicking? In this article, Bernard Erlanger says 'No', drawing his conclusion mainly, but not solely, from the hemoglobin-myoglobin family of proteins, in which X-ray and sequence data show that identical, functional conformations can be assumed by proteins that differ by as many as 137 of 141 amino acids.

Identification of an epitope shared by the DNA-binding domain of glucocorticoid receptor and the B chain of insulin

A monoclonal antibody (8G11-C6) generated by an auto-anti-idiotypic route and directed to a site near the ligand-binding site of the glucocorticoid receptor also binds to native insulin and the B chain of insulin but not to the A chain of insulin. The glucocorticoid receptor and the B chain of insulin, therefore, share a cross-reacting epitope. Examination of the primary sequences of the two proteins revealed a limited number of regions of identity or close homology. Several peptides representative of those regions were synthesized. A heptapeptide sequence of the B chain of insulin with homology to a sequence in the first "zinc finger" of the DNA-binding domain of the glucocorticoid receptor was identified as the cross-reactive epitope. This heptapeptide sequence is restricted to and highly conserved among insulins of various species. Homologous sequences are found in the DNA-binding domains of most steroid receptors and related DNA-binding proteins. Consistent with this is the finding that 8G11-C6 inhibits the binding of glucocorticoid receptor to DNA-cellulose.

Clinical and experimental aspects of viral myocarditis

Picornaviruses are frequently implicated as the etiological agents of acute myocarditis. This association is based historically on serological evidence of rising antibody titers to specific pathogens and more recently on identification of viral genomic material in endocardial biopsy specimens through in situ hybridization. Only rarely is infectious virus isolated from either the patient or the heart during periods of maximum myocardial inflammation and injury. Thus, despite a probable viral etiology, much interest centers on the role of the immune system in cardiac damage and the likelihood that the infection triggers an autoimmune response to heart-specific antigens. Heart-reactive antibodies and T cells are found in most myocarditis patients, and immunosuppressive therapy has proven beneficial in many, though not all, cases. Furthermore, murine models of coxsackievirus group B type 3-induced myocarditis also demonstrate that virus infection initiates autoimmunity and that these autoimmune effectors are predominately responsible for tissue injury. How virus-host interactions overcome presumed self-tolerance to heart antigens is discussed, and evidence supporting various theories of virus-initiated autoimmunity and disease pathogenesis are delineated.

Auto-anti-idiotypy, autoimmunity and some thoughts on the structure of internal images

Application of principles proposed by N.K. Jerne has led to the development of an auto-anti-idiotypic protocol for the preparation of monoclonal antibodies specific for receptors for acetylcholine, adenosine (A1), TSH, glucocorticoids and aldosterone. The properties of these antibodies are described with reference to their behavior as internal images of auto-antibodies found in patients with autoimmune disease or of ligands of the various receptors. The molecular basis of "internal imagery" is discussed in the context of specific antibodies and, in particular, with respect to the hemoglobin-myoglobin family of proteins. We venture the conclusion that immunoglobulins that mimic other biologically active polypeptides need not share primary sequence homologies.

Spike--nucleocapsid interaction in Semliki Forest virus reconstructed using network antibodies

Using in vitro immunization, we have reconstructed three consecutive steps of an idiotype network to show that the nucleocapsid of Semliki Forest virus contains a specific 'receptor' for the cytoplasmic tail of the E2 spike glycoprotein. This interaction could be the basis for the highly selective inclusion of viral glycoproteins--and exclusion of host cell surface proteins--during virus budding.