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PubMedDate not supplied

Idiotypic induction of autoimmunity: do we need an autoantigen?

Autoimmune diseases may be classified into two groups: autoantibody-mediated and cellular-mediated. In many autoimmune conditions the autoantigen is well-defined, immunogenic and, upon immunization of the naive animal, will lead to the production of autoantibodies and, eventually, to the induction of the respective autoimmune disease. However, in certain autoimmune diseases the autoantigen is either ill-defined, or is not immunogenic, or is intracellular. In many of these situations it is difficult to explain the emerging clinical findings by the mere binding of the autoantibody to the autoantigen. We herewith propose an additional mechanism for autoimmune disease induction, employing active idiotypic immunization. The induction of the disease is exemplified by three clinical models-SLE, APS, and Wegener's granulomatosis. The implications for human disease are discussed.

Animals↗
PubMed1994

Clonotype analysis of peripheral blood T cells and autoantigen-reactive T cells from patients with mixed connective tissue disease.

T cells that recognize autoantigens may play a central role in the autoimmune response. We have previously shown that autoantigen-reactive T cells (CD4+) to U1-small nuclear ribonucleoprotein A were found in the PBMC of patients with systemic lupus erythematosus or mixed connective tissue disease. To reveal clonotypes of such T cells that spread to the periphery, T cell clonal accumulations and their TCR-beta chain variable gene usages in fresh PBMC from eight patients with mixed connective tissue disease were analyzed by a new method of single strand conformation polymorphism applying to TCR gene detection. The results revealed that the numbers of accumulated T cell clones (mean: 24.3 clones) were greater than the numbers of clones detected in healthy donors (mean: 4.0 clones). Frequently used V beta genes in these accumulated T cell clones were V beta 1, 3, 4, 5.2, 14, and 16. After the stimulation for these samples with the soluble recombinant U1-small nuclear ribonucleoprotein A protein, proliferative T cell responses were observed. We found that T cell clones expressing more restricted TCR V beta genes (1, 3, 5.2, and 14 families) accumulated in vitro. These results suggest that autoantigen-reactive oligoclonal T cell accumulations are present in the peripheral blood from systemic autoimmune disease patients.

Amino Acid Sequence↗
PubMed1993

Recoverin, but not visinin, is an autoantigen in the human retina identified with a cancer-associated retinopathy.

PURPOSE: We investigated the hypothesis that visinin, a cone-specific protein first characterized in chicken retina, is a cone homologue of recoverin and may be the cancer-associated retinopathy (CAR) autoantigen in human cone cells. METHODS: Visinin was purified from chicken retinas and tested for binding by CAR antisera. In addition, antibodies specific to visinin were used immunocytochemically and for Western analysis to determine whether visinin is present in human or bovine retinas. Anti-peptide antibodies against recoverin were used immunocytochemically to localize recoverin to mammalian cone cells. RESULTS: CAR antisera recognized recoverin but not visinin. Furthermore, visinin could not be detected in mammalian retinas by immunocytochemical methods or by attempts to purify the protein. In contrast to visinin, antibodies specific for different regions of the recoverin molecule stained both rod and cone cells in the human retina. CONCLUSIONS: Visinin is not the CAR autoantigen in human cone cells. Differences between recoverin and visinin probably reflect species differences rather than rod-cone differences. Recoverin, or a nearly identical molecule, is present in mammalian cones and likely is the cone cell CAR autoantigen.

Amino Acid Sequence↗
PubMed1993

Identification of murine erythrocyte autoantigens and cross-reactive rat antigens.

Autoimmune haemolytic anaemia (AIHA) can be induced in mice by repeated injections with rat red blood cells (RBC). Here we describe the identification of murine RBC autoantigens and cross-reactive rat antigens. Sera and RBC eluates from the AIHA-positive mice immunoprecipitated a murine RBC autoantigen of 42,000 MW that comigrates with a zone of glycophorin in PAS-stained polyacrylamide gels. In addition, the eluates immunoprecipitated a 105,000 MW protein corresponding to band 3, the erythrocyte anion channel, and two further components of 34,000 and 29,000 MW within the glycophorin zone. The 42,000 MW band was not detected by immunoblotting, indicating that it bears autoantigenic epitope(s) that are denatured during electrophoresis. Cross-reactive autoantibody in the eluates immunoprecipitated a rat RBC protein that comigrated with band 3, together with two bands of 36,000 MW and 34,000 MW that may represent minor rat glycophorins. In contrast, rat-specific serum IgG from mice with AIHA reacted predominantly with major rat glycophorins of 75,000 MW and 38,000 MW. Immunoblotting revealed that normal murine sera contain IgG that binds autologous spectrin from the RBC membrane skeleton, and that this activity is increased in mice with AIHA. Sera from AIHA-positive mice also reacted with other internal murine RBC components that are not exposed on the surface of intact cells. It is evident from the data that immunization of mice with rat RBC results in the generation of multiple autoantibodies with a complex range of specificities.

Anemia, Hemolytic, Autoimmune↗
PubMed1997

The autoimmunity-inducing xenobiotic mercury interacts with the autoantigen fibrillarin and modifies its molecular and antigenic properties.

The heavy metal mercury elicits a genetically restricted, anti-nucleolar autoantibody response that targets fibrillarin, a 34-kDa protein component of many small nucleolar ribonucleoprotein particles. The mechanisms by which a toxin such as mercury elicits an autoantibody response that predominantly targets a single intracellular protein autoantigen remain uncertain, but may be prefaced by mercury gaining access to the intracellular environment. Mercury-induced cell death was associated with loss of fibrillarin antigenicity and modification of the molecular properties of fibrillarin as revealed by aberrant migration under nonreducing conditions in SDS-PAGE. Addition of mercury to isolated nuclei also resulted in aberrant migration of fibrillarin, but not other nuclear autoantigens. The sensitivity of the HgCl2-induced modification of fibrillarin to 2-ME, iodoacetamide, and hydrogen peroxide suggested interaction of mercury with the two cysteines in the fibrillarin sequence. This was confirmed by mutation of the cysteines to alanines, which abolished the aberrant migration of fibrillarin in the presence of HgCl2. The modification of the molecular structure of fibrillarin by mercury reduced immunoprecipitation by anti-fibrillarin autoantibodies, pointing to unmodified fibrillarin as the B cell Ag and implicating mercury-modified fibrillarin as the source of T cell antigenicity. These observations demonstrate for the first time that an environmental toxin can alter the physicochemical properties of an autoantigen and may help to explain the antigenic specificity of mercury-induced murine autoimmunity.

Antibodies, Monoclonal↗
PubMed1998

IA-2 (islet cell antigen 512) is the primary target of humoral autoimmunity against type 1 diabetes-associated tyrosine phosphatase autoantigens.

IA-2 (islet cell Ag 512) and IA-2 beta (phogrin/IAR) are related autoantigens associated with type 1 diabetes. To determine the critical regions for autoantibody binding and which of these autoantigens is the primary target, mutant and chimeric constructs were used to characterize Ab epitope binding in sera from 217 new onset patients with type 1 diabetes and sequential samples from 141 islet cell Ab positive first degree relatives of patients. All 22 relatives and 121 of 129 patients with IA-2/IA-2 beta Abs had reactivity to IA-2-specific epitopes. These epitopes were in the juxtamembrane region (residues 601-682) and the protein tyrosine phosphatase (PTP)-like domain of IA-2. Chimeras showed that IA-2 residues 795-889 were important for IA-2-specific Ab binding in the PTP-like domain, and mutation of IA-2 residues 877 and 911, previously indicated as relevant for phosphatase activity, also reduced Ab binding. In contrast, Ab binding to IA-2 beta was limited to its PTP-like domain, most IA-2 beta Abs recognized epitopes shared with IA-2, and only 20 patients and 2 relatives had Abs to IA-2 beta-specific epitopes. In 4 relatives, IA-2 and/or IA-2 beta Abs developed in follow-up samples. In each of these, Abs to IA-2-specific epitopes were the first detected. In three, spreading to epitopes shared between IA-2 and IA-2 beta in subsequent samples was seen. In the 17 relatives who developed type 1 diabetes, progression to disease was associated with reactivity to multiple IA-2/IA-2 beta epitopes. These data suggest that IA-2 is the primary phosphatase-like autoantigen associated with type 1 diabetes and that studying autoantibody epitope diversity may assist in disease prediction.

Adolescent↗
PubMed1999

Follicular exclusion and rapid elimination of hen egg lysozyme autoantigen-binding B cells are dependent on competitor B cells, but not on T cells.

In mice with a diverse B cell repertoire, hen egg lysozyme (HEL) autoantigen-binding B cells are excluded from follicles and eliminated in 3 days. To explore the roles of competitor B cells and of T cells in this mechanism of self-tolerance, HEL-specific B cells were transferred into mice containing HEL and deficient in endogenous B cells (muMT), T cells (TCR-/-), or B and T cells (RAG1-/-). Previous studies suggested a dual requirement for B cell receptor (BCR) engagement and competition in HEL autoantigen-binding B cell elimination, but interpretation of these experiments has been confounded by the possible failure to independently regulate autoantigen concentration and competitor B cell frequency. In experiments in this study, we have fixed one variable, HEL concentration, while varying the second, the presence or absence of other B cells. By this approach, we find that follicular exclusion and rapid elimination of autoreactive B cells require BCR engagement plus competition with other B cells, rather than BCR engagement alone. We also find, by transfers into T cell-deficient mice, that T cells are not required for this peripheral tolerance mechanism. Unexpectedly, in mice lacking both T cells and competitor B cells (RAG1-/-), transferred HEL-binding cells survive less well than in mice just lacking competitor B cells. These results suggest T cells can enhance autoreactive B cell survival. Enhanced survival of autoreactive B cells, due to the presence of T cells and the lack of competitor B cells, might contribute to the elevated frequency of autoimmunity in B cell-deficient individuals.

Animals↗
PubMed1996

Activation of T Cells by Autoantigen Immobilized by Specific Antibodies

A convenient microtiter-plate assay that uses immobilized antibody to capture specific antigens for presentation to T cells has been developed. Initial experiments used KLH as the antigen, immune antisera and draining lymph node cells from immunized NOD mice as the source of antibody and T cells, and spleen cells from naive NOD mice as the source of antigen-presenting cells (APCs). The resulting proliferation of the T cells was shown to be antibody- and antigen-specific, suggesting that the APCs had internalized and processed the captured antigen, presenting it to the T cells in the form of peptide/MHC complexes. The approach was also tested for an autoimmune disease as part of an effort to identify autoantigens responsible for the proliferation of T cells in the synovial fluid of rheumatoid arthritis patients. When immunoglobulin from autologous synovial fluid was captured on plates coated with anti-human immunoglobulin antibodies, the addition of HLA-DR4 peripheral blood mononuclear cells as APCs and synovial fluid-reactive HLA-DR4-restricted T-cell clones resulted in significant proliferation, indicating that the specific antigen in the crude synovial fluid was human immunoglobulin. This response was also shown to be antigen-specific and HLA-DR4-restricted. This assay format should permit the definition of autoantigens by capturing with antibodies to crude autoantigen extracts, followed by the addition of the appropriate APC and T-cell populations.

Journal Article↗
PubMedDate not supplied

Apoptosis and redistribution of the Ro autoantigen in Balb/c mouse like in subacute cutaneous lupus erythematosus.

In subacute cutaneous lupus eryhematosus (SCLE) the cutaneous antigens constitute the main source of Ro and La autoantigens. The aim of this investigation was to demonstrate if UV light increases the availability of Ro autoantigen in the skin, also the blocking effect of Ac-DEVD-CMK a caspase inhibitor was assessed. For this purpose newborn Balb/c mice were UVB irradiated (5-30 mJ/cm(2)) equivalent to a moderate to severe sunburn. Animals were injected with monoclonal anti-Ro antibodies from SCLE patients. Apoptosis was also induced by anti-Fas antibody injection. Skin samples were examined by direct immunofluoresence, by TUNEL, and the expression of caspase 3 by RT-PCR. Major findings of present studies were: 1. UVB irradiation and anti-Fas induced apoptosis of keratinocytes. 2. Apoptosis redistribute the Ro antigen on cell surface and is better triggered by Ro antibody. 3. The caspase 3 inhibitor Ac-DEVD-CMK decreases the availability of Ro autoantigen in epidermis and prevents deposition of anti-Ro. In conclusion, the caspase pathway would be blocked to avoid anti-Ro deposition along skin; this finding would be a prospect in the treatment of SCLE patients.

Amino Acid Chloromethyl Ketones↗
PubMed1979

Effects of antigenic competition between sperm autoantigens and ovalbumin upon humoral and cell-mediated immunity and the development of autoimmune aspermatogenic orchitis (AIAO) in guinea pigs.

The effects of antigenic competition between ovalbumin and sperm autoantigens have been studied in guinea pigs. There was an inhibition of antiovalbumin antibody production up to 60 days after immunization. The cell-mediated immunity against ovalbumin was also depressed at day 30. The simultaneous immunization with both antigens has no effect upon the humoral and cell-mediated immunity against spermatozoa. During the period of inhibition of the humoral and cell-mediated antiovalbumin response, the number of animals developing autoimmune aspermatogenic orchitis was diminished compared to those immunized with spermatozoa alone. Later on, there was no difference between the two groups. The transient inhibition of the immune response against ovalbumin can be explained by the particulate nature of the autoantigens. The sperm cells may be easily trapped by the dendritic reticular cells of the draining lymph nodes. This in turn could affect T cell recognition at early stages, orienting it predominantly toward the sperm autoantigens. At day 90 the situation returned to that present in animals immunized with ovalbumin alone.

Animals↗
PubMed1999

Predictions of Immunological Cross-Reactions of C-Terminal Peptide of Human Chorionic Gonadotropin beta-Chain Based Contraceptive Vaccine with Autoantigens.

Cross-reactions of anti-human chorionic gonadotropin-beta (HCG-beta) antibody elicited by HCG-beta based antifertility vaccines with other autoantigens may occur due to identical or homologous protein subsequences. I have detected hitherto unreported identity of HCG-beta sequence with tetrapeptides of PECAM-1, galactosyl transferase-associated protein kinase, insulin receptor-related receptor and carboxypeptidase E. A predicted potential epitope of C-terminal peptide (CTP) of HCG-beta was identical to a tetrapeptide stretch of MCSF-1. The first 30 residue stretch of CTP was found to have yet unknown homologies of more than 56% with many auto-antigens including 60.1% with centromere protein C. The last 30 residue stretch of CTP was found for the first time to have 61.4-65.4% homology with subsequences of autoantigens SP-100, PM-SCL, D1 (64 kDa), lupus KU (p86), small nuclear ribonucleoprotein-associated proteins N, B and B', major centromere autoantigen B, centromere protein C, and dihydrolipoamide acetyl transferase component E2 of pyruvate, respectively.

Journal Article↗
PubMed1988

Autoantibodies: the search for origins, target autoantigens and pathogenicity.

The origins of autoantibodies remain largely unknown. Burnet suggested that self-reactive clones of B lymphocytes are deleted during ontogeny and that 'forbidden' clones of autoantibody-producing B lymphocytes arise as a consequence of somatic mutation of the variable regions of immunoglobulin genes. The alternative view, which is gaining increasing support, is that autoreactive B cells are present in all normal individuals but are held in check by control mechanisms, e.g. by the idiotypic network of Jerne. Autoantibodies segregate with clusters of autoimmune diseases and are useful diagnostic markers of these diseases. The autoantigens targeted by these autoantibodies are largely unknown. The precise molecular characteristics of these autoantigens are currently under active investigation by immunochemical and recombinant DNA methods. Precise definition of these autoepitopes should lead to sensitive immunoassays and studies directed at determining the pathogenicity of the autoantigens. The new knowledge gained in this way may lead to successful restoration of tolerance to self antigens.

Autoantibodies↗
PubMed1990

Characterization of the 70KDA component of the human Ku autoantigen expressed in insect cell nuclei using a recombinant baculovirus vector.

The Ku autoantigen is a human nuclear, DNA-binding heterodimer of 70kDa and 86kDa proteins. It is the target of autoantibodies in several autoimmune diseases. We now report the expression of a cDNA encoding the 70kDa Ku protein. Large amounts of protein were obtained using a recombinant baculovirus vector, in contrast with earlier unsuccessful attempts using other expression systems. We demonstrate that the 70kDa Ku protein is targeted to the nucleus and is associated with the nuclear matrix when expressed in the absence of the 86kDa Ku component. No post-translational modifications were observed. The 70kDa protein binds double and single-stranded DNA with very high affinity. Our results suggest that the baculovirus expression system may be of widespread use in the production and characterization of human autoantigens.

Animals↗
PubMed1995

Suppression of heat-induced hsp70 expression by the 70-kDa subunit of the human Ku autoantigen.

Expression of the 70-kDa polypeptide of human Ku autoantigen in rat cells is shown to suppress specifically the induction of hsp70 upon heat shock. Thermal induction of other heat shock proteins is not significantly affected, nor is the state of phosphorylation or the DNA-binding ability of the heat shock transcription factor HSF1. These findings support a model in which hsp70 gene expression is controlled by a second regulatory factor in addition to the positive activator HSF1. The Ku autoantigen, or a protein closely related to it, is likely to be involved in the regulation of hsp70 expression.

Animals↗
PubMed1996

Human Ku autoantigen binds cisplatin-damaged DNA but fails to stimulate human DNA-activated protein kinase.

We have identified a series of proteins based on an affinity for cisplatin-damaged DNA. One protein termed DRP-1 has been purified to homogeneity and was isolated as two distinct complexes. The first complex is a heterodimer of 83- and 68-kDa subunits, while the second complex is a heterotrimer of 350-, 83-, and 68-kDa subunits in a 1:1:1 ratio. The 83- and 68-kDa subunits in each complex are identical. The 83-kDa subunit of DRP-1 was identified as the p80 subunit of Ku autoantigen by N-terminal protein sequence analysis and reactivity with a monoclonal antibody directed against human Ku p80 subunit. The 68-kDa subunit of DRP-1 cross-reacted with monoclonal antisera raised against the Ku autoantigen p70 subunit. The 350-kDa subunit was identified as DNA-PKcs, the catalytic subunit of the human DNA-activated protein kinase, DNA-PK. DRP-1/Ku DNA binding was assessed in mobility shift assays and competition binding assays using cisplatin-damaged DNA. Results indicate that DNA binding was essentially unaffected by cisplatin-DNA adducts in the presence or absence of DNA-PKcs. DNA-PK activity was only stimulated with undamaged DNA, despite the ability of Ku to bind to cisplatin-damaged DNA. The lack of DNA-PK stimulation by cisplatin-damaged DNA correlated with the extent of cisplatin-DNA adduct formation. These results demonstrate that Ku can bind cisplatin-damaged DNA but fails to activate DNA-PK. These results are discussed with respect to the repair of cisplatin-DNA adducts and the role of DNA-PK in coordinating DNA repair processes.

Antibodies, Monoclonal↗
PubMed1997

KARP-1: a novel leucine zipper protein expressed from the Ku86 autoantigen locus is implicated in the control of DNA-dependent protein kinase activity.

The Ku autoantigen plays an integral role in mammalian DNA double-strand break repair as the DNA binding component of the DNA-dependent protein kinase (DNA-PK) complex. Here, we demonstrate that a second gene, KARP-1 (Ku86 Autoantigen Related Protein-1), is expressed from the Ku86 locus. The KARP-1 gene utilizes an upstream promoter and additional exons which results in an extra 9 kDa of protein appended onto the normal Ku86 polypeptide. The KARP-1-specific domain encodes interdigitating hexa- and penta-heptad repeats of leucine residues flanked by a very basic region. Intriguingly, the catalytic subunit of DNA-PK also contains a hexa-heptad repeat of leucines. Consistent with this observation, we observed that human cell lines stably expressing dominant-negative constructs of KARP-1 resulted in diminished DNA-PK activity and X-ray hypersensitivity and that a KARP-1 antibody significantly neutralized DNA-PK activity in vitro. Finally, we present data which suggests that KARP-1 may be primate-specific. These observations have important repercussions for mammalian DNA double-strand break repair.

Amino Acid Sequence↗
PubMed1989

Molecular cloning of cDNA encoding the p70 (Ku) lupus autoantigen.

The Ku (p70/p80) autoantigen consists of two phosphoproteins of molecular mass approximately 70,000 and 80,000 forming a macromolecular complex that binds DNA. Autoantibodies from a patient with systemic lupus erythematosus were used to isolate cDNA clones encoding the human approximately 70-kDa Ku antigen (p70) from a lambda gt11 expression library. The deduced amino acid sequence of p70 consisted of 609 amino acid residues and was confirmed by partial amino acid sequencing. The protein contains two acidic domains of 61 residues (31% Glu + Asp) and 19 residues (53% Glu + Asp) that are similar in size and charge to those found in a number of proteins involved in transcriptional activation. The 61-residue acidic region is rich in serine, raising the possibility that its charge might be modulated by phosphorylation. The predicted amino acid sequence also contains two regions with periodic repeats of either leucine alone, or leucine alternating with serine every seventh position. The latter repeat displays sequence and secondary structural similarities with the "leucine zipper" regions of the c-myc and v-myc oncogene products. The p70 antigen does not appear to have extensive sequence homology with the 80-kDa Ku autoantigen based on analysis of RNA blots and immunological criteria. A major antigenic determinant or determinants recognized by human autoantibodies is located near a leucine repeat on the carboxyl-terminal 190 amino acid residues of p70.

Amino Acid Sequence↗
PubMed1994

Isolation of cDNA clones encoding the 80-kd subunit protein of the human autoantigen Ku (p70/p80) by antisera raised against ciliary processes of human eye donors.

PURPOSE: To isolate and characterize human nonpigmented ocular ciliary epithelial cDNA clones by screening a cDNA library constructed from the established human nonpigmented ciliary epithelial cell line (ODM-2) with sera raised against ciliary processes of human eye donors (cadavers). METHODS: An ODM-2 cDNA expression library in lambda Uni-ZAP-XR vector was screened with sera of mouse anti-human ciliary processes. The cDNA inserts from plaque-purified clones were sequenced by the dideoxy-chain termination method with T3 and T7 polymerase. Sera were assayed by Western blot analysis and indirect immunofluorescence and were then compared with sera, enriched in anti-Ku antibodies, collected from patients with scleroderma polymyositis overlap syndrome. RESULTS: Immunoscreening of 2.5 x 10(5) independent clones with sera induced experimentally in total tissue homogenates of human ciliary processes led to the isolation of four cDNA-positive clones. Three clones, designated A1, D1, and D3 and containing inserts measuring 1.4 kb to 1.8 kb, were found to be identical in DNA sequence analysis to that of the 80-kd subunit protein of the human autoantigen Ku (p70/p80). The fourth clone, designated D2, failed to show any significantly similarity with previously known genes. Cell extracts from human ciliary processes and ODM-2 cells were analyzed by immunoblotting with anti-human ciliary process sera. The pattern of proteins immunodetected was compared with the profile of proteins immunodetected with human anti-Ku sera from a patient with scleroderma polymyositis overlap syndrome. These results demonstrated that sera from anti-human ciliary processes recognize a variety of antigens in ODM-2 cells and are strikingly rich in antibodies to the 80-kd subunit protein of Ku (p70/p80). Furthermore, indirect immunofluorescence analysis supported the observation that anti-human ciliary processes sera labeled nuclear antigens in a human ciliary epithelium cell line and cross species in bovine ciliary epithelial cell, thus demonstrating the nuclear localization of Ku antigen. The mRNA in the human eye was found to be widely expressed in all tested ocular tissues and in ODM-2 cells. CONCLUSIONS: The ocular ciliary epithelium induces a species-specific immune response in xenogenic animals. In particular, the human ciliary epithelium elicits a strong immune recognition of the 80-kd subunit protein of the human autoantigen Ku (p70/p80) in ODM-2 cells.

Animals↗