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PubMed1988

Generation and characterization of monoclonal antibodies to 28-, 35-, and 65-kilodalton proteins of Mycobacterium tuberculosis.

Three monoclonal antibodies (H60.15, H61.3, and H105.10) directed to protein antigens of Mycobacterium tuberculosis were obtained and characterized. H60.15 recognizes a protein with a molecular mass of 28 kilodaltons (kDa) with broad cross-reactivity on a panel of 12 species and strains of mycobacteria. H61.3 reacts with a 35-kDa protein present in M. tuberculosis, Mycobacterium bovis BCG, and M. africanum. On the basis of the antigen molecular masses and competition experiments with other monoclonal antibodies, H60.15 and H61.3 seem to be the first described monoclonal antibodies to these M. tuberculosis proteins. H105.10 binds to the cross-reactive 65-kDa protein present in mycobacteria. Epitope mapping of H105.10 was performed by using the M. leprae DNA sublibrary available in bacteriophage lambda gt11 for this antigen and revealed that its epitope resides in the region from amino acids 20 to 54. The 28-, 35-, and 65-kDa antigens isolated by immunoblotting and presented on nitrocellulose to pleural effusion T cells from tuberculosis patients induced a proliferative response, indicating the presence of T-cell epitopes. These observations indicate that two protein antigens should be added to the list of antigens detectable in M. tuberculosis by monoclonal antibodies. The common feature of such proteins, the elicitation of an immune response of limited or broad cross-reactivity for mycobacteria, encourages the search for their role in the pathogenesis of mycobacterioses.

Animals↗
PubMed2006

Selection on the human immunodeficiency virus type 1 proteome following primary infection.

Typically during human immunodeficiency virus type 1 (HIV-1) infection, a nearly homogeneous viral population first emerges and then diversifies over time due to selective forces that are poorly understood. To identify these forces, we conducted an intensive longitudinal study of viral genetic changes and T-cell immunity in one subject at < or =17 time points during his first 3 years of infection, and in his infecting partner near the time of transmission. Autologous peptides covering amino acid sites inferred to be under positive selection were powerful for identifying HIV-1-specific cytotoxic-T-lymphocyte (CTL) epitopes. Positive selection and mutations resulting in escape from CTLs occurred across the viral proteome. We detected 25 CTL epitopes, including 14 previously unreported. Seven new epitopes mapped to the viral Env protein, emphasizing Env as a major target of CTLs. One-third of the selected sites were associated with epitopic mutational escapes from CTLs. Most of these resulted from replacement with amino acids found at low database frequency. Another one-third represented acquisition of amino acids found at high database frequency, suggesting potential reversions of CTL epitopic sites recognized by the immune system of the transmitting partner and mutation toward improved viral fitness in the absence of immune targeting within the recipient. A majority of the remaining selected sites occurred in the envelope protein and may have been subjected to humoral immune selection. Hence, a majority of the amino acids undergoing selection in this subject appeared to result from fitness-balanced CTL selection, confirming CTLs as a dominant selective force in HIV-1 infection.

Amino Acid Sequence↗
PubMed2004

Mapping of the immunodominant T cell epitopes of the protein topoisomerase I.

OBJECTIVES: To identify the immunodominant T cell epitopes of the topoisomerase I protein in patients with systemic sclerosis (SSc) and control subjects, using computational analysis software (TEPITOPE) and T cell proliferation assays. METHODS: Six oligopeptides, predicted by TEPITOPE software as potential topoisomerase protein epitopes, were used to perform T cell proliferation assays in 21 patients with SSc and 15 healthy controls. RESULTS: A positive response to at least one of the peptides was seen in 10/21 patients and 7/15 healthy controls. Among responders, the proliferative response was limited to a single peptide in 6/7 healthy controls, whereas 5/10 patients responded to more than one peptide. In responding patients a significant correlation was found between disease duration and number of peptides inducing a response (p = 0.007). CONCLUSIONS: Several T cell epitopes of the topoisomerase I protein have been identified and evidence has been found to suggest epitope spreading in patients with SSc.

Adult↗
PubMed1990

Monoclonal antibodies against the free subunits of human chorionic gonadotrophin.

Discordant results on body fluid levels of human chorionic gonadotrophin (hCG) free alpha- and beta-subunits under physiological and pathophysiological conditions, prompted us to raise a total of 260 monoclonal antibodies (MCA) against free hCG-alpha, free hCG-beta, holo-hCG, human follicle-stimulating hormone and bovine luteinizing hormone; 153 MCA recognizing the human alpha-subunit and 28 reacting with hCG-beta were extensively analysed for their intra- and inter-species cross-reactivity with homologous hormones, and for the compatibility of epitopes recognized by them. The immunological topography of free hCG-alpha and free hCG-beta was resolved by these MCA, and epitope maps were designed. Six antigenic determinants on the free alpha-chain (alpha 1-alpha 6), clustered in three spatially distinct domains, and seven epitopes on the surface of free hCG-beta (beta 1-beta 7), could be distinguished. Strikingly, three alpha-chain epitopes (alpha 4, alpha 5 and alpha 6) were shared between various species, which is in contradiction to the concept of immunological species-specificity of alpha-subunits. Three determinants were found to be present only on the free subunits but not on holo-hCG (alpha 6, beta 6 and beta 7), and only two determinants (beta 1 and beta 7) were hormone-specific for hCG. Based on this information, an immunoenzymometric assay for the free alpha-subunit of human glycoprotein hormones was established, with a sensitivity of 1.3 pg/well and a cross-reactivity with holo-hCG of less than 0.005%.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibodies, Monoclonal↗
PubMed2001

Mapping of hiv-1 Gag epitopes recognized by polyclonal antibodies using gene-fragment phage display system.

Phage display has emerged as a powerful technique for mapping epitopes recognised by monoclonal and polyclonal antibodies. We have recently developed a simple gene-fragment phage display system and have shown its utility in mapping epitope recognised by a monoclonal antibody. In the present study, we have employed this system in mapping epitopes recognised by polyclonal antibodies raised against HIV-1 capsid protein, p24 which is derived from proteolytic cleavage of Gag polyprotein. HIV-1 gag DNA was fragmented by DNase I and the fragments (50-250 bp) were cloned into gene-fragment phage display vector to construct a library of phages displaying peptides. This phage library was used for affinity selection of phages displaying epitopes recognised by rabbit anti-p24 polyclonal antibodies. Selected phages contained sequences from two discrete regions of p24, demonstrating the presence of two antigenic regions. The DNA sequences encoding these regions were also cloned and expressed as GST fusion proteins. The immunoreactivity of these epitopes as GST fusion proteins, or as phage-displayed peptides, was comparable in ELISA system using same anti-p24 polyclonal antibodies. The results indicate that the gene-fragment based phage display system can be used efficiently to identify epitopes recognised by polyclonal antibodies, and phage displayed epitopes can be directly employed in ELISA to detect antibodies.

Animals↗
PubMed1988

Mapping of six epitopes on haemocyanin subunit Aa 6 by immunoelectron microscopy.

Monoclonal antibodies directed against the haemocyanin of the scorpion Androctonus australis were raised in order to map antigenic determinants (epitopes). The method of mapping employed in this study is molecular immunoelectron microscopy. It consists of a direct electron microscopic observation of antigenic molecules labelled with monoclonal antibodies. The epitopes are then localized in a small region of the external surface of the antigenic molecule whose architecture and quaternary structure are well known. Six monoclonal antibodies have been selected and epitopes have been circumscribed within a small area of one subunit among the 24 subunits composing the whole antigenic molecule.

Animals↗
PubMed1996

Clinical and immunological aspects of autoantibodies to RA33/hnRNP-A/B proteins--a link between RA, SLE and MCTD.

Heterogeneous nuclear ribonucleoprotein (hnRNP) complexes are major constituents of the spliceosome. They are composed of approximately 30 different proteins which can bind to nascent pre-mRNA. Among these, the hnRNP-A/B proteins form a subgroup of highly related proteins consisting of two adjacent RNA binding domains (RBD) within the N-terminal parts, whereas the C-terminal halves contain almost 50% glycine residues. These proteins, in particular A2/RA33, are targeted by autoantibodies from patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and mixed connective tissue disease (MCTD). In SLE anti-hnRNP antibodies frequently occur together with antibodies to U1 small nuclear RNP (U1-snRNP) and Sm, other proteins of the spliceosome. Preliminary epitope mapping studies have revealed major antibody binding sites in the RNA binding regions for all three diseases. Nevertheless, there is some indication of disease specific epitope recognition. Studies in animal models have demonstrated anti-RA33/hnRNP-A/B antibodies in lupus-prone mouse strains. Thus, autoantibodies to the spliceosomal hnRNP-A/B proteins are a common feature of RA, SLE, and MCTD. However, these diseases differ in their reactivities to other spliceosomal proteins, especially anti-U1 snRNP and Sm. Therefore, anti-RA33/hnRNP-A/B autoantibodies are not only valuable diagnostic markers but may also allow additional insights into the pathogenesis of rheumatic autoimmune diseases.

Animals↗
PubMed1997

Myelin oligodendrocyte glycoprotein: a novel candidate autoantigen in multiple sclerosis.

Myelin oligodendrocyte glycoprotein (MOG) is a member of the immunoglobulin superfamily expressed exclusively in central nervous system (CNS) myelin. While the function of MOG is unknown, a number of studies have shown that immune responses to MOG contribute to the autoimmune-mediated demyelination seen in animals immunized with whole CNS tissue. This paper summarizes our recent studies, which unequivocally demonstrate that MOG by itself is able to generate both an encephalitogenic T cell response and an autoantibody response in Lewis rats and in several strains of mice. In Lewis rats the injection of both native MOG and MOG35-55 peptide produces a paralytic relapsing-remitting neurological disease with extensive plaque-like demyelination. The antibody response to MOG35-55 was highly restricted, as no reactivity to either other MOG peptides or myelin proteins could be detected. Fine epitope mapping showed that antibody from serum and cerebrospinal fluid of injected rats reacted strongly to MOG37-46, which is contiguous to the dominant T cell epitope contained within MOG44-55. NOD/Lt and C57BL/6 mice were also susceptible to severe neurological disease following injection with recombinant MOG or MOG35-55 peptide, indicating that this specific CNS autoantigen, or some of its determinants, can induce a pathogenic response across animal species. Severe paralysis and extensive demyelination were seen in both strains, but NOD/Lt mice experienced a chronic relapsing disease whereas C57BL/6 mice had a chronic non-remitting disease. Moreover, transfer of MOG35-55 T cells into naive NOD/Lt mice also produced severe neurological impairment as well as histological lesions. These results emphasize that a synergism between a T cell-response and anti-MOG antibodies may be important for the development of severe demyelinating disease. This, together with our demonstration that there is a predominant T cell response to MOG in patients with multiple sclerosis, clearly indicates that MOG is probably an important target autoantigen in this disease.

Animals↗
PubMed2001

Mapping of Escherichia coli H27-specific epitope from H-specific polypeptides.

A murine monoclonal antibody (MAb) reactive to H27 flagellin antigen was produced and characterized. Forty-nine partially purified native H-type flagellins were used to evaluate the specificity of the MAb. The fliC gene of H27 is 1,464 bp in length (487 amino acids [aa]; 50.88 kDa). The central variable region (CVR) of the H27 flagellin gene was defined by comparison with flagellin sequences derived from H8, H34, and H49. To study the distribution of antigenic epitopes, the CVR covering amino acid residues 70 to 457 (388 aa) was dissected into seven overlapping fragments. Fragments carrying the H-type-specific antigenic determinants were identified by H27-specific antiserum. Polyclonal antibodies raised against different H-type flagellin proteins were used to determine the cross-reactive determinants. Three fragments, spanning amino acid residues 240 to 380, which carried the potential H-specific determinants were used for MAb production. A MAb specific to H27 was produced, and the specific epitope was mapped to amino acid residues 330 to 340. In this study, we produced MAbs from predetermined H27-specific polypeptides and used whole flagellin in enzyme-linked immunosorbent assays to circumvent the interference of anti-glutathione S-transferase antibodies. These factors when combined could help to improve the identification of the desired MAb.

Amino Acid Sequence↗
PubMed1992

Structure-function analysis of DNA polymerase-beta using monoclonal antibodies: identification of a putative nucleotide binding domain.

DNA polymerase-beta was purified from Novikoff hepatoma and used as an antigen in an in vitro immunization system to produce monoclonal antibodies. These reagents surprisingly showed cross-reactivity to a number of proteins, including several DNA polymerases. Nearly all of these proteins possess nucleotide binding sites, which suggested the potential value of using the monoclonals to elucidate structure-function relationships within polymerase-beta. Furthermore, these antibodies were able to partially neutralize (40-50%) polymerase-beta activity, and this effect could be blocked by dNTP1 but not by dNMP or rNTP. The limited neutralization phenomenon is at least partially explained by the weak binding affinity of these antibodies. Scatchard analysis of immunoprecipitation data predicted a Kd of 1.8 x 10(-8) M. Epitope mapping studies showed that the region of polymerase-beta recognized by one of the monoclonal antibodies is within residues 235-335, and sequence homology studies indicated that the epitope is probably located in the region of amino acids 283-320. At least a portion of this area, namely residues 301-308 and 311-315, appears to be part of a nucleotide binding domain which has sequence homology with a portion of the highly conserved ATP binding site in adenylate kinase.

Amino Acid Sequence↗
PubMed1996

Analysis of chaperonin-containing TCP-1 subunits in the human keratinocyte two-dimensional protein database: further characterisation of antibodies to individual subunits.

The chaperonin-containing TCP-1 (CCT), found in the eukaryotic cytosol, is currently the focus of extensive research. CCT consists of at least eight different subunit types encoded by independent but related genes, and a set of antibodies that recognise individual subunits has proved useful in the characterisation and functional analysis of CCT. These antibodies were used to identify subunits of CCT in the human keratinocyte two-dimensional protein database. Accurate values for the pI and molecular mass of human CCT subunits were determined from the database, and biological data was obtained regarding changes in subunit levels in response to extracellular agents and growth conditions. The second part of the study describes the characterisation of seven monoclonal antibodies raised against mouse TCP-1, also known as CCT alpha, using a combination of epitope mapping and immunoblot analysis of protein extracts from different species and tissue types. Some antibodies were not monospecific for TCP-1, and a number of epitope-related proteins were identified.

Animals↗
PubMed1992

Use of designer recombinant mitochondrial antigens in the diagnosis of primary biliary cirrhosis.

The appearance of autoantibodies against mitochondria in patients with primary biliary cirrhosis has been known for more than 25 yr. In the past, based on the biochemical complexity of the mitochondrion and the use of crude extracts for immunodiagnosis, a degree of nonspecificity in assaying for antibodies to mitochondria has been present. This problem has been largely circumvented by the cloning of the mitochondrial antigens and the identification of the E2 subunits of the pyruvate dehydrogenase complex and the branched chain 2-oxo-acid dehydrogenase complex as the major and immunodominant autoantigens of primary biliary cirrhosis. More than 90% of patients with primary biliary cirrhosis have been shown to react with one or both of these enzymes using either recombinant antigen or purified native protein. Approximately 10% of patients recognize only E2 subunits of branched chain 2-oxo-acid dehydrogenase complex and not pyruvate dehydrogenase complex. Such patients would be missed by diagnostic assay that has a low sensitivity to antibodies against E2 subunits of branched chain 2-oxo-acid dehydrogenase complex. The use of recombinant and biochemically pure antigens has permitted structural and conformational analysis of epitope mapping. We have taken advantage of the antigenic mapping studies of both primary biliary cirrhosis and branched chain 2-oxo-acid dehydrogenase complex E2 subunits and designed a molecule that expresses the immunodominant epitopes of both. Using this dual-headed molecule that coexpresses the epitope of two different antigens, we report herein a sensitive and reproducible assay for antibodies to mitochondria in patients with primary biliary cirrhosis.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1996

IgE and IgG4 antibodies from patients with mite allergy recognize different epitopes of Dermatophagoides pteronyssinus group II antigen (Der p2).

BACKGROUND: Der p 2, composed of 129 amino acids, is one of the major allergens of Dermatophagoides pteronyssinus. Several groups reported epitope mapping of IgE antibody but not of IgG or IgG subclass antibodies in Der p 2. OBJECTIVE: The purpose of this study was to compare the epitopes recognized by Der p 2-specific IgE antibodies with those recognized by IgG4 antibodies. METHODS: Recombinant fusion proteins containing a full-length peptide or overlapping five fragments of Der p 2 were prepared and analyzed for their reactivity with IgE and IgG subclass antibodies in sera from patients with mite allergy by means of Western blot procedure. RESULTS: IgE antibodies in 12 of 13 sera tested bound to full-length Der p 2 (1-129). In 11 of these 12 sera, IgE antibodies bound to one or more of fragments 41-80, 64-105, or 81-129 but not to those of 1-40 or 20-63. Of the 11 sera in which the IgE antibodies to the fragments were detected, only four contained detectable levels of IgG4 antibodies reactive to the fragments. The binding spectra of the IgG4 antibodies against the fragments were rather wide and differed from those of IgE antibodies. CONCLUSION: Results revealed that there are differences in epitope recognition between IgE and IgG4 antibodies; IgE antibodies recognize restricted parts of Der p 2 antigen compared with IgG4.

Animals↗
PubMed1992

Identification of a neutralizing domain in the external envelope glycoprotein of simian immunodeficiency virus.

Two murine monoclonal antibodies (MAbs), designated MATG2014 and MATG2033, were generated. They are reactive with the external envelope glycoprotein gp130 of the simian immunodeficiency virus of macaque monkey (SIVmac251), and display a cell-free virus neutralizing activity in vitro. In addition, MATG2014 cross-reacts with HIV-2Rod gp140. Epitope mapping of these MAbs was performed by screening and SIVmac peptide library expressed in yeast and confirmed using synthetic peptides. MATG2014 and MATG2033 recognize two overlapping epitopes localized in an 18 residue domain between amino acid 171 and 188 of the SIVmac251 gp130. Sera from experimentally SIV-infected macaques are immunoreactive with this neutralizing domain. Sequence comparison with related SIV and HIV-2 viral strains indicates a low variability of this region, consistent with the cross-reactivity of MATG2014 with HIV-2Rod gp140. This domain should then be considered in designing experimental vaccines.

Amino Acid Sequence↗
PubMed1998

The neutralizing antibody response against a conserved region of human immunodeficiency virus type 1 gp41 (amino acid residues 731-752) is uniquely directed against a conformational epitope.

Amino acids 731-752 (731PRGPDRPEGIEEEGGERDRDRS752) of the transmembrane glycoprotein gp41 of human immunodeficiency virus type 1 (HIV-1) are conserved in most virus isolates and are controversially reported to be implicated in virus neutralization. The humoral response in infected patients against this region is poor and humans immunized with gp160 show high levels of antibodies against the peptide but poor neutralization titres. Nonetheless, several groups have succeeded in obtaining neutralizing antibodies against this sequence using different antigen-presenting systems. In order to identify the sequence(s) against which the neutralizing response was generated, we used the flock house virus (FHV) antigen-presenting system to analyse neutralizing antisera from mice immunized with a cowpea mosaic virus (CPMV) chimera expressing the 731-752 sequence. Data show that the neutralizing response is uniquely directed against a conformational epitope mapping to the ERDRD portion of this sequence, although the major antibody response, which is non-linear, and is not neutralizing, is against an IEEE epitope. These results provide an explanation for the controversy regarding the immunogenicity of this region of gp41 and suggest that this conformational epitope, in the absence of the non-neutralizing epitope, should be considered for a subunit vaccine. In addition, this study highlights the usefulness of antigen-presenting systems that preserve epitope conformation in the investigation of immune responses.

Animals↗
PubMed2001

Probing conformational changes in the I-like domain and the cysteine-rich repeat of human beta 3 integrins following disulfide bond disruption by cysteine mutations: identification of cysteine 598 involved in alphaIIbbeta3 activation.

We have investigated receptor function and epitope expression of recombinant alpha(IIb)beta(3) mutated at Cys(177) or Cys(273) in the I-like domain as well as Cys(598), located in the fourth repeat of the membrane-proximal cysteine-rich region and mutated in a Glanzmann's thrombasthenia type II patient. The beta(3) mutants beta(3)C177A, beta(3)C273A, and beta(3)C598Y exhibited a decreased electrophoretic mobility in SDS-polyacrylamide gel electrophoresis under nonreducing conditions, confirming the disruption of the respective disulfide loops. Despite reduced surface expression, the alpha(IIb)beta(3)C177A, alpha(IIb)beta(3)C273A, and alpha(IIb)beta(3)C598Y receptors mediated cell adhesion to immobilized fibrinogen and translocated into focal adhesion plaques. The beta(3)C598Y mutation, but not the beta(3)C177A or beta(3)C273A mutations, induced spontaneous binding of the ligand mimetic monoclonal antibody PAC-1, while the beta(3)C177A and beta(3)C273A mutants exhibited reduced complex stability in the absence of Ca(2+). Epitope mapping of function-blocking monoclonal antibodies (mAbs) allowed the identification of two distinct subgroups; mAbs A2A9, pl2-46, 10E5, and P256 did not interact with alpha(IIb)beta(3)C273A and bound only weakly to alpha(IIb)beta(3)C177A, while mAbs AP2, LM609 and 7E3 bound normally to mutant alpha(IIb)beta(3)C273A, but interacted only weakly with mutant alpha(IIb)beta(3)C177A. Furthermore, a cryptic epitope recognized by mAb 4D10G3 and not exposed on wild type alpha(IIb)beta(3) became accessible only on mutant alpha(IIb)beta(3)C177A and was mapped to the 60-kDa chymotrypsin fragment of beta(3). Finally, the ligand-induced binding site (LIBS) epitopes AP5, D3, LIBS1, and LIBS2 were spontaneously expressed on all three mutants independent of RGDS or dithiothreitol treatment. Our results provide evidence that disruption of a single cysteine disulfide bond in the cysteine-rich repeat domain, but not in the I-like domain, activates integrin alpha(IIb)beta(3). In contrast, disruption of each of the disulfide bonds in the two long insertions of the I-like domain predicted to be in close contact with the alpha subunit beta-propeller domain affect the stability of the alpha(IIb)beta(3) heterodimer and inhibit complex-specific mAb binding without affecting the RGD binding capacity of the metal ion-dependent adhesion site-like domain.

Animals↗
PubMed1998

Summary report on the ISOBM TD-4 Workshop: analysis of 56 monoclonal antibodies against the MUC1 mucin. San Diego, Calif., November 17-23, 1996.

Sixteen research groups participated in the ISOBM TD-4 Workshop in which the reactivity and specificity of 56 monoclonal antibodies against the MUC1 mucin was investigated using a diverse panel of target antigens and MUC1 mucin-related synthetic peptides and glycopeptides. The majority of antibodies (34/56) defined epitopes located within the 20-amino acid tandem repeat sequence of the MUC1 mucin protein core. Of the remaining 22 antibodies, there was evidence for the involvement of carbohydrate residues in the epitopes for 16 antibodies. There was no obvious relationship between the type of immunogen and the specificity of each antibody. Synthetic peptides and glycopeptides were analyzed for their reactivity with each antibody either by assay of direct binding (e.g. by ELISA or BiaCore) or by determining the capacity of synthetic ligands to inhibit antibody binding interactions. There was good concordance between the research groups in identifying antibodies reactive with peptide epitopes within the MUC1 protein core. Epitope mapping tests were performed using the Pepscan analysis for antibody reactivity against overlapping synthetic peptides, and results were largely consistent between research groups. The dominant feature of epitopes within the MUC1 protein core was the presence, in full or part, of the hydrophilic sequence of PDTRAPAP. Carbohydrate epitopes were less easily characterized and the most useful reagents in this respect were defined oligosaccharides, rather than purified mucin preparations enriched in particular carbohydrate moieties. It was evident that carbohydrate residues were involved in many epitopes, by regulating epitope accessibility or masking determinants, or by stabilizing preferred conformations of peptide epitopes within the MUC1 protein core. Overall, the studies, highlight concordance between groups rather than exposing inconsistencies which gives added confidence to the results of analyses of the specificity of antimucin monoclonal antibodies.

Amino Acid Sequence↗
PubMed1996

Autoantibodies to the A/B proteins of the heterogeneous nuclear ribonucleoprotein complex: novel tools for the diagnosis of rheumatic diseases.

Heterogeneous nuclear ribonucleoprotein (hnRNP) complexes are major constituents of the spliceosome. They are composed of approximately 30 different proteins which can bind to nascent pre-mRNA. Among these, the hnRNP-A/B proteins form a subgroup of highly related proteins: their N-terminal halves consist of two adjacent RNA-binding domains, whereas the C-terminal halves contain almost 50% glycine residues. These proteins represent a group of novel autoantigens which are targeted by autoantibodies from patients with rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and mixed connective tissue disease (MCTD): thus, anti-A2/RA33 autoantibodies target the hnRNP proteins A2, B1, B2 (the 'RA33 complex'), and anti-A1 autoantibodies are directed to the hnRNP proteins A1 and A1b. In SLE, anti-hnRNP-A/B antibodies frequently occur together with antibodies to two other spliceosome-associated antigens, U1 small nuclear RNP (U1-snRNP) and Sm. Epitope-mapping studies have revealed that the major antibody binding sites are located in the RNA-binding regions. Furthermore, there is some indication of disease-specific epitope recognition. Studies in animal models have demonstrated the presence of anti-hnRNP-A/B antibodies in several lupus-prone mouse strains. Thus, autoantibodies to the spliceosomal hnRNP-A/B proteins are a common feature of RA, SLE, and MCTD. However, these diseases differ in their reactivities to other spliceosomal components, such as U1-snRNP and Sm antigens. Therefore, anti-hnRNP-A/B autoantibodies are not only valuable diagnostic markers but may also allow additional insights into the pathogenetic mechanisms of rheumatic autoimmune diseases.

Animals↗