RESUMO
We have cloned and sequenced a 46-kD Ro/SS-A autoantigen gene that is the human homologue of the calcium-binding protein, calreticulin. The sequence of this 46-kD Ro/SS-A protein (calreticulin) has significant homology to lambda Ral-1, a recombinant cDNA clone corresponding to a major antigen of the nematode, Onchocerca volvulus, the infectious agent of onchocerciasis. We therefore sought to determine whether antibodies produced by onchocerciasis patients might crossreact with the human 46-kD Ro/SS-A autoantigen (calreticulin). 20 of 22 sera from Liberian onchocerciasis patients who had no known evidence of autoimmune disease were found to contain antibodies that reacted with the 46-kD Ro/SS-A (calreticulin) by immunoblot analysis. Characteristic of sera reactive with Ro/SS-A antigens, some onchocerciasis sera also immunoprecipitated the Ro/SS-A-associated hY RNAs. In addition, a monoclonal antibody raised against O. volvulus organisms reacted to purified human WiL-2 cell 46 kD Ro/SS-A antigen (calreticulin) by ELISA. These results strongly suggest that onchocerciasis patients produce antibodies that crossreact with the 46-kD human Ro/SS-A autoantigen (calreticulin) and raise the possibility that infectious organisms such as O. volvulus might play a triggering or exacerbating role in the human Ro/SS-A autoimmune response.
Assuntos
Antígenos de Helmintos/imunologia , Autoantígenos/imunologia , Proteínas de Ligação ao Cálcio/imunologia , Proteínas de Helminto/imunologia , Onchocerca/imunologia , RNA Citoplasmático Pequeno , Sequência de Aminoácidos , Animais , Anticorpos Monoclonais , Northern Blotting , Calreticulina , Linhagem Celular Transformada , Reações Cruzadas , Humanos , Immunoblotting , Dados de Sequência Molecular , Oncocercose/imunologia , Testes de Precipitina , RibonucleoproteínasRESUMO
Ro/SS-A antibodies are found in a number of human autoimmune disorders including Sjogren's syndrome and several systemic lupus erythematosus-related disorders. These heterogeneous autoantibodies are known to recognize several distinct cellular antigens. With synthetic oligonucleotides corresponding to amino acid sequence information we have isolated a full-length cDNA clone which encodes a human Ro ribonucleoprotein autoantigen. The 1,890-base pair clone contains an open reading frame that encodes a 417-amino acid, 48-kD polypeptide that migrates aberrantly at 60 kD by SDS-PAGE. Rabbit antibodies raised against this protein's recently described amino-terminal epitope react with a previously identified 52-kD human Ro protein and immunoprecipitate the human cytoplasmic RNAs. Ultraviolet light cross-linking studies suggest that this Ro protein binds each of the four major human cytoplasmic RNAs. The deduced amino acid sequence is 63% homologous to an Onchocerca volvulus antigen. Southern filter hybridization analysis indicates that this gene is not highly polymorphic and exists as a single copy in the human genome. Chromosomal localization studies place this gene on the short arm of chromosome 19 near the gene encoding the low density lipoprotein receptor.
Assuntos
Autoantígenos/genética , Cromossomos Humanos Par 19 , RNA Citoplasmático Pequeno , Ribonucleoproteínas , Sequência de Aminoácidos , Autoantígenos/isolamento & purificação , Sequência de Bases , Northern Blotting , Southern Blotting , Linhagem Celular , Clonagem Molecular , DNA/genética , Expressão Gênica , Biblioteca Gênica , Humanos , Dados de Sequência Molecular , Hibridização de Ácido Nucleico , Sondas de Oligonucleotídeos , Mapeamento por Restrição , Homologia de Sequência do Ácido Nucleico , SoftwareRESUMO
Ro/SS-A is a soluble cellular protein to which antibodies are frequently directed in patients with Sjögren's syndrome (SS) and systemic lupus erythematosus (SLE)-related disorders. The pathogenic significance of these antibodies is uncertain. Our effort to further characterize the immunological and structural nature of Ro/SS-A suggests that the native human Ro/SS-A molecule is not glycosylated and consists of two disulfide linked domains. The amino terminus of the smaller domain contains a major epitope reactive with anti-Ro/SS-A sera. We have isolated and characterized a complementary DNA (cDNA) clone which encodes the Ro/SS-A polypeptide. The Ro/SS-A gene does not appear to be highly polymorphic and exists as a single copy on the short arm of chromosome 19. The isolation of the Ro/SS-A cDNA should allow for a more complete characterization of Ro/SS-A epitopes which should help further elucidate the importance of Ro/SS-A antibodies in the pathogenesis of disease.
