Anti-endothelial cell antibodies in sera of patients with autoimmune diseases: comparison between ELISA and FACS analysis

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Abstract
SUMMARY: In some patients suffering from rheumatoid arthritis (RA), vasculitis is a clear clinical manifestation, mentioned as rheumatoid vasculitis (RV). Autoantibodies directed against endothelial cells (AEA) have been implicated in the pathogenesis of this disorder, and it has been suggested in a number of studies that testing for AEA should be included in diagnosing RV. To test this hypothesis, we have evaluated the presence of AEA in sera of patients suffering from various autoimmune diseases, employing an ELISA with fixed cultured endothelial cells (EC). In ail the groups of patients ELISA-positive sera were present. A significant difference in percentage of positivity was found between the RA and RV group (P <0.05). In addition, our results indicated that not only antibodies directed against antigens on the EC membrane were detected, but also antibodies directed against intracellular components like DNA. histones and cytoskeletal components. Therefore, we also tested all these patient sera on unfixed intact EC using indirect immunofluorescence followed by FACS analysis. Whereas in the total patient population 34 out of 65 patients were AEA-positive as determined in the ELISA, only seven patients were weakly positive when examined by flow cytometry. We conclude that: (i) an ELISA on fixed EC does not specifically detect AEA, A positive test result is. however, to some extent correlated with the occurrence of vasculitis, and may therefore be helpful in diagnosing this disease: (ii) EACS analysis is a more suitable method than ELISA to measure the presence of membrane-specific AEA in patient sera; (iii) specific IgG-AEA are less common in patients suffering from autoimmune disorders than was assumed previously.