Autoantibodies to the Ro/SS-A particle react preferentially with the human antigen

The measurement of autoantibodies frequently employs animal extracts as antigen, and it is widely observed that the autoimmune response to soluble antigens is not species-specific. Published Ouchterlony experiments with anti-Ro/SS-A sera revealed a qualitative reaction of identity when bovine and human extracts are utilized as antigen source [1]. Quantitative studies of the Ro/SS-A-anti-Ro/SS-A reaction employing a sandwich ELISA with human anti-Ro/SS-A to capture antigen coupled with absorption studies reveal that the anti-Ro/SS-A response is directed to the human Ro/SS-A antigen. Quantitative reactivity is best when the sandwich is charged with human spleen or lymphocyte extracts while rat and mouse spleen extracts are far less effective. Anti-Ro/SS-A sera which react well in Ouchterlony experiments with bovine Ro/SS-A could be shown to prefer a human antigen source by quantitative ELISA and to have strong residual reactivity with human Ro/SS-A after absorption with bovine spleen extract. This is the first autoimmune response to a soluble tissue antigen which is recognized to be preferentially reactive with the human antigen. These data support the ideas that the autoimmune response is antigen driven and that the antigen could be involved in the initiation of the response.