An idiotope-specific autoantibody in SLE

The public idiotype Id-16/6 and the public idiotope Id-LLa were originally defined on the same human monoclonal anti-DNA antibody, but they are also known to occur separately on other anti-DNA antibodies. We sought the presence of these immunoglobulin variable region markers in purified immunoglobulins from the serum of nine patients with systemic lupus erythematosus (SLE) and 33 healthy donors. Sera from five patients were positive for Id-16/6, and five were positive for Id-LLa. The immunoglobulin preparations were passed over a Sepharose-Id-16/6 column in order to recover auto-anti-idiotypes. An eluate of that column was obtained from the immunoglobulin preparation of one patient whose serum was Id-16/6+ and Id-LLa-. This eluate was shown by competition assay to bind to IdLLa. This is the first demonstration of spontaneously arising human auto-anti-idiotypes against a specific idiotypic system in SLE. The results suggest that antibodies against the Id-LLa idiotope may play a role in immunoregulation.