A Shared Idiotype among Human

An idiotype is an antigenic determinant unique (private) to a given antibody molecule and is associated with the antigen combining site of the antibody. Crossreactive idiotypes are shared antigenic determinants between antibodies of different antigenic specificities in one individual or among antibodies against the same antigen in different individuals. Monoclonal IgM rheumatoid factors were the first autoantibodies known to share idiotypic reactivity (1). Shared idiotypy has also been demonstrated for autoantibodies found in autoimmune disorders, including human (2) and murine lupus (3). In systemic lupus erythematosus (SLE) and Sjogren's syndrome (SS)' shared idiotypes have been described for antibodies to DNA (2), Sm (4), and IgG (rheumatoid factor) (5). Anti-DNA idiotypes have been related to Ig deposition in the kidneys of SLE patients and mice (6, 7) . Idiotypic specificities are consequently thought to reflect the pathogenic potential of autoantibodies in this disease. Autoantibodies to the RNA protein antigens Ro/SSA and La/SSB are also very common in SLE and SS, often present in serum concentrations >1 mg/ml. These autoantibodies are associated with differences in disease expression (8) . To date, there has been little success in defining idiotypic characteristics ofthese antibodies . Only private idiotypes have been reported for anti-La/SSB in humans (9) and none have been characterized for anti-Ro/SSA . To examine anti-Ro/SSA idiotypes, we prepared a heterologous rabbit antiidiotype to anti-Ro/SSA F(ab')2 affinity purified from the serum of a precipitin positive individual and evaluated the possibility of crossreactive idiotype between anti-Ro/SSA+ individuals.