Idiotypic cross-reaction between MRL autoantibodies and a BALB/c myeloma

Y2, a monoclonal anti-Sm antibody of MRL origin, demonstrates an idiotype commonly expressed in autoimmune MRL mice, although not necessarily associated with anti-Sm activity. To identify non-anti-Sm antibodies with this common idiotype, a rabbit anti-Y2 anti-idiotypic antiserum was tested for activity with other MRL hybridoma products (HP) as well as BALB/c myelomas. Idiotypic cross-reactivity was thus demonstrated for Y2 and the product of the BALB/c fusing cell line 45.6TG1.7 (M45), an antibody without known antigen binding activity. This determinant was denoted the Y2-M45 idiotype and its presence in serum and other antibodies tested by an inhibition ELISA. The idiotype was demonstrated on some, but not all, MRL HP's tested and was not confined to antibodies of a unique specificity. The idiotype was also present in sera of some normal as well as autoimmune strains of mice with highest levels in two strains bearing the lpr gene. These results indicate that idiotypes of anti-Sm antibodies are not exclusive to the pathologic setting but may be found commonly expressed in mice with antibodies of a variety of binding activity.