Idiotypic determinants of immunoglobulins—I Antigenic homology between the heavy and light polypeptide chains from a γA myeloma protein

Abstract A λ-type γA myeloma protein (Hi) was studied in respect of individual-specific or ‘idiotypic’ antigenicity. Rabbit antiserum against γA(Hi) aws rendered specific to the homologous antigen, αA(Hi), by absorption with pooled normal human serum and showed the reaction specific for the idiotypic determinants of the γA(Hi). Absorption of the anti-γA(Hi) with increased amounts of pooled normal human serum resulted in decreased amounts of specific precipitation with the γA(Hi), suggesting that a small quantity of immunoglobulins in the pooled serum may have antigenic determinants similar to the idiotypic determinants of the γA(Hi). To analyze molecular localization of the idiotypic determinants, papain digest, heavy and light polypeptide chains of the γA(Hi) were prepared. The papain digest, heavy chain and intact γA(Hi) showed reactions of identity with the anti-idiotypic antiserum ( anti-Hi-idio ), but the light chain did not show any precipitate line with the anti-Hi-idio upon immunodiffusion. This seems to indicate that the idiotypic determinants of the γA(Hi) localized on the amino terminal portion of the heavy chain. However, the light chain was also found to possess the reactivity with the anti-Hi-idio as clearly demonstrated by pasive hemagglutination of rabbit red blood cells coated with the light chain and by inhibition to the precipitation reactions of the γA(Hi) and the heavy chain with the anti-Hi-idio . The facts that the heavy chain and the intact γA(Hi) showed completely identical reactions with the anti-Hi-idio upon immunodiffusion and that not only the reaction of the intact γA(Hi) but also of the heavy chain were inhibited by the presence of the light chain strongly suggest that, so far as the idiotypic determinants are concerned, there exists some homology in the antigenic structure between the heavy and light chains of γA(Hi). The significance of these findings was discussed.