Monoclonal anti-GAT antibodies with different fine specificities express the same public idiotype

We have studied the idiotypic specificities expressed by 22 anti-GAT hybridoma products (HP). These antibodies, although derived from cells of mice with three distinct heavy-chain linkage groups (BALB/c, Igh-1a, DBA/2, Igh-1c and C57BL/6, Igh-1b) all express the same public idiotypic specificity, p. GAT, defined by the heterologous binding of anti-idiotypic serum 715 to C57BL/6 anti-GAT antibodies. None of these antibodies expressed the strain-restricted idiotypic specificity, s.r. GAT-1, defined by the binding of anti-idiotypic serum JL 122 to BALB/c anti-GAT antibodies. BALB/c anti-GAT HP could be shown to fall into three subsets with respect to their fine antigenic specificity for GAT, GT and GA. An individual idiotypic specificity, i1-GAT (defined by syngeneic anti-idiotypic sera raised against one of the BALB/c HP), was also found on a group of BALB/c HP which all shared a similar fine antigenic specificity pattern. Taken together, these observations suggest that the expressed mouse anti-GAT repertoire derives from a very few V-germ-line genes (VH-GAT and VK-GAT) which are highly conserved in the species, and which determine the structure resulting in the p. GAT idiotypic specificity. The variations in fine specificity and individual idiotype are likely therefore to reflect somatic variations affecting these germ-line genes.