High idiotypic connectivity of the VH7183-encoded antibodies directed to a murine embryonic carbohydrate antigen, Lewis Y, as ascertained by syngenic anti-idiotype monoclonal antibodies.

The Lewis Y Ag is a carbohydrate Ag which is closely related to a well-known murine embryonic Ag, the stage-specific embryonic Ag-1 (SSEA-1), in its biochemical structure. It is expressed at the surface of murine embryonic cells as well as many murine cancer cells. For the analysis of idiotopes carried by the anti-Lewis Y antibodies, we generated two syngenic anti-idiotypic mAb, Id-A1 and Id-B4 (both BALB/c IgG1), which are directed to the idiotypic determinants carried by the anti-Lewis Y mAb, AH-6 (BALB/c IgM). Both Id-A1 and Id-B4 (Ab2) recognized paratope-related idiotopes carried by the AH-6 antibody (Ab1); they specifically inhibited the binding of AH-6 to the Lewis Y Ag. The high idiotypic connectivity of anti-Lewis Y antibodies was noted; the polyclonal anti-idiotype antibody, produced in the sera of BALB/c mice by immunizing AH-6 antibody, cross-reacted with several anti-Lewis Y mAb which has been established in different laboratories. Id-B4 and Id-A1 seem to represent such cross-reactive anti-idiotypic antibodies. Id-A1 recognized an idiotope carried by two out of six panel Ab1 mAb directed to the Lewis Y Ag. Id-B4 reacted with four out of the six panel antibodies, and was considered to recognize a recurrent idiotope of anti-Lewis Y antibodies which occurs more commonly than the idiotope recognized by Id-A1. All of the anti-Lewis Y antibodies which carry idiotopes that react with Id-A1 or Id-B4 were encoded by the VH genes of the VH7183 family; the most D-J proximal VH gene family in BALB/c mice, which is known to be preferentially expressed in embryonic B cells. Immunization of BALB/c mice with keyhole limpet hemocyanin-conjugated Id-B4 and/or Id-A1 induced a significant titer of anti-Lewis Y antibodies (Ab1-like Ab3) in the sera.