Idiotypic profile of the response to phosphorylcholine induced in the absence of the homologous antigen.

In the absence of the homologous antigen, an anti-phosphorylcholine (PC) plaque-forming cell (PFC) response has been induced in vitro which is restricted to the TEPC 15 idiotype (T15). Anti-T15 antibodies were used to focus either the keyhole limpet hemocyanin (KLH) or the fowl gamma-globulin (FGG) carrier molecules on the membrane of B cells carrying the T15 idiotype on their immunoglobulin receptors; thereafter, these cells were allowed to cooperate in vitro for 5 days with T cells primed to the appropriate carrier molecule. A response, virtually 100% T15+, could be induced both in normal BALB/c and in T15 neonatally suppressed mice which had lost the T15+ clonal dominance. The magnitude of this response is comparable to that obtained in the presence of the PC antigen. The role of the membrane-bound immunoglobulin receptor (sIg) in the expression of different anti-PC clones was also investigated. We have focused either the KLH or the FGG carrier molecules on the membrane of B cells via anti-H-2 antibodies and then cultured these cells for 5 days with the appropriate carrier-specific T cells. Under these conditions, B cells are activated in the absence of interaction at the sIg. The idiotypic profile of the anti-PC PFC obtained with the anti-H-2-mediated activation was then compared with the profile of the anti-PC response obtained in the presence of PC antigen. Since similar idiotypic profiles were obtained in both cases, it can be excluded that sIg plays a direct role in favoring the expression of T15+ over T15- anti-PC clones.