BALB/c mice immunized multiple times with ABPC48 (A48 or Ab1), a BALB/c bacterial levan (BL)-binding myeloma proteins, produce anti-Ab1 antibodies (Ab2). Immunization with only tow doses of AB1 often leads to the production of anti (antiA48) (Ab3) as does immunization with hemocyanin conjugates of Ab2. Finally, immunization with hemocyanin conjugates of Abf3 leads to the production of anti- (anti-[anti-A48]) (Ab4). Normal BALB/c mice immunized with BL produce an anti BL antibody response containing no detectable Ab1 idiotype (Id)-bearing molecules. Mice producing Ab3 express substantial amounts of Ab1 Id in their anti-BL response whereas mice producing Ab2 and Ab4 show a generalized inhibition in their anti BL response. These results indicate that states of immunity within an idiotypic chain may have marked effect on antibody responses to the antigen (i.e., BL) which is the putative initiator of the chain. Strikingly, the chain itself has an interesting feature. That is, Ab3 and Ab1 share a cross-reactive Id in that both are bound by Ab4 and Ab2. We propose a model of Id-anti-Id systems to explain this unexpected result. This is based on the concept of regulatory idiotopes on Ab1 molecules which initiate Ab2 (anti-idiotope) responses. In contrast, Ab2 molecules generally fail to initiate anti-Ab2 Id responses eigher because any individual idiotope is present at very low concentration or because Ab2 molecules tend to lack regulatory idiotopes. Thus, Ab2 molecules immunize syngeneic animals because they interact with cells bearing Ab1 like regulatory idiotopes. Thus, Ab3 will share regulatory idiotopes with Ab1. Ab4 and Ab2 will share the ability to bind the Ab1-like regulatory idiotope.

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