Idiotypic manipulations: hierarchy in idiotype expression in rabbits immunized against Micrococcus luteus

Idiotypic cross-reactions were analyzed among three series of anti-peptidoglycan antibodies of the Micrococcus luteus system. The reference idiotype Ab1 was an antibody fraction isolated from an isoelectric focusing preparative column. Cross-reactive idiotypes, Ab1', were induced through the immunization chain (Ab1-Ab2-Ab3). Idiotypic antibodies of Ab1-F1 type were obtained from offspring of female rabbits, actively producing Ab3 during pregnancy. Finally, Ab1 CRI were cross-reactive idiotypes with Ab1 found in a random population of rabbits immunized with M. luteus. Three idiotopes could be characterized within Ab1 antibody. Ab1' usually expressed two of these idiotopes, but never the third specificity which is "private" to Ab1. Ab1-F1 shared one or two idiotopes with Ab1 and Ab1' antibodies. Only one common idiotope appeared to be present on Ab1 CRI. Finally, this idiotope, IdX, could be detected by radioimmunoassay in 20% of rabbits immunized with micrococcal vaccine. It appears that a recurrent idiotype of anti-peptidoglycan antibodies can be preferentially amplified through idiotypic manipulations. On the other side, cascade immunizations lead to the expression on Ab1' and on some Ab1-F1 of a second idiotypic specificity, shared with Ab1. This hierarchy of idiotype expression may well be important in the regulation of antibody synthesis through idiotypes.