1102 DEFINITION OF T CELL IDIOTYPES Assay of IL - 2 Production

The concept of idiotypy of ant igen-binding receptors suggests that in addi t ion to possessing a par t icular b inding site for antigen, each receptor has a set of serologic de terminants (idiotypes) which distinguish it from other receptors. T h e finding of idiotypy of an t ibody molecules (1) eventual ly led to a proposal for a network theory of the i m m u n e response (2). The network theory postulates that idiotypic de terminants on antibodies are recognition sites for other, antiidiotypic antibodies within an individual 's own immunoglobul in repertoire. The interplay of these idiotype-bearing and idiotype-recognizing antibodies is thought to be a major factor in regulat ing an i m m u n e response. Evidence for the occurrence of idiotypy (Id) 1 on immunoglobul in (antibody) molecules is by now abundan t and considerable da ta has accumula ted suggesting that the regulation of a given i m m u n e response involves the interaction of antigen-specific, Id-bear ing an t ibody molecules and antiidiotypic antibodies. In part icular , it can be shown that: (a) xenoand allogeneic antiidiotypic antibodies can induce specific i m m u n e responses in the absence of "an t igen" (3-5), and (b) that auto-ant iidiotypic antibodies (6) can be detected in vivo. Idiotypic interactions at the T cell level have also been defined both directly and indirectly. T h e induction of Id-bear ing helper and suppressor T cells in the an t ibody response to the group A streptococcal ant igen has been studied using antiidiotypic reagents (7). In these studies a striking finding was that when guinea pig ant i Id was fract ionated into IgG1 and IgG2 components , the IgG1 a idinduced specific T helper cells, whereas the IgG2 fraction induced suppressor T cells. In the i m m u n e response to lysozyme, suppressor T cells share idiotype with antibodies (8). Alloreactive T cells (9, 10) and antigen-specific helper T cells (11) can also be shown to possess idiotypic determinants . In the case of alloreactive T cells, antiidiotypic antibodies can elicit specific i m m u n e reactions in the absence of antigen; they st imulate the product ion of a l loant ibody in vivo and the induction ofcyto toxic T lymphocytes (CTL) in vitro (9). The major i ty of the above studies relied on ant i Id produced against specific antibodies