It has been shown that the activation of T cells by an anti-idiotypic antibody (anti-Id) TB71 containing an internal image of the corresponding mycobacterial antigen (38 kDa) was achieved by the interaction of anti-Id TB71 with the T cell receptor complex (CD3/Ti). The accessory cell requirement in this response could not be replaced by anti-Id TB71 coupled to Sepharose beads and was not inhibited by Fc receptor blockade. When taken together with the finding that anti-Id TB71-induced proliferation of a T cell clone was restricted by determinants encoded by the major histocompatibility complex, these findings suggested that anti-Id TB71 was presented to 38-kDa antigen-reactive T cells by the same mechanisms as conventional antigenic determinants. That is, both stimulated T cells through the CD3/Ti complex and had to be presented in the context of class II molecules on accessory cells. The finding that the disruption of the integrity of the anti-Id TB71 combining site did not affect T cell responsiveness although antibody binding was ablated implied that anti-Id TB71 may be partially degraded and re-expressed with MHC class II determinants.

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Rabbit antisera against twelve mouse monoclonal antibodies to mycobacterial antigens showed idiotype-specificity following cross-absorption with normal mouse globulin. The functional aspects have been partly evaluated so far with two of these reagents. The represen tation of ML04 idiotype appeared to be associated with Igh alleles. Injection of mice with Rb04 anti-Id in incomplete Freunds adjuvant induced Id+ serum levels but without corres ponding antigen binding specificity. In contrast, Rb7 1 anti-Id revealed internal image pro perties corresponding to the homologous 38kd protein antigen of tubercle bacilli. This was demonstrated by the potency of Rb7 1 to sensitize mice in vivo and to elicit T cell prolifera tive and DTH responses.