Recognition of idiotypes in lymphocyte interactions. II. Antigen-independent cooperation between T and B lymphocytes that possess similar and complementary idiotypes.

Antigen-independent cooperation between T and B lymphocytes is demonstrated in vitro in two different experimental protocols: (a) B cells from A/J mice immunized in vivo either with Group A streptococcal vaccine (Strep A) or with the IgG1 fraction of guinea pig anti-idiotypic antibody to the A5A idiotype, mature into plaque-forming cells (PFC) with specificity for Group A streptococcal carbohydrate (A-CHO) during a 4-day culture together with T cells from A/J mice immunized in vivo with A5A idiotypic antibody. (b) B cells from A/J mice immunized in vivo with Strep.A generate PFC specific for A-CHO when cultured in the presence of small concentrations of anti-A5A idiotypic antibody and of T cells primed with Strep.A. In both cases, antigen-independent cooperation is idiotypically selective, such that only those B cells respond that secrete antibody with the A5A idiotype. The data are interpreted to suggest that, in addition to antigen-specific helper cells, idiotype-specific may participate in antibody responses, and that the latter type of help may be responsible for the idiotypic selectivity in T-B cooperation observed previously. Furthermore, idiotype-specific cooperation may be a means to generate and maintain B cell diversity during the evolution and ontogeny of the immune system.