The J558 VH CDR3 region contributes little to antibody avidity;: however, it is the recognition element for cognate T cell control of the α(1→3) dextran-specific antibody response

Analysis of the humoral immune response of BALB/c mice to alpha(1-->3) dextran (Dex) reveals novel aspects of T cell-mediated control of 'type 2 thymus-independent' responses against polysaccharide antigens, The IgM and IgG antibody response, dominated by the J558 idiotype (Id), is controlled by Id-specific T cells. These regulatory T cells, for which the T cell clone 178-4 Ts with characterized TCR alpha and beta chain sequences is the prototype, expand in ail BALB/c mice upon immunization with Dex, They suppress in a cognate interaction the expansion of J558 Id-bearing B cells, committed for production of IgG antibodies, Furthermore they provide a gate which precludes variability in the V-H CDR3 region of IgG antibodies appearing occasionally in the periphery, The V-H CDR3 region is the recognition element of 178-4 Ts analogous T cells but contributes little to affinity for the antigen. For recognition by 178-4 Ts cells not even minimal sequence deviations of the J558 Id peptide are allowed, The tight germline programmed complementarity between J558 Id-bearing Dex-specific B and J558 Id-specific 178-4 Ts analogous T cells leaves little room on both sides for ontogenetic variability.