GAT-specific IgG plaque-forming cell (PFC) responses by syngeneic mice to GAT complexed to the immunogenic carrier methylated bovine serum albumin (GAT-MBSA) in vitro and in vivo

Immunization of mice bearing the nonresponder haplotypes, H 2 ~" q" s. with the terpolymer L-glutamic acid6°-L-alanine3°-L-tyrosine TM (GAT) 1 stimulates suppressor T cells (Ts) that specifically inhibit GAT-specific IgG plaque-forming cell (PFC) responses by syngeneic mice to GAT complexed to the immunogenic carrier methylated bovine serum albumin (GAT-MBSA) in vitro and in vivo (1, 2). Analogous to the results of Tada and Taraguchi with other systems (3, 4), previous studies from our laboratory have shown that cell-free extracts of spleens or thymuses from GAT-primed, nonresponder DBA/1 ( H 2 Q) or A.SW ( H 2 "~) mice suppress the PFC responses to GAT-MBSA, but not to sheep red blood cells (SRBC) in the strains of origin (5). In the previous paper of this series, we have described and evaluated the in vitro assay for the activity of GAT-specific suppressive factor, defined the activity of $5o units/ml as the inverse of the dilution of the extracts that cause 50% inhibition of PFC responses, verified the reproducibility of the suppression observed with different extracts, and demonstrated that the suppressive factor(s) extracted from lymphoid cells of GAT-primed nonresponder mice is obtained from T cells (6). These techniques have permitted an initial characterization of the properties of the GAT-specific suppressor T-cell factor (GAT-TsF) in the crude extracts of lymphoid cells from GAT-primed DBA]I mice that is described in this communication. Two main issues were then addressed. First, the fine specificity of GAT-T~F was