Immunosuppressive factor(s) specific for L‐glutamic acid⁵⁰‐L‐tyrosine⁵⁰ IV. In vitro activity and immunochemical properties

The responsiveness of BALB/c spleen cells to the terpolymer L‐glutamic acid⁶⁰‐L‐alanine³⁰‐L‐tyrosine¹⁰(GAT), the copolymer of L‐glutamic acid⁵⁰‐L‐tyrosine⁵⁰ (GT) and the corresponding complexes with methylated bovine serum albumin (MBSA) has been studied in vitro in a modified Mishell‐Dutton culture system, Cultures of BALB/c spleen cells respond to GAT, GAT‐MBSA and GT‐MBSA over a wide dose range. Contrary to in vivo findings BALB/c spleen cell cultures respond to GT in vitro although in a much narrower dose range. Lymphoid extracts from GT‐primed BALB/c or B10.BR mice (GT‐T_SF) specifically suppress the GT‐MBS A response in vitro. This culture system has allowed us to further investigate immunochemical properties of both BALB/c and B10.BR GT‐T_SF. GT‐T_SF from both strains display affinity for GT‐Sepharose and bear determinants encoded by the I region of the H‐2 complex. Moreover, we demonstrate that the suppressive activity from B10.BR mice is a molecule or a molecular complex which displays affinity for GT and bears determinants of the I‐J subregion of the H‐2^k haplotype.