T cell replacing factor substitutes for an I-J+ idiotype-specific T helper cell.

An in vitro system for the study of idiotype (Id) expression on antitrimethylamino hapten antibody-producing cells and its regulation by two classes of helper T cells is described. These cells are distinguished in four ways: one requires a hapten-carrier bridge and gives a good response that is low in Id; it does not bind to Id-coated dishes and is not affected by anti-I-J plus complement. The other requires antigen but not a hapten-carrier bridge, is bound by Id-coated dishes and is killed by anti-I-J and complement. The Id-specific cell appears to be antigen specific and acts via a soluble factor(s).