Antigen-specific T-helper and -suppressor factors in the control of the immune response.

Antigen-specific T-helper and -suppressor molecules usually have a two-moiety, disulphide-bonded structure. One chain binds antigen, while the other chain bears I-A in the case of helper factor and I-J in the case of suppressor factor. Their genetic restriction, when it exists, parallels the 'MHC' determinants that they carry and probably reflects the fact that helper cells are activated by antigen in the context of I-A, while suppressor cells are activated by antigen in the context of I-J. T-helper factor probably augments the induction of contact sensitivity by approximating antigen with its own I-A determinants. Different factors act at the induction and the effector stage and they may be antigen or idiotype directed. The antigen-specific factors characteristically are part of complex circuits involving both antigen-specific and non-specific cells and factors and often have a mode of action through the macrophage.