Immunoregulatory activity of T-cell subsets activated in human mixed lymphocyte reaction.

Unseparated human T cells or isolated OKT4+ and OKT8+ subsets were stimulated in allogeneic MLR and subsequently tested for their capacity to suppress fresh autologous responding cells in a second MLR. Contrary to the bulk of evidence regarding the immunoregulation of B-cell function, both OKT4+ and OKT8+ cells could be activated to form suppressors of the MLR and were equally radioresistant. An early peak of blastogenesis was observed when OKT4+ suppressors were used, and this event was completely radiosensitive. When the fresh responding cells were also fractionated into OKT4+ and OKT8+ subsets, no preference for suppressibility of either subset could be demonstrated, indicating that OKT4+ suppressors were acting directly and not through an inductive mechanism requiring OKT8+ effectors. It is suggested that when alloantigenic responses are involved, the human T-cell subsets defined by these monoclonal antibodies may be more accurately defined by the class of MHC antigen to which they respond than by their effector function.