Unique Ia epitopes of T cells (Iat) are involved in the recognition of stimulator cells in the allo-MLR.

Anti-Iat monoclonal antibodies (mAbs) were found to block the recognition phase of allogeneic mixed lymphocyte reaction (allo-MLR) by reacting with responder T cells but not stimulators. The inhibitory pattern was dependent on the major histocompatibility complex (MHC) of both the responder and stimulator cells. Certain molecules, including IgVH and I-J of stimulator cells were also important. It is suggested that Iat epitopes on alloreactive T cells may serve as a marker of a novel type of a T cell recognition site for Ia. The model of T cell receptor complex with two distinct sites for MHC recognition is proposed.