Antigen recognition by T cells activated in the mixed lymphocyte reaction: specific binding of allogeneic cell material after removal of surface-bound antigen by trypsin.

T cell blasts activated in the mixed lymphocyte reaction (MLR) carry on their surface stimulator alloantigens which can be removed by treatment of the blasts with trypsin. After overnight incubation in trypsin-free medium, the treated cells exhibit specific alloantigen binding ability: they bind much more effectively cellular material, either obtained from the corresponding MLR supernatant or released by nitrogen cavitation from fresh cells from the stimulating strain, than that from an unrelated H-2 different strain. Trypsin-treated cells which have been incubated in the presence of low concentrations of puromycin are unable to bind stimulator cell fragments.