Specific binding of radiolabeled membrane vesicles by T cells activated in the mixed lymphocyte reaction

An assay was developed to quantitate binding of radiolabeled membrane vesicles by T cells activated in the primary mixed lymphocyte reaction (MLR). T blasts generated in unidirectional, reciprocal MLR combinations were found to bind much more effectively membrane vesicles prepared by nitrogen cavitation from allogeneic stimulator cells than from syngeneic spleen and lymph node cells which had been previously labeled biosynthetically with [3H]leucine. Specific inhibition of binding with cold vesicles prepared from stimulator cells but not from responder cells was observed. The number of specific antigen‐binding cells is proportional to the concentration of membrane vesicles used. The proportion of labeled cells increases between 15 and 60 min of incubation with membrane vesicles, but thereafter remains constant. The binding of stimulator material is H‐2‐specific: cells bind membrane vesicles from congeneic mouse strains only if they share the H‐2 antigens of the original stimulator strain. Responder blasts bind labeled stimulator membrane fragments after as early as 2 days of primary MLR culture; no binding of membrane vesicles by small lymphocytes was detected between 2 and 5 days of culture. However, between 8 and 12 days of culture, a significant proportion of small lymphocytes bind specifically stimulator membrane vesicles. The recognition function is sensitive to trypsin treatment but is regenerated within 5 to 6 h.