In vivo responses of alloreactive lymphocytes stimulated in vitro. Helper-cell activity of MLR-primed lymphocytes.

Populations of mouse lymphocytes enriched in specific alloreactive cells by priming in a mixed lymphocyte response (MLR) include cells which, when injected into congenic nude mice, enable them to make alloantibody after immunization. Helper cells for the priming H-2 alloantigens (H-2b or H-2k) were enriched relative to helper cells for the other H-2 type. Furthermore, the alloantibody responses of nude mice reconstituted with lymphocytes primed twice in vitro were virtually monospecific for the priming alloantigens. These studies suggest that lymphocytes that proliferate in MLR include lymphocytes capable of giving specific help for H-2 antigens in vivo. Nude mice reconstituted with MLR-primed lymphocytes made less antibody to bacteriophage T4 and phix than mice reconstituted with unprimed cells, and fewer mice responded. Priming of cells a second time in MLR further depleted the population of phage helper cells. Similar results were sometimes, but not always, obtained when testing reconstituted nude mice for their ability to make anti-sheep erythrocyte (SRBC) responses. These results suggest that lymphocytes primed against H-2b or H-2k alloantigens do not have specificity for antigens of T4 or phix. These alloreactive cells may also lack specificity for SRBC. However, the results do not allow a definitive conclusion to be drawn.