Generation of T Memory Cells in One‐Way Mixed Lymphocyte Culture

The peak of blast response in primary, one‐way mixed lymphocyte culture of CBA plus DBA ‐m took place on culture day 6 to 7 whereafter the number of Masts per culture declined. Concomitantly with the disappearance of blast cells from these cultures, the number of lymphocytes increased, indicating that a certain number of blasts reverts back to lymphocytes (‘secondary lymphocytes’). The number of antigen‐reactive cells in primary mixed culture (quantitated by hydroxyurea block) was on the order of 3% to 5%, whereas when the same cultures were reprimed with the original antigen, the number of antigen‐reactive cells was on the order of 90% . Thus most lymphocytes surviving prolonged primary mixed lymphocyte culture are in fact secondary lymphocytes–that is, blast‐derived. The secondary lymphocytes thus obtained responded promptly and in a biphasic manner to the original and H‐2 cross‐reactive stimulator cells in secondary mixed culture The first, major response peak took place on culture day 2 to 3 and the second, minor peak on culture day 5 to 6. Although the secondary lymphocytes were sensitive to anti‐θ plui complement, they did not respond to phytohemagglutinin The secondary lymphocytes were themselves cytotoxic to relevant allogeneic target cells in vitro, and they were promptly reinduced to maximal cytotoxicity by a second priming with the original antigen. We suggest that these functions are character‐istic to T memory cells primed against histoincompatible cells.