Mouse lymph node activating factor released during contact of HL-A-different blood lymphocytes

Ten-fold concentrated supernatants from the 4-hr mixed cultures of lymphocytes from two humans different at two haplotypes were inoculated s.c. into the hind footpad of mice. Twenty-four to forty-eight hours later, the cellularity and the synthesis of ribonucleic acid increased significantly in the popliteal lymph nodes draining the site of injection. The supernatants from cultures of HL-A-identical cells of cells different at one haplotype lacked this activity. The results suggest that human imcompatible lymphoid cells upon mutual contact liberate a soluble mediator capable of activating the draining lymph nodes; i.e., it is able to trap cells from the circulation and to stimulate them. The mediator is species-nonspecific; the activity produced by human lymphocytes can be tested on mice.