Modification of hybrid responsiveness in the local graft-versus-host reaction by injection of parental lymphocytes.

The local graft-versus-host reaction in F1 hybrid rats, assayed by popliteal lymph node enlargement, is specifically depressed by pretreating the host with parental lymphocytes. The conditions for demonstrating specific depression are injection of a small dose of parental lymphocytes and assay 7 days later. Pretreatment with cells from thymus and bone marrow is ineffective, as is pretreatment with purified B lymphocytes. The structures which stimulate the suppressed response of F1 hybrids are not present on parental B lymphocytes.