Differences in thymus dependency among the alloreactive T-cell subpopulations in their development: Graft-versus-host reaction appears to be mediated by delayed-type hypersensitivity of tuberculin type

The effects of thymectomy at various times after birth, 1 and 7 days (Tx-1, Tx-7), on delayed footpad reactions, cell-mediated cytotoxicity (CMC), production of migration inhibitory factor (MIF), and graft-versus-host reactions (GVHR) against allogeneic antigens were determined by experiments with 8-week-old mice. Delayed footpad reactions were detected in Tx-1 mice, but CMC, production of MIF, and the ability to raise GVHR were not detected in such mice. CMC was detected in Tx-7 mice. However, the ability to raise GVHR and to produce MIF was abolished by thymectomy at 7 days after birth. These results suggest that the effector mechanism to mount a GVHR might be mediated by delayed-type hypersensitivity of tuberculin type rather than CMC to host antigens.