Effects of thymectomy at various times after birth (Tx-1, Tx-3, Tx-7, Tx-14) on mixed lymphocyte reaction (MLR), cell-mediated cytotoxicity (CMC), and graft-versus-host reaction (GVHR) were examined by experiments with spleen cells obtained at 8 weeks of age. All of MLR, CMC, and GVHR were detected in spleen cells of Tx-14 mice. However, the ability of spleen cells to induce GVHR was abolished by thymectomy at 7 days after birth. On the other hand, MLR and CMC were not affected in such mice. In Tx-1 or Tx-3 mice, only MLR was detected in spleen cells. These results suggest that thymus dependency of T cells responsible for MLR are lower in their maturation than those for CMC and that thymus dependency of T cells responsible for GVHR are the highest among these T-cell subpopulations.
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