Influence of the recipient thymus on the maturation of T-lymphocytes in H-2 different radiation chimeras.

Graft-versus-host reactions in mice can be suppressed by incubation of the donor cells with T-cell-specific antibodies prior to transplanting them into lethally irradiated recipients. Since reconstitution of the immune functions in these recipients requires the formation of a new T-lymphocyte population, we investigated whether H-2 differences between recipient thymus and donor stem cells as well as an age dependent thymic involution impaired the maturation of immunocompetent T-lymphocytes. For this purpose the immune response of different chimeric mice against SRBC and third party skin grafts as well as the repopulation of the lymphatic organs with T-lymphocytes was evaluated. Chimeras of the type CBL leads to CBL/CBA and CBL/CBA leads to CBA were used for the experiments. In addition chimeras which had been thymectomized, transplanted with the thymus of one parent strain, lethally irradiated and transfused with bone marrow from other parent strain were analyzed. In all chimeric combinations, even in the case of complete H-2 difference between donor cells and recipient thymus, a normal or almost normal reconstitution of the immune response against SRBC and incompatible skin grafts were detected. Furthermore age-involuted thymi returned to normal morphologically and functionally after bone marrow transplantation. The repopulation of the lymphatic organs in the investigated chimeric mice was remarkably similar to normal controls. This indicates that hemopoietic stem cells and/or lymphopoietic progenitors may differentiate in a thymus in spite of H-2 differences to functional T-lymphocytes able to respond against SRBC and incompatible skin grafts.