Thymus grafting in allogeneic radiation chimaeras.

CBA/H mice were lethally irradiated and treated with C57BL/H bone marrow cells. 8–14 days thereafter they were grafted under the kidney capsule with thymus derived either from CBA or from C57BL donors, 4–8 days old. Only 8 per cent of non-grafted animals survived 4 months, but 39 per cent of those grafted with CBA thymus, and 48 per cent of those grafted with C57BL thymus survived the same period. Grafted chimaeras of both groups had significantly more leucocytes in the peripheral blood, and more colony-forming units in the bone marrow, than chimaeras without a graft. A thymus graft syngeneic either with the donor or with the recipient of bone marrow improved the reactivity against bacterial antigens of , but did not influence the reactivity against tissue antigens of sheep erythrocytes. It is concluded that immunological functions of allogeneic radiation chimaeras can not be restored entirely by stem cells from the bone marrow, but require normal (or even increased) cellular and humoral influence from non-irradiated thymus tissue as well.