Bone marrow transplantation following total lymphoid irradiation. I. Correlation with field size and suppressor cell induction.

Total lymphoid irradiation (TLI) induces a unique state of immunosuppression. Although permanent bone marrow chimerism has been obtained in rodents prepared by TLI, uniform marrow engraftment has been more difficult to obtain in larger mammals. Accordingly, studies were performed to assess the immunologic perturbations induced by TLI in inbred LEW rats, and to explore the effect of altering field size of irradiation on the induction of suppressor cells and the success of allogeneic bone marrow transplantation. Additional abdominal shielding to protect a single kidney (right) from irradiation during TLI presented successful of bone marrow engraftment (WF leads to LEW, N = 5) but chimerism was uniformly obtained (N = 3) using the full irradiation field (P less than .05) Lymphopenia and a relative monocytosis were noted in all rats subjected to TLI. Although TLI using the full irradiation field eliminated alloreactivity of nylon-wool-purified spleen cells, significant, if reduced, alloreactivity was noted in rats subjected to TLI using smaller irradiation fields. Irradiated (1500 rads) nylon-wool-purified splenic T cells of rats subjected to TLI using the full field effected significantly greater suppression (P less than .001) of a normal mixed lymphocyte culture than did cells from rats subjected to TLI with right kidney shields in place (relative response reduced to 15.2 +/- 5.7% versus 64.3 +/- 11.7%). Success of bone marrow engraftment in rats prepared by TLI was correlated, therefore, with the induction of a profound lymphopenia, elimination of alloreactivity, and the development of a potent splenic suppressor system.