Thymus independence of hybrid resistance against a panel of T-cell lymphomas of H-2b origin.

Adult thymectomy, followed by whole-body irradiation and reconstitution with fetal liver, was performed to study the T-cell dependence of F1 hybrid resistance to a panel of lymphomas of H-2b origin. Previously, the pattern of hybrid resistance against the same lymphomas was found to correlate with the pattern of NK-activity in a spectrum of F1 hybrids (Kiessling et al., 1975). We now show that hybrid resistance against three lymphomas of C57BL/6 origin, P-52-127-166, RBL-5 and EL-4 and against YLD, of C57L origin, is expressed in the absence of thymus. In another series of experiments, the effectors responsible for hybrid resistance to the transplanted lymphoma EL-4 were studied by reconstituting thymectomized and non-thymectomized C57BL mice with syngeneic bone marrow from NK-deficient beige mutant or wild-type C57BL donors. While the recipients of beige bone marrow had a clearly reduced tumor resistance, thymectomy did not decrease resistance further. This study supports the hypothesis that resistance to these lymphomas in F1 hybrids as well as in syngeneic mice is mainly mediated by natural killer cells.