Factors from lymphoid cell tumor affecting immune responses

Friend leukemia virus induces erythroblastic leukemia in genetically susceptible BALB/c mice. FLV-containing leukemic cells markedly depressed the humoral immune response to SRBC in the appropriate mouse strain. Both immunosuppression and leukemogenesis were readily transmitted by cell-free virus-containing homogenates of the FLV leukemic splenocytes into normal BALB/c mice. In the present study it was found that both Friend leukemic splenocytes as well as virus containing extracts from the leukemic cells were neutralized by heating and by specific antisera. Suppressive activity passed through a 0.45 mu filter but not a 300,000 MW filter and could be pelleted at 100,000 x g. They were also highly resistant to inactivation by irradiation. Mice given leukemic splenocytes after irradiation with up to 32.000 rads still developed leukemia. Addition of either normal or irradiated FLV-leukemic cells to normal spleen cell cultures in vitro markedly suppressed antibody formation. At least 32,000 rads were required to significantly impair the immuno-suppressive activity of the FLV-leukemic cells. Thus, virus per se appears to be directly responsible for suppression of antibody formation to FLV.