The cellular basis of immunosuppression caused by the radiation leukaemia virus.

Infection of adult C57B1/6 mice with the radiation leukaemia virus resulted in suppression of the ability of the animals to respond to an immunizing inoculum of sheep erythrocytes. Results of the transfer experiments indicated that the immunosuppressive effect was expressed at the immunocompetent cell level, and that the virus affected the thymus-derived population of immunocytes. The immunosuppressive effect of the virus on thymus cells, independent of any contribution by cells of bone marrow origin, was verified with thymus-independent immunogens, polyvinylpyrrolidone (PVP) or pneumococcal polysaccharide SIII (PPS). Mice inoculated with the radiation leukaemia virus produced nearly normal amounts of plaque-forming cells producing antibodies against PVP and PPS, thereby confirming that the immunosuppressive effect of the radiation leukaemia virus was on thymus-derived cells.