Immunosuppression by Leukemia Viruses

Abstract

Abstract Spleens of mice infected with Friend leukemia virus (FLV) were assayed for antibody-precursor cells by an indirect cell transfer method. Drug-treated syngeneic mice were used as immunologically inert recipients. Varying numbers of spleen cells from either normal control or FLV-infected animals were injected intravenously into the recipient mice, followed immediately by challenge immunization with sheep erythrocytes. At various times thereafter spleens of the recipients were tested for the number of individual antibody-forming cells, as well as for hemolytic antibody foci, regarded as clusters of progeny antibody-forming cells. There was a significant diminution in the number of both plaque-forming cells (PFC) and foci in recipients of spleen cells from donor mice infected with FLV. The greatest suppression occurred when donors were infected 7 to 14 days before sacrifice. There was a slight to moderate suppression when the donor spleen cells were obtained from animals infected shortly before sacrifice. The calculated number of antibody-precursor cells present in the donor spleen cell suspension from infected mice was less depressed than would be expected from the suppression observed in the number of PFC appearing directly in the spleens of infected and directly immunized mice. Although the pool of spleen cells capable of responding to antigen and developing into PFC was depleted in spleens of infected animals, it appeared that there was also a secondary effect by virus on the proliferative capacity of such precursor cells and their progeny. The nature and significance of immune suppression at the cellular level are discussed in relation to the mechanism of virus-induced leukemogenesis.