Lymphocyte surface receptors and leukemia virus-induced immunosuppression

The number and distribution patterns of lymphocytes in the spleens and lymph nodes of Balb/c mice which express immunoglobulin surface receptors were studied in terms of the effects of a murine leukemia virus on the immune-response mechanism. Friend leukemia virus induces a prompt, marked depression of the immune response of mice to antigens such as sheep erythrocytes and E. coli LPS. A functioning T- and B-lymphocyte system is necessary for the response to the SRBC's whereas E. coli LPS, a T cell-independent antigen, stimulates B cells alone. Although the responses to both classes of antigen were markedly depressed in FLV-infected mice, the major defect appeared to be impairment of B-cell function, at least early in the course of infection. In order to examine in more detail the mechanism of interaction between FLV and lymphoid cells with Ig surface receptors, presumably B cells, immmunofluorescent analyses were performed with spleen, and lymph node cells from FLV-infected mice. Within a few days after infection there was a marked decrease in the percentage of spleen cells with Ig surface molecules, although the absolute number of these cells was either unchanged or increased due to marked splenomegaly caused by the virus. A marked decrease in the percentage of splenocytes with theta antigen, considered a marker for mature T cells, also was evident in infected mice. The number of spleen cells showing evidence of FLV infection (i.e., positive for FLV-associated antigens) increased rapidly during the first few days after infection, and within 2 to 2 1/2 weeks nearly all of the nucleated splenocytes were positive for the tumor antigen. In contrast to the results for spleen cells, there were increases rather than decreases in the percentages of Ig-positive and theta-positive cells in the lymph nodes after infection. The number of lymph-node cells that showed the presence of FLV antigen was much lower than in the spleen, and their appearance was also much slower as the leukemic process progressed. Despite these differences between spleen and lymph-node cells in terms of relative percentages of Ig- and theta-positive lymphocytes, relatively similar depressions were evident for the percentages of lymphoid cells that could redistribute their surface Ig receptors into polar caps when incubated with anti-Ig serum at 37 C. Marked impairment of the Ig-capping responses for both spleen and lymph-node cells paralleled the course of infection and development of immunosuppression. These observations indicate that murine leukemia virus infection can both alter the responsiveness of immunocompetent cells to T-dependent and independent antigens and depress the number and normal functional activity of these cells, as reflected by altered surface Ig receptors and antigens.