Leukemia Virus-Induced Immunosuppression

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Abstract
Measurements of lymphocyte mediated cytolysis of allogeneic target cells (C57BL/6 EL4) by sensitized BALB/c spleen cells revealed a rapid depression of this in vitro correlate of cellular immunity after infection with Friend leukemia virus (FLV). Immunosuppression occurred with infection either before or after alloantigen sensitization. Cell-mediated cytotoxicity by sensitized lymphocytes from the leukemia resistant C57BL/6 strain for DBA/2 mastocytoma cells was unimpaired when FLV was administered after immunization. However, a significant, but transient, depression of the response was observed when C57BL/6 mice were infected 4 days before immunization, but not at 8 or more days before immunization. A kinetic analysis of the cytolysis indicated that there was a decreased number of cytolytic effectors present in the spleens of the FLV-infected BALB/c mice rather than a diminution of the lytic efficiency of the cytolytic cells. The cytolytic activity carried out by the remaining effectors still occurred via a single interaction between a target cell and a sensitized lymphocyte as in the noninfected mice. The lowered cytotoxicity by BALB/c lymphocytes was proportional to the infecting dose of FLV and could not be accounted for by a simple dilution of effector cells with neoplastic cells. The number of cytolytic lymphocytes decreased logarithmically with time after FLV infection. These results demonstrate that FLV is capable of interfering with a T cell (Θ-bearing) dependent event as well as the B cell function of antibody formation. The depression of cell-mediated immunity by infection with FLV after immunization clearly contrasts with the absence of depression of humoral antibody formation when FLV is administered after antigen.

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