Impaired Generation of Anti‐Viral Cytotoxicity against Lymphocytic Choriomeningitis and Vaccinia Virus in Mice Treated with CD4‐Specific Monoclonal Antibody

The role of CD4 + helper T cells in induction of anti‐viral cytotoxic T‐cell response was investigated by treating normal and thymectomized C57B1/6 mice with CD4‐speciflc monoclonal antibodies (MoAb). In CD4‐specific MoAb‐treated mice infected with Vaccinia or lymphocytic choriomeningitis virus (LCMV), cytotoxic T‐cell activity was 5–15 times lower than in normal controls when measured in a 51 Cr release assay and computed as lytic units 6 and 8 days respectively after virus inoculation. This difference in the levels of effector T‐cell activities did not reflect slower kinetics of cytotoxic T‐cell induction in antibody‐treated versus control mice, since it was also obvious at 8 days after infection for Vaccinia virus and 10 and 12 days after inoculation with LCMV, CD4‐specific MoAb‐induced inhibition of cytotoxic T‐cell responses in vivo was seen up to 150 days after treatment in thymectomized mice. However, no significant suppressive effect of the same antibody treatment on T‐cell cytotoxicity could be observed in animals treated on day 3 or later after infection with Vaccinia virus. Injection of CD4‐depleted mice with recombinant interleukin 2 (rIL‐2) partially corrected the impaired virus‐specific cytotoxic T‐cell response, suggesting that IL‐2 supply may be limiting in mice licking T helper cells.