Mechanisms of in vitro immunosuppression in canine distemper virus infection

The in vitro immunosuppressive effects of canine distemper virus (CDV) infection in gnotobiotic dogs was studied by co-culture of lymphocytes from those dogs with uninfected responder canine lymphocytes. Lymphocytes from viremic dogs suppressed the phytomitogen responses of responder dogs. Cell viability and total cells/ml in culture remained at or near control levels. The presence of immunofluorescence (IF) positive syncytial cells in co-cultures was noted and their numbers were increased in cultures containing pokeweed mitogen. Lymphocytes from nonviremic dogs also suppressed the phytomitogen responses of responder dogs. This effect was not dependent on the presence of viral antigen by IF and was abrogated by pre-incubation of the suppressor cell population in vitro for 48 hr prior to use in the suppressor assay. Thus, infection with CDV results in both virus-dependent and virus-independent immunosuppression.