Effects of selective depletion of L3T4+ T-lymphocytes on herpes simplex virus encephalitis.

The L3T4 surface molecule defines a subset of murine lymphocytes which are homologous to CD4+ lymphocytes in humans, and are functionally characterized as "helper/inducer" cells. To determine the role of helper/inducer lymphocytes in the host defense against herpes simplex virus type 1 (HSV-1) encephalitis, we utilized a monoclonal antibody to selectively deplete L3T4+ lymphocytes from BALB/c mice prior to experimental HSV infection. Susceptibility to HSV was only minimally increased by the depletion of L3T4+ cells, although mice receiving anti-L3T4 were profoundly immunosuppressed; splenic lymphocytes did not respond to stimulation by virus antigen in vitro, and L3T4+ lymphocyte-depleted mice failed to produce antibodies to HSV-1. However, mice receiving anti-L3T4 had a prolonged increase in natural killer cell activity following HSV infection as compared to controls. These data demonstrate that L3T4+ lymphocytes contribute minimally to host resistance to acute neural HSV infection, even though elimination of these lymphocytes markedly inhibits the genesis of immune responses.