Immune reactivity of Visna virus-inoculated mice

Visna virus inoculation of mice before immunization with unrelated antigens caused suppression of humoral and cell-mediated immune responses. The immunosuppressive effect was dependent on the virus dose and time of administration. The number of "background" antibody-producing spleen cells increased slightly after inoculation of Visna virus. Heat treatment of Visna virus abolished its immunosuppressive effect. Replication of Visna virus in mice seemed to be a prerequisite for its immunomodulating effect.