The Role of superantigens in virus infection

Murine mammary tumor viruses are retroviruses which encode superantigens capable of stimulating T cells via superantigen-reactive T-cell receptor Vß chains. Murine mammary tumor viruses are transmitted to the suckling offspring through the milk. We have established that B cell-deficient pups which were foster-nursed by virus-secreting mice do not transfer infectious murine mammary tumor viruses to their offspring. No murine mammary tumor virus proviruses could be detected in the spleen and mammary tissue of these mice. We conclude that B cells are essential for the completion of the viral life cyclein vivo. This indicates that B cells are infected first and that viral amplification takes place only if infected B cells present the murine mammary tumor virus superantigen on their surface, which, in turn, results in activation of T cells expressing the appropriate T-cell receptor Vß chains. These activated T cells secrete factors which stimulate B cells, enabling viral replication.