B-CELLS ARE ESSENTIAL FOR MURINE MAMMARY-TUMOR VIRUS TRANSMISSION, BUT NOT FOR PRESENTATION OF ENDOGENOUS SUPERANTIGENS

Murine mammary tumor viruses (MMTVs) are retroviruses that encode supe rantigens capable of stimulating T cells via superantigen-reactive T c ell receptor V beta chains. MMTVs are transmitted to the suckling offs pring through milk. Here we show that B cell-deficient mice foster nur sed by virus-secreting mice do not transfer infectious MMTVs to their offspring. No MMTV proviruses could be detected in the spleen and mamm ary tissue of these mice, and no deletion of MMTV superantigen-reactiv e T cells occurred. By contrast, T cell deletion and positive selectio n due to endogenous MMTV superantigens occurred in B cell-deficient mi ce. We conclude that B cells are essential for the completion of the v iral life cycle in vivo, but that endogenous MMTV superantigens can be presented by cell types other than B cells.