NEW INFECTIOUS MAMMARY-TUMOR VIRUS SUPERANTIGEN WITH V-BETA-SPECIFICITY IDENTICAL TO STAPHYLOCOCCAL-ENTEROTOXIN-B (SEB)

Only few infectious mouse mammary tumor viruses (MMTV) have been characterized which induce a potent superantigen response in vivo. Here we describe the characterization of an MMTV which was isolated from milk of the highly mammary tumor-prone SHN mouse strain. Exposure of newborn mice to milk-borne MMTV (SHN) results in a very slow deletion of V(beta)7, 8.1, 8.2 and 8.3 expressing peripheral T cells. Subcutaneous injection of adult mice with this virus induces a rapid and strong stimulation of all four affected V-beta-subsets in vivo. Besides the strong T cell effect we observed an early proliferation and activation of the local B cell pool leading to the initial secretion of IgM followed by preferential secretion of IgG(2a) by day 6. Sequence comparison of the polymorphic C terminus with known open reading frames revealed high homology to the endogenous provirus MtV-RCS. This is the first report of a virus having a complete overlap in V beta-specificity with a bacterial superantigen stimulating as many as 35 % of the whole CD4(+) T cell repertoire including V(beta)8.2.