A NOVEL V-BETA 2-SPECIFIC ENDOGENOUS MOUSE MAMMARY-TUMOR VIRUS WHICH IS CAPABLE OF PRODUCING A MILK-BORNE EXOGENOUS VIRUS

We have previously reported new Mtv loci, Mtv-48 and -51, in the Japan ese laboratory mouse strains CS and NC. Here we show by backcross anal ysis that both Mtv-48 and 51 cosegregate with very slow deletion of T cells bearing V beta 2. The nucleotide sequences of the open reading f rames in the 3' long terminal repeats of Mtv-48 and -51 were very simi lar to those of Mtv-DDO, mouse mammary tumor virus C4 [MMTV(C4)]), and MMTV(BALB/cV), which encode V beta 2-specific superantigens. Furtherm ore, backcross female mice carrying Mtv-48 but not Mtv-51 were found t o be able to produce milk-borne MMTV(CS), which can vigorously stimula te V beta 2-expressing T cells after local injection in vivo in an I-E -dependent manner. On the other hand, mice carrying Mtv-51 but not Mtv -48 could not produce such an MMTV in milk. The nucleotide sequences o f MMTV(CS) open reading frame were completely matched with those of Mt v-48. These results indicate that the provirus Mtv-48 but not Mtv-51 i s capable of producing a milk-borne virus of which the superantigen st imulates V beta 2-expressing T cells.