Both T and B cells shed infectious mouse mammary tumor virus

Mouse mammary tumor virus (MMTV) infected both B and T tissue culture cells and primary B and T cells in vivo after milk-borne transmission of the virus. The infected tissue culture cells processed viral proteins, and both these and primary B and T cells shed virus when cultured in vitro. Moreover, the infected B and T tissue culture cells transmitted virus to uninfected mammary gland cells in vitro. The level of infection of these different cell types in vivo was dependent on the strain of mouse, with C3H/HeN mice showing greater B-cell infection and BALB/c mice greater T-cell infection after nursing on MMTV-infected C3H/HeN mothers. Although their B cells were less infected, BALB/c mice developed tumors more rapidly than C3H/HeN mice. These results indicate that both infected T and B cells are potential carriers of MMTV in vivo. Mouse mammary tumor virus (MMTV) is a milk-borne ret-rovirus that causes mammary tumors in mice (15). MMTV encodes a superantigen (Sag) protein in its long terminal re-peat (LTR) that is required for its transmission (1, 17). MMTV first infects B cells in the Peyer’s patches of the gut, and these infected B cells present the Sag to cognate T cells (14). B-cell infection is required for stimulation of T cells, and infectio