IN-VIVO EFFECTS OF A RECOMBINANT VACCINIA VIRUS EXPRESSING A MOUSE MAMMARY-TUMOR VIRUS SUPERANTIGEN

Early after infection, the mouse mammary tumor virus (MMTV) expresses a superantigen (SAg) at the surface of B lymphocytes. Interaction with the T-cell receptor V beta domain induces a polyclonal proliferative response of the SAg-reactive T cells. Stimulated T cells become anergi c and are deleted from the T-cell repertoire. We have used a recombina nt vaccinia virus encoding the MMTV(GR) SAg to dissect the effects of the retroviral SAg during an unrelated viral infection. Subcutaneous i nfection with this recombinant vaccinia virus induces a very rapid inc rease of V beta 14 T cells in the draining lymph node. This stimulatio n does not require a large number of infectious particles and is not s trictly dependent on the expression of the major histocompatibility co mplex class II I-E molecule, as it is required after MMTV(GR) infectio n, In contrast to MMTV infection during which B cells are infected, we do not observe any clonal deletion of the reactive T cells following the initial stimulation phase. Our data show that contrary to the case with MMTV, macrophages but not B cells are the targets of infection b y vaccinia virus in the lymph node, indicating the ability of these ce lls to present a retroviral SAg, The altered SAg expression in a diffe rent target cell observed during recombinant vaccinia virus infection therefore results in significant changes in the SAg response.