A V-BETA-4-SPECIFIC SUPERANTIGEN ENCODED BY A NEW EXOGENOUS MOUSE MAMMARY-TUMOR VIRUS

The superantigen (SAg) expressed by mouse mammary tumor virus (MMTV) h as been shown to play an essential role in the course of the viral lif e cycle. In the present study, we describe a V beta 4-specific SAg enc oded by a new exogenous MMTV carried by the SIM mouse strain. This is the first report of a viral or bacterial SAg reacting with mouse V bet a 4(+) T cells. Injection of MMTV(SIM) into adult BALB/c mice leads to a rapid and strong stimulation of V beta 4(+) CD4(+) T cells, followe d by a slow deletion of these cells. Neonatal exposure to the virus al so leads to a progressive deletion of V beta 4(+) T cells. In contrast to other strong MMTV SAg, this new SAg requires the presence of major histocompatibility complex class II I-E molecules to be presented eff iciently to T cells. Sequence analysis revealed a new predicted amino acid sequence in the C-terminal polymorphic region of this SAg. Furthe rmore, sequence comparisons to the most closely related SAg with diffe rent V beta specificities hint at the specific residues involved in th e interaction with the T cell receptor.