Mls superantigens: how retroviruses influence the expressed T cell receptor repertoire.

The murine Mls antigens were originally discovered because they have an enormous T cell stimulatory capacity, exceeding in strength any other antigen. The finding that Mls interacts directly with the V beta segment of the T cell receptor, leading to in vivo deletion and in vitro stimulation of T cells expressing particular V beta genes, provided an explanation for this phenomenon and led to the formulation of the new term of superantigen. Recently it was discovered by several groups that these superantigens are encoded by type B retroviruses, the mammary tumor viruses which are transmitted vertically as infectious particles or exist as proviruses in the murine genome.