A maternally inherited superantigen encoded by a mammary tumour virus

Abstract

A COLLECTION of superantigens, molecules which in combination with class II major histocompatibility complex (MHC) engage T cells bearing particular Vβ chains as part of their αβ receptors, have recently been described^1,2. The mouse self superantigen, Mls-l^a, for example, in conjunction with many MHC class II proteins, engages mouse T cells bearing Vβ6,7,8.1 and 9, almost regardless of the sequences of the other variable components of the receptors on the T cells^3–5. Two types of superantigen have been identified so far: first, superantigens encoded in the mouse genome, such as Mls-la; second, superantigens produced by bacteria, such as the staphylococcal enterotoxins^1,2. Although the latter type of super-antigens are in many cases known to be proteins of about 220 amino acids^6,7, nothing is known about the structures of any of the superantigens encoded in mouse. Here we describe the properties of a new mouse superantigen. The antigen is maternally transmitted in milk and is probably encoded by a mammary tumour virus (MTV). Given the known genetic linkage between at least one of the mouse genomic superantigens and endogenous MTV integration sites⁸, it is tempting to speculate that the superantigen described here and some of the endogenous mouse superantigens are encoded by MTVs.