Selective Elements for the Vß Region of the T Cell Receptor: MIs and the Bacterial Toxic Mitogens

This chapter focuses on Mls and the bacterial toxic mitogens. The mouse expresses products of several genes mapping to different chromosomes whose effect is to influence the expressed repertoire of T cell receptors solely in terms of the Vβ gene segment utilized in the receptor. Allelic polymorphisms of some of these genes can directly stimulate T cell proliferative responses and they are known as “minor lymphocyte stimulating (Mls) genes.” These structures are called “Vβ selective elements,” or Vbse. Although much is known about Vbse, the crucial questions in this field remain to be answered. The determination of responsiveness by Vβ gene segment usage readily explained the very high precursor frequency of responding T cells, because 5–15% of normal T cells can express receptors encoded by a single Vβ gene segment. The chapter broadens the consideration of Mls to include two other sets of molecules with similar functional effects. The first are bacterial proteins that mimic all of the properties of Mls, the staphylococcal enterotoxins and their relatives. The second are products of genes that produce some but not all of the effects of Mls in the mouse.