DOMINANT EXPRESSION OF A DISTINCTIVE V14+ T-CELL ANTIGEN RECEPTOR ALPHA-CHAIN IN MICE

A distinctive variable region 14-positive (V14+) alpha-chain (V-alpha-14+) of the T-cell antigen receptor is predominantly expressed in multiple mouse subspecies. The V-alpha-14 family has two members, V-alpha-14.1 and V-alpha-14.2, which differ by only three amino acids at positions 50-52. Based on the EcoRI restriction fragment length polymorphism of the gene encoding V-alpha-14, mice can be divided into three groups: type I with an 11.2-kilobase (kb) fragment, type II with a 2.0-kb fragment, and type III with the 2.0-kb and 11.2-kb fragments. Usage of V-alpha-14-J-alpha-281, where J-alpha-281 is an alpha-chain joining segment, with a one-base N region dominates at the level of 0.02-1.5% of alpha-chains in all laboratory strains, Mus musculus castaneus, and Mus musculus domesticus but not in Mus musculus molossinus, Mus musculus musculus, and Mus spicilegus samples. The preferential V-alpha-14-J-alpha-281 expression seems to be due to positive selection because the V-J junctional region is always glycine, despite the ability of the V-alpha-14 gene to associate with J-alpha other than J-alpha-281. As V-alpha-14-J-alpha-281 expression is independent of known major histocompatibility complex antigens, including H-2, TLA, Qa, and HMT, the selecting ligand must be a monomorphic molecule of the mouse, expressed in a subspecies-specific manner. Additional observations, such as the expression of homogeneous V-alpha-14-J-alpha-281 in athymic mice, suggest that the positive selection of V-alpha-14+ T cells occurs extrathymically.