The rat T-cell differentiation marker RT6.1 is more polymorphic than its alloantigenic counterpart RT6.2.

Utilizing allotype-specific antibodies to immunoprecipitate RT6.2 from DA.6B rat lymphocyte lysates, we have shown this antigen recently to be composed of two related, non-glycosylated polypeptides with apparent molecular weights (MW) of 24,000 and 26,000 (reducing conditions), which evidently are anchored in the cell membrane by covalent linkage to phosphatidylinositol. The present report shows that RT6.1 allotype-specific antibodies precipitate a more complex pattern of bands from LEW.6A rat lymphocyte lysates. These consist of an endo-F-resistant RT6.2-like 25/27,000 MW doublet (reducing conditions) as well as at least five additional endo-F-sensitive, endo-H-resistant polypeptides of 30,000, 32,000, 33,000, 34,000, 35,000 MW. Endo-F treatment seems to convert the additional higher to the lower molecular weight forms. In contrast to the endo-F-resistant 25/27,000 MW doublet, the higher MW forms of RT6.1 partly bind to lentil lectin and concanavalin A (Con A). Two-dimensional electrophoretic analyses (NEPHGE/SDS-PAGE) reveal similar patterns of charge heterogeneity of the lower and higher MW forms of RT6.1. Neuraminidase treatment does not affect the pIs of the lower MW forms but shifts the pIs of the higher MW forms to those of the lower ones. All forms of RT6.1 evidently employ the covalent linkage to phosphatidylinositol for membrane anchorage. Identical patterns of molecular forms--the doublet for RT6.2, the polymorphic pattern for RT6.1--are observed upon immunoprecipitation of the alloantigens from the lysates of corresponding series of inbred strains of rats with both allotype-specific antibodies and a polyclonal rabbit serum recognizing a common determinant on both alloantigens.