[50] Immunochemical Purification and Analysis of Qa and TL Antigens

This chapter describes the methodology used to isolate and characterize murine Qa and TL antigens. These isolations rely heavily on radiolabeling and immunoprecipitation techniques reported previously, but have been modified to permit the isolation and characterization of cell surface molecules present in minute quantities. These techniques have allowed isolating and obtaining NH2-terminal sequence information of the Qa-2 antigen. The chapter reviews that Qa and TL antigens are encoded in the Tla region by genes located telomeric to the H-2 complex. Immunochemical studies have demonstrated that at least three of these loci (Qa-l, Qa-2, and TL) encode molecules consisting of a 40,000–44,000 MW heavy chain noncovalently associated with β2-microglobulin. Thus, these cell surface structures bear a striking resemblance to the major self-recognition antigens H-2K, -D, and -L. Unlike H-2 antigens, however, Tla region antigens have a restricted tissue distribution and are expressed at levels several folds below those of H-2 antigens.