Journal of Immunogenetics zyxwvut (1987) zyxwv 14, 8 1-87 MOLECULAR COMPLEXITY OF Qa-2 ANTIGENS ELECTROPHORESIS DEMONSTRATED zyxw BY TWO-DIMENSIONAL GEL P. zyxwvut J. ROBINSON,*t I. LEFKOVITS? AND K. FISCHER LINDAHLtS *Department of Immunology, German Cancer Research Centre, zyxw 06900 Heidelberg, F.R.G., ?The Basel Institute for Immunology, Grenzacherstrasse 487, CH-400s Basel, Switzerland, $Howard Hughes Medical Institute and Departments of Microbiology and Biochemistry, University of Texas Health Science Center at Dallas, Dallas, Texas, 75235-9050, US. A. (Workshop: new MHC genetic markers and minor histocompatibility antigens: their roles in ihe immune response) SUMMARY Biosynthetically labelled Qa-2 antigens were isolated from mouse spleen cells by immunoprecipitation with anti-Qa-2 antisera. When newly synthesized Qa-2 molecules from several different inbred strains were analysed by two-dimensional (2D) gel electrophoresis; four different phenotypes were observed that differed in the number of polypeptides present. The ability to distinguish Qa-2+ phenotypes was used to map the recombination points in two congenic strains, B6.Tlaa and A.Tlab. No alternative Qa-2-like polypeptides were detected in B6.Kl (Qa-2-) cells using a polyspecific rabbit antiserum against mouse class I antigens, but a new molecule was detected in BALB/cBy (Qa-2-) cells. Pulse-chase and surface- labelling experiments showed that some, but not all, of the newly synthesized Qa-2 precursor forms are processed to mature cell surface molecules. INTRODUCTION The zyxwvut Qa region of the mouse major histocompatibility complex contains a group of structural genes homologous to those encoding the H-2K, D, and L transplantation antigens (Steinmetz et al., 1982; Weiss et al., 1984).This locus encodes the Qa-2 antigen (Flaherty, 1976) which, like H-2, is a cell surface glycoprotein associated with P,-microglobulin (Michaelson et af., 1981). Qa-2 differs from H-2 in several respects. It is clearly less polymorphic than H-2K, D, or L (Michaelson et al., 1982), and all inbred strains typed by conventional methods are either Qa-2+ or Qa-2-. In contrast to H-2, which is expressed in most tissues, Qa-2 has been found only on cells of the haematopoietic system (Harris et al., 1984). Although Qa-2 is a Abbreviations: &m, beta-2 microglobulin; IEF, isoelectric focusing; SDS-PAGE, polyacrylamide gel Correspondence: Dr P. J. Robinson, Dept. of Immunology, German Cancer Research Centre, D6900 electrophoresis in sodium dodecyl sulphate; 2D gels, two-dimensional gel electrophoresis. Heidelberg, F.R.C. zyxwvutsr 81