Description of a new Qa antigenic specificity, "Qa-m9," whose expression is under complex genetic control.

The "Qa-m9" specificity has been defined by a monoclonal antibody, and evidence for three-gene control of its expression has been demonstrated. The Qa allocation was made on the basis of H-2 linkage (H-2 congenic strains, Rl lines), differential reaction with B6.K1 and B6.K2, and biochemical analysis (two chains: 39,000 Mr and 12,000 Mr). "Qa-m9" is expressed on T and B cells in spleen and lymph node; it is present on a small population of bone marrow cells but is absent from thymocytes. The three genes involved in the expression of the antigen are: a) an H-2 linked Qa gene (possibly encoded by a gene different from Qa-2-6); b) an H-3 linked gene--probably beta 2m; and c) an H-2D linked gene that controls the amount of antigen present. It is likely that the determinant is of the "combinatorial" or conformational type, whereby the C57BL/6-type Qa heavy chain and the appropriate beta 2m light chain must both be in association. Thus, the study provides evidence for a multi-gene control of antigen expression and demonstrates the potential for generating new antigens with diversity at a post-translational level.