Variation in H-2 antigen expression in F1 hybrid mice: Analysis using monoclonal antibodies

Cells of (CBA/H X BALB/c)F1 hybrid mice express CBA/H-derived H-2k antigens more weakly than do CBA/H cells, but H-2d antigens are similarly expressed by F1 and BALB/c cells. This was evident when F1 hybrid macrophages were compared with CBA/H and BALB/c macrophages as targets for both alloreactive and H-2 restricted anti-viral TC cells. Quantitative absorption of anti-H-2Kk serum by spleen cells of F1 or CBA/H mice also suggested about 3-fold less H-2Kk antigen on F1 cells. With the use of two anti-H-2Kk monoclonal antibodies, 30R3 and 27R9, the reduced expression of H-2Kk in this F1 hybrid was further analysed in a two-stage radio-immunoassay employing the uptake of 125I-protein A to measure antibody binding. By a thermodynamic approach, estimates were made of the dissociation constant for antibody binding, and of the relative numbers of H-2 molecules expressed by both F1 hybrid and CBA/H spleen cells. The results indicate that there is a two-fold reduction in the number of H-2Kk molecules expressed on the surface of F1 cells. Similar dissociation constants for F1 and CBA/H cells indicated no detectable qualitative difference in their H-2Kk antigens with respect to sites recognized by 30R3 and 27R9.