Mice peritoneal mast cells previously treated with alloantibodies directed against private and public major histocompatibility antigens became partially resistant to subsequent passive sensitization with homologous IgG1-rich serum. 2. Sensitization of the mast cells was evaluated in terms of the percentage of cells that degranulated upon challenge with the specific antigen. 3. The phenomenon was immunologically specific and the responsible alloantigens were shown to be coded by the H-2K or H-2D regions.
