Immunogenicity for T cell-independent B-cell response assessed by splenic plaque-forming cell (PFC) response and cell-surface expression measured by laser flow cytometry of various class I H-2 antigens on mouse red blood cells (RBC) were compared. It was found that the order of magnitude of both immunogenicity and cell-surface expression on RBC is H-2Dd>>H-2Db>H-2Ka, H-2K b. Furthermore, H-2 d public antigens and H-2L ~ antigens were neither immunogenic nor easily demonstrable on RBC. These findings contrasted with poor immunogenicity for PFC response (Nakashima et al. 1982(Nakashima et al. , 1983) and proportionally strong expression of H-2 antigens on lymphoid cells. Immunogenicity and cell-surface expression of H-2D d antigen on RBC were not shown to be controlled by the action of genes outside H-2D. It was therefore suggested that a number of H-2 antigens, including H-2K d private, H-2K b private, and H-2 d public specificities are at least functionally defective on RBC. This is possibly due to the structural characteristics of the antigens. Since immunogenicity and cell-surface expression were in parallel, the expression of H-2 antigens on RBC must be dictated by a subset of B cells whose activity was assessed by PFC response.
This finding supports the view that the H-2 molecules display a new category of activity which is different from their ability to activate T cells and depends on their expression on RBC.