Expression of HLA‐A and ‐B antigens on differentiating U‐937 cells

Cells from the human immature monocytoid cell line U‐937 were induced with 12‐0‐Tetradecanoyl‐phorbol‐13‐acetate (TPA) to differentiate towards macrophage‐like cells. The expression of HLA‐antigens during differentiation was examined with a panel of monoclonal antibodies directed against monomorphic and polymorphic determinants. Class II antigens could be detected neither on uninduced nor on TPA‐induced U‐937 cells. While the expression of HLA‐A3 did not change significantly during differentiation, the “supertypic” specificities HLA‐Bw4 and Bw6 as well as the “private” specificity HLA‐B18 could be detected only on a drastically decreased number of cells after 4 days of exposure to TPA. This may imply a selective loss of HLA‐B molecules from the cell membrane and therefore a separate regulatory control of HLA‐A and ‐B antigens.