POSSIBLE INVOLVEMENT OF PROTEIN-KINASE-C ACTIVATION IN DOWN-REGULATION OF CD3 ANTIGEN ON ADULT T-CELL LEUKEMIA-CELLS

The role of protein kinase C (PKC) system on CD3 expression on adult T -cell leukaemia (ATL) was examined. The down-regulation of CD3 on ATL cells is reportedly induced by CD3 down-regulating factor (CD3DF) cont ained in serum and culture supernatants of leukaemia cells from acute type ATL patients. After we cultured normal PBMC with a PKC inhibitor, H-7, CD3DF activity for PBMC was reduced significantly. Culture with H-7 of HTLV-1 transformed T cells, ATL-2 cells whose CD3 expression ha d been decreased, led to enhancement of CD3 expression in a time-depen dent manner. These findings suggest that CD3DF may play an important r ole as a PKC system activator, resulting in CD3 down-regulation.