The pattern of HLA-DR and HLA-DQ antigen expression on clonable subpopulations of human myeloid progenitor cells

Three subpopulations of human myeloid progenitor cells (CFU-GM) can be distinguished by differences in their kinetics of development; the liquid phase pre-CFU-GM, the day 14 CFU-GM, and the day 7 CFU-GM. The relative cell membrane densities of the HLA-DR and HLA-DQ antigens expressed by the three subpopulations was investigated by comparing the amount of antibody required to deplete bone marrow cell preparations of each cell type. Three separate approaches were used--complement (C') cytotoxicity, antiglobulin/C'-cytotoxicity and immune rosette depletion. Similar results were obtained for all three procedures, although the latter two gave a tenfold greater sensitivity over the standard C'-cytotoxicity method. At saturating anti-HLA-DR antibody concentrations, 85% to 95% of cells within the three myeloid subpopulations were found to express HLA-DR antigens. However, the relative amount of HLA-DR expressed by these subpopulations increased from the pre-CFU-GM to the day 7 CFU-GM. The expression of HLA-DQ antigens was considerably lower and could only be detected by using the more sensitive procedures. Only 50% of day 7 and 14 CFU-GM progenitor cells expressed detectable HLA-DQ antigens, whereas a greater proportion (80%) of the pre-CFU-GM were HLA-DQ positive. The pattern of HLA-DQ expression on these clonable precursors was quite distinct and opposite to the cell membrane density of the HLA-DR antigens. Because these three progenitor cell populations are thought to be linked in differentiation sequence, these results provide indirect support for the hypothesis that HLA class II antigens are implicated in regulatory mechanisms during normal myeloid cell differentiation.