HLA-DR inhibits granulocytic differentiation without inducing apoptosis ofCD34 cells

H0ematopoietic progenitors express HLA-DR molecules. However the significan ce of HLA-class II molecules on CD34+ cells remains unknown. The primary ro le of HLA-class-II molecules is antigen presentation although a second role , that of signal transduction, has been established in B cells. The role of HLA-DR in hemaropoiesis was examined by determining the ability of CD34+ p rogenitor cells to differentiate to "Colony Forming Unit Granulocyte-Macrop hage" (CFU-GM) and "Burst Forming Unit Erythrocyte" (BFU-E) in the presence of anti-HLA-DR monoclonal antibody. We observed a reduction in the number of CFU-GM which was due in parr to down regulation of granulocyte rather th an monocyte differentiation. These observations suggest that HLA-DR signals can regulate myelopoiesis. We point our: especially the role of the HLA-DR molecule in the switch of CFU-GM between granulocyte or monocyte lineages. Although HLA-DR mediated apoptosis has been described in mature B lymphocy tes apoptosis of CD34+ cells was excluded as a mechanism. (C) American Soci ety for Histocompatibility and Immunogenetics, 1999. Published by Elsevier Science Inc.