HLA-DR-triggered inhibition of hemopoiesis involves Fas/Fas ligand interactions and is prevented by c-kit ligand.
The function of MHC class II (HLA-DR) Ags in hemopoiesis is not well defined. Here we investigated the effect of anti-HLA-DR mAb H81.9 on human marrow cells. mAb H81.9 inhibited colony formation from purified CD34+ marrow cells in long term culture-initiating cell assays. Inhibition was prevented, however, if c-kit ligand (stem cell factor (SCF)) was added to cultures concurrently with H81.9. DNA histograms from cultured untreated marrow mononuclear cells showed 2+/-1.2% apoptotic nuclei, whereas 14.1+/-5.4% were apoptotic after 12-h exposure to mAb H81.9. The apoptotic peak was reduced to 1.2+/-0.8% when SCF was added to cultures concurrently with mAb H81.9. The addition of Fas-Ig, a fusion protein that neutralizes Fas ligand (Fas-L), also prevented mAb H81.9-induced apoptosis. As determined by terminal deoxynucleotidyl transferase assays, agonistic anti-Fas mAb also induced apoptosis (in 13+/-4% of cells), and combined treatment with anti-Fas mAb and H81.9 was additive (27% apoptotic nuclei). The extent of apoptosis induced by anti-Fas mAb was significantly reduced by SCF. After H81.9 exposure, Fas was up-regulated on CD34+ cells, and Fas-L expression was 2.5-fold higher than in controls or CD34- cells, particularly within a small cell window with low orthogonal scatter (lymphocyte gate). These findings show that HLA-DR-mediated signals inhibit hemopoiesis in human marrow by a mechanism involving Fas/Fas-L-dependent signals that are blocked by c-kit ligand. These data suggest a possible role for MHC class II molecules in the regulation of hemopoiesis.
Lee
J W
JW
Transplantation Biology Program, Fred Hutchinson Cancer Research Center, Seattle, WA 98104, USA.
Gersuk
G M
GM
Kiener
P A
PA
Beckham
C
C
Ledbetter
J A
JA
Deeg
H J
HJ
D000911:Antibodies, Monoclonal / Q000494:pharmacology; D018952:Antigens, CD34 / Q000096:biosynthesis; D017209:Apoptosis / Q000187:drug effects / Q000276:immunology*; D001854:Bone Marrow Cells; D002478:Cells, Cultured; D053222:Fas Ligand Protein; D006131:Growth Inhibitors / Q000502:physiology; D006684:HLA-DR Antigens / Q000276:immunology / Q000502:physiology*; D006410:Hematopoiesis / Q000187:drug effects / Q000276:immunology*; D006801:Humans; D007141:Immunoglobulin Fc Fragments / Q000235:genetics / Q000502:physiology; D008024:Ligands; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000276:immunology* / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000502:physiology; D019089:Stem Cell Factor / Q000235:genetics / Q000502:physiology*; D013997:Time Factors; D019014:fas Receptor / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*
D000911:Antibodies, Monoclonal; D018952:Antigens, CD34; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D006131:Growth Inhibitors; D006684:HLA-DR Antigens; D007141:Immunoglobulin Fc Fragments; D008024:Ligands; D008562:Membrane Glycoproteins; D011993:Recombinant Fusion Proteins; D019089:Stem Cell Factor; D019014:fas Receptor