EXPRESSION OF MHC CLASS-II ANTIGENS ON RAT BONE-MARROW CELLS AND MACROPHAGES, AND THEIR MODULATION DURING CULTURE WITH MURINE GM-CSF OR M-CSF

Flow cytometric analysis employing MRC OX 6 and MRC OX 17 monoclonal a ntibodies recognizing determinants on RT1.B or RT1.D molecules, equiva lent to murine I-A and I-E, respectively, was used to detect rat MHC c lass II antigen (Ag) expression. Approximately 5 % of freshly isolated rat bone marrow cells (BMC) expressed RT1.B and over 30 % displayed R T1.D molecules. The RT1.D+ cells were W3/13(+), OX 7(+), OX 19(-) and OX 22(-). After one week culture of BMC with murine recombinant granul ocyte/macrophage colony-stimulating factor (GM-CSF), regardless of con centrations, 90 to 95 % of the cells were scored as bone marrow-derive d macrophages (BMDM Phi), and over 30% expressed both RT1.B and RT1.D Ag. GM-CSF increases the percentage of BMDM Phi bearing MHC class II A g in a concentration-dependent manner. This effect seems to be specifi c because antibodies to interferon-gamma, tumor necrosis factor-alpha or interleukin-4 did not reduce the number of cells expressing RT1.B a nd RT1.D Ag. Furthermore, GM-CSF was able to trigger expression of cla ss II molecules on rat peritoneal macrophages (M Phi) and BMDM Phi res ulted from cultures of BMC with mouse M Phi-CSF (M-CSF), and the RT1.B and RT1.D inducing effect of GM-CSF was opposed by M-CSF, and by anti -GM-CSF antibodies. The induction of MHC class II Ag synthesis by GM-C SF on rat BMDM Phi was confirmed at the mRNA level by Northern blot an alysis employing cDNA probes encoding the RT1.B-alpha.