Modulation of HLA-G antigens expression in myelomonocytic cells

As trophoblast cells and macrophages share cellular characteristics, we inv estigated the expression of HLA-G antigens during the myelomonocytic differ entiation. Analyses with the 87G and 16G1 monoclonal antibodies demonstrate d that HLA-G was not expressed in peripheral blood monocytes, in in vitro d ifferentiated dendritic cells and macrophages, and in resident mononuclear phagocytes infiltrating healthy tissues. Conversely, activated macrophages and dendritic cells localized in tumoral biopsies of some lung carcinomas e xpressed HLA-G antigens. Induction of HLA-G expression at the cell surface of the monohistiocytic cell line U 937 with different cytokines strongly su ggests that cytokines secreted during inflammation may be involved in this specific upregulation. Bronchoalveolar macrophages collected from patients suffering from acute HCMV pneumonitis also expressed HLA-G molecules. In vi tro, we thus demonstrated that HLA-G antigens are produced during viral rea ctivation in the macrophages generated after allogeneic stimulation of HCMV latently infected monocytes. Our data suggest that inflammatory processes in lung tissues, like tumoral transformation and HCMV acute infection, are likely to induce HLA-G molecules in infiltrating macrophages and dendritic cells. The expression of molecules capable of downregulating both the innat e and adoptive immunity could be a mechanism that helps tumoral and HCMV in fected cells to escape immune response. (C) American Society for Histocompa tibility and Immunogenetics, 2000. Published by Elsevier Science Inc.