The influence of interferon-gamma and various phagocytic stimuli on the expression of MHC-class II antigens on human monocytes--relation to the generation of reactive oxygen intermediates.

Human monocytes show a dose-dependent decrease of the MHC-class II antigen expression (HLA-DR and HLA-DQ) after addition of zymosan or Staphylococcus aureus Cowan I particles. Interferon-gamma did not prevent this process. The expression of MHC-class I antigens was not affected. The dose-response and kinetic curves showed individual differences. An association between the capacity to form reactive oxygen intermediates and the downregulation of MHC-class II antigen expression was observed. In addition, after digestion of the phagocytosed particles interferon-gamma could restore the MHC-class II antigen expression on the cultured monocytes. The possible biological significance of these interactions between interferon-gamma and phagocytosis for the function of monocytes/macrophages in the local inflammatory process is discussed.