Serum-mediated inhibition of the interferon-gamma-induced HLA-DR expression on monocytes in patients with psoriasis

Psoriatic patients have a decreased proportion of monocytes expressing class II major histocompatibility complex antigens (DR+ monocytes) in their peripheral blood. The expression of the DR antigen on monocytes after culture in the presence of either autologous lymphocytes (endogenous interferon-gamma, IFN-gamma) or exogenous IFN-gamma was investigated. In normal AB serum the lymphocytes of the majority of the patients showed a spontaneous IFN-gamma production which was sufficient for DR antigen induction, while the monocytes displayed approximate normal susceptibility to exogenous IFN-gamma as judged by DR antigen expression. However, the sera of psoriatic patients contained one or more factors that interfered with the IFN-gamma-mediated DR antigen expression on cultured monocytes of the same patients. Restoration of IFN-gamma-induced DR antigen expression on monocytes in the presence of the patient's sera was achieved by the addition of superoxide dismutase, 2-mercaptoethanol, or indomethacin. The clinical significance of these observations is discussed.