Pure interferon gamma enhances class II HLA antigens on human monocyte cell lines

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Abstract
Human recombinant interferon gamma (IFN‐γ) with a chemical purity of over 90% was shown to enhance membrane expression of HLA‐DR antigens on cells from 3 human myelomonocytic lines (HL‐60, U‐937 and THP‐1). Immunofluorescence techniques using a series of anti‐HLA‐DR monoclonal antibodies showed that the low, although variable, levels of DR‐positive cells were clearly enhanced as soon as 24 h after incubation with IFN‐γ. Only IFN‐γ was able to exert this effect, since incubation with high concentrations of IFN‐α or ‐β did not induce any significant modification of the percentage of HLA‐DR‐positive cells. In contrast, doses of IFN‐γ as low as 2 units were effective, indicating a highly preferential, apparently selective effect of IFN‐γ for enhancement of HLA‐DR expression. Private class II antigen expression was also enhanced by IFN‐γ on the U‐937 cell line. Through its enhancing effect on class II public and private HLA antigens on the membrane of human monocytes, the IFN‐γ lymphokine may have a critical role in the modulation of antigen presentation by monocytes and on the regulation of HLA‐DR‐restricted cell cooperation.