ABSTRACT
The interferons (IFN) are naturally occurring cytokines with various biological functions; were originally identified by their ability to protect cells and the host from the cytopathic effect of viruses. These molecules possess also a variety of immunoregulatory and antiproliferative effects. It became clear that several polypeptides had IFN activity. IFN-a., previously called leukocyte IFN, and IFN-~, previously called fibroblast IFN, had primarily antiviral and antiproliferative activity (l). IFN-y, previously called immune IFN, is produced by activated T cells and has immunomodulatory as well as antiviral and antiproliferative properties (2). As a macrophage-activating factor (3), it increases the biosynthesis rate and the membrane density of class II histocompatibility molecules in cells presenting a basal expression of class II molecules such as 1a+ monocytes and thymic epithelium (4,5). Human recombinant CFN-y (hrCFN-y) may also induce de novo expression of class II antigens on cells that in normal conditions do not express these antigens on their surface, such as vascular endothelium and fibroblasts (6) and also articular chondrocytes (7). By increasing the density of the class II expression on the membranes of the antigen-presenting cells, IFN-y enhances the activation of specific T-helper lymphocytes and consequently also T-helper-cell-dependent immunity (8). The enhancement of antibody-dependent cellular cytotoxicity and of natural killer-cell activity is also documented. There
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