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Compound IX 207-887 is a novel antiarthritic agent which inhibits the release of interleukin-1 (IL-1) from human monocytes and mouse peritoneal macrophages in vitro at concentrations which are achieved therapeutically in human rheumatoid arthritis and in animal models of arthritis. In the present studies IL-1 activity in conditioned media, homogenates or lysates was monitored using four independent assay systems. Biologically active IL-1 was determined by, a) the induction of latent metalloproteinase-release from rabbit articular chondrocytes, which is relatively specific for IL-1 and b) by a sensitive thymocyte proliferation assay. Immunoreactive IL-1-beta was assayed by RIA and ELISA. In all test systems IX 207-887 significantly reduced both biologically active and immunoreactive IL-1 in culture media, whereas the levels of IL-1 in homogenates or lysates were either unaffected or only marginally reduced. The release of other monokines tested, such as interleukin-6 and tumour necrosis factor-alpha, and the secretion of lysozyme were only marginally influenced. IX 207-887 neither affected the adherence of human monocytes nor markedly inhibited IL-1 or IL-2-induced thymocyte proliferation. In the chondrocyte test no IL-1 antagonistic activity of IX 207-887 could be observed. All of these data indicate that IX 207-887 has the novel property of being an inhibitor of IL-1 release.

Stimulation of macrophages by zymosan phagocytosis triggers the respiratory burst and induces an early release of lysosomal hydrolases and E-type prostaglandins (PGE). We have studied whether antigen presentation by macrophages to helper T-cells elicits a comparable sequence of events. Cloned T-helper cells specific for hen egg albumin (EA) were added to histocompatible or histoincompatible resident mouse peritoneal macrophages in the presence of EA or an unrelated antigen, and the changes in biochemical parameters were monitored. The interaction between macrophages. T-helper cells and EA induced the production of PGE, but no release of lysosomal hydrolases or activation of the respiratory burst. In addition T-cell proliferation was observed. By contrast, no proliferation and no biochemical changes were observed when histoincompatible macrophages or unrelated antigen were used. When the experiments were done in the presence of indomethacin to inhibit PGE release, T-cell proliferation was enhanced. These results suggest that the PGE released may exert a feed-back control of the T-cell response.