Modulation of granuloma formation in vitro by endogenous mediators

We have reported previously that in vitro granulomas are inducible by culturing murine spleen cells in the presence of artificial microparticles, dextran beads, and that macrophages and macrophage-derived cytokines (monokines) including interleukin 1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) play a critical role in the initiation of bead-induced granulomas in vitro. To investigate regulatory mechanisms of granuloma formation, we examined the modulatory effects of various mediators such as IL-1, TNF-alpha, interferon-gamma (IFN-gamma), IL-4, IL-6, transforming growth factor-beta (TGF-beta), dexamethasone and prostaglandin E2 (PGE2) on the development of lesions, because these mediators are known to play a pivotal role in inflammatory responses. The lesions were suppressed by the addition of dexamethasone, PGE2 or certain T cell-derived lymphokines such as IL-4 and IFN-gamma. These results suggest that suppressive signals are different from granulomatogenic cytokines including IL-1 and TNF-alpha and that granulomas are regulated by multi-factor dependent mechanisms.