IFN-γ primes macrophages for enhanced TNF-α expression in response to stimulatory and non-stimulatory amounts of microparticulate β-glucan

beta-(1 -> 3)-D-Glucan is an integral cell wall component of a variety of fungi, plants, and bacteria. Like the prototypic inflammatory mediator lipopolysaccharide (LPS), some beta-(1 -> 3)-D-glucan-containing preparations have been shown to induce the production of proinflammatory cytokines by macrophages. In the present study, we have tested a new microparticulate form of beta-(1 -> 3)-D-glucan (MG) from Saccharomyces cerevisiae for its ability to induce proinflammatory cytokine secretion in mouse peritoneal macrophages in vitro, and we have examined the effect of IFN-gamma. MG was rapidly phagocytized by peritoneal macrophages, and these MG-treated macrophages upregulated TNF-alpha, IL-6, and IL-1 beta mRNAs and secreted these proinflammatory cytokines. IFN-gamma treatment alone did not induce unstimulated macrophages to produce TNF-alpha. However a 4 h IFN-gamma pretreatment augmented TNF-alpha secretion by peritoneal macrophages Subsequently treated with an optimally stimulatory dose of MG. IFN-gamma pretreatment for 2 h followed by thorough washing and a further 2 h incubation without IFN-gamma still resulted in enhanced TNF-alpha production in response to MG, suggesting that IFN-gamma can prime macrophages for a subsequent proinflammatory response. Most interestingly. we found that IFN-gamma pretreatment of peritoneal macrophages enhanced the TNF-alpha response to amounts of MG that were poorly stimulatory or non-stimulatory in the absence of IFN-gamma printing. These data suggest that a synergy between IFN-gamma and beta-glucan may have evolved to lower the threshold of sensitivity of the innate immune response to fungal pathogens. (c) 2004 Elsevier B.V. All rights reserved.