Fungal beta-glucans modulate macrophage release of tumor necrosis factor-alpha in response to bacterial lipopolysaccharide.
Tumor necrosis factor-alpha (TNF alpha) is a potent cytokine believed to participate in the development of endotoxin-induced shock and the adult respiratory distress syndrome. Treatment of animals with beta-glucan prior to bacterial challenge reduces TNF alpha release and prevents death. We therefore hypothesized that beta-glucan might regulate TNF alpha secretion from macrophages in response to lipopolysaccharide (LPS). Rat alveolar macrophages were cultured in the presence of beta-glucan alone and the TNF alpha secretion quantified using an L929 cytotoxicity assay. Concentrations of beta-glucan less than 500 micrograms/ml were found to stimulate TNF alpha release from macrophages. However, concentrations of beta-glucan greater than 500 micrograms/ml resulted in suppression of the TNF alpha activity released. This reduction in TNF alpha release was not mediated by a toxic effect of beta-glucan, as large concentrations of beta-glucan had no effect on macrophage viability. We further observed that the incubation of macrophages with large concentrations of beta-glucan (500 micrograms/ml) also inhibited the secretion of TNF alpha induced by bacterial LPS. Furthermore, interferon-gamma (IFN gamma), a potent activator of TNF alpha expression, failed to overcome the inhibition of TNF alpha caused by beta-glucan. These data suggest an immunomodulatory role for beta-glucan which may explain both the TNF alpha-stimulating and -inhibiting effects of fungal beta-glucans during infection.
Hoffman
O A
OA
Thoracic Disease Research Unit, Mayo Clinic, Rochester, MN 55905.
Olson
E J
EJ
Limper
A H
AH
D000818:Animals; D002470:Cell Survival; D002478:Cells, Cultured; D003601:Cytotoxicity Tests, Immunologic; D005936:Glucans / Q000276:immunology*; D007371:Interferon-gamma / Q000276:immunology; D008070:Lipopolysaccharides; D008262:Macrophage Activation / Q000276:immunology; D008264:Macrophages / Q000276:immunology*; D016676:Macrophages, Alveolar / Q000276:immunology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins; D012441:Saccharomyces cerevisiae / Q000276:immunology*; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis*
D005936:Glucans; D008070:Lipopolysaccharides; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma