REACTION OF HUMAN ALVEOLAR MACROPHAGES TO EXPOSURE TO ASPERGILLUS-FUMIGATUS AND INERT PARTICLES

In vitro interaction of human alveolar macrophages (AM) with heat-kill ed conidia from Aspergillus fumigatus and inert silica particles of si milar size, about 3 mu m, was studied. The conidia were phagocytized s ignificantly faster by AM than were the control particles partly due t o the faster rate of attachment but especially due to the faster rate of ingestion. Quantitative nitroblue tetrazolium (NET) reduction by AM , reflecting their release of oxygen radicals, was increased by a fact or of 2 to 3 in response to the conidia during phagocytosis. The silic a particles induced a moderate but significant increase in NET reducti on. Conidia, but not silica particles, showed a considerable percentag e (around 8%) of phagolysosomes with neutral pH after 3 h and a smalle r percentage (around 1%) after 24 h of incubation. The pH of phagolyso somes with conidia tended to be higher after 3 h, but was significantl y lower after 24 h than the pH of phagolysosomes with silica particles . Despite the markedly increased oxidative metabolism there was no inc rease in cytokine production [interleukins (IL) 6 and 8 and tumor necr osis factor alpha (TNF-alpha)] after exposure to conidia. The silica p articles induced a significant decrease in IL-6 and IL-8 production an d a tendency toward decreased production of TNF-alpha. The occurrence of phagolysosomes with neutral pH suggests unsealed phagolysosomes fro m which not only oxygen metabolites but also enzymes might escape from the cell. Lung damage may thus be the result of repeated or long-term exposure to Aspergillus conidia. (C) 1997 Academic Press.