EFFECTS OF ASPERGILLUS-FUMIGATUS CULTURE FILTRATE ON ANTIFUNGAL ACTIVITY OF HUMAN PHAGOCYTES IN-VITRO

Background-Aspergillus fumigatus can colonise the airways and the lung s with localised underlying conditions and occasionally invade the sur rounding lung tissues even in subjects without systemic predisposing f actors, presumably by escaping the local host defences. The aim of thi s study was to investigate the effects of A fumigatus culture filtrate (ACF) on the activities of human phagocytes-inhibition of germination of A fumigatus spores by alveolar macrophages (AMs) and hyphal damage by polymorphonuclear leucocytes (PMNs)-which are the critical host de fences against A fumigatus. Methods-Spores were incubated with AMs at a ratio of 1:1 in a medium containing different concentrations of ACF for 10 hours at 37 degrees C. Spore germination was visualised with li ght microscopy and the inhibition rate was calculated. The percentage of hyphal damage caused by PMNs pretreated with various concentrations of ACF was measured by a colorimetric tetrazolium metabolic assay. Re sults-The inhibition rate of spore germination by AMs cultured with me dium alone (control) was 90 (0.8)% whereas that by AMs cultured with t he medium containing 10% ACF; was significantly (p < 0.05) reduced to 41.7 (4.6)%. ACF suppressed the inhibition of spore germination in a d ose dependent manner without altering the phagocytosing activity again st the spores. The percentage of hyphal damage caused by PMNs pretreat ed with medium-199 (control) was 78.1 (2.3)% compared with 65.3 (2.8)% when PMNs were pretreated with 50% ACF (p < 0.05). Conclusions-A fumi gatus releases biologically active substance(s) which suppress the inh ibition of spore germination by AMs and also suppress PMN mediated hyp hal damage, and thus may contribute to the pathogenicity of this fungu s.