GM-CSF-modulated phagocytosis of Trichosporon beigelii by human neutrophils

Trichosporon beigelii has emerged as a lethal opportunist pathogen in granulocytopenic and corticosteroid-treated patients. Little is known of the host defence mechanisms against this yeast. The interaction between human neutrophils and serum-opsonised T. beigelii and the effect of GM-CSF on binding and ingestion of the yeast by neutrophils were investigated by a microscopic analysis of neutrophil monolayers stained with FITC-Concanavalin A. Positive staining with FITC-Concanavalin A distinguished between intracellular and extracellular yeast cells. Binding of T. beigelii to neutrophils was an energy- and complement-dependent process involving movement of actin in the neutrophil cytoskeleton. The mean percentage binding of T. beigelii was 37.5% and the mean binding index (BI) was 1.30 whereas the mean percentage ingestion was 3.5% and the mean phagocytic index (PI) was 1.34. GM-CSF increased percentage ingestion of T. beigelli from 2.8% to 30.5% and the PI was increased from 1.3 to 1.86. The percentage binding was 36.8% and the mean BI was 1.3 in control experiments compared with 49.3% and 1.6, respectively, in the presence of GM-CSF. In conclusion, GM-CSF significantly increased percentage ingestion of opsonised T. beigelii by neutrophils, but its effect on percentage binding of the yeast was not statistically significant.