Differential expression of reactive oxygen species in human neutrophils stimulated by the yeast phase of Sporothrix Schenckii and Candida albicans

Abstract

Objective To compare the reactive oxygen species (ROS) expression in human neutrophils phagocytizing Sporothrix Schenckii and Candida albicans yeast cells,and to compare the fungicidal activity of human neutrophils against Sporothrix Schenckii and Candida albicans.Methods Human neutrophils were isolated from peripheral blood by using density gradient centrifugation method,and cultured with the presence of the yeast phase of a Sporothrix Schenckii clinical isolate and a standard strain of Candida albicans (ATCC 90028)at a multiplicity of infection of 10 or 1 for 60-210 minutes.Subsequently,flow cytometry with ROS probe (2',7'-dichlorofluorescein diacetate,DCFH-DA) was carried out to for the real time detection of intracellular ROS level,confocal laser scanning microscopy (CLSM) for the observation of ROS distribution.In addition,the fungicidal efficiency of neutrophils against Sporothrix Schenckii and Candida albicans was estimated by the number of colonies after additional culture of neutrophil lysates on brain-heart infusion agar (BHIA) medium.Statistical analysis was done by using univariate analysis of variance and LSD-t test.Results The intracellular ROS level peaked at 60 minutes in neutrophils incubated with Sporothrix Schenckii yeast cells,then decreased rapidly from 60 minutes to 210 minutes.Compared with the neutrophils incubated with Candida albicans yeast cells,those with Sporothrix Schenckii yeast cells showed a higher ROS level (expressed as mean fluorescence intensity) at 60minutes (159.67 ± 11.34 vs.112.22 ± 9.66,P＜ 0.01),but a lower ROS level at 120 minutes (89.01 ± 9.81 vs.110.25 ± 7.28,P＜ 0.05) and 180 minutes (57.63 ± 8.46 vs.109.98 ± 9.00,P＜ 0.01).CLSM revealed that ROS was mainly distributed in neutrophils with phagocytized fungal spores,and especially on the surface of phagocytized spores.Furthermore,the percentage of yeast cells killed by neutrophils was significantly lower for Sporothrix Schenckii than for Candida albicans at 180 minutes (19.21％ ± 3.68％ vs.26.63％ ± 4.97％,P ＜ 0.01).Conclusions Differential expression of intracellular ROS was observed in neutrophils after phagocytosis of Candida albicans and Sporothrix schenckii.Neutrophils exert a stronger fungicidal activity against Sporothrix Schenckii in comparison with Candida albicans,which may be associated with the rapid decrease of ROS level in neutrophils after phagocytosis. Key words: Sporothrix; Candida albicans; Neutrophils; Reactive oxygen species