Evaluation of the early neutrophil response to candida albicans bloodstream infection

Candida albicans is the most common isolated fungal agent from bloodstream infections caused by Candida spp. (candidemia) in human. C. albicans normally colonizes at the skin, urogenital or intestinal mucosa of 30-70% of healthy individuals. With the contribution of the risk factors C. albicans could derive from commensal form to opportunistic pathogen form in the infection course which is directly associated with the induction of key virulence factors of C. albicans such as ability to change morphotype. Neutrophils are the most effective and important defence elements in candidemia. The different responses of neutrophils to commensal, colonization, and infection phases of C. albicans at the stages of infection have not yet been fully elucidated. This study aims to investigate the early response of neutrophils against C. albicans different morphologies in molecular and cellular aspects. Neutrophils were collected from healthy volunteers and incubated with yeast and hyphae form of opsonized-C. albicans for 30 min, 1 h and 4 h at MOI:1 infectious dose. All experimental sets were included one Gram (+) (S. aureus) and one Gram (-) (E. coli) bacteria as controls. After stimulation, neutrophil activation was investigated with the expression analysis of myeloperoxidase (MPO) and neutrophil elastase (ELANE) by qRT-PCR, detection of surface receptors as CD66b and CD11b by flow cytometry, determining of different cytokines release by ELISA and the activation demonstrated by confocal microscopy also the candidacidal activity of human neutrophils assay conducted with colony counting. In all time intervals, the highest expression level of MPO (10.97 folds) and ELANE (7.49 folds) were detected to C. albicans hyphae form when compared to other microorganisms (p<0.05). From the surface activation marker side, in one hour of interaction, CD66b level of neutrophils encountering with live C. albicans (69%) was stimulated more than heat-killed form of C. albicans (39%) (p:0.007). IL-17A secretion results of C. albicans heat-killed stimulated neutrophils demonstrated that significant increases at 4 hours of interaction (p<0.05) while any significant IL-17A cytokine increase was not observed against C. albicans hyphae morphotype. Also, the effective and lethally phagocytic interest of human neutrophils against opsonized-Candida is also observed with the confocal images. Overall, the unique comparisons of the C. albicans morphotypes described in this study offer a new approach on neutrophil and C. albicans interactions in the context of different time-manner of the infection. All our experiments show us neutrophils trying to defeat principally the hyphae form of C. albicans by using their oxidative mechanism, granular enzymes, and phagocytic effects. The infection between C. albicans and neutrophils occurs with the perfect timing which is the neutrophil activation peaked at the first 1 hour of interaction.