Roles of Dectin-1 in phagocytosis of Candida albicans by macrophage-like cells derived from a human acute monocytic leukemia cell line THP-1

Abstract

Objective To investigate the roles of Dectin-1 in phagocytosis of Candida albicans (C. albicans) by macrophage-like cells derived from a human acute monocytic leukemia cell line THP-1. Methods THP-1 macrophage-like cells served as the target cells, and were transfected with small interfering RNA (siRNA) targeting Dectin-1 to down-regulate the expression of Dectin-1 receptor (siRNA-Dectin-1 group) . THP-1 macrophage-like cells transfected with nonsense siRNA (siRNA-NC) served as a negative control group. After transfection, the THP-1 macrophage-like cells in the above 2 groups were co-cultured with heat-killed C. albicans separately. And then, fluorescence microscopy was performed to count THP-1 macrophage-like cells phagocytosing C. albicans, and flow cytometry was used to determine the mean fluorescence intensity (MFI) of dihydrorhodamine (DHR) -123 fluorescent cells. Statistical analysis was done by one-way analysis of variance (ANOVA) and t test with the SPSS19.0 software. Results After transfection with siRNA-Dectin-1, the mRNA and protein expression of Dectin-1 significantly decreased in THP-1 macrophage-like cells (t= 26.163, P < 0.001) . After 1-, 2-, 4-hour co-culture of THP-1 macrophage-like cells with C. albicans, fluorescence microscopy showed that the phagocytosis rates of C. albicans by THP-1 macrophage-like cells were significantly lower in the siRNA-Dectin-1 group than in the negative control group (17.5% vs. 22.1%, 18.6% vs. 24.3%, 39.2% vs. 59.1%, respectively, all P < 0.05) , so were the percentage of THP-1 macrophage-like cells phagocytosing more than 3 C. albicans cells (2.2% vs. 4.7%, 2.5% vs. 5.4%, 5.1% vs. 8.3%, respectively, all P < 0.05) . After 30-minute, 1-, 2- and 4-hour co-culture of THP-1 macrophage-like cells with DHR-123-labelled C. albicans, flow cytometry showed that the MFI of C. albicans-phagocytosing cells was significantly lower in the siRNA-Dectin-1 group than in the negative control group (36.8 vs. 45.7, 54.3 vs. 62.4, 72.1 vs. 84.9, 93.6 vs. 116.7, respectively, all P < 0.05) . Conclusion Dectin-1 receptor plays an important role in the phagocytosis of C. albicans by macrophages. Key words: Candida albicans; Macrophages; Phagocytosis; Leukemia, monocytic, acute; Dectin-1