Mechanism of human airway epithelial cell injury induced by Candida albicans infection

Abstract

Objective: To investigate the immune mechanism of human airway epithelial cell injury induced by invasion of Candida albicans with different biofilm formation abilities. Methods: Twenty-five strains of Candida albicans isolated and cultured in General Hospital of Ningxia Medical University from June to December 2019 were selected, and quality control strain SC5314 was used as the standard strain. An in vitro model of Candida albicans biofilm was established, and the biofilm formation ability of different Candida albicans was detected by crystal violet staining and enzyme plate method. The absorbance value at 570 nm (A570) was determined by enzyme plate method. A570≥0.5, 0.25<A570<0.5 and A570≤0.25 indicated strong biofilm Candida albicans form (SBF), moderate biofilm Candida albicans form (DRF) and weak biofilm Candida albicans form (WBF), respectively. The gas-liquid phase culture model of human airway epithelial cells was isolated and established in vitro and divided into five groups, including blank control group (n=20), standard strain group (n=20), strong biofilm group (n=19), weak biofilm group (n=17) and fluconazole-resistant group (n=18).The morphology of the epithelial cells was observed by scanning electron microscope (SEM), and the expression of marker protein in the model was detected by immunofluorescence in vitro. The level of lactate dehydrogenase (LDH) in cells was detected by microplate method, and the secretion of β-defensin (hBD2), granulocyte macrophage colony stimulating factor(GM-CSF) and granulocyte colony-stimulating factor (G-CSF) was detected by enzyme-linked immunosorbent assay (ELISA). Results: The strong biofilm strains grew with interlacing mycelia, and very few yeast cells could be seen wrapped in them.SEM observed that the mycelia of epithelial cells in gas-liquid phase culture could actively invade epithelial cells, and the expression of acetylated tubulin and keratin in cilia were significantly reduced, while the expression of Ki67 was down-regulated.The LDH levels in the blank control group, standard strain group, strong biofilm group, weak biofilm group, and fluconazole-resistant group were (12.21±5.68), (46.35±6.35), (18.69±4.38), (12.56±3.69), and (13.48±4.28) U/L, respectively, with statistically significant differences (P<0.001). Compared with standard strain group, LDH level in strong biofilm group, weak biofilm group and fluconazole resistant group were significantly decreased (all P<0.01). The hBD2 levels of the five groups were (26.14±0.77), (56.18±0.83), (30.66±2.59), (29.22±0.48), (28.28±1.56) ng/L, respectively, with statistically significant differences(P<0.001). Compared with the blank control group, SC5314-treated epithelial cells induced an increase of intracellular hBD2 expression (P<0.001). The differences in the expression of GM-CSF and G-CSF between different groups were not statistically significant(all P>0.05). Conclusion: Strong biofilm Candida albican can inhibit cell proliferation, disrupt the integrity of epithelial cells and induce cell damage by down-regulating the expression of cell proliferation-related protein.