Effects of Candida albicans on the expression of tumor necrosis factor-α and activation of the intracellular signaling molecule p38MAPK in a human acute monocytic leukemia cell line THP-1

Objective To investigate the effects of Candida albicans on the expression of tumor necrosis factor-α (TNF-α) and activation of the intracellular signaling molecule p38 mitogen-activated protein kinase (p38MAPK) in a human acute monocytic leukemia cell line THP-1. Methods Some THP-1 cells were divided into several groups in vitro: two C. albicans groups treated with 105 CFU/ml and 106 CFU/ml heat-killed C. albicans respectively, a lipopolysaccharide (LPS) group treated with 100 μg/L LPS, a blank control group treated with RPMI 1640 medium, two dexamethasone-inhibited groups pretreated with 40 μg/L dexamethasone for 30 minutes followed by treatment with 106 CFU/ml heat-killed C. albicans and LPS respectively. After treatment for 1, 3 and 6 hours, real-time fluorescence-based quantitative PCR was performed to measure TNF-α mRNA expression in THP-1 cells in the above groups. Enzyme-linked immunosorbent assay (ELISA) was conducted to determine the level of TNF-α protein in the supernatant of THP-1 cells treated with 106 CFU/ml heat-killed C. albicans, 100 μg/L LPS or RPMI 1640 medium (blank control group) for 24 hours. Western blot was performed to measure the protein expression of p38MAPK and phosphorylated p38MAPK in THP-1 cells after treatment with 106 CFU/ml heat-killed C. albicans or RPMI 1640 medium (blank control group) for 30 and 60 minutes. Statistical analysis was carried out by using two-way analysis of variance, one-way analysis of variance and the least significant difference (LSD)-t test. Results Significant differences were observed in the mRNA expression level of TNF-α among the C. albicans groups, LPS group and blank control group (F=110.98, P< 0.001). The mRNA expression level of TNF-α in THP-1 cells increased over time in a time-dependent manner after C. albicans treatment, with significant differences among different time points (F=701.680, P< 0.001). Compared with the blank control group, both 106-CFU/ml C. albicans group and LPS group showed a significant increase in TNF-α protein expression (6385.70±533.99 ng/L and 3212.06±353.00 ng/L vs. 147.10±0.53 ng/L, P< 0.001 and 0.005, respectively). An obvious increase was observed in the expression level of phosphorylated p38MAPK protein, but no significant changes were noted in that of p38MAPK protein, in THP-1 cells treated with 106 CFU/ml C. albicans for 30 and 60 minutes compared with the blank control group. The mRNA expression level of TNF-α significantly decreased in dexamethasone-pretreated 106-CFU/ml C. albicans group and LPS group compared with those without dexamethasone pretreatment (3.77±0.62 vs. 208.50±10.50, 6.20±1.93 vs. 161.35±1.65, both P< 0.001). Conclusions Heat-killed C. albicans can induce the activation of p38MAPK in and secretion of TNF-α by human THP-1 cells, which then participate in the innate immune response against C. albicans. Key words: Candida albicans; Leukemia, monocytic, acute; Tumor necrosis factor-alpha; p38 Mitogen-activated protein kinases; Cell line, tumor