Effect of Aspergillus fumigatus on the expression of tumor necrosis factor-α and activation of intracellular signaling molecule p38 mitogen-activated protein kinase by a human acute monocytic leukemia cell line THP-1

Objective To evaluate the effect of Aspergillus fumigatus on the expression of tumor necrosis factor-α (TNF-α) and activation of intracellular signaling molecule p38 mitogen-activated protein kinase (p38MAPK) in a human acute monocytic leukemia cell line THP-1. Methods Cultured THP-l cells (2 × 105/ml) were divided into 4 groups to be treated with Aspergillus fumigatus suspensions at concentrations of 106 and 107 colony-forming units (CFU) /ml (106-and 107-CFU/ml Aspergillus fumigatus groups) , 100 mg/L β-glucan (a positive stimulus, β-glucan group) , culture medium (blank control group) respectively for 1, 3 and 6 hours. Real-time fluorescence-based quantitative PCR (qPCR) was conducted to determine the mRNA expression of TNF-α in the THP-1 cells in the above groups. Some other THP-l cells were treated with 107 CFU/ml Aspergillus fumigatus suspensions (107-CFU/ml Aspergillus fumigatus group) , β-glucan (β-glucan group) and culture medium (blank control group) separately for 24 hours, and enzyme-linked immunosorbent assay (ELISA) was performed to detect the level of TNF-α in the culture supernatant of THP-1 cells. Western blot analysis was conducted to detect the levels of p38MAPK and phosphorylated p38MAPK in THP-1 cells after 15-, 30- and 60-minute treatment with 107 CFU/ml Aspergillus fumigatus suspensions. After 2-hour incubation with the p38MAPK inhibitor SB203580 (20 μmol/L) , some THP-1 cells were additionally treated with 107 CFU/ml Aspergillus fumigatus suspensions, β-glucan and culture medium separately for 6 hours, and those without SB203580 treatment served as the control group. Then, qPCR was performed to measure the mRNA expression of TNF-α in the THP-1 cells in the above groups. Results The mRNA expression of TNF-α significantly differed among the 106- and 107-CFU/ml Aspergillus fumigatus groups, β-glucan group and blank control group (F=110.983, P < 0.001) , and significantly increased over time (F=701.680, P < 0.001) . After 24-hour treatment with 107 CFU/ml Aspergillus fumigatus suspensions, the TNF-α level (6 236.30 ± 437.12 ng/L) significantly increased compared with the blank control group (132.10 ± 0.61 ng/L, P < 0.01) . Thirty minutes after the treatment with 107 CFU/ml Aspergillus fumigatus suspensions, the phosphorylated p38MAPK level significantly increased, but started to decrease at 60 minutes. The mRNA expression of TNF-α was significantly lower in the SB203580-treated Aspergillus fumigatus groups (3.83 ± 0.62) than in the SB203580-untreated Aspergillus fumigatus groups (187.23 ± 21.62) . Conclusion After the treatment with Aspergillus fumigatus, human THP-1 cells can activate the signal molecule p38MAPK and secrete TNF-α, suggesting that monocytes may participate in the innate immune response to Aspergillus fumigatus infection. Key words: Aspergillus fumigatus; Tumor necrosis factor-alpha; p38 Mitogen-activated protein kinases; THP-1 cells