To determine the expression of interleukin-6 (IL-6) in cystic lesions of patients with acne vulgaris, and to evaluate the in vitro effect of Propionibacterium acnes (P. acnes) on the production of IL-6 and activation of p38 mitogen-activated protein kinase (p38MAPK) in the human acute monocytic leukemia cell line THP-1.

Real-time fluorescence-based quantitative PCR was performed to determine the mRNA expression of IL-6 in cystic lesions of 6 patients with acne vulgaris, as well as in skin tissues of 6 healthy persons. Some cultured THP-1 cells were divided into 5 groups to betreated with 2 × 10⁶ CFU/ml, 2 × 10⁷ CFU/ml and 2 × 10⁸ CFU/ml heat-killed P. acnes suspensions (P. acnes groups) , 100 μg/L lipopolysaccharide (LPS group) and RPMI 1640 medium (control group) respectively. After 1-, 3- and 6-hour treatment, real-time fluorescence-based quantitative PCR was conducted to determine the mRNA expression of IL-6 in the above groups. Enzyme-linked immunosorbent assay (ELISA) was performed to detect the level of IL-6 in the culture supernatant of cells in the 2 × 10 ⁸-CFU/ml P. acnes group, LPS group and control group at 24 hours after the treatment. Western blot analysis was conducted to determine the protein expression of p38MAPK and phosphorylated p38MAPK in the 2 × 10⁸-CFU/ml P. acnes group after 15-, 30- and 60-minute treatment, as well as in the LPS group after 30-minute treatment and in the control group. Some other THP-1 cells were divided into 3 groups: 2 × 10⁸-CFU/ml P. acnes group treated with 2 × 10⁸ CFU/ml P. acnes suspensions, SB203580 (an inhibitor of p38MAPK) group treated with 20 μmol/L SB203580 for 30 minutes followed by the treatment with 2 × 10 ⁸ CFU/ml P. acnes suspensions, and control group treated with RPMI 1640 medium alone. After 6-hour treatment, the mRNA expression of IL-6 in the above 3 groups was measured by real-time fluorescence-based quantitative PCR.

The mRNA expression of IL-6 was significantly higher in the cystic lesions of acne vulgaris than in the normal skin tissues (3.680 ± 0.790 vs. 1.155 ± 0.250, t= 3.047, P < 0.05) . Two-way analysis of variance showed that there were significant difference in the mRNA expression of IL-6 among the 2 × 10 ⁶-CFU/ml, 2 × 10⁷-CFU/ml and 2 × 10⁸-CFU/ml P. acnes groups, LPS group and control group (F= 532.3, P < 0.001, v= 4) , and the mRNA expression of IL-6 significantly differed among different time points (F= 526.6, P < 0.001, v= 2) . There were also significant differences in the IL-6 level in the culture supernatant of cells among the 2 × 10⁸-CFU/ml P. acnes group ([1 618.22 ± 32.23]ng/L) , LPS group ([3 212.06 ± 353.00]ng/L) and control group ([147.10 ± 0.53]ng/L;v= 2, F= 102.35, P < 0.01) . After 15-, 30- and 60-minute treatment with 2 × 10 ⁸ CFU/ml P. acnes suspensions, the protein expression of phosphorylated p38MAPK obviously increased. The mRNA expression of IL-6 in THP-1 cells was significantly lower in the SB203580 group than in the 2 × 10⁸-CFU/ml P. acnes group (t= 15.91, P= 0.004) .

The mRNA expression of IL-6 evidently increases in the cystic lesions of patients with acne vulgaris. P. acnes can activate the signaling molecule p38MAPK in THP-1 cells, and promote the production of IL-6 by THP-1 cells.

Acne vulgaris; Propionibacterium acnes; Interleukin-6; Leukemia, monocytic, acute; p38 Mitogen-activated protein kinases