AhR agonist Ficz modulates T follicular helper cells and ameliorates skin fibrosis in a bleomycin-induced SSc mouse model.

OBJECTIVES

T follicular helper (Tfh) cells are involved in the pathogenesis of systemic sclerosis (SSc). Recent investigations have revealed aryl hydrocarbon receptor (AhR) regulated skin fibrosis in SSc. This study aims to explore the effect of AhR agonist Ficz on Tfh in a bleomycin (BLM)-induced SSc mouse model.

METHODS

BALB/c mice were randomly assigned to the control group (Ctrl), BLM-induced SSc mouse group (BLM) and the Ficz treatment group (BLM+Ficz). BLM (1 mg/kg/day) and Ficz (1 µg/mouse/48 hours) were injected subcutaneously for 4 weeks. Skin lesions were harvested for HE staining, Masson's trichrome (Masson) staining, double immunofluorescence as well as real-time quantitative PCR. Flow cytometry analysis was carried out to determine the proportion of peripheral Tfh cells.

RESULTS

We found that Ficz treatment effectively attenuated dermal thickness, collagen content and the expression of fibrosis-related genes, including Col1a1, Col3a1, Fn1 and Tgfβ1 compared with the BLM-induced mice. Moreover, the percentage of peripheral Tfh cells (CD4+CXCR5+PD-1+) was significantly elevated in BLM-induced mice and Ficz appeared to reduce the percentage of peripheral Tfh cells. Double immunofluorescence staining verified the presence of Tfh-like cells (CXCR5+PD-1+) in skin lesions of BLM-induced mice. In addition, the messenger RNA level of a key Tfh cytokine, Il21 was decreased in skin of Ficz treated BLM-induced mice, with elevated expression of Cyp1a1, a marker of AhR signalling.

CONCLUSIONS

Ficz, an AhR agonist, can alleviate skin fibrosis in BLM-induced SSc mice, which may relate to the reduction of Tfh cells and its downstream cytokine interleukin-21 expression through the activation of AhR pathway.