The effect of tocilizumab treatment for skin fibrosis by inhibiting CD38⁺ macrophages in systemic sclerosis

Background: Dermal and pulmonary fibrosis are the main clinical symptoms of systemic scleroderma (SSc), for which there are no effective therapeutic agents. Tocilizumab is thought to improve the symptoms of fibrosis, but the effect of tocilizumab on dermal fibrosis has not been explored. This study aims to investigate the therapeutic effect of tocilizumab on skin fibrosis by inhibiting CD38⁺ macrophages in the bleomycin-induced SSc mice model.

Methods: The 8-week-old BALB/c mice were randomly divided into three groups: control group (PBS group), model group (BLM group), and tocilizumab group (TCZ group). The mRNA expression of VIMENTIN, TIMP1, and COL1A1 was measured by qPCR. Western blot was used to detect the protein expression of α-SMA, TGF-β, and COL1A1 in skin tissues. The expression of CD38⁺ macrophages in the BLM-induced fibrosis mouse model was verified by flow cytometry and immunofluorescence.

Results: In comparison to the PBS control group, mice in the BLM group showed skin fibrosis, edema, thickness, and collagen deposition. The percentage of macrophages in the skin, peripheral blood, and spleen was significantly increased in the BLM group, and the percentage of CD38⁺ macrophages increased in the skin and peripheral blood but decreased in the spleen. After co-cultured with macrophages, L929 fibroblasts differentiated into myofibroblasts, with increased mRNA expression of COL1A1, COL3A, TGF-β, and Fibronectin. Furthermore, after being stimulated by LPS, RAW264.7 cells showed increased expression of IL-6 and CD38. The mRNA levels of COL1A1, COL1A2, COL3A, TGF-β, and Fibronectin in L929 fibroblasts were markedly increased when co-cultured with LPS-stimulated RAW264.7 cells. Tocilizumab treatment reduced dermal thickness and collagen deposition induced by BLM. Furthermore, the percentage of total macrophages and CD38⁺ macrophages in the skin and peripheral blood significantly decreased after tocilizumab treatment.

Conclusion: This study revealed that tocilizumab improved skin fibrosis in the SSc mice model, which was mediated by inhibiting skin and peripheral CD38⁺ macrophages.