The Fibrosis and Immunological Features of Hypochlorous Acid Induced Mouse Model of Systemic Sclerosis.

Fibrotic animal models are critical for the pathogenesis investigations and drug explorations in systemic sclerosis (SSc). The bleomycin (BLM)-induced mouse model is the classical and most widely used fi brosis model. However, traditional subcutaneous injection of BLM rarely induced diffuse skin and lung lesions. Hypochlorous acid (HOCl)induced mice are a more representative model that have diffuse cutaneous lesions, lung fi brosis and renal involvement. However, the fi brotic and immunological features of this model are not fully elucidated. Here, we injected BALB/c mice subcutaneously with HOCl used at different concentrations of HOCl (1:55, 1:70, and 1:110 NaClO: KH2PO4, hereafter named HOCl55, HOCl70, and HOCl110, respectively) for 6 weeks to induce fi brosis, and also used HOCl110 at different time course (4, 5, and 6 weeks). Morphological changes were observed via HE and Masson ' s trichrome staining. Immunohistochemistry or real-time PCR was used to detect in fl ammatory in fi ltrates, important fi brosis pathways and pro-in fl ammatory mediator expression. Flow cytometry was used to detect the alteration of immune cells in mouse spleen. Skin and lung fi brosis were most obvious in the HOCl55 group compared to lower concentration groups. In the HOCl110 group, dominant in fl ammatory in fi ltrates were found after 5 weeks, and signi fi cant fi brosis was found after 6 weeks. Then we explored the fi brosis and immunological pro fi les in the HOCl110 (6 weeks) group. Important fi brosis pathway proteins such as TGF-beta, NF-kappa B, Smad3, p-Smad3, STAT3, and p-STAT3 were signi fi cantly elevated at week 6 in the HOCl110 group. Increased in fi ltration of CD4+T cells, CD8+T cells, CD20+B cells, and myo fi broblasts was found both in skin and lung tissues. However, decreased CD4+T cells, CD8+T cells, monocytes and macrophages and increased CD19+B cells were found in the spleen tissues. The mRNA expression of fi brosis mediators such as IL-1 beta, IL-6, IL-17, IL-33, TNF-alpha, and CTGF was also upregulated in skin and lung tissues. In conclusion, HOCl induced fi brosis mouse model displayed systemic immune cell in fi ltration, pro-in fl ammatory mediator release, vasculopathy and fi brosis, which better mimicked human SSc than BLM-induced mice.