Inhibition of the Progression of Skin Inflammation, Fibrosis, and Vascular Injury by Blockade of the CX3CL1/CX3CR1 Pathway in Experimental Mouse Models of Systemic Sclerosis

Objective To assess the preclinical efficacy and mechanism of action of an anti‐ CX 3 CL 1 monoclonal antibody ( mA b) in systemic sclerosis ( SS c). Methods Cultured human dermal fibroblasts were used to evaluate the direct effect of anti‐ CX 3 CL 1 mA b on fibroblasts. In addition, bleomycin‐induced and growth factor–induced models of SS c were used to investigate the effect of anti‐ CX 3 CL 1 mA b on leukocyte infiltration, collagen deposition, and vascular damage in the skin. Results Anti‐ CX 3 CL 1 mA b treatment significantly inhibited Smad3 phosphorylation ( P < 0.05) and expression of type I collagen and fibronectin 1 ( P < 0.01) in dermal fibroblasts stimulated with transforming growth factor β1 ( TGF β1). In the bleomycin model, daily subcutaneous bleomycin injection increased serum CX 3 CL 1 levels ( P < 0.05) and augmented lesional CX 3 CL 1 expression. Simultaneous administration of anti‐ CX 3 CL 1 mA b or CX 3 CR 1 deficiency significantly suppressed the dermal thickness, collagen content, and capillary loss caused by bleomycin ( P < 0.05). Injection of bleomycin induced expression of pS mad3 and TGF β1 in the skin, which was inhibited by anti‐ CX 3 CL 1 mA b. Further, the dermal infiltration of CX 3 CR 1+ cells, macrophages (inflammatory and alternatively activated [M2‐like] subsets), and CD 3+ cells significantly decreased following anti‐ CX 3 CL 1 mA b therapy ( P < 0.05), as did the enhanced skin expression of fibrogenic molecules, such as thymic stromal lymphopoietin and secreted phosphoprotein 1 ( P < 0.05). However, the treatment did not significantly reduce established skin fibrosis. In the second model, simultaneous anti‐ mCX 3 CL 1 mA b therapy significantly diminished the skin fibrosis induced by serial subcutaneous injection of TGF β and connective tissue growth factor ( P < 0.01). Conclusion Anti‐ CX 3 CL 1 mA b therapy may be a novel approach for treating early skin fibrosis in inflammation‐driven fibrotic skin disorders such as SS c.