Tissue-remodelling M2 Macrophages Recruits Matrix Metallo-proteinase-9 for Cryotherapy-induced Fibrotic Resolution during Keloid Treatment

Cryotherapy is used to treat keloid scars; however, the molecular and pathological mechanisms are not clearly understood. This study retrospectively evaluated the efficacy of combined treatment with cryotherapy and intralesional triamcinolone injection (Cryo+TA) or intralesional TA monotherapy (TA) in 40 Asian patients with keloid scars. Scar improvement was assessed using the Vancouver Scar Scale and Global Improvement Scale. Clinical improvement in scars, especially reduced vascularity and redness, was significantly greater in the Cryo+TA group than in the TA group. Cryotherapy-treated and untreated keloid tissue was collected from six patients for analysis. Histologically, collagen bundles from cryotherapy-treated keloid tissue were more fibrillar and abnormal thickness was reduced. Immunohistochemical staining showed a reduced number of dermal vessels after cryotherapy. Moreover, CD163(+) M2 macrophages and matrix metalloproteinase-9 (MMP-9) were significantly increased in cryotherapy-treated tissue. Double immunofluorescence staining revealed co-expression of CD163 and MMP-9. These data indicate that cryotherapy recruits tissue-remodelling M2 macrophages with accompanying MMP-9, suggesting that cryotherapy-recruited M2 macrophages function in fibrotic resolution during keloid treatment.