Increased mast cell density and protease content in actinic cheilitis

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Abstract
Actinic cheilitis (AC) is a pre-malignant lesion caused by ultraviolet (UV) radiation and characterized by epithelial and connective tissue alterations. Mast cells (MCs), key contributors to solar elastosis in murine UV-irradiated skin, were characterized in order to assess their potential contribution to connective tissue degeneration in AC. Actinic cheilitis (n = 15) and normal lip (n = 8) biopsies were stained immunohistochemically for tryptase and enzymehistochemically for chymase to determine MC density and protease content. MC subpopulations (i.e. MC(T) containing only tryptase, and MC(TC) containing chymase and tryptase) and their distribution were also determined. Mast cells and their proteases were increased in AC as compared with normal lip (P < 0.0001), and appeared degranulated especially around elastotic areas. MC(T) predominated over MC(TC) in AC and normal lip (P < 0.05). However, in AC MC(T) were increased in the epithelium/connective junction and connective area (P < 0.05), while in normal lip MC(T) predominated in connective and submucosal areas (P < 0.05). The results suggest that increased MC density and protease content may contribute to elastosis formation in AC. In addition, changes in MC(T) distribution may favor AC malignization.