Increased mast cell density and protease content in actinic cheilitis

Background:  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. Methods:  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. MCT containing only tryptase, and MCTC containing chymase and tryptase) and their distribution were also determined. Results:  Mast cells and their proteases were increased in AC as compared with normal lip (P < 0.0001), and appeared degranulated especially around elastotic areas. MCT predominated over MCTC in AC and normal lip (P < 0.05). However, in AC MCT were increased in the epithelium/connective junction and connective area (P < 0.05), while in normal lip MCT predominated in connective and submucosal areas (P < 0.05). Conclusion:  The results suggest that increased MC density and protease content may contribute to elastosis formation in AC. In addition, changes in MCT distribution may favor AC malignization.