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. MC_T containing only tryptase, and MC_TC 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 degranulaated 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). CONCLUSION: 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.