Abnormal accumulation of inter-α-trypsin inhibitor and hyaluronic acid in lichen sclerosus

Inter‐α‐trypsin inhibitor (ITI) is a recently identified extracellular hyaluronic acid (HA)‐binding protein which greatly improves extracellular HA stability. In lichen sclerosus (LS), a broad hyalinized zone of superficial dermis is the most prominent pathological change. To assess the pathogenic role of ITI in accumulation of HA in a broad hyalinized zone in LS, we examined the expression and localization of ITI and HA immunohistochemically. In LS lesional skin sections, ITI staining revealed a strong, diffuse immunoreactivity predominantly in the upper dermis, whereas no staining was detected in normal skin sections. HA staining clearly showed positive reactivity in the superficial dermis, the epidermis, and occasionally the perivascular inflammatory infiltrate in LS skin sections. In normal skin, HA was present only in the epidermis. Double staining for ITI and HA demonstrated that ITI was localized in the areas where HA was abnormally deposited in the superficial dermis of LS. Other HA‐binding proteins, CD44 and versican, did not show enhanced staining in the upper dermis of LS compared to normal skin specimens. These findings strongly suggest that ITI is closely implicated in the accumulation of HA in a broad hyalinized zone of the superficial dermis of LS.