ACQUISITION OF GRANZYME-B AND FAS LIGAND PROTEINS BY HUMAN KERATINOCYTES CONTRIBUTES TO EPIDERMAL-CELL DEFENSE

In vertebrate tissues, cell integrity is maintained by at least three mechanisms, During an immune response, injured cells are eliminated by cytotoxic lymphoid cells that produce perforin, granzyme B, and Fas l igand (FasL), Second, epithelial cells can produce FasL as an immunosu ppressive protein, probably to protect the tissue against immune-media ted damage, Third, locally secreted antimicrobial peptides can be oper ative in the protection of animal and human epithelia, In this work, a s another contribution to local mechanisms of host defense, the abilit y of human epidermal keratinocytes to produce cytotoxic proteins was i nvestigated, To address this question, freshly isolated human epiderma l cells and keratinocytes grown in vitro were studied. Freshly isolate d epidermal cells did not express the cytolytic proteins. In contrast, keratinocyte growth to confluence was associated with granzyme B, per forin, and FasL mRNA and protein synthesis. These proteins were secret ed in the culture medium. Further analysis showed that they were ident ical with the ones used by cytotoxic lymphocytes. Their function was t hen investigated with a view to a potential role in epidermal cell int egrity. The data showed that activated human keratinocytes were able t o protect against invading pathogens through granzyme B expression. Th is was demonstrated by the ability of granzyme B to greatly decrease t he bacterial growth of Staphylococcus epidermidis. In addition, kerati nocytes expressing FasL were found to prevent immune epidermal cell da mage, Apoptosis of Fas-sensitive T cells occurred during coculture wit h confluent epidermal keratinocytes and was largely reduced by the add ition of a FasL inhibitor. The data favor keratinocyte involvement in the regulation of dermal inflammatory responses.