Expression and regulation of antimicrobial peptide psoriasin (S100A7) at the ocular surface and in the lacrimal apparatus.

PURPOSE Psoriasin, originally isolated from psoriasis as an overexpressed molecule of unknown function, has recently been identified as a principal Escherichia coli-killing antimicrobial peptide of healthy skin. The purpose of this study was to investigate the expression and antimicrobial role of psoriasin at the ocular surface and in the lacrimal apparatus. METHODS Different tissues of the lacrimal apparatus and ocular surface were systematically analyzed by means of RT-PCR, Western blot, and immunohistochemistry for their ability to express and produce psoriasin. The inducibility and regulation of psoriasin were studied in human corneal as well as conjunctival epithelial cell lines after challenge with ocular pathogens and proinflammatory cytokines. Real-time RT-PCR was performed to evaluate the expression and induction of psoriasin. In addition, tear fluid obtained from different healthy volunteers was examined by ELISA for its psoriasin concentration. RESULTS RT-PCR and Western blot analyses revealed a constitutive expression of psoriasin in cornea, conjunctiva, nasolacrimal ducts, and lacrimal gland. Immunohistochemistry showed strong staining of meibomian glands for psoriasin. No induction of psoriasin was observed after stimulation with supernatants of E. coli, whereas supernatants of Staphylococcus aureus and Haemophilus influenzae significantly increased the psoriasin mRNA expression. Stimulation with IL-1β and VEGF also strongly increased psoriasin transcription. The highest amounts of psoriasin protein were detected in the tear fluid (~170 ng/mL) of healthy volunteers. CONCLUSIONS The results suggest that psoriasin is produced by the structures of the ocular surface and is part of the innate immune system at the ocular surface and tear film.