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.