The spectrum of antimicrobial peptide expression at the ocular surface

Antimicrobial peptides are the eukaryotic analogues of antibiotics. In addition to their antimicrobial activity, these peptides can signal to host cells and are therefore intermediaries between the innate and adaptive immune systems. Results in a prior study showed that beta-defensins-1 and -2 are made by ocular surface epithelial cells. In the present study, a survey was made of antimicrobial peptide expression, including 17 previously described members of the beta-defensin family, at the surface of the human eye.

Total RNA was obtained from 43 fresh and cultured corneal and conjunctival samples, including 9 samples from patients with clinical infections. The expression of 21 antimicrobial peptides was determined using reverse transcription-PCR. Where detected, relative expression was quantitated using real-time PCR.

Expression of 7 of the 21 antimicrobial peptides investigated, beta-defensin-1 to -4, liver expressed antimicrobial peptide (LEAP)-1 and -2, and LL37/cathelicidin, were detected frequently in samples of ocular surface epithelia. Distinct but overlapping profiles of expression were detected in cornea and conjunctiva, with expression of beta-defensin-3 and -4 and LEAP1 and -2 most common in cultured corneal epithelia. Expression of beta-defensin-3 was detected in a greater percentage of corneal and conjunctival samples with infection.

Together with known lacrimal antimicrobial activities, these results extend the knowledge of antimicrobial activity at an important mucosal site, the ocular surface, allowing synergistic interactions to be investigated. The findings has significant implications both for the understanding of the normal homeostasis of mucosal surfaces and for antimicrobial and anti-inflammatory therapies.