The cornea is the major refracting optical
element of the eye and therefore critical for forming a
retinal image. The exposed surface of the eye is protected from pathogens by the innate immune system whose components include
defensins, naturally occurring
peptides with antimicrobial properties, and the physical barrier formed by the outer epithelial layer of the cornea. The proteomic approach has revealed that tear levels of
defensins are correlated with the course of healing of an experimental corneal
wound. Tears were collected from New Zealand White rabbits prior to (day 0) and daily for 5 days (days 1-5) following a standard unilateral 6 mm diameter corneal epithelial abrasion. Tear
protein profiles obtained from wounded and contra-lateral control eyes were compared using SELDI ProteinChip technology.
Peptides and
proteins of interest were purified by RP-HPLC and characterized by nanoESI-MS/MS. Mass spectra of tears on post-
wound day 1, revealed 13 peaks whose level decreased and five that increased. During wound healing the tear
protein profile correlated with
wound closure. An important finding was that the levels of rabbit
defensins (NP-1 and NP-2), which were elevated after wounding returned to normal levels by the time the
corneal abrasion healed. Relative quantification of NP-2 in tear fluid prior to (day 0) and after corneal wounding (days 1- 3) was determined using iTRAQ technology. A corneal
wound eliminates the barrier function of innate immunity and puts the cornea at risk from microbial attack until the epithelial cells restore the surface barrier. The increased availability of
defensins in the tears during healing suggests that these
peptides could protect the cornea from microbial attack during a period of increased vulnerability.