The tear film is a rich source of growth factors, proteases, protease inhibitors, antioxidants,
11 mucins, and lipids that has been only partially characterized. Future-capture ELISAs of specific tear proteins and tear proteomics together offer potentially useful indicators of the health of the ocular surface.
12 Mechanisms underlying dysfunction might also be gleaned; for example, the lipophile lipocalin-1
13 and phospholipase A2 are increased in tears of patients intolerant to wearing contact lenses.
14 Comparison of tears from Sjögren's syndrome dry eye versus normal subjects by mass spectrometry revealed seven proteins peaks downregulated and three upregulated.
15 Three human dry eye-related conditions have been scrutinized to date by unbiased screens coupled to proteomics and sequencing. Although HGF, IGF, NGF, and EGF can be detected in normal tears,
16 “lacritin” was the only growth-like factor (and only one of nine tear proteins) downregulated of hundreds of proteins identified in tears from patients suffering from blepharitis.
17 Blepharitis is a common inflammation of the eyelid, associated as noted above with EDE. The other eight downregulated proteins were albumin, Ig k chain-VIII, pyruvate kinase, α1-antitrypsin, prolactin-inducible protein, cystatin SA-III, and lysozyme.
17 Lactoferrin, lipocalin-1, lysozyme, and prolactin-inducible protein were reported to be downregulated in a screen of tears from patients with non-Sjögren's syndrome dry eye.
18 Recently Nichols and Green reported that lacritin is selectively downregulated more than any other tear protein in contact lens–related dry eye.
19 Lacritin stimulates MUC16 production by human corneal epithelial cells at levels matching or exceeding that of serum (Laurie GE, et al.
IOVS 2006;47:ARVO E-Abstract 1606). Autologous serum is a reportedly successful method of treating dry eye.
20 Lacritin also promotes basal tear secretion by cultured rat
21 and monkey
22 lacrimal acinar cells and stimulates human corneal epithelial cell growth.
23