Antimicrobial compounds in tears

Abstract

The tear film coats the cornea and conjunctiva and serves several important functions. It provides lubrication, prevents drying of the ocular surface epithelia, helps provide a smooth surface for refracting light, supplies oxygen and is an important component of the innate defense system of the eye providing protection against a range of potential pathogens. This review describes both classic antimicrobial compounds found in tears such as lysozyme and some more recently identified such as members of the cationic antimicrobial peptide family and surfactant protein-D as well as potential new candidate molecules that may contribute to antimicrobial protection. As is readily evident from the literature review herein, tears, like all mucosal fluids, contain a plethora of molecules with known antimicrobial effects. That all of these are active in vivo is debatable as many are present in low concentrations, may be influenced by other tear components such as the ionic environment, and antimicrobial action may be only one of several activities ascribed to the molecule. However, there are many studies showing synergistic/additive interactions between several of the tear antimicrobials and it is highly likely that cooperativity between molecules is the primary way tears are able to afford significant antimicrobial protection to the ocular surface in vivo. In addition to effects on pathogen growth and survival some tear components prevent epithelial cell invasion and promote the epithelial expression of innate defense molecules. Given the protective role of tears a number of scenarios can be envisaged that may affect the amount and/or activity of tear antimicrobials and hence compromise tear immunity. Two such situations, dry eye disease and contact lens wear, are discussed here.

TSP-1 Deficiency Alters Ocular Microbiota: Implications for Sjögren's Syndrome Pathogenesis

“…Many other tear proteins, including a-and b-defensins, and cathelicidin have antimicrobial activities against commensals and pathogens; however, only few (eg, lipocalin-derived peptide) are insensitive to the ionic strength of normal tear fluid. [27][28][29] Similarly, other TSP-derived peptides were previously reported to carry an antimicrobial activity against Escherichia -/ -(n = 7) and C57BL/6/(n = 7) mice. To determine the antibody titers, serial dilutions of serum derived from the TSP-1 -/ -and wild-type (WT) mice were exposed to bind to the CNS sp.…”

Tear Interferon-Gamma as a Biomarker for Evaporative Dry Eye Disease

“…Another analytical approach involves the quantification of cytokine levels relative to total tear protein or constitutive proteins. 46 Although the measurement of total tear protein was Numbers represent Spearman correlation coefficients. Significant (P < 0.05) correlations are shown in bold.…”

Both CD8+and CD4+T Cells Contribute to Corneal Clouding and Viral Clearance following Vaccinia Virus Infection in C57BL/6 Mice

“…For some infections, like HSV infections, blood vessels and lymphatics infiltrate into the cornea, amplifying the response. One of the primary barriers to infection is the mucin layer of the ocular surface, which prevents pathogen attachment, and the tear film, which has numerous antimicrobial molecules (25). It is generally believed that mechanical damage to the cornea that breaches the infection barrier is required in most cases of keratitis; thus, scarification is frequently used in animal models.…”