Subnormal Cytokine Profile in the Tear Fluid of Keratoconus Patients

Abstract

Keratoconus, historically viewed as a non-inflammatory disease, is an ectatic corneal disorder associated with progressive thinning of the corneal stroma. Recently, a few inflammatory mediators have been reported to be elevated in the tear fluid of keratoconus patients. Consequently, we investigated a wide range of inflammation regulating cytokines in the tears and sera of keratoconus and control subjects. Interleukin (IL)-1β, IL-4, IL-6, IL-10, IL-12, IL-13, IL-17, interferon (IFN)-γ, chemokine C-C motif ligand 5 (CCL5) and tumor necrosis factor (TNF)-α were tested in tear samples and sera of keratoconus and control individuals by multiplex immuno-bead assays. Selected cytokines were further tested by standard ELISA on pooled tear samples. All cytokines in the sera were generally low, with no significant changes between keratoconus and control subjects. However, in tear fluids, clear differences were detected between the two groups. These differences include increased IL-6, and decreased IL-12, TNF-α, IFN-γ, IL-4, IL-13 and CCL5 in keratoconus compared to control tear fluids. The decreases in IL-12, TNF-α and CCL5 were statistically significant, while the IL-13 decrease was statistically significant in the severe keratoconus group only. IL-17 could not be detected by multiplex immuno-bead assay, but showed an increase in keratoconus by conventional ELISA on a limited number of pooled tear samples. Our findings confirm increased IL-6, but dispute earlier reports of increased TNF-α, and suggest a cytokine imbalance in keratoconus disrupting corneal homeostasis. Moreover, an increase in IL-17 suggests tissue degenerative processes at work, contributing to the thinning and weakening of the corneal connective tissue in keratoconus.

Keratoconus: an inflammatory disorder?

“…Their baseline findings that keratoconus index measured by Pentacam correlated negatively with Chemokine (C-C motif) ligand 5 (CCL5) was in line with Jun et al's report. 103 Their baseline observation and the reversely significant association found by them between the thinnest corneal thickness as measured by Pentacam and CCL5, 1 year after corneal cross-linking, might indicate a role of CCL5 in the etiopathology of the condition. 105 Several researchers have concluded that inadequate balance between cytokines (pro-inflammatory and antiinflammatory) may lead to an altered corneal structure and function, triggering an increase in metalloproteinases and keratocyte apoptosis.…”

“…105 Several researchers have concluded that inadequate balance between cytokines (pro-inflammatory and antiinflammatory) may lead to an altered corneal structure and function, triggering an increase in metalloproteinases and keratocyte apoptosis. 74,103,106 Kolozsvári et al 107 also recently found a significant positive association between CCL5, MMP-13, and NGF and several topographic indices in keratoconic corneas. In addition, they found a significant negative correlation between IL-6 and Klyce/Maeda keratoconus index.…”

“…In addition, they found lower levels of TNF-α, an observation that disagrees with reports from Lema et al 20,21,22 and Balasubramanian et al 18 The possible reasons for this disparity could be either artefactual differences in the antibody-based assays or real differences between patient populations. 103 Whether the altered protein composition of tears in eyes suffering from keratoconus is an effect of events in the corneal epithelium or has a direct influence in the development of the disease remains to be elucidated. 96 Cheung et al 86 recently analyzed ex vivo the modulation of the healing process of corneas with keratoconus and of non-keratoconic corneas.…”

“…Jun et al 103 found that in the sera of keratoconus patients, there were no statistically significant differences between them and control subjects for several cytokines tested, and suggested that the cytokine changes detected in the tear film were most likely a consequence of localized events in the eye and not of systemic changes.…”

Polymorphisms of the Apoptosis-Related FAS and FAS Ligand Genes in Keratoconus and Fuchs Endothelial Corneal Dystrophy

“…It has been reported that these polymorphisms are involved in the development of several types of cancers in which apoptosis is an essential element of pathogenesis, including esophageal cancer (Sun et al 2004), lung cancer (Wang et al 2003;Zhang et al 2005), epithelial ovarian cancer (Li et al 2013), pancreatic cancer (Yang et al 2008), cervical cancer , breast cancer (Zhang et al 2007), and acute myeloid leukemia (Sibley et al 2003). Interestingly, it was shown that the immune system has been implicated in the pathogenesis of KC because thinning of the cornea seems to be associated with increased levels of intracorneal inflammatory mediators, such as interleukin 1, 6 and 17 (Jun et al 2011). In addition, associations between keratoconus and immune disorders, such as rheumatoid arthritis, ulcerative colitis, autoimmune chronic active hepatitis, Hashimoto's thyroiditis, arthropathy, asthma, irritable bowel syndrome and environmental allergy were shown (Nemet et al 2010).…”