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Roderick Fullard, John Bradley, Larezia Williams, My-Tho Tran, Nicole Guyette, Tammy Than, Pearl Shin; Correlations between non-stimulated tear levels and conjunctival surface expression of inflammation-related biomarkers in normal and aqueous-deficient dry eye patients. Invest. Ophthalmol. Vis. Sci. 2013;54(15):4360. doi: https://doi.org/.
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In a recent study in this lab of normal and aqueous-deficient (AD) dry eye patients, non-stimulated (NS) tear IL-1β, IL-8, G-CSF, IL-1RA, IL-9, IL-12p70, IL-15, Eotaxin, and VEGF were all significantly elevated in the AD versus normal group. The current study relates tear levels of these cytokines with concurrent conjunctival surface expression of 93 inflammation-related biomarkers.
62 patients, defined by Schirmer I test as normal or AD dry eye, participated in the study. NS tear samples were collected by micropipette and stored in PBS-antiprotease buffer at -80°C prior to BioRad 27-Plex polystyrene bead-based cytokine assay on a Luminex 200 system. At the same patient visit, 8 conjunctival impression cytology (CIC) specimens were collected from each eye, RNA extracted by Qiagen RNEasy Plus Minikit, and real-time qPCR conducted on TaqMan 384-well low density array cards in 96 gene format.
NS Tear G-CSF, while not the strongest discriminator between normal and AD groups, showed the largest number of significant positive correlations with conjunctival expression of biomarkers, including pro-inflammatory cytokines, cytokine receptors, G-protein coupled receptors, proteases, transcription factors and calcium-binding proteins. Tear G-CSF also correlated strongly with conjunctival G-CSF receptor expression, other CSF receptors and most strongly with IL-1β (p<0.001 in all cases). Surprisingly, tear IL-1β and IL-8 correlated with expression of a narrower range of biomarkers, mainly pro-inflammatory cytokines and receptors, as did IL-1RA, IL-9, IL-12p70, IL-15, Eotaxin, and VEGF.
All NS tear cytokines previously found to differentiate between normal and AD dry eye patients showed showed patterns that correlated with conjunctival inflammatory biomarker expression. Tear G-CSF elicited the strongest correlations. Colony stimulating factors have been shown by others to be linked to pro-inflammatory cytokines, including IL-1, and may share connections with the IL-23/IL-17 pathway. These findings are confirmed by the conjunctival expression data in the current study. While tear IL-1β and IL-8 showed definite associations with pro-inflammatory cytokine and receptor expression in the current study, G-CSF showed broader and stronger associations. G-CSF may therefore be an important biomarker in AD dry eye.
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