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Meng Lin, Joycelyn Niimi, Nancy McNamara, Yixiu Zhou, Jeremy Shumaker, Heather French, Tiana Leung, Shiyin Wang, Karyn Siemasko, Michael Stern; Gender, Ethnicity, and Time After Awakening Affect Tear Film Cytokine Concentrations. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5403.
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To investigate how cytokine concentrations in the tear film of normal eyes differ by gender, ethnicity, and time after awakening. The potential impact of these factors on baseline cytokine levels in healthy eyes will provide an important reference for deciphering comparisons with ocular surface diseases.
42 subjects (ages 18-30 years; 22 Asians, 20 non-Asians; 22 males, 20 females) with no prior history of contact lens wear and no dry eye symptoms (OSDI score < 13) underwent an ocular surface screening evaluation. Baseline tear samples were collected on all subjects before sleep using capillary tubes held at the tear meniscus. Of the 42 subjects studied, 14 subjects slept in the research lab and their tear samples were collected immediately after awakening, and again 3 hrs after. Tear samples from each eye were analyzed separately with multiplex bead-based assays for the concentrations (pg/ml) of 11 cytokines, including IFN-γ, IL-12p(70), TNF-α, IL-1α, IL-1β, IL-6, IL-8, IL-17, IL-10, IL-13, IL-15. Correlations between measurements on fellow eyes were accounted for using linear mixed effects modeling.
With the exception of IL-8 and IL-17, the average baseline concentrations of all cytokines were higher in the tears of female subjects compared with males and significant gender differences (p-values <0.05) were found for IFN-γ, IL-1α, IL-1β, IL-6, IL-12p(70), IL-13 and TNF-α. With the exception of IL-8 and IL-13, Asians had lower concentrations compared with non-Asians and significant ethnic differences (p-values <0.05) were found for IFN-γ, IL-1α, IL-6, IL-10, IL-12p(70), and IL-17 in their tears compared with non-Asians. IL-8 was the only cytokine to exhibit an increase (p<0.05) in concentration upon awakening, while all others decreased. The concentrations of all cytokines recovered to baseline after 3 hrs of awakening.
Baseline cytokine concentrations vary significantly by gender and ethnicity. The impact of these differences must be considered in studies that use tear cytokine levels as a quantitative measure of inflammation during disease. It is also important to note that eye closure significantly altered tear cytokine concentrations, which subsequently recovered to baseline levels within 3 hrs of awakening. The increased concentration of IL-8 in tears upon awakening may be related to a substantial infiltration of PMN cells into the tears during sleep.
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