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R. J. Fullard, M. W. LaFrance, L. E. Kehinde; Nonstimulated and Stimulated Tear Levels of 27 Cytokines in Normal Human Patients. Invest. Ophthalmol. Vis. Sci. 2008;49(13):428.
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Tear levels of inflammatory markers, such as cytokines, chemokines and growth factors, can provide valuable information about ocular surface disease and injury. Because stimulus has been shown to affect the levels of many tear proteins, it is likely that tear levels of inflammatory markers would also be affected by stimulus. This study evaluates the effect of stimulus on the tear levels of 27 inflammatory markers in normal human patients.
6.5 µL nonstimulated tear samples and paired stimulated samples (nasal stimulus, sample preceded by 20 µL washout) were collected atraumatically by micropipette from 29 normal patients. Samples were immediately frozen (-80°C) in assay buffer and subsequently assayed using Bio-Rad 27-Plex cytokine assay kits (recently validated by the authors for tear assay) on a Luminex 200 cytometric bead-based assay system.
22 of the 27 inflammatory markers were detected in both tear samples of more than half the study patients. Overall, nonstimulated and stimulated levels correlated well (r2 = 0.94), but paired t-tests showed significantly higher levels of Eotaxin, GM-CSF, IFN-γ, IL-1β, 2, 4, 5, 7, 9, 10, 12, 12p70, 13, 17, MIP-1α and RANTES in stimulated tears, and IL-1Ra and IL-8 in nonstimulated tears. IFN-γ and IL-5 levels were substantially higher in stimulated tears suggesting predominantly lacrimal gland production. Substantially higher IL-1Ra and IL-8 in nonstimulated tears may indicate a primarily ocular surface source.
Many cytokines can be detected using either nonstimulated or stimulated tear collection methods. However, factored into the high correlation of cytokine levels between sample types is a significantly higher stimulated tear level for more than half of the assayed cytokines. Because the levels of many cytokines may differ significantly with stimulus, consistent stimulus control should be used in tear studies to allow comparison across tear samples.
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