Intra- and inter-day variation of cytokines and chemokines in tears of healthy subjects.

Tear levels of certain cytokines/chemokines can potentially serve as biomarkers for dry eye and other ocular surface diseases if they remain stable from day-to-day in healthy eyes. The aim of this study was to determine the normal intra- and inter-day variation of selected tear cytokines/chemokines. Tear samples from 24 young, healthy adults were collected 11:00 AM-1:00 PM (mid-day) and 5:00-7:00 PM (evening) on three non-consecutive days. Concentrations of 18 cytokines/chemokines (EGF, eotaxin, CX3CL1/fractalkine, GM-CSF, IFN-γ, IL-10, IL-1β, IL-13, IL-17A, IL-1RA, IL-5, IL-6, CXCL8/IL-8, IL-9, CXCL10/IP-10, CCL5/RANTES, TNF-α, and VEGF) were measured by multiplex bead analysis. Ocular surface disease was ruled out by clinical tests. A random-effects ANOVA model was used to evaluate intra- and inter-day effects on cytokine/chemokine levels. Repeatability of intra-subject inter-day measurements was assayed by coefficient of variation. Ten out of the 18 molecules had detectable tear levels in >50% of the subjects. Of those, only IL-10 and IL-1β levels had significant inter-day variations. EGF, CX3CL1/fractalkine, CXCL10/IP-10, and VEGF were consistently higher in the evening compared to the mid-day measurements. EGF, CXCL10/IP-10, VEGF and CXCL8/IL-8had good intra-subject reproducibility. In conclusion, tear cytokines/chemokines can be measured reproducibly over time, with most not having significant inter-day variability. Some varied significantly depending upon the time of tear collection, and these variations should be taken into account when comparisons are made. The good intra-subject reproducibility for EGF, CXCL10/IP-10, CXCL8/IL-8, and VEGF indicates that these molecules could potentially serve as biomarkers of ocular surface disease.