Diurnal changes and topographical distribution of ocular surface epithelial dendritic cells in humans, and repeatability of density and morphology assessment

Abstract

AbstractPurposeDendritic cells (DC) play a crucial role in ocular surface defence. DC can be visualisedin vivoby confocal microscopy but have not yet been fully characterised in humans. This study investigated the diurnal variation, topographical distribution, and repeatability of DC density and morphology measurement.MethodsIn vivoconfocal microscopy was conducted on 20 healthy participants (mean age 32.7±6.4 years, 50% F) at baseline and repeated after 30 minutes, 2, 6, and 24 hours. Images were captured at the corneal centre, inferior whorl, corneal periphery, limbus, and bulbar conjunctiva. DC density was counted manually, and morphology of DC was assessed for the largest cell body size, presence of dendrites, presence of long dendrites, and presence of thick dendrites. Mixed model analysis, non-parametric analyses, Bland & Altman plots, the Coefficient of Repeatability (CoR), and kappa were used.ResultsThere were no significant changes in DC density (p≥0.74) or morphology (p>0.07) at any location over the 24-hour period. Highest DC density was observed at the corneal limbus followed by the peripheral cornea (p<0.001), with lowest density at the corneal centre, inferior whorl, and bulbar conjunctiva. Most DC at the corneal periphery, limbus, and bulbar conjunctiva had larger cell bodies compared to the corneal centre (p≤0.01), and presence of long dendrites was observed mostly at non-central locations. DC with thick dendrites were mostly observed at the limbus. Day-to-day CoR for DC density ranged from ±28.1 cells/mm2at the corneal centre to ±56.4 cells/mm2at the limbus. Day-to-day agreement of DC morphology determined by kappa ranged from 0.5 to 0.95 for cell body size, 0.60 to 0.95 for presence of dendrites, and 0.55 to 0.80 for presence of long dendrites, at various locations.ConclusionsNo diurnal changes are apparent in corneal or conjunctival DC. Substantial topographical differences exist in DC density and morphology.In vivoconfocal microscopy provides good repeatability of DC density and acceptable agreement of DC morphology.Key pointsThere was no diurnal variation in dendritic cell density, morphology, or topographical distribution at the ocular surface in healthy individuals.A gradient from high density of dendritic cells at the limbus to low density at the corneal centre was observed inin vivoconfocal microscope images of healthy corneas. Density was lowest in the bulbar conjunctiva.The morphology of dendritic cells at the corneal periphery, limbus and bulbar conjunctiva suggests a greater antigen capture capacity compared to dendritic cells at the corneal centre.