Increased dendritic cell density and altered morphology in allergic conjunctivitis

Abstract

Background Corneal and conjunctival epithelial dendritic cells (DC) have an established role in vernal keratoconjunctivitis, however, their role in more prevalent forms of allergic eye disease remains unclear. This study evaluated corneal and conjunctival epithelial DC density, morphology, and distribution observed using in vivo confocal microscopy (IVCM) in allergic conjunctivitis. Methods In this prospective, observational study, 66 participants (mean age 36.6 ± 12.0 years, 56% female): 33 with allergic conjunctivitis and 33 controls were recruited. IVCM was performed at the corneal centre, inferior whorl, corneal periphery, corneal limbus, and temporal bulbar conjunctiva. DC were counted and their morphology was assessed as follows: largest cell body size, presence of dendrites, and presence of long and thick dendrites. Mixed model analysis (DC density) and non-parametric tests (DC morphology) were used. Results DC density was higher in allergic participants at all locations (p ≤ 0.01), (corneal centre median (IQR) 21.9 (8.7–50.9) cells/mm2 vs 13.1 (2.8–22.8) cells/mm2; periphery 37.5 (15.6-67.2) cells/mm2 vs 20 (9.4–32.5) cells/mm2; limbus 75 (60-120) cells/mm2 vs 58.1 (44.4–66.2) cells/mm2; conjunctiva 10 (0–54.4) cells/mm2 vs 0.6 (0–5.6) cells/mm2, but not at the inferior whorl 21.9 (6.2–34.4) cells/mm2 vs 12.5 (1.9–37.5) cells/mm2, p = 0.20. At the corneal centre, allergic participants had larger DC bodies (p = 0.02), a higher proportion of DC with dendrites (p = 0.02) and long dendrites (p = 0.003) compared to controls. Conclusions Corneal and conjunctival DC density was increased, and morphology altered in allergic conjunctivitis. These findings imply that the ocular surface immune response was upregulated and support an increased antigen-capture capacity of DC in allergic conjunctivitis.

Dendritiform immune cells with reduced antigen-capture capacity persist in the cornea during the asymptomatic phase of allergic conjunctivitis

“…However, in more than half of the participants during the active phase and a quarter in the asymptomatic phase, conjunctival DC presented in a wire netting pattern, similar to that previously reported in the conjunctiva of VKC patients [5]. This appearance was not observed in the non-allergic group [4]. This suggests a possible pattern-specific inflammatory response at the conjunctiva and might be representative of a higher degree of response during the active phase of allergy.…”

“…In addition, DC density and morphology during the asymptomatic phase was compared to previously reported results for 33 healthy nonallergic participants [4]. A linear mixed model with a random effect for individuals and fixed effect of group and ocular surface location was used to examine differences in DC density between groups.…”

“…Avoidance of allergens such as pollens and dust mites may not always be feasible and thus a preventative approach which involves prophylactic treatment of allergic patients during their asymptomatic phase could perhaps expressed as median (IQR). Data for the non-allergic participants are from a previous study, reported elsewhere [4].…”

“…A prospective, observational, two visit study was conducted. The participants were a subgroup from a larger cross-sectional study involving 33 participants with allergic conjunctivitis and 33 healthy controls, the results of which have been reported elsewhere [4]. Twenty allergic participants who responded to the invitation to attend a second visit study were included in the current study.…”

“…Dendritic cells (DC) are a subtype of immune cells which play a pivotal role in the ocular surface defence system, and the initiation of the immune response in allergic conjunctivitis [1][2][3]. A higher density and altered morphology of DC has been shown in the cornea and conjunctiva during the active, symptomatic phase of allergic conjunctivitis using in vivo confocal microscopy (IVCM) [4]. In severe forms of ocular allergy including vernal keratoconjunctivitis (VKC), DC have been described as hyperreflective cells with dendritic processes and their density was higher at the corneal and conjunctivital locations compared to the healthy group [5][6][7].…”