Increased dendritic cell density and altered morphology in allergic conjunctivitis

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/mm(2) vs 13.1 (2.8–22.8) cells/mm(2); periphery 37.5 (15.6-67.2) cells/mm(2) vs 20 (9.4–32.5) cells/mm(2); limbus 75 (60-120) cells/mm(2) vs 58.1 (44.4–66.2) cells/mm(2); conjunctiva 10 (0–54.4) cells/mm(2) vs 0.6 (0–5.6) cells/mm(2), but not at the inferior whorl 21.9 (6.2–34.4) cells/mm(2) vs 12.5 (1.9–37.5) cells/mm(2), 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.