Conjunctival mast cell modulation of conjunctival epithelial cell activity in ocular allergic inflammation: Effect of mast cell stabilization and role of TNFalpha

Purpose. Allergic diseases are among the most common disorders presented to ophthalmologists, yet mechanisms discriminating between allergic ocular diseases are poorly understood. Conjunctival epithelium exhibits differences in chemokine and receptor expression profiles in acute versus chronic ocular allergic inflammation. The goal of these studies was to examine, in vitro, whether conjunctival epithelial cell (EC) responses vary according to different mechanisms of activation known to occur in vivo in ocular allergic disease. These included supernates from IgE-activated mast cells (IgE-MCS) and pro-inflammatory cytokines (reflecting in vivo conditions of acute [TNFα, IL-1β] versus chronic [IFNγ] inflammation). Variables examined included ICAM-1 and HLA-DR expression, IL-8 and RANTES release, and adhesion and degranulation of peripheral blood eosinophils. Methods. Human mast cells (MC) and EC were purified from cadaveric conjunctival tissues. Mechanisms of IgE-MCS mediated activation of EC were examined using a degranulation inhibitor (olopatadine) and TNFα-blocking antibody. Other techniques included flow cytometry, ELISA, RIA, and spectrophotometric cellular adhesion assay. In vivo comparisons of cytokine concentrations in tears (non-allergics versus allergics) were examined utilizing cytometric bead array flow cytometry to measure six cytokines simultaneously per sample. Results. IgE-activated MC released TNFα, which was inhibited by olopatadine. IgE-MCS enhanced ICAM-1 expression on EC via a TNFα specific mechanism. IgE-MCS did not enhance HLA-DR expression or RANTES release, but enhanced IL-8 release. IgE-MCS enhanced both eosinophil adhesion to EC and degranulation. Enhancement of IL-8 release and eosinophil adhesion by IgE-MCS was not dependent on TNFα and was independent of MC degranulation. Pro-inflammatory cytokines induced individual and combined effects on EC activation, which corresponded to profiles on the ocular surface in acute versus chronic disease. Differences in relative concentrations of cytokines in tears were observed between allergic and non-allergic subjects, even in the absence of allergen. Conclusions. These data suggest that IgE-mediated activation of MC could account for the pattern of EC activation in acute ocular allergic inflammation and promote eosinophil adhesion and activation, while combinations of pro-inflammatory cytokines which included IFNγ could stimulate the profile of epithelial cell activation observed in chronic disease. Furthermore, basic differences in tear cytokines may exist between allergic and non-allergic individuals.