The Role of IFN– in the Pathophysiology of TH2 Inflammation in the Mouse Model of Allergic Conjunctivitis

Abstract

Abstract: : Purpose: IFN–γ is classified as an inducer of T_H1 type inflammation.The purpose of this study is to determine the role of IFN–γ in a mouse model of allergic conjunctivitis in the absence or presence of induced keratoconjunctivitis sicca (KCS). Methods: 1) Multi–Hit Ag Challenge: On day 1, BALB/c wild type (WT+) and IFN–γ –/– mice were injected (sensitization) in the hind footpad with 20 µg of short ragweed pollen (SRW) in 5 mg alum. Starting on day 10, topical secondary challenges of 2 mg SRW in 10µl PBS were applied to each eye 1X/day for 6 consecutive days. 2) Multi–Hit Ag challenge + Blower Model: To determine the effect of KCS on allergic conjunctival responses, mice received SRW sensitization and multiple challenge in a desiccating environment (blower hood and fan), and were injected with 0.5 mg scopolamine 3X/day. 24 hrs after the last secondary challenge, globes with lids attached were collected. Cellular infiltrates into the conjunctiva were evaluated by H & E staining. Results:SRW sensitized and challenged WT+ mice contained 53+/–7.8 eosinophils and 88.5+/–17.9 neutrophils in the conjunctiva 24 hrs after the last topical SRW challenge. In contrast, SRW sensitized and challenged IFNγ –/– mice had significantly fewer eosinophils (11.7+/–1.6, 77% decrease, P=0.007) and neutrophils (30+/–7.6, 66% decrease, P=0.046) as compared to the sensitized and challenged WT+ mice. WT+ mice receiving SRW sensitization and challenge in a desiccating environment had 58.4+/–1.5 eosinophils and 221.1+/–4.3 neutrophils. In contrast, IFNγ –/– mice receiving the SRW sensitization and challenge in a desiccating environment had significantly fewer eosinophils (22+/–1.3, 62 % decrease, P<0.001) and neutrophils (120+/–2.2, 46% decrease, P<0.001) as compared to WT+ mice challenged in a desiccating environment. Conclusions:These data indicate that allergy, typically thought to be a strict T_H2 inflammatory event, requires the T_H1 cytokine IFN–γ for initiation. Our results suggest that IFN–γ plays an unexpected but essential role in the immunopathology of allergic conjunctivitis by enhancing or facilitating the recruitment of the neutrophils and eosinophils required for the allergic conjunctivitis response. This study shows the interdependency of T_H1 and T_H2 cells in allergic ocular inflammatory disease and demonstrates that these two cell populations are not mutually exclusive.

Keywords: conjunctiva • cornea: tears/tear film/dry eye • inflammation