Th1- and Th2-type cytokines in chronic ocular allergy

Background: Previous reports have suggested that Th2-type cytokines are important in the pathogenesis of ocular allergic diseases. The purpose of this study is to measure levels and mRNA expression of Th1- and Th2-type cytokines in patients with active vernal keratoconjunctivitis (VKC) and atopic keratoconjunctivitis (AKC). Methods: Tear samples and tear-isolated cells were obtained from 9 healthy participants (CT-controls), 28 VKC, and 6 AKC patients. IL-4, IL-13, and interferon gamma (IFN gamma) tear levels were determined by ELISA, and IL-4 and IFN gamma tear cell mRNA expression by RT-PCR. Effects of these cytokines on IL-6 and IL-8 secretion, and on ICAM-1 expression by conjunctival fibroblasts, were evaluated by ELISA and flow cytometry respectively. Results: Interleukin-4 tear levels were increased in VKC and AKC compared with CT, but only IFN gamma significantly correlated with corneal involvement. An IL-4/13-dominant profile was found in 50% of VKC and in 17% of AKC patients, while a IFN gamma -dominant profile was found in 18% of VKC and in 17% of AKC patients. IL-4 and IFN gamma transcripts were detected in tear cells from 11 out of 12 VKC patients. IFN gamma upregulated expression of ICAM-1 on conjunctival fibroblasts and the secretion of IL-6 and IL-8. Conclusions: Although both IL-4 and IFN gamma are detected in tears, only IFN gamma levels correlated with disease severity and upregulated ICAM-1 on conjunctival fibroblasts, suggesting the role of IFN gamma in the inflammatory phase of chronic allergic eye diseases.