Purpose: Pterygia are common ocular surface lesions that are thought to be induced by exposure to ultraviolet (UV) radiation. The hypothesis tested in the current study is that UV radiation modulates the expression of interleukin (IL)-6 and -8, which could promote the neovascularization and chronic inflammation regularly observed in pterygia.
Methods: Immunohistochemical analysis was performed on 10 pterygia and 14 specimens of normal conjunctiva (4 of which contained limbus), to identify the cellular source of these cytokines. Pterygium epithelial cells were exposed to UVB (0-100 mJ/cm(2)) and the expression of cytokine mRNA and protein was determined by reverse transcription-polymerase chain reaction (RT-PCR), RNase protection assay (RPA), and enzyme immunoassay. Similarly, pterygium tissue in organ culture was UVB irradiated and the supernatants analyzed for cytokine production.
Results: IL-6 and -8 proteins were abundantly expressed, predominantly by the pterygium epithelium, with additional IL-8 immunoreactivity associated with the vascular endothelium. In contrast, significantly less staining for both cytokines was observed in normal conjunctiva, cornea, and limbus. Expression of both IL-6 and -8 mRNA and protein was induced in UVB-irradiated pterygium epithelial cells in a time- and dose-dependent manner. Similarly, IL-6 and -8 proteins were significantly elevated in UVB-treated compared with nonirradiated pterygia.
Conclusions: This study provides the first direct experimental evidence that implicates UV in the pathogenesis of pterygia. The two proinflammatory cytokines that are induced by UV radiation may play a key role in the development of pterygia, by initiating blood vessel formation, cellular proliferation, tissue invasion, and inflammation. Strategies aimed at reducing ocular exposure to UV light may decrease the incidence and recurrence of pterygia.