Although the pathogenesis of pterygia is still poorly understood, epidemiologic evidence suggests that environmental stress may have a role. Of the potential agents, UV irradiation has received the greatest attention.
2 3 31 In the present study, we observed the induction of IL-6 and -8 mRNA and protein in UVB-irradiated PECs
(Figs. 3 4 5 6) and in UVB-exposed pterygia
(Fig. 7) . It is well established that ocular surface epithelial cells produce these cytokines either constitutively or in response to a stimulus.
14 32 Corroborating data have also been presented by other investigators, who have shown that UVB-exposed human skin keratinocytes produce TNF-α and IL-8, which correlates with increased expression of E-selectin and accumulation of neutrophils.
33 Other studies in UVB-irradiated and implanted human cutaneous melanomas have demonstrated increased expression of IL-8 that correlates with angiogenesis, tumorigenicity, and metastatic ability, possibly because of enhanced expression of MMPs.
34 In addition, abundant epidermal expression of bFGF and VEGF has been noted in UVB-exposed mouse skin.
35 Similar in vitro investigations have shown increased production of IL-1, -6, and -8 and TNF-α in cultured human corneal fibroblasts,
20 and corneal epithelium
21 after UVB irradiation. de Vos et al.
22 irradiated human keratinocytes with exposures similar in duration and dose to those used in the present study and found that IL-6 mRNA was enhanced in a time- and dose-dependent manner. Other investigators have linked UVB irradiation to the production of the immunosuppressive cytokine IL-10 from human keratinocytes.
36 37 Although most epithelial cell–derived cytokines seem to be induced after UVB exposure, perhaps as a consequence of enhancing mRNA stability,
22 the same cannot be said for IL-7. The downregulated expression of this cytokine is thought to be mediated by the enhancement of a transcription repressor.
38