Corneal epithelial cells and stromal keratocytes efficently produce CC chemokine-ligand 20 (CCL20) and attract cells expressing its receptor CCR6 in mouse herpetic stromal keratitis

Purpose. CC chemokine-ligand 20 (CCL20) is known to be selectively expressed by surface-lining mucosal epithelial cells and skin epidermal keratinocytes and to attract cells such as immature dendritic cells and effector T cells via CCR6. This study evaluated the ability of corneal epithelial cells and stromal keratocytes to produce CCL20 in vitro and in vivo. Methods. Human corneal epithelial cells (HCE) and corneal keratocytes (HCK) were treated without or with various cytokines and expression of CCL20 mRNA and secreion of its protein were evaluated by RT-PCR and ELISA. Induction of CCL20 mRNA in HCE and HCK was also examined upon in vitro infection with HSV-1. Using a mouse model of herpetic stromal keratitis (HSK), induction of CCL20 expression and accumulation of cells expressing CCR6 were evaluated by RT-PCR and immunohistochemistry. Results. Not only corneal epithelial cells but also stromal keratocytes efficiently expressed CCL20 mRNA and protein upon stimulation with IL-1ß and TNF-a. In vitro infection with HSV-1 also induced CCL20 mRNA in both types of cells. In a mouse herpetic stromal keratitis model, prominent accumulation of CCL20 and CCR6 mRNA was revealed in HSV-1-infected corneas. Furthermore, immunohistochemistry demonstrated production of CCL20 by corneal epithelial cells as well as stromal keratocytes and stromal infiltration of DEC205 + dendritic cells, CD4 + T cells and CD8 + T cells. Double staining revealed that CCR6-expressing cells were mostly MHC class II + dendritic cells. Conclusions. Not only epithelial cells but also stromal keratocytes are efficient producers of CCL20 in the cornea and recruit CCR6-expressing cells such as dendritic cells into inflamed cornea.