We found that CXCL2 effectively restored neutrophil infiltration into the inoculated corneas and caused typical CaK in nude mice (Fig. 7). In fact, coadministration
of CXCL2 with blastospores exacerbated the severity of CaK and neutrophil infiltration in the corneas of BALB/c mice (Fig. 7). We compared the effect of IL-17 neutralization in mice concurrently inoculated with Candida in ear skin and the cornea. Contrary to its effect in cornea, IL-17 neutralization worsened the infection in skin (Fig. 8A). Histological analysis revealed check details that while IL-17 neutralization inhibited leukocytes infiltration at both sites, it led to fungal expansion in the skin (Fig. 8B and C). These results suggest that IL-17 inhibition elicits protective
and destructive responses in corneas and skin, respectively. The pathogenic role of lymphocytes in infectious keratitis has been previously reported in experimental models of other pathogens. Over three decades ago, it was noted that nude mice did not develop viral keratitis when challenged with the herpes Pifithrin-�� ic50 simplex virus [23]. Pearlman et al. showed that immunocompetent mice no longer developed Onchocerca volvulus keratitis when depleted of CD4+ cells [24]. By studying related mechanisms, Rouse and colleagues identified bystander activation of lymphocytes in the pathogenesis of herpes simplex keratitis [25, 26]. We report, for the first time, that CaK cannot be induced in either nude mice or CD4+ T-cell-depleted BALB/c mice, and that IL-17 is a critical factor in CaK initiation. We further showed that neutrophils and CD4+ T cells (supposed Th17 cells) are the main producers of IL-17
during CaK initiation (Fig. 4 and 5). On the other hand, Treg cells 2-hydroxyphytanoyl-CoA lyase and γδ T cells, which are key players in other systems [27, 28], were not involved in CaK formation in cornea (Supporting Information Fig. 2). Though the differential roles of these cell types in CaK and herpes simplex keratitis could be explained by the significant difference in the properties of the two pathogens, more extensive studies are needed to investigate why Treg cells and γδ T cells are not seemingly involved in pathogenesis of FK. Lastly, the differential effects of IL-17 neutralization on CaK and fungal dermatitis in the same mouse (Fig. 8) underscore the duality of IL-17 activity and the importance of cellular context in the pathogenesis of keratitis [29-33]. Thus, the effects of C. albicans may not be recapitulated by other fungal genera. While highlighting a critical role for IL-17 in CaK initiation, our results also bring to light several intriguing questions concerning corneal infections. The first involves the mechanism of efficient fungal clearance in corneas of nude mice. It has been proposed that structural features, as well as some innate factors, afford corneas the ability to hinder pathogens [34] or blastospore-pseudohypha transformation [35].