Flagellin‐induced expression of CXCL10 mediates direct fungal killing and recruitment of NK cells to the cornea in response to Candida albicans infection

Abstract

We previously showed that topical flagellin induces profound mucosal innate protection in the cornea against microbial infection, a response involving multiple genes and cell types. In this study, we used a Candida albicans (CA)-C57BL/6 mouse keratitis model to delineate the contribution of CXCL10 and CXCR3-expressing cells in flagellin-induced protection. Flagellin-pretreatment markedly enhanced CXCL10 expression at 6 hours post CA infection (hpi), but significantly dampened CXCL10 expression at 24 hpi. At the cellular level, CXCL10 was expressed in the epithelia at 6 hpi in flagellin-pretreated corneas, and concentrated at lesion sites 24 hpi. CXCR3-expressing cells were detected in great numbers at 24 hpi, organized within clusters at the lesion sites in CA-infected corneas. CXCL10 or CXCR3 neutralization increased keratitis severity and dampened flagellin-induced protection. CXCR3-positive cells were identified as NK cells, the depletion of which resulted in severe CA keratitis. Contributions from NK T-cells were excluded by finding no change in flagellin-induced protection in Rag1 knockout mice. Recombinant CXCL10 inhibited CA growth in vitro and accelerated fungal clearance and inflammation resolution in vivo. Taken together, our data indicate that epithelium-expressed CXCL10 plays a critical role in fungal clearance and that CXCR3-expressing NK cells contribute to CA eradication in mouse corneas.

Chitinase 3-Like 1 Promotes Candida albicans Killing and Preserves Corneal Structure and Function by Controlling Host Antifungal Responses

“…This is different from flagellin-treated corneas, where CXCR3-positive cells were found in the stroma beneath the epithelium (29). At 1 dpi, as shown above, CXCL10 was mostly expressed in the damaged epithelium, while CXCR3 was found in the infiltrating cells in the stroma or in an intraepithelial cell cluster that contained mainly natural killer cells and neutrophils (29). Interestingly, exogenous CHI3L1 markedly increased epithelial expression of CXCL10 and the number of CXCR3-positive cells in the stroma.…”

“…CHI3L1 alone induced CXCL10 and CXCR3 expression at 4 h, mostly in the basal layers of the epithelium. This is different from flagellin-treated corneas, where CXCR3-positive cells were found in the stroma beneath the epithelium (29). At 1 dpi, as shown above, CXCL10 was mostly expressed in the damaged epithelium, while CXCR3 was found in the infiltrating cells in the stroma or in an intraepithelial cell cluster that contained mainly natural killer cells and neutrophils (29).…”

“…Our recent studies of P. aeruginosa keratitis identified CXCL10 as a major chemokine induced by infection and augmented by flagellin pretreatment in a gamma interferon-and interferon regulatory factor 1 (IRF1)-dependent manner (30). We also found that epithelium-expressed CXCL10 had fungicidal activity and played a role in C. albicans eradication in mouse corneas (29). We next investigated whether CHI3L1 regulates CXCL10 expression and CXCR3 signaling in vivo.…”

“…We showed that CHI3L1 expression was induced in response to C. albicans infection and that flagellin pretreatment greatly augmented this upregulation in B6 mouse corneas. While the downregulation of CHI3L1 increases the severity of C. albicans keratitis, recombinant CHI3L1 prevented corneal infection through its ability to induce the expression of antimicrobial peptides (AMPs) and the chemokine CXCL10, which was recently shown to control fungal burden in a CXCR3-dependent manner (29), in the corneas. Our results reveal that CHI3L1 plays a role in regulating mucosal innate immunity against fungal infection and that it might be developed as an adjuvant treatment for microbial keratitis.…”

Toll-like receptor-5 agonist, entolimod, suppresses metastasis and induces immunity by stimulating an NK-dendritic-CD8 + T-cell axis

“…A recent study demonstrated that flagellin up-regulated CXCL10 expression in the cornea and that this contributed to fungal clearance through a CXCR3-dependent NK cell response (43). CXCL9, CXCL10, and CXCL11 are members of the IFN-inducible CXC chemokine family that act through interaction with the CXCR3 (44,45) receptor found on a variety of cell types, including NK cells (45,46).…”