Role of IL-36γ/IL-36R Signaling in Corneal Innate Defense AgainstCandida albicansKeratitis

Abstract

PURPOSE. Interleukin (IL)-36 cytokines have been shown to play either beneficial or detrimental roles in the infection of mucosal tissues in a pathogen-dependent manner, but their involvement in fungal keratitis remains elusive. We herein investigated their expression and function in mediating corneal innate immunity against Candida albicans infection. METHODS.Gene expression in mouse corneas with or without C. albicans infection was determined by regular RT-and real-time (q)-PCR, Western blot analysis, ELISA or proteome profile assay. The severity of C. albicans keratitis was assessed using clinical scoring, bacterial counting, and myeloperoxidase (MPO) activity as an indicator of neutrophil infiltration. IL36R knockout mice and IL-33-specific siRNA were used to assess the involvement IL-33 signaling in C. albicans-infected corneas. B6 CD11c-DTR mice and clodronate liposomes were used to define the involvement of dendritic cells (DCs) and macrophages in IL-36R signaling and C. albicans keratitis, respectively.RESULTS. IL-36γ were up-regulated in C57BL6 mouse corneas in response to C. albicans infection. IL-36 receptor-deficient mice display increased severity of keratitis, with a higher fungal load, MPO, and IL-1β levels, and lower soluble sIL-1Ra and calprotectin levels. Exogenous IL-36γ prevented fungal keratitis pathogenesis with lower fungal load and MPO activity, higher expression of sIL-1Ra and calprotectin, and lower expression of IL-1β, at mRNA or protein levels. Protein array analysis revealed that the expression of IL-33 and REG3G were related to IL-36/IL36R signaling, and siRNA downregulation of IL-33 increased the severity of C. albicans keratitis. Depletion of dendritic cells or macrophages resulted in severe C. albicans keratitis and yet exhibited minimal effects on exogenous IL-36γ -induced protection against C. albicans infection in B6 mouse corneas. CONCLUSIONS.IL-36/IL36R signaling plays a protective role in fungal keratitis by promoting AMP expression and by suppressing fungal infection-induced expression of proinflammatory cytokines in a dendritic cell-and macrophage-independent manner.

Interleukin-36 Receptor Signaling Attenuates Epithelial Wound Healing in C57BL/6 Mouse Corneas

“…Our previous study revealed that the disturbance of IL-1β/IL-1Ra balanced expression is an important contributor to the pathogenesis of microbial keratitis and delayed epithelial wound healing in DM corneas [ 2 , 21 , 35 ]. To determine whether IL-36R signaling also modulates IL-1β and IL-1Ra expression, we assessed their expression levels in WT and IL-36R −/− mice with or without diabetes.…”

“…Our previous study showed that IL-36 cytokines have basal expression in corneas, particularly epithelial cells, unlike members of the IL-1 cytokine subfamily [ 21 , 35 ]. While IL-36β is expressed in monocytes, B cells, neurons, and glia, IL-36α is mostly expressed in skin adaptive cells and upregulated in injured kidneys associated with the development of renal pathologies as well as hepatocellular carcinoma and some inflammatory/immune diseases [ 38 , 39 ].…”

“…In many tissues, IL-1β and IL-1Ra are paired to control inflammation [ 51 ]. Our previous studies showed that increasing IL-1Ra expression and/or the IL-1Ra/IL-1β balance promotes epithelial wound healing and innate corneal defense against Candida albicans and Pa Keratitis [ 35 , 52 ]. This study provides further support for the positive role of IL-1Ra in promoting epithelial wound healing, particularly in diabetic corneas.…”

A murine commensal protozoan relievesClostridium difficileinfection through regulating the arginine metabolism and the host intestinal immune response

“…In inflammatory bowel disease, IL-36G was found to be expressed in intestinal epithelial cells, where the IL-36R signaling pathway control recruitment of white blood cells to the inflammatory site 38 . In Candida albicans infection 39 , Streptococcus pneumoniae 40,41 , and herpes simplex virus type 2 42 , IL-36G promotes the recruitment of neutrophils to inflammatory centers and accelerates phagocytosis and clearance of pathogens. Our results showed that CDI also caused the high expression of IL-36G, which may be related to the recruitment of neutrophil-scavenging bacteria by IL-36G, and the inflammatory response caused by excess neutrophils aggravated the intestinal injury.…”

Involvement of cGAS/STING Signaling in the Pathogenesis of Candida albicans Keratitis: Insights From Genetic and Pharmacological Approaches

“…C. albicans has been reported to be one of the main pathogens of FK, 41 , 42 and a murine C. albicans keratitis model has been widely used to investigate the pathogenesis and treatment of FK. 43 , 44 Recently, with the wide use of contact lenses and the abuse of glucocorticoids and antibiotics, C. albicans keratitis has become a worldwide problem, and its incidence is on the rise. 45 In this study, we established a C. albicans keratitis model to explore the involvement of cGAS/STING signaling in the pathogenesis of FK.…”