Delinking CARD9 and IL-17: CARD9 Protects against Candida tropicalis Infection through a TNF-α-Dependent, IL-17-Independent Mechanism.

Natasha Whibley,Julie A Taylor,Gordon D Brown,Delyth Reid,Sarah L Gaffen,Cornelius J Clancy,Partha S Biswas,M Hong Nguyen,Jillian R Jaycox,Abhishek V Garg,Mandy J Mcgeachy

doi:10.4049/jimmunol.1500870

Abstract

Candida is the third most common cause of bloodstream infections in hospitalized patients. Immunity to C. albicans, the most frequent species to be isolated in candidiasis, involves a well-characterized Dectin-1/caspase-associated recruitment domain adaptor 9 (CARD9)/IL-17 signaling axis. Infections caused by non-albicans Candida species are on the rise, but surprisingly little is known about immunity to these pathogens. In this study, we evaluated a systemic infection model of C. tropicalis, a clinically relevant, but poorly understood, non-albicans Candida. Mice lacking CARD9 were profoundly susceptible to C. tropicalis, displaying elevated fungal burdens in visceral organs and increased mortality compared with wild-type (WT) controls. Unlike C. albicans, IL-17 responses were induced normally in CARD9−/− mice following C. tropicalis infection. Moreover, there was no difference in susceptibility to C. tropicalis infection between WT and IL-23p19−/−, IL-17RA−/−, or Act1−/− mice. However, TNF-α expression was markedly impaired in CARD9−/− mice. Consistently, WT mice depleted of TNF-α were more susceptible to C. tropicalis, and CARD9-deficient neutrophils and monocytes failed to produce TNF-α following stimulation with C. tropicalis Ags. Both neutrophils and monocytes were necessary for defense against C. tropicalis, because their depletion in WT mice enhanced susceptibility to C. tropicalis. Disease in CARD9−/− mice was not due to defective neutrophil or monocyte recruitment to infected kidneys. However, TNF-α treatment of neutrophils in vitro enhanced their ability to kill C. tropicalis. Thus, protection against systemic C. tropicalis infection requires CARD9 and TNF-α, but not IL-17, signaling. Moreover, CARD9-dependent production of TNF-α enhances the candidacidal capacity of neutrophils, limiting fungal disease during disseminated C. tropicalis infection.

Highlights

Materials and MethodsWild-type (WT) mice (C57BL/6) were from The Jackson Laboratory (Bar Harbor, ME). Rag22/2 and Rag22/2Il2rg2/2 mice were from Taconic Farms
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Only the yeast form of C. tropicalis was observed in WT kidneys, whereas both yeast and filamentous hyphae were detected in CARD92/2 kidneys (Fig. 1D), suggesting that an effective immune response limits hyphal formation in vivo

Summary

Materials and Methods

Wild-type (WT) mice (C57BL/6) were from The Jackson Laboratory (Bar Harbor, ME). Rag22/2 and Rag22/2Il2rg2/2 mice were from Taconic Farms. Mice were injected via the tail vein with 100 ml sterile saline or 1 3 104 CFU/g C. tropicalis yeast cells. Serial dilutions of organ homogenates were plated on yeast extract peptone dextrose agar with antibiotics, and fungal burdens were determined by CFU enumeration. To assess neutrophil and monocyte depletion, blood was collected from the tail vein immediately before C. albicans infection on day 0, and cell populations were enumerated by flow cytometry. Blood cells were treated or not with HK C.t with Golgi Plug (BD Biosciences) for 3 h, and TNF-a was measured by flow cytometry. Neutrophils and monocytes from bone marrow or blood were plated at 1 3 105 cells/well. C. tropicalis was added to neutrophils or monocytes at 0.5 3 105 yeast cells/well (ratio of 2:1).

Results

Discussion

Disclosures