Methods: Functional analyses were performed in immune cells from a patient with CARD9 deficiency and Candida infection of the CNS. Wild-type (WT) and Card9 knockout (KO) mice were infected with Candida and the immune response in the infected CNS was assessed with a combination of cellular and molecular assays.
Results: Here, we report a novel CARD9 c.170G>A missense mutation in a child with Candida meningoencephalitis. Strikingly, the patient had a distinct absence of neutrophils in the cerebrospinal fluid (CSF) despite uncontrolled fungal disease. Absence of neutrophils in the CSF was not due to peripheral neutropenia, impaired neutrophil survival or a neutrophil-intrinsic chemotaxis defect. Instead, neutrophil-recruiting chemokines were absent in the patient CSF, which was not chemotactic for neutrophils ex vivo. We phenocopied the patient susceptibility in Card9-deficient mice, which developed uncontrolled brain candidiasis with profound tissue invasion, and had severely impaired neutrophil accumulation in the infected brain. Card9 was dispensable for neutrophil production in the bone marrow, egress into the blood, survival and induction of neutrophil-targeted adhesion molecules in the Card9-/- brain. While Card9-/- neutrophils showed no cell-intrinsic chemotaxis defect in mixed bone marrow chimera experiments, the induction of neutrophil-recruiting chemokines was significantly impaired in infected Card9-/-brains from both myeloid and non-myeloid cellular sources.
Conclusion: CARD9 is critical for control of fungal invasion in the CNS, acting to promote neutrophil trafficking from the blood into the infected tissue via production of neutrophil-targeted chemokines.
M. Swamydas, None
M. Lionakis, None