Grant: CIHR Fellowship

Patients with mutations in the caspase recruitment domain-containing protein 9 (CARD9) gene are prone to many types of invasive fungal infections, as the protein CARD9 is critically involved in the recognition of fungal pathogens. Strikingly, these patients frequently present with life-threatening fungal infections in the brain, which are difficult to treat due to a lack of therapeutic options. Fungal brain infections develop in CARD9 deficient patients due to an inability to recruit immune cells to the site of infection, largely due to a defect of the resident immune cells of the brain, the microglia. However, evidence suggests that the requirement of CARD9 is not restricted to microglia, and that other cell types of the brain play a key role in mounting an immune response. We will take an unbiased approach to investigate other potential Card9+ cell types by studying the response of normal and Card9-deficient mice to fungal brain infections using single-cell RNA and epigenetic sequencing. Through this approach we will determine what genes are expressed in response to infection by all immune and non-immune cells, and which genes are dependent on CARD9 signaling. We will then use this list of CARD9-dependent genes to do a more thorough study of the mechanism behind the immune response. We will determine which identified genes are necessary for an effective immune response through the use of genetic deletion mice and dissect the roles they play through immunophenotyping. Any clinically relevant findings we discover in mice will be confirmed using tissue samples obtained from our CARD9-deficient patients treated for fungal infections at our facility. Through this work we will expand our understanding of how the brain fights fungal infections, and to what extent it is orchestrated by CARD9 signaling. Additionally, this study will shed light on the brain's general antimicrobial response and has the potential to identify novel cell types participating in this response.