Description
The Role of the CARD9/GM-CSF Axis in Immunity to Candida albicans
M. Landekic, M.Sc.1, I. Angers, M.Sc.3, S. Qureshi, M.D.2,3, M. Divangahi, PhD,1,3, D. Vinh, M.D.2,3,4
1Dept of Microbiology and Immunology, 2Dept of Medicine, McGill University; 3Meakins-Christie Institue, Montreal, Canada;4Infectious Diseases in Global Health, RI-MUHC, Montreal, Canada
Introduction: Candida albicans is an opportunistic fungal pathogen with a propensity for systemic disease as well as a high mortality rate. The recently identified p.Y91H mutation in the gene for Caspase Recruitment Domain-containing protein 9 (CARD9) causes invasive candidiasis in the central nervous system, termed “spontaneous CNS candidiasis” (sCNSc). How this mutation leads to invasive candidiasis is poorly understood. CARD9 is selectively expressed by myeloid cells, especially macrophages and monocytes. Monocyte-derived cells from p.Y91H patients showed impaired expression of the gene csf2, which codes for granulocyte and macrophage colony stimulating factor (GM-CSF). Patients with sCNSc treated with adjunt GM-CSF cleared the infection where anti-fungal therapy alone was insufficient. The mechanism of CARD9-mediated GM-CSF protection during anti-fungal immunity remains enigmatic.
Methods: A knock-in mouse model of CARD9Y91H was generated using CRISPR/Cas9 gene editing. Disseminated candidiasis was modelled using I.V. inoculation with C. albicans SC5413. Mortality was evaluated by Kaplan-Meier analysis. Histopathology of brain tissue was done to assess extent of fungal growth and in vivo host response. Immunophenotyping of the myeloid compartment was done by multi-parametric flow cytometry. Bone-marrow derived macrophages were challenged with C. albicans yeast, and qPCR performed to assess csf2 expression levels.
Results: When compared to age/sex-matched infected CARD9-wild-type controls, mice homozygous for the p.Y91H mutation demonstrate significantly earlier morbidity and mortality. The immune response to infection is impaired in the brain, with a specific defect in the microglia compartment of CARD9p.Y91H mice. BMDM derived from CARD9p.Y91H mice showed impaired csf2 expression upon C. albicans challenge.
Conclusions: This model of CARD9 deficiency can now be used to assess the role of GM-CSF and myeloid cells in the response to disseminated candidiasis, helping us to understand the mechanisms of CARD9-mediated GM-CSF protection during anti-fungal immunity.