Card9 Broadly Regulates Host Immunity against Experimental Pulmonary Cryptococcus neoformans 52D Infection.

The ubiquitous soil-associated fungus Cryptococcus neoformans causes pneumonia that may progress to fatal meningitis. Recognition of fungal cell walls by C-type lectin receptors (CLRs) has been shown to trigger the host immune response. Caspase recruitment domain-containing protein 9 (Card9) is an intracellular adaptor that is downstream of several CLRs. Experimental studies have implicated Card9 in host resistance against C. neoformans ; however, the mechanisms that are associated with susceptibility to progressive infection are not well defined. To further characterize the role of Card9 in cryptococcal infection, Card9 ^em1Sq mutant mice that lack exon 2 of the Card9 gene on the Balb/c genetic background were created using CRISPR-Cas9 genome editing technology and intratracheally infected with C. neoformans 52D. Card9 ^em1Sq mice had significantly higher lung and brain fungal burdens and shorter survival after C. neoformans 52D infection. Susceptibility of Card9 ^em1Sq mice was associated with lower pulmonary cytokine and chemokine production, as well as reduced numbers of CD4 ⁺ lymphocytes, neutrophils, monocytes, and dendritic cells in the lungs. Histological analysis and intracellular cytokine staining of CD4 ⁺ T cells demonstrated a Th2 pattern of immunity in Card9 ^em1Sq mice. These findings demonstrate that Card9 broadly regulates the host inflammatory and immune response to experimental pulmonary infection with a moderately virulent strain of C. neoformans .