The Inflammasome NLRC4 Protects against Cryptococcus gattii by Inducing the Classic Caspase-1 to Activate the Pyroptosis Signal

Cryptococcus is one of the most pathogenic invasive fungi, and its interaction with the host's natural immunity, especially the role of the inflammasome family, has not been fully elucidated. As an important member of the inflammasome family, NOD-like receptor (NLR) family caspase recruitment domain (CARD) containing 4 (NLRC4) has been proven to protect lungs from damage from a variety of pathogens. In this study, we investigated the protective effect and mechanism of NLRC4 on cryptococcal pulmonary infection using NLRC4-/-mice in vivo and NLRC4-/-macrophages in vitro models stimulated by cryptococcal cells. We apply small animal fluorescence imaging to detect the fungal burden in the lungs and living body micro-CT scans of mice and in vitro tissue micro-CT scans to compare differences in infection foci nodules and histopathological lesions, and the activation of caspase-1 and downstream cytokines were detected by Western bolt and ELISA, etc. The results demonstrated that cryptococcal infection can activate the Nod-like receptors of caspase-1 activation and NLRC4 inflammasomes in macrophages and dendritic cells and affect downstream IL-1 beta and IL-18 release. After cryptococcal infection, the survival rate, lung fungal burden, and histopathological damage of NLRC4(-/-) mice were significantly impaired. NLRC4(-/-) macrophages showed a lower release of inflammatory factors, reactive oxygen species (ROS), and lactate dehydrogenase (LDH). Collectively, our results demonstrated that the activation of caspase-1 and downstream cytokines mediated by NLRC4 inflammasome in immune cells during Cryptococcus infection can enhance pyroptosis of macrophages, affect the phagocytic ability of macrophages, and inhibit the intracellular parasitism of cryptococcus, eventually reducing the burden of fungi.