In Vivo and In Vitro Impairments in T Helper Cell and Neutrophil Responses against Mucor irregularis in Card9 Knockout Mice

Abstract

Mucor irregularis is a frequently found fungus in Asia, especially China, and it causes primary cutaneous mucormycosis with a high rate of disfigurement. Caspase recruitment domain-containing protein 9 (Card9) is an essential adaptor molecule downstream of C-type lectin receptors. It mediates the activation of nuclear factor kappa B (NF-κB), regulates T helper (Th)1 and Th17 differentiation and plays an important role in fungal immune surveillance. CARD9 deficiency correlates with the increased susceptibility to many fungal infections, including cutaneous mucormycosis caused by M. irregularis. However, the underlying immunological mechanisms were not elucidated. Our study established a murine model of subcutaneous M. irregularis infection, and we isolated immune cells, including bone marrow-derived macrophages, bone marrow-derived dendritic cells, naïve T cells and neutrophils, from wild-type (WT) and Card9 knockout (Card9-/-) mice to examine the antifungal effect of Card9 on M. irregularis in vivo and in vitro. Card9-/- mice exhibited increased susceptibility to M. irregularis infection. Impaired local cytokine and chemokine production, NF-κB (p65) activation and Th1/17 cell differentiation and partially impaired neutrophil-dependent antifungal immunity were observed in Card9-/- mice. This work enriches our knowledge of the relationship between CARD9 deficiency and mucormycosis.

CARD9 in host immunity to fungal, bacterial, viral, and parasitic infections: An update

“…Local infection provides the necessary CXC signal to induce neutrophil recruitment indirectly, in which CARD9 has been proven to play a crucial part. Recent studies found that the neutrophil-targeting chemokines CXCL1 and CXCL2 were a low expression in Card9 −/− mice, and CARD9 could promote the neutrophils chemotaxis by regulating the production of neutrophil-recruiting IL-1β and CXCL1 in the central nervous system, thereby confirming the importance of CARD9 in neutrophil-induced immune response (Drummond et al, 2019 ; Sun et al, 2021 ). In addition to these, the increased susceptibility of Card9 −/− mice to R. arrhizus and M. irregularis were reported as well, and they were attributed to impaired cytokine and chemokine production, NF-κB (p65) activation, and Th cell differentiation (Sun et al, 2019 , 2021 ).…”

“…Remarkably, neutrophil phagocytosis and reactive oxygen species (ROS) production remained normal. Similarly, in a study of susceptibility to M. irregularis , the release of neutrophil extracellular traps (NETs) and the expression of IL-6 and TNF-α showed an impaired state in neutrophils, whereas intact phagocytosis and ROS production were observed (Sun et al, 2021 ). Different from the impaired neutrophil antifungal immunity, the functions of phagocytosis and ROS production are seemingly conflicting.…”

“…Earlier studies have found that a deficiency of CARD9 makes many fungi susceptible (Wu et al, 2018 ), such as Cryptococcus neoformans (Yamamoto et al, 2014 ) and Phialophora verrucose (Wu et al, 2016 ). However, recent studies have further broadened this range by proving the susceptibility to Aspergillus (Zhang et al, 2021 ), Pneumocystis (Kottom et al, 2020b ), Mucor irregularis (Sun et al, 2021 ), and Rhizopus arrhizus (Sun et al, 2019 ). For instance, Guo et al ( 2019 ) reported that individuals with homozygous CARD9 alleles (C/C) were more susceptible to Pallidocercospora crystalline compared to those with heterozygous (G/C) or wild-type (G/G) CARD9 alleles.…”

Role of CARD9 in Cell- and Organ-Specific Immune Responses in Various Infections

“…CARD9-deficient mice exhibited increased susceptibility to M. irregularis infection and impaired cytokine and chemokine production compared to the wild type [ 49 ]. Cytokines (IL-1β, IL-6, IL-12p70, IL-17A, IL-23, IFN-γ, and TNF-α) and chemokines (CXCL1 and CXCL2) were reduced in CARD9-deficient mice in response to an M. irregularis infection, but IL-4, IL-10, IL-17A, and IFN-γ increased over time to the levels of the wild type [ 49 ]. Neutrophils of CARD9-deficient mice showed reduced formation of neutrophil extracellular traps (NETs), and BMDMs showed impaired NF-κB activation [ 49 ].…”

What Is New in Pulmonary Mucormycosis?

“…Few cases of mucormycosis have also been reported among other primary immune deficiencies, including caspase recruitment domain-containing protein 9 (CARD9) deficiency and STAT1 gain-of-function [ 63 , 64 ]. Finally, neutrophil responses and T Helper cell were impaired in CARD9 knockout mice in a model of subcutaneous Mucor irregularis infection [ 65 ].…”