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

Development of a Combat-Relevant Murine Model of Wound Mucormycosis: A Platform for the Pre-Clinical Investigation of Novel Therapeutics for Wound-Invasive Fungal Diseases

Wound-invasive fungal diseases (WIFDs), especially mucormycosis, have emerged as life-threatening infections during recent military combat operations. Many combat-relevant fungal pathogens are refractory to current antifungal therapy. Therefore, animal models of WIFDs are urgently needed to investigate new therapeutic solutions. Our study establishes combat-relevant murine models of wound mucormycosis using Rhizopus arrhizus and Lichtheimia corymbifera, two Mucorales species that cause wound mucormycosis worldwide. These models recapitulate the characteristics of combat-related wounds from explosions, including blast overpressure exposure, full-thickness skin injury, fascial damage, and muscle crush. The independent inoculation of both pathogens caused sustained infections and enlarged wounds. Histopathological analysis confirmed the presence of necrosis and fungal hyphae in the wound bed and adjacent muscle tissue. Semi-quantification of fungal burden by colony-forming units corroborated the infection. Treatment with liposomal amphotericin B, 30 mg/kg, effectively controlled R. arrhizus growth and significantly reduced residual fungal burden in infected wounds (p < 0.001). This study establishes the first combat-relevant murine model of wound mucormycosis, paving the way for developing and evaluating novel antifungal therapies against combat-associated WIFDs.

Molecular mechanisms that govern infection and antifungal resistance in Mucorales

SUMMARYThe World Health Organization has established a fungal priority pathogens list that includes species critical or highly important to human health. Among them is the order Mucorales, a fungal group comprising at least 39 species responsible for the life-threatening infection known as mucormycosis. Despite the continuous rise in cases and the poor prognosis due to innate resistance to most antifungal drugs used in the clinic, Mucorales has received limited attention, partly because of the difficulties in performing genetic manipulations. The COVID-19 pandemic has further escalated cases, with some patients experiencing the COVID-19-associated mucormycosis, highlighting the urgent need to increase knowledge about these fungi. This review addresses significant challenges in treating the disease, including delayed and poor diagnosis, the lack of accurate global incidence estimation, and the limited treatment options. Furthermore, it focuses on the most recent discoveries regarding the mechanisms and genes involved in the development of the disease, antifungal resistance, and the host defense response. Substantial advancements have been made in identifying key fungal genes responsible for invasion and tissue damage, host receptors exploited by the fungus to invade tissues, and mechanisms of antifungal resistance. This knowledge is expected to pave the way for the development of new antifungals to combat mucormycosis. In addition, we anticipate significant progress in characterizing Mucorales biology, particularly the mechanisms involved in pathogenesis and antifungal resistance, with the possibilities offered by CRISPR-Cas9 technology for genetic manipulation of the previously intractable Mucorales species.

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

The caspase recruitment domain-containing protein 9 (CARD9) is an intracellular adaptor protein that is abundantly expressed in cells of the myeloid lineage, such as neutrophils, macrophages, and dendritic cells. CARD9 plays a critical role in host immunity against infections caused by fungi, bacteria, and viruses. A CARD9 deficiency impairs the production of inflammatory cytokines and chemokines as well as migration and infiltration, thereby increasing susceptibility to infections. However, CARD9 signaling varies depending on the pathogen causing the infection. Furthermore, different studies have reported altered CARD9-mediated signaling even with the same pathogen. Therefore, this review focuses on and elucidates the current literature on varied CARD9 signaling in response to various infectious stimuli in humans and experimental mice models.

Hyphae of Rhizopus arrhizus and Lichtheimia corymbifera Are More Virulent and Resistant to Antifungal Agents Than Sporangiospores In Vitro and in Galleria mellonella

Mucorales species cause debilitating, life-threatening sinopulmonary diseases in immunocompromised patients and penetrating wounds in trauma victims. Common antifungal agents against mucormycosis have significant toxicity and are often ineffective. To evaluate treatments against mucormycosis, sporangiospores are typically used for in vitro assays and in pre-clinical animal models of pulmonary infections. However, in clinical cases of wound mucormycosis caused by traumatic inoculation, hyphal elements found in soil are likely the form of the inoculated organism. In this study, Galleria mellonella larvae were infected with either sporangiospores or hyphae of Rhizopus arrhizus and Lichtheimia corymbifera. Hyphal infections resulted in greater and more rapid larval lethality than sporangiospores, with an approximate 10-16-fold decrease in LD50 of hyphae for R. arrhizus (p = 0.03) and L. corymbifera (p = 0.001). Liposomal amphotericin B, 10 mg/kg, was ineffective against hyphal infection, while the same dosage was effective against infections produced by sporangiospores. Furthermore, in vitro, antifungal susceptibility studies show that minimum inhibitory concentrations of several antifungal agents against hyphae were higher when compared to those of sporangiospores. These findings support using hyphal elements of Mucorales species for virulence testing and antifungal drug screening in vitro and in G. mellonella for studies of wound mucormycosis.

Percentage of Th1 and Th17 cells and serum level of IL-17 and IFN-γ cytokines in COVID-19-associated mucormycosis

The considerable number of the 2019 coronavirus disease (COVID-19) patients who developed mucormycosis infections in West and Central Asia urged a need to investigate the underlying causes of this fatal complication. It was hypothesized that an immunocompromised state secondary to the excessive administration of anti-inflammatory drugs was responsible for the outburst of mucormycosis in COVID-19 patients. Therefore, we aimed to study the implication of two major subsets of adaptive immunity T helper (Th)-1 and Th17 cells in disease development. Thirty patients with COVID-19-associated mucormycosis, 38 with COVID-19 without any sign or symptom of mucormycosis, and 26 healthy individuals were included. The percentage of Th1 and Th17 cells in peripheral blood, as well as the serum levels of interleukin (IL)-17 and interferon-gamma (IFN-γ), were evaluated using flow cytometry and ELISA techniques, respectively. Th17 cell percentage in patients with COVID-19-associated mucormycosis was significantly lower than in COVID-19 patients (P-value: <0.001) and healthy subjects (P-value: 0.01). In addition, the serum level of IL-17 in COVID-19 patients was significantly higher than that of healthy individuals (P-value: 0.01). However, neither the frequency of Th1 cells nor the serum level of IFN-γ was different between the study groups. Given the critical role of Th17 cells in the defense against mucosal fungal infections, these findings suggest that low numbers of Th17 and insufficient levels of IL-17 might be a predisposing factor for the development of mucormycosis during or after COVID-19 infection.

What Is New in Pulmonary Mucormycosis?

Mucormycosis is a rare but life-threatening fungal infection due to molds of the order Mucorales. The incidence has been increasing over recent decades. Worldwide, pulmonary mucormycosis (PM) presents in the lungs, which are the third main location for the infection after the rhino-orbito-cerebral (ROC) areas and the skin. The main risk factors for PM include hematological malignancies and solid organ transplantation, whereas ROC infections are classically favored by diabetes mellitus. The differences between the ROC and pulmonary locations are possibly explained by the activation of different mammalian receptors—GRP78 in nasal epithelial cells and integrin β1 in alveolar epithelial cells—in response to Mucorales. Alveolar macrophages and neutrophils play a key role in the host defense against Mucorales. The diagnosis of PM relies on CT scans, cultures, PCR tests, and histology. The reversed halo sign is an early, but very suggestive, sign of PM in neutropenic patients. Recently, the serum PCR test showed a very encouraging performance for the diagnosis and follow-up of mucormycosis. Liposomal amphotericin B is the drug of choice for first-line therapy, together with correction of underlying disease and surgery when feasible. After a stable or partial response, the step-down treatment includes oral isavuconazole or posaconazole delayed release tablets until a complete response is achieved. Secondary prophylaxis should be discussed when there is any risk of relapse, such as the persistence of neutropenia or the prolonged use of high-dose immunosuppressive therapy. Despite these novelties, the mortality rate from PM remains higher than 50%. Therefore, future research must define the place for combination therapy and adjunctive treatments, while the development of new treatments is necessary.

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

Microbial infection, caused by fungi, bacteria, viruses, and parasites, significantly contributes to the global death burden and health costs. The innate and adaptive immune systems orchestrate a multifaceted signaling response to invading pathogens as the human antimicrobial system. In this process, caspase recruitment domain-containing protein 9 (CARD9) emerges as a critical intermediary adaptor molecule to participate in regulating a series of antimicrobial immune reactions. Previous publications have confirmed that CARD9 plays a crucial role in fungal, bacterial, viral, and parasitic infections. In this study, we aim to provide an update on the recent clinical and basic studies where the mechanism and function of CARD9 have been further studied and understood. In addition, we summarize the latest treatment and prevention strategies based on CARD9 and discuss the current perspectives and future direction of CARD9.