CARD9 mediates Dectin-1-induced ERK activation by linking Ras-GRF1 to H-Ras for antifungal immunity

Innate immune signal transduction pathways to fungal infection: Components and regulation

Candida species are significant causes of mucosal and systemic infections in immune compromised populations, including HIV-infected individuals and cancer patients. Drug resistance and toxicity have limited the use of anti-fungal drugs. A good comprehension of the nature of the immune responses to the pathogenic fungi will aid in the developing of new approaches to the treatment of fungal diseases. In recent years, extensive research has been done to understand the host defending systems to fungal infections. In this review, we described how pattern recognition receptors senses the cognate fungal ligands and the cellular and molecular mechanisms of anti-fungal innate immune responses. Furthermore, particular focus is placed on how anti-fungal signal transduction cascades are being activated for host defense and being modulated to better treat the infections in terms of immunotherapy. Understanding the role that these pathways have in mediating host anti-fungal immunity will be crucial for future therapeutic development.

Increased susceptibility to Mycobacterium avium complex infection in miniature Schnauzer dogs caused by a codon deletion in CARD9

Mammals are generally resistant to Mycobacterium avium complex (MAC) infections. We report here on a primary immunodeficiency disorder causing increased susceptibility to MAC infections in a canine breed. Adult Miniature Schnauzers developing progressive systemic MAC infections were related to a common founder, and pedigree analysis was consistent with an autosomal recessive trait. A genome-wide association study and homozygosity mapping using 8 infected, 9 non-infected relatives, and 160 control Miniature Schnauzers detected an associated region on chromosome 9. Whole genome sequencing of 2 MAC-infected dogs identified a codon deletion in the CARD9 gene (c.493_495del; p.Lys165del). Genotyping of Miniature Schnauzers revealed the presence of this mutant CARD9 allele worldwide, and all tested MAC-infected dogs were homozygous mutants. Peripheral blood mononuclear cells from a dog homozygous for the CARD9 variant exhibited a dysfunctional CARD9 protein with impaired TNF-α production upon stimulation with the fungal polysaccharide β-glucan that activates the CARD9-coupled C-type lectin receptor, Dectin-1. While CARD9-deficient knockout mice are susceptible to experimental challenges by fungi and mycobacteria, Miniature Schnauzer dogs with systemic MAC susceptibility represent the first spontaneous animal model of CARD9 deficiency, which will help to further elucidate host defense mechanisms against mycobacteria and fungi and assess potential therapies for animals and humans.

Mitochondria-mediated ferroptosis induced by CARD9 ablation prevents MDSCs-dependent antifungal immunity

BACKGROUND

Caspase Recruitment Domain-containing protein 9 (CARD9) expressed in myeloid cells has been demonstrated to play an antifungal immunity role in protecting against disseminated candidiasis. Hereditary CARD9 ablation leads to fatal disseminated candidiasis. However, the myeloid cell types and molecular mechanisms implicated in CARD9 protecting against disseminated candidiasis remain wholly elusive.

METHODS

The role of CARD9 ablation in exacerbating disseminated candidiasis was determined in vivo and in vitro. The molecular mechanism by which CARD9 ablation promotes acute kidney injury in disseminated candidiasis was identified by RNA-sequencing analysis. The expression of mitochondrial proteins and ferroptosis-associated proteins were measured by Quantitative real-time PCR and western blot.

RESULTS

CARD9 ablation resulted in a reduced proportion of myeloid-derived suppressor cells (MDSCs) and a substantially lower expression of solute carrier family 7 member 11 (SLC7A11) in the kidneys, which increased susceptibility to acute kidney injury and renal ferroptosis during disseminated Candida tropicalis (C. tropicalis) infection. Moreover, CARD9-deficient MDSCs were susceptible to ferroptosis upon stimulation with C. tropicalis, which was attributed to augmented mitochondrial oxidative phosphorylation (OXPHOS) caused by reduced SLC7A11 expression. Mechanistically, C-type lectin receptors (CLRs)-mediated recognition of C. tropicalis promoted the expression of SLC7A11 which was transcriptionally manipulated by the Syk-PKCδ-CARD9-FosB signaling axis in MDSCs. FosB enhanced SLC7A11 transcription by binding to the promoter of SLC7A11 in MDSCs stimulated with C. tropicalis. Mitochondrial OXPHOS, which was negatively regulated by SLC7A11, was responsible for inducing ferroptosis of MDSCs upon C. tropicalis stimulation. Finally, pharmacological inhibition of mitochondrial OXPHOS or ferroptosis significantly increased the number of MDSCs in the kidneys to augment host antifungal immunity, thereby attenuating ferroptosis and acute kidney injury exacerbated by CARD9 ablation during disseminated candidiasis.

CONCLUSIONS

Collectively, our findings show that CARD9 ablation enhances mitochondria-mediated ferroptosis in MDSCs, which negatively regulates antifungal immunity. We also identify mitochondria-mediated ferroptosis in MDSCs as a new molecular mechanism of CARD9 ablation-exacerbated acute kidney injury during disseminated candidiasis, thus targeting mitochondria-mediated ferroptosis is a novel therapeutic strategy for acute kidney injury in disseminated candidiasis.

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.

Regulatory roles of CARD9-BCL10-Rac1 (CBR) signalome in islet β-cell function in health and metabolic stress: Is there room for MALT1?

It is widely accepted that pancreatic islet β-cell failure and the onset of type 2 diabetes (T2DM) constitute an intricate interplay between the genetic expression of the disease and a host of intracellular events including increased metabolic (oxidative, endoplasmic reticulum) stress under the duress of glucolipotoxicity. Emerging evidence implicates unique roles for Caspase Recruitment Domain containing protein 9 (CARD9) in the onset of metabolic diseases, including obesity and insulin resistance. Mechanistically, CARD9 has been implicated in the regulation of p38MAPK and NFkB signaling pathways culminating in cellular dysfunction. Several regulatory factors, including B-cell lymphoma/leukemia 10 (BCL10) have been identified as modulators of CARD9 function in multiple cell types. Despite this evidence on regulatory roles of CARD9-BCL10 signalome in the onset of various pathological states, putative roles of this signaling module in islet β-cell dysfunction in metabolic stress remain less understood. This brief review is aimed at highlighting roles for CARD9 in islet β-cell function under acute (physiological insulin secretion) and long-term (cell dysfunction) exposure to glucose. Emerging roles of other signaling proteins, such as Rac1, BCL10 and MALT1 as contributors to CARD9 signaling in the islet β-cells are also reviewed. Potential avenues for future research toward the development of novel therapeutics for the prevention CARD9-BCL10-Rac1 (CBR) signalome-induced β-cell defects under metabolic stress are discussed.

Pathogenicity and virulence of Aspergillus fumigatus

Pulmonary infections caused by the mould pathogen Aspergillus fumigatus are a major cause of morbidity and mortality globally. Compromised lung defences arising from immunosuppression, chronic respiratory conditions or more recently, concomitant viral or bacterial pulmonary infections are recognised risks factors for the development of pulmonary aspergillosis. In this review, we will summarise our current knowledge of the mechanistic basis of pulmonary aspergillosis with a focus on emerging at-risk populations.

Regulatory Roles of Histone Deacetylation in Metabolic Stress-Induced Expression of Caspase Recruitment Domain-Containing Protein 9 (CARD9) in Pancreatic β-Cells

CARD9, a scaffolding protein, has been implicated in the pathogenesis of metabolic diseases, including obesity and diabetes. We recently reported novel roles for CARD9 in islet β-cell dysregulation under duress of gluco (HG)- and glucolipotoxic (GLT) stress. CARD9 expression was also increased in β-cells following exposure to HG and GLT stress. The current study is aimed at understanding the putative roles of histone deacetylation in HG- and GLT-induced expression of CARD9. Using two structurally distinct inhibitors of histone deacetylases (HDACs), namely trichostatin (TSA) and suberoylanilide hydroxamic acid (SAHA), we provide the first evidence to suggest that the increased expression of CARD9 seen under duress of HG and GLT stress is under the regulatory control of histone deacetylation. Interestingly, the expression of protein kinase Cδ (PKCδ), a known upstream regulator of CARD9 activation, is also increased under conditions of metabolic stress. However, it is resistant to TSA and SAHA, suggesting that it is not regulated via histone deacetylation. Based on these data, we propose that targeting the appropriate HDACs, which mediate the expression (and function) of CARD9, might be the next step to further enhance our current understanding of the roles of CARD9 in islet dysfunction under metabolic stress and diabetes.

Macrophage CARD9 mediates cardiac injury following myocardial infarction through regulation of lipocalin 2 expression

Immune cell infiltration in response to myocyte death regulates extracellular matrix remodeling and scar formation after myocardial infarction (MI). Caspase-recruitment domain family member 9 (CARD9) acts as an adapter that mediates the transduction of pro-inflammatory signaling cascades in innate immunity; however, its role in cardiac injury and repair post-MI remains unclear. We found that Card9 was one of the most upregulated Card genes in the ischemic myocardium of mice. CARD9 expression increased considerably 1 day post-MI and declined by day 7 post-MI. Moreover, CARD9 was mainly expressed in F4/80-positive macrophages. Card9 knockout (KO) led to left ventricular function improvement and infarct scar size reduction in mice 28 days post-MI. Additionally, Card9 KO suppressed cardiomyocyte apoptosis in the border region and attenuated matrix metalloproteinase (MMP) expression. RNA sequencing revealed that Card9 KO significantly suppressed lipocalin 2 (Lcn2) expression post-MI. Both LCN2 and the receptor solute carrier family 22 member 17 (SL22A17) were detected in macrophages. Subsequently, we demonstrated that Card9 overexpression increased LCN2 expression, while Card9 KO inhibited necrotic cell-induced LCN2 upregulation in macrophages, likely through NF-κB. Lcn2 KO showed beneficial effects post-MI, and recombinant LCN2 diminished the protective effects of Card9 KO in vivo. Lcn2 KO reduced MMP9 post-MI, and Lcn2 overexpression increased Mmp9 expression in macrophages. Slc22a17 knockdown in macrophages reduced MMP9 release with recombinant LCN2 treatment. In conclusion, our results demonstrate that macrophage CARD9 mediates the deterioration of cardiac function and adverse remodeling post-MI via LCN2.

How metals fuel fungal virulence, yet promote anti-fungal immunity

Invasive fungal infections represent a significant global health problem, and present several clinical challenges, including limited treatment options, increasing rates of antifungal drug resistance and compounding comorbidities in affected patients. Metals, such as copper, iron and zinc, are critical for various biological and cellular processes across phyla. In mammals, these metals are important determinants of immune responses, but pathogenic microbes, including fungi, also require access to these metals to fuel their own growth and drive expression of major virulence traits. Therefore, host immune cells have developed strategies to either restrict access to metals to induce starvation of invading pathogens or deploy toxic concentrations within phagosomes to cause metal poisoning. In this Review, we describe the mechanisms regulating fungal scavenging and detoxification of copper, iron and zinc and the importance of these mechanisms for virulence and infection. We also outline how these metals are involved in host immune responses and the consequences of metal deficiencies or overloads on how the host controls invasive fungal infections.

Role of Dectin-1 in immune response of macrophages induced by Fonsecaea monophora wild strain and melanin-deficient mutant strain

Chromoblastomycosis is a chronic granulomatous subcutaneous fungal disease caused mainly by Fonsecaea monophora in southern China. Melanin is an important virulence factor in wild strain (Mel+), and the strains lack of the polyketide synthase gene is a melanin-deficient mutant strain (Mel-). We investigated the effect of melanin in F. monophora on Dectin-1 receptor-mediated immune responses in macrophages. Conidia and tiny hyphae of Mel+ and Mel- were co-cultured with THP-1 macrophages expressing normal or low levels of Dectin-1. Compare the killing rate, phagocytosis rate, and expression levels of the inflammatory cytokines tumour necrosis factor-α, interleukin-1β, interleukin-6, and nitric oxide in each group. The results showed that the killing rate, phagocytosis rate, and pro-inflammatory factor levels of Mel+ infected macrophages with normal expression of Dectin-1 were lower than those of Mel-. And the knockdown of Dectin-1 inhibited the phagocytic rate, killing rate, and proinflammatory factor expression in macrophages infected with Mel+ and Mel-. And there was no significant difference in the above indexes between Mel+ and Mel- groups in Dectin-1 knockdown macrophages. In summary, the study reveals that melanin of F. monophora inhibits the immune response effect of the host by hindering its binding to Dectin-1 on the surface of macrophage, which may lead to persistent fungal infections.

Innate (learned) memory

With the growing body of evidence, it is now clear that not only adaptive immune cells but also innate immune cells can mount a more rapid and potent nonspecific immune response to subsequent exposures. This process is known as trained immunity or innate (learned) immune memory. This review discusses the different immune and nonimmune cell types of the central and peripheral immune systems that can develop trained immunity. This review highlights the intracellular signaling and metabolic and epigenetic mechanisms underlying the formation of innate immune memory. Finally, this review explores the health implications together with the potential therapeutic interventions harnessing trained immunity.

Heterozygous CARD9 mutation favors the development of allergic bronchopulmonary aspergillosis

BACKGROUND

Previous research demonstrated that a homozygous mutation of g.136372044G>A (S12N) in caspase recruitment domain family member 9 ( CARD9 ) is critical for producing Aspergillus fumigatus -induced ( Af -induced) T helper 2 (T H 2)-mediated responses in allergic bronchopulmonary aspergillosis (ABPA). However, it remains unclear whether the CARD9S12N mutation, especially the heterozygous occurrence, predisposes the host to ABPA.

METHODS

A total of 61 ABPA patients and 264 controls (including 156 healthy controls and 108 asthma patients) were recruited for sequencing the CARD9 locus to clarify whether patients with this heterozygous single-nucleotide polymorphisms are predisposed to the development of ABPA. A series of in vivo and in vitro experiments, such as quantitative real-time polymerase chain reaction, flow cytometry, and RNA isolation and quantification, were used to illuminate the involved mechanism of the disease.

RESULTS

The presence of the p.S12N mutation was associated with a significant risk of ABPA in ABPA patients when compared with healthy controls and asthma patients, regardless of Aspergillus sensitivity. Relative to healthy controls without relevant allergies, the mutation of p.S12N was associated with a significant risk of ABPA (OR: 2.69 and 4.17 for GA and AA genotypes, P = 0.003 and 0.029, respectively). Compared with patients with asthma, ABPA patients had a significantly higher heterozygous mutation (GA genotype), indicating that p.S12N might be a significant ABPA-susceptibility locus ( aspergillus sensitized asthma: OR: 3.02, P = 0.009; aspergillus unsensitized asthma: OR: 2.94, P = 0.005). The mutant allele was preferentially expressed in ABPA patients with heterozygous CARD9S12N , which contributes to its functional alterations to facilitate Af -induced T H 2-mediated ABPA development. In terms of mechanism, Card9 wild-type ( Card9WT ) expression levels decreased significantly due to Af -induced decay of its messenger RNA compared to the heterozygous Card9S12N . In addition, ABPA patients with heterozygous CARD9S12N had increased Af -induced interleukin-5 production.

CONCLUSION

Our study provides the genetic evidence showing that the heterozygous mutation of CARD9S12N , followed by allele expression imbalance of CARD9S12N , facilitates the development of ABPA.

The nucleotide receptor STING translocates to the phagosomes to negatively regulate anti-fungal immunity

STING (stimulator of interferon genes) exerts protective cellular responses to viral infection via induction of interferon production and autophagy. Here, we report the role of STING in modulating the immune responses toward fungal infection. Upon Candida albicans stimulation, STING transited alongside the endoplasmic reticulum (ER) to the phagosomes. In phagosomes, STING directly bound with Src via the N-terminal 18 amino acids of STING, and this binding prevented Src from recruiting and phosphorylating Syk. Consistently, Syk-associated signaling and production of pro-inflammatory cytokines and chemokines were increased in mouse BMDCs (bone-marrow-derived dendritic cells) lacking STING with fungal treatment. STING deficiency improved anti-fungal immunity in systemic C. albicans infection. Importantly, administration of the N-terminal 18-aa (amino acid) peptide of STING improved host outcomes in disseminated fungal infection. Overall, our study identifies a previously unrecognized function of STING in negatively regulating anti-fungal immune responses and offers a potential therapeutic strategy for controlling C. albicans infection.

Exploiting antifungal immunity in the clinical context

The continuous expansion of immunocompromised patient populations at-risk for developing life-threatening opportunistic fungal infections in recent decades has helped develop a deeper understanding of antifungal host defenses, which has provided the foundation for eventually devising immune-based targeted interventions in the clinic. This review outlines how genetic variation in certain immune pathway-related genes may contribute to the observed clinical variability in the risk of acquisition and/or severity of fungal infections and how immunogenetic-based patient stratification may enable the eventual development of personalized strategies for antifungal prophylaxis and/or vaccination. Moreover, this review synthesizes the emerging cytokine-based, cell-based, and other immunotherapeutic strategies that have shown promise as adjunctive therapies for boosting or modulating tissue-specific antifungal immune responses in the context of opportunistic fungal infections.

CARD9 gene rs4077515 polymorphism is associated with the susceptibility of Hashimoto's thyroiditis and the development of thyroid cancer

AMIS: Hashimoto's thyroiditis (HT) is the most common type of autoimmune thyroiditis and is a risk factor for the occurrence of thyroid papillary carcinoma (PTC). The study aimed to explore the distribution of CARD9 rs4077515 polymorphism in HT and PTC patients, in order to evaluate its association with the occurrence and development of HT.

METHODS

150 HT patients and 120 PTC cases were included. Genotypes of CARD9 rs40775155 polymorphism were sequenced and counted.

RESULTS

A remarkable increase trend of rs4077515 AA genotype was found in HT cases in comparison with the control group, while GG genotype frequency exhibited a down trend. An excess of A allele was also detected in HT group. HT cases carrying AG and AA genotypes had high risk to receive hormonotherapy and needed a much larger dose. In comparison with HT cases, both AG and AA appeared more frequently in PTC patients, and are associated with the tumor size, LN metastasis and surgical margin. The AG (OR = 2.566, 95 % CI = 1.376-4.786) and AA (OR = 3.040, 95 % CI = 1.525-6.060) genotype carriers had a greater risk of developing PTC. The A allele of rs4077515 polymorphism was a risk allele for the onset of PTC among HT cases (OR = 1.775, 95 % CI = 1.260-2.502).

CONCLUSION

CARD9 rs4077515 polymorphism is likely to be a risk factor for HT in the Chinese Han population, it also contributes to the development of PTC for HT patients.

PD-L1 negatively regulates antifungal immunity by inhibiting neutrophil release from bone marrow

Programmed death ligand 1 (PD-L1) has been shown to be inducibly expressed on neutrophils to suppress host immunity during polymicrobial sepsis, virus and parasite infections. However, the role of PD-L1 on neutrophil-mediated antifungal immunity remains wholly unknown. Here, we show that the expression of PD-L1 on murine and human neutrophils was upregulated upon the engagement of C-type lectin receptor Dectin-1 with its ligand β-glucans, exposed on fungal pathogen Candida albicans yeast. Moreover, β-glucan stimulation induced PD-L1 translocation into nucleus to regulate the production of chemokines CXCL1 and CXCL2, which control neutrophil mobilization. Importantly, C. albicans infection-induced expression of PD-L1 leads to neutrophil accumulation in bone marrow, through mediating their autocrine secretion of CXCL1/2. Furthermore, neutrophil-specific deficiency of PD-L1 impaired CXCL1/2 secretion, which promoted neutrophil migration from bone marrow into the peripheral circulation, thereby conferring host resistance to C. albicans infection. Finally, either PD-L1 blockade or pharmacological inhibition of PD-L1 expression significantly increased neutrophil release from bone marrow to enhance host antifungal immunity. Our data together indicate that activation of Dectin-1/PD-L1 cascade by β-glucans inhibits neutrophil release from bone marrow reserve, contributing to the negative regulation of antifungal innate immunity, which functions as a potent immunotherapeutic target against life-threatening fungi infections.

The role of the CBM complex in allergic inflammation and disease

The caspase activation and recruitment domain-coiled-coil (CARD-CC) family of proteins-CARD9, CARD10, CARD11, and CARD14-is collectively expressed across nearly all tissues of the body and is a crucial mediator of immunologic signaling as part of the CARD-B-cell lymphoma/leukemia 10-mucosa-associated lymphoid tissue lymphoma translocation protein 1 (CBM) complex. Dysfunction or dysregulation of CBM proteins has been linked to numerous clinical manifestations known as "CBM-opathies." The CBM-opathy spectrum encompasses diseases ranging from mucocutaneous fungal infections and psoriasis to combined immunodeficiency and lymphoproliferative diseases; however, there is accumulating evidence that the CARD-CC family members also contribute to the pathogenesis and progression of allergic inflammation and allergic diseases. Here, we review the 4 CARD-CC paralogs, as well as B-cell lymphoma/leukemia 10 and mucosa-associated lymphoid tissue lymphoma translocation protein 1, and their individual and collective roles in the pathogenesis and progression of allergic inflammation and 4 major allergic diseases (allergic asthma, atopic dermatitis, food allergy, and allergic rhinitis).

SEC5 is involved in M2 polarization of macrophages via the STAT6 pathway, and its dysfunction in decidual macrophages is associated with recurrent spontaneous abortion

Decidual macrophages (dMϕs) play critical roles in the establishment of microhomeostasis at the maternal-fetal interface during pregnancy. Impaired macrophage polarization during early pregnancy is associated with recurrent spontaneous abortion (RSA). In the present study, the SEC5 expression level was found to be significantly decreased in primary dMϕs of patients with RSA, and downregulation of SEC5 expression inhibited M2 polarization and STAT6 phosphorylation, whereas SEC5 overexpression in the Mϕs promoted M2 polarization and STAT6 phosphorylation in vitro. We subsequently found that SEC5 interacted with STAT6 in THP-1-derived Mϕs. The abundance of phosphorylated STAT6 (pSTAT6) protein was obviously increased, with a predominant distribution in the nucleus, after M2 polarization of Mϕs, and SEC5 protein was colocalized with pSTAT6. Moreover, a significantly reduced pSTAT6 expression level was observed in the dMϕs of patients with RSA. M2 polarization of Mϕs showed a stimulatory effect on the proliferation and invasion of human extravillous trophoblasts (EVTs) in vitro, and downregulation of SEC5 expression in Mϕs effectively reversed this effect. In a mouse model of LPS-induced early pregnancy loss, the uterine SEC5 expression level and the number of M2-Mϕs at the maternal-fetal interface were significantly reduced. More interestingly, heterozygous SEC5-deficient (SEC5^−/+) pregnant mice were more sensitive to LPS-induced pregnancy loss. Taken together, these data indicate that SEC5 participates in the regulation of M2 polarization of Mϕs by interacting with STAT6 and that decreased SEC5 expression inhibits the M2 polarization of dMϕs and results in early pregnancy loss by interfering with the physical activities of EVTs and immunotolerance at the maternal-fetal interface.

Progranulin aggravates lethal Candida albicans sepsis by regulating inflammatory response and antifungal immunity

Candida albicans is the most frequent pathogen of fungal sepsis associated with substantial mortality in critically ill patients and those who are immunocompromised. Identification of novel immune-based therapeutic targets from a better understanding of its molecular pathogenesis is required. Here, we reported that the production of progranulin (PGRN) levels was significantly increased in mice after invasive C.albicans infection. Mice that lacked PGRN exhibited attenuated kidney injury and increased survival upon a lethal systemic infection with C. albicans. In mice, PGRN deficiency protected against systemic candidiasis by decreasing aberrant inflammatory reactions that led to renal immune cell apoptosis and kidney injury, and by enhancing antifungal capacity of macrophages and neutrophils that limited fungal burden in the kidneys. PGRN in hematopoietic cell compartment was important for this effect. Moreover, anti-PGRN antibody treatment limited renal inflammation and fungal burden and prolonged survival after invasive C. albicans infection. In vitro, PGRN loss increased phagocytosis, phagosome formation, reactive oxygen species production, neutrophil extracellular traps release, and killing activity in macrophages or neutrophils. Mechanistic studies demonstrated that PGRN loss up-regulated Dectin-2 expression, and enhanced spleen tyrosine kinase phosphorylation and extracellular signal-regulated kinase activation in macrophages and neutrophils. In summary, we identified PGRN as a critical factor that contributes to the immunopathology of invasive C.albicans infection, suggesting that targeting PGRN might serve as a novel treatment for fungal infection.

Antifungal immunity mediated by C-type lectin receptors may be a novel target in immunotherapy for urothelial bladder cancer

Immunotherapies, such as immune-checkpoint blockade and adoptive T-cell therapy, offer novel treatment options with good efficacy for patients with urothelial bladder cancer. However, heterogeneity and therapeutic resistance have limited the use of immunotherapy. Further research into immune-regulatory mechanisms in bladder cancer is urgently required. Emerging evidence demonstrates that the commensal microbiota and its interactions with host immunity play pivotal roles in a variety of physiological and pathological processes, including in cancer. The gut microbiota has been identified as a potentially effective target of treatment that can be synergized with immunotherapy. The urothelial tract is also a key site for multiple microbes, although the immune-regulatory role of the urinary microbiome in the process of carcinogenesis of bladder cancer remains to be elucidated. We performed a comprehensive analysis of the expression and biological functions of C-type lectin receptors (CLRs), which have been recognized as innate pathogen-associated receptors for fungal microbiota, in bladder cancer. In line with previous research on fungal colonization of the urothelial tract, we found that CLRs, including Dectin-1, Dectin-2, Dectin-3, and macrophage-inducible Ca²⁺-dependent lectin receptor (Mincle), had a significant association with immune infiltration in bladder cancer. Multiple innate and adaptive pathways are positively correlated with the upregulation of CLRs. In addition, we found a significant correlation between the expression of CLRs and a range of immune-checkpoint proteins in bladder cancer. Based on previous studies and our findings, we hypothesize that the urinary mycobiome plays a key role in the pathogenesis of bladder cancer and call for more research on CLR-mediated anti-fungal immunity against bladder cancer as a novel target for immunotherapy in urothelial bladder cancer.

Infection and inflammation: New perspectives on Alzheimer's disease

Neuroinflammation has been recognized as a component of Alzheimer's Disease (AD) pathology since the original descriptions by Alois Alzheimer and a role for infections in AD pathogenesis has long been hypothesized. More recently, this hypothesis has gained strength as human genetics and experimental data suggest key roles for inflammatory cells in AD pathogenesis. To review this topic, Duke/University of North Carolina (Duke/UNC) Alzheimer's Disease Research Center hosted a virtual symposium: "Infection and Inflammation: New Perspectives on Alzheimer's Disease (AD)." Participants considered current evidence for and against the hypothesis that AD could be caused or exacerbated by infection or commensal microbes. Discussion focused on connecting microglial transcriptional states to functional states, mouse models that better mimic human immunity, the potential involvement of inflammasome signaling, metabolic alterations, self-reactive T cells, gut microbes and fungal infections, and lessons learned from Covid-19 patients with neurologic symptoms. The content presented in the symposium, and major topics raised in discussions are reviewed in this summary of the proceedings.

CARD9 Signaling, Inflammation, and Diseases

Caspase-recruitment domain 9 (CARD9) protein is expressed in many cells especially in immune cells, and is critically involved in the function of the innate and adaptive immune systems through extensive interactions between CARD9 and other signaling molecules including NF-κB and MAPK. CARD9-mediated signaling plays a central role in regulating inflammatory responses and oxidative stress through the productions of important cytokines and chemokines. Abnormalities of CARD9 and CARD9 signaling or CARD9 mutations or polymorphism are associated with a variety of pathological conditions including infections, inflammation, and autoimmune disorders. This review focuses on the function of CARD9 and CARD9-mediated signaling pathways, as well as interactions with other important signaling molecules in different cell types and the relations to specific disease conditions including inflammatory diseases, infections, tumorigenesis, and cardiovascular pathologies.

Candidalysin, a Virulence Factor of Candida albicans, Stimulates Mast Cells by Mediating Cross-Talk Between Signaling Pathways Activated by the Dectin-1 Receptor and MAPKs

PURPOSE

Although mast cells (MCs) modulate the activity of effector cells during Candida albicans infection, their role in the pathogenesis of candidiasis remains unclear. Candidalysin, a C. albicans-derived peptide toxin, is a crucial factor in fungal infections. We aimed to investigate the effect of candidalysin on MC activation and the underlying molecular mechanism.

METHODS

Serum from candidalysin-immunized mice was used to measure candidalysin expression in patients infected with C. albicans. MC degranulation and migration were evaluated by β-hexosaminidase release assay and chemotaxis assay, respectively. EIA and ELISA were used to evaluate the production of eicosanoids and cytokines/chemokines, respectively. The production of nitric oxide (NO) was measured with a DAF-FM diacetate kit, while reactive oxygen species (ROS) production was analyzed by flow cytometry. MAPK activation was evaluated by Western blotting.

RESULTS

We detected high candidalysin expression in the lesions of patients infected with C. albicans, and the MC number was increased in these lesions. LL-37 colocalized with MCs in the lesions of candidiasis patients. Candidalysin-enhanced MC accumulation in mice and treating LAD2 and HMC-1 cells with candidalysin induced their degranulation, migration, and production of pro- and anti-inflammatory cytokines/chemokines, eicosanoids, ROS, NO, and LL-37. Interestingly, C. albicans strains lacking candidalysin failed to induce MC activation. Moreover, candidalysin increased dectin-1 expression, and the inhibition of dectin-1 decreased MC activation. Downstream dectin-1 signaling involved the MAPK pathways.

CONCLUSION

The finding that candidalysin causes cutaneous MC activation may improve our understanding of the role of MCs in the pathology of cutaneous C. albicans infection.

CARD9 Mediates Pancreatic Islet Beta-Cell Dysfunction Under the Duress of Hyperglycemic Stress

BACKGROUND/AIMS

Published evidence implicates Caspase recruitment domain containing protein 9 (CARD9) in innate immunity. Given its recently suggested roles in obesity and insulin resistance, we investigated its regulatory role(s) in the onset of islet beta cell dysfunction under chronic hyperglycemic (metabolic stress) conditions.

METHODS

Islets from mouse pancreas were isolated by the collagenase digestion method. Expression of CARD9 was suppressed in INS-1 832/13 cells by siRNA transfection using the DharmaFect1 reagent. The degree of activation of Rac1 was assessed by a pull-down assay kit. Interactions between CARD9, RhoGDIβ and Rac1 under metabolic stress conditions were determined by co-immunoprecipitation assay. The degree of phosphorylation of stress kinases was assessed using antibodies directed against phosphorylated forms of the respective kinases.

RESULTS

CARD9 expression is significantly increased following exposure to high glucose, not to mannitol (both at 20 mM; 24 hrs.) in INS-1 832/13 cells. siRNA-mediated knockdown of CARD9 significantly attenuated high glucose-induced activation of Rac1 and phosphorylation of p38MAPK and p65 subunit of NF-κB (RelA), without significantly impacting high glucose-induced effects on JNK1/2 and ERK1/2 activities. CARD9 depletion also suppressed high glucose-induced CHOP expression (a marker for endoplasmic reticulum stress) in these cells. Co-immunoprecipitation studies revealed increased association between CARD9-RhoGDIβ and decreased association between RhoGDIβ-Rac1 in cells cultured under high glucose conditions.

CONCLUSION

Based on these data, we conclude that CARD9 regulates activation of Rac1-p38MAPK-NFκB signaling pathway leading to functional abnormalities in beta cells under metabolic stress conditions.

Dectin-1 Signaling Update: New Perspectives for Trained Immunity

The C-type lectin receptor Dectin-1 was originally described as the β-glucan receptor expressed in myeloid cells, with crucial functions in antifungal responses. However, over time, different ligands both of microbial-derived and endogenous origin have been shown to be recognized by Dectin-1. The outcomes of this recognition are diverse, including pro-inflammatory responses such as cytokine production, reactive oxygen species generation and phagocytosis. Nonetheless, tolerant responses have been also attributed to Dectin-1, depending on the specific ligand engaged. Dectin-1 recognition of their ligands triggers a plethora of downstream signaling pathways, with complex interrelationships. These signaling routes can be modulated by diverse factors such as phosphatases or tetraspanins, resulting either in pro-inflammatory or regulatory responses. Since its first depiction, Dectin-1 has recently gained a renewed attention due to its role in the induction of trained immunity. This process of long-term memory of innate immune cells can be triggered by β-glucans, and Dectin-1 is crucial for its initiation. The main signaling pathways involved in this process have been described, although the understanding of the above-mentioned complexity in the β-glucan-induced trained immunity is still scarce. In here, we have reviewed and updated all these factors related to the biology of Dectin-1, highlighting the gaps that deserve further research. We believe on the relevance to fully understand how this receptor works, and therefore, how we could harness it in different pathological conditions as diverse as fungal infections, autoimmunity, or cancer.

CARD9 Expression Pattern, Gene Dosage, and Immunodeficiency Phenotype Revisited

BACKGROUND

CARD9 deficiency is an autosomal recessive primary immunodeficiency underlying increased susceptibility to fungal infection primarily presenting as invasive CNS Candida and/or cutaneous/invasive dermatophyte infections. More recently, a rare heterozygous dominant negative CARD9 variant c.1434 + 1G > C was reported to be protective from inflammatory bowel disease.

OBJECTIVE

We studied two siblings carrying homozygous CARD9 variants (c.1434 + 1G > C) and born to heterozygous asymptomatic parents. One sibling was asymptomatic and the other presented with candida esophagitis, upper respiratory infections, hypogammaglobulinemia, and low class-switched memory B cells.

METHODS AND RESULTS

The CARD9 c.1434 + 1G > C variant generated two mutant transcripts confirmed by mRNA and protein expression: an out-of-frame c.1358-1434 deletion/ ~ 55 kDa protein (CARD9Δex.11) and an in-frame c.1417-1434 deletion/ ~ 61 kDa protein (CARD9Δ18 nt.). Neither transcript was able to form a complete/functional CBM complex, which includes TRIM62. Based on the index patient's CVID-like phenotype, CARD9 expression was tested and detected in lymphocytes and monocytes from humans and mice. The functional impact of different CARD9 mutations and gene dosage conditions was evaluated in heterozygous and homozygous c.1434 + 1 G > C members of the index family, and in WT (two WT alleles), haploinsufficiency (one WT, one null allele), and null (two null alleles) individuals. CARD9 gene dosage impacted lymphocyte and monocyte functions including cytokine generation, MAPK activation, T-helper commitment, transcription, plasmablast differentiation, and immunoglobulin production in a differential manner.

CONCLUSIONS

CARD9 exon 11 integrity is critical to CBM complex function. CARD9 is expressed and affects particular T and B cell functions in a gene dosage-dependent manner, which in turn may contribute to the phenotype of CARD9 deficiency.

Emerging roles of Dectin-1 in noninfectious settings and in the CNS

Dectin-1 is a C-type lectin receptor (CLR) expressed on the surface of various mammalian myeloid cells. Dectin-1 recognizes β-glucans and elicits antifungal proinflammatory immune responses. Recent studies have begun to examine the biology of Dectin-1 in previously less explored settings, such as homeostasis, sterile inflammation, and in the central nervous system. Indeed, in certain contexts, Dectin-1 is now known to promote tolerance, and anti-inflammatory and neuroprotective responses. In this review, we provide an overview of the current understanding of the roles of Dectin-1 in immunology beyond the context of fungal infections, mainly focusing on in vivo neuroimmunology studies, which could reveal new therapeutic approaches to modify innate immune responses in neurologic disorders.

Signaling through Syk or CARD9 Mediates Species-Specific Anti-Candida Protection in Bone Marrow Chimeric Mice

The spleen tyrosine kinase (Syk) and the downstream adaptor protein CARD9 are crucial signaling molecules in antimicrobial immunity. Candida parapsilosis is an emerging fungal pathogen with a high incidence in neonates, while Candida albicans is the most common agent of candidiasis. While signaling through Syk/CARD9 promotes protective host mechanisms in response to C. albicans, its function in immunity against C. parapsilosis remains unclear. Here, we generated Syk-/- and CARD9-/- bone marrow chimeric mice to study the role of Syk/CARD9 signaling in immune responses to C. parapsilosis compared to C. albicans. We demonstrate various functions of this pathway (e.g., phagocytosis, phagosome acidification, and killing) in Candida-challenged, bone marrow-derived macrophages with differential involvement of Syk and CARD9 along with species-specific differences in cytokine production. We report that Syk-/- or CARD9-/- chimeras rapidly display high susceptibility to C. albicans, while C. parapsilosis infection exacerbates over a prolonged period in these animals. Thus, our results establish that Syk and CARD9 contribute to systemic resistance to C. parapsilosis and C. albicans differently. Additionally, we confirm prior studies but also detail new insights into the fundamental roles of both proteins in immunity against C. albicans. Our data further suggest that Syk has a more prominent influence on anti-Candida immunity than CARD9. Therefore, this study reinforces the Syk/CARD9 pathway as a potential target for anti-Candida immune therapy. IMPORTANCE While C. albicans remains the most clinically significant Candida species, C. parapsilosis is an emerging pathogen with increased affinity to neonates. Syk/CARD9 signaling is crucial in immunity to C. albicans, but its role in in vivo responses to other pathogenic Candida species is largely unexplored. We used mice with hematopoietic systems deficient in Syk or CARD9 to comparatively study the function of these proteins in anti-Candida immunity. We demonstrate that Syk/CARD9 signaling has a protective role against C. parapsilosis differently than against C. albicans. Thus, this study is the first to reveal that Syk can exert immune responses during systemic Candida infections species specifically. Additionally, Syk-dependent immunity to a nonalbicans Candida species in an in vivo murine model has not been reported previously. We highlight that the contribution of Syk and CARD9 to fungal infections are not identical and underline this pathway as a promising immune-therapeutic target to fight Candida infections.

Allergen-specific immunotherapy induces the suppressive secretoglobin 1A1 in cells of the lower airways

BACKGROUND

While several systemic immunomodulatory effects of allergen-specific immunotherapy (AIT) have been discovered, local anti-inflammatory mechanisms in the respiratory tract are largely unknown. We sought to elucidate local and epithelial mechanisms underlying allergen-specific immunotherapy in a genome-wide approach.

METHODS

We induced sputum in hay fever patients and healthy controls during the pollen peak season and stratified patients by effective allergen immunotherapy or as untreated. Sputum was directly processed after induction and subjected to whole transcriptome RNA microarray analysis. Nasal secretions were analyzed for Secretoglobin1A1 (SCGB1A1) and IL-24 protein levels in an additional validation cohort at three defined time points during the 3-year course of AIT. Subsequently, RNA was extracted and subjected to an array-based whole transcriptome analysis.

RESULTS

Allergen-specific immunotherapy inhibited pro-inflammatory CXCL8, IL24, and CCL26mRNA expression, while SCGB1A1, IL7, CCL5, CCL23, and WNT5BmRNAs were induced independently of the asthma status and allergen season. In our validation cohort, local increase of SCGB1A1 occurred concomitantly with the reduction of local IL-24 in upper airways during the course of AIT. Additionally, SCGB1A1 was identified as a suppressor of epithelial gene expression.

CONCLUSIONS

Allergen-specific immunotherapy induces a yet unknown local gene expression footprint in the lower airways that on one hand appears to be a result of multiple regulatory pathways and on the other hand reveals SCGB1A1 as novel anti-inflammatory mediator of long-term allergen-specific therapeutic intervention in the local environment.

CLec-TM1-ERK-GSK3β Pathway Regulates Vibrio splendidus-Induced IL-17 Production in Oyster

C-type lectins are a family of pattern recognition receptors that recognize microbial components and subsequently activate the signaling cascade to induce the production of proinflammatory cytokines. In the current study, the homologs of ERK (named as CgERK) and GSK3β (named as CgGSK3β) and a novel C-type lectin with a transmembrane domain (named as CgCLec-TM1) were identified from oyster Crassostrea gigas CgCLec-TM1 was able to bind Escherichia coli and Vibrio splendidus through its carbohydrate recognition domain and then activated CgERK by inducing its phosphorylation. The activated CgERK interacted with CgGSK3β to phosphorylate it at Ser⁹, which eventually induced the expressions of CgIL-17-1 and CgIL-17-5. The interaction between CgERK and CgGSK3β, as well as the phosphorylation of CgGSK3β, could be inhibited by ERK inhibitor (PD98059) to reduce the expressions of CgIL-17-1 and CgIL-17-5. CgGSK3β in oyster was proposed as a new substrate of CgERK. The results defined a CLec-TM1-ERK-GSK3β signaling pathway in oyster, which was activated by V. splendidus and then induced CgIL-17 productions.

CARD9 mediates glucose-stimulated insulin secretion in pancreatic beta cells

Caspase recruitment domain containing protein 9 (CARD9) plays key regulatory role(s) in innate and adaptive immune responses. Recent evidence implicates CARD9 in the onset of metabolic diseases including insulin resistance. However, potential contributory roles of CARD9 in glucose-stimulated insulin secretion (GSIS) remain unknown. Herein, we report that CARD9 is expressed in human islets, rat islets, mouse islets and clonal INS-1 832/13 cells. Subcellularly, CARD9 is predominantly cytosolic (~75%) in INS-1 832/13 cells. siRNA-mediated depletion of CARD9 expression significantly (~50%) suppressed GSIS in INS-1 832/13 cells. Interestingly, glucose-induced activation of Rac1, a small G-protein, which is a requisite for GSIS to occur, is unaffected in CARD9-si transfected cells, suggesting that CARD9-mediates GSIS in a Rac1-independent fashion. Furthermore, insulin secretion promoted by KCl or mastoparan (a global G protein activator), remained resistant to CARD9 depletion in INS-1 832/13 cells. In addition, pharmacological inhibition (BRD5529) of interaction between CARD9 and TRIM62, its ubiquitin ligase, exerted no significant effects on GSIS. Lastly, depletion of CARD9 prevented glucose-induced p38, not ERK1/2 phosphorylation in beta cells. Based on these observations, we propose that CARD9 might regulate GSIS via a Rac1-independent and p38-dependent signaling module.

E3 ligase c-Cbl regulates intestinal inflammation through suppressing fungi-induced noncanonical NF-κB activation

Intestinal fungi are critical for modulating host immune homeostasis and underlying mechanisms remain unclear. We show that dendritic cell (DC)-specific deficiency of casitas B-lineage lymphoma (c-Cbl) renders mice susceptible to dextran sodium sulfate (DSS)-induced colitis. Mechanistically, we identify that c-Cbl functions downstream of Dectin-2 and Dectin-3 to mediate the ubiquitination and degradation of noncanonical nuclear factor κB subunit RelB. Thus, c-Cbl deficiency in DCs promotes α-mannan-induced activation of RelB, which suppresses p65-mediated transcription of an anti-inflammatory cytokine gene, il10, thereby aggravating DSS-induced colitis. Moreover, suppressing fungal growth with fluconazole or inhibition of RelB activation in vivo attenuates colitis in mice with DC-specific deletion of c-Cbl. We also demonstrate an interaction between c-Cbl and c-Abl tyrosine kinase and find that treatment with DPH, a c-Abl agonist, synergistically increases fungi-induced c-Cbl activation to restrict colitis. Together, these findings unravel a previously unidentified fungi-induced c-Cbl/RelB axis that sustains intestinal homeostasis and protects against intestinal inflammation.

OTUD1 Regulates Antifungal Innate Immunity through Deubiquitination of CARD9

CARD9 is an essential adaptor protein in antifungal innate immunity mediated by C-type lectin receptors. The activity of CARD9 is critically regulated by ubiquitination; however, the deubiquitinases involved in CARD9 regulation remain incompletely understood. In this study, we identified ovarian tumor deubiquitinase 1 (OTUD1) as an essential regulator of CARD9. OTUD1 directly interacted with CARD9 and cleaved polyubiquitin chains from CARD9, leading to the activation of the canonical NF-κB and MAPK pathway. OTUD1 deficiency impaired CARD9-mediated signaling and inhibited the proinflammatory cytokine production following fungal stimulation. Importantly, Otud1 ^-/- mice were more susceptible to fungal infection than wild-type mice in vivo. Collectively, our results identify OTUD1 as an essential regulatory component for the CARD9 signaling pathway and antifungal innate immunity through deubiquitinating CARD9.

Effect of Ras-guanine nucleotide release factor 1-mediated H-Ras/ERK signaling pathway on glioma

OBJECTIVE

To investigate the function of Ras-guanine nucleotide release factor 1 (Ras-GRF1) in glioma through mediating H-Ras/ERK signaling pathway.

METHODS

Ras-GRF1, H-Ras, K-Ras and N-Ras expressions in glioma and normal brain tissues were detected via Immunohistochemistry. Glioma cells (U87 cells, U251 cells and primary human glioma cells) were transfected with Ras-GRF1 siRNA, H-Ras siRNA and/or Ras-GRF1 lentivirus activation particles. Then, the following aspects were evaluated: cell proliferation by MTT assay, clonogenic ability by the plate clone formation experiment, cell migration and invasion by Wound-healing and Transwell assays, and cell apoptosis by Annexin-V-FITC/PI staining. The protein expressions were measured by Western blotting. Subcutaneous and orthotopic mouse models of glioma were conducted to determine the role of Ras-GRF1 in glioma tumorigenesis.

RESULTS

Ras-GRF1, H-Ras, K-Ras and N-Ras expressions were upregulated in the glioma tissues, which were correlated with the WHO grade of glioma. Besides, Ras-GRF1 expression was positively related to H-Ras expression. Ras-GRF1 siRNA could reduce the expression of H-Ras and p-ERK/ERK in glioma cell. H-Ras siRNA inhibited the proliferation, clone formation, migration and invasion, and enhance the apoptosis of glioma cells, which, however, were reversed by Ras-GRF1 lentivirus activation particles. In vivo experiments also revealed that Ras-GRF1 shRNA reduced the volume and weight of the tumors in the nude mice, with down-regulations of H-Ras and p-ERK/ERK.

CONCLUSION

Ras-GRF1 was upregulated in glioma tissues and correlated with its malignancy and prognosis. Silencing Ras-GRF1, through mediating H-Ras/ERK pathway, may suppress the growth and metastasis of glioma.

Intestinal lamina propria macrophages upregulate interleukin-10 mRNA in response to signals from commensal bacteria recognized by MGL1/CD301a

Ligand-induced cellular signaling involved in interleukin 10 (IL-10) production by lamina propria macrophages (LPMs) during their interactions with commensal bacteria is not clearly understood. We previously showed, using mice lacking a C-type lectin MGL1/CD301a, that this molecule on colonic LPMs plays an important role in the induction of IL-10 upon interaction with commensal bacteria, Streptococcus sp.

In the present report, we show that the physical engagement of MGL1/CD301a on LPMs with in-situ isolated Streptococcus sp. bacteria leads to IL-10 messenger RNA (mRNA) induction. Spleen tyrosine kinase (Syk), caspase recruitment domain 9 (CARD9) and extracellular signal-regulated kinase (ERK), but not NF-κB pathway, are shown to be indispensable for IL-10 mRNA induction after stimulation with heat-killed Streptococcus sp. Guanidine hydrochloride treatment of Streptococcus sp., which is known to extract bacterial cell surface glycan-rich components, abolished bacterial binding to recombinant MGL1/CD301a. The extract contained materials which bound rMGL1 in ELISA and appeared to induce IL-10 mRNA expression in LPMs in vitro. Lectin blotting showed that the extract contained glycoproteins that are considered as putative ligands for MGL1. Some human commensal Lactobacillus species also induced IL-10 mRNA expression by colonic LPMs in vitro, which depends on the presence of MGL1/CD301a and CARD9. The present results are the first to show that MGL1/CD301a acts as a signal transducer during colonic host–microbe interactions.

Inflammatory Bowel Diseases (IBD) and the Microbiome-Searching the Crime Scene for Clues

Inflammatory bowel diseases (IBD) develop via convergence of environmental, microbial, immunological, and genetic factors. Alterations in the gut microbiota have been associated with development and progression of IBD, but it is not clear which populations of microbes are involved or how they might contribute to IBD. We review the genetic and environmental factors affecting the gut microbiota, the roles of gut microbes and their bioproducts in the development and clinical course of IBD, and strategies by which microbiome-based therapies can be used to prevent, manage, and eventually cure IBD. We discuss research findings that help bridge the gap between the basic sciences and clinical application.

Fungal Dysbiosis Aggravates Pouchitis in a Rat Model of Ileal Pouch Anal Anastomosis

BACKGROUND

Although the interaction between gut microbiota and pouchitis after ileal pouch anal anastomosis (IPAA) for ulcerative colitis (UC) has been confirmed, evidence of commensal mycobiota in the etiology of pouchitis is still lacking. This study aimed to investigate the role of fungi in the pathogenesis of pouchitis.

METHODS

Fecal samples were collected from UC patients with or without pouchitis after IPAA. Experimental pouchitis was induced by 5% dextran sulfate sodium for 7 consecutive days in a rat model of IPAA. Fungal dysbiosis was induced by 0.5% fluconazole (Flu), and commensal fungal recognition through dectin-1 was blocked by 5% laminarin. Fecal fungal composition was analyzed using internal transcribed spacer 2 sequencing. Severity of pouchitis and activation of the CARD9-nuclear factor kappa-B pathway was determined among different groups.

RESULTS

Patients with pouchitis had a lower alpha (α) diversity in mycobiota composition and a higher abundance of Saccharomyces at the genus level compared with those with a normal pouch. In the rat model of pouchitis, Flu treatment decreased fungal burden but induced fungal dysbiosis, characterized by increased α diversity, a decreased relative abundance of Kazachstania, and increased Polythrincium and Saccharomyces. In addition, Flu treatment worsened dextran sulfate sodium pouchitis, as indicated by increased mortality, weight loss, higher histological score, and CD4+ cell infiltration. Laminarin also increased the severity of pouchitis. In the Flu and laminarin groups, the expression of interferon-γ, tumor necrosis factor-α, CARD9, and phosphorylated nuclear factor kappa-B inhibitor alpha was decreased.

CONCLUSIONS

Patients with pouchitis had altered fungal composition. Fungal dysbiosis or recognition deficiency by the host may exacerbate experimental pouchitis. Strategies targeting commensal mycobiota may provide therapeutic potential against pouchitis, especially for antibiotic-refractory patients.

The first line of defense: effector pathways of anti-fungal innate immunity

The innate immune system is critical to proper host defense against fungal pathogens, which is highlighted by increased susceptibility to invasive disease in immunocompromised patients. Innate cells (e.g. macrophages, neutrophils, dendritic cells, eosinophils) are equipped with intricate cell machinery to detect invading fungi and facilitate fungal killing, recruit additional immune cells, and direct the adaptive immune system responses. Understanding the mechanisms that govern a protective response will enable the development of novel treatment strategies. This review focuses on recent insights of signaling and regulation of C-type lectin receptors and their effector mechanisms enabling an effective host antifungal immunity.

Priming with FLO8-deficient Candida albicans induces Th1-biased protective immunity against lethal polymicrobial sepsis

The morphological switch between yeast and hyphae of Candida albicans is essential for its interaction with the host defense system. However, the lack of understanding of host–pathogen interactions during C. albicans infection greatly hampers the development of effective immunotherapies. Here, we found that priming with the C. albicans FLO8-deficient (flo8) mutant, locked in yeast form, protected mice from subsequent lethal C. albicans infection. Deficiency of Dectin-2, a fungus-derived α-mannan recognition receptor, completely blocked flo8 mutant-induced protection. Mechanistically, the flo8 mutant-induced Dectin-2/CARD9-mediated IL-10 production in DCs and macrophages to block thymus atrophy by inhibiting the C. albicans-induced apoptosis of thymic T cells, which facilitated the continuous output of naive T cells from the thymus to the spleen. Continuous recruitment of naive T cells to the spleen enhanced Th1-biased antifungal immune responses. Consequently, depletion of CD4+ T cells or blockade of IL-10 receptor function using specific antibodies in mice completely blocked the protective effects of flo8 mutant priming against C. albicans infection. Moreover, mannans exposed on the surface of the flo8 mutant were responsible for eliciting protective immunity by inhibiting the C. albicans-induced apoptosis of thymic T cells to sustain the number of naive T cells in the spleen. Importantly, priming with the flo8 mutant extensively protected mice from polymicrobial infection caused by cecal ligation and puncture (CLP) by enhancing Th1-biased immune responses. Together, our findings imply that targeting FLO8 in C. albicans elicits protective immune responses against polymicrobial infections and that mannans extracted from the flo8 mutant are potential immunotherapeutic candidate(s) for controlling infectious diseases.

The adaptor protein CARD9, from fungal immunity to tumorigenesis

The adaptor protein CARD9 is in charge of mediating signals from PRRs of myeloid cells to downstream transcription factor NF-κB. CARD9 plays an indispensable role in innate immunity. Both mice and humans with CARD9 deficiency show increased susceptibility to fungal and bacterial infections. CARD9 signaling not only activates but also shapes adaptive immune responses. The role of this molecule in tumor progression is increasingly being revealed. Our early study found that CARD9 is associated with the development of colon cancer and functions as a regulator of antitumor immunity. In this review, we focus on the upstream and downstream signaling pathways of CARD9, then we summarize the immunological recognition and responses induced by CARD9 signaling. Furthermore, we review the function of CARD9 in multiple aspects of host immunity, ranging from fungal immunity to tumorigenesis.

During Aspergillus Infection, Monocyte-Derived DCs, Neutrophils, and Plasmacytoid DCs Enhance Innate Immune Defense through CXCR3-Dependent Crosstalk

Aspergillus fumigatus, a ubiquitous mold, is a common cause of invasive aspergillosis (IA) in immunocompromised patients. Host defense against IA relies on lung-infiltrating neutrophils and monocyte-derived dendritic cells (Mo-DCs). Here, we demonstrate that plasmacytoid dendritic cells (pDCs), which are prototypically antiviral cells, participate in innate immune crosstalk underlying mucosal antifungal immunity. Aspergillus-infected murine Mo-DCs and neutrophils recruited pDCs to the lung by releasing the CXCR3 ligands, CXCL9 and CXCL10, in a Dectin-1 and Card9- and type I and III interferon signaling-dependent manner, respectively. During aspergillosis, circulating pDCs entered the lung in response to CXCR3-dependent signals. Via targeted pDC ablation, we found that pDCs were essential for host defense in the presence of normal neutrophil and Mo-DC numbers. Although interactions between pDC and fungal cells were not detected, pDCs regulated neutrophil NADPH oxidase activity and conidial killing. Thus, pDCs act as positive feedback amplifiers of neutrophil effector activity against inhaled mold conidia.

CARD9 mediates T cell inflammatory response in Coxsackievirus B3-induced acute myocarditis

Cardiac inflammation in Coxsackievirus B3 (CVB3)-induced myocarditis is a consequence of viral-related cardiac injury and immune response. Caspase-associated recruitment domain 9 (CARD9) is a critical adaptor protein involved in transduction of signals from various innate pattern recognition receptors. In this study, the role of CARD9 in acute viral myocarditis was evaluated. CARD9^-/- and C57BL/6 mice were infected with CVB3. On day 7 postinfection, myocardial tissue and blood samples were collected and examined. After CARD9 knockout, mRNA and protein levels of transforming growth factor-β(TGF-β), interleukin-17A(IL-17A), and CARD domain of B-cell CLL/lymphoma 10(BCL-10) in the myocardium were markedly lower in CARD9^-/- mice than in C57BL/6 mice with CVB3-induced viral myocarditis. This trend was similar for the pathological scores for inflammation and serum levels of cytokines interleukin-6(IL-6), interleukin-10(IL-10), interferon -γ(IFN-γ), TGF-β, and IL-17A. These results suggest that the CARD9-mediated secretion of pro-inflammatory cytokines plays an important role in the immune response to acute viral myocarditis.

Immunoregulatory Property of C-Type Lectin-Like Receptors in Fibrosing Interstitial Lung Diseases

The innate immune system identifies exogenous threats or endogenous stress through germline-encoded receptors called pattern recognition receptors (PRRs) that initiate consecutive downstream signaling pathways to control immune responses. However, the contribution of the immune system and inflammation to fibrosing interstitial lung diseases (ILD) remains poorly understood. Immunoreceptor tyrosine-based motif-bearing C-type lectin-like receptors (CTLRs) may interact with various immune cells during tissue injury and wound repair processes. Dectin-1 is a CTLR with dominant mechanisms manifested through its intracellular signaling cascades, which regulate fibrosis-promoting properties through gene transcription and cytokine activation. Additionally, immune impairment in ILD facilitates microbiome colonization; hence, Dectin-1 is the master protector in host pulmonary defense against fungal invasion. Recent progress in determining the signaling pathways that control the balance of fibrosis has implicated immunoreceptor tyrosine-based motif-bearing CTLRs as being involved, either directly or indirectly, in the pathogenesis of fibrosing ILD.

Friend or Foe? Recent Strategies to Target Myeloid Cells in Cancer

The tumor microenvironment (TME) is a complex network of epithelial and stromal cells, wherein stromal components provide support to tumor cells during all stages of tumorigenesis. Among these stromal cell populations are myeloid cells, which are comprised mainly of tumor-associated macrophages (TAM), dendritic cells (DC), myeloid-derived suppressor cells (MDSC), and tumor-associated neutrophils (TAN). Myeloid cells play a major role in tumor growth through nurturing cancer stem cells by providing growth factors and metabolites, increasing angiogenesis, as well as promoting immune evasion through the creation of an immune-suppressive microenvironment. Immunosuppression in the TME is achieved by preventing critical anti-tumor immune responses by natural killer and T cells within the primary tumor and in metastatic niches. Therapeutic success in targeting myeloid cells in malignancies may prove to be an effective strategy to overcome chemotherapy and immunotherapy limitations. Current therapeutic approaches to target myeloid cells in various cancers include inhibition of their recruitment, alteration of function, or functional re-education to an antitumor phenotype to overcome immunosuppression. In this review, we describe strategies to target TAMs and MDSCs, consisting of single agent therapies, nanoparticle-targeted approaches and combination therapies including chemotherapy and immunotherapy. We also summarize recent molecular targets that are specific to myeloid cell populations in the TME, while providing a critical review of the limitations of current strategies aimed at targeting a single subtype of the myeloid cell compartment. The goal of this review is to provide the reader with an understanding of the critical role of myeloid cells in the TME and current therapeutic approaches including ongoing or recently completed clinical trials.

The Role of CARD9 in Metabolic Diseases

Caspase recruitment domain containing protein 9 (CARD9) is an adaptor protein that plays a critical role in pattern recognition receptors (PRRs)-mediated activation of NF-?B and mitogen-activated protein kinase (MAPK). This elicits initiation of the pro-inflammatory cytokines and leads to inflammatory responses, which has been recognized as a critical contributor to chronic inflammation. Current researches demonstrate that CARD9 is strongly associated with metabolic diseases, such as obesity, insulin resistance, atherosclerosis and so on. In this review, we summarize CARD9 signaling pathway and the role of CARD9 in metabolic diseases.

TAGAP instructs Th17 differentiation by bridging Dectin activation to EPHB2 signaling in innate antifungal response

The TAGAP gene locus has been linked to several infectious diseases or autoimmune diseases, including candidemia and multiple sclerosis. While previous studies have described a role of TAGAP in T cells, much less is known about its function in other cell types. Here we report that TAGAP is required for Dectin-induced anti-fungal signaling and proinflammatory cytokine production in myeloid cells. Following stimulation with Dectin ligands, TAGAP is phosphorylated by EPHB2 at tyrosine 310, which bridges proximal Dectin-induced EPHB2 activity to downstream CARD9-mediated signaling pathways. During Candida albicans infection, mice lacking TAGAP mount defective immune responses, impaired Th17 cell differentiation, and higher fungal burden. Similarly, in experimental autoimmune encephalomyelitis model of multiple sclerosis, TAGAP deficient mice develop significantly attenuated disease. In summary, we report that TAGAP plays an important role in linking Dectin-induced signaling to the promotion of effective T helper cell immune responses, during both anti-fungal host defense and autoimmunity.

TAGAP gene variants are linked to human autoimmunity. Here the authors identify TAGAP as a Dectin-1 and EphB2-binding protein mediating antifungal innate immune signaling and cytokine production, and demonstrate TAGAP in non-T cells promotes Th17 response in mouse models of infection and autoimmunity.

Cellular and molecular mechanisms of antifungal innate immunity at epithelial barriers: The role of C-type lectin receptors

Humans are constantly exposed to fungi, either in the form of commensals at epithelial barriers or as inhaled spores. Innate immune cells play a pivotal role in maintaining commensal relationships and preventing skin, mucosal, or systemic fungal infections due to the expression of pattern recognition receptors that recognize fungal cell wall components and modulate both their activation status and the ensuing adaptive immune response. Commensal fungi also play a critical role in the modulation of homeostasis and disease susceptibility at epithelial barriers. This review will outline cellular and molecular mechanisms of anti-fungal innate immunity focusing on C-type lectin receptors and their relevance in the context of host-fungi interactions at skin and mucosal surfaces in murine experimental models as well as patients susceptible to fungal infections.

Upregulated miR-155 inhibits inflammatory response induced by C. albicans in human monocytes derived dendritic cells via targeting p65 and BCL-10

Background

Candida albicans (C. albicans) is one of the most common fungal pathogens causing superficial and systemic infections. The innate immune system is the first defense line against C. albicans infection. MiR-155, a multifunctional microRNA (miRNA), has been proved to be a crucial regulator in innate immune response against bacterial and virus. However, the biological function of miR-155 in innate immune response against C. albicans infection remains unknown.

Methods

The expression miR-155, as well as inflammatory factors [interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ)], in monocytes derived dendritic cells (DCs) during heat-killed C. albicans infection was detected by quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR). The biological functions of miR-155 were investigated with "gain- and loss-of-function" experiments. Potential targets of miR-155 were identified by bioinformatics analysis, luciferase assay and western blot. Small interfering RNA (siRNA) was used to validate the function of miR-155 target.

Results

C. albicans increased the expression of miR-155 and pro-inflammatory factors. MiR-155 induced by C. albicans was depended on Dectin-1-spleen tyrosine kinase (Syk)/Raf-1-MAPK signaling pathway. Furthermore, miR-155 suppressed the secretion of pro-inflammatory cytokines induced by C. albicans by targeting NF-κB p65 and B cell leukemia/lymphoma 10 (BCL-10).

Conclusions

In conclusion, up-regulated miR-155 acts as a negative feedback regulator in the innate immune response against C. albicans infection.