Regulation of C-Type Lectin Receptor-Mediated Antifungal Immunity

Adjuvant activity of Mycobacteria-derived mycolic acids

Successful vaccination, especially with safe vaccines such as component/subunit vaccines, requires proper activation of innate immunity and, for this purpose, adjuvant is used. For clinical use, alum is frequently used while, for experimental use, CFA, containing Mycobacterial components, was often used. In this report, we demonstrated that mycolic acids (MA), major and essential lipid components of the bacterial cell wall of the genus Mycobacterium, has adjuvant activity. MA plus model antigen-immunization induced sufficient humoral response, which was largely comparable to conventional CFA plus antigen-immunization. Importantly, while CFA plus antigen-immunization induced Th17-biased severe and destructive inflammatory responses at the injected site, MA plus antigen-immunization induced Th1-biased mild inflammation at the site. MA induced dendritic cell activation by co-stimulatory molecule induction as well as inflammatory cytokine/chemokine induction. MA plus antigen-immunization successfully protected mice from tumor progression both in prevention and in therapy models. We thus submit that MA is a promising adjuvant candidate material for clinical purposes and for experimental purposes from a perspective of animal welfare.

Pseudozyma Priming Influences Expression of Genes Involved in Metabolic Pathways and Immunity in Zebrafish Larvae

Fungi, particularly yeasts, are known essential components of the host microbiota but their functional relevance in development of immunity and physiological processes of fish remains to be elucidated. In this study, we used a transcriptomic approach and a germ-free (GF) fish model to determine the response of newly hatched zebrafish larvae after 24 h exposure to Pseudozyma sp. when compared to conventionally-raised (CR) larvae. We observed 59 differentially expressed genes in Pseudozyma-exposed GF zebrafish larvae compared to their naïve control siblings. Surprisingly, in CR larvae, there was not a clear transcriptome difference between Pseudozyma-exposed and control larvae. Differentially expressed genes in GF larvae were involved in host metabolic pathways, mainly peroxisome proliferator-activated receptors, steroid hormone biosynthesis, drug metabolism and bile acid biosynthesis. We also observed a significant change in the transcript levels of immune-related genes, namely complement component 3a, galectin 2b, ubiquitin specific peptidase 21, and aquaporins. Nevertheless, we did not observe any significant response at the cellular level, since there were no differences between neutrophil migration or proliferation between control and yeast-exposed GF larvae. Our findings reveal that exposure to Pseudozyma sp. may affect metabolic pathways and immune-related processes in germ-free zebrafish, suggesting that commensal yeast likely play a significant part in the early development of fish larvae.

A new insight into the intestine of Pacific white shrimp: Regulation of intestinal homeostasis and regeneration in Litopenaeus vannamei during temperature fluctuation

Litopenaeus vannamei (L. vannamei) is an essential aquaculture shrimp throughout the world, but its aquaculture industry is threatened by temperature fluctuation. In this study, our histological results indicated that the shrimp intestine has a self-repairing ability during temperature fluctuation; however the potential mechanisms were still unknown. Therefore, transcriptome profiles of the intestine were collected from shrimp at 28 °C (C28), 13 °C (T13) and 28 °C after their temperature rose back (R28) and were analyzed. A total of 2229 differentially expressed genes (DEGs) (986 up- and 1243 downregulated) were identified in the C28 group, and 1790 DEGs (933 up- and 857 downregulated) were identified in the R28 group when compared to their expression levels in the T13 group. According to the functional annotation using KEGG, we found that the immune system was the most enriched section of organismal systems and that the shrimp can mobilize the body's immune response to regulate organism homeostasis during temperature fluctuation, although cold stress decreased the immunity. Additionally, metabolic inhibition is a strategy to cope with cold stress, and the regulation of lipid metabolism was especially important for shrimp during temperature fluctuation. Remarkably, the Hippo signaling pathway might help the repair of intestinal structure. Our research provides the first histological analysis and transcriptome profiling for the L. vannamei intestine during the temperature fluctuation stage. These results enrich our understanding of the mechanism of intestinal self-repair and homeostasis and could provide guidance for shrimp farming.

The signaling relations between three adaptors of porcine C-type lectin receptor pathway

As one family of pattern recognition receptors (PRRs), The C-type lectin receptors (CLRs) play a key role in the anti-fungal infection. The CLR pathway signaling is relayed by adaptor complex which comprises CARD9, BCL10 and MALT1. However, the relationship between these three adaptors has not been investigated. In this study, we isolated porcine CARD9, BCL10 and MALT1 and examined their signaling functions. The three ectopic adaptors were similarly and uniformly expressed in cytoplasm, with CARD9 inactive, BCL10 significant active, and MALT1 slightly active for downstream NF-κB signaling and gene expressions. With the three adaptors together, NF-κB signaling and gene expressions were strongly activated, however, no IFN signal was activated in any case. The signaling relationship between the adaptors were dissected, the NF-κB signaling results showed that CARD9 could inhibit both BCL10 and MALT1 activities, while BCL10 and MALT1 synergized each other particularly when moderate amount of BCL10 plus low amount of MALT1 were considered. Low amount of CARD9 could further synergized with BCL10 and MALT1, maximizing signaling activity of the adaptor complex. This study revealed the porcine CLR pathway adaptor signaling functions and their optimal collective activity, thus providing a unique insight into the porcine innate immunity.

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.

Mannan detecting C-type lectin receptor probes recognise immune epitopes with diverse chemical, spatial and phylogenetic heterogeneity in fungal cell walls

During the course of fungal infection, pathogen recognition by the innate immune system is critical to initiate efficient protective immune responses. The primary event that triggers immune responses is the binding of Pattern Recognition Receptors (PRRs), which are expressed at the surface of host immune cells, to Pathogen-Associated Molecular Patterns (PAMPs) located predominantly in the fungal cell wall. Most fungi have mannosylated PAMPs in their cell walls and these are recognized by a range of C-type lectin receptors (CTLs). However, the precise spatial distribution of the ligands that induce immune responses within the cell walls of fungi are not well defined. We used recombinant IgG Fc-CTLs fusions of three murine mannan detecting CTLs, including dectin-2, the mannose receptor (MR) carbohydrate recognition domains (CRDs) 4–7 (CRD4-7), and human DC-SIGN (hDC-SIGN) and of the β-1,3 glucan-binding lectin dectin-1 to map PRR ligands in the fungal cell wall of fungi grown in vitro in rich and minimal media. We show that epitopes of mannan-specific CTL receptors can be clustered or diffuse, superficial or buried in the inner cell wall. We demonstrate that PRR ligands do not correlate well with phylogenetic relationships between fungi, and that Fc-lectin binding discriminated between mannosides expressed on different cell morphologies of the same fungus. We also demonstrate CTL epitope differentiation during different phases of the growth cycle of Candida albicans and that MR and DC-SIGN labelled outer chain N-mannans whilst dectin-2 labelled core N-mannans displayed deeper in the cell wall. These immune receptor maps of fungal walls of in vitro grown cells therefore reveal remarkable spatial, temporal and chemical diversity, indicating that the triggering of immune recognition events originates from multiple physical origins at the fungal cell surface.

Invasive fungal infections remain an important health problem in immunocompromised patients. Immune recognition of fungal pathogens involves binding of specific cell wall components by pathogen recognition receptors (PRRs) and subsequent activation of immune defences. Some cell wall components are conserved among fungal species while other components are species-specific and phenotypically diverse. The fungal cell wall is dynamic and capable of changing its composition and organization when adapting to different growth niches and environmental stresses. Differences in the composition of the cell wall lead to differential immune recognition by the host. Understanding how changes in the cell wall composition affect recognition by PRRs is likely to be of major diagnostic and clinical relevance. Here we address this fundamental question using four soluble immune receptor-probes which recognize mannans and β-glucan in the cell wall. We use this novel methodology to demonstrate that mannan epitopes are differentially distributed in the inner and outer layers of fungal cell wall in a clustered or diffuse manner. Immune reactivity of fungal cell surfaces was not correlated with relatedness of different fungal species, and mannan-detecting receptor-probes discriminated between cell surface mannans generated by the same fungus growing under different conditions. These studies demonstrate that mannan-epitopes on fungal cell surfaces are differentially distributed within and between the cell walls of fungal pathogens.

PRRDB 2.0: a comprehensive database of pattern-recognition receptors and their ligands

PRRDB 2.0 is an updated version of PRRDB that maintains comprehensive information about pattern-recognition receptors (PRRs) and their ligands. The current version of the database has ~2700 entries, which are nearly five times of the previous version. It contains extensive information about 467 unique PRRs and 827 pathogens-associated molecular patterns (PAMPs), manually extracted from ~600 research articles. It possesses information about PRRs and PAMPs that has been extracted manually from research articles and public databases. Each entry provides comprehensive details about PRRs and PAMPs that includes their name, sequence, origin, source, type, etc. We have provided internal and external links to various databases/resources (like Swiss-Prot, PubChem) to obtain further information about PRRs and their ligands. This database also provides links to ~4500 experimentally determined structures in the protein data bank of various PRRs and their complexes. In addition, 110 PRRs with unknown structures have also been predicted, which are important in order to understand the structure-function relationship between receptors and their ligands. Numerous web-based tools have been integrated into PRRDB 2.0 to facilitate users to perform different tasks like (i) extensive searching of the database; (ii) browsing or categorization of data based on receptors, ligands, source, etc. and (iii) similarity search using BLAST and Smith-Waterman algorithm.

Mechanistic insight into the roles of Pseudomonas plecoglossicida clpV gene in host-pathogen interactions with Larimichthys crocea by dual RNA-seq

Large yellow croaker (Larimichthys crocea) is an economical important farmed fish in China. "Visceral White Spot Disease" caused by Pseudomonas plecoglossicida is a disease with a high mortality rate in cage-cultured L. crocea in recent years and resulted in heavy economy lossess. The dual RNA-seq results of previous study showed that the expression of clpV gene in P. plecoglossicida was significantly up-regulated during infection. RNAi significantly reduced the expression of clpV in P. plecoglossicida with maximum silencing efficiency of 96.1%. Compared with the wild type strain, infection of clpV-RNAi strain resulted in a delayed onset time and a 25% reduction in mortality of L. crocea, as well as lessening the symptoms of the spleen. The results of dual RNA-seq of L. crocea infected by clpV-RNAi strain of P. plecoglossicida changed considerably, compared with the counterpart infected with the wild strain. The KEGG enrichment analysis showed that Cytokine-cytokine receptor interaction, Toll-like receptor signaling pathway, C-type lectin receptor signaling pathway and MAPK signaling pathway of L. crocea were most affected by the silence of clpV in P. plecoglossicida. RNAi of clpV resulted in the downregulation of genes in flagella assembly pathway and a weaker immune response of host.

The Phytopathogenic Fungus Pallidocercospora crystallina-Caused Localized Subcutaneous Phaeohyphomycosis in a Patient with a Homozygous Missense CARD9 Mutation

PURPOSE

In the past decade, an increasing number of otherwise healthy individuals suffered from invasive fungal infections due to inherited CARD9 mutations. Herein, we present a patient with a homozygous CARD9 mutation who was suffering from localized subcutaneous phaeohyphomycosis caused by the phytopathogenic fungus Pallidocercospora crystallina which has not been reported to cause infections in humans.

METHODS

The medical history of our patient was collected. P. crystallina was isolated from the biopsied tissue. To characterize this novel pathogen, the morphology was analyzed, whole-genome sequencing was performed, and the in vivo immune response was explored in mice. Whole-exome sequencing was carried out with samples from the patient's family. Finally, the expression and function of mutated CARD9 were investigated.

RESULTS

A dark red plaque was on the patient's left cheek for 16 years and was diagnosed as phaeohyphomycosis due to a P. crystallina infection. Whole-genome sequencing suggested that that this strain had a lower pathogenicity. The in vivo immune response in immunocompetent or immunocompromised mice indicated that P. crystallina could be eradicated within a few weeks. Whole-exome sequencing revealed ahomozygous missense mutation in CARD9 (c.1118G>C p.R373P). The mRNA and protein expression levels were similar among cells carrying homozygous (C/C), heterozygous (G/C), and wild-type (G/G) CARD9 alleles. Compared to PBMCs or neutrophils with heterozygous or wild-type CARD9 alleles, however, PBMCs or neutrophils with homozygous CARD9 alleles showed impaired anti-P. crystallina effects.

CONCLUSION

Localized subcutaneous phaeohyphomycosis caused by P. crystallina was reported in a patient with a homozygous CARD9 mutation. Physicians should be aware of the possibility of a CARD9 mutation in seemingly healthy patients with unexplainable phaeohyphomycosis.

Cell wall mannoprotein of Candida albicans polarizes macrophages and affects proliferation and apoptosis through activation of the Akt signal pathway

Candida albicans is a commensal fungus that associates with human hosts. Under normal circumstances this interaction does not produce any severe life-threatening disease, as macrophages of the innate immune system will result in its clearance. However, disorders may arise in immunosuppressed individuals. To understand the bioactivity of Candida albicans cell wall polysaccharides, which represent an important component of its function, mannoprotein from this fungus was extracted, purified and analyzed. Mannoprotein with α-(1,2) and α-(1,6) linkages was investigated with use of HPLC and NMR. Co-incubation of mannoprotein with macrophages resulted in a mannoprotein with the potential to polarize macrophages to M1 and promote phagocytosis/microbial killing ability thus increasing the clearance of pathogens through Akt2. Moreover, mannoprotein within the cell wall promoted cell proliferation and inhibited apoptosis by activation of the Akt signaling pathway. Collectively, α-(1,6)(1,2)-mannoprotein, one of the five polysaccharides extracted from the cell wall of Candida albicans, demonstrates immune-enhancing effects by activation of the Akt signaling pathway. These findings provide important new insights into the biological effects of polysaccharides on macrophages. Such information can then serve as the foundation for the development of novel anti-fungal medications.

The planarian Schmidtea mediterranea is a new model to study host-pathogen interactions during fungal infections

Candida albicans is one of the most common fungal pathogens of humans. Currently, there are limitations in the evaluation of C. albicans infection in existing animal models, especially in terms of understanding the influence of specific infectious stages of the fungal pathogen on the host. We show that C. albicans infects, grows and invades tissues in the planarian flatworm Schmidtea mediterranea, and that the planarian responds to infection by activating components of the host innate immune system to clear and repair host tissues. We study different stages of C. albicans infection and demonstrate that planarian stem cells increase division in response to fungal infection, a process that is likely evolutionarily conserved in metazoans. Our results implicate MORN2 and TAK1/p38 signaling pathways as possible mediators of the host innate immune response to fungal infection. We propose the use of planarians as a model system to investigate host-pathogen interactions during fungal infections.

Regulation of immune responses by E3 ubiquitin ligase Cbl-b

Casitas B lymphoma-b (Cbl-b), a RING finger E3 ubiquitin ligase, has been identified as a critical regulator of adaptive immune responses. Cbl-b is essential for establishing the threshold for T cell activation and regulating peripheral T cell tolerance through various mechanisms. Intriguingly, recent studies indicate that Cbl-b also modulates innate immune responses, and plays a key role in host defense to pathogens and anti-tumor immunity. These studies suggest that targeting Cbl-b may represent a potential therapeutic strategy for the management of human immune-related disorders such as autoimmune diseases, infections, tumors, and allergic airway inflammation. In this review, we summarize the latest developments regarding the roles of Cbl-b in innate and adaptive immunity, and immune-mediated diseases.