Neutrophil-suppressive activity over T-cell proliferation and fungal clearance in a murine model of Fonsecaea pedrosoi infection.

Neutrophils are essential to control several fungal infections. These cells are commonly known for their pro-inflammatory activities. However, some studies have demonstrated the anti-inflammatory properties of neutrophils during certain infectious diseases, culminating in the inhibition of T cell proliferation. Chromoblastomycosis (CBM) is a deep and progressive mycosis that affects thousands of people worldwide. Although neutrophil infiltrates are observed in the lesion histopathology, the fungus can overtake the immune system response and destroy the host-infected tissue. The present study demonstrated that neutropenic animals had an increase in the IL-6 production in the spleen and liver, followed by a lower fungal burden in these organs up to 14 days of infection. Neutropenic animals also showed a lower F. pedrosoi-specific antibody production 14-days post infection and higher T-cell proliferation in the in vitro experiments after stimulation with F. pedrosoi-purified proteins. Taken together, our results suggest that the presence of regulatory neutrophils in the mouse model of F. pedrosoi infection could act favoring the spread of the fungus and the chronicity of the infection. These findings shed light on the CBM treatment, which might target neutrophil polarization as a new therapy approach to treat CBM lesions.

Fonsecaeapedrosoi Conidia and Hyphae Activate Neutrophils Distinctly: Requirement of TLR-2 and TLR-4 in Neutrophil Effector Functions.

Chromoblastomycosis is a chronic and progressive subcutaneous mycosis caused mainly by the fungus Fonsecaea pedrosoi. The infection is characterized by erythematous papules and histological sections demonstrating an external layer of fibrous tissue and an internal layer of thick granulomatous inflammatory tissue containing mainly macrophages and neutrophils. Several groups are studying the roles of the innate and adaptive immune systems in F. pedrosoi infection; however, few studies have focused on the role of neutrophils in this infection. In the current study, we verify the importance of murine neutrophils in the killing of F. pedrosoi conidia and hyphae. We demonstrate that phagocytosis and reactive oxygen species during infection with conidia are TLR-2- and TLR-4-dependent and are essential for conidial killing. Meanwhile, hyphal killing occurs by NET formation in a TLR-2-, TLR-4-, and ROS-independent manner. In vivo experiments show that TLR-2 and TLR-4 are also important in chromoblastomycosis infection. TLR-2KO and TLR-4KO animals had lower levels of CCL3 and CXCL1 chemokines and impaired neutrophil migration to the infected site. These animals also had higher fungal loads during infection with F. pedrosoi conidia, confirming that TLR-2 and TLR-4 are essential receptors for F. pedrosoi recognition and immune system activation. Therefore, this study demonstrates for the first time that neutrophil activation during F. pedrosoi is conidial or hyphal-specific with TLR-2 and TLR-4 being essential during conidial infection but unnecessary for hyphal killing by neutrophils.

Intracellular PRRs Activation in Targeting the Immune Response Against Fungal Infections.

The immune response against fungal infections is complex and exhibits several factors involving innate elements that participate in the interaction with the fungus. The innate immune system developed pattern recognition receptors that recognize different pathogen-associated molecular patterns present both on the surface of the fungi cell wall and on their genetic material. These receptors have the function of activating the innate immune response and regulating a subsequent adaptive immune response. Among pattern recognition receptors, the family of Toll-like receptors and C-type lectin receptors are the best described and characterized, they act directly in the recognition of pathogen-associated molecular patterns expressed on the wall of the fungus and consequently in directing the immune response. In recent years, the role of intracellular pattern recognition receptors (TLR3, TLR7, TLR8, and TLR9) has become increasingly important in the pathophysiology of some mycoses, as paracoccidioidomycosis, cryptococcosis, aspergillosis, and candidiasis. The recognition of nucleic acids performed by these receptors can be essential for the control of some fungal infections, as they can be harmful to others. Therefore, this review focuses on highlighting the role played by intracellular pattern recognition receptors both in controlling the infection and in the host's susceptibility against the main fungi of medical relevance.

Silencing of OCH1 unveils the role of Sporothrix schenckii N-linked glycans during the host-fungus interaction.

BACKGROUND: Sporothrix schenckii is a neglected fungal pathogen for the human being and other mammals. In several fungal systems, Och1 is a Golgi α1,6-mannosyltransferase with a key function in the synthesis of N-linked glycans; which are important elements during the host-fungus interplay. The role of OCH1 in fungal virulence seems to be species-specific, being an essential component for Candida albicans virulence and dispensable during the interaction of Aspergillus fumigatus with the host. METHODS: Here, we silenced S. schenckii OCH1 and characterized the phenotype of the mutant strains. RESULTS: The mutant strains did not show defects in the cell or colony morphology, the growth rate or the ability to undergo dimorphism; but the cell wall changed in both composition and exposure of inner components at the surface. When interacting with human monocytes, the silenced strains had a reduced ability to stimulate TNFα and IL-6 but stimulated higher levels of IL-10. The interaction with human macrophages was also altered, with reduced numbers of silenced cells phagocytosed. These strains showed virulence attenuation in both Galleria mellonella and in the mouse model of sporotrichosis. Nonetheless, the cytokine levels in infected organs did not vary significantly when compared with the wild-type strain. CONCLUSION: Our data demonstrate that OCH1 silencing affects different aspects of the S. schenckii-host interaction.

Extracellular Vesicles From Sporothrix brasiliensis Are an Important Virulence Factor That Induce an Increase in Fungal Burden in Experimental Sporotrichosis.

Sporotrichosis is a mycosis that affects the skin, lymphatic system and other organs in humans and animals. The disease has a worldwide distribution, with endemic areas in Brazil, and is caused by a complex of species, including Sporothrix brasiliensis. Some fungi release extracellular vesicles (EVs) that can interact with the host cell and modulate the host immune response. The aim of this study was to analyze the participation of S. brasiliensis EVs in the modulation of dendritic cells (DCs) and in the control of infection in vivo. Our results showed that in vitro, the EVs isolated from S. brasiliensis induced an increase in the phagocytic index and fungal burden in DCs. In addition, we observed a significant increase in IL-12p40 and TNF-α cytokine production. Then, the EVs were inoculated into BALB/c mice before subcutaneous infection with yeast, and the lesion was analyzed after 21, 35, and 42 days. An increase in fungal burden and lesion diameter were observed after 21 days in mice inoculated with a high concentration of EVs. However, after 35 days, we observed a regression of the lesion, which persisted until 42 days after infection. Interestingly, we observed an increase in fungal burden in these mice. In addition, we observed the presence of immunogenic components and proteins that could be related with virulence in EVs. These results suggest that EVs can play an important role in virulence and modulation of the host immune system during experimental S. brasiliensis infection.

Notch Signaling is Required for Dendritic Cell Maturation and T Cell Expansion in Paracoccidioidomycosis.

The Notch signaling pathway participates in several cellular functional aspects. This signaling has an important role in targeting both DC maturation and DC-mediated T cell responses. Thus, it is essential to investigate the influence of this signaling pathway in the role played by DCs in the pathogenesis of experimental paracoccidioidomycosis. This disease is a granulomatous and systemic mycosis that mainly affects lung tissue and can spread to any other organ and system. In this study, we demonstrated that bone marrow-derived DCs infected with yeasts from Paracoccidioides brasiliensis strain 18 performed efficiently their maturation after the activation of Notch signaling, with an increase in CD80, CD86, CCR7, and CD40 expression and the release of cytokines such as IL-6 and TNF-α. We observed that the inhibition of the γ-secretase DAPT impaired the proliferation of T cells induced by DC stimulation. In conclusion, our data suggest that Notch signaling contributes effectively to the maturation of DCs and the DC-mediated activation of the T cell response in P. brasiliensis infections.

An immunoproteomic approach revealing peptides from Sporothrix brasiliensis that induce a cellular immune response in subcutaneous sporotrichosis.

Sporothrix brasiliensis is the most virulent fungus of the Sporothrix complex and is the main species recovered in the sporotrichosis zoonotic hyperendemic area in Rio de Janeiro. A vaccine against S. brasiliensis could improve the current sporotrichosis situation. Here, we show 3 peptides from S. brasiliensis immunogenic proteins that have a higher likelihood for engaging MHC-class II molecules. We investigated the efficiency of the peptides as vaccines for preventing subcutaneous sporotrichosis. In this study, we observed a decrease in lesion diameters in peptide-immunized mice, showing that the peptides could induce a protective immune response against subcutaneous sporotrichosis. ZR8 peptide is from the GP70 protein, the main antigen of the Sporothrix complex, and was the best potential vaccine candidate by increasing CD4+ T cells and higher levels of IFN-γ, IL-17A and IL-1ß characterizing a strong cellular immune response. This immune environment induced a higher number of neutrophils in lesions that are associated with fungus clearance. These results indicated that the ZR8 peptide induces a protective immune response against subcutaneous sporotrichosis and is a vaccine candidate against S. brasiliensis infection.

TLR3 Is a Negative Regulator of Immune Responses Against Paracoccidioides brasiliensis.

Toll-like receptors (TLRs) comprise the best-characterized pattern-recognition receptor (PRR) family able to activate distinct immune responses depending on the receptor/adaptor set assembled. TLRs, such as TLR2, TLR4 and TLR9, and their signaling were shown to be important in Paracoccidioides brasiliensis infections. However, the role of the endosomal TLR3 in experimental paracoccidioidomycosys remains obscure. In vitro assays, macrophages of the bone marrow of WT or TLR3-/- mice were differentiated for evaluation of their microbicidal activity. In vivo assays, WT or TLR3-/- mice were infected intratracheally with Paracoccidioides brasiliensis yeasts for investigation of the lung response type induced. The cytotoxic activity of CD8+ T cells was assessed by cytotoxicity assay. To confirm the importance of CD8+ T cells in the control of infection in the absence of tlr3, a depletion assay of these cells was performed. Here, we show for the first time that TLR3 modulate the infection against Paracoccidioides brasiliensis by dampening pro-inflammatory response, NO production, IFN+CD8+T, and IL-17+CD8+T cell activation and cytotoxic function, associated with granzyme B and perforin down regulation. As conclusion, we suggest that TLR3 could be used as an escape mechanism of the fungus in an experimental paracoccidioidomycosis.

The Critical Role of Notch1-TLR 4 Signaling in the Inflammatory and Fungicidal Activity of Macrophages Against Paracoccidioides brasiliensis Strain Pb18.

Paracoccidioidomycosis is a systemic mycosis of deep nature that primarily affects the lung and can spread via lymphatic and hematogenous to other organs and tissues. It is mainly caused by Paracoccidioides brasiliensis fungus which exhibits thermal dimorphism. The innate immune system mediated by macrophages is extremely important for the control of infection and is involved in the induction and regulation of immune/inflammatory response. These cells are able to recognize pathogens through pattern recognition receptors (PRRs) such as Toll-like receptors (TLR). Beyond these PRRs, the importance of Notch signaling has recently been demonstrated in the innate immune system and the regulation of macrophage activity. Our data demonstrate that the Pb18 strain of P. brasiliensis is able to activate the transcription of Notch1 receptor in J774 macrophages. Activation of this receptor with also activation of TLR 4 (via LPS) induces IL-6 production, which favors the pathogenesis. By using a γ-secretase pharmacological inhibitor (DAPT) for inhibiting the activation of Notch1 receptor on macrophages, it is possible to observe the decreased fungal burden, less production of IL-6, and increased TNF-α and phagocytosis. Taken together, these results showed that Pb18 is able to induce the transcription of Notch1 receptor on macrophages and may provide a new immunity study approach in experimental paracoccidioidomycosis.

The Atypical Response Regulator AtvR Is a New Player in Pseudomonas aeruginosa Response to Hypoxia and Virulence.

Two-component systems are widespread in bacteria, allowing adaptation to environmental changes. The classical pathway is composed of a histidine kinase that phosphorylates an aspartate residue in the cognate response regulator (RR). RRs lacking the phosphorylatable aspartate also occur, but their function and contribution during host-pathogen interactions are poorly characterized. AtvR (PA14_26570) is the only atypical response regulator with a DNA-binding domain in the opportunistic pathogen Pseudomonas aeruginosa Macrophage infection with the atvR mutant strain resulted in higher levels of tumor necrosis factor alpha secretion as well as increased bacterial clearance compared to those for macrophages infected with the wild-type strain. In an acute pneumonia model, mice infected with the atvR mutant presented increased amounts of proinflammatory cytokines, increased neutrophil recruitment to the lungs, reductions in bacterial burdens, and higher survival rates in comparison with the findings for mice infected with the wild-type strain. Further, several genes involved in hypoxia/anoxia adaptation were upregulated upon atvR overexpression, as seen by high-throughput transcriptome sequencing (RNA-Seq) analysis. In addition, atvR was more expressed in hypoxia in the presence of nitrate and required for full expression of nitrate reductase genes, promoting bacterial growth under this condition. Thus, AtvR would be crucial for successful infection, aiding P. aeruginosa survival under conditions of low oxygen tension in the host. Taken together, our data demonstrate that the atypical response regulator AtvR is part of the repertoire of transcriptional regulators involved in the lifestyle switch from aerobic to anaerobic conditions. This finding increases the complexity of regulation of one of the central metabolic pathways that contributes to Pseudomonas ubiquity and versatility.

scFv from Antibody That Mimics gp43 Modulates the Cellular and Humoral Immune Responses during Experimental Paracoccidioidomycosis.

Paracoccidioidomycosis (PCM), caused by Paracoccidioides species is a prevalent systemic and progressive mycosis that occurs in Latin America. It is caused by Paracoccidioides species. Immunization with dendritic cells transfected with a plasmid encoding the scFv (pMAC/PS-scFv) that mimics the main antigen of P. brasiliensis (gp43) confers protection in experimental PCM. DCs link innate and adaptive immunity by recognizing invading pathogens and selecting the type of effector T cell to mediate the immune response. Here, we showed that DC-pMAC/PS-scFv induces the activation of CD4+ and CD8+ T cells. Moreover, our results demonstrated that BALB/c mice infected with P. brasiliensis and treated with DC-pMAC/PS-scFv showed the induction of specific IgG production against gp43 and IFN-γ, IL-12 and IL-4 cytokines. Analysis of regional lymph nodes revealed increases in the expression of clec7a, myd88, tlr2, gata3 and tbx21, which are involved in the immune response. Taken together, our results indicate that the scFv modulates the humoral and cellular immune responses and presents epitopes to CD4+ and CD8+ T cells.

Therapeutic vaccine using a monoclonal antibody against a 70-kDa glycoprotein in mice infected with highly virulent Sporothrix schenckii and Sporothrix brasiliensis.

Sporotrichosis is a chronic granulomatous mycosis caused by the dimorphic fungi that comprise the Sporothrix complex. The latter are widely distributed in nature, developing a saprophytic mycelial form on plant debris and soil. Formerly, the S. schenckii species was thought to be the only species capable of causing sporotrichosis. However, in recent years, the existence of a group of highly genotypically and phenotypically variable species has been reported as etiologic agents of this mycosis. Recently, it has become important to study aspects such as virulence and the immune response against key members of the Sporothrix complex and to observe the presence of glycoprotein (gp) 70 and efficacy of the P6E7 monoclonal antibody against more virulent strains. The data presented here demonstrate that the strain isolated from a case of feline sporotrichosis, that is, strain 5110 (American Type Culture Collection MYA-4823) is the most virulent and the only one able to secrete gp70. This glycoprotein is apparently an important factor in the virulence of Sporothrix spp. because treatment with MAb P6E7 resulted in the reduction of fungal burden in the analyzed organs. Additional studies of the role of gp70 in modulating the immune response of the host are needed to understand the pathology of sporotrichosis.