The relative importance of CD4+ and CD8+T cells in immunity to pulmonary paracoccidioidomycosis

Myeloid-derived suppressor cells are associated with impaired Th1 and Th17 responses and severe pulmonary paracoccidioidomycosis which is reversed by anti-Gr1 therapy

Previous studies on paracoccidioidomycosis (PCM), the most prevalent systemic mycosis in Latin America, revealed that host immunity is tightly regulated by several suppressive mechanisms mediated by tolerogenic plasmacytoid dendritic cells, the enzyme 2,3 indoleamine dioxygenase (IDO-1), and regulatory T-cells (Tregs). IDO-1 orchestrates local and systemic immunosuppressive effects through the recruitment and activation of myeloid-derived suppressor cells (MDSCs), a heterogeneous population of myeloid cells possessing a potent ability to suppress T-cell responses. However, the involvement of MDSCs in PCM remains uninvestigated. The presence, phenotype, and immunosuppressive activity of MDSCs were evaluated at 96 h, 2 weeks, and 8 weeks of pulmonary infection in C57BL/6 mice. Disease severity and immune responses were assessed in MDSC-depleted and nondepleted mice using an anti-Gr1 antibody. Both monocytic-like MDSCs (M-MDSCs) and polymorphonuclear-like MDSCs (PMN-MDSCs) massively infiltrated the lungs during Paracoccidioides brasiliensis infection. Partial reduction of MDSC frequency led to a robust Th1/Th17 lymphocyte response, resulting in regressive disease with a reduced fungal burden on target organs, diminishing lung pathology, and reducing mortality ratio compared with control IgG2b-treated mice. The suppressive activity of MDSCs on CD4 and CD8 T-lymphocytes and Th1/Th17 cells was also demonstrated in vitro using coculture experiments. Conversely, adoptive transfer of MDSCs to recipient P. brasiliensis-infected mice resulted in a more severe disease. Taken together, our data showed that the increased influx of MDSCs into the lungs was linked to more severe disease and impaired Th1 and Th17 protective responses. However, protective immunity was rescued by anti-Gr1 treatment, resulting in a less severe disease and controlled tissue pathology. In conclusion, MDSCs have emerged as potential target cells for the adjuvant therapy of PCM.

Paracoccidioidomycosis: Current Status and Future Trends

Paracoccidioidomycosis (PCM), initially reported in 1908 in the city of São Paulo, Brazil, by Adolpho Lutz, is primarily a systemic and neglected tropical mycosis that may affect individuals with certain risk factors around Latin America, especially Brazil. Paracoccidioides brasiliensis sensu stricto, a classical thermodimorphic fungus associated with PCM, was long considered to represent a monotypic taxon. However, advances in molecular taxonomy revealed several cryptic species, including Paracoccidioides americana, P. restrepiensis, P. venezuelensis, and P. lutzii, that show a preference for skin and mucous membranes, lymph nodes, and respiratory organs but can also affect many other organs. The classical diagnosis of PCM benefits from direct microscopy culture-based, biochemical, and immunological assays in a general microbiology laboratory practice providing a generic identification of the agents. However, molecular assays should be employed to identify Paracoccidioides isolates to the species level, data that would be complemented by epidemiological investigations. From a clinical perspective, all probable and confirmed cases should be treated. The choice of treatment and its duration must be considered, along with the affected organs, process severity, history of previous treatment failure, possibility of administering oral medication, associated diseases, pregnancy, and patient compliance with the proposed treatment regimen. Nevertheless, even after appropriate treatment, there may be relapses, which generally occur 5 years after the apparent cure following treatment, and also, the mycosis may be confused with other diseases. This review provides a comprehensive and critical overview of the immunopathology, laboratory diagnosis, clinical aspects, and current treatment of PCM, highlighting current issues in the identification, treatment, and patient follow-up in light of recent Paracoccidioides species taxonomic developments.

T cell responses to control fungal infection in an immunological memory lens

In recent years, fungal vaccine research emanated significant findings in the field of antifungal T-cell immunity. The generation of effector T cells is essential to combat many mucosal and systemic fungal infections. The development of antifungal memory T cells is integral for controlling or preventing fungal infections, and understanding the factors, regulators, and modifiers that dictate the generation of such T cells is necessary. Despite the deficiency in the clear understanding of antifungal memory T-cell longevity and attributes, in this review, we will compile some of the existing literature on antifungal T-cell immunity in the context of memory T-cell development against fungal infections.

NLRC4 inhibits NLRP3 inflammasome and abrogates effective antifungal CD8+ T cell responses

The recognition of fungi by intracellular NOD-like receptors (NLRs) induces inflammasome assembly and activation. Although the NLRC4 inflammasome has been extensively studied in bacterial infections, its role during fungal infections is unclear. Paracoccidioidomycosis (PCM) is a pathogenic fungal disease caused by Paracoccidioides brasiliensis. Here, we show that NLRC4 confers susceptibility to experimental PCM by regulating NLRP3-dependent cytokine production and thus protective effector mechanisms. Early after infection, NLRC4 suppresses prostaglandin E₂ production, and consequently reduces interleukin (IL)-1β release by macrophages and dendritic cells in the lungs. IL-1β is required to control fungal replication via induction of the nitric oxide synthase 2 (NOS2) pathway. At a later stage of the disease, NLRC4 impacts IL-18 release, dampening robust CD8⁺IFN-γ⁺ T cell responses and enhancing mortality of mice. These findings demonstrate that NLRC4 promotes disease by regulating the production of inflammatory cytokines and cellular responses that depend on the NLRP3 inflammasome activity.

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NLRC4 promotes susceptibility to a highly pathogenic fungus.

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NLRC4 regulates NLRP3 activity.

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NLRC4 inhibits early NLRP3/IL-1β/NOS2/NO axis and promotes fungal replication.

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NLRC4 dampens late IL-18 production, suppressing CD8⁺IFN-γ⁺ T cell responses.

Invariant Natural Killer T Cells as Key Players in Host Resistance against Paracoccidioides brasiliensis

Invariant Natural Killer T (iNKT) cells are key players in the immunity to several pathogens; however, their involvement in the resistance to Paracoccidioides brasiliensis infection remains unknown. Using splenocytes from CD1d (CD1d^−/−) and iNKT-deficient (Jα18^−/−) mice, we found that iNKT cells are the innate source of IFN-γ after P. brasiliensis infection and are required to potentiate macrophage oxidative burst and control fungal growth. To determine whether iNKT cells contribute in vivo to host resistance against P. brasiliensis infection, we infected intratracheally wild-type and Jα18^−/− C57BL/6 mouse strains with the virulent Pb18 isolate. iNKT cell deficiency impaired the airway acute inflammatory response, resulting in decreased airway neutrophilia and reduced IFN-γ, KC, and nitric oxide (NO) production. The deficient innate immune response of Jα18^−/− mice to Pb18 infection resulted in increased fungal burden in the lungs and spleen. Besides, the activation of iNKT cells in vivo by administration of the exogenous iNKT ligand α-galactosylceramide (α-GalCer) improved host resistance to P. brasiliensis infection. Although the mechanisms responsible for this phenomenon remain to be clarified, α-GalCer treatment boosted the local inflammatory response and reduced pulmonary fungal burden. In conclusion, our study is the first evidence that iNKT cells are important for the protective immunity to P. brasiliensis infection and their activation by an exogenous ligand is sufficient to improve the host resistance to this fungal infection.

Paracoccidioidomycosis Protective Immunity

Protective immunity against Paracoccidioides consists of a stepwise activation of numerous effector mechanisms that comprise many cellular and soluble components. At the initial phase of non-specific innate immunity, resistance against Paracoccidioides comes from phagocytic polymorphonuclear neutrophils, natural killer (NK) cells and monocytes, supplemented by soluble factors such as cytokines and complement system components. Invariant receptors (Toll-like receptors (TLRs), Dectins) which are present in cells of the immune system, detect patterns present in Paracoccidioides (but not in the host) informing the hosts cells that there is an infection in progress, and that the acquired immunity must be activated. The role of components involved in the innate immunity of paracoccidioidomycosis is herein presented. Humoral immunity, represented by specific antibodies which control the fungi in the blood and body fluids, and its role in paracoccidioidomycosis (which was previously considered controversial) is also discussed. The protective mechanisms (involving various components) of cellular immunity are also discussed, covering topics such as: lysis by activated macrophages and cytotoxic T lymphocytes, the participation of lytic products, and the role of cytokines secreted by T helper lymphocytes in increasing the efficiency of Paracoccidioides, lysis.

The Role of the Interleukin-17 Axis and Neutrophils in the Pathogenesis of Endemic and Systemic Mycoses

Systemic and endemic mycoses are considered life-threatening respiratory diseases which are caused by a group of dimorphic fungal pathogens belonging to the genera Histoplasma, Coccidioides, Blastomyces, Paracoccidioides, Talaromyces, and the newly described pathogen Emergomyces. T-cell mediated immunity, mainly T helper (Th)1 and Th17 responses, are essential for protection against these dimorphic fungi; thus, IL-17 production is associated with neutrophil and macrophage recruitment at the site of infection accompanied by chemokines and proinflammatory cytokines production, a mechanism that is mediated by some pattern recognition receptors (PRRs), including Dectin-1, Dectine-2, TLRs, Mannose receptor (MR), Galectin-3 and NLPR3, and the adaptor molecules caspase adaptor recruitment domain family member 9 (Card9), and myeloid differentiation factor 88 (MyD88). However, these PRRs play distinctly different roles for each pathogen. Furthermore, neutrophils have been confirmed as a source of IL-17, and different neutrophil subsets and neutrophil extracellular traps (NETs) have also been described as participating in the inflammatory process in these fungal infections. However, both the Th17/IL-17 axis and neutrophils appear to play different roles, being beneficial mediating fungal controls or detrimental promoting disease pathologies depending on the fungal agent. This review will focus on highlighting the role of the IL-17 axis and neutrophils in the main endemic and systemic mycoses: histoplasmosis, coccidioidomycosis, blastomycosis, and paracoccidioidomycosis.

Insulin Modulates Inflammatory Cytokine Release in Acute Stages and Augments Expression of Adhesion Molecules and Leukocytes in Lungs on Chronic Stages of Paracoccidioidomycosis

Type 1 diabetesmellitus (T1D) is caused by partial destruction of the insulin-producing beta cells in the pancreas and is a major issue for public health care worldwide. Reduced or impaired immunological responses, which render patients more susceptible to infections, have been observed in T1D, and this dysfunction is often related to a lack of insulin in the blood. Paracoccidioidomycosis is an important systemic mycosis endemic in Latin America. To evaluate the effects of T1D on this fungal infection and the modulatory effects of insulin, we induced diabetes in C57Bl/6 male mice (alloxan, 60 mg/kg), infected the mice (Pb18, 1 x 106 cells), and treated the mice with neutral protamine Hagedorn (NPH) insulin (2 IU/600 mg/dL blood glucose). Twenty-four hours after infection, infected diabetic mice showed reduced secretion of interferon (IFN)-γ and interleukine (IL)-12 p70 compared to infected nondiabetic controls. On the 45th day of infection, infected diabetic mice presented higher IFN-γ levels, a higher tumor necrosis factor (TNF)-α:IL-10 ratio, and lower adhesion molecule expression levels than nondiabetic mice. In the in vitro experiments, alveolar macrophages from diabetic animals showed reduced phagocytic activity compared to those from control animals at 4, 12, and 24 h. In infected diabetic mice, treatment with insulin restored IL-12 p70 levels at 24 h of infection, reduced IFN-γ levels and the TNF-α:IL-10 ratio at 45 days, and restored vascular cell adhesion molecule (VCAM)-1 expression in pulmonary blood vessels, and this treatment reduced the diminished phosphorylation of extracellular signal-regulated kinases (ERK) and increased nuclear factor-kappa-B(iκb)-α and jun amino-terminal kinases (JNK) p46 levels in infected nondiabetic mice. In addition, insulin promoted increased phagocytic activity in the alveolar macrophages of diabetic mice. These data suggest that T1D mice are more susceptible to Pb18 infection and that insulin modulates this inflammation in diabetic mice by augmenting the expression of adhesion molecules and leukocytes in the lungs and by reducing chronic inflammation.

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.

Depletion of regulatory T cells in ongoing paracoccidioidomycosis rescues protective Th1/Th17 immunity and prevents fatal disease outcome

In human paracoccidioidomycosis (PCM), a primary fungal infection typically diagnosed when the disease is already established, regulatory T cells (Treg) cells are associated with disease severity. Experimental studies in pulmonary PCM confirmed the detrimental role of these cells, but in most studies, Tregs were depleted prior to or early during infection. These facts led us to study the effects of Treg cell depletion using a model of ongoing PCM. Therefore, Treg cell depletion was achieved by treatment of transgenic C57BL/6DTR/eGFP (DEREG) mice with diphtheria toxin (DT) after 3 weeks of intratracheal infection with 1 × 106 Paracoccidioides brasiliensis yeasts. At weeks 6 and 10 post-infection, DT-treated DEREG mice showed a reduced number of Treg cells associated with decreased fungal burdens in the lungs, liver and spleen, reduced tissue pathology and mortality. Additionally, an increased influx of activated CD4+ and CD8+ T cells into the lungs and elevated production of Th1/Th17 cytokines was observed in DT-treated mice. Altogether, our data demonstrate for the first time that Treg cell depletion in ongoing PCM rescues infected hosts from progressive and potentially fatal PCM; furthermore, our data indicate that controlling Treg cells could be explored as a novel immunotherapeutic procedure.

Insulin Modulates Paracoccidioides brasiliensis-Induced Inflammation by Restoring the Populations of NK Cells, Dendritic Cells, and B Lymphocytes in Lungs

Paracoccidioidomycosis, a key issue for Brazilian health service, can be aggravated in patients with impaired immunological responses, such as diabetic patients. We evaluated the role of insulin in inflammatory parameters in diabetic and nondiabetic mice using a systemic mycosis Paracoccidioides brasiliensis (Pb) model. Diabetic C57BL-6 mice and controls were infected with Pb18 and treated with insulin for 12 days prior to experiments. After 55 days, infected diabetic mice exhibited fewer leukocytes in both peritoneal lavage fluid (PeLF) and bronchoalveolar lavage fluid and reduced secretion of interleukin- (IL-) 6 in lungs. In addition, diabetic mice presented a reduced influx of TCD4+ cells, TCD8+ cells, B lymphocytes, NK cells, and dendritic cells compared to control infected groups. Insulin treatment restored the leukocyte number in PeLF and restored the presence of B lymphocytes, dendritic cells, and NK cells in lungs of diabetic animals. The data suggest that diabetic mice present impaired immunological response to Pb18 infection and insulin modulates inflammation by reducing IL-6 levels in lung and CINC-1 levels in spleen and liver homogenates, restoring leukocyte concentrations in PeLF and also restoring populations of dendritic cells and B lymphocytes in lungs of diabetic mice, permitting the host to better control the infection.

Paracoccidioidomycosis: Epidemiological and Clinical Aspects in 546 Cases Studied in the State of Espírito Santo, Brazil

Paracoccidioidomycosis (PCM) is an endemic disease in the southeast region of Brazil, which includes the state of Espírito Santo (ES). This historic case series analyses 546 patients treated in this state from 1978 to 2012. Patients aged from 7 to 83 years, 509 males and 37 females, yielding a ratio of 13.7:1. Most of the patients (81.4%) originated from rural areas in ES, 71.0% being farmers. A higher concentration of cases was observed in municipalities located along the western range of the state. Sixty patients (11.0%) had an acute/subacute form of the disease, 485 (88.9%) had a chronic form, and one had a subclinical form. The most affected organs included the lungs, oropharyngeal mucosa, lymph nodes, skin, and larynx. The diagnosis was confirmed by histopathology in 252 (46.2%) cases, direct examination in 168 (30.7%), both exams in 111 (20.3%) and serology in 15 (2.8%). Tuberculosis, acquired immune deficiency syndrome, leishmaniasis, and intestinal parasites were the most frequently associated infectious diseases. From 328 patients followed up, total regression of the lesions was observed in 17.4%, partial regression in 77.4%, and no regression in 17 (5.2%) cases. Regarding the number of cases in this series, ES emerges as an important endemic area for PCM in Brazil.

The IDO-AhR Axis Controls Th17/Treg Immunity in a Pulmonary Model of Fungal Infection

In infectious diseases, the enzyme indoleamine 2,3 dioxygenase-1 (IDO1) that catalyzes the tryptophan (Trp) degradation along the kynurenines (Kyn) pathway has two main functions, the control of pathogen growth by reducing available Trp and immune regulation mediated by the Kyn-mediated expansion of regulatory T (Treg) cells via aryl hydrocarbon receptor (AhR). In pulmonary paracoccidioidomycosis (PCM) caused by the dimorphic fungus Paracoccidioides brasiliensis, IDO1 was shown to control the disease severity of both resistant and susceptible mice to the infection; however, only in resistant mice, IDO1 is induced by TGF-β signaling that confers a stable tolerogenic phenotype to dendritic cells (DCs). In addition, in pulmonary PCM, the tolerogenic function of plasmacytoid dendritic cells was linked to the IDO1 activity. To further evaluate the function of IDO1 in pulmonary PCM, IDO1-deficient (IDO1^-/-) C57BL/6 mice were intratracheally infected with P. brasiliensis yeasts and the infection analyzed at three postinfection periods regarding several parameters of disease severity and immune response. The fungal loads and tissue pathology of IDO1^-/- mice were higher than their wild-type controls resulting in increased mortality rates. The evaluation of innate lymphoid cells showed an upregulated differentiation of the innate lymphoid cell 3 phenotype accompanied by a decreased expansion of ILC1 and NK cells in the lungs of infected IDO1^-/- mice. DCs from these mice expressed elevated levels of costimulatory molecules and cytokine IL-6 associated with reduced production of IL-12, TNF-α, IL-1β, TGF-β, and IL-10. This response was concomitant with a marked reduction in AhR production. The absence of IDO1 expression caused an increased influx of activated Th17 cells to the lungs with a simultaneous reduction in Th1 and Treg cells. Accordingly, the suppressive cytokines IL-10, TGF-β, IL-27, and IL-35 appeared in reduced levels in the lungs of IDO1^-/- mice. In conclusion, the immunological balance mediated by the axis IDO/AhR is fundamental to determine the balance between Th17/Treg cells and control the severity of pulmonary PCM.

NOD-Like Receptor P3 Inflammasome Controls Protective Th1/Th17 Immunity against Pulmonary Paracoccidioidomycosis

The NOD-like receptor P3 (NLRP3) inflammasome is an intracellular multimeric complex that triggers the activation of inflammatory caspases and the maturation of IL-1β and IL-18, important cytokines for the innate immune response against pathogens. The functional NLRP3 inflammasome complex consists of NLRP3, the adaptor protein apoptosis-associated speck-like protein, and caspase-1. Various molecular mechanisms were associated with NLRP3 activation including the presence of extracellular ATP, recognized by the cell surface P2X7 receptor (P2X7R). Several pattern recognition receptors on innate immune cells recognize Paracoccidioides brasiliensis components resulting in diverse responses that influence adaptive immunity and disease outcome. However, the role of NLRP3 inflammasome was scantily investigated in pulmonary paracoccidioidomycosis (PCM), leading us to use an intratracheal (i.t.) model of infection to study the influence of this receptor in anti-fungal immunity and severity of infection. For in vivo studies, C57BL/6 mice deficient for several NLRP3 inflammasome components (Nlrp3^−/−, Casp1/11^−/−, Asc^−/−) as well as deficient for ATP receptor (P2x7r^−/−) were infected via i.t. with P. brasiliensis and several parameters of immunity and disease severity analyzed at the acute and chronic periods of infection. Pulmonary PCM was more severe in Nlrp3^−/−, Casp1/11^−/−, Asc^−/−, and P2x7r^−/− mice as demonstrated by the increased fungal burdens, mortality rates and tissue pathology developed. The more severe disease developed by NLRP3, ASC, and Caspase-1/11 deficient mice was associated with decreased production of IL-1β and IL-18 and reduced inflammatory reactions mediated by PMN leukocytes and activated CD4⁺ and CD8⁺ T cells. The decreased T cell immunity was concomitant with increased expansion of CD4⁺CD25⁺Foxp3 regulatory T (Treg) cells. Characterization of intracellular cytokines showed a persistent reduction of CD4⁺ and CD8⁺ T cells expressing IFN-γ and IL-17 whereas those producing IL-4 and TGF-β appeared in increased frequencies. Histopathological studies showed that all deficient mouse strains developed more severe lesions containing elevated numbers of budding yeast cells resulting in increased mortality rates. Altogether, these findings led us to conclude that the activation of the NLRP3 inflammasome has a crucial role in the immunoprotection against pulmonary PCM by promoting the expansion of Th1/Th17 immunity and reducing the suppressive control mediated by Treg cells.

Genetically Engineered Virus Nanofibers as an Efficient Vaccine for Preventing Fungal Infection

Candida albicans (CA) is a kind of fungus that can cause high morbidity and mortality in immunocompromised patients. However, preventing CA infection in these patients is still a daunting challenge. Herein, inspired from the fact that immunization with secreted aspartyl proteinases 2 (Sap2) can prevent the infection, it is proposed to use filamentous phage, a human-safe virus nanofiber specifically infecting bacteria (≈900 nm long and 7 nm wide), to display an epitope peptide of Sap2 (EPS, with a sequence of Val-Lys-Tyr-Thr-Ser) on its side wall and thus serve as a vaccine for preventing CA infection. The engineered virus nanofibers and recombinant Sap2 (rSap2) are then separately used to immunize mice. The humoral and cellular immune responses in the immunized mice are evaluated. Surprisingly, the virus nanofibers significantly induce mice to produce strong immune response as rSap2 and generate antibodies that can bind Sap2 and CA to inhibit the CA infection. Consequently, immunization with the virus nanofibers in mice dramatically increases the survival rate of CA-infected mice. All these results, along with the fact that the virus nanofibers can be mass-produced by infecting bacteria cost-effectively, suggest that virus nanofibers displaying EPS can be a vaccine candidate against fungal infection.

New insights into a complex fungal pathogen: the case of Paracoccidioides spp

Paracoccidioidomycosis is a systemic mycosis endemic to Latin America, with Paracoccidioides brasiliensis and P. lutzii being the causal agents of this disorder. Several issues have been raised in the 100 years since its discovery and in this article we discuss features of this fascinating fungal pathogen, including its biology, eco-epidemiology and aspects of its pathogenicity. We also consider some of its virulence determinants, the most recent advances in the study of its metabolic pathways and the molecular and genetic research tools developed for this research. We also review the animal models used to study host-fungal interactions and how the host defence mechanisms against this pathogen work.

Paracoccidioides-host Interaction: An Overview on Recent Advances in the Paracoccidioidomycosis

Paracoccidioides brasiliensis and P. lutzii are etiologic agents of paracoccidioidomycosis (PCM), an important endemic mycosis in Latin America. During its evolution, these fungi have developed characteristics and mechanisms that allow their growth in adverse conditions within their host through which they efficiently cause disease. This process is multi-factorial and involves host-pathogen interactions (adaptation, adhesion, and invasion), as well as fungal virulence and host immune response. In this review, we demonstrated the glycoproteins and polysaccharides network, which composes the cell wall of Paracoccidioides spp. These are important for the change of conidia or mycelial (26°C) to parasitic yeast (37°C). The morphological switch, a mechanism for the pathogen to adapt and thrive inside the host, is obligatory for the establishment of the infection and seems to be related to pathogenicity. For these fungi, one of the most important steps during the interaction with the host is the adhesion. Cell surface proteins called adhesins, responsible for the first contact with host cells, contribute to host colonization and invasion by mediating this process. These fungi also present the capacity to form biofilm and through which they may evade the host's immune system. During infection, Paracoccidioides spp. can interact with different host cell types and has the ability to modulate the host's adaptive and/or innate immune response. In addition, it participates and interferes in the coagulation system and phenomena like cytoskeletal rearrangement and apoptosis. In recent years, Paracoccidioides spp. have had their endemic areas expanding in correlation with the expansion of agriculture. In response, several studies were developed to understand the infection using in vitro and in vivo systems, including alternative non-mammal models. Moreover, new advances were made in treating these infections using both well-established and new antifungal agents. These included natural and/or derivate synthetic substances as well as vaccines, peptides, and anti-adhesins sera. Because of all the advances in the PCM study, this review has the objective to summarize all of the recent discoveries on Paracoccidioides-host interaction, with particular emphasis on fungi surface proteins (molecules that play a fundamental role in the adhesion and/or dissemination of the fungi to host-cells), as well as advances in the treatment of PCM with new and well-established antifungal agents and approaches.

Expression of dectin-1 and enhanced activation of NALP3 inflammasome are associated with resistance to paracoccidioidomycosis

Dectin-1 is a pattern recognition receptor (PRR) that recognizes β-glucans and plays a major role in the immunity against fungal pathogens. Paracoccidioides brasiliensis, the causative agent of paracoccidioidomycosis, has a sugar-rich cell wall mainly composed of mannans and glucans. To investigate the role of dectin-1 in the innate immunity of resistant (A/J) and susceptible (B10.A) mice to P. brasiliensis infection, we evaluated the role of curdlan (a dectin-1 agonist) and laminarin (a dectin-1 antagonist) in the activation of macrophages from both mouse strains. We verified that curdlan has a negligible role in the activation of B10.A macrophages but enhances the phagocytic and fungicidal abilities of A/J macrophages. Curdlan up-regulated the expression of costimulatory molecules and PRRs in A/J macrophages that express elevated levels of dectin-1, but not in B10.A cells. In addition, curdlan treatment inhibited arginase-1 and enhanced NO-synthase mRNA expression in infected A/J macrophages but had not effect in B10.A cells. In contrast, laminarin reinforced the respective M2/M1 profiles of infected A/J and B10.A macrophages. Following curdlan treatment, A/J macrophages showed significantly higher Syk kinase phosphorylation and expression of intracellular pro-IL-1β than B10.A cells. These findings led us to investigate if the NRLP3 inflammasome was differently activated in A/J and B10.A cells. Indeed, compared with B10.A cells A/J macrophages showed an increased expression of NALP3, ASC, and IL-1β mRNA. They also showed elevated caspase-1 activity and secreted high levels of mature IL-β and IL-18 after curdlan treatment and P. brasiliensis infection. Our data demonstrate that soluble and particulate β-glucans exert opposed modulatory activities on macrophages of diverse genetic patterns. Moreover, the synergistic action of dectin-1 and NALP3 inflammasome were for the first time associated with the innate response of resistant hosts to P. brasiliensis infection.

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.

Synchronous oral paracoccidioidomycosis and pulmonary tuberculosis in an immunocompetent patient

Paracoccidioidomycosis (PCM) and tuberculosis (TB) are chronic granulomatous infectious diseases, in which the main form of contraction is through inhalation of the microorganism-Paracoccidioides brasiliensis and Mycobacterium tuberculosis. Oral involvement of PCM is observed in up to 70 % of the cases and usually presents clinically as ulcerations with granular surface showing tiny hemorrhagic areas. Oral presentation of TB is rare with prevalence smaller than 0.5 % of all cases. Clinical presentation of oral TB mainly consists of single ulcers with irregular limits and necrotic base. A 70-year-old immunocompetent man presented simultaneously oral PCM and pulmonary TB. Medical history revealed a previous diagnosis of pulmonary TB; however, even under treatment for TB, the patient remained with oral lesions and intense pulmonary fibrosis. The physician requested P. brasiliensis serological analysis, which resulted positive. Although the combination of PCM and TB has been reported in the literature, it is still considered an uncommon condition and their diagnosis may represent a challenge to healthcare professionals because of the similarity between their clinical and radiological presentations.

Indoleamine 2,3-dioxygenase controls fungal loads and immunity in Paracoccidioidomicosis but is more important to susceptible than resistant hosts

Background

Paracoccidioidomycosis, a primary fungal infection restricted to Latin America, is acquired by inhalation of fungal particles. The immunoregulatory mechanisms that control the severe and mild forms of paracoccidioidomycosis are still unclear. Indoleamine 2,3-dioxygenase (IDO), an IFN-γ induced enzyme that catalyzes tryptophan metabolism, can control host-pathogen interaction by inhibiting pathogen growth, T cell immunity and tissue inflammation.

Methodology/Principal Findings

In this study, we investigated the role of IDO in pulmonary paracoccidioidomycosis of susceptible and resistant mice. IDO was blocked by 1-methyl-dl-tryptophan (1MT), and fungal infection studied in vitro and in vivo. Paracoccidioides brasiliensis infection was more severe in 1MT treated than untreated macrophages of resistant and susceptible mice, concurrently with decreased production of kynurenines and IDO mRNA. Similar results were observed in the pulmonary infection. Independent of the host genetic pattern, IDO inhibition reduced fungal clearance but enhanced T cell immunity. The early IDO inhibition resulted in increased differentiation of dendritic and Th17 cells, accompanied by reduced responses of Th1 and Treg cells. Despite these equivalent biological effects, only in susceptible mice the temporary IDO blockade caused sustained fungal growth, increased tissue pathology and mortality rates. In contrast, resistant mice were able to recover the transitory IDO blockade by the late control of fungal burdens without enhanced tissue pathology.

Conclusions/Significance

Our studies demonstrate for the first time that in pulmonary paracoccidioidomycosis, IDO is an important immunoregulatory enzyme that promotes fungal clearance and inhibits T cell immunity and inflammation, with prominent importance to susceptible hosts. In fact, only in the susceptible background IDO inhibition resulted in uncontrolled tissue pathology and mortality rates. Our findings open new perspectives to understand the immunopathology of paracoccidioidomycosis, and suggest that an insufficient IDO activity could be associated with the severe cases of human PCM characterized by inefficient fungal clearance and excessive inflammation.

Immunoprotection to paracoccidiodomycosis, a systemic mycosis endemic in Latin America, is mediated by T cell immunity whereas immunosuppression characterizes the severe forms of the disease. Indoleamine 2,3-dioxygenase (IDO), an enzyme mainly induced by IFN-γ, catabolizes tryptophan along the kynurenines pathway. Tryptophan deficiency has been associated with reduced pathogen growth, while elevated levels of kynurenines with suppressed immune responses. In this study, the role of IDO in pulmonary paracoccidioidomycosis was investigated using resistant and susceptible mice. In both mouse strains, IDO blockade by 1-methyl tryptophan resulted in inefficient fungal clearance accompanied by enhanced T cell immunity. Despite these equivalent biological effects, only in susceptible mice IDO inhibition caused progressive fungal growth and tissue pathology resulting in increased mortality. Our findings demonstrate for the first time that IDO exert a yet unexplored immunoregulatory role in pulmonary paracoccidioidomycosis that can be particularly important in the severe cases of the disease.

Adaptive immunity to fungi

Life-threatening fungal infections have risen sharply in recent years, owing to the advances and intensity of medical care that may blunt immunity in patients. This emerging crisis has created the growing need to clarify immune defense mechanisms against fungi with the ultimate goal of therapeutic intervention. We describe recent insights in understanding the mammalian immune defenses that are deployed against pathogenic fungi. We focus on adaptive immunity to the major medically important fungi and emphasize three elements that coordinate the response: (1) dendritic cells and subsets that are mobilized against fungi in various anatomical compartments; (2) fungal molecular patterns and their corresponding receptors that signal responses and shape the differentiation of T-cell subsets and B cells; and, ultimately (3) the effector and regulatory mechanisms that eliminate these invaders while constraining collateral damage to vital tissue. These insights create a foundation for the development of new, immune-based strategies for prevention or enhanced clearance of systemic fungal diseases.

Dectin-1 induces M1 macrophages and prominent expansion of CD8+IL-17+ cells in pulmonary Paracoccidioidomycosis

Dectin-1, the innate immune receptor that recognizes β-glucan, plays an important role in immunity against fungal pathogens. Paracoccidioides brasiliensis, the etiological agent of paracoccidioidomycosis, has a sugar-rich cell wall mainly composed of mannans and glucans. This fact motivated us to use dectin-1-sufficient and -deficient mice to investigate the role of β-glucan recognition in the immunity against pulmonary paracoccidioidomycosis. Initially, we verified that P. brasiliensis infection reinforced the tendency of dectin-1-deficient macrophages to express an M2 phenotype. This prevalent antiinflammatory activity of dectin-1(-/-) macrophages resulted in impaired fungicidal ability, low nitric oxide production, and elevated synthesis of interleukin 10 (IL-10). Compared with dectin-1-sufficient mice, the fungal infection of dectin-1(-/-) mice was more severe and resulted in enhanced tissue pathology and mortality rates. The absence of dectin-1 has also impaired the production of T-helper type 1 (Th1), Th2, and Th17 cytokines and the activation and migration of T cells to the site of infection. Remarkably, dectin-1 deficiency increased the expansion of regulatory T cells and reduced the differentiation of T cells to the IL-17(+) phenotype, impairing the migration of IL-17(+)CD8(+) T cells and polymorphonuclear cells to infected tissues. In conclusion, dectin-1 exerts an important protective role in pulmonary paracoccidioidomycosis by controlling the innate and adaptive phases of antifungal immunity.

Immunohistochemical dissimilarity between allergic fungal and nonfungal chronic rhinosinusitis

BACKGROUNDS

Diagnosis of allergic fungal rhinosinusitis (AFRS) is complicated because of the presence of fungi on mucosal surfaces of sinonasal passages. The objectives of this study were to define, using immunohistochemistry, lymphocyte populations associated with noninvasive fungal-related chronic rhinosinusitis (CRS; AFRS and FBs [FB]) relative to CRS with nasal polyposis (CRSwNP) and CRS without nasal polyposis (CRSsNP) as a means of diagnosing different forms of CRS.

METHODS

Sinus CT scans, nasal endoscopy scores, and the presence of eosinophilic fungal mucin or FBs were used to prospectively define patient groups with CRS who had failed medical treatment and were undergoing endoscopic sinus surgery. Four patient groups were identified: AFRS, FB, CRSwNP, and CRSsNP. Tissue specimens were studied and graded for histopathological changes. Immunophenotyping of mucosal lymphocytes was performed using anti-CD3, -CD20, -CD4, -CD8, -CD56, and -perforin antibodies.

RESULTS

Nasal polyposis scores were similar between AFRS and CRSwNP. Radiological changes associated with AFRS can also be present in CRSwNP, e.g., heterogenicity in 9/30 (30%), expansion in 25/30 (83%), and bony attenuation of the ethmoid trabeculae in 19/30 (63%). Different grades of basement membrane thickness, edema, and fibrosis were observed. In both types of noninvasive fungal rhinosinusitis, CD3+ T lymphocytes were most commonly identified. In cases of AFRS, most T cells were CD8+ (p < 0.001). In FB cases, CD4+ lymphocytes were dominant (p < 0.001). In nonfungal CRS cases, CD20+ lymphocytes (B lymphocytes) predominated (p < 0.001).

CONCLUSION

Although CT scans and histological examination can assist the diagnosis of rhinosinusitis, tissue immunophenotyping can be used in defining different types of fungal and nonfungal CRS cases.

TNF-α and CD8+ T cells mediate the beneficial effects of nitric oxide synthase-2 deficiency in pulmonary paracoccidioidomycosis

BACKGROUND

Nitric oxide (NO), a key antimicrobial molecule, was previously shown to exert a dual role in paracoccidioidomycosis, an endemic fungal infection in Latin America. In the intravenous and peritoneal models of infection, NO production was associated with efficient fungal clearance but also with non-organized granulomatous lesions. Because paracoccidioidomycosis is a pulmonary infection, we aimed to characterize the role of NO in a pulmonary model of infection.

METHODOLOGY/PRINCIPAL FINDINGS

C57Bl/6 wild type (WT) and iNOS(-/-) mice were i.t. infected with 1×10(6) Paracoccidioides brasiliensis yeasts and studied at several post-infection periods. Unexpectedly, at week 2 of infection, iNOS(-/-) mice showed decreased pulmonary fungal burdens associated with an M2-like macrophage profile, which expressed high levels of TGF-β impaired ability of ingesting fungal cells. This early decreased fungal loads were concomitant with increased DTH reactions, enhanced TNF-α synthesis and intense migration of activated macrophages, CD4(+) and CD8(+) T cells into the lungs. By week 10, iNOS(-/-) mice showed increased fungal burdens circumscribed, however, by compact granulomas containing elevated numbers of activated CD4(+) T cells. Importantly, the enhanced immunological reactivity of iNOS(-/-) mice resulted in decreased mortality rates. In both mouse strains, depletion of TNF-α led to non-organized lesions and excessive influx of inflammatory cells into the lungs, but only the iNOS(-/-) mice showed increased mortality rates. In addition, depletion of CD8(+) cells abolished the increased migration of inflammatory cells and decreased the number of TNF-α and IFN-γ CD4(+) and CD8(+) T cells into the lungs of iNOS(-/-) mice.

CONCLUSIONS/SIGNIFICANCE

Our study demonstrated that NO plays a deleterious role in pulmonary paracoccidioidomycosis due to its suppressive action on TNF-α production, T cell immunity and organization of lesions resulting in precocious mortality of mice. It was also revealed that uncontrolled fungal growth can be overcome by an efficient immune response.

Myeloid dendritic cells (DCs) of mice susceptible to paracoccidioidomycosis suppress T cell responses whereas myeloid and plasmacytoid DCs from resistant mice induce effector and regulatory T cells

The protective adaptive immune response in paracoccidioidomycosis, a mycosis endemic among humans, is mediated by T cell immunity, whereas impaired T cell responses are associated with severe, progressive disease. The early host response to Paracoccidioides brasiliensis infection is not known since the disease is diagnosed at later phases of infection. Our laboratory established a murine model of infection where susceptible mice reproduce the severe disease, while resistant mice develop a mild infection. This work aimed to characterize the influence of dendritic cells in the innate and adaptive immunity of susceptible and resistant mice. We verified that P. brasiliensis infection induced in bone marrow-derived dendritic cells (DCs) of susceptible mice a prevalent proinflammatory myeloid phenotype that secreted high levels of interleukin-12 (IL-12), tumor necrosis factor alpha, and IL-β, whereas in resistant mice, a mixed population of myeloid and plasmacytoid DCs secreting proinflammatory cytokines and expressing elevated levels of secreted and membrane-bound transforming growth factor β was observed. In proliferation assays, the proinflammatory DCs from B10.A mice induced anergy of naïve T cells, whereas the mixed DC subsets from resistant mice induced the concomitant proliferation of effector and regulatory T cells (Tregs). Equivalent results were observed during pulmonary infection. The susceptible mice displayed preferential expansion of proinflammatory myeloid DCs, resulting in impaired proliferation of effector T cells. Conversely, the resistant mice developed myeloid and plasmacytoid DCs that efficiently expanded gamma interferon-, IL-4-, and IL-17-positive effector T cells associated with increased development of Tregs. Our work highlights the deleterious effect of excessive innate proinflammatory reactions and provides new evidence for the importance of immunomodulation during pulmonary paracoccidioidomycosis.

Anti-CD25 treatment depletes Treg cells and decreases disease severity in susceptible and resistant mice infected with Paracoccidioides brasiliensis

Regulatory T (Treg) cells are fundamental in the control of immunity and excessive tissue pathology. In paracoccidioidomycosis, an endemic mycosis of Latin America, the immunoregulatory mechanisms that control the progressive and regressive forms of this infection are poorly known. Due to its modulatory activity on Treg cells, we investigated the effects of anti-CD25 treatment over the course of pulmonary infection in resistant (A/J) and susceptible (B10.A) mice infected with Paracoccidioides brasiliensis. We verified that the resistant A/J mice developed higher numbers and more potent Treg cells than susceptible B10.A mice. Compared to B10.A cells, the CD4⁺CD25⁺Foxp3⁺ Treg cells of A/J mice expressed higher levels of CD25, CTLA4, GITR, Foxp3, LAP and intracellular IL-10 and TGF-β. In both resistant and susceptible mice, anti-CD25 treatment decreased the CD4⁺CD25⁺Foxp3⁺ Treg cell number, impaired indoleamine 2,3-dioxygenase expression and resulted in decreased fungal loads in the lungs, liver and spleen. In A/J mice, anti-CD25 treatment led to an early increase in T cell immunity, demonstrated by the augmented influx of activated CD4⁺ and CD8⁺ T cells, macrophages and dendritic cells to the lungs. At a later phase, the mild infection was associated with decreased inflammatory reactions and increased Th1/Th2/Th17 cytokine production. In B10.A mice, anti-CD25 treatment did not alter the inflammatory reactions but increased the fungicidal mechanisms and late secretion of Th1/Th2/Th17 cytokines. Importantly, in both mouse strains, the early depletion of CD25⁺ cells resulted in less severe tissue pathology and abolished the enhanced mortality observed in susceptible mice. In conclusion, this study is the first to demonstrate that anti-CD25 treatment is beneficial to the progressive and regressive forms of paracoccidioidomycosis, potentially due to the anti-CD25-mediated reduction of Treg cells, as these cells have suppressive effects on the early T cell response in resistant mice and the clearance mechanisms of fungal cells in susceptible mice.

Experimental medical mycological research in Latin America - a 2000-2009 overview

An overview of current trends in Latin American Experimental Medical Mycological research since the beginning of the 21(st) century is done (search from January 2000 to December 2009). Using the PubMed and LILACS databases, the authors have chosen publications on medically important fungi which, according to our opinion, are the most relevant because of their novelty, interest, and international impact, based on research made entirely in the Latin American region or as part of collaborative efforts with laboratories elsewhere. In this way, the following areas are discussed: 1) molecular identification of fungal pathogens; 2) molecular and clinical epidemiology on fungal pathogens of prevalence in the region; 3) cell biology; 4) transcriptome, genome, molecular taxonomy and phylogeny; 5) immunology; 6) vaccines; 7) new and experimental antifungals.

Expression of activation and cytotoxic molecules by peripheral blood lymphocytes of patients with paracoccidioidomycosis

In a previous study, we reported an increased number of T CD8(+) cells in the bronchoalveolar lavage (BAL) of patients with pulmonary paracoccidioidomycosis, suggesting a role for these cells in the local immune response. The aims of this study were to verify, by flow cytometry, the activation state, as well as the production of cytotoxic molecules by peripheral blood lymphocytes (CD8(+) and CD4(+)). Specimens were obtained from patients with paracoccidioidomycosis (PCM), individuals with PCM-infection, i.e., healthy individuals with demonstrated strong cellular response against the fungus (PI) and controls, with studies conducted both ex-vivo and in vitro, after stimulation with Paracoccidioides brasiliensis yeast cells. The ex-vivo analysis demonstrated that PCM patients presented a lower frequency of granzyme A, B and perforin-positive cells, as compared to individuals with PCM infection (PI). P. brasiliensis stimulation led to a discrete increase in CD69(+) cells and a reduction in cytotoxic granule expression in all groups. The addition of IL-15 induced an increase in the frequency of CD69(+) cells only in PI individuals and controls. The effect of IL-15 on granzyme A and B expression was low, but a higher frequency of CD8(+) perforin(+) was detected in PI individuals than in patients with active PCM. IL-15Ralpha expression was lower in CD4(+) T cells from patients, in relation to the PI group. Furthermore, low levels of granulysin were detected in sera from PCM patients, but a tendency for an increase in these levels was observed after antifungal therapy. Taken together, these results indicate that lymphocytes from PCM patients are poorly activated, express low levels of IL-15Ralpha and produce basal levels of cytotoxic granules. These findings may account for the defective cytotoxic activity in patients and, consequently, a low capacity to kill the fungus.

CD28 exerts protective and detrimental effects in a pulmonary model of paracoccidioidomycosis

T-cell immunity has been claimed as the main immunoprotective mechanism against Paracoccidioides brasiliensis infection, the most important fungal infection in Latin America. As the initial events that control T-cell activation in paracoccidioidomycosis (PCM) are not well established, we decided to investigate the role of CD28, an important costimulatory molecule for the activation of effector and regulatory T cells, in the immunity against this pulmonary pathogen. Using CD28-deficient (CD28(-/-)) and normal wild-type (WT) C57BL/6 mice, we were able to demonstrate that CD28 costimulation determines in pulmonary paracoccidioidomycosis an early immunoprotection but a late deleterious effect associated with impaired immunity and uncontrolled fungal growth. Up to week 10 postinfection, CD28(-/-) mice presented increased pulmonary and hepatic fungal loads allied with diminished production of antibodies and pro- and anti-inflammatory cytokines besides impaired activation and migration of effector and regulatory T (Treg) cells to the lungs. Unexpectedly, CD28-sufficient mice progressively lost the control of fungal growth, resulting in an increased mortality associated with persistent presence of Treg cells, deactivation of inflammatory macrophages and T cells, prevalent presence of anti-inflammatory cytokines, elevated fungal burdens, and extensive hepatic lesions. As a whole, our findings suggest that CD28 is required for the early protective T-cell responses to P. brasiliensis infection, but it also induces the expansion of regulatory circuits that lately impair adaptive immunity, allowing uncontrolled fungal growth and overwhelming infection, which leads to precocious mortality of mice.

Co-infection with paracoccidioidomycosis and human immunodeficiency virus: report of a case with esophageal involvement

Paracoccidioiodomycosis (PCM) is a systemic and deep mycosis endemic in Latin America, especially in Brazil. In patients infected with human immunodeficiency virus (HIV), PCM can manifest with prominent involvement of the reticuloendothelial system. There are no reports in the literature of esophageal involvement by PCM in that population. We report a case of PCM with pulmonary and esophageal involvement without radiologic evidence of an esophageal-bronchial fistula in an HIV-infected patient.

Characterization of cytotoxic immune response in skin and mucosal lesions of paracoccidioidomycosis

BACKGROUND

CD8+ T cells and natural killer (NK) cells are involved in the immune response against some pathogens. For this purpose, we investigated the in situ paracoccidioidomycosis (PCM) immune response addressing the participation of NK cells, CD8+ T cells, perforin and granzyme B expression.

METHODS

Sixty biopsies of PCM skin and mucosa were classified according to the presence of compact granulomas (G1), poorly organized granulomas (G2) and both kinds in the same lesion (G3). CD8+ T cells, NK cells, perforin and granzyme B were showed by immunohistochemistry.

RESULTS

CD8+ T cells were increased over NK cells in cutaneous G1 and G2 lesions. There was no difference regarding such cells in G3 lesions, although they were abundant in such lesions. In mucosa, CD8+ T cells were increased in number over NK cells in all groups. Granzyme B in skin increased in G2 and G3. The number of granzyme did not differ in mucosal lesions in the three groups.

CONCLUSIONS

CD8+ T cells and NK cells play a role in PCM cutaneous and mucosal lesions. The predominance of CD8+ T cells over NK cells may represent an effective response against the fungi. Moreover, the high number of granzyme B expressing cells corroborates this possibility.