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.

Paracoccidioides brasiliensis activates mesenchymal stem cells through TLR2, TLR4, and Dectin-1

Numerous researchers have described the potential of bone marrow-derived mesenchymal stem cells (BM-MSCs) for the treatment of various infectious and inflammatory diseases. However, contrary to what has been reported, the transplantation of BM-MSCs in a mouse model of Paracoccidioides brasiliensis-induced pulmonary fibrosis exacerbated the inflammatory process and fibrosis, worsening the course of the infection. The aim of this work was to determine whether P. brasiliensis exerts an immunomodulatory effect on BM-MSCs. The results indicate that P. brasiliensis can activate BM-MSCs through a mechanism dependent on TLR2, TLR4 and Dectin-1. In addition, it was found that these fungal cells can adhere and internalize within BM-MSCs. Nonetheless, this process did not affect the survival of the fungus and on the contrary, triggered the expression of inflammatory mediators such as IL-6, IL-17, TNF-α, and TGF-β. The present findings correlate with the loss of a fungicidal effect and poor control of the fungus, evidenced by the count of the colony-forming units. Previously reported in vivo results are thus confirmed, showing that P. brasiliensis induces an inflammatory profile in BM-MSCs when producing pro-inflammatory molecules that amplify such response. Numerous researchers have described the potential of bone marrow-derived mesenchymal stem cells (BM-MSCs) for the treatment of various infectious and inflammatory diseases. However, contrary to what has been reported, the transplantation of BM-MSCs in a mouse model of Paracoccidioides brasiliensis-induced pulmonary fibrosis exacerbated the inflammatory process and fibrosis, worsening the course of the infection. The aim of this work was to determine whether P. brasiliensis exerts an immunomodulatory effect on BM-MSCs. The results indicate that P. brasiliensis can activate BM-MSCs through a mechanism dependent on TLR2, TLR4 and Dectin-1. In addition, it was found that these fungal cells can adhere and internalize within BM-MSCs. Nonetheless, this process did not affect the survival of the fungus and on the contrary, triggered the expression of inflammatory mediators such as IL-6, IL-17, TNF-α, and TGF-β. The present findings correlate with the loss of a fungicidal effect and poor control of the fungus, evidenced by the count of the colony-forming units. Previously reported in vivo results are thus confirmed, showing that P. brasiliensis induces an inflammatory profile in BM-MSCs when producing pro-inflammatory molecules that amplify such response.

β2 Integrin-Mediated Susceptibility to Paracoccidioides brasiliensis Experimental Infection in Mice

The earliest interaction between macrophages and Paracoccidioides brasiliensis is particularly important in paracoccidioidomycosis (PCM) progression, and surface proteins play a central role in this process. The present study investigated the contribution of β2 integrin in P. brasiliensis-macrophage interaction and PCM progression. We infected β2-low expression (CD18^low) and wild type (WT) mice with P. brasiliensis 18. Disease progression was evaluated for fungal burden, lung granulomatous lesions, nitrate levels, and serum antibody production. Besides, the in vitro capacity of macrophages to internalize and kill fungal yeasts was investigated. Our results revealed that CD18^low mice infected with Pb18 survived during the time analyzed; their lungs showed fewer granulomas, a lower fungal load, lower levels of nitrate, and production of high levels of IgG1 in comparison to WT animals. Our results revealed that in vitro macrophages from CD18^low mice slowly internalized yeast cells, showing a lower fungal burden compared to WT cells. The migration capacity of macrophages was compromised and showed a higher intensity in the lysosome signal when compared with WT mice. Our data suggest that β2 integrins play an important role in fungal survival inside macrophages, and once phagocytosed, the macrophage may serve as a protective environment for P. brasiliensis.

Lung CD103+ Dendritic cells of mice infected with Paracoccidioides brasiliensis contribute to Treg differentiation

The DC subsets that express αE integrin (CD103) have been described to exert antagonistic functions, driving T cells towards either an inflammatory (Th1/Th17) or immunosuppressive phenotype (regulatory T cells - Treg). These functions depend on the tissue they reside and microenvironment factors or stimuli that this Antigen-presenting cell (APC) subpopulation receive. In this regard, immunoregulatory phenotype has been described in small subsets of CD103⁺ DCs from lung and intestinal mucosa. The function of this APC subpopulation in pulmonary Paracoccidioides brasiliensis infection is poorly described. Here, we showed that lung CD103⁺ DCs contribute to Treg differentiation in a pulmonary P. brasiliensis infection model, which was attributed to downregulation of costimulatory molecules analyzed in these APC subtypes 21 days post-infection. Overall, this data suggests that P. brasiliensis infection caused an immunosuppression that has also been observed in patients with the most severe form of Paracoccidioidomycosis (PCM) - a sickness caused by this fungus genus. Furthermore, these results open new perspectives for knowledge of the mechanisms that underlie the higher percentage of Treg cells found in peripheral blood of PCM patients.

Transcriptional Remodeling Patterns in Murine Dendritic Cells Infected with Paracoccidioides brasiliensis: More Is Not Necessarily Better

Most people infected with the fungus Paracoccidioides spp. do not get sick, but approximately 5% develop paracoccidioidomycosis. Understanding how host immunity determinants influence disease development could lead to novel preventative or therapeutic strategies; hence, we used two mouse strains that are resistant (A/J) or susceptible (B10.A) to P. brasiliensis to study how dendritic cells (DCs) respond to the infection. RNA sequencing analysis showed that the susceptible strain DCs remodeled their transcriptomes much more intensely than those from the resistant strain, agreeing with a previous model of more intense innate immunity response in the susceptible strain. Contrastingly, these cells also repress genes/processes involved in antigen processing and presentation, such as lysosomal activity and autophagy. After the interaction with P. brasiliensis, both DCs and macrophages from the susceptible mouse reduced the autophagy marker LC3-II recruitment to the fungal phagosome compared to the resistant strain cells, confirming this pathway’s repression. These results suggest that impairment in antigen processing and presentation processes might be partially responsible for the inefficient activation of the adaptive immune response in this model.

FCN-A mediates the inflammatory response and the macrophage polarization in Aspergillus fumigatus keratitis of mice by activating the MAPK signaling pathway

Fungal keratitis (FK) is a severe corneal disease that may cause vision loss. Previous studies indicate that the innate immune response produces the most effective anti-Aspergillus immune resistance. Ficolin-A (FCN-A), a soluble pattern-recognition receptor (PRR) family plays an important role in the innate immunity. In this study, we aimed to study the role of FCN-A in the A. fumigatus infected cornea. Here for the first time, we reported that the expression of FCN-A increases after A. fumigatus infection in the cornea of mice. Then, our results showed that the down-regulation of FCN-A reduced the inflammatory response of the cornea infected mice and decreased the expression of the TNF-a, p-p38, p-JNK. We also found that FCN-A can affect the recruitment of macrophages in the cornea of mice with A. fumigatus keratitis. In the mouse model of A. fumigatus keratitis and the A. fumigatus stimulation of RAW 264.7 cells, knocking down of FCN-A expression promoted the macrophage polarization toward M2. Furthermore, we observed that both the p38 and JNK inhibitors pretreatment decreased the proportion of M1/M2 in RAW 264.7 cells. Taken together, our data provide evidence that FCN-A participated in the inflammatory response of A. fumigatus keratitis in mice. Moreover, FCN-A mediates the inflammatory response and the polarization of the macrophages by activating the MAPK signaling pathway in A. fumigatus keratitis.

Disease Tolerance Mediated by Phosphorylated Indoleamine-2,3 Dioxygenase Confers Resistance to a Primary Fungal Pathogen

Resistance to primary fungal pathogens is usually attributed to the proinflammatory mechanisms of immunity conferred by interferon-γ activation of phagocytes that control microbial growth, whereas susceptibility is attributed to anti-inflammatory responses that deactivate immunity. This study challenges this paradigm by demonstrating that resistance to a primary fungal pathogen such as Paracoccidiodes brasiliensis can be mediated by disease tolerance, a mechanism that preserves host fitness instead of pathogen clearance. Among the mechanisms of disease tolerance described, a crucial role has been ascribed to the enzyme indoleamine-2,3 dioxygenase (IDO) that concomitantly controls pathogen growth by limiting tryptophan availability and reduces tissue damage by decreasing the inflammatory process. Here, we demonstrated in a pulmonary model of paracoccidioidomycosis that IDO exerts a dual function depending on the resistant pattern of hosts. IDO activity is predominantly enzymatic and induced by IFN-γ signaling in the pulmonary dendritic cells (DCs) from infected susceptible (B10.A) mice, whereas phosphorylated IDO (pIDO) triggered by TGF-β activation of DCs functions as a signaling molecule in resistant mice. IFN-γ signaling activates the canonical pathway of NF-κB that promotes a proinflammatory phenotype in B10.A DCs that control fungal growth but ultimately suppress T cell responses. In contrast, in A/J DCs IDO promotes a tolerogenic phenotype that conditions a sustained synthesis of TGF-β and expansion of regulatory T cells that avoid excessive inflammation and tissue damage contributing to host fitness. Therefore, susceptibility is unexpectedly mediated by mechanisms of proinflammatory immunity that are usually associated with resistance, whereas genetic resistance is based on mechanisms of disease tolerance mediated by pIDO, a phenomenon never described in the protective immunity against primary fungal pathogens.

Elucidating the role of leptin in systemic inflammation: a study targeting physiological leptin levels in rats and their macrophages

To elucidate the role of leptin in acute systemic inflammation, we investigated how its infusion at low, physiologically relevant doses affects the responses to bacterial lipopolysaccharide (LPS) in rats subjected to 24 h of food deprivation. Leptin was infused subcutaneously (0–20 μg·kg−1·h−1) or intracerebroventricularly (0–1 μg·kg−1·h−1). Using hypothermia and hypotension as biomarkers of systemic inflammation, we identified the phase extending from 90 to 240 min post-LPS as the most susceptible to modulation by leptin. In this phase, leptin suppressed the rise in plasma TNF-α and accelerated the recoveries from hypothermia and hypotension. Suppression of TNF-α was not accompanied by changes in other cytokines or prostaglandins. Leptin suppressed TNF-α when infused peripherally but not when infused into the brain. Importantly, the leptin dose that suppressed TNF-α corresponded to the lowest dose that limited food consumption; this dose elevated plasma leptin within the physiological range (to 5.9 ng/ml). We then conducted in vitro experiments to investigate whether an action of leptin on macrophages could parallel our in vivo observations. The results revealed that, when sensitized by food deprivation, LPS-stimulated peritoneal macrophages can be inhibited by leptin at concentrations that are lower than those reported to promote cytokine release. It is concluded that physiological levels of leptin do not exert a proinflammatory effect but rather an anti-inflammatory effect involving selective suppression of TNF-α via an action outside the brain. The mechanism of this effect might involve a previously unrecognized, suppressive action of leptin on macrophage subpopulations sensitized by food deprivation, but future studies are warranted.

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.

Modulation of the immune response by Fonsecaea pedrosoi morphotypes in the course of experimental chromoblastomycosis and their role on inflammatory response chronicity

A common theme across multiple fungal pathogens is their ability to impair the establishment of a protective immune response. Although early inflammation is beneficial in containing the infection, an uncontrolled inflammatory response is detrimental and may eventually oppose disease eradication. Chromoblastomycosis (CBM), a cutaneous and subcutaneous mycosis, caused by dematiaceous fungi, is capable of inducing a chronic inflammatory response. Muriform cells, the parasitic form of Fonsecaea pedrosoi, are highly prevalent in infected tissues, especially in long-standing lesions. In this study we show that hyphae and muriform cells are able to establish a murine CBM with skin lesions and histopathological aspects similar to that found in humans, with muriform cells being the most persistent fungal form, whereas mice infected with conidia do not reach the chronic phase of the disease. Moreover, in injured tissue the presence of hyphae and especially muriform cells, but not conidia, is correlated with intense production of pro-inflammatory cytokines in vivo. High-throughput RNA sequencing analysis (RNA-Seq) performed at early time points showed a strong up-regulation of genes related to fungal recognition, cell migration, inflammation, apoptosis and phagocytosis in macrophages exposed in vitro to muriform cells, but not conidia. We also demonstrate that only muriform cells required FcγR and Dectin-1 recognition to be internalized in vitro, and this is the main fungal form responsible for the intense inflammatory pattern observed in CBM, clarifying the chronic inflammatory reaction observed in most patients. Furthermore, our findings reveal two different fungal-host interaction strategies according to fungal morphotype, highlighting fungal dimorphism as an important key in understanding the bipolar nature of inflammatory response in fungal infections.

Extracellular vesicles from Paracoccidioides brasiliensis induced M1 polarization in vitro

Extracellular vesicles (EVs) released by eukaryotes, archaea, and bacteria contain proteins, lipids, polysaccharides, and other molecules. The cargo analysis of EVs shows that they contain virulence factors suggesting a role in the pathogenesis of infection. The proteome, lipidome, RNA content, and carbohydrate composition of EVs from Paracoccidioides brasiliensis and Paracoccidioides lutzii were characterized. However, the effects of P. brasiliensis EVs on the host immune system have not yet been investigated. Herein, we verified that EVs from P. brasiliensis induce the production of proinflammatory mediators by murine macrophages in a dose-dependent manner. Addition of EV to macrophages also promoted transcription of the M1-polarization marker iNOs and diminish that of the M2 markers Arginase-1, Ym-1, and FIZZ-1. Furthermore, the augmented expression of M2-polarization markers, stimulated by IL-4 plus IL-10, was reverted toward an M1 phenotype in response to secondary stimulation with EVs from P. brasiliensis. The ability of EVs from P. brasiliensis to promote M1 polarization macrophages favoring an enhanced fungicidal activity, demonstrated by the decreased CFU recovery of internalized yeasts, with comparable phagocytic efficacy. Our results suggest that EVs from P. brasiliensis can modulate the innate immune response and affect the relationship between P. brasiliensis and host immune cells.

Identification and characterisation of elongation factor Tu, a novel protein involved in Paracoccidioides brasiliensis-host interaction

Paracoccidioides spp., which are temperature-dependent dimorphic fungi, are responsible for the most prevalent human systemic mycosis in Latin America, the paracoccidioidomycosis. The aim of this study was to characterise the involvement of elongation factor Tu (EF-Tu) in Paracoccidioides brasiliensis-host interaction. Adhesive properties were examined using recombinant PbEF-Tu proteins and the respective polyclonal anti-rPbEF-Tu antibody. Immunogold analysis demonstrated the surface location of EF-Tu in P. brasiliensis. Moreover, PbEF-Tu was found to bind to fibronectin and plasminogen by enzyme-linked immunosorbent assay, and it was determined that the binding to plasminogen is at least partly dependent on lysine residues and ionic interactions. To verify the participation of EF-Tu in the interaction of P. brasiliensis with pneumocytes, we blocked the respective protein with an anti-rPbEF-Tu antibody and evaluated the consequences on the interaction index by flow cytometry. During the interaction, we observed a decrease of 2- and 3-fold at 8 and 24 h, respectively, suggesting the contribution of EF-Tu in fungal adhesion/invasion.

Paracoccin Induces M1 Polarization of Macrophages via Interaction with TLR4

The fungal human pathogen Paracoccidioides brasiliensis contains paracoccin (PCN), a multi-domain protein that has lectin and N-acetyl-glucosaminidase activities, which account for its effects on the growth and morphogenesis of the fungus and on the activation of host macrophages through its interaction with TLR N-glycans. With the purpose of detailing the knowledge on the effects of PCN on macrophages, we used recombinant PCN expressed in Pichia pastoris (p-rPCN) to stimulate isolated murine peritoneal macrophages. The activation of these cells manifested through the release of high levels of inflammatory mediators, such as nitric oxide, TNF-α, IL-12p40, and IL-6. Furthermore, peritoneal macrophages stimulated with p-rPCN increased the relative expression of STAT1, SOCS3, and iNOS2 mRNA (M1 polarization markers). However, the expression of Arginase-1, Ym-1, and FIZZ1 (M2 polarization markers) remained at basal levels. Interestingly, the observed M1 macrophages’ polarization triggered by p-rPCN was abolished in cells obtained from knockout Toll-like receptor-4 mice. In this case, the p-rPCN-induced production of pro-inflammatory mediators was blocked too. These results demonstrate that the classical activation of macrophages induced by paracoccin depends on TLR4. Taken together, the results of our study indicate that paracoccin acts as a TLR agonist able to modulate immunity and exerts biological activities that favor its applicability as an immunotherapeutic agent to combat systemic fungal infections.

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.

The Effects of Paracoccidioides brasiliensis Infection on GM-CSF- and M-CSF-Induced Mouse Bone Marrow-Derived Macrophage from Resistant and Susceptible Mice Strains

Considering the importance of macrophages as the first line of defense against fungal infection and the different roles played by the two M1- and M2-like polarized macrophages, we decided to evaluate the effects of Paracoccidioides brasiliensis infection on GM-CSF- and M-CSF-induced bone marrow-derived macrophages (BMM) from the A/J and B10.A mouse strains, an established model of resistance/susceptibility to PCM, respectively. Upon differentiation, the generated GM- or M-BMMs were characterized by morphological analyses, gene expression profiles, and cytokines production. Our main results demonstrate that GM-BMMs derived from A/J and B.10 produced high levels of pro- and anti-inflammatory cytokines that may contribute to generate an unbalanced early immune response. In accordance with the literature, the B10.A susceptible mice lineage has an innate tendency to polarize into M1-like phenotype, whereas the opposite phenotype occurs in A/J resistance mice. In this context, our data support that susceptibility and resistance are strongly correlated with M1 and M2 polarization, respectively.

Lipoxin Inhibits Fungal Uptake by Macrophages and Reduces the Severity of Acute Pulmonary Infection Caused by Paracoccidioides brasiliensis

Cysteinyl leukotrienes (CysLTs) and lipoxins (LXs) are lipid mediators that control inflammation, with the former inducing and the latter inhibiting this process. Because the role played by these mediators in paracoccidioidomycosis was not investigated, we aimed to characterize the role of CysLT in the pulmonary infection developed by resistant (A/J) and susceptible (B10.A) mice. 48 h after infection, elevated levels of pulmonary LTC₄ and LXA₄ were produced by both mouse strains, but higher levels were found in the lungs of susceptible mice. Blocking the CysLTs receptor by MTL reduced fungal loads in B10.A, but not in A/J mice. In susceptible mice, MLT treatment led to reduced influx of PMN leukocytes, increased recruitment of monocytes, predominant synthesis of anti-inflammatory cytokines, and augmented expression of 5- and 15-lipoxygenase mRNA, suggesting a prevalent LXA₄ activity. In agreement, MTL-treated macrophages showed reduced fungal burdens associated with decreased ingestion of fungal cells. Furthermore, the addition of exogenous LX reduced, and the specific blockade of the LX receptor increased the fungal loads of B10.A macrophages. This study showed for the first time that inhibition of CysLTs signaling results in less severe pulmonary paracoccidioidomycosis that occurs in parallel with elevated LX activity and reduced infection of macrophages.

Distinct patterns of yeast cell morphology and host responses induced by representative strains of Paracoccidioides brasiliensis (Pb18) and Paracoccidioides lutzii (Pb01)

Paracoccidioidomycosis (PCM) is a systemic mycosis, widespread in Latin America. PCM is a granulomatous disease characterized by a polymorphism of lesions depending on the pathogen's virulence, the immune status of the host and its genetic susceptibility. The thermodimorphic fungus Paracoccidioides brasiliensis was considered the only etiologic agent of PCM, yet recent works have shown significant genetic diversity among different strains of P. brasiliensis. Therefore, it has been proposed for a new species within the Paracoccidioides genus, named Paracoccidioides lutzii. To better understand the fungus-host interactions elicited by strains Pb01 and Pb18 as key representatives of P. lutzii and P. brasiliensis, respectively, we carried out studies to investigate differences in morphology, induced immune response, virulence and pathology between these two Paracoccidioides species. Our results demonstrate distinct patterns of host-parasite interaction and pathology caused by Pb18 and Pb01. These results open up new fronts for NEW: clinical studies, which may result in significant consequences for the diagnosis and treatment of PCM. Considering that our results cannot be extended to all strains of both species, more studies about the virulence among Paracoccioides must be explored in the future.

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.

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.

The leukotriene B₄/BLT₁ axis is a key determinant in susceptibility and resistance to histoplasmosis

The bioactive lipid mediator leukotriene B₄ (LTB₄) greatly enhances phagocyte antimicrobial functions against a myriad of pathogens. In murine histoplasmosis, inhibition of the LT-generating enzyme 5-lypoxigenase (5-LO) increases the susceptibility of the host to infection. In this study, we investigated whether murine resistance or susceptibility to Histoplasma capsulatum infection is associated with leukotriene production and an enhancement of in vivo and/or in vitro antimicrobial effector function. We show that susceptible C57BL/6 mice exhibit a higher fungal burden in the lung and spleen, increased mortality, lower expression levels of 5-LO and leukotriene B₄ receptor 1 (BLT₁) and decreased LTB₄ production compared to the resistant 129/Sv mice. Moreover, we demonstrate that endogenous and exogenous LTs are required for the optimal phagocytosis of H. capsulatum by macrophages from both murine strains, although C57BL/6 macrophages are more sensitive to the effects of LTB₄ than 129/Sv macrophages. Therefore, our results provide novel evidence that LTB₄ production and BLT₁ signaling are required for a histoplasmosis-resistant phenotype.

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.

Comparative proteomics in the genus Paracoccidioides

The genus Paracoccidioides comprises a complex of phylogenetic species of dimorphic pathogenic fungi, the etiologic agents of paracoccidioidomycosis (PCM), a disease confined to Latin America and of marked relevance in its endemic areas due to its high frequency and severity. The members of the Paracoccidioides genus are distributed in distinct phylogenetic species (S1, PS2, PS3 and 01-like) that potentially differ in their biochemical and molecular characteristics. In this work, we performed the proteomic characterization of different members of the genus Paracoccidioides. We compared the proteomic profiles of Pb01 (01-like), Pb2 (PS2), Pb339 (S1) and PbEPM83 (PS3) using 2D electrophoresis and mass spectrometry. The proteins/isoforms were selected based on the staining intensity of the spots as determined by image analysis. The proteins/isoforms were in-gel digested and identified by peptide mass fingerprinting and ion fragmentation. A total of 714 spots were detected, of which 343 were analyzed. From these spots, 301 represented differentially expressed proteins/isoforms among the four analyzed isolates, as determined by ANOVA. After applying the FDR correction, a total of 267 spots were determined to be differentially expressed. From the total, 193 proteins/isoforms were identified by PMF and confirmed by ion fragmentation. Comparing the expression profiles of the isolates, the proteins/isoforms that were related to glycolysis/gluconeogenesis and to alcohol fermentation were more abundant in Pb01 than in other representatives of the genus Paracoccidioides, indicating ahigher use of anaerobic pathways for energy production. Those enzymes related to the oxidative stress response were more abundant in Pb01, Pb2 and Pb339, indicating a better response to ROS in these members of the Paracoccidioides complex. The enzymes of the pentose phosphate pathway were abundant in Pb2. Antigenic proteins, such as GP43 and a 27-kDa antigenic protein, were less abundant in Pb01 and Pb2. The proteomic profile indicates metabolic differences among the analyzed members of the Paracoccidioides genus.

Low concentrations of hydrogen peroxide or nitrite induced of Paracoccidioides brasiliensis cell proliferation in a Ras-dependent manner

Paracoccidioides brasiliensis, a causative agent of paracoccidioidomycosis (PCM), should be able to adapt to dramatic environmental changes inside the infected host after inhalation of air-borne conidia and transition to pathogenic yeasts. Proteins with antioxidant functions may protect fungal cells against reactive oxygen (ROS) and nitrogen (RNS) species generated by phagocytic cells, thus acting as potential virulence factors. Ras GTPases are involved in stress responses, cell morphology, and differentiation in a range of organisms. Ras, in its activated form, interacts with effector proteins and can initiate a kinase cascade. In lower eukaryotes, Byr2 kinase represents a Ras target. The present study investigated the role of Ras in P. brasiliensis after in vitro stimulus with ROS or RNS. We have demonstrated that low concentrations of H₂O₂ (0.1 mM) or NO₂ (0.1–0.25 µM) stimulated P. brasiliensis yeast cell proliferation and that was not observed when yeast cells were pre-incubated with farnesyltransferase inhibitor. We constructed an expression plasmid containing the Byr2 Ras-binding domain (RBD) fused with GST (RBD-Byr2-GST) to detect the Ras active form. After stimulation with low concentrations of H₂O₂ or NO₂, the Ras active form was observed in fungal extracts. Besides, NO₂ induced a rapid increase in S-nitrosylated Ras levels. This alternative posttranslational modification of Ras, probably in residue Cys123, would lead to an exchange of GDP for GTP and consequent GTPase activation in P. brasiliensis. In conclusion, low concentrations of H₂O₂ or NO₂ stimulated P. brasiliensis proliferation through Ras activation.

5-Lipoxygenase activity increases susceptibility to experimental Paracoccidioides brasiliensis infection

Paracoccidioidomycosis (PCM) is a systemic mycosis caused by the thermodimorphic fungus Paracoccidioides brasiliensis. Leukotrienes and lipoxins are lipid mediators produced after 5-lipoxygenase (5-LO) activation that exhibit pro- and anti-inflammatory roles, respectively. Here, we have investigated the contribution of 5-LO enzymatic activity in PCM using an experimental model of P. brasiliensis infection. B6.129 wild-type (B6.129) and 5-LO-deficient (5-LO(-/-)) mice were intravenously inoculated with a virulent strain of P. brasiliensis (Pb18), and the survival rate of the infected mice was investigated on different days after yeast infection. 5-LO(-/-) mice exhibited an increased survival rate associated with a decreased number of CFU. The resistance of 5-LO(-/-) during PCM was associated with augmented nitric oxide (NO) production and the formation of compact granulomas. In addition, the absence of 5-LO was associated with a diminished number of CD4(+) CD25(+) regulatory T cells, higher levels of gamma interferon and interleukin-12, and increased T-bet (a T-box transcription factor that directs Th1 lineage commitment) mRNA levels in the lungs. Taken together, our results show for the first time that 5-LO enzymatic activity increases susceptibility to P. brasiliensis, suggesting that this pathway may be a potential target for therapeutic intervention during PCM.

Mannosyl-recognizing receptors induce an M1-like phenotype in macrophages of susceptible mice but an M2-like phenotype in mice resistant to a fungal infection

In addition to alpha1,3 glucan, mannan and mannan-linked proteins are expressed in the outer layer of Paracoccidioides brasiliensis yeasts. The recognition of mannosyl residues by multiple pathogen recognition receptors, such as the mannose receptor (MR), complement receptor 3 (CR3) and toll-like receptor 4 (TLR4) on macrophage membranes can influence macrophage activation and the mechanisms of innate immunity against fungal pathogens. The aim of this study was to clarify the role of these receptors in the interaction between P. brasiliensis and macrophages from resistant (A/J) and susceptible (B10.A) mice. Therefore, the phagocytic, fungicidal and secretory abilities of macrophages were evaluated in the presence of mannan and antibodies against MR, CR3 and TLR4. We verified that mannan increased and anti-MR antibody decreased the killing ability and nitric oxide production of macrophages. The specific blockade of MR, CR3 and TLR4 by monoclonal antibodies impaired fungal recognition and modulated the production of cytokines. Mannan or P. brasiliensis induced decreased expression of MR and TLR2 on A/J macrophages, whereas CR3, TLR4 and TLR2 were reduced on B10.A cells. Importantly, both mannan and P. brasiliensis induced the production of IL-12 by B10.A macrophages, whereas TGF-β, TNF-α and IL-6 were produced by A/J cells. In addition, B10.A macrophages exhibited a prevalent expression of inducible NO-synthase and SOCS3 (suppressor of cytokine signaling-3), indicating a pro-inflammatory, "M1-like" differentiation. In contrast, the elevated expression of arginase-1, found in inflammatory zone-1 (FIZZ1), YM1 (CHI313, chitinase-like lectin), and SOCS1, typical markers of alternatively activated macrophages, indicates a prevalent "M2-like" differentiation of A/J macrophages. In conclusion, our data reveal that several mannosyl-recognizing receptors coordinate the apparently paradoxical innate response to paracoccidioidomycosis, in which resistance is initially mediated by alternatively activated phagocytes and tolerance to fungal growth, whereas susceptibility is linked to classically activated macrophages and the efficient control of fungal growth.

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.

Important aspects of oral paracoccidioidomycosis--a literature review

Paracoccidioidomycosis is a deep mycosis endemic to Latin America, with considerable morbidity and mortality. It is caused by the dimorphic fungus Paracoccidioides brasiliensis, which affects, among other organs in the human body, the oral cavity. Fungus virulence and immunocompetence of the host determine the establishment of infection or active disease, whose severity and clinical behaviour depend mostly on the cellular immune response of the host. Often, oral lesions constitute the first sign and site of confirmation of diagnosis, which in most cases is delayed. The success of the treatment depends on early and correct diagnosis, as well as on the patient's adherence to the drug therapy.

Paracoccidioides brasiliensis lipids modulate macrophage activity via Toll-dependent or independent mechanisms

The macrophages are the first host cells that interact with the fungus Paracoccidioides brasiliensis, but the main mechanisms that regulate this interaction are not well understood. Because the role played by P. brasiliensis lipids in macrophage activation was not previously investigated, we aimed to assess the influence of diverse lipid fractions from P. brasiliensis yeasts in this process. The possible participation of TLR2 and TLR4 signaling was also evaluated using TLR2- and TLR4-defective macrophages. Four lipid-rich fractions were studied as follows: F1, composed by membrane phospholipids and neutral lipids, F2 by glycolipids of short chain, F3a by membrane glycoproteins anchored by glycosylphosphatidylinositol (GPI) groups, and F3b by glycolipids of long chain. All assayed lipid fractions were able to activate peritoneal macrophages and induce nitric oxide (NO) production. Importantly, the F1 and F3a fractions exerted opposite effects in the control of P. brasiliensis uptake and killing, but both fractions inhibited cytokines production. Furthermore, the increased NO production and expression of costimulatory molecules induced by F3a was shown to be TLR2 dependent although F1 used Toll-independent mechanisms. In conclusion, our work suggests that lipid components may play a role in the innate immunity against P. brasiliensis infection using Toll-dependent and independent mechanisms to control macrophage activation.

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.

The malate synthase of Paracoccidioides brasiliensis is a linked surface protein that behaves as an anchorless adhesin

BACKGROUND

The pathogenic fungus Paracoccidioides brasiliensis is the agent of paracoccidioidomycosis (PCM). This is a pulmonary mycosis acquired by inhalation of fungal airborne propagules that can disseminate to several organs and tissues leading to a severe form of the disease. Adhesion and invasion to host cells are essential steps involved in the internalization and dissemination of pathogens. Inside the host, P. brasiliensis may use the glyoxylate cycle for intracellular survival.

RESULTS

Here, we provide evidence that the malate synthase of P. brasiliensis (PbMLS) is located on the fungal cell surface, and is secreted. PbMLS was overexpressed in Escherichia coli, and polyclonal antibody was obtained against this protein. By using Confocal Laser Scanning Microscopy, PbMLS was detected in the cytoplasm and in the cell wall of the mother, but mainly of budding cells of the P. brasiliensis yeast phase. PbMLSr and its respective polyclonal antibody produced against this protein inhibited the interaction of P. brasiliensis with in vitro cultured epithelial cells A549.

CONCLUSION

These observations indicated that cell wall-associated PbMLS could be mediating the binding of fungal cells to the host, thus contributing to the adhesion of fungus to host tissues and to the dissemination of infection, behaving as an anchorless adhesin.

Toll-like receptor 4 signaling leads to severe fungal infection associated with enhanced proinflammatory immunity and impaired expansion of regulatory T cells

Toll-like receptors (TLRs) present in innate immune cells recognize pathogen molecular patterns and influence immunity to control the host-parasite interaction. The objective of this study was to characterize the involvement of TLR4 in the innate and adaptive immunity to Paracoccidioides brasiliensis, the most important primary fungal pathogen of Latin America. We compared the responses of C3H/HeJ mice, which are naturally defective in TLR4 signaling, with those of C3H/HePas mice, which express functional receptors, after in vitro and in vivo infection with P. brasiliensis. Unexpectedly, we verified that TLR4-defective macrophages infected in vitro with P. brasiliensis presented decreased fungal loads associated with impaired synthesis of nitric oxide, interleukin-12 (IL-12), and macrophage chemotactic protein 1 (MCP-1). After intratracheal infection with 1 million yeasts, TLR4-defective mice developed reduced fungal burdens and decreased levels of pulmonary nitric oxide, proinflammatory cytokines, and antibodies. TLR4-competent mice produced elevated levels of IL-12 and tumor necrosis factor alpha (TNF-alpha), besides cytokines of the Th17 pattern, indicating a proinflammatory role for TLR4 signaling. The more severe infection of TLR4-normal mice resulted in increased influx of activated macrophages and T cells to the lungs and progressive control of fungal burdens but impaired expansion of regulatory T cells (Treg cells). In contrast, TLR4-defective mice were not able to clear their diminished fungal burdens totally, a defect associated with deficient activation of T-cell immunity and enhanced development of Treg cells. These divergent patterns of immunity, however, resulted in equivalent mortality rates, indicating that control of elevated fungal growth mediated by vigorous inflammatory reactions is as deleterious to the hosts as low fungal loads inefficiently controlled by limited inflammatory reactions.

Paracoccidioides brasiliensis pancreatic destruction in Calomys callosus experimentally infected

BACKGROUND

The wild rodent Calomys callosus is notably resistant to Trypanosoma cruzi infection. In order to better characterize this animal model for experimental infections, we inoculated C. callosus intraperitoneally with Paracoccidioides brasiliensis, a thermally dimorphic fungus that causes a chronic disease with severe granuloma formation in the mouse and humans. The dissemination of P. brasiliensis cells through the lungs, liver, pancreas, and spleen was assessed by histological analysis.

RESULTS

The animals were susceptible to infection and showed a granulomatous reaction. C. callosus presented peritonitis characterized by the presence of exudates containing a large number of yeast cells. Extensive accumulation of yeast cells with intense destruction of the parenchyma was observed in the pancreas, which reduced the glucose levels of infected animals. These lesions were regressive in the liver, spleen, and lungs until complete recovery. The role of estrogen during C. callosus infection with P. brasiliensis was addressed by infecting ovariectomized animals. It was observed a reduced inflammatory response as well as reduced extension of tissue damage. Removal of ovaries reestablished the normal glucose levels during infection.

CONCLUSION

Taken together, the results presented here reveal the pancreas as being an important organ for the persistence of P. brasiliensis during infection of C. callosus and that estrogen plays an important role in the susceptibility of the animals to this pathogen.