The unappreciated intracellular lifestyle of Blastomyces dermatitidis

"We've got to get out"-Strategies of human pathogenic fungi to escape from phagocytes

Human fungal pathogens are a deadly and underappreciated risk to global health that most severely affect immunocompromised individuals. A virulence attribute shared by some of the most clinically relevant fungal species is their ability to survive inside macrophages and escape from these immune cells. In this review, we discuss the mechanisms behind intracellular survival and elaborate how escape is mediated by lytic and non-lytic pathways as well as strategies to induce programmed host cell death. We also discuss persistence as an alternative to rapid host cell exit. In the end, we address the consequences of fungal escape for the host immune response and provide future perspectives for research and development of targeted therapies.

A Rare Case of Uterine Blastomycosis and Its Management: A Case Report and Literature Review

The report delineates the rare occurrence of uterine blastomycosis, an atypical systemic presentation of Blastomyces dermatitidis infection prevalent in North America. Focused on a 51-year-old immunocompetent female displaying abdominal pain and irregular vaginal bleeding, it underscores the intricate diagnostic hurdles posed by symptoms mirroring common gynecological conditions. Despite fewer than 10 recorded cases, the rarity of uterine involvement highlights the imperative for heightened clinical suspicion. The multifaceted diagnostic strategy integrates risk factors, travel history, imaging, and histopathological examinations. Emphasizing a multidisciplinary treatment helmed by gynecologists, pathologists, and infectious disease specialists, the utilization of antifungal agents, notably itraconazole, is pivotal. Addressing the scarcity of literature and the condition's clinical resemblance to prevalent ailments, further research becomes paramount in devising tailored diagnostic and treatment protocols for uterine blastomycosis. This study enriches the existing literature by providing critical insights into a scarcely documented condition, contributing novel perspectives essential for clinical understanding and management strategies.

Blastomycosis Presenting as a Primary Tracheal Tumor: A Rare Presentation

Blastomycosis is a rare fungal infection that typically presents as a pulmonary infection. Systemic involvement of blastomycosis from the lungs commonly occurs in the skin and bones. Tracheal involvement is an unusual presentation of blastomycosis, which makes it a formidable diagnostic challenge. We herein report an unusual case of an 85-year-old man presenting with tracheal blastomycosis presenting as a primary tracheal tumor. We also highlight the challenges that were faced in the diagnosis of such an uncommon presentation. To the best of our knowledge, this is only the third occurrence of blastomycosis with tracheal involvement.

The unforeseen intracellular lifestyle of Enterococcus faecalis in hepatocytes

Enterococcus faecalis is a bacterial species present at a subdominant level in the human gut microbiota. This commensal turns into an opportunistic pathogen under specific conditions involving dysbiosis and host immune deficiency. E. faecalis is one of the rare pathobionts identified to date as contributing to liver damage in alcoholic liver disease. We have previously observed that E. faecalis is internalized in hepatocytes. Here, the survival and fate of E. faecalis was examined in hepatocytes, the main epithelial cell type in the liver. Although referred to as an extracellular pathogen, we demonstrate that E. faecalis is able to survive and divide in hepatocytes, and form intracellular clusters in two distinct hepatocyte cell lines, in primary mouse hepatocytes, as well as in vivo. This novel process extends to kidney cells. Unraveling the intracellular lifestyle of E. faecalis, our findings contribute to the understanding of pathobiont-driven diseases.

Blastomycosis

Blastomycosis is the fungal disease caused by thermally dimorphic fungi in the genus Blastomyces, with B dermatitidis complex causing most cases. It is considered hyperendemic in areas adjacent to the Great Lakes and along the St. Lawrence, Mississippi, and Ohio rivers, but definitive geographic distribution of blastomycoses remains obscure. Clinical presentation is variable. Disseminated blastomycosis with extrapulmonary manifestations is more common in immunosuppressed individuals. Culture positivity is required for definitive diagnosis, but compatible histology is often sufficient for presumptive diagnosis and initiation of treatment. Treatment should be provided to all symptomatic cases to prevent progression or recurrence.

Clinical Manifestations and Outcomes in Immunocompetent and Immunocompromised Patients With Blastomycosis

BACKGROUND

Blastomyces is a dimorphic fungus that infects persons with or without underlying immunocompromise. To date, no study has compared the clinical features and outcomes of blastomycosis between immunocompromised and immunocompetent persons.

METHODS

A retrospective study of adult patients with proven blastomycosis from 2004-2016 was conducted at the University of Wisconsin. Epidemiology, clinical features, and outcomes were analyzed among solid-organ transplantation (SOT) recipients, persons with non-SOT immunocompromise (non-SOT IC), and persons with no immunocompromise (NIC).

RESULTS

A total of 106 cases met the inclusion criteria including 74 NIC, 19 SOT, and 13 non-SOT IC (malignancy, HIV/AIDS, idiopathic CD4+ lymphopenia). The majority of patients (61.3%) had at least 1 epidemiologic risk factor for acquisition of Blastomyces. Pneumonia was the most common manifestation in all groups; however, immunocompromised patients had higher rates of acute pulmonary disease (P = .03), more severe infection (P = .007), respiratory failure (P = .010), and increased mortality (P = .02). Receipt of SOT primarily accounted for increased severity, respiratory failure, and mortality in immunosuppressed patients. SOT recipients had an 18-fold higher annual incidence of blastomycosis than the general population. The rate of disseminated blastomycosis was similar among NIC, SOT, and non-SOT IC. Relapse rates were low (5.3-7.7%).

CONCLUSIONS

Immunosuppression had implications regarding the acuity, severity, and respiratory failure. The rate of dissemination was similar across the immunologic spectrum, which is in sharp contrast to other endemic fungi. This suggests that pathogen-related factors have a greater influence on dissemination for blastomycosis than immune defense.

Direct Tissue PCR and Genotyping for Species Identification in a Case of Laryngeal Blastomycosis

Otolaryngologic manifestations of infection with Blastomyces species are extremely rare and restricted geographically to recognized endemic regions. Here, we describe a case of laryngeal blastomycosis that presented as slowly progressive dysphonia. While a preliminary diagnosis was made using routine histopathology, a species identification of Blastomyces dermatitidis was made using polymerase chain reaction amplification and rapid genotyping without the need for fungal culture. All symptoms resolved following 1 month of antifungal therapy. Rapid molecular differentiation of B dermatitidis from Blastomyces gilchristii provides important insights into pathogenesis given recent recognition of differences in clinical spectra.

Modulation of Immune Responses by Particle Size and Shape

The immune system has to cope with a wide range of irregularly shaped pathogens that can actively move (e.g., by flagella) and also dynamically remodel their shape (e.g., transition from yeast-shaped to hyphal fungi). The goal of this review is to draw general conclusions of how the size and geometry of a pathogen affect its uptake and processing by phagocytes of the immune system. We compared both theoretical and experimental studies with different cells, model particles, and pathogenic microbes (particularly fungi) showing that particle size, shape, rigidity, and surface roughness are important parameters for cellular uptake and subsequent immune responses, particularly inflammasome activation and T cell activation. Understanding how the physical properties of particles affect immune responses can aid the design of better vaccines.

Bronchoscopy in the diagnosis of pulmonary blastomycosis

OBJECTIVES

Diagnosing pulmonary blastomycosis (PB) requires the detection of Blastomyces dermatitidis in pulmonary secretions or tissue, which can be achieved via bronchoscopic procedures like bronchoalveolar lavage (BAL) or brush and transbronchial biopsy (TBBx). This descriptive study retrieved the data of PB that was diagnosed by bronchoscopy to define which bronchoscopic procedure produced the highest yield.

METHODS

Retrospectively, all patients diagnosed with PB via bronchoscopic approach were identified. Non-invasive BAL was referred to when performed first in the order of bronchoscopic procedures, and invasive BAL was used when it was performed after other bronchoscopic procedures.

RESULTS

A total of 111 patients were included in the study. BAL produced the highest yield of all bronchoscopic procedures (>87%), regardless if it was performed first in order (non-invasive, 87.3%) or not (invasive BAL, 89.6%) (p = 0.43). Performing bronchoscopy and BAL earlier in the course of the disease resulted in a significantly better diagnostic yield.

CONCLUSIONS

BAL is probably enough to diagnose PB. Also, it had the best yield when performed earlier, regardless of whether it was performed first in order or not. BAL culture had a better yield in detecting Blastomyces dermatitidis over fungal stain and cytology.

Monocytes and the Host Response to Fungal Pathogens

Monocytes and their derivatives, including macrophages and dendritic cells, play diverse roles in the response to fungal pathogens. Sensing of fungi by monocytes triggers signaling pathways that mediate direct effects like phagocytosis and cytokine production. Monocytes can also present fungal antigens to elicit adaptive immune responses. These monocyte-mediated pathways may be either beneficial or harmful to the host. In some instances, fungi have developed mechanisms to evade the consequences of monocyte activation and subvert these cells to promote disease. Thus, monocytes are critically involved in mediating the outcomes of these often highly fatal infections. This review will highlight the roles of monocytes in the immune response to some of the major fungi that cause invasive human disease, including Aspergillus, Cryptococcus, Candida, Histoplasma, Blastomyces, and Coccidioides, and discuss potential strategies to manipulate monocyte responses in order to enhance anti-fungal immunity in susceptible hosts.

How Environmental Fungi Cause a Range of Clinical Outcomes in Susceptible Hosts

Environmental fungi are globally ubiquitous and human exposure is near universal. However, relatively few fungal species are capable of infecting humans, and among fungi, few exposure events lead to severe systemic infections. Systemic infections have mortality rates of up to 90%, cost the US healthcare system $7.2 billion annually, and are typically associated with immunocompromised patients. Despite this reputation, exposure to environmental fungi results in a range of outcomes, from asymptomatic latent infections to severe systemic infection. Here we discuss different exposure outcomes for five major fungal pathogens: Aspergillus, Blastomyces, Coccidioides, Cryptococcus, and Histoplasma species. These fungi include a mold, a budding yeast, and thermal dimorphic fungi. All of these species must adapt to dramatically changing environments over the course of disease. These dynamic environments include the human lung, which is the first exposure site for these organisms. Fungi must defend themselves against host immune cells while germinating and growing, which risks further exposing microbe-associated molecular patterns to the host. We discuss immune evasion strategies during early infection, from disruption of host immune cells to major changes in fungal cell morphology.

Incidental findings of blastomycosis lung nodules in five asymptomatic patients

Asymptomatic blastomycosis infections are rarely identified or described in the literature, but are believed to comprise 50% of cases. In this report we describe five sporadic cases of blastomycosis in asymptomatic patients. All of these cases were initially identified as incidental findings of lung nodules on CXR or CT. To our knowledge, these are the first detailed descriptions of asymptomatic blastomycosis, occurring as sporadic disease, in the literature.

Turning on virulence: Mechanisms that underpin the morphologic transition and pathogenicity of Blastomyces

This review article focuses on the mechanisms underlying temperature adaptation and virulence of the etiologic agents of blastomycosis, Blastomyces dermatitidis, Blastomyces gilchristii, and Blastomyces percursus. In response to temperature, Blastomyces undergoes a reversible morphologic switch between hyphae and yeast known as the phase transition. The conversion to yeast for Blastomyces and related thermally dimorphic fungi is essential for virulence. In the yeast phase, Blastomyces upregulates the essential virulence factor, BAD1, which promotes attachment to host cells, impairs activation of immune cells, and blunts cytokine release. Blastomyces yeast also secrete dipeptidyl-peptidase IVA (DPPIVA), a serine protease that blunts the action of cytokines released from host immune cells. In vivo transcriptional profiling of Blastomyces yeast has uncovered genes such as PRA1 and ZRT1 involved in zinc scavenging that contribute to virulence during murine pulmonary infection. The discovery and characterization of genes important for virulence has led to advances at the bedside regarding novel diagnostics, vaccine development, and new targets for drug discovery.

Helper T-cell responses and pulmonary fungal infections

The mucosal surface of the respiratory tract encounters microbes, such as fungal particles, with every inhaled breath. When pathogenic fungi breach the physical barrier and innate immune system within the lung to establish an infection, adaptive immunity is engaged, often in the form of helper CD4 T-cell responses. Type 1 responses, characterized by interferon-γ production from CD4 cells, promote clearance of Histoplasma capsulatum and Cryptococcus neoformans infection. Likewise, interleukin-17A (IL-17A) production from Th17 cells promotes immunity to Blastomyces dermatitidis and Coccidioides species infection by recruiting neutrophils. In contrast the development of T helper type 2 responses, characterized by IL-5 production from T cells and eosinophil influx into the lungs, drives allergic bronchopulmonary aspergillosis and poor outcomes during C. neoformans infection. Experimental vaccines against several endemic mycoses, including Histoplasma capsulatum, Coccidioides, Cryptococcus and Blastomyces dermatitidis, induce protective T-cell responses and foreshadow the development of vaccines against pulmonary fungal infections for use in humans. Additionally, recent work using antifungal T cells as immunotherapy to protect immune-compromised patients from opportunist fungal infections also shows great promise. This review covers the role of T-cell responses in driving protection and pathology in response to pulmonary fungal infections, and highlights promising therapeutic applications of antifungal T cells.

Lung Epithelial Cells Coordinate Innate Lymphocytes and Immunity against Pulmonary Fungal Infection

Lung epithelial cells (LECs) are strategically positioned in the airway mucosa to provide barrier defense. LECs also express pattern recognition receptors and a myriad of immune genes, but their role in immunity is often concealed by the activities of "professional" immune cells, particularly in the context of fungal infection. Here, we demonstrate that NF-κB signaling in LECs is essential for immunity against the pulmonary fungal pathogen Blastomyces dermatitidis. LECs orchestrate innate antifungal immunity by augmenting the numbers of interleukin-17A (IL-17A)- and granulocyte-macrophage colony-stimulating factor (GM-CSF)-producing innate lymphocytes, specifically "natural" Th17 (nTh17) cells. Innate lymphocyte-derived IL-17A and GM-CSF in turn enable phagocyte-driven fungal killing. LECs regulate the numbers of nTh17 cells via the production of chemokines such as CCL20, a process dependent on IL-1α-IL-1 receptor (IL-1R) signaling on LECs. Therefore, LECs orchestrate IL-17A- and GM-CSF-mediated immunity in an IL-1R-dependent manner and represent an essential component of innate immunity to pulmonary fungal pathogens.

Metals in fungal virulence

Metals are essential for life, and they play a central role in the struggle between infecting microbes and their hosts. In fact, an important aspect of microbial pathogenesis is the 'nutritional immunity', in which metals are actively restricted (or, in an extended definition of the term, locally enriched) by the host to hinder microbial growth and virulence. Consequently, fungi have evolved often complex regulatory networks, uptake and detoxification systems for essential metals such as iron, zinc, copper, nickel and manganese. These systems often differ fundamentally from their bacterial counterparts, but even within the fungal pathogens we can find common and unique solutions to maintain metal homeostasis. Thus, we here compare the common and species-specific mechanisms used for different metals among different fungal species-focusing on important human pathogens such as Candida albicans, Aspergillus fumigatus or Cryptococcus neoformans, but also looking at model fungi such as Saccharomyces cerevisiae or A. nidulans as well-studied examples for the underlying principles. These direct comparisons of our current knowledge reveal that we have a good understanding how model fungal pathogens take up iron or zinc, but that much is still to learn about other metals and specific adaptations of individual species-not the least to exploit this knowledge for new antifungal strategies.

"The Impact of Mycobacterium tuberculosis Immune Evasion on Protective Immunity: Implications for TB Vaccine Design" - Meeting report

Tuberculosis (TB) is the major cause of death from infectious diseases around the world, particularly in HIV infected individuals. TB vaccine design and development have been focused on improving Bacille Calmette-Guérin (BCG) and evaluating recombinant and viral vector expressed Mycobacterium tuberculosis (Mtb) proteins, for boosting BCG-primed immunity, but these approaches have not yet yielded significant improvements over the modest effects of BCG in protecting against infection or disease. On March 7-8, 2016, the National Institute of Allergy and Infectious Diseases (NIAID) convened a workshop on "The Impact of Mtb Immune Evasion on Protective Immunity: Implications for TB Vaccine Design" with the goal of defining immune mechanisms that could be targeted through novel research approaches, to inform vaccine design and immune therapeutic interventions for prevention of TB. The workshop addressed early infection events, the impact of Mtb evolution on the development and maintenance of an adaptive immune response, and the factors that influence protection against and progression to active disease. Scientific gaps and areas of study to revitalize and accelerate TB vaccine design were discussed and prioritized. These included a comprehensive evaluation of innate and Mtb-specific adaptive immune responses in the lung at different stages of disease; determining the role of B cells and antibodies (Abs) during Mtb infection; development of better assays to measure Mtb burden following exposure, infection, during latency and after treatment, and approaches to improving current animal models to study Mtb immunogenicity, TB disease and transmission.

Clinical Manifestations and Treatment of Blastomycosis

The causal agents of blastomycosis, Blastomyces dermatitidis and Blastomyces gilchristii, belong to a group of thermally dimorphic fungi that can infect healthy and immunocompromised individuals. Following inhalation of mycelial fragments and spores into the lungs, Blastomyces spp convert into pathogenic yeast and evade host immune defenses to cause pneumonia and disseminated disease. The clinical spectrum of pulmonary blastomycosis is diverse. The diagnosis of blastomycosis requires a high degree of clinical suspicion and involves culture-based and non-culture-based fungal diagnostic tests. The site and severity of infection, and the presence of underlying immunosuppression or pregnancy, influence the selection of antifungal therapy.

Fungal Dimorphism and Virulence: Molecular Mechanisms for Temperature Adaptation, Immune Evasion, and In Vivo Survival

The thermally dimorphic fungi are a unique group of fungi within the Ascomycota phylum that respond to shifts in temperature by converting between hyphae (22–25°C) and yeast (37°C). This morphologic switch, known as the phase transition, defines the biology and lifestyle of these fungi. The conversion to yeast within healthy and immunocompromised mammalian hosts is essential for virulence. In the yeast phase, the thermally dimorphic fungi upregulate genes involved with subverting host immune defenses. This review highlights the molecular mechanisms governing the phase transition and recent advances in how the phase transition promotes infection.

Blastomycosis in Children: An Analysis of Clinical, Epidemiologic, and Genetic Features

BACKGROUND

Blastomyces spp. are endemic in regions of the United States and result in blastomycosis, a serious and potentially fatal infection. Little is known about the presentation, clinic course, epidemiology, and genetics of blastomycosis in children.

METHODS

A retrospective review of children with blastomycosis confirmed by culture or cytopathology between 1999 and 2014 was completed. Blastomyces sp. isolates were genotyped by using microsatellite typing, and species were typed by sequencing of internal transcribed spacer 2 (its2).

RESULTS

Of the 114 children with blastomycosis identified, 79% had isolated pulmonary involvement and 21% had extrapulmonary disease. There were more systemic findings, including fever (P = .01), poor intake (P = .01), elevated white blood cell count (P < .01), and elevated C-reactive protein level (P < .01), in children with isolated pulmonary disease than in children with extrapulmonary disease. Children with extrapulmonary disease had more surgeries (P = .01) and delays in diagnosis (P < .01) than those with isolated pulmonary infection. Of 52 samples genotyped, 48 (92%) were Blastomyces gilchristii and 4 (8%) were Blastomyces dermatitidis.

CONCLUSION

This is the first large-scale study of the clinical, epidemiologic, and genetic features of blastomycosis in children. The majority of the children had isolated pulmonary disease with systemic findings. Patients with extrapulmonary disease were less likely to have systemic symptoms or additional laboratory evidence of infection, which made delays in diagnosis more common. More than 90% of the pediatric cases were caused by B gilchristii.

Evidence of delayed dissemination or re-infection with Blastomyces in two immunocompetent hosts

Relapse or recurrence of blastomycosis in patients is rare. Re-infection of a patient with blastomycosis has not been previously reported. In this report, we describe relapse or reinfection with Blastomyces in 2 immunocompetent patients. This is the first study in which genetic typing was performed on paired Blastomyces isolates from the same patient obtained months apart.

Blastomyces Virulence Adhesin-1 Protein Binding to Glycosaminoglycans Is Enhanced by Protein Disulfide Isomerase

Blastomyces adhesin-1 (BAD-1) protein mediates the virulence of the yeast Blastomyces dermatitidis, in part by binding host lung tissue, the extracellular matrix, and cellular receptors via glycosaminoglycans (GAGs), such as heparan sulfate. The tandem repeats that make up over 90% of BAD-1 appear in their native state to be tightly folded into an inactive conformation, but recent work has shown that they become activated and adhesive upon reduction of a disulfide linkage. Here, atomic force microscopy (AFM) of a single BAD-1 molecule interacting with immobilized heparin revealed that binding is enhanced upon treatment with protein disulfide isomerase and dithiothreitol (PDI/DTT). PDI/DTT treatment of BAD-1 induced a plateau effect in atomic force signatures that was consistent with sequential rupture of tandem binding domains. Inhibition of PDI in murine macrophages blunted BAD-1 binding to heparin in vitro. Based on AFM, we found that a short Cardin-Weintraub sequence paired with a WxxWxxW sequence in the first, degenerate repeat at the N terminus of BAD-1 was sufficient to initiate heparin binding. Removal of half of the 41 BAD-1 tandem repeats led to weaker adhesion, illustrating their role in enhanced binding. Mass spectroscopy of the tandem repeat revealed that the PDI-induced interaction with heparin is characterized by ruptured disulfide bonds and that cysteine thiols remain reduced. Further binding studies showed direct involvement of thiols in heparin ligation. Thus, we propose that the N-terminal domain of BAD-1 governs the initial association with host GAGs and that proximity to GAG-associated host PDI catalyzes activation of additional binding motifs conserved within the tandem repeats, leading to enhanced avidity and availability of reduced thiols.

Pathogenic fungi and other microbes must adhere to host tissue to initiate infection. Surface adhesins promote this event and may be required for disease pathogenesis. We studied a fungal adhesin essential for virulence (BAD-1; Blastomyces adhesin-1) and found that host products induce its structural reconfiguration and foster its optimal binding to tissue structures.

Blastomyces Antigen Detection for Diagnosis and Management of Blastomycosis

Blastomyces spp. antigen testing was evaluated over a 10-year period in an area where blastomycosis is endemic. Antigen testing was less sensitive than previously reported, but serial urine testing was useful in monitoring disease resolution or progression. Culture and cytopathology remain the gold standard for diagnosis and exclusion of this infection.