Common and emerging fungal pulmonary infections

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.

Treatment-Related Mortality From Infectious Complications in an Acute Leukemia Clinic

Background

The main causes of mortality in patients with acute leukemia are the infectious complications. The author wanted to know the induction-related mortality and treatment-related mortality in the acute leukemia patients at the Instituto Nacional de Cancerologia (INCan), Mexico. Also the author is interested in finding out the micro-organism and the main site of infection to make some changes in the management of patients in these clinics. Primary objective was induction chemotherapy-related mortality and treatment-related mortality. Secondary objective was to determine the site of infection, micro-organism, type of chemotherapy related with more mortality and relapse mortality.

Methods

This was a retrospective case-series analysis of all patients who were admitted to the INCan Acute Leukemia Clinic between January 2012 and December 2015 with febrile neutropenic complications. We reviewed the case histories of all patients, including those with acute lymphoblastic leukemia (ALL), acute myeloblastic leukemia (AML), acute biphenotypic leukemia and acute promyelocytic leukemia, regardless of disease status (newly diagnosed or relapsed) at the time of clinic attendance. Patients who died as the result of an infectious complication during the analysis window were identified, and their demographics, disease characteristics, treatment history (chemotherapy within 45 days of date of death) and details of the infectious complication resulting in death were collected.

Results

Of the 313 patients studied during that time period, 84 (27%) died as a result of infectious complications. Lung infections were the most common, accounting for 67% of all deaths from infectious complications. Escherichia coli producing extended-spectrum beta-lactamases was the most frequently isolated infectious organism (12 patients; 14%). The majority of deaths occurred during either induction therapy (27 patients; 32%) or treatment for a first relapse (25 patients; 30%). Hyperfractionated cyclophosphamide, vincristine, doxorubicin and dexamethasone (hyper-CVAD) was the chemotherapy regimen most commonly received within 45 days prior to death (17 patients; 20%).

Conclusions

Our findings suggest a need for long-term management and supportive care to prevent infectious complication-associated fatalities during both initial chemotherapy and subsequent disease relapse in patients with acute leukemia. The use of prophylaxis will help patients to prevent complications.

Bronchoscopic fibered confocal fluorescence microscopy for longitudinal in vivo assessment of pulmonary fungal infections in free-breathing mice

Respiratory diseases, such as pulmonary infections, are an important cause of morbidity and mortality worldwide. Preclinical studies often require invasive techniques to evaluate the extent of infection. Fibered confocal fluorescence microscopy (FCFM) is an emerging optical imaging technique that allows for real-time detection of fluorescently labeled cells within live animals, thereby bridging the gap between in vivo whole-body imaging methods and traditional histological examinations. Previously, the use of FCFM in preclinical lung research was limited to endpoint observations due to the invasive procedures required to access lungs. Here, we introduce a bronchoscopic FCFM approach that enabled in vivo visualization and morphological characterisation of fungal cells within lungs of mice suffering from pulmonary Aspergillus or Cryptococcus infections. The minimally invasive character of this approach allowed longitudinal monitoring of infection in free-breathing animals, thereby providing both visual and quantitative information on infection progression. Both the sensitivity and specificity of this technique were high during advanced stages of infection, allowing clear distinction between infected and non-infected animals. In conclusion, our study demonstrates the potential of this novel bronchoscopic FCFM approach to study pulmonary diseases, which can lead to novel insights in disease pathogenesis by allowing longitudinal in vivo microscopic examinations of the lungs.

Anti-PD-1 Antibody Treatment Promotes Clearance of Persistent Cryptococcal Lung Infection in Mice

Activation of immunomodulatory pathways in response to invasive fungi can impair clearance and promote persistent infections. The programmed cell death protein-1 (PD-1) signaling pathway inhibits immune effector responses against tumors, and immune checkpoint inhibitors that block this pathway are being increasingly used as cancer therapy. The objective of this study was to investigate whether this pathway contributes to persistent fungal infection and to determine whether anti-PD-1 Ab treatment improves fungal clearance. Studies were performed using C57BL/6 mice infected with a moderately virulent strain of Cryptococcus neoformans (52D), which resulted in prolonged elevations in fungal burden and histopathologic evidence of chronic lung inflammation. Persistent infection was associated with increased and sustained expression of PD-1 on lung lymphocytes, including a mixed population of CD4⁺ T cells. In parallel, expression of the PD-1 ligands, PD-1 ligands 1 and 2, was similarly upregulated on specific subsets of resident and recruited lung dendritic cells and macrophages. Treatment of persistently infected mice for 4 wk by repetitive administration of neutralizing anti-PD-1 Ab significantly improved pulmonary fungal clearance. Treatment was well tolerated without evidence of morbidity. Immunophenotyping revealed that anti-PD-1 Ab treatment did not alter immune effector cell numbers or myeloid cell activation. Treatment did reduce gene expression of IL-5 and IL-10 by lung leukocytes and promoted sustained upregulation of OX40 by Th1 and Th17 cells. Collectively, this study demonstrates that PD-1 signaling promotes persistent cryptococcal lung infection and identifies this pathway as a potential target for novel immune-based treatments of chronic fungal disease.

Cellular and Molecular Defects Underlying Invasive Fungal Infections-Revelations from Endemic Mycoses

The global burden of fungal diseases has been increasing, as a result of the expanding number of susceptible individuals including people living with human immunodeficiency virus (HIV), hematopoietic stem cell or organ transplant recipients, patients with malignancies or immunological conditions receiving immunosuppressive treatment, premature neonates, and the elderly. Opportunistic fungal pathogens such as Aspergillus, Candida, Cryptococcus, Rhizopus, and Pneumocystis jiroveci are distributed worldwide and constitute the majority of invasive fungal infections (IFIs). Dimorphic fungi such as Histoplasma capsulatum, Coccidioides spp., Paracoccidioides spp., Blastomyces dermatiditis, Sporothrix schenckii, Talaromyces (Penicillium) marneffei, and Emmonsia spp. are geographically restricted to their respective habitats and cause endemic mycoses. Disseminated histoplasmosis, coccidioidomycosis, and T. marneffei infection are recognized as acquired immunodeficiency syndrome (AIDS)-defining conditions, while the rest also cause high rate of morbidities and mortalities in patients with HIV infection and other immunocompromised conditions. In the past decade, a growing number of monogenic immunodeficiency disorders causing increased susceptibility to fungal infections have been discovered. In particular, defects of the IL-12/IFN-γ pathway and T-helper 17-mediated response are associated with increased susceptibility to endemic mycoses. In this review, we put together the various forms of endemic mycoses on the map and take a journey around the world to examine how cellular and molecular defects of the immune system predispose to invasive endemic fungal infections, including primary immunodeficiencies, individuals with autoantibodies against interferon-γ, and those receiving biologic response modifiers. Though rare, these conditions provide importance insights to host defense mechanisms against endemic fungi, which can only be appreciated in unique climatic and geographical regions.

Enhanced virulence of Histoplasma capsulatum through transfer and surface incorporation of glycans from Cryptococcus neoformans during co-infection

Cryptococcus neoformans (Cn) and Histoplasma capsulatum (Hc) co-exist in the environment and occasionally co-infect individuals, which can lead to severe disease/lethal outcomes. We investigated specific interactions between Cn-Hc to determine the impact of synchronous infection in virulence and disease. Co-infected mice had significantly higher mortality than infection with either species or acapsular Cn-Hc. Coating of Hc with cryptococcal glycans (Cn-gly) resulted in higher pulmonary fungal burden in co-infected animals relative to control. Co-cultivation or addition of Cn-gly resulted in enhanced pellicle formation with a hybrid polysaccharide matrix with higher reactivity to GXM mAbs. Transfer and incorporation of Cn polysaccharide onto Hc surface was time and temperature dependent. Cn-gly transfer altered the zeta potential of Hc and was associated with increased resistance to phagocytosis and killing by macrophages. Mice infected with Hc and subsequently injected with purified Cn-gly died significantly more rapidly than Hc alone infected, establishing the precedent that virulence factors from one fungus can enhance the virulence of unrelated species. These findings suggest a new mechanism of microbial interaction involving the transfer of virulence traits that translates into enhanced lethality during mixed fungal infections and highlights the importance of studying heterogeneous microbial populations in the setting of infection.

Early or late IL-10 blockade enhances Th1 and Th17 effector responses and promotes fungal clearance in mice with cryptococcal lung infection

The potent immunoregulatory properties of IL-10 can counteract protective immune responses and, thereby, promote persistent infections, as evidenced by studies of cryptococcal lung infection in IL-10-deficient mice. To further investigate how IL-10 impairs fungal clearance, the current study used an established murine model of C57BL/6J mice infected with Cryptococcus neoformans strain 52D. Our results demonstrate that fungal persistence is associated with an early and sustained expression of IL-10 by lung leukocytes. To examine whether IL-10-mediated immune modulation occurs during the early or late phase of infection, assessments of fungal burden and immunophenotyping were performed on mice treated with anti-IL-10R-blocking Ab at 3, 6, and 9 d postinfection (dpi) (early phase) or at 15, 18, and 21 dpi (late phase). We found that both early and late IL-10 blockade significantly improved fungal clearance within the lung compared with isotype control treatment when assessed 35 dpi. Immunophenotyping identified that IL-10 blockade enhanced several critical effector mechanisms, including increased accumulation of CD4(+) T cells and B cells, but not CD8(+) T cells; specific increases in the total numbers of Th1 and Th17 cells; and increased accumulation and activation of CD11b(+) dendritic cells and exudate macrophages. Importantly, IL-10 blockade effectively abrogated dissemination of C. neoformans to the brain. Collectively, this study identifies early and late cellular and molecular mechanisms through which IL-10 impairs fungal clearance and highlights the therapeutic potential of IL-10 blockade in the treatment of fungal lung infections.

Interleukin-17A enhances host defense against cryptococcal lung infection through effects mediated by leukocyte recruitment, activation, and gamma interferon production

Infection of C57BL/6 mice with the moderately virulent Cryptococcus neoformans strain 52D models the complex adaptive immune response observed in HIV-negative patients with persistent fungal lung infections. In this model, Th1 and Th2 responses evolve over time, yet the contribution of interleukin-17A (IL-17A) to antifungal host defense is unknown. In this study, we show that fungal lung infection promoted an increase in Th17 T cells that persisted to 8 weeks postinfection. Our comparison of fungal lung infection in wild-type mice and IL-17A-deficient mice (IL-17A(-/-) mice; C57BL/6 genetic background) demonstrated that late fungal clearance was impaired in the absence of IL-17A. This finding was associated with reduced intracellular containment of the organism within lung macrophages and deficits in the accumulation of total lung leukocytes, including specific reductions in CD11c+ CD11b+ myeloid cells (dendritic cells and exudate macrophages), B cells, and CD8+ T cells, and a nonsignificant trend in the reduction of lung neutrophils. Although IL-17A did not alter the total number of CD4 T cells, decreases in the total number of CD4 T cells and CD8 T cells expressing gamma interferon (IFN-γ) were observed in IL-17A(-/-) mice. Lastly, expression of major histocompatibility complex class II (MHC-II) and the costimulatory molecules CD80 and CD86 on CD11c+ CD11b+ myeloid cells was diminished in IL-17A(-/-) mice. Collectively, these data indicate that IL-17A enhances host defenses against a moderately virulent strain of C. neoformans through effects on leukocyte recruitment, IFN-γ production by CD4 and CD8 T cells, and the activation of lung myeloid cells.

Endemic mycoses in immunocompromised hosts

Endemic mycoses remain a significant cause of morbidity and mortality among immunocompromised patients. As the number of immunosuppressed individuals increases worldwide, the incidence of endemic mycoses is also expected to rise. In immunocompromised patients, endemic mycoses can present in atypical fashion, cause more severe and/or disseminated disease, and result in higher mortality. Despite several noteworthy advances over the past decade, significant challenges remain with regard to the prevention, diagnosis, and therapy of endemic mycoses in immunocompromised hosts. This review highlights important developments related to the epidemiology, diagnosis, treatment, and prevention of commonly encountered endemic mycoses. We also discuss emerging topics, knowledge gaps, and areas of future research.

Opportunistic and fungal infections of the lung

Opportunistic infections are a major cause of morbidity and mortality in severely immunocompromised patients, such as those receiving chemotherapy or with haematological malignancy, aplastic anaemia or HIV infection, or recipients of solid-organ or stem cell transplants. In addition, the increasing use of biological therapies will result in more patients at risk of opportunistic infections, albeit to a lesser degree than classic causes of immunocompromise. The type and degree of immune defect dictates the profile of potential opportunistic pathogens; T-cell mediated defects increase the risk of viral (cytomegalovirus and respiratory viruses) and Pneumocystis jirovecii infections, whereas neutrophil defects are associated with bacterial pneumonia and invasive aspergillosis. However, patients often have combinations of immune defects and a wide range of other opportunistic infections can cause pneumonia. The radiological pattern of disease (best assessed by CT scan) and speed of onset also help identify the likely pathogen(s), which can then be supported by targeted investigation including early use of bronchoscopy in selected patients. Rapid and expert clinical assessment can identify the most likely pathogens, which can then be treated aggressively and so provide the best opportunity for a positive outcome.

Clinical analysis of 68 patients with pulmonary mycosis in China

Background

Due to the lack of specific clinical manifestations and imaging features, the diagnosis of pulmonary mycosis is difficult. This study aimed to investigate the pathogens, clinical manifestations, imaging features, diagnosis and management of pulmonary mycosis.

Methods

Data on 68 patients diagnosed as pulmonary mycosis in Xiang Ya hospital from January 2001 to December 2010 were collected and their clinical manifestations, radiographic characterization, diagnostic methods and management were analyzed.

Results

All patients were diagnosed by pathological examination. Of the 68 cases, 38 (55.9%) had pulmonary aspergillosis and 19 (27.9%) pulmonary cryptococcosis. Open-lung surgery was performed in 38 patients (55.9%), transbronchial biopsy in 15 (22.0%), and computerized tomography (CT) guided percutaneous needle biopsy in 11 (16.2%). Main symptoms were as follows: cough in 51 cases (75.0%), expectoration in 38 (55.9%), hemoptysis in 25 (37.8%), fever in 20 (29.4%), while 6 cases (11.1%) were asymptomatic. X-ray and chest CT showed masses or nodular lesions in 52 cases (76.5%), patchy lesions in 10 (14.7%), cavity formation in 15 (22.0%), and diffuse miliary nodules in 1 case. In 51 cases (75.0%) misdiagnosis before pathological examination occurred. Surgical resection was performed in 38 patients (55.9%). In 25 patients (36.7%) systemic antifungal therapy was administered, and 20 patients (29.4%) experienced complete responses or partial responses.

Conclusion

The main pathogens of pulmonary mycosis are Aspergillus, followed by cryptococcosis. Final diagnosis of pulmonary mycosis mainly depends on pathological examination. The clinical manifestations, imaging features, diagnostic methods and management differ depending on the pathogens. Satisfactory therapy can be obtained by both antifungal and surgical treatment.

Recent advances in invasive pulmonary aspergillosis

PURPOSE OF REVIEW

This review highlights the most important and salient recent developments with regards to invasive pulmonary aspergillosis (IPA), currently the most common opportunistic fungal pneumonia in patients with hematological malignancies.

RECENT FINDINGS

Besides patients in hematology units, other immunosuppressed and critically ill patients are also at risk of IPA. Identification of patients who possess specific polymorphisms of Toll-like receptor 4 and dectin-1, both of which are involved in the immune sensing of Aspergillus spp., may facilitate risk-stratification. The use of the galactomannan assay in bronchoalveolar fluid to improve diagnosis of IPA is undergoing validation. Trending galactomannan and other biomarker results may prognosticate clinical outcomes. During intensive chemotherapy for leukemia, posaconazole and aerosolized liposomal amphotericin B (L-AMB) have demonstrated efficacy as prophylaxis against invasive fungal infection. However, fluconazole remains an effective prophylactic agent in the setting of hematopoietic stem cell transplantation despite availability of newer antifungal agents. Although voriconazole is still the drug of choice for IPA, both caspofungin and L-AMB are viable alternatives.

SUMMARY

Despite increasing knowledge of IPA and availability of newer antifungal agents, clinical management remains a challenge in the setting of a compromised host defense system that is unable to mount an appropriate immune response against the pathogen.