Role of granulocyte macrophage colony-stimulating factor in host defense against pulmonary Cryptococcus neoformans infection during murine allergic bronchopulmonary mycosis

Effect of intranasal administration of Granulocyte-Macrophage Colony-Stimulating Factor on pulmonary Cryptococcus gattii infection

Cryptococcosis, caused by infections with C. neoformans and C. gattii, presents a serious threat to global health and necessitates effective treatment strategies. Granulocyte-Macrophage Colony-Stimulating Factor, GM-CSF, is an immune-modulating cytokine that has been utilized clinically to improve host defense against infection; however, the impact of GM-CSF treatment in C. gattii infection has not been elucidated. Our current study aimed to investigate the effect of GM-CSF treatment on pulmonary immune response during C. gattii infection. In response to C. gattii infection, GM-CSF-expressing T helper cells and CD11b+ myeloid were enhanced in the lungs. The intranasal administration of GM-CSF during C. gattii infection significantly reduced pulmonary cryptococcal load, promoted an increase in pulmonary Th17 cells, as well as neutrophil infiltration in the lungs. Exposure of neutrophils to C. gattii in the presence of GM-CSF resulted in an increased neutrophil phagocytosis and fungal killing capacity, generation of reactive oxygen species (ROS), and upregulation of inflammatory cytokines and anti-microbial peptides. Although GM-CSF treatment in C. neoformans-infected mice had a comparable impact on the reduction of lung fungal burden, it resulted in the enhancement of Th1-type cytokine IFN-γ and the activation of M1 macrophages. Altogether, this study demonstrated that the intranasal delivery of GM-CSF has distinct effects on promoting the protection against C. gattii and C. neoformans by activating neutrophil/type-17 immune response and stimulating M1 macrophage/type-1 immunity, respectively.

Inhibition of host 5-lipoxygenase reduces overexuberant inflammatory responses and mortality associated with Cryptococcus meningoencephalitis

Cryptococcosis, caused by fungi of the genus Cryptococcus, manifests in a broad range of clinical presentations, including severe pneumonia and disease of the central nervous system (CNS) and other tissues (bone and skin). Immune deficiency or development of overexuberant inflammatory responses can result in increased susceptibility or host damage, respectively, during fungal encounters. Leukotrienes help regulate inflammatory responses against fungal infections. Nevertheless, studies showed that Cryptococcus exploits host 5-lipoxygenase (5-LO), an enzyme central to the metabolism of arachidonic acid into leukotrienes, to facilitate transmigration across the brain-blood barrier. To investigate the impact of host 5-LO on the development of protective host immune responses and mortality during cryptococcosis, wild-type (C57BL/6) and 5-lipoxygenase-deficient (5-LO-/-) mice were given experimental pulmonary and systemic Cryptococcus sp., infections. Our results showed that 5-LO-/- mice exhibited reduced pathology and better disease outcomes (i.e., no mortality or signs associated with cryptococcal meningoencephalitis) following pulmonary infection with C. deneoformans, despite having detectable yeast in the brain tissues. In contrast, C57BL/6 mice exhibited classical signs associated with cryptococcal meningoencephalitis. Additionally, brain tissues of 5-LO-/- mice exhibited lower levels of cytokines (CCL2 and CCL3) clinically associated with Cryptococcus-related immune reconstitution inflammatory syndrome (C-IRIS). In a systemic mouse model of cryptococcosis, 5-LO-/- mice and those treated with a Federal Drug Administration (FDA)-approved 5-LO synthesis inhibitor, zileuton, displayed significantly reduced mortality compared to C57BL/6 infected mice. These results suggest that therapeutics designed to inhibit host 5-LO signaling could reduce disease pathology and mortality associated with cryptococcal meningoencephalitis.

IMPORTANCE

Cryptococcosis is a mycosis with worldwide distribution and has a broad range of clinical manifestations, including diseases of the CNS. Globally, there is an estimated 179,000 cases of cryptococcal meningitis, resulting in approximately 112,000 fatalities per annum and 19% of AIDS-related deaths. Understanding how host immune responses are modulated during cryptococcosis is central to mitigating the morbidity and mortality associated with cryptococcosis. Leukotrienes (LTs) have been shown to modulate inflammatory responses during infection. In this study, we show that mice deficient in 5-lipoxygenase (5-LO), an enzyme central to the metabolism of arachidonic acid into leukotrienes, exhibit reduced pathology, disease, and neurological signs associated with cryptococcal meningitis. Additionally, mice given an experimental cryptococcal infection and subsequently treated with an FDA-approved 5-LO synthesis inhibitor exhibited significantly reduced mortality rates. These results suggest that therapeutics designed to inhibit host 5-LO activity could significantly reduce pathology and mortality rates associated with cryptococcal meningitis.

Alternatively activated lung alveolar and interstitial macrophages promote fungal growth

How lung macrophages, especially interstitial macrophages (IMs), respond to invading pathogens remains elusive. Here, we show that mice exhibited a rapid and substantial expansion of macrophages, especially CX3CR1+ IMs, in the lung following infection with Cryptococcus neoformans, a pathogenic fungus leading to high mortality among patients with HIV/AIDS. The IM expansion correlated with enhanced CSF1 and IL-4 production and was affected by the deficiency of CCR2 or Nr4a1. Both alveolar macrophages (AMs) and IMs were observed to harbor C. neoformans and became alternatively activated following infection, with IMs being more polarized. The absence of AMs by genetically disrupting CSF2 signaling reduced fungal loads in the lung and prolonged the survival of infected mice. Likewise, infected mice depleted of IMs by the CSF1 receptor inhibitor PLX5622 displayed significantly lower pulmonary fungal burdens. Thus, C. neoformans infection induces alternative activation of both AMs and IMs, which facilitates fungal growth in the lung.

Role of GM-CSF in lung balance and disease

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a hematopoietic growth factor originally identified as a stimulus that induces the differentiation of bone marrow progenitor cells into granulocytes and macrophages. GM-CSF is now considered to be a multi-origin and pleiotropic cytokine. GM-CSF receptor signals activate JAK2 and induce nuclear signals through the JAK-STAT, MAPK, PI3K, and other pathways. In addition to promoting the metabolism of pulmonary surfactant and the maturation and differentiation of alveolar macrophages, GM-CSF plays a key role in interstitial lung disease, allergic lung disease, alcoholic lung disease, and pulmonary bacterial, fungal, and viral infections. This article reviews the latest knowledge on the relationship between GM-CSF and lung balance and lung disease, and indicates that there is much more to GM-CSF than its name suggests.

GM-CSF+ Tc17 cells are required to bolster vaccine immunity against lethal fungal pneumonia without causing overt pathology

GM-CSF co-expressing T17 cells instigate pathologic inflammation during autoimmune disorders, but their function in immunity to infections is unclear. Here, we demonstrate the role of GM-CSF⁺Tc17 cells for vaccine immunity against lethal fungal pneumonia and the cytokine requirements for their induction and memory homeostasis. Vaccine-induced GM-CSF⁺ Tc17 cells are necessary to bolster pulmonary fungal immunity without inflating pathology. Although GM-CSF expressing Tc17 cells preferentially elevate during the memory phase, their phenotypic attributes strongly suggest they are more like Tc17 cells than IFNγ-producing Tc1 cells. IL-1 and IL-23, but not GM-CSF, are necessary to elicit GM-CSF⁺Tc17 cells following vaccination. IL-23 is dispensable for memory Tc17 and GM-CSF⁺ Tc17 cell maintenance, but recall responses of effector or memory Tc17 cells in the lung require it. Our study reveals the beneficial, nonpathological role of GM-CSF⁺ Tc17 cells during fungal vaccine immunity.

GM-CSF⁺ and IL-17A⁺ lineages of T cells are instrumental in controlling many fungal and bacterial infections and implicated in autoimmune pathology, host-microbial interactions at the mucosal surfaces, and neuro-immune nexus. Mudalagiriyappa et al. show that GM-CSF expressing Tc17 cells are necessary for mediating fungal vaccine immunity without augmenting pathology.

Immunological Predictors of Post Infectious Inflammatory Response Syndrome in HIV-Negative Immunocompetent Cryptococcal Meningitis

Objective

This research aims to study the correlation between serum immune factors and post-infectious inflammatory response syndrome (PIIRS) in immunocompetent cryptococcal meningitis (CM), and explore whether serum immune factors could be used to predict the development of PIIRS.

Methods

A cohort of 30 patients with PIIRS and 87 patients without PIIRS was selected from 347 CM patients. We analyzed the general clinical information and immunological indexes (cytokines, complement, immunoglobulin, inflammation, related cytological and biochemical indexes). Spearman correlation analysis and principal component analysis were used to explore the effects of the variables on PIIRS. Additionally, the variables were identified by a random forest-based classifier for predicting the development of PIIRS. The clinical value of predictors was verified by survival analysis.

Results

Compared with patients without PIIRS, patients with PIIRS had lower baseline serum interleukin-6 (IL-6, P = 0.006), immunoglobulin M (IgM, P = 0.004), and a higher baseline neutrophil ratio (P <0.001). The baseline neutrophil ratio (r = 0.359, P = 0.001), IgM (r = −0.272, P = 0.025), and IL-6 (r = −0.259, P = 0.027) were significantly correlated with PIIRS. Combining principal component analysis and random forest results, neutrophil ratio, neutrophil count, IgM, IL-6, and D-dimer were useful predictors. The accuracy of random forest prediction was 75.00%, AUC, and sensitivity were 0.76 and 70%, respectively. Further survival analysis of the time from treatment to PIIRS revealed that the development of PIIRS was associated with IgM (more than 98 days of treatment) and neutrophil ratio/count.

Conclusion

Baseline neutrophils ratio, neutrophil count, IgM, IL-6, and D-dimer may be clinically useful predictors of PIIRS in HIV-negative immunocompetent CM patients.

An Immunogenic and Slow-Growing Cryptococcal Strain Induces a Chronic Granulomatous Infection in Murine Lungs

Many successful pathogens cause latent infections, remaining dormant within the host for years but retaining the ability to reactivate to cause symptomatic disease. The human opportunistic fungal pathogen Cryptococcus neoformans establishes latent pulmonary infections in immunocompetent individuals upon inhalation from the environment. These latent infections are frequently characterized by granulomas, or foci of chronic inflammation, that contain dormant and persistent cryptococcal cells. Immunosuppression can cause these granulomas to break down and release fungal cells that proliferate, disseminate, and eventually cause lethal cryptococcosis. This course of fungal latency and reactivation is understudied due to limited models, as chronic pulmonary granulomas do not typically form in mouse cryptococcal infections. A loss-of-function mutation in the Cryptococcus-specific MAR1 gene was previously described to alter cell surface remodeling in response to host signals. Here, we demonstrate that the mar1Δ mutant strain persists long term in a murine inhalation model of cryptococcosis, inducing a chronic pulmonary granulomatous response. We find that murine infections with the mar1Δ mutant strain are characterized by reduced fungal burden, likely due to the low growth rate of the mar1Δ mutant strain at physiological temperature, and an altered host immune response, likely due to inability of the mar1Δ mutant strain to properly employ virulence factors. We propose that this combination of features in the mar1Δ mutant strain collectively promotes the induction of a more chronic inflammatory response and enables long-term fungal persistence within these granulomatous regions.

Proteomics of Cryptococcus neoformans: From the Lab to the Clinic

Fungal pathogens cause an array of diseases by targeting both immunocompromised and immunocompetent hosts. Fungi overcome our current arsenal of antifungals through the emergence and evolution of resistance. In particular, the human fungal pathogen, Cryptococcus neoformans is found ubiquitously within the environment and causes severe disease in immunocompromised individuals around the globe with limited treatment options available. To uncover fundamental knowledge about this fungal pathogen, as well as investigate new detection and treatment strategies, mass spectrometry-based proteomics provides a plethora of tools and applications, as well as bioinformatics platforms. In this review, we highlight proteomics approaches within the laboratory to investigate changes in the cellular proteome, secretome, and extracellular vesicles. We also explore regulation by post-translational modifications and the impact of protein-protein interactions. Further, we present the development and comprehensive assessment of murine models of cryptococcal infection, which provide valuable tools to define the dynamic relationship between the host and pathogen during disease. Finally, we explore recent quantitative proteomics studies that begin to extrapolate the findings from the bench to the clinic for improved methods of fungal detection and monitoring. Such studies support a framework for personalized medical approaches to eradicate diseases caused by C. neoformans.

Transcriptional Changes in Pulmonary Phagocyte Subsets Dictate the Outcome Following Interaction With The Fungal Pathogen Cryptococcus neoformans

With over 220,000 cases and 180,000 deaths annually, Cryptococcus neoformans is the most common cause of fungal meningitis and a leading cause of death in HIV/AIDS patients in Sub-Saharan Africa. Either C. neoformans can be killed by innate airway phagocytes, or it can survive intracellularly. Pulmonary murine macrophage and dendritic cell (DC) subsets have been identified in the naïve lung, and we hypothesize that each subset has different interactions with C. neoformans. For these studies, we purified murine pulmonary macrophage and DC subsets from naïve mice - alveolar macrophages, Ly6c^- and Ly6c⁺ monocyte-like macrophages, interstitial macrophages, CD11b⁺ and CD103⁺ DCs. With each subset, we examined cryptococcal association (binding/internalization), fungicidal activity, intracellular fungal morphology, cytokine secretion and transcriptional profiling in an ex vivo model using these pulmonary phagocyte subsets. Results showed that all subsets associate with C. neoformans, but only female Ly6c^- monocyte-like macrophages significantly inhibited growth, while male CD11b⁺ DCs significantly enhanced fungal growth. In addition, cytokine analysis revealed that some subsets from female mice produced increased amounts of cytokines compared to their counterparts in male mice following exposure to C. neoformans. In addition, although cells were analyzed ex vivo without the influence of the lung microenviroment, we did not find evidence of phagocyte polarization following incubation with C. neoformans. Imaging flow cytometry showed differing ratios of cryptococcal morphologies, c-shaped or budding, depending on phagocyte subset. RNA sequencing analysis revealed the up- and down-regulation of many genes, from immunological pathways (including differential regulation of MHC class I in the antigen processing pathway and the cell adhesion pathway) and pathways relating to relating to metabolic activity (genes in the Cytochrome P450 family, genes related to actin binding, calcium voltage channels, serine proteases, and phospholipases). Future studies gaining a more in-depth understanding on the functionality of individual genes and pathways specific to permissive and non-permissive pulmonary phagocytes will allow identification of key targets when developing therapeutic strategies to prevent cryptococcal meningitis.

Cryptococcal infection in haematologic malignancies and haematopoietic stem cell transplantation

This review summarises both the recent and relevant studies about cryptococcal infections in haematologic malignancies and haematopoietic stem cell transplantation. Although uncommon in this patient population, this infection carries a high mortality, especially if left untreated. Given the limited data, we draw some conclusions with respect to management from the solid organ transplantation and HIV-infected literature. Herein, we discuss cryptococcosis with a particular attention to its background, epidemiology, risk factors, clinical presentation, diagnosis, treatment and prevention in this group.

T Cell Antifungal Immunity and the Role of C-Type Lectin Receptors

Fungi can cause disease in humans, from mucocutaneous to life-threatening systemic infections. Initiation of antifungal immunity involves fungal recognition by pattern recognition receptors such as C-type lectin receptors (CLRs). These germline-encoded receptors trigger a multitude of innate responses including phagocytosis, fungal killing, and antigen presentation which can also shape the development of adaptive immunity. Recently, studies have shed light on how CLRs directly or indirectly modulate lymphocyte function. Moreover, CLR-mediated recognition of commensal fungi maintains homeostasis and prevents invasion from opportunistic commensals. We present an overview of current knowledge of antifungal T cell immune responses, with emphasis on the role of C-type lectins, and discuss how these receptors modulate these responses at different levels.

CLRs are essential pattern recognition receptors involved in fungal recognition and initiation of protective antifungal immunity.

CLRs promote the differentiation of mammalian T helper cell subsets essential for the control of systemic (Th1) and mucosal (Th17) fungal infections.

CLRs are involved in antigen presentation, the expression of co-stimulatory molecules, and cytokine secretion; therefore, they can regulate lymphocyte function and adaptive immune responses at different levels.

Fungal morphological changes, such as the transition from yeast to hyphae in Candida albicans during tissue invasion, affects recognition by CLRs and impacts on adaptive immune responses.

CLRs recognize the fungal component of the microbiome that can influence T cell responses during infection at intestinal and peripheral sites.

Hepatoprotective immune response during Trichinella spiralis infection in mice

Infections with gastrointestinal nematodes provoke immune and inflammatory responses mediated by cytokines released from T-helper type-2 (Th2) cells. Infections with Trichinella species have been reported to differ by the host species. Previously, in rats, we observed acute liver inflammation in response to infection with Trichinella spiralis, and the rat hosts showed a series of biochemical changes characterized by a decrease in serum paraoxonase (PON) 1 activity associated with the down-regulation of hepatic PON1 synthesis. In the present study, we investigated the effect(s) of species differences on the immune response against T. spiralis infection by analyzing serum PON1 activity and the associated inflammatory/anti-inflammatory mediators in mice. There were inconsistent changes in the serum PON1 activity of mice infected with T. spiralis, and these changes were associated with significant increases in the serum levels of interleukin (IL)-2, IL-4, IL-10, IL-12 (p70), granulocyte-macrophage colony-stimulating factor, and tumor necrosis factor α during the enteric phase of the infection, while the levels of IL-5 and interferon γ were significantly increased throughout the entire experimental period. Moreover, T. spiralis infection in mice was associated with little inflammatory cell infiltration in hepatic tissues. Given the zoonotic prevalence of T. spiralis, further mechanistic research in this area is warranted.

Consequences of Hypoxia for the Pulmonary Alveolar Epithelial Cell Innate Immune Response

Pulmonary innate immune responses involve a highly regulated multicellular network to defend the enormous surface area of the lung. Disruption of these responses renders the host susceptible to pneumonia. Alveolar epithelial cells (AEC) are a critical source of innate immune molecules such as GM-CSF, which determine the functional maturation of alveolar macrophages. In many pulmonary diseases, heterogeneous ventilation leads to regional hypoxia in the lung. The effect of hypoxia on AEC innate immune function is unknown. We now report that exposure of primary murine AEC to hypoxia (1% oxygen) for 24 h results in significant suppression of key innate immune molecules, including GM-CSF, CCL2, and IL-6. This exposure did not cause toxicity but did induce stabilization of hypoxia-inducible factor 1α protein (HIF-1α) and shift to glycolytic metabolism. Focusing on GM-CSF, we found that hypoxia greatly decreased the rate of GM-CSF transcription. Hypoxia both decreased NF-κB signaling in AEC and induced chromosomal changes, resulting in decreased accessibility in the GM-CSF proximal promoter of target sequences for NF-κB binding. In mice exposed to hypoxia in vivo (12% oxygen for 2 d), lung GM-CSF protein expression was reduced. In vivo phagocytosis of fluorescent beads by alveolar macrophages was also suppressed, but this effect was reversed by treatment with GM-CSF. These studies suggest that in critically ill patients, local hypoxia may contribute to the susceptibility of poorly ventilated lung units to infection through complementary effects on several pathways, reducing AEC expression of GM-CSF and other key innate immune molecules.

Inhaled Cryptococcus neoformans elicits allergic airway inflammation independent of Nuclear Factor Kappa B signalling in lung epithelial cells

Pulmonary challenge with the ubiquitous fungus Cryptococcus neoformans results in allergic airway inflammation (AAI) characterized by robust recruitment of eosinophils and T cells producing type 2 cytokines to the lungs. Previous studies have demonstrated a critical role for Nuclear Factor Kappa B (NF-κB) activation within lung epithelial cells (LECs) in driving AAI in response to protein allergens, yet the role of LEC-intrinsic NF-κB in promoting AAI following exposure to C. neoformans is poorly understood. To investigate the role of LEC-intrinsic NF-κB in promoting AAI following C. neoformans challenge, we used IKK^∆LEC mice, which lack canonical NF-κB activation specifically within LECs. IKK^∆LEC and littermate control mice were intranasally challenged with 10⁶ CFU of C. neoformans strain 52D, and lung tissues were collected at 7, 14 and 21 days post infection to assess the development of AAI. Notably, the absence of epithelial NF-κB signalling did not affect the magnitude or kinetics of lung eosinophilia when compared with the response in wild-type control mice. The total numbers of lung T cells producing the type 2 cytokines interleukin-5 and interleukin-13 were also unchanged in IKK^∆LEC mice. Furthermore, IKK^∆LEC mice showed no defect in the recruitment of protective interferon-γ-producing CD4 T cells to the lungs, fungal clearance, or host survival compared with control mice. Immunofluorescence imaging surprisingly revealed no evidence of nuclear localization of NF-κB in LECs in response to C. neoformans challenge, indicating that NF-κB is not activated within these cells. Taken together, these data strongly suggest that NF-κB signalling within LECs does not promote AAI observed in response to C. neoformans.

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.

Competent antigen-presenting cells are generated from the long-term culture of splenocytes with granulocyte-macrophage colony-stimulating factor

Dendritic cells (DCs) are routinely produced from the culture of mouse bone marrow (BM) with granulocyte-macrophage colony-stimulating factor (GM-CSF) within a period of 10days. Although splenic extramedullary myelopoiesis was suggested to occur under the influence of GM-CSF, the hematopoietic outcome of splenic culture with GM-CSF has not been scrutinized. We have cultured mouse splenocytes with GM-CSF for an extended period of time, where we discovered that the CD11b⁺CD11c⁺ cells began to proliferate prominently after 10days and their number increased until the 4th week of the culture. In parallel experiments, FMS-like tyrosine kinase 3 (FLT3) and its ligand, FLT3L, were not found to influence the culture of splenocytes. Like DCs in the culture of BM with GM-CSF, a distinct population of CD11b⁺CD11c⁺MHC II^hi cells was readily identified as DCs in the long-term culture of splenocytes. After being isolated and plated overnight the CD11b⁺CD11c⁺MHC II^hi cells exhibited non-adherent dendritic morphology, while the other CD11b⁺CD11c⁺ cells became adherent. Besides, these CD11b⁺CD11c⁺MHC II^hi cells possessed relatively weak endocytic and phagocytic abilities but displayed strong antigen-presenting capacities, revealing DC-like characteristics; in contrast, the other CD11b⁺CD11c⁺ cells showed strong endocytosis and phagocytosis of antigens but were poor at antigen presentation, indicating macrophage-like traits. Therefore, we demonstrated that phenotypically as well as functionally genuine DCs are generated in the long-term culture of splenocytes with GM-CSF.

Immunoregulation in Fungal Diseases

This review addresses specific regulatory mechanisms involved in the host immune response to fungal organisms. We focus on key cells and regulatory pathways involved in these responses, including a brief overview of their broader function preceding a discussion of their specific relevance to fungal disease. Important cell types discussed include dendritic cells and regulatory T cells, with a focus on specific studies relating to their effects on immune responses to fungi. We highlight the interleukin-10, programmed cell death 1, and cytotoxic T lymphocyte-associated protein 4 signaling pathways and emphasize interrelationships between these pathways and the regulatory functions of dendritic cells and regulatory T cells. Throughout our discussion, we identify selected studies best illustrating the role of these cells and pathways in response to specific fungal pathogens to provide a contextual understanding of the tightly-controlled network of regulatory mechanisms critical to determining the outcome of exposure to fungal pathogens. Lastly, we discuss two unique phenomena relating to immunoregulation, protective tolerance and immune reactivation inflammatory syndrome. These two clinically-relevant conditions provide perspective as to the range of immunoregulatory mechanisms active in response to fungi.

Role of dendritic cell-pathogen interactions in the immune response to pulmonary cryptococcal infection

This review discusses the unique contributions of dendritic cells (DCs) to T-cell priming and the generation of effective host defenses against Cryptococcus neoformans (C.neo) infection. We highlight DC subsets involved in the early and later stages of anticryptococcal immune responses, interactions between C.neo pathogen-associated molecular patterns and pattern recognition receptors expressed by DC, and the influence of DC on adaptive immunity. We emphasize recent studies in mouse models of cryptococcosis that illustrate the importance of DC-derived cytokines and costimulatory molecules and the potential role of DC epigenetic modifications that support maintenance of these signals throughout the immune response to C.neo. Lastly, we stipulate where these advances can be developed into new, immune-based therapeutics for treatment of this global pathogen.

GM-CSF has disparate roles during intranasal and intradermal Francisella tularensis infection

Our laboratory has employed in vitro and in vivo mouse models based on Francisella tularensis Live Vaccine Strain (LVS)-induced protection to elucidate immune correlates for intracellular bacteria. Among the effectors found was GM-CSF, a pleiotropic cytokine that is integral to the development and proliferation of myeloid cells, including alveolar macrophages. GM-CSF has roles in resistance to primary murine infection with several intracellular pathogens, but its role during Francisella infection is unknown. Francisella is an intracellular pathogen that infects lungs after inhalation, primarily invading alveolar macrophages. Here we show that GM-CSF has route-dependent roles during primary infection of mice with LVS. GM-CSF deficient (GM-CSF KO) mice were slightly more susceptible than wild type to intradermal infection, but had increased resistance to intranasal infection. Similarly, these mice had increased resistance to pulmonary infection with virulent F. tularensis (SchuS4). LVS-vaccinated GM-CSF KO mice had normal adaptive immune responses, as measured by T cell activities after LVS intradermal or intranasal vaccination, and survived lethal secondary LVS challenge. GM-CSF KO mice also had robust humoral responses, producing elevated levels of serum antibodies following LVS vaccination compared to wild type mice. Taken together, our data demonstrates that the absence of GM-CSF improves resistance to pulmonary, but not intradermal, infection with Francisella.

Autoantibody-Mediated Pulmonary Alveolar Proteinosis in Rasgrp1-Deficient Mice

Pulmonary alveolar proteinosis (PAP) is a rare lung syndrome caused by the accumulation of surfactants in the alveoli. The most prevalent clinical form of PAP is autoimmune PAP (aPAP) whereby IgG autoantibodies neutralize GM-CSF. GM-CSF is a pleiotropic cytokine that promotes the differentiation, survival, and activation of alveolar macrophages, the cells responsible for surfactant degradation. IgG-mediated neutralization of GM-CSF thereby inhibits alveolar macrophage homeostasis and function, leading to surfactant accumulation and innate immunodeficiency. Importantly, there are no rodent models for this disease; therefore, underlying immune mechanisms regulating GM-CSF-specific IgG in aPAP are not well understood. In this article, we identify that autoimmune-prone Rasgrp1-deficient mice develop aPAP: 1) Rasgrp1-deficient mice exhibit reduced pulmonary compliance and lung histopathology characteristic of PAP; 2) alveolar macrophages from Rasgrp1-deficient mice are enlarged and exhibit reduced surfactant degradation; 3) the concentration of GM-CSF-specific IgG is elevated in both serum and bronchoalveolar lavage fluid from Rasgrp1-deficient mice; 4) GM-CSF-specific IgG is capable of neutralizing GM-CSF bioactivity; and 5) Rasgrp1-deficient mice also lacking CD275/ICOSL, a molecule necessary for conventional T cell-dependent Ab production, have reduced GM-CSF-specific autoantibody and do not develop PAP. Collectively, these studies reveal that Rasgrp1-deficient mice, to our knowledge, represent the first rodent model for aPAP.

Reduced expression of granule proteins during extended survival of eosinophils in splenocyte culture with GM-CSF

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is a multifaceted hematopoietic cytokine and the culture of mouse bone marrow with GM-CSF produces a variety of myeloid cells including granulocytes, macrophages, and dendritic cells. In the present study, we cultured mouse splenocytes with GM-CSF and examined the changes in hematopoietic cell populations over a week. Most of the splenic hematopoietic cells disappeared significantly from culture within 6days with or without the presence of GM-CSF. Among the splenic granulocyte populations, only eosinophils fully survived throughout the culture with GM-CSF for more than a week. During 10days of culture with GM-CSF, splenic eosinophils maintained their morphology as well as most of their surface molecules at high levels, including CCR3 and Siglec F. Meanwhile, the expression of mRNAs encoding major basic protein-1 (MBP-1) and eosinophil peroxidase (EPO), two major eosinophil-derived granule proteins, was diminished significantly from the cultured eosinophils. EPO assays also revealed that eosinophils in culture for more than 5days retained 30% or less EPO activity compared to those in uncultured splenocytes. In contrast, culture of splenocytes with GM-CSF did not change the capacity of eosinophils to migrate in response to eotaxin-1. Our results indicate that mouse splenic eosinophils are effectively cultured for lengthy periods while their expression of eosinophil-derived granule proteins is specifically suppressed. The relevance of these findings to eosinophilic inflammatory response is discussed.

Local GM-CSF-Dependent Differentiation and Activation of Pulmonary Dendritic Cells and Macrophages Protect against Progressive Cryptococcal Lung Infection in Mice

Patients with acquired deficiency in GM-CSF are susceptible to infections with Cryptococcus neoformans and other opportunistic fungi. We previously showed that GM-CSF protects against progressive fungal disease using a murine model of cryptococcal lung infection. To better understand the cellular and molecular mechanisms through which GM-CSF enhances antifungal host defenses, we investigated temporal and spatial relationships between myeloid and lymphoid immune responses in wild-type C57BL/6 mice capable of producing GM-CSF and GM-CSF-deficient mice infected with a moderately virulent encapsulated strain of C. neoformans (strain 52D). Our data demonstrate that GM-CSF deficiency led to a reduction in: 1) total lung leukocyte recruitment; 2) Th2 and Th17 responses; 3) total numbers of CD11b(+) dendritic cells (DC) and CD11b(-) and CD11b(+) macrophages (Mϕ); 4) DC and Mϕ activation; and 5) localization of DC and Mϕ to the microanatomic sites of alveolar infection. In contrast, GM-CSF deficiency resulted in increased accumulation of DC and Mϕ precursors, namely Ly-6C(high) monocytes, in the blood and lungs of infected mice. Collectively, these results show that GM-CSF promotes the local differentiation, accumulation, activation, and alveolar localization of lung DC and Mϕ in mice with cryptococcal lung infection. These findings identify GM-CSF as central to the protective immune response that prevents progressive fungal disease and thus shed new light on the increased susceptibility to these infections observed in patients with acquired GM-CSF deficiency.

Effect of Granulocyte-Macrophage Colony-Stimulating Factor on Prevention and Treatment of Invasive Fungal Disease in Recipients of Allogeneic Stem-Cell Transplantation: A Prospective Multicenter Randomized Phase IV Trial

PURPOSE

For recipients of allogeneic hematopoietic stem-cell transplantation (alloHSCT), we hypothesized that prophylactic therapy during neutropenia with granulocyte-macrophage colony-stimulating factor (GM-CSF) decreases invasive fungal disease (IFD).

PATIENTS AND METHODS

We randomly assigned 206 patients undergoing alloHSCT to receive once-daily subcutaneous GM-CSF (5 to 7 μg/kg per day), granulocyte colony-stimulating factor (G-CSF; 5 to 7 μg/kg per day), or a combination of G-CSF and GM-CSF (2 to 3 μg/kg per day each). Treatment was started on day 5 after transplantation and was continued until the absolute neutrophil count was ≥ 1.5 × 10(9)/L for 2 consecutive days. The primary outcomes were 100-day incidence of proven and probable IFD and response rate of antifungal treatment.

RESULTS

For the intent-to-treat population, there was no significant difference in 100-day incidences of proven and probable IFD among the three groups. The antifungal treatment response was better in the GM-CSF group and G-CSF+GM-CSF group than in G-CSF group from day 22 to day 100 (P = .009). The 100-day cumulative mortality after transplantation was lower in the GM-CSF group than in the G-CSF group (10.3% v 24.6%, respectively; P = .037). The GM-CSF and G-CSF+GM-CSF groups had lower 100-day transplantation-related mortality than the G-CSF group (8.8%, 8.7%, and 21.7%, respectively; P = .034). After a median follow-up of 600 days, IFD-related mortality was lower in the groups that received GM-CSF or G-CSF+GM-CSF compared with G-CSF (1.47%, 1.45%, and 11.59%, respectively; P = .016). There were no significant differences in relapse, graft-versus-host disease, or hemorrhage-related mortality among the three groups of patients.

CONCLUSION

For recipients of alloHSCT, compared with G-CSF, prophylactic GM-CSF was associated with lower 100-day transplantation-related mortality, lower 100-day cumulative mortality, and lower 600-day IFD-related mortality.

Is Cryptococcus gattii a Primary Pathogen?

The two etiologic agents of cryptococcal meningoencephalitis, Cryptococcus neoformans and C. gattii, have been commonly designated as either an opportunistic pathogen for the first species or as a primary pathogen for the second species. Such a distinction has been based on epidemiological findings that the majority of patients presenting meningoencephalitis caused by C. neoformans are immunocompromised while C. gattii infection has been reported more often in immunocompetent patients. A recent report, however, showed that GM-CSF (granulocyte-macrophage colony-stimulating factor) neutralizing antibodies were prevalent in the plasma of "apparently immunocompetent" C. gattii patients with meningoencephalitis. Because GM-CSF is essential for differentiation of monocytes to macrophages and modulating the immune response, it is not surprising that the lack of GM-CSF function predisposes otherwise healthy individuals to infection via inhalation of environmental pathogens such as C. gattii. Since the test for anti-GM-CSF autoantibodies is not included in routine immunological profiling at most hospitals, healthy patients with GM-CSF neutralizing antibodies are usually categorized as immunocompetent. It is likely that a comprehensive immunological evaluation of patients with C. gattii meningoencephalitis, who had been diagnosed as immunocompetent, would reveal a majority of them had hidden immune dysfunction. This paper reviews the relationship between GM-CSF neutralizing antibodies and the risk for C. gattii infection with CNS involvement.

Analysis of asthma patients for cryptococcal seroreactivity in an urban German area

Cryptococcus neoformans is an opportunistic fungal pathogen that causes lung inflammation and meningoencephalitis in immunocompromised patients but is also able to asymptomatically infect immunocompetent individuals. C. neoformans is found ubiquitously especially in urban areas where it is spread by pigeons, and fungal exposure may predispose for asthma development already at an early age, as soon as confronted with pigeon droppings. In the study presented here, we investigated the presence of specific immunoglobulin G (IgG) against C. neoformans in sera from patients suffering from asthma in comparison to a healthy control cohort, accrued from the Leipzig Research Centre for Civilization Diseases (LIFE). For serological analysis we developed a flow cytometry (FACS) based assay specific for an acapsular strain of C. neoformans to comprehensively analyze different cryptococcal serotypes. Compared with the non-asthmatic cohort, asthmatics exhibited, as expected, an elevated level of total serum immunoglobulin E (IgE), whereas the IgG seroreactivity against C. neoformans was not significantly different among the two groups (P = .118). Nevertheless, there was a trend toward increased Cryptococcus-specific IgG antibodies in the serum of asthmatics. Additionally, in male asthmatics an increased IgG-mediated seroreactivity compared to female asthmatics was found. This points to a higher prevalence of subclinical C. neoformans infection in male asthmatics and may support the hypothesis of C. neoformans as a risk factor for the development of asthma in urban areas.

Cryptococcal heat shock protein 70 homolog Ssa1 contributes to pulmonary expansion of Cryptococcus neoformans during the afferent phase of the immune response by promoting macrophage M2 polarization

Numerous virulence factors expressed by Cryptococcus neoformans modulate host defenses by promoting nonprotective Th2-biased adaptive immune responses. Prior studies demonstrate that the heat shock protein 70 homolog, Ssa1, significantly contributes to serotype D C. neoformans virulence through the induction of laccase, a Th2-skewing and CNS tropic factor. In the present study, we sought to determine whether Ssa1 modulates host defenses in mice infected with a highly virulent serotype A strain of C. neoformans (H99). To investigate this, we assessed pulmonary fungal growth, CNS dissemination, and survival in mice infected with either H99, an SSA1-deleted H99 strain (Δssa1), and a complement strain with restored SSA1 expression (Δssa1::SSA1). Mice infected with the Δssa1 strain displayed substantial reductions in lung fungal burden during the innate phase (days 3 and 7) of the host response, whereas less pronounced reductions were observed during the adaptive phase (day 14) and mouse survival increased only by 5 d. Surprisingly, laccase activity assays revealed that Δssa1 was not laccase deficient, demonstrating that H99 does not require Ssa1 for laccase expression, which explains the CNS tropism we still observed in the Ssa1-deficient strain. Lastly, our immunophenotyping studies showed that Ssa1 directly promotes early M2 skewing of lung mononuclear phagocytes during the innate phase, but not the adaptive phase, of the immune response. We conclude that Ssa1's virulence mechanism in H99 is distinct and laccase-independent. Ssa1 directly interferes with early macrophage polarization, limiting innate control of C. neoformans, but ultimately has no effect on cryptococcal control by adaptive immunity.

IL-17 and neutrophils: unexpected players in the type 2 immune response

The study of immunity to helminth infection has been central to understanding the function of type 2 cytokines and their targets. Although type 2 cytokines are considered anti-inflammatory and promote tissue repair, they also contribute to allergy and fibrosis. Here, we utilise data from helminth infection models, to illustrate that IL-17 and neutrophils, typically associated with pro-inflammatory responses, are intimately linked with type 2 immunity. Neutrophils work with IL-4Rα-activated macrophages to control incoming larvae but this comes at a cost of enhanced tissue damage. Chitinase like proteins (CLPs) bridge these diverse outcomes, inducing both protective IL-17 and reparative Th2 responses. Dysregulation of CLPs, IL-17 and neutrophils likely contribute to disease severity and pathology associated with type 2 immunity.

Interleukin-17 induces an atypical M2-like macrophage subpopulation that regulates intestinal inflammation

Interleukin 17 (IL-17) is a pleiotropic cytokine that acts on both immune and non-immune cells and is generally implicated in inflammatory and autoimmune diseases. Although IL-17 as well as their source, mainly but not limited to Th17 cells, is also abundant in the inflamed intestine, the role of IL-17 in inflammatory bowel disease remains controversial. In the present study, by using IL-17 knockout (KO) mice, we investigated the role of IL-17 in colitis, with special focus on the macrophage subpopulations. Here we show that IL-17KO mice had increased susceptibility to DSS-induced colitis which was associated with decrease in expression of mRNAs implicated in M2 and/or wound healing macrophages, such as IL-10, IL-1 receptor antagonist, arginase 1, cyclooxygenase 2, and indoleamine 2,3-dioxygenase. Lamina propria leukocytes from inflamed colon of IL-17KO mice contained fewer CD11b⁺Ly6C⁺MHC Class II⁺ macrophages, which were derived, at least partly, from blood monocytes, as compared to those of WT mice. FACS-purified CD11b⁺ cells from WT mice, which were more abundant in Ly6C⁺MHC Class II⁺ cells, expressed increased levels of genes associated M2/wound healing macrophages and also M1/proinflammatory macrophages. Depletion of this population by topical administration of clodronate-liposome in the colon of WT mice resulted in the exacerbation of colitis. These results demonstrate that IL-17 confers protection against the development of severe colitis through the induction of an atypical M2-like macrophage subpopulation. Our findings reveal a previously unappreciated mechanism by which IL-17 exerts a protective function in colitis.

STAT1 signaling is essential for protection against Cryptococcus neoformans infection in mice

Nonprotective immune responses to highly virulent Cryptococcus neoformans strains, such as H99, are associated with Th2-type cytokine production, alternatively activated macrophages, and inability of the host to clear the fungus. In contrast, experimental studies show that protective immune responses against cryptococcosis are associated with Th1-type cytokine production and classical macrophage activation. The protective response induced during C. neoformans strain H99γ (C. neoformans strain H99 engineered to produce murine IFN-γ) infection correlates with enhanced phosphorylation of the transcription factor STAT1 in macrophages; however, the role of STAT1 in protective immunity to C. neoformans is unknown. The current studies examined the effect of STAT1 deletion in murine models of protective immunity to C. neoformans. Survival and fungal burden were evaluated in wild-type and STAT1 knockout (KO) mice infected with either strain H99γ or C. neoformans strain 52D (unmodified clinical isolate). Both strains H99γ and 52D were rapidly cleared from the lungs, did not disseminate to the CNS, or cause mortality in the wild-type mice. Conversely, STAT1 KO mice infected with H99γ or 52D had significantly increased pulmonary fungal burden, CNS dissemination, and 90-100% mortality. STAT1 deletion resulted in a shift from Th1 to Th2 cytokine bias, pronounced lung inflammation, and defective classical macrophage activation. Pulmonary macrophages from STAT1 KO mice exhibited defects in NO production correlating with inefficient inhibition of fungal proliferation. These studies demonstrate that STAT1 signaling is essential not only for regulation of immune polarization but also for the classical activation of macrophages that occurs during protective anticryptococcal immune responses.

Human secreted stabilin-1-interacting chitinase-like protein aggravates the inflammation associated with rheumatoid arthritis and is a potential macrophage inflammatory regulator in rodents

OBJECTIVE

To study the relationship between the human secreted protein stabilin-1-interacting chitinase-like protein (SI-CLP) and rheumatoid arthritis (RA).

METHODS

The expression of SI-CLP in peripheral blood mononuclear cells (PBMCs) and synovial fluid from patients with RA and the effects of cytokines on SI-CLP expression were examined by Western blotting. Fluorescence-activated cell sorting analysis was performed to investigate the binding between SI-CLP and cells. Bone marrow-derived macrophages were isolated from wild-type and SI-CLP(-/-) mice, and real-time quantitative polymerase chain reaction was performed to detect the levels of messenger RNA for cytokines or SI-CLP in SI-CLP- or cytokine-treated macrophages. Histologic studies were conducted to evaluate inflammation and the expression of interleukin-12 (IL-12), IL-13, and SI-CLP in lesions. Enzyme-linked immunosorbent assays were used to detect the cytokine levels in bone marrow-derived macrophages. Rats or mice with collagen-induced arthritis (CIA) and SI-CLP(-/-) mice were used to study the function of SI-CLP in RA.

RESULTS

SI-CLP expression was increased in PBMCs and detectable in synovial fluid from patients with RA. Administration of SI-CLP to rats with CIA aggravated arthritis-associated inflammation. SI-CLP was specifically attached to the surface protein of macrophages, which elevated the expression of IL-1β, IL-6, IL-12, and IL-13 in macrophages and mouse bone marrow-derived macrophages, up-regulating ERK phosphorylation. Moreover, SI-CLP was up-regulated by both IL-12 and IL-13 through JNK and JAK/STAT signaling, respectively. Knockout of SI-CLP resulted in a decrease in the expression of IL-1β, IL-6, IL-12, and IL-13 and lower susceptibility to CIA compared with wild-type mice. SI-CLP treatment also aggravated arthritis-related inflammation in wild-type and SI-CLP(-/-) mice.

CONCLUSION

SI-CLP functions as a regulator of the inflammatory response by macrophages. The decrease in inflammation-associated cytokine levels resulting from SI-CLP knockout may explain the lower susceptibility to CIA in SI-CLP(-/-) mice.

IL-4 receptor-alpha-dependent control of Cryptococcus neoformans in the early phase of pulmonary infection

Cryptococcus neoformans is an opportunistic fungal pathogen that causes lung inflammation and meningoencephalitis in immunocompromised people. Previously we showed that mice succumb to intranasal infection by induction of pulmonary interleukin (IL)-4Rα-dependent type 2 immune responses, whereas IL-12-dependent type 1 responses confer resistance. In the experiments presented here, IL-4Rα⁻/⁻ mice unexpectedly show decreased fungal control early upon infection with C. neoformans, whereas wild-type mice are able to control fungal growth accompanied by enhanced macrophage and dendritic cell recruitment to the site of infection. Lower pulmonary recruitment of macrophages and dendritic cells in IL-4Rα⁻/⁻ mice is associated with reduced pulmonary expression of CCL2 and CCL20 chemokines. Moreover, IFN-γ and nitric oxide production are diminished in IL-4Rα⁻/⁻ mice compared to wild-type mice. To directly study the potential mechanism(s) responsible for reduced production of IFN-γ, conventional dendritic cells were stimulated with C. neoformans in the presence of IL-4 which results in increased IL-12 production and reduced IL-10 production. Together, a beneficial role of early IL-4Rα signaling is demonstrated in pulmonary cryptococcosis, which contrasts with the well-known IL-4Rα-mediated detrimental effects in the late phase.

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.

A novel subset of helper T cells promotes immune responses by secreting GM-CSF

Helper T cells are crucial for maintaining proper immune responses. Yet, they have an undefined relationship with one of the most potent immune stimulatory cytokines, granulocyte macrophage-colony-stimulating factor (GM-CSF). By depleting major cytokines during the differentiation of CD4(+) T cells in vitro, we derived cells that were found to produce large amounts of GM-CSF, but little of the cytokines produced by other helper T subsets. By their secretion of GM-CSF, this novel subset of helper T cells (which we have termed ThGM cells) promoted the production of cytokines by other T-cell subtypes, including type 1 helper T cell (Th1), type 2 helper T cell (Th2), type 1 cytotoxic T cell (Tc1), type 2 cytotoxic T cell (Tc2), and naive T cells, as evidenced by the fact that antibody neutralization of GM-CSF abolished this effect. ThGM cells were found to be highly prone to activation-induced cell death (AICD). Inhibitors of TRAIL or granzymes could not block AICD in ThGM cells, whereas inhibition of FasL/Fas interaction partially rescued ThGM cells from AICD. Thus, ThGM cells are a novel subpopulation of T helper cells that produce abundant GM-CSF, exhibit exquisite susceptibility to apoptosis, and therefore play a pivotal role in the regulation of the early stages of immune responses.

Abrogation of IL-4 receptor-α-dependent alternatively activated macrophages is sufficient to confer resistance against pulmonary cryptococcosis despite an ongoing T(h)2 response

In the murine model of pulmonary infection with Cryptococcus neoformans, IL-4 receptor α (IL-4Rα)-dependent polyfunctional T(h)2 cells induce disease progression associated with alternative activation of lung macrophages. To characterize the effector role of IL-4Rα-dependent alternatively activated macrophages (aaMph), we intra-nasally infected mice with genetically ablated IL-4Rα expression on macrophages (LysM(Cre)IL-4Rα(-/lox) mice) and IL-4Rα(-/lox) littermates. LysM(Cre)IL-4Rα(-/lox) mice were significantly more resistant to pulmonary cryptococcosis with higher survival rates and lower lung burden than non-deficient heterozygous littermates. Infected LysM(Cre)IL-4Rα(-/lox) mice had reduced but detectable numbers of aaMph expressing arginase-1, chitinase-like enzyme (YM1) and CD206. Similar pulmonary expression of inducible nitric oxide synthase was found in LysM(Cre)IL-4Rα(-/lox) and IL-4Rα(-/lox) control mice, but macrophages from LysM(Cre)IL-4Rα(-/lox) mice showed a higher potential to produce nitric oxide. In contrast to the differences in the macrophage phenotype, pulmonary T(h)2 responses were similar in infected LysM(Cre)IL-4Rα(-/lox) and IL-4Rα(-/lox) mice with each mouse strain harboring polyfunctional T(h)2 cells. Consistently, type 2 pulmonary allergic inflammation associated with eosinophil recruitment and epithelial mucus production was present in lungs of both LysM(Cre)IL-4Rα(-/lox) and IL-4Rα(-/lox) mice. Our results demonstrate that, despite residual IL-4Rα-independent alternative macrophage activation and ongoing T(h)2-dependent allergic inflammation, abrogation of IL-4Rα-dependent aaMph is sufficient to confer resistance in pulmonary cryptococcosis. This is even evident on a relatively resistant heterozygous IL-4Rα(+/-) background indicating a key contribution of macrophage IL-4Rα expression to susceptibility in allergic bronchopulmonary mycosis.

Cryptococcus neoformans growth and protection from innate immunity are dependent on expression of a virulence-associated DEAD-box protein, Vad1

The fungus Cryptococcus neoformans has emerged as a major cause of meningoencephalitis worldwide. Host response to the fungus involves both innate and adaptive immunity, but fungal genes that modulate these processes are poorly understood. Previous studies demonstrated attenuated virulence of a mutant of a virulence-associated DEAD-box protein (VAD1) in mice, despite normal growth at host temperatures, suggesting modulation of the immune response. In the present study, the Δvad1 mutant demonstrated progressive clearance from lung and was unable to induce pathological lesions or to cause extrapulmonary disease, despite retaining its ability to grow in mouse serum and a J774.16 macrophage cell line. Pulmonary clearance occurred with a minimal cellular infiltrate, marked by reduced CD4 cells, CD11b(+) Ly6C(high) monocytes, and F4/80(+) macrophages, but the mutant strain retained recruitment of CD8 cells, compared to infections with wild-type fungi. Adaptive cytokine responses were reduced, including Th1, Th2, and Th17 cytokines; however, early gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α) responses were retained while nonprotective interleukin 4 (IL-4) and IL-5 were diminished. Furthermore, the Δvad1 mutant was controlled in lungs despite CD4/CD8 cell depletion. These data, along with improved phagocytosis by macrophages and increases in early/innate IL-1α, IFN-γ, and chemokines elicited in the lungs within 3 days of infection with the Δvad1 mutant, indicate that VAD1 expression reduces innate recognition of C. neoformans, rendering the yeast resistant to elimination by the innate mechanisms of host defense. Thus, our studies define a novel role of the cryptococcal Vad1 protein as a central regulator of cryptococcal virulence and illustrate that Vad1 promotes microbe resistance to innate host defenses.

Interleukin-4-induced β-catenin regulates the conversion of macrophages to multinucleated giant cells

The cytokine interleukin-4 (IL-4) exerts pleiotropic effects on macrophages as it plays a key role in the immune response to infectious agents, allergens, and vaccines. Macrophages exposed to IL-4 drastically change their gene expression and metabolic state to adjust to new functional requirements. IL-4 also induces macrophages to fuse together and form multinucleated giant cells (MGCs). MGC formation is associated with chronic inflammation resulting from persistence of pathogenic microorganisms or foreign materials in tissues. Very little is known, however, about the mechanisms regulating IL-4-induced macrophage-to-MGC conversion. We observed a dramatic increase in β-catenin protein but not mRNA amount in mouse macrophages following exposure to IL-4. To investigate the role of β-catenin in macrophages, we generated mice with a myeloid cell-specific deletion of the β-catenin gene. Ablation of β-catenin expression did not affect the viability of macrophages or impair expression of known IL-4-inducible genes. Intriguingly, β-catenin-deficient macrophages incubated with IL-4 formed MGCs with markedly greater efficiency than wild-type macrophages. Similar increases in multinucleated cell formation were detected in the peritoneal cavity of myeloid cell-specific β-catenin knockout mice injected with chitin, which is known to induce endogenous IL-4 production. Our findings reveal β-catenin as a novel regulator of macrophage responses to IL-4, and suggest that therapeutic modulation of its expression or function may help enhance the effectiveness or ameliorate the pathology of IL-4-driven immune responses.

Mesenchymal stromal cells of human umbilical cord Wharton's jelly accelerate wound healing by paracrine mechanisms

BACKGROUND AIMS

Mesenchymal stromal cells (MSC) can be isolated from the perivascular connective tissue of umbilical cords, called Wharton's jelly. These human umbilical cord perivascular cells (HUCPVC) might provide therapeutic benefits when treating skeletal or cutaneous malformations in neonatal patients.

METHODS

HUCPVC were isolated, and their proliferation rate, marker expression and multilineage differentiation potential determined. HUCPVC or their conditioned medium (HUCPVC-CM) was injected into the excisional wound of a mouse splinted-wound model. The effects of the treatment on wound closure were examined by morphohistochemical and gene expression analyses.

RESULTS

HUCPVC expressed typical MSC markers and could differentiate into osteoblastic and adipogenic lineages. HUCPVC transplanted into the mouse wound accelerated wound closure. Immunohistologic analysis showed that the HUCPVC accelerated wound healing by enhancing collagen deposition and angiogenesis via paracrine mechanisms. Furthermore, treatment with HUCPVC-CM alone significantly enhanced wound closure. HUCPVC-CM increased the number of anti-inflammatory M2 macrophages expressing resistin-like molecule (RELM)-α/CD11b and promoted neovessel maturation. Quantitative polymerase chain reaction (PCR) analysis showed that HUCPVC-CM increased the expression of tissue-repairing cytokines interleukin (IL)-10, transforming growth factor (TGF)-β1, vascular endothelial growth factor (VEGF)-1 and angiopoietin-1 at the healing wound.

CONCLUSIONS

Our results show that HUCPVC promotes wound healing via multifaceted paracrine mechanisms. Together with their ability to differentiate into the osteogenic linage, HUCPVC may provide significant therapeutic benefits for treating wounds in neonatal patients.

Macrophage dectin-1 expression is controlled by leukotriene B4 via a GM-CSF/PU.1 axis

Pattern recognition receptors for fungi include dectin-1 and mannose receptor, and these mediate phagocytosis, as well as production of cytokines, reactive oxygen species, and the lipid mediator leukotriene B(4) (LTB(4)). The influence of G protein-coupled receptor ligands such as LTB(4) on fungal pattern recognition receptor expression is unknown. In this study, we investigated the role of LTB(4) signaling in dectin-1 expression and responsiveness in macrophages. Genetic and pharmacologic approaches showed that LTB(4) production and signaling through its high-affinity G protein-coupled receptor leukotriene B(4) receptor 1 (BLT1) direct dectin-1-dependent binding, ingestion, and cytokine production both in vitro and in vivo. Impaired responses to fungal glucans correlated with lower dectin-1 expression in macrophages from leukotriene (LT)- and BLT1-deficent mice than their wild-type counterparts. LTB(4) increased the expression of the transcription factor responsible for dectin-1 expression, PU.1, and PU.1 small interfering RNA abolished LTB(4)-enhanced dectin-1 expression. GM-CSF controls PU.1 expression, and this cytokine was decreased in LT-deficient macrophages. Addition of GM-CSF to LT-deficient cells restored expression of dectin-1 and PU.1, as well as dectin-1 responsiveness. In addition, LTB(4) effects on dectin-1, PU.1, and cytokine production were blunted in GM-CSF(-/-) macrophages. Our results identify LTB(4)-BLT1 signaling as an unrecognized controller of dectin-1 transcription via GM-CSF and PU.1 that is required for fungi-protective host responses.

TLR4-dependent GM-CSF protects against lung injury in Gram-negative bacterial pneumonia

Toll-like receptors (TLRs) are required for protective host defense against bacterial pathogens. However, the role of TLRs in regulating lung injury during Gram-negative bacterial pneumonia has not been thoroughly investigated. In this study, experiments were performed to evaluate the role of TLR4 in pulmonary responses against Klebsiella pneumoniae (Kp). Compared with wild-type (WT) (Balb/c) mice, mice with defective TLR4 signaling (TLR4(lps-d) mice) had substantially higher lung bacterial colony-forming units after intratracheal challenge with Kp, which was associated with considerably greater lung permeability and lung cell death. Reduced expression of granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA and protein was noted in lungs and bronchoalveolar lavage fluid of TLR4 mutant mice postintratracheal Kp compared with WT mice, and primary alveolar epithelial cells (AEC) harvested from TLR4(lps-d) mice produced significantly less GM-CSF in vitro in response to heat-killed Kp compared with WT AEC. TLR4(lps-d) AEC underwent significantly more apoptosis in response to heat-killed Kp in vitro, and treatment with GM-CSF protected these cells from apoptosis in response to Kp. Finally, intratracheal administration of GM-CSF in TLR4(lps-d) mice significantly decreased albumin leak, lung cell apoptosis, and bacteremia in Kp-infected mice. Based on these observations, we conclude that TLR4 plays a protective role on lung epithelium during Gram-negative bacterial pneumonia, an effect that is partially mediated by GM-CSF.

Induction of protective immunity against cryptococcosis

Cryptococcus neoformans, the predominant etiological agent of cryptococcosis, is an encapsulated fungal pathogen that can cause life-threatening infections of the central nervous system in immune compromised individuals resulting in high morbidity and mortality. Consequently, several studies have endeavored to understand those mechanisms that mediate resistance and susceptibility to Cryptococcus infection. In this review, we will examine the contributions of various components of the innate and adaptive immune response toward protection against cryptococcosis. We will focus our discussion on studies presented at the 8th International Conference on Cryptococcus and Cryptococcosis (ICCC). Remarkable progress has been made toward our understanding of host immunity and susceptibility to cryptococcal infection and the potential for vaccine development.

Cryptococcus-Related Immune Reconstitution Inflammatory Syndrome(IRIS): Pathogenesis and Its Clinical Implications

This review provides an overview of Cryptococcus neoformans immunology and focuses on the pathogenesis of Cryptococcus-related paradoxical immune reconstitution inflammatory syndrome (IRIS). Cryptococcal IRIS has three phases: (1) before antiretroviral therapy (ART), with a paucity of cerebrospinal fluid (CSF) inflammation and defects in antigen clearance; (2) during initial ART immune recovery, with pro-inflammatory signaling by antigen-presenting cells without an effector response; and (3) at IRIS, a cytokine storm with a predominant type-1 helper T-cell (Th(1)) interferon-gamma (IFN-γ) response. Understanding IRIS pathogenesis allows for risk stratification and customization of HIV/AIDS care. In brief, persons at high IRIS risk may benefit from enhancing microbiologic clearance by use of adjunctive agents in combination with amphotericin, prolonging initial induction therapy, and/or increasing the initial consolidation antifungal therapy dose to at least 800 mg of fluconazole daily until the 2-week CSF culture is known to be sterile. Prophylactic anti-inflammatory therapies or undue delay of ART initiation in an attempt to prevent IRIS is unwarranted and may be dangerous.

Effect of cytokine interplay on macrophage polarization during chronic pulmonary infection with Cryptococcus neoformans

The immune response to Cryptococcus neoformans following pulmonary infection of C57BL/6 wild-type (WT) mice results in the development of persistent infection with characteristics of allergic bronchopulmonary mycosis (ABPM). To further clarify the role of Th1/Th2 polarizing cytokines in this model, we performed kinetic analysis of cytokine responses and compared cytokine profiles, pathologies, and macrophage (Mac) polarization status in C. neoformans-infected WT, interleukin-4-deficient (IL-4(-/-)), and gamma interferon-deficient (IFN-γ(-/-)) C57BL/6 mice. Results show that cytokine expression in the infected WT mice is not permanently Th2 biased but changes dynamically over time. Using multiple Mac activation markers, we further demonstrate that IL-4 and IFN-γ regulate the polarization state of Macs in this model. A higher IL-4/IFN-γ ratio leads to the development of alternatively activated Macs (aaMacs), whereas a higher IFN-γ/IL-4 ratio leads to the generation of classically activated Macs (caMacs). WT mice that coexpress IL-4 and IFN-γ during fungal infection concurrently display both types of Mac polarization markers. Concurrent stimulation of Macs with IFN-γ and IL-4 results in an upregulation of both sets of markers within the same cells, i.e., formation of an intermediate aaMac/caMac phenotype. These cells express both inducible nitric oxide synthase (important for clearance) and arginase (associated with chronic/progressive infection). Together, our data demonstrate that the interplay between Th1 and Th2 cytokines supports chronic infection, chronic inflammation, and the development of ABPM pathology in C. neoformans-infected lungs. This cytokine interplay modulates Mac differentiation, including generation of an intermediate caMac/aaMac phenotype, which in turn may support chronic "steady-state" fungal infection and the resultant ABPM pathology.

Human gingiva-derived mesenchymal stem cells elicit polarization of m2 macrophages and enhance cutaneous wound healing

Increasing evidence has supported the important role of mesenchymal stem cells (MSCs) in wound healing, however, the underlying mechanism remains unclear. Recently, we have isolated a unique population of MSCs from human gingiva (GMSCs) with similar stem cell-like properties, immunosuppressive, and anti-inflammatory functions as human bone marrow-derived MSCs (BMSCs). We describe here the interplay between GMSCs and macrophages and the potential relevance in skin wound healing. When cocultured with GMSCs, macrophages acquired an anti-inflammatory M2 phenotype characterized by an increased expression of mannose receptor (MR; CD206) and secretory cytokines interleukin (IL)-10 and IL-6, a suppressed production of tumor necrosis factor (TNF)-α, and decreased ability to induce Th-17 cell expansion. In vivo, we demonstrated that systemically infused GMSCs could home to the wound site in a tight spatial interaction with host macrophages, promoted them toward M2 polarization, and significantly enhanced wound repair. Mechanistically, GMSC treatment mitigated local inflammation mediated by a suppressed infiltration of inflammatory cells and production of IL-6 and TNF-α, and an increased expression of IL-10. The GMSC-induced suppression of TNF-α secretion by macrophages appears to correlate with impaired activation of NFκB p50. These findings provide first evidence that GMSCs are capable to elicit M2 polarization of macrophages, which might contribute to a marked acceleration of wound healing.

Clinical features and serum biomarkers in HIV immune reconstitution inflammatory syndrome after cryptococcal meningitis: a prospective cohort study

BACKGROUND

Although antiretroviral therapy (ART) improves survival in persons with cryptococcal meningitis (CM) and AIDS, ART frequently elicits HIV immune reconstitution inflammatory syndrome (IRIS), an exaggerated and frequently deadly inflammatory reaction that complicates recovery from immunodeficiency. The pathogenesis of IRIS is poorly understood and prediction of IRIS is not possible.

METHODS AND FINDINGS

We prospectively followed 101 ART-naïve Ugandans with AIDS and recent CM for one year after initiating ART, and used Luminex multiplex assays to compare serum cytokine levels in participants who did or did not develop IRIS. IRIS occurred in 45% of participants with recent CM on ART, including 30% with central nervous system (CNS) manifestations. The median time to CM-IRIS was 8.8 wk on ART. Overall mortality on ART was 36% with IRIS and 21% without IRIS. CM-IRIS was independently associated with death (HR = 2.3, 95% CI 1.1-5.1, p = 0.04). Patients experiencing subsequent CM-IRIS had 4-fold higher median serum cryptococcal antigen (CRAG) levels pre-ART (p = 0.006). Higher pre-ART levels of interleukin (IL)-4 and IL-17 as well as lower tumor necrosis factor (TNF)-α, granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), and vascular endothelial growth factor (VEGF) predicted future IRIS in multivariate analyses (area under the curve [AUC] = 0.82). An algorithm based on seven pre-ART serum biomarkers was a robust tool for stratifying high (83%), moderate (48%), and low risk (23%) for IRIS in the cohort. After ART was initiated, increasing levels of C-reactive protein (CRP), D-dimer, IL-6, IL-7, IL-13, G-CSF, or IL-1RA were associated with increasing hazard of IRIS by time-to-event analysis (each p≤0.001). At the time of IRIS onset, multiple proinflammatory cytokine responses were present, including CRP and IL-6. Mortality was predicted by pre-ART increasing IL-17, decreasing GM-CSF, and CRP level >32 mg/l (highest quartile). Pre-ART CRP level >32 mg/l alone was associated with future death (OR = 8.3, 95% CI 2.7-25.6, p<0.001).

CONCLUSIONS

Pre-ART increases in Th(17) and Th(2) responses (e.g., IL-17, IL-4) and lack of proinflammatory cytokine responses (e.g., TNF-α, G-CSF, GM-CSF, VEGF) predispose individuals to subsequent IRIS, perhaps as biomarkers of immune dysfunction and poor initial clearance of CRAG. Although requiring validation, these biomarkers might be an objective tool to stratify the risk of CM-IRIS and death, and could be used clinically to guide when to start ART or use prophylactic interventions.

Rat eosinophils stimulate the expansion of Cryptococcus neoformans-specific CD4(+) and CD8(+) T cells with a T-helper 1 profile

Experimental Cryptococcus neoformans infection in rats has been shown to have similarities with human cryptococcosis, revealing a strong granulomatous response and a low susceptibility to dissemination. Moreover, it has been shown that eosinophils are components of the inflammatory response to C. neoformans infections. In this in vitro study, we demonstrated that rat peritoneal eosinophils phagocytose opsonized live yeasts of C. neoformans, and that the phenomenon involves the engagement of FcγRII and CD18. Moreover, our results showed that the phagocytosis of opsonized C. neoformans triggers eosinophil activation, as indicated by (i) the up-regulation of major histocompatibility complex (MHC) class I, MHC class II and costimulatory molecules, and (ii) an increase in interleukin (IL)-12, tumour necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) production. However, nitric oxide (NO) and hydrogen peroxide (H(2) O(2) ) synthesis by eosinophils was down-regulated after interaction with C. neoformans. Furthermore, this work demonstrated that CD4(+) and CD8(+) T lymphocytes isolated from spleens of infected rats and cultured with C. neoformans-pulsed eosinophils proliferate in an MHC class II- and class I-dependent manner, respectively, and produce important amounts of T-helper 1 (Th1) type cytokines, such as TNF-α and IFN-γ, in the absence of T-helper 2 (Th2) cytokine synthesis. In summary, the present study demonstrates that eosinophils act as fungal antigen-presenting cells and suggests that C. neoformans-loaded eosinophils might participate in the adaptive immune response.