Type I IFN Induction via Poly-ICLC Protects Mice against Cryptococcosis

Lung-resident memory Th2 cells regulate pulmonary cryptococcosis by inducing type-II granuloma formation

Lung-resident memory T cells (lung TRMs) settle in the lung and respond rapidly to external antigens, and are therefore considered to have great potential for development of respiratory vaccines. Here, we demonstrate that lung-resident memory Th2 cells (lung TRM2) protect against pulmonary mycosis caused by Cryptococcus gattii. We developed novel whole-cell intranasal vaccines using a heat-inactivated C.gattii capsule-deficient strain cap59Δ, which induced ST-2+ Gata-3+ lung TRM2 specifically responding to C.gattii whole-cell antigen. Lung fungal burden and survival rate were significantly improved in immunized mice after infection challenge. The immunosuppressive agent FTY720 did not impact vaccine effectiveness, and adoptive transfer of lung TRMs into Rag-1-deficient mice decreased the lung fungal burden. In IL-4/IL-13 double-knockout (DKO) mice, immunization did not efficiently induce eosinophil recruitment and granuloma formation, and the fungal burden was not decreased after infection challenge. Co-culture of lung TRM2 with myeloid lineages induced multinucleated giant cells (MGCs) in the presence of antigen, which phagocytosed live C.gattii cells without opsonization, whereas lung TRM2 from DKO mice did not induce MGCs. These findings provide a new model in which lung TRM2 suppress C.gattii infection via granuloma induction.

A rare case report of concurrent cryptococcal, streptococcal, and tuberculous meningitis in a patient with pulmonary tuberculosis

RATIONALE

Meningitis caused by concurrent infections with Cryptococcus neoformans, Streptococcus equi subsp. equi, and Mycobacterium tuberculosis is extremely rare.

PATIENT CONCERNS

We present the case of a 63-year-old male patient who presented with headaches, dizziness, nausea, vomiting, and fever for the past 3 weeks.

DIAGNOSES

The patient was diagnosed with concurrent cryptococcal, streptococcal, and tuberculous meningitis.

INTERVENTIONS

The patient received isoniazid, rifampicin, ethambutol, and levofloxacin for 1 month, in addition to liposomal amphotericin B with flucytosine for 2 weeks, followed by fluconazole with flucytosine for additional 2 weeks.

OUTCOMES

The symptoms improved, and outpatient therapy was continued.

LESSONS

Infectious meningitis requires a combination of microscopy, culture, and rapid molecular diagnostics for early diagnosis and treatment.

Inbred Mouse Models in Cryptococcus neoformans Research

Animal models are frequently used as surrogates to understand human disease. In the fungal pathogen Cryptococcus species complex, several variations of a mouse model of disease were developed that recapitulate different aspects of human disease. These mouse models have been implemented using various inbred and outbred mouse backgrounds, many of which have genetic differences that can influence host response and disease outcome. In this review, we will discuss the most commonly used inbred mouse backgrounds in C. neoformans infection models.

Sex-specific circulating unconventional neutrophils determine immunological outcome of auto-inflammatory Behçet's uveitis

Neutrophils are the most abundant immune cells that first respond to insults in circulation. Although associative evidence suggests that differences in neutrophils may be linked to the sex-specific vulnerability of inflammatory diseases, mechanistic links remain elusive. Here, we identified extensive sex-specific heterogeneity in neutrophil composition under normal and auto-inflammatory conditions at single-cell resolution. Using a combination of single-cell RNA sequencing analysis, neutrophil-specific genetic knockouts and transfer experiments, we discovered dysregulation of two unconventional (interferon-α responsive and T cell regulatory) neutrophil subsets leading to male-biased incidence, severity and poor prognosis of auto-inflammatory Behçet's uveitis. Genome-wide association study (GWAS) and exosome study revealed that male-specific negative effects of both genetic factors and circulating exosomes on unconventional neutrophil subsets contributed to male-specific vulnerability to disease. Collectively, our findings identify sex-specifically distinct neutrophil subsets and highlight unconventional neutrophil subsets as sex-specific therapeutic targets to limit inflammatory diseases.

Chronic infection control relies on T cells with lower foreign antigen binding strength generated by N-nucleotide diversity

The breadth of pathogens to which T cells can respond is determined by the T cell receptors (TCRs) present in an individual's repertoire. Although more than 90% of the sequence diversity among TCRs is generated by terminal deoxynucleotidyl transferase (TdT)-mediated N-nucleotide addition during V(D)J recombination, the benefit of TdT-altered TCRs remains unclear. Here, we computationally and experimentally investigated whether TCRs with higher N-nucleotide diversity via TdT make distinct contributions to acute or chronic pathogen control specifically through the inclusion of TCRs with lower antigen binding strengths (i.e., lower reactivity to peptide-major histocompatibility complex (pMHC)). When T cells with high pMHC reactivity have a greater propensity to become functionally exhausted than those of low pMHC reactivity, our computational model predicts a shift toward T cells with low pMHC reactivity over time during chronic, but not acute, infections. This TCR-affinity shift is critical, as the elimination of T cells with lower pMHC reactivity in silico substantially increased the time to clear a chronic infection, while acute infection control remained largely unchanged. Corroborating an affinity-centric benefit for TCR diversification via TdT, we found evidence that TdT-deficient TCR repertoires possess fewer T cells with weaker pMHC binding strengths in vivo and showed that TdT-deficient mice infected with a chronic, but not an acute, viral pathogen led to protracted viral clearance. In contrast, in the case of a chronic fungal pathogen where T cells fail to clear the infection, both our computational model and experimental data showed that TdT-diversified TCR repertoires conferred no additional protection to the hosts. Taken together, our in silico and in vivo data suggest that TdT-mediated TCR diversity is of particular benefit for the eventual resolution of prolonged pathogen replication through the inclusion of TCRs with lower foreign antigen binding strengths.

Inbred SJL mice recapitulate human resistance to Cryptococcus infection due to differential immune activation

IMPORTANCE

Cryptococcosis studies often utilize the common C57BL/6J mouse model. Unfortunately, infection in these mice fails to replicate the basic course of human disease, particularly hampering immunological studies. This work demonstrates that SJL/J mice can recapitulate human infection better than other mouse strains. The immunological response to Cryptococcus infection in SJL/J mice was markedly different from C57BL/6J and much more productive in combating this infection. Characterization of infected mice demonstrated strain-specific genetic linkage and differential regulation of multiple important immune-relevant genes in response to Cryptococcus infection. While our results validate many of the previously identified immunological features of cryptococcosis, we also demonstrate limitations from previous mouse models as they may be less translatable to human disease. We concluded that SJL/J mice more faithfully recapitulate human cryptococcosis serving as an exciting new animal model for immunological and genetic studies.

Cryptococcal Immune Reconstitution Inflammatory Syndrome: From Clinical Studies to Animal Experiments

Cryptococcus neoformans is an encapsulated pathogenic fungus that initially infects the lung but can migrate to the central nervous system (CNS), resulting in meningoencephalitis. The organism causes the CNS infection primarily in immunocompromised individuals including HIV/AIDS patients, but also, rarely, in immunocompetent individuals. In HIV/AIDS patients, limited inflammation in the CNS, due to impaired cellular immunity, cannot efficiently clear a C. neoformans infection. Antiretroviral therapy (ART) can rapidly restore cellular immunity in HIV/AIDS patients. Paradoxically, ART induces an exaggerated inflammatory response, termed immune reconstitution inflammatory syndrome (IRIS), in some HIV/AIDS patients co-infected with C. neoformans. A similar excessive inflammation, referred to as post-infectious inflammatory response syndrome (PIIRS), is also frequently seen in previously healthy individuals suffering from cryptococcal meningoencephalitis. Cryptococcal IRIS and PIIRS are life-threatening complications that kill up to one-third of affected people. In this review, we summarize the inflammatory responses in the CNS during HIV-associated cryptococcal meningoencephalitis. We overview the current understanding of cryptococcal IRIS developed in HIV/AIDS patients and cryptococcal PIIRS occurring in HIV-uninfected individuals. We also describe currently available animal models that closely mimic aspects of cryptococcal IRIS observed in HIV/AIDS patients.

Cryptococcus neoformans Infection in the Central Nervous System: The Battle between Host and Pathogen

Cryptococcus neoformans (C. neoformans) is a pathogenic fungus with a global distribution. Humans become infected by inhaling the fungus from the environment, and the fungus initially colonizes the lungs. If the immune system fails to contain C. neoformans in the lungs, the fungus can disseminate to the blood and invade the central nervous system, resulting in fatal meningoencephalitis particularly in immunocompromised individuals including HIV/AIDS patients. Following brain invasion, C. neoformans will encounter host defenses involving resident as well as recruited immune cells in the brain. To overcome host defenses, C. neoformans possesses multiple virulence factors capable of modulating immune responses. The outcome of the interactions between the host and C. neoformans will determine the disease progression. In this review, we describe the current understanding of how C. neoformans migrates to the brain across the blood–brain barrier, and how the host immune system responds to the invading organism in the brain. We will also discuss the virulence factors that C. neoformans uses to modulate host immune responses.

MDA5 signaling induces type 1 IFN- and IL-1-dependent lung vascular permeability which protects mice from opportunistic fungal infection

Lungs balance threat from primary viral infection, secondary infection, and inflammatory damage. Severe pulmonary inflammation induces vascular permeability, edema, and organ dysfunction. We previously demonstrated that poly(I:C) (pICLC) induced type 1 interferon (t1IFN) protected mice from Cryptococcus gattii (Cg) via local iron restriction. Here we show pICLC increased serum protein and intravenously injected FITC-dextran in the lung airspace suggesting pICLC induces vascular permeability. Interestingly, pICLC induced a pro-inflammatory signature with significant expression of IL-1 and IL-6 which depended on MDA5 and t1IFN. Vascular permeability depended on MDA5, t1IFN, IL-1, and IL-6. T1IFN also induced MDA5 and other MDA5 signaling components suggesting that positive feedback contributes to t1IFN dependent expression of the pro-inflammatory signature. Vascular permeability, induced by pICLC or another compound, inhibited Cg by limiting iron. These data suggest that pICLC induces t1IFN which potentiates pICLC-MDA5 signaling increasing IL-1 and IL-6 resulting in leakage of antimicrobial serum factors into lung airspace. Thus, induced vascular permeability may act as an innate defense mechanism against opportunistic fungal infection, such as cryptococcosis, and may be exploited as a host-directed therapeutic target.

Migration-induced cell shattering due to DOCK8 deficiency causes a type 2-biased helper T cell response

Mutations that impact immune cell migration and result in immune deficiency illustrate the importance of cell movement in host defense. In humans, loss-of-function mutations in DOCK8, a guanine exchange factor involved in hematopoietic cell migration, lead to immunodeficiency and, paradoxically, allergic disease. Here, we demonstrate that, like humans, Dock8-/- mice have a profound type 2 CD4+ helper T (TH2) cell bias upon pulmonary infection with Cryptococcus neoformans and other non-TH2 stimuli. We found that recruited Dock8-/-CX3CR1+ mononuclear phagocytes are exquisitely sensitive to migration-induced cell shattering, releasing interleukin (IL)-1β that drives granulocyte-macrophage colony-stimulating factor (GM-CSF) production by CD4+ T cells. Blocking IL-1β, GM-CSF or caspase activation eliminated the type-2 skew in mice lacking Dock8. Notably, treatment of infected wild-type mice with apoptotic cells significantly increased GM-CSF production and TH2 cell differentiation. This reveals an important role for cell death in driving type 2 signals during infection, which may have implications for understanding the etiology of type 2 CD4+ T cell responses in allergic disease.

It's all in your head: antifungal immunity in the brain

As the incidence rate of invasive fungal infections has increased with the use of modern medical interventions, so too has the occurrence of fungi invading the brain. Fungi such as Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus often infect immunocompromised individuals, and can use several strategies to invade the central nervous system (CNS) by penetrating the blood-brain barrier. Once in the brain parenchyma the specialized resident immune cells need to effectively recognize the fungus and mount an appropriate immune response to clear the infection, without causing debilitating immune-mediated toxicity and neuronal damage. Here we review the current knowledge pertaining to the antifungal response of the CNS and highlight areas where future research is required.

MDA5 Is an Essential Sensor of a Pathogen-Associated Molecular Pattern Associated with Vitality That Is Necessary for Host Resistance against Aspergillus fumigatus

RIG-I-like receptors (RLR) are cytosolic RNA sensors that signal through the MAVS adaptor to activate IFN responses against viruses. Whether the RLR family has broader effects on host immunity against other pathogen families remains to be fully explored. In this study, we demonstrate that MDA5/MAVS signaling was essential for host resistance against pulmonary Aspergillus fumigatus challenge through the regulation of antifungal leukocyte responses in mice. Activation of MDA5/MAVS signaling was driven by dsRNA from live A. fumigatus serving as a key vitality-sensing pattern recognition receptor. Interestingly, induction of type I IFNs after A. fumigatus challenge was only partially dependent on MDA5/MAVS signaling, whereas type III IFN expression was entirely dependent on MDA5/MAVS signaling. Ultimately, type I and III IFN signaling drove the expression of CXCL10. Furthermore, the MDA5/MAVS-dependent IFN response was critical for the induction of optimal antifungal neutrophil killing of A. fumigatus spores. In conclusion, our data broaden the role of the RLR family to include a role in regulating antifungal immunity against A. fumigatus.

What came first, the virus or the egg: Innate immunity during viral coinfections

Infections with any pathogen can be severe and present with numerous complications caused by the pathogen or the host immune response to the invading microbe. However, coinfections, also called polymicrobial infections or secondary infections, can further exacerbate disease. Coinfections are more common than is often appreciated. In this review, we focus specifically on coinfections between viruses and other viruses, bacteria, parasites, or fungi. Importantly, innate immune signaling and innate immune cells that facilitate clearance of the initial viral infection can affect host susceptibility to coinfections. Understanding these immune imbalances may facilitate better diagnosis, prevention, and treatment of such coinfections.

Type I Interferons Ameliorate Zinc Intoxication of Candida glabrata by Macrophages and Promote Fungal Immune Evasion

Host and fungal pathogens compete for metal ion acquisition during infectious processes, but molecular mechanisms remain largely unknown. Here, we show that type I interferons (IFNs-I) dysregulate zinc homeostasis in macrophages, which employ metallothionein-mediated zinc intoxication of pathogens as fungicidal response. However, Candida glabrata can escape immune surveillance by sequestering zinc into vacuoles. Interestingly, zinc-loading is inhibited by IFNs-I, because a Janus kinase 1 (JAK1)-dependent suppression of zinc homeostasis affects zinc distribution in macrophages as well as generation of reactive oxygen species (ROS). In addition, systemic fungal infections elicit IFN-I responses that suppress splenic zinc homeostasis, thereby altering macrophage zinc pools that otherwise exert fungicidal actions. Thus, IFN-I signaling inadvertently increases fungal fitness both in vitro and in vivo during fungal infections. Our data reveal an as yet unrecognized role for zinc intoxication in antifungal immunity and suggest that interfering with host zinc homeostasis may offer therapeutic options to treat invasive fungal infections.

Pathogen and host genetics underpinning cryptococcal disease

Cryptococcosis is a severe fungal disease causing 220,000 cases of cryptococcal meningitis yearly. The etiological agents of cryptococcosis are taxonomically grouped into at least two species complexes belonging to the genus Cryptococcus. All of these yeasts are environmentally ubiquitous fungi (often found in soil, leaves and decaying wood, tree hollows, and associated with bird feces especially pigeon guano). Infection in a range of animals including humans begins following inhalation of spores or aerosolized yeasts. Recent advances provide fundamental insights into the factors from both the pathogen and its hosts which influence pathogenesis and disease. The complex interactions leading to disease in mammalian hosts have also updated from the availability of better genomic tools and datasets. In this review, we discuss recent genetic research on Cryptococcus, covering the epidemiology, ecology, and evolution of Cryptococcus pathogenic species. We also discuss the insights into the host immune response obtained from the latest genetic modified host models as well as insights from monogenic disorders in humans. Finally we highlight outstanding questions that can be answered in the near future using bioinformatics and genomic tools.

Viral infection triggers interferon-induced expulsion of live Cryptococcus neoformans by macrophages

Cryptococcus neoformans is an opportunistic human pathogen, which causes serious disease in immunocompromised hosts. Infection with this pathogen is particularly relevant in HIV+ patients, where it leads to around 200,000 deaths per annum. A key feature of cryptococcal pathogenesis is the ability of the fungus to survive and replicate within the phagosome of macrophages, as well as its ability to be expelled from host cells via a novel non-lytic mechanism known as vomocytosis. Here we show that cryptococcal vomocytosis from macrophages is strongly enhanced by viral coinfection, without altering phagocytosis or intracellular proliferation of the fungus. This effect occurs with distinct, unrelated human viral pathogens and is recapitulated when macrophages are stimulated with the anti-viral cytokines interferon alpha or beta (IFNα or IFNβ). Importantly, the effect is abrogated when type-I interferon signalling is blocked, thus underscoring the importance of type-I interferons in this phenomenon. Lastly, our data help resolve previous, contradictory animal studies on the impact of type I interferons on cryptococcal pathogenesis and suggest that secondary viral stimuli may alter patterns of cryptococcal dissemination in the host.

Pulmonary Iron Limitation Induced by Exogenous Type I IFN Protects Mice from Cryptococcus gattii Independently of T Cells

Cryptococcus neoformans and Cryptococcus gattii cause fatal infection in immunodeficient and immunocompetent individuals. While these fungi are sibling species, C. gattii infects very few AIDS patients, while C. neoformans infection is an AIDS-defining illness, suggesting that the host response to HIV selects C. neoformans over C. gattii. We used a viral mimic molecule (pICLC) to stimulate the immune response, and pICLC treatment improved mouse outcomes from both species. pICLC-induced action against C. neoformans was due to activation of well-defined immune pathways known to deter C. neoformans, whereas these immune pathways were dispensable for pICLC treatment of C. gattii. Since these immune pathways are eventually destroyed by HIV/AIDS, our data help explain why the antiviral immune response in AIDS patients is unable to control C. neoformans infection but is protective against C. gattii. Furthermore, pICLC induced tighter control of iron in the lungs of mice, which inhibited C. gattii, thus suggesting an entirely new mode of nutritional immunity activated by viral signals.

Cryptococcus neoformans causes deadly mycosis primarily in AIDS patients, whereas Cryptococcus gattii infects mostly non-HIV patients, even in regions with high burdens of HIV/AIDS and an established environmental presence of C. gattii. As HIV induces type I IFN (t1IFN), we hypothesized that t1IFN would differentially affect the outcome of C. neoformans and C. gattii infections. Exogenous t1IFN induction using stabilized poly(I·C) (pICLC) improved murine outcomes in either cryptococcal infection. In C. neoformans-infected mice, pICLC activity was associated with C. neoformans containment and classical Th1 immunity. In contrast, pICLC activity against C. gattii did not require any immune factors previously associated with C. neoformans immunity: T, B, and NK cells, IFN-γ, and macrophages were all dispensable. Interestingly, C. gattii pICLC activity depended on β-2-microglobulin, which impacts iron levels among other functions. Iron supplementation reversed pICLC activity, suggesting C. gattii pICLC activity requires iron limitation. Also, pICLC induced a set of iron control proteins, some of which were directly inhibitory to cryptococcus in vitro, suggesting t1IFN regulates iron availability in the pulmonary air space fluids. Thus, exogenous induction of t1IFN significantly improves the outcome of murine infection by C. gattii and C. neoformans but by distinct mechanisms; the C. gattii effect was mediated by iron limitation, while the effect on C. neoformans infection was through induction of classical T-cell-dependent immunity. Together this difference in types of T-cell-dependent t1IFN immunity for different Cryptococcus species suggests a possible mechanism by which HIV infection may select against C. gattii but not C. neoformans.

A dendritic cell-based systemic vaccine induces long-lived lung-resident memory Th17 cells and ameliorates pulmonary mycosis

Tissue-resident memory T cells (TRMs) are a novel nonvascular memory T cell subset. Although CD8⁺ TRMs are well-characterized, CD4⁺ TRMs-especially lung-resident memory Th17 cells-are still being defined. In this study, we characterized lung-resident memory Th17 cells (lung TRM17) and their role in protection against the highly virulent fungus Cryptococcus gattii. We found that intravenously transferred DCs preferentially migrated to lungs and attracted recipient DCs and led to the induction of long-lived Th17 cells expressing characteristic markers. This population could be clearly discriminated from circulating T cells by intravascular staining and was not depleted by the immunosuppressive agent FTY720. The C. gattii antigen re-stimulation assay revealed that vaccine-induced lung Th17 cells produced IL-17A but not IFNγ. The DC vaccine significantly increased IL-17A production and suppressed fungal burden in the lungs and improved the survival of mice infected with C. gattii. This protective effect was significantly reduced in the IL-17A knockout (KO) mice, but not in the FTY720-treated mice. The protective effect also coincided with the activation of neutrophils and multinucleated giant cells, and these inflammatory responses were suppressed in the vaccinated IL-17A KO mice. Overall, these data demonstrated that the systemic DC vaccine induced lung TRM17, which played a substantial role in anti-fungal immunity.

Exogenous Stimulation of Type I Interferon Protects Mice with Chronic Granulomatous Disease from Aspergillosis through Early Recruitment of Host-Protective Neutrophils into the Lung

Invasive aspergillosis (IA) remains the primary cause of morbidity and mortality in chronic granulomatous disease (CGD) patients, often due to infection by Aspergillus species refractory to antifungals. This motivates the search for alternative treatments, including immunotherapy. We investigated the effect of exogenous type I interferon (IFN) activation on the outcome of IA caused by three Aspergillus species, A. fumigatus, A. nidulans, and A. tanneri, in CGD mice. The animals were treated with poly(I):poly(C) carboxymethyl cellulose poly-l-lysine (PICLC), a mimetic of double-stranded RNA, 24 h preinfection and postinfection. The survival rates and lung fungal burdens were markedly improved by PICLC immunotherapy in animals infected with any one of the three Aspergillus species. While protection from IA was remarkable, PICLC induction of type I IFN in the lungs surged 24 h posttreatment and returned to baseline levels by 48 h, suggesting that PICLC altered early events in protection against IA. Immunophenotyping of recruited leukocytes and histopathological examination of tissue sections showed that PICLC induced similar cellular infiltrates as those in untreated-infected mice, in both cases dominated by monocytic cells and neutrophils. However, the PICLC immunotherapy resulted in a marked earlier recruitment of the leukocytes. Unlike with conidia, infection with A. nidulans germlings reduced the protective effect of PICLC immunotherapy. Additionally, antibody depletion of neutrophils totally reversed the protection, suggesting that neutrophils are crucial for PICLC-mediated protection. Together, these data show that prophylactic PICLC immunotherapy prerecruits these cells, enabling them to attack the conidia and thus resulting in a profound protection from IA.IMPORTANCE Patients with chronic granulomatous disease (CGD) are highly susceptible to invasive aspergillosis (IA). While Aspergillus fumigatus is the most-studied Aspergillus species, CGD patients often suffer IA caused by A. nidulans, A. tanneri, and other rare species. These non-fumigatus Aspergillus species are more resistant to antifungal drugs and cause higher fatality rates than A. fumigatus Therefore, alternative therapies are needed to protect CGD patients. We report an effective immunotherapy of mice infected with three Aspergillus species via PICLC dosing. While protection from IA was long lasting, PICLC induction of type I IFN surged but quickly returned to baseline levels, suggesting that PICLC was altering early events in IA. Interestingly, we found responding immune cells to be similar between PICLC-treated and untreated-infected mice. However, PICLC immunotherapy resulted in an earlier recruitment of the leukocytes and suppressed fungal growth. This study highlights the value of type I IFN induction in CGD patients.

Emerging Mechanisms of Innate Immunity and Their Translational Potential in Inflammatory Bowel Disease

Activation of the innate immune system through pattern-recognition receptor (PRR) signaling plays a pivotal role in the early induction of host defense following exposure to pathogens. Loss of intestinal innate immune regulation leading aberrant immune responses has been implicated in the pathogenesis of inflammatory bowel disease (IBD). The precise role of PRRs in gut inflammation is not well understood, but considering their role as bacterial sensors and their genetic association with IBD, they likely contribute to dysregulated immune responses to the commensal microbiota. The purpose of this review is to evaluate the emerging functions of PRRs including their functional cross-talk, how they respond to mitochondrial damage, induce mitophagy or autophagy, and influence adaptive immune responses by interacting with the antigen presentation machinery. The review also summarizes some of the recent attempts to harness these pathways for therapeutic approaches in intestinal inflammation.

Production of RNase III-knockout, auxotrophic Edwardsiella tarda mutant for delivery of long double-stranded RNA and evaluation of its immunostimulatory potential

The artificially synthesized polyinosinic-polycytidylic acid (poly IC) has been widely used to induce type I IFN responses in various vertebrates including fish. However, as poly IC is too expensive to use in aquaculture, the development of another economical long dsRNA producing method is needed to practically use long dsRNAs in aquaculture farms for the control of infectious diseases. In the present study, to produce long dsRNAs economically, we developed a novel long dsRNA production system based on the RNase III gene deleted auxotrophic mutant E. tarda (ΔalrΔrncΔasd E. tarda) and a long dsRNA-producing vector that was equipped with two modified λ phage P_R promoters arranged in a head-to-head fashion. As the present genetically engineered E. tarda cannot live without supplementation of d-alanine and DAP, environmental and medicinal risks are minimized. Olive flounder (Paralichthys olivaceus) fingerlings administered the long dsRNA-producing auxotrophic E. tarda mutant (Δalr ΔrncΔasd E. tarda) showed significantly higher expressions of TLR22, Mx1, and ISG15 genes, indicating a potential to increase type I interferon responses.

Trojan Horse Transit Contributes to Blood-Brain Barrier Crossing of a Eukaryotic Pathogen

The blood-brain barrier (BBB) protects the central nervous system (CNS) by restricting the passage of molecules and microorganisms. Despite this barrier, however, the fungal pathogen Cryptococcus neoformans invades the brain, causing a meningoencephalitis that is estimated to kill over 600,000 people annually. Cryptococcal infection begins in the lung, and experimental evidence suggests that host phagocytes play a role in subsequent dissemination, although this role remains ill defined. Additionally, the disparate experimental approaches that have been used to probe various potential routes of BBB transit make it impossible to assess their relative contributions, confounding any integrated understanding of cryptococcal brain entry. Here we used an in vitro model BBB to show that a “Trojan horse” mechanism contributes significantly to fungal barrier crossing and that host factors regulate this process independently of free fungal transit. We also, for the first time, directly imaged C. neoformans-containing phagocytes crossing the BBB, showing that they do so via transendothelial pores. Finally, we found that Trojan horse crossing enables CNS entry of fungal mutants that cannot otherwise traverse the BBB, and we demonstrate additional intercellular interactions that may contribute to brain entry. Our work elucidates the mechanism of cryptococcal brain invasion and offers approaches to study other neuropathogens.

The fungal pathogen Cryptococcus neoformans invades the brain, causing a meningoencephalitis that kills hundreds of thousands of people each year. One route that has been proposed for this brain entry is a Trojan horse mechanism, whereby the fungus crosses the blood-brain barrier (BBB) as a passenger inside host phagocytes. Although indirect experimental evidence supports this intriguing mechanism, it has never been directly visualized. Here we directly image Trojan horse transit and show that it is regulated independently of free fungal entry, contributes to cryptococcal BBB crossing, and allows mutant fungi that cannot enter alone to invade the brain.

Clash of the Cytokine Titans: counter-regulation of interleukin-1 and type I interferon-mediated inflammatory responses

Over the past decades the notion of 'inflammation' has been extended beyond the original hallmarks of rubor (redness), calor (heat), tumor (swelling) and dolor (pain) described by Celsus. We have gained a more detailed understanding of the cellular players and molecular mediators of inflammation which is now being applied and extended to areas of biomedical research such as cancer, obesity, heart disease, metabolism, auto-inflammatory disorders, autoimmunity and infectious diseases. Innate cytokines are often central components of inflammatory responses. Here, we discuss how the type I interferon and interleukin-1 cytokine pathways represent distinct and specialized categories of inflammatory responses and how these key mediators of inflammation counter-regulate each other.

Bacterial RNA as a signal to eukaryotic cells as part of the infection process

The discovery of regulatory RNA has identified an underappreciated area for microbial subversion of the host. There is increasing evidence that RNA can be delivered from bacteria to host cells associated with membrane vesicles or by direct release from intracellular bacteria. Once inside the host cell, RNA can act by activating sequence-independent receptors of the innate immune system, where recent findings suggest this can be more than simple pathogen detection, and may contribute to the subversion of immune responses. Sequence specific effects are also being proposed, with examples from nematode, plant and human models providing support for the proposition that bacteria-to-human RNA signaling and the subversion of host gene expression may occur.

A subdose of fluconazole alters the virulence of Cryptococcus gattii during murine cryptococcosis and modulates type I interferon expression

Cryptococcosis is an invasive infection caused by yeast-like fungus of the genera Cryptococcus spp. The antifungal therapy for this disease provides some toxicity and the incidence of infections caused by resistant strains increased. Thus, we aimed to assess the consequences of fluconazole subdoses during the treatment of cryptococcosis in the murine inflammatory response and in the virulence factors of Cryptococcus gattii. Mice infected with Cryptococcus gattii were treated with subdoses of fluconazole. We determined the behavior of mice and type 1 interferon expression during the treatment; we also studied the virulence factors and susceptibility to fluconazole for the colonies recovered from the animals. A subdose of fluconazole prolonged the survival of mice, but the morbidity of cryptococcosis was higher in treated animals. These data were linked to the increase in: (i) fluconazole minimum inhibitory concentration, (ii) capsule size and (iii) melanization of C. gattii, which probably led to the increased expression of type I interferons in the brains of mice but not in the lungs. In conclusion, a subdose of fluconazole altered fungal virulence factors and susceptibility to this azole, leading to an altered inflammatory host response and increased morbidity.

Diagnostic Challenges of Cryptococcus neoformans in an Immunocompetent Individual Masquerading as Chronic Hydrocephalus

Cryptococcus neoformans can cause disseminated meningoencephalitis and evade immunosurveillance with expression of a major virulence factor, the polysaccharide capsule. Direct diagnostic assays often rely on the presence of the cryptococcal glucuronoxylomannan capsular antigen (CrAg) or visualization of the capsule. Strain specific phenotypic traits and environmental conditions influence differences in expression that can thereby compromise detection and timely diagnosis. Immunocompetent hosts may manifest clinical signs and symptoms indolently, often expanding the differential and delaying appropriate treatment and diagnosis. We describe a 63-year-old man who presented with a progressive four-year history of ambulatory dysfunction, headache, and communicating hydrocephalus. Serial lumbar punctures (LPs) revealed elevated protein (153–300 mg/dL), hypoglycorrhachia (19–47 mg/dL), lymphocytic pleocytosis (89–95% lymphocyte, WBC 67–303 mg/dL, and RBC 34–108 mg/dL), and normal opening pressure (13–16 cm H₂O). Two different cerebrospinal fluid (CSF) CrAg assays were negative. A large volume CSF fungal culture grew unencapsulated C. neoformans. He was initiated on induction therapy with amphotericin B plus flucytosine and consolidation/maintenance therapy with flucytosine, but he died following discharge due to complications. Elevated levels of CSF Th1 cytokines and decreased IL6 may have affected the virulence and detection of the pathogen.

Inhibition of clinical pathogenic herpes simplex virus 1 strains with enzymatically created siRNA pools

Herpes simplex virus (HSV) is a common human pathogen causing severe diseases such as encephalitis, keratitis, and neonatal herpes. There is no vaccine against HSV and the current antiviral chemotherapy fails to treat certain forms of the disease. Here, we evaluated the antiviral activity of enzymatically created small interfering (si)RNA pools against various pathogenic HSV strains as potential candidates for antiviral therapies. Pools of siRNA targeting 0.5-0.8 kbp of essential HSV genes UL54, UL29, or UL27 were enzymatically synthesized. Efficacy of inhibition of each siRNA pool was evaluated against multiple clinical isolates and laboratory wild type HSV-1 strains using three cell lines representing host tissues that support HSV-1 replication: epithelial, ocular, and cells that originated from the nervous system. The siRNA pools targeting UL54, UL29, and UL27, as well as their equimolar mixture, inhibited HSV replication, with the pool targeting UL29 having the most prominent antiviral effect. In contrast, the non-specific control siRNA pool did not have such an effect. Moreover, the UL29 pool elicited only a minimal innate immune response in the HSV-infected cells, thus evidencing the safety of its potential clinical use. These results are promising for the development of a topical RNA interference approach for clinical treatment of HSV infection. J. Med. Virol. 88:2196-2205, 2016. © 2016 Wiley Periodicals, Inc.

Cryptococcal therapies and drug targets: the old, the new and the promising

Half a century after the introduction of Amphotericin B the management of cryptococcosis remains unsatisfactory. The disease, caused primarily by the two fungal species Cryptococcus neoformans and Cryptococcus gattii, remains responsible for considerable morbidity and mortality despite standard medical care. Current therapeutic options are limited to Amphotericin B, azoles and 5-flucytosine. However, this organism has numerous well-characterized virulence mechanisms that are amenable to pharmacological interference and are thus potential therapeutic targets. Here, we discuss existing approved antifungal drugs, resistance mechanisms to these drugs and non-standard antifungal drugs that have potential in treatment of cryptococcosis, including immunomodulatory strategies that synergize with antifungal drugs, such as cytokine administration or monoclonal antibodies. Finally, we summarize attempts to target well-described virulence factors of Cryptococcus, the capsule or fungal melanin. This review emphasizes the pressing need for new therapeutic alternatives for cryptococcosis.

Real-time in vivo imaging reveals the ability of neutrophils to remove Cryptococcus neoformans directly from the brain vasculature

Although neutrophils are typically the first immune cells attracted to an infection site, little is known about how neutrophils dynamically interact with invading pathogens in vivo. Here, with the use of intravital microscopy, we demonstrate that neutrophils migrate to the arrested Cryptococcus neoformans, a leading agent to cause meningoencephalitis, in the brain microvasculature. Following interactions with C. neoformans, neutrophils were seen to internalize the organism and then circulate back into the bloodstream, resulting in a direct removal of the organism from the endothelial surface before its transmigration into the brain parenchyma. C. neoformans infection led to enhanced expression of adhesion molecules macrophage 1 antigen on neutrophils and ICAM-1 on brain endothelial cells. Depletion of neutrophils enhanced the brain fungal burden. Complement C3 was critically involved in the recognition of C. neoformans by neutrophils and subsequent clearance of the organism from the brain. Together, our finding of the direct removal of C. neoformans by neutrophils from its arrested site may represent a novel mechanism of host defense in the brain, in addition to the known, direct killing of microorganisms at the infection sites. These data are the first to characterize directly the dynamic interactions of leukocytes with a microbe in the brain of a living animal.