Differential roles of CC chemokine ligand 2/monocyte chemotactic protein-1 and CCR2 in the development of T1 immunity

Single-cell immune profiling of Meniere Disease patients

BACKGROUND

Meniere Disease (MD) is an inner ear syndrome, characterized by episodes of vertigo, tinnitus and fluctuating sensorineural hearing loss. The pathological mechanism leading to sporadic MD is still poorly understood, however an allergic inflammatory response seems to be involved in some patients with MD.

OBJECTIVE

Decipher an immune signature associated with the syndrome.

METHODS

We performed mass cytometry immune profiling on peripheral blood from MD patients and controls. We analyzed differences in state and differences in abundance of the different cellular subsets. IgE levels were quantified through ELISA on supernatant of cultured whole blood.

RESULTS

We have identified two clusters of individuals according to the single cell cytokine profile. These clusters presented differences in IgE levels, immune cell population abundance, including a reduction of CD56^dim NK-cells, and changes in cytokine expression with a different response to bacterial and fungal antigens.

CONCLUSION

Our results support a systemic inflammatory response in some MD patients that show a type 2 response with allergic phenotype, which could benefit from personalized IL-4 blockers.

The molecular link between obesity and genomic instability in cancer development

Obesity has been known to be a major risk factor for various types of cancers for several decades. More recently, the relationship between dysregulated adipokines and cancer development has been the focus of much research. Adipose tissue is an important endocrine organ that secretes adipokines that affect both autocrine and paracrine signaling. These adipokines modulate inflammation, induce insulin resistance, and regulate their own behavior and production. Adipokine-production dysregulation is due to physiological changes in adipose tissue that prompt molecular modifications, including low-grade inflammation and the stimulatory production of reactive oxygen species. Additionally, studies have linked DNA damage response, genomic instability, and the innate immune response to tumorigenesis. Further investigation of adipokines and their role in the promotion of genomic instability may clarify the link between obesity and cancer, as well as elucidate potential pharmaceutical targets. In this review, we discuss the progress of recent literature, focusing on the impact of adipokines, genomic instability, and the innate immune response on increasing the risk of cancer.

Rapid screening and scaled manufacture of immunogenic virus-like particles in a tobacco BY-2 cell-free protein synthesis system

Several vaccine platforms have been developed to fight pathogenic threats, with Virus-Like Particles (VLPs) representing a very promising alternative to traditional platforms. VLPs trigger strong and lasting humoral and cellular immune responses with fewer safety concerns and higher stability than other platforms. The use of extensively characterized carrier VLPs modified with heterologous antigens was proposed to circumvent the viral complexity of specific viruses that could lead to poor VLP assembly and yields. Although carrier VLPs have been successfully produced in a wide variety of cell-based systems, these are limited by low protein yields and protracted clone selection and optimization workflows that limit VLP screening approaches. In response, we have demonstrated the cell-free protein synthesis (CFPS) of several variants of the hepatitis B core (HBc) carrier VLP using a high-yielding tobacco BY-2 lysate (BYL). High VLP yields in the BYL system allowed in-depth characterization of HBc variants. Insertion of heterologous sequences at the spike region of the HBc monomer proved more structurally demanding than at the N-terminus but removal of the C-terminal domain allowed higher particle flexibility and insert acceptance, albeit at the expense of thermal and chemical stability. We also proved the possibility to scale the CFPS reaction up to 1L in batch mode to produce 0.45 grams of the native HBc VLP within a 48-hour reaction window. A maximum yield of 820 µg/ml of assembled VLP particles was observed at the 100µl scale and most remarkably the CFPS reaction was successfully scaled from 50µl to 1L without any reduction in protein yield across this 20,000-fold difference in reaction volumes. We subsequently proved the immunogenicity of BYL-derived VLPs, as flow cytometry and microscopy clearly showed prompt recognition and endocytosis of fluorescently labelled VLPs by human dendritic cells. Triggering of inflammatory cytokine production in human peripheral blood mononuclear cells was also quantitated using a multiplex assay. This research establishes BYL as a tool for rapid production and microscale screening of VLP variants with subsequent manufacturing possibilities across scales, thus accelerating discovery and implementation of new vaccine candidates using carrier VLPs.

Role of CCL2/CCR2 axis in the pathogenesis of COVID-19 and possible Treatments: All options on the Table

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is cause of the novel coronavirus disease (COVID-19). In the last two years, SARS-CoV-2 has infected millions of people worldwide with different waves, resulting in the death of many individuals. The evidence disclosed that the host immune responses to SARS-CoV-2 play a pivotal role in COVID-19 pathogenesis and clinical manifestations. In addition to inducing antiviral immune responses, SARS-CoV-2 can also cause dysregulated inflammatory responses characterized by the noticeable release of proinflammatory mediators in COVID-19 patients. Among these proinflammatory mediators, chemokines are considered a subset of cytokines that participate in the chemotaxis process to recruit immune and non-immune cells to the site of inflammation and infection. Researchers have demonstrated that monocyte chemoattractant protein-1 (MCP-1/CCL2) and its receptor (CCR2) are involved in the recruitment of monocytes and infiltration of these cells into the lungs of patients suffering from COVID-19. Moreover, elevated levels of CCL2 have been reported in the bronchoalveolar lavage fluid (BALF) obtained from patients with severe COVID-19, initiating cytokine storm and promoting CD163⁺ myeloid cells infiltration in the airways and further alveolar damage. Therefore, CCL2/CCR axis plays a key role in the immunopathogenesis of COVID-19 and targeted therapy of involved molecules in this axis can be a potential therapeutic approach for these patients. This review discusses the biology of the CCL2/CCR2 axis as well as the role of this axis in COVID-19 immunopathogenesis, along with therapeutic options aimed at inhibiting CCL2/CCR2 and modulating dysregulated inflammatory responses in patients with severe SARS-CoV-2 infection.

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.

CCR2 contributes to host defense against Staphylococcus aureus orthopedic implant-associated infections in mice

C-C motif chemokine receptor 2 (CCR2) is an important mediator of myeloid cell chemotaxis during inflammation and infection. Myeloid cells such as monocytes, macrophages, and neutrophils contribute to host defense during orthopedic implant-associated infections (OIAI), but whether CCR2-mediated chemotaxis is involved remains unclear. Therefore, a Staphylococcus aureus OIAI model was performed by surgically placing an orthopedic-grade titanium implant and inoculating a bioluminescent S. aureus strain in knee joints of wildtype (wt) and CCR2-deficient mice. In vivo bioluminescent signals significantly increased in CCR2-deficient mice compared with wt mice at later time points (Days 14-28), which was confirmed with ex vivo colony-forming unit enumeration. S. aureus γ-hemolysin utilizes CCR2 to induce host cell lysis. However, there were no differences in bacterial burden when the OIAI model was performed with a parental versus a mutant γ-hemolysin-deficient S. aureus strain, indicating that the protection was mediated by the host cell function of CCR2 rather than γ-hemolysin virulence. Although CCR2-deficient and wt mice had similar cellular infiltrates in the infected joint tissue, CCR2-deficient mice had reduced myeloid cells and γδ T cells in the draining lymph nodes. Taken together, CCR2 contributed to host defense at later time points during an OIAI by increasing immune cell infiltrates in the draining lymph nodes, which likely contained the infection and prevented invasive spread.

MCP-1: Function, regulation, and involvement in disease

MCP-1 (Monocyte chemoattractant protein-1), also known as Chemokine (CC-motif) ligand 2 (CCL2), is from family of CC chemokines. It has a vital role in the process of inflammation, where it attracts or enhances the expression of other inflammatory factors/cells. It leads to the advancement of many disorders by this main mechanism of migration and infiltration of inflammatory cells like monocytes/macrophages and other cytokines at the site of inflammation. MCP-1 has been inculpated in the pathogenesis of numerous disease conditions either directly or indirectly like novel corona virus, cancers, neuroinflammatory diseases, rheumatoid arthritis, cardiovascular diseases. The elevated MCP-1 level has been observed in COVID-19 patients and proven to be a biomarker associated with the extremity of disease along with IP-10. This review will focus on involvement and role of MCP-1 in various pathological conditions.

Targeting the CCL2/CCR2 Axis in Cancer Immunotherapy: One Stone, Three Birds?

CCR2 is predominantly expressed by monocytes/macrophages with strong proinflammatory functions, prompting the development of CCR2 antagonists to dampen unwanted immune responses in inflammatory and autoimmune diseases. Paradoxically, CCR2-expressing monocytes/macrophages, particularly in tumor microenvironments, can be strongly immunosuppressive. Thus, targeting the recruitment of immunosuppressive monocytes/macrophages to tumors by CCR2 antagonism has recently been investigated as a strategy to modify the tumor microenvironment and enhance anti-tumor immunity. We present here that beneficial effects of CCR2 antagonism in the tumor setting extend beyond blocking chemotaxis of suppressive myeloid cells. Signaling within the CCL2/CCR2 axis shows underappreciated effects on myeloid cell survival and function polarization. Apart from myeloid cells, T cells are also known to express CCR2. Nevertheless, tissue homing of Treg cells among T cell populations is preferentially affected by CCR2 deficiency. Further, CCR2 signaling also directly enhances Treg functional potency. Thus, although Tregs are not the sole type of T cells expressing CCR2, the net outcome of CCR2 antagonism in T cells favors the anti-tumor arm of immune responses. Finally, the CCL2/CCR2 axis directly contributes to survival/growth and invasion/metastasis of many types of tumors bearing CCR2. Together, CCR2 links to two main types of suppressive immune cells by multiple mechanisms. Such a CCR2-assoicated immunosuppressive network is further entangled with paracrine and autocrine CCR2 signaling of tumor cells. Strategies to target CCL2/CCR2 axis as cancer therapy in the view of three types of CCR2-expessing cells in tumor microenvironment are discussed.

IL-27 Negatively Regulates Tip-DC Development during Infection

Tumor necrosis factor (TNF)/inducible nitric oxide synthase (iNOS)-producing dendritic cells (Tip-DCs) have profound impacts on host immune responses during infections. The mechanisms regulating Tip-DC development remain largely unknown. Here, using a mouse model of infection with African trypanosomes, we show that a deficiency in interleukin-27 receptor (IL-27R) signaling results in escalated intrahepatic accumulation of Ly6C-positive (Ly6C⁺) monocytes and their differentiation into Tip-DCs. Blocking Tip-DC development significantly ameliorates liver injury and increases the survival of infected IL-27R^−/− mice. Mechanistically, Ly6C⁺ monocyte differentiation into pathogenic Tip-DCs in infected IL-27R^−/− mice is driven by a CD4⁺ T cell-interferon gamma (IFN-γ) axis via cell-intrinsic IFN-γ signaling. In parallel, hyperactive IFN-γ signaling induces cell death of Ly6C-negative (Ly6C⁻) monocytes in a cell-intrinsic manner, which in turn aggravates the development of pathogenic Tip-DCs due to the loss of the negative regulation of Ly6C⁻ monocytes on Ly6C⁺ monocyte differentiation into Tip-DCs. Thus, IL-27 inhibits the dual-track exacerbation of Tip-DC development induced by a CD4⁺ T cell–IFN-γ axis. We conclude that IL-27 negatively regulates Tip-DC development by preventing the cell-intrinsic effects of IFN-γ and that the regulation involves CD4⁺ T cells and Ly6C⁻ monocytes. Targeting IL-27 signaling may manipulate Tip-DC development for therapeutic intervention.

Airway Redox Homeostasis and Inflammation Gone Awry: From Molecular Pathogenesis to Emerging Therapeutics in Respiratory Pathology

As aerobic organisms, we are continuously and throughout our lifetime subjected to an oxidizing atmosphere and, most often, to environmental threats. The lung is the internal organ most highly exposed to this milieu. Therefore, it has evolved to confront both oxidative stress induced by reactive oxygen species (ROS) and a variety of pollutants, pathogens, and allergens that promote inflammation and can harm the airways to different degrees. Indeed, an excess of ROS, generated intrinsically or from external sources, can imprint direct damage to key structural cell components (nucleic acids, sugars, lipids, and proteins) and indirectly perturb ROS-mediated signaling in lung epithelia, impairing its homeostasis. These early events complemented with efficient recognition of pathogen- or damage-associated recognition patterns by the airway resident cells alert the immune system, which mounts an inflammatory response to remove the hazards, including collateral dead cells and cellular debris, in an attempt to return to homeostatic conditions. Thus, any major or chronic dysregulation of the redox balance, the air-liquid interface, or defects in epithelial proteins impairing mucociliary clearance or other defense systems may lead to airway damage. Here, we review our understanding of the key role of oxidative stress and inflammation in respiratory pathology, and extensively report current and future trends in antioxidant and anti-inflammatory treatments focusing on the following major acute and chronic lung diseases: acute lung injury/respiratory distress syndrome, asthma, chronic obstructive pulmonary disease, pulmonary fibrosis, and cystic fibrosis.

The Diverse Roles of Monocytes in Cryptococcosis

Monocytes are considered to play a central role in the pathogenesis of Cryptococcus neoformans infection. Monocytes and monocyte-derived macrophages and dendritic cells are key components for the control of infection, but paradoxically they can also contribute to detrimental host responses and may even support fungal proliferation and dissemination. Simultaneously, the C. neoformans polysaccharide capsule can impair the functions of monocytes. Although monocytes are often seen as simple precursor cells, they also function as independent immune effector cells. In this review, we summarize these monocyte-specific functions during cryptococcal infection and the influence of C. neoformans on monocyte responses. We also cover the most recent findings on the functional and phenotypic heterogeneity of monocytes and discuss how new advanced technologies provide a platform to address outstanding questions in the field.

Exploring the complex role of chemokines and chemoattractants in vivo on leukocyte dynamics

Chemotaxis is fundamental for leukocyte migration in immunity and inflammation and contributes to the pathogenesis of many human diseases. Although chemokines and various other chemoattractants were initially appreciated as important mediators of acute inflammation, in the past years they have emerged as critical mediators of cell migration during immune surveillance, organ development, and cancer progression. Such advances in our knowledge in chemokine biology have paved the way for the development of specific pharmacological targets with great therapeutic potential. Chemoattractants may belong to different classes, including a complex chemokine system of approximately 50 endogenous molecules that bind to G protein-coupled receptors, which are expressed by a wide variety of cell types. Also, an unknown number of other chemoattractants may be generated by pathogens and damaged/dead cells. Therefore, blocking chemotaxis without causing side effects is an extremely challenging task. In this review, we focus on recent advances in understanding how the chemokine system orchestrates immune cell migration and positioning at the whole organ level in homeostasis, inflammation, and infection.

Circulating Picomolar Levels of CCL2 Downregulate Ongoing Chronic Experimental Autoimmune Encephalomyelitis by Induction of Regulatory Mechanisms

Multiple sclerosis is an inflammatory disease of the CNS characterized by neurologic impairment resulting from primary demyelination and axonal damage. The pathogenic mechanisms of disease development include Ag-specific T cell activation and Th1 differentiation, followed by T cell and macrophage migration into the CNS. CCL2 is a chemokine that induces migration of monocytes, memory T cells, and dendritic cells. We previously demonstrated that picomolar levels of CCL2 strongly restrict the development of inflammation in models of inflammatory bowel disease. Moreover, CCR2 deficiency in T cells promotes a program inducing the accumulation of Foxp3⁺ regulatory T cells while decreasing the levels of Th17 cells in vivo. In the current study, the effect of picomolar levels of CCL2 on the autoimmune inflammatory response associated with a multiple sclerosis-like disease in mice was analyzed. We found that low dosages of CCL2 were effective in suppressing MOG-induced experimental autoimmune encephalomyelitis (EAE), and they downregulated chronic EAE. The modulation of EAE by CCL2 was associated with downregulation of Th1/Th17 cells and upregulation of TGF-β and induction of regulatory CD4⁺Foxp3 T cells. Most strikingly, these low levels of CCL2 induced formation of highly functional regulatory T cells. Thus, this study strongly supports the potential use of CCL2 as a regulatory mediator for treating inflammatory autoimmune diseases.

Inflammatory monocytes are detrimental to the host immune response during acute infection with Cryptococcus neoformans

Cryptococcus neoformans is a leading cause of invasive fungal infections among immunocompromised patients. However, the cellular constituents of the innate immune response that promote clearance versus progression of infection upon respiratory acquisition of C. neoformans remain poorly defined. In this study, we found that during acute C. neoformans infection, CCR2⁺ Ly6C^hi inflammatory monocytes (IM) rapidly infiltrate the lungs and mediate fungal trafficking to lung-draining lymph nodes. Interestingly, this influx of IM is detrimental to the host, since ablating IM or impairing their recruitment to the lungs improves murine survival and reduces fungal proliferation and dissemination. Using a novel conditional gene deletion strategy, we determined that MHC class II expression by IM did not mediate their deleterious impact on the host. Furthermore, although ablation of IM reduced the number of lymphocytes, innate lymphoid cells, and eosinophils in the lungs, the effects of IM were not dependent on these cells. We ascertained that IM in the lungs upregulated transcripts associated with alternatively activated (M2) macrophages in response to C. neoformans, consistent with the model that IM assume a cellular phenotype that is permissive for fungal growth. We also determined that conditional knockout of the prototypical M2 marker arginase 1 in IM and deletion of the M2-associated transcription factor STAT6 were not sufficient to reverse the harmful effects of IM. Overall, our findings indicate that C. neoformans can subvert the fungicidal potential of IM to enable the progression of infection through a mechanism that is not dependent on lymphocyte priming, eosinophil recruitment, or downstream M2 macrophage polarization pathways. These results give us new insight into the plasticity of IM function during fungal infections and the level of control that C. neoformans can exert on host immune responses.

Cryptococcus neoformans is a fungus that is prevalent throughout the environment and can cause a fatal infection of the central nervous system when inhaled into the lungs by patients with impaired immune systems. Our understanding of the immune responses that either help clear C. neoformans from the lungs or permit development of disease remains limited. In this study, we used a mouse model of lethal C. neoformans infection to determine that inflammatory monocytes, immune cells that are often among the first responders to infections, actually facilitate the progression of infection rather than clearance. These findings establish a foundation for future work to target the immune response of inflammatory monocytes as a strategy to improve the outcomes of patients that develop C. neoformans infections.

A review of inflammatory mechanism in airway diseases

BACKGROUND

Inflammation in the lung is the body's natural response to injury. It acts to remove harmful stimuli such as pathogens, irritants, and damaged cells and initiate the healing process. Acute and chronic pulmonary inflammation are seen in different respiratory diseases such as; acute respiratory distress syndrome, chronic obstructive pulmonary disease (COPD), asthma, and cystic fibrosis (CF).

FINDINGS

In this review, we found that inflammatory response in COPD is determined by the activation of epithelial cells and macrophages in the respiratory tract. Epithelial cells and macrophages discharge transforming growth factor-β (TGF-β), which trigger fibroblast proliferation and tissue remodeling. Asthma leads to airway hyper-responsiveness, obstruction, mucus hyper-production, and airway-wall remodeling. Cytokines, allergens, chemokines, and infectious agents are the main stimuli that activate signaling pathways in epithelial cells in asthma. Mutation of the CF transmembrane conductance regulator (CFTR) gene results in CF. Mutations in CFTR influence the lung epithelial innate immune function that leads to exaggerated and ineffective airway inflammation that fails to abolish pulmonary pathogens. We present mechanistic computational models (based on ordinary differential equations, partial differential equations and agent-based models) that have been applied in studying the complex physiological and pathological mechanisms of chronic inflammation in different airway diseases.

CONCLUSION

The scope of the present review is to explore the inflammatory mechanism in airway diseases and highlight the influence of aging on airways' inflammation mechanism. The main goal of this review is to encourage research collaborations between experimentalist and modelers to promote our understanding of the physiological and pathological mechanisms that control inflammation in different airway diseases.

Immunobiology of Inherited Muscular Dystrophies

The immune response to acute muscle damage is important for normal repair. However, in chronic diseases such as many muscular dystrophies, the immune response can amplify pathology and play a major role in determining disease severity. Muscular dystrophies are inheritable diseases that vary tremendously in severity, but share the progressive loss of muscle mass and function that can be debilitating and lethal. Mutations in diverse genes cause muscular dystrophy, including genes that encode proteins that maintain membrane strength, participate in membrane repair, or are components of the extracellular matrix or the nuclear envelope. In this article, we explore the hypothesis that an important feature of many muscular dystrophies is an immune response adapted to acute, infrequent muscle damage that is misapplied in the context of chronic injury. We discuss the involvement of the immune system in the most common muscular dystrophy, Duchenne muscular dystrophy, and show that the immune system influences muscle death and fibrosis as disease progresses. We then present information on immune cell function in other muscular dystrophies and show that for many muscular dystrophies, release of cytosolic proteins into the extracellular space may provide an initial signal, leading to an immune response that is typically dominated by macrophages, neutrophils, helper T-lymphocytes, and cytotoxic T-lymphocytes. Although those features are similar in many muscular dystrophies, each muscular dystrophy shows distinguishing features in the magnitude and type of inflammatory response. These differences indicate that there are disease-specific immunomodulatory molecules that determine response to muscle cell damage caused by diverse genetic mutations. © 2018 American Physiological Society. Compr Physiol 8:1313-1356, 2018.

Characterization and allergic role of IL-33-induced neutrophil polarization

Neutrophils are involved in the pathogenesis of allergy. However, the contribution of the different functionally polarized neutrophils in allergy needs to be clarified. We sought to define the characteristics of interleukin (IL)-33-induced neutrophils and the involvement of this subset of polarized neutrophils in allergic pathogenesis. Freshly isolated neutrophils were treated with different cytokines and the cytokine expression levels were detected by real-time PCR. The gene expression profile of IL-33-induced neutrophils was determined by microarray assay. Adoptive transfer assay was used to investigate the function of IL-33-induced neutrophils in an ovalbumin (OVA)-induced allergic asthma model. IL-33-treated neutrophils selectively produced IL-4, IL-5, IL-9 and IL-13 (referred as to N(IL-33) cells) and displayed a distinctive gene expression profile in sharp contrast to resting and lipopolysaccharide (LPS)-treated neutrophils. IL-33-induced neutrophils expressed high Levels of IL-1R2 on cell surface, whereas resting and LPS-treated neutrophils did not, indicating IL-1R2 might be used as a biomarker for N(IL-33) cells. Importantly, N(IL-33) neutrophils exist in the lungs of OVA-induced allergic asthma mice. Adoptive transfer of N(IL-33) neutrophils significantly promotes the severity of the lung pathogenesis in this model. IL-33 induces neutrophil polarization through c-Jun N-terminal kinase- and nuclear factor-κB-dependent pathways. A previously unappreciated neutrophil polarization driven by IL-33 with unique cell surface markers and cytokine/chemokine-producing gene profile was defined. The newly identified N(IL-33) subpopulation may have significant contribution to IL-33-related pathogenesis.

Inflammatory monocytes contribute to the persistence of CXCR3hi CX3CR1lo circulating and lung-resident memory CD8+ T cells following respiratory virus infection

Phenotypically diverse memory CD8⁺ T cells are present in the lungs that either re-circulate or reside within the tissue. Understanding the key cellular interactions that regulate the generation and then persistence of these different subsets is of great interest. Recently, DNGR-1⁺ dendritic cell (DC) mediated priming was reported to control the generation of lung-resident but not circulating memory cells following respiratory viral infection. Here, we report an important role for Ly6C⁺ inflammatory monocytes (IMs) in contributing to the persistence of memory CD8⁺ T cells but not their generation. Effector CD8⁺ T cells expanded and contracted normally in the absence of IMs, but the memory compartment declined significantly over time. Quite unexpectedly, this defect was confined to tissue resident and circulating CXCR3^hi CX3CR1^lo memory cells but not CXCR3^hi CX3CR1^int and CXCR3^lo CX3CR1^hi subsets. Thus, two developmentally distinct innate cells orchestrate the generation and persistence of memory T cell subsets following a respiratory virus infection. See also: News and Commentary by Lafouresse & Groom.

The F-Box Protein Fbp1 Shapes the Immunogenic Potential of Cryptococcus neoformans

Cryptococcus neoformans is the main etiologic agent of cryptococcal meningitis and causes a significant number of deadly infections per year. Although it is well appreciated that host immune responses are crucial for defense against cryptococcosis, our understanding of factors that control the development of effective immunity to this fungus remains incomplete. In previous studies, we identified the F-box protein Fbp1 as a novel determinant of C. neoformans virulence. In this study, we found that the hypovirulence of the fbp1Δ mutant is linked to the development of a robust host immune response. Infection with the fbp1Δ mutant induces a rapid influx of CCR2⁺ monocytes and their differentiation into monocyte-derived dendritic cells (mo-DCs). Depletion of CCR2⁺ monocytes and their derivative mo-DCs resulted in impaired activation of a protective inflammatory response and the rapid death of mice infected with the fbp1Δ mutant. Mice lacking B and T cells also developed fungal meningitis and succumbed to infection with the fbp1Δ mutant, demonstrating that adaptive immune responses to the fbp1Δ mutant help to maintain the long-term survival of the host. Adaptive immune responses to the fbp1Δ mutant were characterized by enhanced differentiation of Th1 and Th17 CD4⁺ T cells together with diminished Th2 responses compared to the H99 parental strain. Importantly, we found that the enhanced immunogenicity of fbp1Δ mutant yeast cells can be harnessed to confer protection against a subsequent infection with the virulent H99 parental strain. Altogether, our findings suggest that Fbp1 functions as a novel virulence factor that shapes the immunogenicity of C. neoformansIMPORTANCECryptococcus neoformans is the most common cause of deadly fungal meningitis, with over 270,000 infections per year. Immune responses are critically required for the prevention of cryptococcosis, and patients with impaired immunity and low CD4⁺ T cell numbers are at high risk of developing these deadly infections. Although it is well appreciated that the development of protective immunity is shaped by the interactions of the host immune system with fungal cells, our understanding of fungal products that influence this process remains poor. In this study, we found that the activity of F-box protein 1 (Fbp1) in highly virulent C. neoformans clinical strain H99 shapes its immunogenicity and thus affects the development of protective immune responses in the host. The identification of this new mechanism of virulence may facilitate the future development of therapeutic interventions aimed at boosting antifungal host immunity.

CCR2 Regulates the Immune Response by Modulating the Interconversion and Function of Effector and Regulatory T Cells

Chemokines and chemokine receptors establish a complex network modulating immune cell migration and localization. These molecules were also suggested to mediate the differentiation of leukocytes; however, their intrinsic, direct regulation of lymphocyte fate remained unclear. CCR2 is the main chemokine receptor inducing macrophage and monocyte recruitment to sites of inflammation, and it is also expressed on T cells. To assess whether CCR2 directly regulates T cell responses, we followed the fates of CCR2^-/- T cells in T cell-specific inflammatory models. Our in vitro and in vivo results show that CCR2 intrinsically mediates the expression of inflammatory T cell cytokines, and its absence on T cells results in attenuated colitis progression. Moreover, CCR2 deficiency in T cells promoted a program inducing the accumulation of Foxp3⁺ regulatory T cells, while decreasing the levels of Th17 cells in vivo, indicating that CCR2 regulates the immune response by modulating the effector/regulatory T ratio.

Genetic susceptibility to severe asthma with fungal sensitization

Severe asthma is problematic and its pathogenesis poorly understood. Fungal sensitization is common, and many patients with severe asthma with fungal sensitization (SAFS), used to denote this subgroup of asthma, respond to antifungal therapy. We have investigated 325 haplotype-tagging SNPs in 22 candidate genes previously associated with aspergillosis in patients with SAFS, with comparisons in atopic asthmatics and healthy control patients, of whom 47 SAFS, 279 healthy and 152 atopic asthmatic subjects were genotyped successfully. Significant associations with SAFS compared with atopic asthma included Toll-like receptor 3 (TLR3) (p = .009), TLR9 (p = .025), C-type lectin domain family seven member A (dectin-1) (p = .043), interleukin-10 (IL-10) (p = .0010), mannose-binding lectin (MBL2) (p = .007), CC-chemokine ligand 2 (CCL2) (2 SNPs, p = .025 and .041), CCL17 (p = .002), plasminogen (p = .049) and adenosine A2a receptor (p = .024). These associations differ from those found in ABPA in asthma, indicative of contrasting disease processes. Additional and broader genetic association studies in SAFS, combined with experimental work, are likely to contribute to our understanding of different phenotypes of problematic asthma.

Scavenger Receptor MARCO Orchestrates Early Defenses and Contributes to Fungal Containment during Cryptococcal Infection

The scavenger receptor macrophage receptor with collagenous structure (MARCO) promotes protective innate immunity against bacterial and parasitic infections; however, its role in host immunity against fungal pathogens, including the major human opportunistic fungal pathogen Cryptococcus neoformans, remains unknown. Using a mouse model of C. neoformans infection, we demonstrated that MARCO deficiency leads to impaired fungal control during the afferent phase of cryptococcal infection. Diminished fungal containment in MARCO^-/- mice was accompanied by impaired recruitment of Ly6C^high monocytes and monocyte-derived dendritic cells (moDC) and lower moDC costimulatory maturation. The reduced recruitment and activation of mononuclear phagocytes in MARCO^-/- mice was linked to diminished early expression of IFN-γ along with profound suppression of CCL2 and CCL7 chemokines, providing evidence for roles of MARCO in activation of the CCR2 axis during C. neoformans infection. Lastly, we found that MARCO was involved in C. neoformans phagocytosis by resident pulmonary macrophages and DC. We conclude that MARCO facilitates early interactions between C. neoformans and lung-resident cells and promotes the production of CCR2 ligands. In turn, this contributes to a more robust recruitment and activation of moDC that opposes rapid fungal expansion during the afferent phase of cryptococcal infection.

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.

Disruption of Early Tumor Necrosis Factor Alpha Signaling Prevents Classical Activation of Dendritic Cells in Lung-Associated Lymph Nodes and Development of Protective Immunity against Cryptococcal Infection

Anti-tumor necrosis factor alpha (anti-TNF-α) therapies have been increasingly used to treat inflammatory diseases and are associated with increased risk of invasive fungal infections, including Cryptococcus neoformans infection. Using a mouse model of cryptococcal infection, we investigated the mechanism by which disruption of early TNF-α signaling results in the development of nonprotective immunity against C. neoformans We found that transient depletion of TNF-α inhibited pulmonary fungal clearance and enhanced extrapulmonary dissemination of C. neoformans during the adaptive phase of the immune response. Higher fungal burdens in TNF-α-depleted mice were accompanied by markedly impaired Th1 and Th17 responses in the infected lungs. Furthermore, early TNF-α depletion also resulted in disrupted transcriptional initiation of the Th17 polarization program and subsequent upregulation of Th1 genes in CD4(+) T cells in the lung-associated lymph nodes (LALN) of C. neoformans-infected mice. These defects in LALN T cell responses were preceded by a dramatic shift from a classical toward an alternative activation of dendritic cells (DC) in the LALN of TNF-α-depleted mice. Taken together, our results indicate that early TNF-α signaling is required for optimal DC activation, and the initial Th17 response followed by Th1 transcriptional prepolarization of T cells in the LALN, which further drives the development of protective immunity against cryptococcal infection in the lungs. Thus, administration of anti-TNF-α may introduce a particularly greater risk for newly acquired fungal infections that require generation of protective Th1/Th17 responses for their containment and clearance.

IMPORTANCE

Increased susceptibility to invasive fungal infections in patients on anti-TNF-α therapies underlines the need for understanding the cellular effects of TNF-α signaling in promoting protective immunity to fungal pathogens. Here, we demonstrate that early TNF-α signaling is required for classical activation and accumulation of DC in LALN of C. neoformans-infected mice. Subsequent transcriptional initiation of Th17 followed by Th1 programming in LALN results in pulmonary accumulation of gamma interferon- and interleukin-17A-producing T cells and effective fungal clearance. All of these crucial steps are severely impaired in mice that undergo anti-TNF-α treatment, consistent with their inability to clear C. neoformans This study identified critical interactions between cells of the innate immune system (DC), the emerging T cell responses, and cytokine networks with a central role for TNF-α which orchestrate the development of the immune protection against cryptococcal infection. This information will be important in aiding development and understanding the potential side effects of immunotherapies.

First Line of Defense: Innate Cell-Mediated Control of Pulmonary Aspergillosis

Mycotic infections and their effect on the human condition have been widely overlooked and poorly surveilled by many health organizations even though mortality rates have increased in recent years. The increased usage of immunosuppressive and myeloablative therapies for the treatment of malignant as well as non-malignant diseases has contributed significantly to the increased incidence of fungal infections. Invasive fungal infections have been found to be responsible for at least 1.5 million deaths worldwide. About 90% of these deaths can be attributed to Cryptococcus, Candida, Aspergillus, and Pneumocystis. A better understanding of how the host immune system contains fungal infection is likely to facilitate the development of much needed novel antifungal therapies. Innate cells are responsible for the rapid recognition and containment of fungal infections and have been found to play essential roles in defense against multiple fungal pathogens. In this review we summarize our current understanding of host-fungi interactions with a focus on mechanisms of innate cell-mediated recognition and control of pulmonary aspergillosis.

Successful protection against tularemia in C57BL/6 mice is correlated with expansion of Francisella tularensis-specific effector T cells

Francisella tularensis is an intracellular, Gram-negative bacterium that causes the fatal disease tularemia. Currently, there are no licensed vaccines for tularemia and the requirements for protection against infection are poorly defined. To identify correlates of vaccine-induced immunity against tularemia, we compared different strains of the live vaccine strain (LVS) for their relative levels of virulence and ability to protect C57BL/6 mice against challenge with virulent F. tularensis strain SchuS4. Successful vaccination, as defined by survival of C57BL/6 mice, was correlated with significantly greater numbers of effector T cells in the spleen and lung. Further, lung cells and splenocytes from fully protected animals were more effective than lung cells and splenocytes from vaccinated but nonimmune animals in limiting intracellular replication of SchuS4 in vitro. Together, our data provide a unique model to compare efficacious vaccines to nonefficacious vaccines, which will enable comprehensive identification of host and bacterial components required for immunization against tularemia.

The potential role of monocyte chemoattractant protein-1 for major depressive disorder

The immune hypothesis of major depressive disorder (MDD) fits well with the supposed interaction between genetic and environmental factors in disorders with a complicated etiopathogenesis. It has been suggested that infectious diseases are associated with MDD in that cytokines may play a critical role as a key modulator in the transition between infection and the development of MDD. It has been also suggested that antidepressants have immunomodulatory effects on some cytokines and cytokine receptors, although the exact mechanism has not yet been fully elucidated. Among cytokines, monocyte chemoattractant protein-1 (MCP-1) is especially well known and has attracted considerable interest owing to its immunomodulatory functions. MCP-1 is expressed in highly regionalized neuronal areas in the brain, leading to kind of modulation of neuronal activity and neuroendocrine functions commonly seen in patients with MDD. Additionally, it is involved in the control of other cytokines that have been consistently proposed as associated with the development of MDD. It also has a possible role in the neurodegenerative process of a number of central nervous system (CNS) diseases. Hence, this paper draws from the perspective of immunology to offer several suggestions about the role of MPC-1 in the development of MDD.

Immunosuppressive monocytes: possible homeostatic mechanism to restrain chronic intestinal inflammation

Chronic colitis is accompanied by extensive myelopoiesis and accumulation of CD11b+Gr-1+ cells in spleens and secondary lymphoid tissues. Although cells with similar phenotype have been described in cancer, chronic infection, or autoimmunity, where they were associated with suppression of T cell responses, little is known regarding how these cells affect CD4 T cell responses in the context of chronic intestinal inflammation. Therefore, we undertook this study to characterize the interplay between colitis-induced myeloid cells and CD4 T cell. Within the CD11b+Gr-1+ population, only monocytes (Ly6G(neg)Ly6C(high)) but not other myeloid cell subsets suppressed proliferation and production of cytokines by CD4 T cells. Suppression was mediated by cell-contact, NO and partially by IFN-γ and PGs. Interestingly, Ly6C(high) MDCs, isolated from colitic colons, showed up-regulation of iNOS and arginase-1 and were more potent suppressors than those isolated from spleen. On a single-cell level, MDCs inhibited Th1 responses but enhanced generation of foxp3+ T cells. MDCs, cocultured with activated/Teffs, isolated from inflamed colons under hypoxic (1% O2) conditions typical for the inflamed intestine, suppressed proliferation but not their production of proinflammatory cytokines and chemokines. Taken together, expansion of monocytes and MDCs and activation of their suppressive properties may represent a homeostatic mechanism aimed at restraining excessive T cell activation during chronic inflammatory settings. The contribution of immunosuppressive monocytes/MDCs to chronic colitis and their role in shaping T cell responses in vivo require further investigation.

CD8 T cells regulate allergic contact dermatitis by modulating CCR2-dependent TNF/iNOS-expressing Ly6C+ CD11b+ monocytic cells

Monocytes and their derived cells have critical roles in inflammation and immune defense. However, their function in skin diseases such as allergic contact dermatitis remains poorly defined. Using a model of contact hypersensitivity (CHS) toward 2,4-dinitrochlorobenzene, we show that Ly6C+ CD11b+ monocytic cells participate in the pathophysiology of CHS and their accumulation is regulated by effector CD8 T cells. These Ly6C+ CD11b+ monocytic cells are the primary contributors of tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS) and derive from Ly6C(hi)CCR2+ monocytes, as they were absent in non-inflamed skin and accumulate as a consequence of inflammation in a C-C chemokine receptor type 2 (CCR2)-dependent manner. Importantly, CCR2(-/-) mice, or wild-type mice depleted of monocytes via clodronate liposomes, display a marked decrease in TNF-α and iNOS expression accompanied by attenuated skin inflammation. Using transgenic mice and antibody depletion, we show that effector CD8 T cells regulate the accumulation of Ly6C+ CD11b+ monocytic cells through IL-17 and activate them for TNF-α and iNOS through IFN-γ. CD8 T cell-derived IFN-γ was also critical for the accumulation of the major histocompatibility complex II-expressing Ly6C+ CD11b+ subset, which expressed intermediate levels of CD11c and costimulatory molecules. Taken together, our findings provide further insight into the pathophysiology of allergic contact dermatitis by showing that CD8 T cells regulate the inflammatory cascade through TNF/iNOS-expressing Ly6C+ CD11b+ monocytic cells.

Heterogeneity of lung mononuclear phagocytes during pneumonia: contribution of chemokine receptors

Bacterial pneumonia is a common and dangerous illness. Mononuclear phagocytes, which comprise monocyte, resident and recruited macrophage, and dendritic cell subsets, are critical to antimicrobial defenses, but the dynamics of their recruitment to the lungs in pneumonia is not established. We hypothesized that chemokine-mediated traffic of mononuclear phagocytes is important in defense against bacterial pneumonia. In a mouse model of Klebsiella pneumonia, circulating Ly6C(hi) and, to a lesser extent, Ly6C(lo) monocytes expanded in parallel with accumulation of inflammatory macrophages and CD11b(hi) dendritic cells and plasmacytoid dendritic cells in the lungs, whereas numbers of alveolar macrophages remained constant. CCR2 was expressed by Ly6C(hi) monocytes, recruited macrophages, and airway dendritic cells; CCR6 was prominently expressed by airway dendritic cells; and CX3CR1 was ubiquitously expressed by blood monocytes and lung CD11b(hi) dendritic cells during infection. CCR2-deficient, but not CCL2-, CX3CR1-, or CCR6-deficient animals exhibited worse outcomes of infection. The absence of CCR2 had no detectable effect on neutrophils but resulted in reduction of all subsets of lung mononuclear phagocytes in the lungs, including alveolar macrophages and airway and plasmacytoid dendritic cells. In addition, absence of CCR2 skewed the phenotype of lung mononuclear phagocytes, abrogating the appearance of M1 macrophages and TNF-producing dendritic cells in the lungs. Taken together, these data define the dynamics of mononuclear phagocytes during pneumonia.

Absence of CCL2 is sufficient to restore hippocampal neurogenesis following cranial irradiation

Cranial irradiation for the treatment of brain tumors causes a delayed and progressive cognitive decline that is pronounced in young patients. Dysregulation of neural stem and progenitor cells is thought to contribute to these effects by altering early childhood brain development. Earlier work has shown that irradiation creates a chronic neuroinflammatory state that severely and selectively impairs postnatal and adult neurogenesis. Here we show that irradiation induces a transient non-classical cytokine response with selective upregulation of CCL2/monocyte chemoattractant protein-1 (MCP-1). Absence of CCL2 signaling in the hours after irradiation is alone sufficient to attenuate chronic microglia activation and allow the recovery of neurogenesis in the weeks following irradiation. This identifies CCL2 signaling as a potential clinical target for moderating the long-term defects in neural stem cell function following cranial radiation in children.

Altered immune response differentially enhances susceptibility to Cryptococcus neoformans and Cryptococcus gattii infection in mice expressing the HIV-1 transgene

Cryptococcus neoformans var. grubii is the most frequent cause of AIDS-associated cryptococcosis worldwide, while Cryptococcus gattii usually infects immunocompetent people. To understand the mechanisms which cause differential susceptibility to these cryptococcal species in HIV infection, we established and characterized a model of cryptococcosis in CD4C/HIV(MutA) transgenic (Tg) mice expressing gene products of HIV-1 and developing an AIDS-like disease. Tg mice infected intranasally with C. neoformans var. grubii strain H99 or C23 consistently displayed reduced survival compared to non-Tg mice at three graded inocula, while shortened survival of Tg mice infected with C. gattii strain R265 or R272 was restricted to a single high inoculum. HIV-1 transgene expression selectively augmented systemic dissemination to the liver and spleen for strains H99 and C23 but not strains R265 and R272. Histopathologic examination of lungs of Tg mice revealed large numbers of widely scattered H99 cells, with a minimal inflammatory cell response, while in the non-Tg mice H99 was almost completely embedded within extensive mixed inflammatory cell infiltrates. In contrast to H99, R265 was dispersed throughout the lung parenchyma and failed to induce a strong inflammatory response in both Tg and non-Tg mice. HIV-1 transgene expression reduced pulmonary production of CCL2 and CCL5 after infection with H99 or R265, and production of these two chemokines was lower after infection with R265. These results indicate that an altered immune response in these Tg mice markedly enhances C. neoformans but not C. gattii infection. This model therefore provides a powerful new tool to further investigate the immunopathogenesis of cryptococcosis.

Early induction of CCL7 downstream of TLR9 signaling promotes the development of robust immunity to cryptococcal infection

We investigated mechanisms by which TLR9 signaling promoted the development of the protective response to Cryptococcus neoformans in mice with cryptococcal pneumonia. The afferent (week 1) and efferent (week 3) phase immune parameters were analyzed in the infected wild-type (TLR9(+/+)) and TLR-deficient (TLR9(-/-)) mice. TLR9 deletion diminished 1) accumulation and activation of CD11b(+) dendritic cells (DCs), 2) the induction of IFN-γ and CCR2 chemokines CCL7, CCL12, but not CCL2, at week 1, and 3) pulmonary accumulation and activation of the major effector cells CD4(+) and CD8(+) T cells, CD11b(+) lung DCs, and exudate macrophages at week 3. The significance of CCL7 induction downstream of TLR9 signaling was investigated by determining whether CCL7 reconstitution would improve immunological parameters in C. neoformans-infected TLR9(-/-) mice. Early reconstitution with CCL7 1) improved accumulation and activation of CD11b(+) DCs at week 1, 2) restored early IFN-γ production in the lungs, and 3) restored the accumulation of major effector cell subsets. CCL7 administration abolished the difference in lung fungal burdens between TLR9(+/+) and TLR9(-/-) mice at week 3; however, significant reduction of fungal burdens between PBS- and CCL7-treated mice has not been observed, suggesting that additional mechanism(s) apart from early CCL7 induction contribute to optimal fungal clearance in TLR9(+/+) mice. Collectively, we show that TLR9 signaling during the afferent phase contributes to the development of protective immunity by promoting the early induction of CCL7 and IFN-γ and the subsequent early recruitment and activation of DCs and additional effector cells in mice with cryptococcal pneumonia.

Adaptive immunity to fungi

Only a handful of the more than 100,000 fungal species on our planet cause disease in humans, yet the number of life-threatening fungal infections in patients has recently skyrocketed as a result of advances in medical care that often suppress immunity intensely. This emerging crisis has created pressing needs to clarify immune defense mechanisms against fungi, with the ultimate goal of therapeutic applications. Herein, we describe recent insights in understanding the mammalian immune defenses deployed against pathogenic fungi. The review focuses on adaptive immune responses to the major medically important fungi and emphasizes how dendritic cells and subsets in various anatomic compartments respond to fungi, recognize their molecular patterns, and signal responses that nurture and shape the differentiation of T cell subsets and B cells. Also emphasized is how the latter deploy effector and regulatory mechanisms that eliminate these nasty invaders while also constraining collateral damage to vital tissue.

Monocyte recruitment during infection and inflammation

Monocytes originate from progenitors in the bone marrow and traffic via the bloodstream to peripheral tissues. During both homeostasis and inflammation, circulating monocytes leave the bloodstream and migrate into tissues where, following conditioning by local growth factors, pro-inflammatory cytokines and microbial products, they differentiate into macrophage or dendritic cell populations. Recruitment of monocytes is essential for effective control and clearance of viral, bacterial, fungal and protozoal infections, but recruited monocytes also contribute to the pathogenesis of inflammatory and degenerative diseases. The mechanisms that control monocyte trafficking under homeostatic, infectious and inflammatory conditions are being unravelled and are the focus of this Review.

Association of monocyte chemotactic protein-1 and CC chemokine receptor 2 gene variants with preeclampsia

Preeclampsia complicates 10% of pregnancies in developing countries. It is one of the leading causes of maternal and fetal/neonatal mortality and morbidity worldwide. It has been suggested that maladaptation of the maternal immune response during pregnancy might be a causal factor for preeclampsia. According to immune maladaptation hypothesis, preeclampsia is due to an inappropriate regulation of normally Th2-deviated maternal immune responses, leading to a shift toward harmful Th1 immunity. Several studies indicate that monocyte chemotactic protein-1 (MCP-1) and CC chemokine receptor 2 (CCR2) are involved in Th1 and Th2 immunity. In this study, we investigated the association between MCP-1 A-2518G and CCR2-V64I polymorphisms and preeclampsia. One hundred eighty preeclamptic pregnant women and 145 healthy controls were included in the study. We observed that in preeclamptic women, MCP-1 G: CCR2 Val haplotype was significantly higher when compared with other haplotypes. In conclusion, we stated that MCP-1 and CCR2 gene variants might be associated with preeclampsia.

Vitamin A modifies the intestinal chemokine and cytokine responses to norovirus infection in Mexican children

Vitamin A supplementation is associated with divergent clinical norovirus (NoV) outcomes in Mexican children. Fecal cytokine concentrations following NoV genogroup infections among 127 Mexican children 5-15 mo old enrolled in a randomized, double-blind, placebo-controlled, vitamin A supplementation trial were determined to clarify the role the gut immune response plays in these associations. Stools collected from supplemented children [20,000 IU retinol (3.3 IU = 1 μg retinol) for children < 12 mo of age; 45,000 iu for children ≥ 12 mo] or children in the placebo group were screened for NoV genogroups I (GI) and II (GII). Monocyte chemoattractant protein-1 (MCP-1), TNFα, IL-5, IL-6, IL-8, IL-4, IFNγ, and IL-10 fecal concentrations were also determined. Differences in cytokine levels between the 2 groups following GI and GII infections were determined using ordered logistic regression models. MCP-1 and IL-8 levels were greater among GI- and GII-infected children, respectively, compared with uninfected children, whereas IL-5 levels were greater following both genogroup infections. MCP-1, IL-8, and IL-6 fecal levels were reduced among supplemented children with GII-associated diarrhea compared with the placebo group. Vitamin A-supplemented, GII-infected children had reduced MCP-1 and TNFα levels compared with GII-infected children in the placebo group (P-interaction = 0.02 and 0.03, respectively). Supplemented children with GI-associated diarrhea had higher TNFα and IL-4 levels compared with children in the placebo group with diarrhea (P-interaction = 0.02 and 0.02, respectively). The divergent effects of supplementation on NoV outcomes may result from the different effects vitamin A has on the genogroup-specific immune responses.

Chemokine receptor 2-mediated accumulation of fungicidal exudate macrophages in mice that clear cryptococcal lung infection

Clearance of pulmonary infection with the fungal pathogen Cryptococcus neoformans is associated with the accumulation and activation of lung macrophages. However, the phenotype of these macrophages and the mechanisms contributing to their accumulation are not well-defined. In this study, we used an established murine model of cryptococcal lung infection and flow cytometric analysis to identify alveolar macrophages (AMs) and the recently described exudate macrophages (ExMs). Exudate macrophages are distinguished from AMs by their strong expression of CD11b and major histocompatibility complex class II and modest expression of costimulatory molecules. Exudate macrophages substantially outnumber AMs during the effector phase of the immune response; and accumulation of ExMs, but not AMs, was chemokine receptor 2 (CCR2) dependent and attributable to the recruitment and subsequent differentiation of Ly-6C(high) monocytes originating from the bone marrow and possibly the spleen. Peak ExM accumulation in wild-type (CCR2(+/+)) mice coincided with maximal lung expression of mRNA for inducible nitric oxide synthase and correlated with the known onset of cryptococcal clearance in this strain of mice. Exudate macrophages purified from infected lungs displayed a classically activated effector phenotype characterized by cryptococcal-enhanced production of inducible nitric oxide synthase and tumor necrosis factor α. Cryptococcal killing by bone marrow-derived ExMs was CCR2 independent and superior to that of AMs. We conclude that clearance of cryptococcal lung infection requires the CCR2-mediated massive accumulation of fungicidal ExMs derived from circulating Ly-6C(high) monocytes.

Tick saliva regulates migration, phagocytosis, and gene expression in the macrophage-like cell line, IC-21

We studied the effects of tick saliva on cell migration, cell signaling, phagocytosis, and gene expression in the murine macrophage cell line, IC-21. Saliva increased both basal- and platelet-derived growth factor (PDGF)-stimulated migration in IC-21 cells. However, saliva did not affect PDGF-stimulated extracellular signal-regulated kinase (ERK) activity. Zymosan-mediated interleukin-1 receptor associated kinase (IRAK) activity increased when cells were pretreated with saliva. Saliva suppressed phagocytosis of zymosan particles by IC-21 cells. An RT(2) Profiler™ PCR Array revealed that saliva regulates gene expression in a manner consistent with an immune response skewed toward a Th2 reaction, which is characterized by production of anti-inflammatory cytokines IL-4 and IL-10. Our results using IC-21 cells suggest that Dermacentor variabilis has evolved a mechanism for regulating macrophage function, which may contribute to the tick's ability to modulate immune function.

CCR2 regulates monocyte recruitment as well as CD4 T1 allorecognition after lung transplantation

Graft rejection remains a formidable problem contributing to poor outcomes after lung transplantation. Blocking chemokine pathways have yielded promising results in some organ transplant systems. Previous clinical studies have demonstrated upregulation of CCR2 ligands following lung transplantation. Moreover, lung injury is attenuated in CCR2-deficient mice in several inflammatory models. In this study, we examined the role of CCR2 in monocyte recruitment and alloimmune responses in a mouse model of vascularized orthotopic lung transplantation. The CCR2 ligand MCP-1 is upregulated in serum and allografts following lung transplantation. CCR2 is critical for the mobilization of monocytes from the bone marrow into the bloodstream and for the accumulation of CD11c(+) cells within lung allografts. A portion of graft-infiltrating recipient CD11c(+) cells expresses both recipient and donor MHC molecules. Two-photon imaging demonstrates that recipient CD11c(+) cells are associated with recipient T cells within the graft. While recipient CCR2 deficiency does not prevent acute lung rejection and is associated with increased graft infiltration by T cells, it significantly reduces CD4(+) T(h)1 indirect and direct allorecognition. Thus, CCR2 may be a potential target to attenuate alloimmune responses after lung transplantation.

CCR2 plays a critical role in dendritic cell maturation: possible role of CCL2 and NF-kappa B

We postulated that CCR2-driven activation of the transcription factor NF-kappaB plays a critical role in dendritic cell (DC) maturation (e.g., migration, costimulation, and IL-12p70 production), necessary for the generation of protective immune responses against the intracellular pathogen Leishmania major. Supporting this notion, we found that CCR2, its ligand CCL2, and NF-kappaB were required for CCL19 production and adequate Langerhans cell (LC) migration both ex vivo and in vivo. Furthermore, a role for CCR2 in upregulating costimulatory molecules was indicated by the reduced expression of CD80, CD86, and CD40 in Ccr2(-/-) bone marrow-derived dendritic cells (BMDCs) compared with wild-type (WT) BMDCs. Four lines of evidence suggested that CCR2 plays a critical role in the induction of protective immunity against L. major by regulating IL-12p70 production and migration of DC populations such as LCs. First, compared with WT, Ccr2(-/-) lymph node cells, splenocytes, BMDCs, and LCs produced lower levels of IL-12p70 following stimulation with LPS/IFN-gamma or L. major. Second, a reduced number of LCs carried L. major from the skin to the draining lymph nodes in Ccr2(-/-) mice compared with WT mice. Third, early treatment with exogenous IL-12 reversed the susceptibility to L. major infection in Ccr2(-/-) mice. Finally, disruption of IL-12p70 in radioresistant cells, such as LCs, but not in BMDCs resulted in the inability to mount a fully protective immune response in bone marrow chimeric mice. Collectively, our data point to an important role for CCR2-driven activation of NF-kappaB in the regulation of DC/LC maturation processes that regulate protective immunity against intracellular pathogens.

Antigen-presenting dendritic cells rescue CD4-depleted CCR2-/- mice from lethal Histoplasma capsulatum infection

Excessive production of interleukin-4 impairs clearance of the fungal pathogen Histoplasma capsulatum in mice lacking the chemokine receptor CCR2. An increase in the interleukin-4 level is associated with decreased recruitment of dendritic cells to lungs; therefore, we investigated the possibility that these cells influence interleukin-4 production. Adoptive transfer of wild-type or CCR2(-/-) bone marrow-derived dendritic cells loaded with heat-killed yeast cells to infected CCR2(-/-) mice suppressed interleukin-4 transcription. Surprisingly, transfer of cells did not reduce the fungal burden despite the fact that it limited interleukin-4 transcription. Yeast cell-loaded bone marrow-derived dendritic cell-mediated regulation of interleukin-4 transcription was dependent on major histocompatibility complex II antigen presentation to CD4(+) T cells. We previously showed that CD4(+) T cells were a source of interleukin-4 in infected CCR2(-/-) mice, but their contribution to the TH2 phenotype was unclear. Here we demonstrated that these cells were functionally important since elimination of them prior to infection, but not elimination of them at the time of infection, reduced the interleukin-4 level in infected CCR2(-/-) mice. However, the fungal burden was reduced only in CD4-depleted CCR2(-/-) mice that received yeast cell-loaded bone marrow-derived dendritic cells. Taken together, the data indicate that generation of excess interleukin-4 in lungs of H. capsulatum-infected CCR2(-/-) mice is at least partially a consequence of decreased recruitment of dendritic cells capable of antigen presentation. Furthermore, CD4(+) T cells had a deleterious impact on immunity in infected CCR2(-/-) mice.

Transport of Bacillus anthracis from the lungs to the draining lymph nodes is a rapid process facilitated by CD11c+ cells

Inhalational anthrax is established after inhaled Bacillus anthracis spores are transported to the lung associated lymph nodes. Dendritic cells (CD11c+ cells) located in the lungs are phagocytes that maintain many capabilities consistent with transport. This study investigates the role of dendritic cells as conduits of spores from the lung to the draining lymph nodes. The intratracheally spore-challenged mouse model of inhalational anthrax was utilized to investigate in vivo activities of CD11c+ cells. FITC labeled spores were delivered to the lungs of mice. Subsequently lung associated lymph nodes were isolated after infection and CD11c+ cells were found in association with the labeled spores. Further investigation of CD11c+ cells in early anthrax events was facilitated by use of the CD11c-diphtheria toxin (DT) receptor-green fluorescent protein transgenic mice in which CD11c+ cells can be transiently depleted by treatment with DT. We found that the presence of CD11c+ cells was necessary for efficient traffic of the spore to lung associated lymph nodes at early times after infection. Cultured dendritic cells were used to determine that these cells are capable of B. anthracis spore phagocytosis, and support germination and outgrowth. This data demonstrates that CD11c+ cells are likely carriers of B. anthracis spores from the point of inhalation in the lung to the lung associated lymph nodes. The cultured dendritic cell allows for spore germination and outgrowth supporting the concept that the CD11c+ cell responsible for this function can be a dendritic cell.

Critical protective role for MCP-1 in pneumonic Burkholderia mallei infection

Burkholderia mallei is a gram-negative bacterial pathogen of domestic equidae and humans that can cause severe, rapidly life-threatening pneumonic infections. Little is known regarding the role of chemokines and early cellular immune responses in protective immunity to pulmonary infection with B. mallei. Although the role of MCP-1 in gram-positive bacterial infections has been previously investigated, the role of MCP-1 in immunity to acute pneumonia caused by gram-negative bacteria, such as B. mallei, has not been assessed. In a mouse model of pneumonic B. mallei infection, we found that both MCP-1(-/-) mice and CCR2(-/-) mice were extremely susceptible to pulmonary infection with B. mallei, compared with wild-type (WT) C57Bl/6 mice. Bacterial burden and organ lesions were significantly increased in CCR2(-/-) mice, compared with WT animals, following B. mallei challenge. Monocyte and dendritic cell recruitment into the lungs of CCR2(-/-) mice was significantly reduced in comparison with that in WT mice following B. mallei infection, whereas neutrophil recruitment was actually increased. Depletion of monocytes and macrophages prior to infection also greatly raised the susceptibility of WT mice to infection. Production of IL-12 and IFN-gamma in the lungs after B. mallei infection was significantly impaired in both MCP-1(-/-) and CCR2(-/-) mice, whereas treatment of CCR2(-/-) mice with rIFN-gamma restored protection against lethal challenge with B. mallei. Thus, we conclude that MCP-1 plays a key role in regulating cellular immunity and IFN-gamma production following pneumonic infection with B. mallei and therefore may also figure importantly in other gram-negative pneumonias.

Accumulation of CD11b+ lung dendritic cells in response to fungal infection results from the CCR2-mediated recruitment and differentiation of Ly-6Chigh monocytes

Pulmonary clearance of the encapsulated yeast Cryptococcus neoformans is associated with the CCR2-mediated accumulation of lung dendritic cells (DC) and the development of a T1 adaptive immune response. The objective of this study was to identify the circulating DC precursor(s) responsible for this large increase in lung DC numbers. An established murine model was used to evaluate putative DC precursors in the blood, bone marrow, and lungs of CCR2(+/+) mice and CCR2(-/-) mice throughout a time course following infection with C. neoformans. Results demonstrate that numbers of Ly-6C(high) monocytes increased in parallel in the peripheral blood and lungs of CCR(+/+) mice, whereas CD11c(+) MHC class II(+) pre-DC were 10-fold less prevalent in the peripheral blood and did not differ between the two strains. Accumulation of Ly-6C(high) monocytes correlated with a substantial increase in the numbers of CD11b(+) DC in the lungs of infected CCR2(+/+) mice. Comparative phenotypic analysis of lung cells recovered in vivo suggests that Ly-6C(high) monocytes differentiate into CD11b(+) DC in the lung; differentiation is associated with up-regulation of costimulatory molecules and decreased Ly-6C expression. Furthermore, in vitro experiments confirmed that Ly-6C(high) monocytes differentiate into CD11b(+) DC. Accumulation of Ly-6C(high) monocytes and CD11b(+) DC was not attributable to their proliferation in situ. We conclude that the CCR2-mediated accumulation of CD11b(+) DC in the lungs of Cryptococcus-infected mice is primarily attributable to the continuous recruitment and differentiation of Ly-6C(high) monocytes.

The CCL7-CCL2-CCR2 axis regulates IL-4 production in lungs and fungal immunity

Expression of the chemokine receptor CCR2 can be detrimental or beneficial for infection resolution. Herein, we examined whether CCR2 was requisite for control of infection by the dimorphic fungus Histoplasma capsulatum. H. capsulatum-infected CCR2(-/-) mice manifested defects in inflammatory cell recruitment, increased IL-4, and progressive infection. Increased IL-4 in CCR2(-/-) mice primarily contributed to decreased host resistance as demonstrated by the ability of IL-4-neutralized CCR2(-/-) mice to resolve infection without altering inflammatory cell recruitment. Surprisingly, numerous alveolar macrophages and dendritic cells contributed to IL-4 production in CCR2(-/-) mice. IL-4-mediated impairment of immunity in CCR2(-/-) mice was associated with increased arginase-1 and YM1 transcription and increased transferrin receptor expression by phagocytic cells. Immunity in mice lacking the CCR2 ligand CCL2 was not impaired despite decreased inflammatory cell recruitment. Neutralization of the CCR2 ligand CCL7 in CCL2(-/-) mice, but not wild type, resulted in increased IL-4 and fungal burden. Thus, CCL7 in combination with CCL2 limits IL-4 generation and exerts control of host resistance. Furthermore, increased phagocyte-derived IL-4 in CCR2(-/-) mice is associated with the presence of alternatively activated phagocytic cells.

Role of dendritic cells and alveolar macrophages in regulating early host defense against pulmonary infection with Cryptococcus neoformans

Successful pulmonary clearance of the encapsulated yeast Cryptococcus neoformans requires a T1 adaptive immune response. This response takes up to 3 weeks to fully develop. The role of the initial, innate immune response against the organism is uncertain. In this study, an established model of diphtheria toxin-mediated depletion of resident pulmonary dendritic cells (DC) and alveolar macrophages (AM) was used to assess the contribution of these cells to the initial host response against cryptococcal infection. The results demonstrate that depletion of DC and AM one day prior to infection results in rapid clinical deterioration and death of mice within 6 days postinfection; this effect was not observed in infected groups of control mice not depleted of DC and AM. Depletion did not alter the microbial burden or total leukocyte recruitment in the lung. Mortality (in mice depleted of DC and AM) was associated with increased neutrophil and B-cell accumulation accompanied by histopathologic evidence of suppurative neutrophilic bronchopneumonia, cyst formation, and alveolar damage. Collectively, these data define an important role for DC and AM in regulating the initial innate immune response following pulmonary infection with C. neoformans. These findings provide important insight into the cellular mechanisms which coordinate early host defense against an invasive fungal pathogen in the lung.

Cryptococcal urease promotes the accumulation of immature dendritic cells and a non-protective T2 immune response within the lung

Urease, a major virulence factor for Cryptococcus neoformans, promotes lethal meningitis/encephalitis in mice. The effect of urease within the lung, the primary site of most invasive fungal infections, is unknown. An established model of murine infection that utilizes either urease-producing (wt and ure1::URE1) or urease-deficient (ure1) strains (H99) of C. neoformans was used to characterize fungal clearance and the resultant immune response evoked by these strains within the lung. Results indicate that mice infected with urease-producing strains of C. neoformans demonstrate a 100-fold increase in fungal burden beginning 2 weeks post-infection (as compared with mice infected with urease-deficient organisms). Infection with urease-producing C. neoformans was associated with a highly polarized T2 immune response as evidenced by increases in the following: 1) pulmonary eosinophils, 2) serum IgE levels, 3) T2 cytokines (interleukin-4, -13, and -4 to interferon-gamma ratio), and 4) alternatively activated macrophages. Furthermore, the percentage and total numbers of immature dendritic cells within the lung-associated lymph nodes was markedly increased in mice infected with urease-producing C. neoformans. Collectively, these data define cryptococcal urease as a pulmonary virulence factor that promotes immature dendritic cell accumulation and a potent, yet non-protective, T2 immune response. These findings provide new insights into mechanisms by which microbial factors contribute to the immunopathology associated with invasive fungal disease.