Circulatory Inflammatory Proteins as Early Diagnostic Biomarkers for Invasive Aspergillosis in Patients with Hematologic Malignancies-an Exploratory Study

OBJECTIVES

Invasive aspergillosis (IA) is a major cause of mortality in immunocompromised patients and it is difficult to diagnose because of the lack of reliable highly sensitive diagnostics. We aimed to identify circulating immunological markers that could be useful for an early diagnosis of IA.

METHODS

We collected longitudinally serum samples from 33 cases with probable/proven IA and two matched control cohorts without IA (one with microbiological and clinical evidence of bacterial or viral non-fungal pneumonia and one without evidence of infection, all matched for neutropenia, primary underlying disease, and receipt of corticosteroids/other immunosuppressants) at a tertiary university hospital. In addition, samples from an independent cohort (n = 20 cases of proven/probable IA and 20 matched controls without infection) were obtained. A panel of 92 circulating proteins involved in inflammation was measured by proximity extension assay. A random forest model was used to predict the development of IA using biomarkers measured before diagnosis.

RESULTS

While no significant differences were observed between IA cases and infected controls, concentrations of 30 inflammatory biomarkers were different between cases and non-infected controls, of which nine were independently replicated: PD-L1, MMP-10, Interleukin(IL)-10, IL-15RA, IL-18, IL-18R1, CDCP1, CCL19 and IL-17C. From the differential abundance analysis of serum samples collected more than 10 days before diagnosis and at diagnosis, increased IL-17C concentrations in IA patients were replicated in the independent cohort.

CONCLUSIONS

An increased circulating concentration of IL-17C was detected both in the discovery and independent cohort, both at the time of diagnosis and in samples 10 days before the diagnosis of IA, suggesting it should be evaluated further as potential (early) biomarker of infection.

Experimental Models of Infectious Pulmonary Complications Following Hematopoietic Cell Transplantation

Pulmonary infections remain a major cause of morbidity and mortality in hematopoietic cell transplantation (HCT) recipients. The prevalence and type of infection changes over time and is influenced by the course of immune reconstitution post-transplant. The interaction between pathogens and host immune responses is complex in HCT settings, since the conditioning regimens create periods of neutropenia and immunosuppressive drugs are often needed to prevent graft rejection and limit graft-versus-host disease (GVHD). Experimental murine models of transplantation are valuable tools for dissecting the procedure-related alterations to innate and adaptive immunity. Here we review mouse models of post-HCT infectious pulmonary complications, primarily focused on three groups of pathogens that frequently infect HCT recipients: bacteria (often P. aeruginosa), fungus (primarily Aspergillus fumigatus), and viruses (primarily herpesviruses). These mouse models have advanced our knowledge regarding how the conditioning and HCT process negatively impacts innate immunity and have provided new potential strategies of managing the infections. Studies using mouse models have also validated clinical observations suggesting that prior or occult infections are a potential etiology of noninfectious pulmonary complications post-HCT as well.

Effects of Hematopoietic Cell Transplantation on the Pulmonary Immune Response to Infection

Pulmonary infections are common in hematopoietic cell transplant (HCT) patients of all ages and are associated with high levels of morbidity and mortality. Bacterial, viral, fungal, and parasitic pathogens are all represented as causes of infection. The lung mounts a complex immune response to infection and this response is significantly affected by the pre-HCT conditioning regimen, graft characteristics, and ongoing immunomodulatory therapy. We review the published literature, including animal models as well as human data, to describe what is known about the pulmonary immune response to infection in HCT recipients. Studies have focused on the pulmonary immune response to Aspergillus fumigatus, gram-positive and gram-negative bacteria, and viruses, and show a range of defects associated with both the innate and adaptive immune responses after HCT. There are still many open areas for research, to delineate novel therapeutic targets for pulmonary infections as well as to explore linkages to non-infectious inflammatory lung conditions.

Aspergillus fumigatus Infection-Induced Neutrophil Recruitment and Location in the Conducting Airway of Immunocompetent, Neutropenic, and Immunosuppressed Mice

Susceptibility to fungal infection is commonly associated with impaired neutrophil responses. To study the mechanisms underlying this association, we investigated neutrophil recruitment to the conducting airway wall after Aspergillus fumigatus conidium inhalation in mouse models of drug-induced immunosuppression and antibody-mediated neutrophil depletion (neutropenia) by performing three-dimensional confocal laser-scanning microscopy of whole-mount primary bronchus specimens. Actin staining enabled visualization of the epithelial and smooth muscle layers that mark the airway wall. Gr-1⁺ or Ly6G⁺ neutrophils located between the epithelium and smooth muscles were considered airway wall neutrophils. The number of airway wall neutrophils for immunocompetent, immunosuppressed, and neutropenic mice before and 6 h after A. fumigatus infection were analyzed and compared. Our results show that the number of conducting airway wall neutrophils in immunocompetent mice significantly increased upon inflammation, while a dramatic reduction in this number was observed following immunosuppression and neutropenia. Interestingly, a slight increase in the infiltration of neutrophils into the airway wall was detected as a result of infection, even in immunosuppressed and neutropenic mice. Taken together, these data indicate that neutrophils are present in intact conducting airway walls and the number elevates upon A. fumigatus infection. Conducting airway wall neutrophils are affected by both neutropenia and immunosuppression.

CCR7 deficient inflammatory Dendritic Cells are retained in the Central Nervous System

Dendritic cells (DC) accumulate in the CNS during neuroinflammation, yet, how these cells contribute to CNS antigen drainage is still unknown. We have previously shown that after intracerebral injection, antigen-loaded bone marrow DC migrate to deep cervical lymph nodes where they prime antigen-specific T cells and exacerbate experimental autoimmune encephalomyelitis (EAE) in mice. Here, we report that DC migration from brain parenchyma is dependent upon the chemokine receptor CCR7. During EAE, both wild type and CCR7−/− CD11c-eYFP cells infiltrated into the CNS but cells that lacked CCR7 were retained in brain and spinal cord while wild type DC migrated to cervical lymph nodes. Retention of CCR7-deficient CD11c-eYFP cells in the CNS exacerbated EAE. These data are the first to show that CD11c^high DC use CCR7 for migration out of the CNS, and in the absence of this receptor they remain in the CNS in situ and exacerbate EAE.

A computational model of invasive aspergillosis in the lung and the role of iron

Background

Invasive aspergillosis is a severe infection of immunocompromised hosts, caused by the inhalation of the spores of the ubiquitous environmental molds of the Aspergillus genus. The innate immune response in this infection entails a series of complex and inter-related interactions between multiple recruited and resident cell populations with each other and with the fungal cell; in particular, iron is critical for fungal growth.

Results

A computational model of invasive aspergillosis is presented here; the model can be used as a rational hypothesis-generating tool to investigate host responses to this infection. Using a combination of laboratory data and published literature, an in silico model of a section of lung tissue was generated that includes an alveolar duct, adjacent capillaries, and surrounding lung parenchyma. The three-dimensional agent-based model integrates temporal events in fungal cells, epithelial cells, monocytes, and neutrophils after inhalation of spores with cellular dynamics at the tissue level, comprising part of the innate immune response. Iron levels in the blood and tissue play a key role in the fungus’ ability to grow, and the model includes iron recruitment and consumption by the different types of cells included. Parameter sensitivity analysis suggests the model is robust with respect to unvalidated parameters, and thus is a viable tool for an in silico investigation of invasive aspergillosis.

Conclusions

Using laboratory data from a mouse model of invasive aspergillosis in the context of transient neutropenia as validation, the model predicted qualitatively similar time course changes in fungal burden, monocyte and neutrophil populations, and tissue iron levels. This model lays the groundwork for a multi-scale dynamic mathematical model of the immune response to Aspergillus species.

Electronic supplementary material

The online version of this article (doi:10.1186/s12918-016-0275-2) contains supplementary material, which is available to authorized users.

Monocyte-mediated defense against bacteria, fungi, and parasites

Circulating blood monocytes are a heterogeneous leukocyte population that contributes critical antimicrobial and regulatory functions during systemic and tissue-specific infections. These include patrolling vascular tissue for evidence of microbial invasion, infiltrating peripheral tissues and directly killing microbial invaders, conditioning the inflammatory milieu at sites of microbial tissue invasion, and orchestrating the activation of innate and adaptive immune effector cells. The central focus of this review is the in vivo mechanisms by which monocytes and their derivative cells promote microbial clearance and immune regulation. We include an overview of murine models to examine monocyte functions during microbial challenges and review our understanding of the functional roles of monocytes and their derivative cells in host defense against bacteria, fungi, and parasites.

Mononuclear phagocyte-mediated antifungal immunity: the role of chemotactic receptors and ligands

Over the past two decades, fungal infections have emerged as significant causes of morbidity and mortality in patients with hematological malignancies, hematopoietic stem cell or solid organ transplantation and acquired immunodeficiency syndrome. Besides neutrophils and CD4(+) T lymphocytes, which have long been known to play an indispensable role in promoting protective antifungal immunity, mononuclear phagocytes are now being increasingly recognized as critical mediators of host defense against fungi. Thus, a recent surge of research studies has focused on understanding the mechanisms by which resident and recruited monocytes, macrophages and dendritic cells accumulate and become activated at the sites of fungal infection. Herein, we critically review how a variety of G-protein coupled chemoattractant receptors and their ligands mediate mononuclear phagocyte recruitment and effector function during infection by the most common human fungal pathogens.

Inflammatory monocytes orchestrate innate antifungal immunity in the lung

Aspergillus fumigatus is an environmental fungus that causes invasive aspergillosis (IA) in immunocompromised patients. Although -CC-chemokine receptor-2 (CCR2) and Ly6C-expressing inflammatory monocytes (CCR2⁺Mo) and their derivatives initiate adaptive pulmonary immune responses, their role in coordinating innate immune responses in the lung remain poorly defined. Using conditional and antibody-mediated cell ablation strategies, we found that CCR2⁺Mo and monocyte-derived dendritic cells (Mo-DCs) are essential for innate defense against inhaled conidia. By harnessing fluorescent Aspergillus reporter (FLARE) conidia that report fungal cell association and viability in vivo, we identify two mechanisms by which CCR2⁺Mo and Mo-DCs exert innate antifungal activity. First, CCR2⁺Mo and Mo-DCs condition the lung inflammatory milieu to augment neutrophil conidiacidal activity. Second, conidial uptake by CCR2⁺Mo temporally coincided with their differentiation into Mo-DCs, a process that resulted in direct conidial killing. Our findings illustrate both indirect and direct functions for CCR2⁺Mo and their derivatives in innate antifungal immunity in the lung.

Despite the significant impact of fungal infections to human health our understanding of immunity to these pathogens remains incomplete. Human mycoses are associated with high morbidity and mortality, even with modern antifungal therapies. Aspergillus fumigatus is the most common etiologic agent of invasive aspergillosis (IA), a serious infection that develops in immunodeficient patients. In this study we employ a combination of cell ablation strategies to examine the role of CCR2⁺Ly6C⁺ inflammatory monocytes (CCR2⁺Mo) in innate responses against a pulmonary infection with A.fumigatus conidia. We find that CCR2⁺Mo and their derivative dendritic cells (Mo-DCs) are required for defense against IA and that mice lacking these cells succumb to infection with A.fumigatus. Our studies indicate that CCR2⁺Mo and Mo-DCs exert crucial innate antifungal defense by two main mechanisms: 1) CCR2⁺Mo and Mo-DCs are a significant source of inflammatory mediators that augment the killing capacity of neutrophils and 2) conidial uptake by CCR2⁺Mo is coincident with their differentiation into Mo-DCs that directly kill fungal conidia via partially NADPH oxidase-dependent mechanisms. In aggregate, our studies find a novel essential function for CCR2⁺Mo in innate defense against a pulmonary fungal pathogen by mediating indirect and direct containment of fungal cells at the portal of infection.

A myriad of functions and complex regulation of the CCR7/CCL19/CCL21 chemokine axis in the adaptive immune system

The chemokine receptor CCR7 and its ligands CCL19 and CCL21 control a diverse array of migratory events in adaptive immune function. Most prominently, CCR7 promotes homing of T cells and DCs to T cell areas of lymphoid tissues where T cell priming occurs. However, CCR7 and its ligands also contribute to a multitude of adaptive immune functions including thymocyte development, secondary lymphoid organogenesis, high affinity antibody responses, regulatory and memory T cell function, and lymphocyte egress from tissues. In this survey, we summarise the role of CCR7 in adaptive immunity and describe recent progress in understanding how this axis is regulated. In particular we highlight CCX-CKR, which scavenges both CCR7 ligands, and discuss its emerging significance in the immune system.

Natural killer cells and antifungal host response

As a result of improved experimental methodologies and a better understanding of the immune system, there is increasing insight into the antifungal activity of natural killer (NK) cells. Murine and human NK cells are able to damage fungi of different genera and species in vitro, and they exert both direct and indirect antifungal activity through cytotoxic molecules such as perforin and through cytokines and interferons, respectively. On the other hand, recent data suggest that fungi exhibit immunosuppressive effects on NK cells. Whereas clear in vivo data are lacking in humans, the importance of NK cells in the host response against fungi has been demonstrated in animal models. Further knowledge of the interaction of NK cells with fungi might help to better understand the pathogenesis of invasive fungal infections and to improve treatment strategies.

Neutrophils mediate maturation and efflux of lung dendritic cells in response to Aspergillus fumigatus germ tubes

Invasive aspergillosis is a life-threatening complication of neutrophil deficiency or dysfunction. Neutropenia has previously been associated with enhanced influx of CD11b-expressing conventional dendritic cells to the lungs in response to Aspergillus species, but whether neutrophils directly modulate the function of dendritic cells in this infection is not known. We hypothesized that, in the setting of intrapulmonary challenge with Aspergillus, neutrophils promote the maturation and traffic of lung conventional dendritic cells to draining mediastinal lymph nodes. We report that neutropenia results in a marked accumulation of dendritic cells in the lungs of mice challenged with Aspergillus but greatly diminishes their egress to mediastinal lymph nodes independent of neutrophil microbicidal functions. Furthermore, the phenotype of lung dendritic cells was more immature in neutropenic animals than in nonneutropenic mice exposed to the microorganism. Consistent with this, coincubation with neutrophils greatly enhanced the upregulation of costimulatory molecules on dendritic cells exposed to Aspergillus in vitro, a process that was dependent on cell contact and the dendritic cell receptor DC-SIGN. Taken together, our data support an immunomodulatory cross talk between neutrophils and dendritic cells in the context of host response to Aspergillus that promotes the maturation and efflux of lung dendritic cells.

TLR3 essentially promotes protective class I-restricted memory CD8⁺ T-cell responses to Aspergillus fumigatus in hematopoietic transplanted patients

Aspergillus fumigatus is a model fungal pathogen and a common cause of severe infections and diseases. CD8⁺ T cells are present in the human and murine T-cell repertoire to the fungus. However, CD8⁺ T-cell function in infection and the molecular mechanisms that control their priming and differentiation into effector and memory cells in vivo remain elusive. In the present study, we report that both CD4⁺ and CD8⁺ T cells mediate protective memory responses to the fungus contingent on the nature of the fungal vaccine. Mechanistically, class I MHC-restricted, CD8⁺ memory T cells were activated through TLR3 sensing of fungal RNA by cross-presenting dendritic cells. Genetic deficiency of TLR3 was associated with susceptibility to aspergillosis and concomitant failure to activate memory-protective CD8⁺ T cells both in mice and in patients receiving stem-cell transplantations. Therefore, TLR3 essentially promotes antifungal memory CD8⁺ T-cell responses and its deficiency is a novel susceptibility factor for aspergillosis in high-risk patients.

Immune responses against Aspergillus fumigatus: what have we learned?

PURPOSE OF REVIEW

Aspergillus fumigatus causes invasive and allergenic disease. Host defense relies on the ability of the respiratory immune system to restrict spore germination into invasive hyphae and to limit fungus-induced or inflammation-induced damage in infected tissues. This review covers the molecular and cellular events that mediate innate and CD4 T-cell responses to A. fumigatus and fungal attributes that counter hostile microenvironments and, in turn, affect host responses.

RECENT FINDINGS

Host recognition of fungal cell wall components is critical for fungal uptake, killing, and the formation of protective innate and CD4 T-cell effector populations. Beyond the known role of neutrophils and macrophages, circulating monocytes, dendritic cells, and natural killer cells contribute to optimal defense against A. fumigatus. Genetic and pharmacologic manipulation of A. fumigatus reveals that hypoxia adaptation, cell wall assembly, and secondary metabolite production in mammalian tissues contribute to fungal pathogenesis and the outcome of infection.

SUMMARY

Greater understanding of the immune mechanisms that underlie protective responses and fungal pathways that promote microbial adaptation and growth in mammalian tissue provide a conceptual framework for improving current antifungal therapies.

IL-13 receptor α1 differentially regulates aeroallergen-induced lung responses

IL-13 and IL-4 are hallmark cytokines of Th2-associated diseases including asthma. Recent studies revealed that IL-13Rα1 regulates asthma pathogenesis by mediating both IL-4- and IL-13-mediated responses. Nonetheless, the relative contribution of each cytokine in response to aeroallergen challenge and the degree of functional dichotomy between IL-4 and IL-13 in asthma remains unclear. Consistent with prior publications, we demonstrate that IL-13Rα1 regulates aeroallergen-induced airway resistance and mucus production but not IgE and Th2 cytokine production. We demonstrate that aeroallergen-induced eosinophil recruitment and chemokine production were largely dependent on IL-13Rα1 after Aspergillus but not house dust mite (HDM) challenges. Notably, Aspergillus-challenged mice displayed increased IL-13Rα1-dependent accumulation of dendritic cell subsets into lung-draining lymph nodes in comparison with HDM-challenged mice. Comparison of IL-4 and IL-13 levels in the different experimental models revealed increased IL-4/IL-13 ratios after HDM challenge, likely explaining the IL-13Rα1-independent eosinophilia and chemokine production. Consistently, eosinophil adoptive transfer experiments revealed near ablation of lung eosinophilia in response to Aspergillus in Il13ra1(-/-) mice, suggesting that Aspergillus-induced lung eosinophil recruitment is regulated by IL-13-induced chemokine production rather than altered IL-13 signaling in eosinophils. Furthermore, the near complete protection observed in Il13ra1(-/-) mice in response to Aspergillus challenge was dependent on mucosal sensitization, as alum/Aspergillus-sensitized mice that were rechallenged with Aspergillus developed IL-13Rα1-independent eosinophilia although other asthma parameters remained IL-13Rα1 dependent. These results establish that IL-13Rα1 is required for aeroallergen-induced airway resistance and that allergen-induced chemokine production and consequent eosinophilia is dictated by the balance between IL-4 and IL-13 production in situ.

A nonredundant role for plasmacytoid dendritic cells in host defense against the human fungal pathogen Aspergillus fumigatus

While plasmacytoid dendritic cells (pDCs), a natural type I interferon (IFN)-producing cell type, are regarded as critical for innate immunity to viruses, their role in defense against fungal infections remains unknown. We examined the interactions of pDCs with hyphae of the invasive human fungal pathogen Aspergillus fumigatus. Human pDCs spread over hyphae and inhibited their growth. Antifungal activity was retained in pDC lysates, did not require direct fungal contact, and was partially reversed by zinc. Incubation with hyphae resulted in pDC cytotoxicity, partly due to fungal gliotoxin secretion. Following hyphal stimulation, pDCs released proinflammatory cytokines via a TLR9-independent mechanism. Pulmonary challenge of mice with A. fumigatus resulted in a substantial influx of pDCs into lungs, and pDC-depleted mice were hypersusceptible to invasive aspergillosis. These data demonstrate the antifungal activity of pDCs against A. fumigatus and establish their nonredundant role in host defenses against invasive aspergillosis in vivo.

Human sinonasal epithelial cells direct dendritic function and T-cell T helper 1/T helper 2 skewing following Aspergillus exposure

BACKGROUND

In lower airway disease such as asthma, epithelial cells have been shown to be potent regulators of dendritic cell (DC) functions. However, it is unclear how human sinonasal epithelial cells (HSNECs) from patients with sinusitis regulate DC functions. Therefore, in these studies we investigated the ability of Aspergillus fumigatus exposed HSNECs to regulate DC antigen uptake, maturation, and direction of T-cell T helper 1 (Th1)/Th2 skewing.

METHODS

Primary HSNECs were cultured from control (n = 8), chronic sinusitis without nasal polyps (CRSsNP) (n = 9), and chronic sinusitis with nasal polyps (CRSwNP) (n = 7) patients and exposed to Aspergillus. Conditioned media was placed upon monocyte-derived DCs from healthy controls. DC antigen uptake was assessed by dextran-fluorescein isothiocyanate (FITC) uptake. DC differentiation and maturation was assessed by immunostaining for CD209, CD80, and CD86 followed by flow cytometric analysis. DC direction of T-cell Th1/Th2 skewing was evaluated by immunostaining followed by intracellular flow cytometric analysis for interferon (IFN)-γ and interleukin (IL)-5.

RESULTS

Control and CRSsNP HSNECs have the capacity to stimulate DC antigen uptake, differentiation, and maturation following Aspergillus exposure. CRSwNP HSNECs stimulate DC activation independent of Aspergillus exposure. Furthermore, Aspergillus-exposed CRSwNP HSNECs skew T-cells toward a Th2 phenotype.

CONCLUSION

CRSwNP-derived HSNECs stimulate DC maturation and Th2 skewing independent of Aspergillus exposure. However, control and CRSsNP HSNECs induce DC maturation and Th2 skewing after Aspergillus exposure. These in vitro studies demonstrate that HSNECs are key regulators of DC functions in the sinus microenvironment.

CCR7 impairs hematopoiesis after hematopoietic stem cell transplantation increasing susceptibility to invasive aspergillosis

Hematopoietic stem cell transplantation (HSCT) is limited by patient susceptibility to opportunistic infections. One of the most devastating infections after HSCT is invasive aspergillosis (IA), a life-threatening disease caused by Aspergillus fumigatus. Transplantation of hematopoietic stem cells (HSCs) and myeloid progenitor cells (MPCs) has been shown to mediate protection against IA, but little is known about the factors that regulate HSC and MPC cell expansion after transplantation. Herein, we investigated the role of CCR7 in a murine model of IA after combined HSC and MPC transplantation into lethally irradiated wild-type (WT) mice. Nonirradiated CCR7−/− mice had expanded populations of HSCs in the bone marrow and spleen, compared with WT mice. Irradiated WT mice reconstituted with CCR7−/− HSCs and MPCs had increased survival, decreased fungal burden, and enhanced myeloid leukocyte numbers during IA, compared with WT controls. In addition, WT mice reconstituted with WT HSCs and MPCs and treated with anti-CCR7 exhibited accelerated myeloid cell expansion similar to that observed in CCR7−/−→WT chimeras. Thus, removal of the inhibitory effects of CCR7 through genetic alteration or ligand immunoneutralization enhanced myeloid reconstitution, thereby accelerating fungal clearance in a murine model of IA.

Neutropenia enhances lung dendritic cell recruitment in response to Aspergillus via a cytokine-to-chemokine amplification loop

Current understanding of specific defense mechanisms in the context of neutropenic infections is limited. It has previously been reported that invasive aspergillosis, a prototypic opportunistic infection in neutropenic hosts, is associated with marked accumulation of inflammatory dendritic cells (DCs) in the lungs. Given recent data indicating that neutrophils can modulate immune responses independent of their direct microbial killing, we hypothesized that neutropenia impacts the host response to Aspergillus by determining the migration and phenotype of lung DCs. Inflammatory DCs, but not other DC subsets, were found to accumulate in the lungs of neutropenic hosts challenged with killed or live-attenuated Aspergillus as compared with nonneutropenic hosts, indicating that the accumulation was independent of neutrophil microbicidal activity. The mechanism of this accumulation in neutropenic hosts was found to be augmented influx of DCs, or their precursors, from the blood to the lungs. This effect was attributable to greatly elevated lung TNF expression in neutropenic as compared with nonneutropenic animals. This resulted in greater lung expression of the chemokine ligands CCL2 and CCL20, which, in turn, mediated enhanced recruitment of TNF-producing inflammatory DCs, resulting in a positive feedback cycle. Finally, in the context of neutropenic invasive aspergillosis, depletion of DCs resulted in impaired fungal clearance, indicating that this mechanism is protective for the host. These observations identify what we believe is a novel defense mechanism in invasive aspergillosis that is the result of alterations in DC traffic and phenotype and is specific to neutropenic hosts.

Chemokine receptor 7 knockout attenuates atherosclerotic plaque development

BACKGROUND

Atherosclerosis is a systemic inflammatory disease characterized by the formation of atherosclerotic plaques. Both innate immunity and adaptive immunity contribute to atherogenesis, but the mode of interaction is poorly understood. Chemokine receptor 7 (CCR7) is critically involved in the transition from innate to adaptive immune activation by coordinating the migration to and positioning of antigen-presenting dendritic cells and T cells in secondary lymphoid organs. More recently, it was shown that CCR7 is also responsible for T-cell migration into inflamed tissues and T-cell egress from these tissues via the afferent lymph. Thus, we investigated the influence of a systemic CCR7 deficiency on atherogenesis in atherosclerosis-prone low-density lipoprotein receptor (ldlr) knockout mice.

METHODS AND RESULTS

CCR7 deficiency resulted in reduced atherosclerotic plaque development. CCR7(-/-) T cells showed impaired entry and exit behavior from atherosclerotic lesions. Oxidized low-density lipoprotein, a key molecule for atherogenesis with antigenic features, was used to pulse dendritic cells and to expand T cells ex vivo. Adoptive transfer of C57BL/6 wild-type T cells but not ccr7(-/-)-derived T cells primed with oxidized low-density lipoprotein-pulsed dendritic cells resulted in a reconstitution of atherogenesis in ccr7(-/-)/ldlr(-/-) mice.

CONCLUSION

These results demonstrate that both CCR7-dependent T-cell priming in secondary lymphoid organs and CCR7-dependent recirculation of T cells between secondary lymphoid organs and inflamed tissue are crucially involved in atherosclerotic plaque development.

Interaction of phagocytes with filamentous fungi

Phagocytosis of conidia by macrophages and destruction of hyphae by neutrophils are key processes in the defense against infections caused by filamentous fungi. Impairment in phagocytic function leads to increased susceptibility for an infection with Aspergillus species. The fact that a Th1-based immune response to an infection with Aspergillus species results in an improved prognosis for survival underlines the importance of the phagocytic response. Recognition of conidia by macrophages occurs after shedding of the hydrophobic rodlet layer during swelling and germination. Whereas Aspergillus conidia are killed by various immune effector cells, hyphae are in particular targeted and killed by neutrophils. Moreover, both conidia and hyphae are trapped in neutrophil extracellular traps (NETs) that form a containment to localize the infection and to prevent systemic spreading of the fungus in the host. In addition, A. fumigatus interferes with the innate immunity, with both the complement system and defense mechanisms of phagocytes, thereby evading at least in part the innate immune system.

CCR7 deficiency leads to leukocyte activation and increased clearance in response to pulmonary Pseudomonas aeruginosa infection

CCR7 is a chemokine receptor expressed on the surfaces of T cells, B cells, and mature dendritic cells that controls cell migration in response to the cognate ligands CCL19 and CCL21. CCR7 is critical for the generation of an adaptive T cell response. However, the roles of CCR7 in the host defense against pulmonary infection and innate immunity are not well understood. We investigated the role of CCR7 in the host defense against acute pulmonary infection with Pseudomonas aeruginosa. We intranasally infected C57BL/6 mice with P. aeruginosa and characterized the expression of CCR7 ligands and the surface expression of CCR7 on pulmonary leukocytes. In response to infection, expression of CCL19 and expression of CCL21 were oppositely regulated, and myeloid dendritic cells upregulated CCR7 expression. We further examined the effects of CCR7 deficiency on the inflammatory response to P. aeruginosa infection. We infected Ccr7(-/-) and wild-type mice with P. aeruginosa and characterized the accumulation of pulmonary leukocytes, production of proinflammatory mediators, neutrophil activation, and bacterial clearance. CCR7 deficiency led to an accumulation of myeloid dendritic cells and T cells in the lung in response to infection. CCR7 deficiency resulted in higher expression of CD80 and CD86 on dendritic cells; increased production of interleukin-12/23p40 (IL-12/23p40), gamma interferon (IFN-gamma), and IL-1 alpha; increased neutrophil respiratory burst; and, ultimately, increased clearance of acute P. aeruginosa infection. In conclusion, our results suggest that CCR7 deficiency results in a heightened proinflammatory environment in response to acute pulmonary P. aeruginosa infection and contributes to more efficient clearance.