CD11c+ antigen presenting cells from the alveolar space, lung parenchyma and spleen differ in their phenotype and capabilities to activate naïve and antigen-primed T cells

The role of radiotherapy in immunotherapy strategies in the central nervous system

The clinical efficacy and relative tolerability of adverse effects of immune checkpoint immunotherapy have led to its increasingly routine use in the management of multiple advanced solid malignancies. Radiation therapy (RT) is well-known to have both local and distant immunomodulatory effects, which has led to extensive investigation into the synergism of these 2 therapies. While the central nervous system (CNS) has historically been thought to be a sanctuary site, well-protected by the blood-brain barrier from the effects of immunotherapy, over the last several years studies have shown the benefits of these drugs, particularly in metastatic disease involving the CNS. This review explores current progress and the future of combination therapy with immune checkpoint inhibitors and RT.

The effect of organ-specific tumor microenvironments on response patterns to immunotherapy

Immunotherapy, particularly immune checkpoint inhibitors, have become widely used in various settings across many different cancer types in recent years. Whilst patients are often treated on the basis of the primary cancer type and clinical stage, recent studies have highlighted disparity in response to immune checkpoint inhibitors at different sites of metastasis, and their impact on overall response and survival. Studies exploring the tumor immune microenvironment at different organ sites have provided insights into the immune-related mechanisms behind organ-specific patterns of response to immunotherapy. In this review, we aimed to highlight the key learnings from clinical studies across various cancers including melanoma, lung cancer, renal cell carcinoma, colorectal cancer, breast cancer and others, assessing the association of site of metastasis and response to immune checkpoint inhibitors. We also summarize the key clinical and pre-clinical findings from studies exploring the immune microenvironment of specific sites of metastasis. Ultimately, further characterization of the tumor immune microenvironment at different metastatic sites, and understanding the biological drivers of these differences, may identify organ-specific mechanisms of resistance, which will lead to more personalized treatment approaches for patients with innate or acquired resistance to immunotherapy.

Impact of intrarectal chromofungin treatment on dendritic cells-related markers in different immune compartments in colonic inflammatory conditions

BACKGROUND

Chromofungin (CHR: chromogranin-A 47-66) is a chromogranin-A derived peptide with anti-inflammatory and anti-microbial properties. Ulcerative colitis (UC) is characterized by a colonic decrease of CHR and a dysregulation of dendritic CD11c⁺ cells.

AIM

To investigate the association between CHR treatment and dendritic cells (DCs)-related markers in different immune compartments in colitis.

METHODS

A model of acute UC-like colitis using dextran sulphate sodium (DSS) was used in addition to biopsies collected from UC patients.

RESULTS

Intrarectal CHR treatment reduced the severity of DSS-induced colitis and was associated with a significant decrease in the expression of CD11c, CD40, CD80, CD86 and interleukin (IL)-12p40 in the inflamed colonic mucosa and CD11c, CD80, CD86 IL-6 and IL-12p40 within the mesenteric lymph nodes and the spleen. Furthermore, CHR treatment decreased CD80 and CD86 expression markers of splenic CD11c⁺ cells and decreased NF-κB expression in the colon and of splenic CD11c⁺ cells. In vitro, CHR decreased CD40, CD80, CD86 IL-6 and IL-12p40 expression in naïve bone marrow-derived CD11c⁺ DCs stimulated with lipopolysaccharide. Pharmacological studies demonstrated an impact of CHR on the NF-κB pathway. In patients with active UC, CHR level was reduced and showed a negative linear relationship with CD11c and CD86.

CONCLUSION

CHR has protective properties against intestinal inflammation via the regulation of DC-related markers and CD11c⁺ cells. CHR could be a potential therapy of UC.

Combined Toxicity of Metal Nanoparticles: Comparison of Individual and Mixture Particles Effect

Toxicity of metal nanoparticles (NPs) are closely associated with increasing intracellular reactive oxygen species (ROS) and the levels of pro-inflammatory mediators. However, NP interactions and surface complexation reactions alter the original toxicity of individual NPs. To date, toxicity studies on NPs have mostly been focused on individual NPs instead of the combination of several species. It is expected that the amount of industrial and highway-acquired NPs released into the environment will further increase in the near future. This raises the possibility that various types of NPs could be found in the same medium, thereby, the adverse effects of each NP either could be potentiated, inhibited or remain unaffected by the presence of the other NPs. After uptake of NPs into the human body from various routes, protein kinases pathways mediate their toxicities. In this context, family of mitogen-activated protein kinases (MAPKs) is mostly efficient. Despite each NP activates almost the same metabolic pathways, the toxicity induced by a single type of NP is different than the case of co-exposure to the combined NPs. The scantiness of toxicological data on NPs combinations displays difficulties to determine, if there is any risk associated with exposure to combined nanomaterials. Currently, in addition to mathematical analysis (Response surface methodology; RSM), the quantitative-structure-activity relationship (QSAR) is used to estimate the toxicity of various metal oxide NPs based on their physicochemical properties and levels applied. In this chapter, it is discussed whether the coexistence of multiple metal NPs alter the original toxicity of individual NP. Additionally, in the part of "Toxicity of diesel emission/exhaust particles (DEP)", the known individual toxicity of metal NPs within the DEP is compared with the data regarding toxicity of total DEP mixture.

Corrected Super-Resolution Microscopy Enables Nanoscale Imaging of Autofluorescent Lung Macrophages

Observing the cell surface and underlying cytoskeleton at nanoscale resolution using super-resolution microscopy has enabled many insights into cell signaling and function. However, the nanoscale dynamics of tissue-specific immune cells have been relatively little studied. Tissue macrophages, for example, are highly autofluorescent, severely limiting the utility of light microscopy. Here, we report a correction technique to remove autofluorescent noise from stochastic optical reconstruction microscopy (STORM) data sets. Simulations and analysis of experimental data identified a moving median filter as an accurate and robust correction technique, which is widely applicable across challenging biological samples. Here, we used this method to visualize lung macrophages activated through Fc receptors by antibody-coated glass slides. Accurate, nanoscale quantification of macrophage morphology revealed that activation induced the formation of cellular protrusions tipped with MHC class I protein. These data are consistent with a role for lung macrophage protrusions in antigen presentation. Moreover, the tetraspanin protein CD81, known to mark extracellular vesicles, appeared in ring-shaped structures (mean diameter 93 ± 50 nm) at the surface of activated lung macrophages. Thus, a moving median filter correction technique allowed us to quantitatively analyze extracellular secretions and membrane structure in tissue-derived immune cells.

No pathogenic responses in rat lung upon exposure to ground granulated blast furnace slag (GGBS)

Objective: Granulated blast furnace slag (GBS) is a by-product of the manufacture of iron by thermochemical reduction in a blast furnace. Blast furnace slag is generated at temperatures above 1500 °C. If the liquid slag is quenched very rapidly with water, a glassy slag is generated (GBS). It is used - after grinding <100 µm - [ground granulated blast furnace slag (GGBS)] for cement and concrete production. A small particulate fraction of GGBS might be accessible to the pulmonary alveoli, where it could settle down and induces physiological inflammatory responses. Within the scope of the 'Registration, Evaluation, Authorization and Restriction of Chemicals' (REACH), GGBS was already tested in rats in an acute toxicity inhalation study, as well as in a dose range finding study as a predecessor study for this study. Both did not show systemic and local toxic effect in rats upon inhalation of high-dose GGBS.Material and methods: In this study, low (4.3 mg/m³), intermediate (9.5 mg/m³), and high-dose (24.9 mg/m³) repetitive exposure of GGBS to rats was tested over a period of 4 weeks with 6 h exposure per day for 5 days per week. Results and conclusion: Even at high doses, GGBS was inactive and did not induce clinically relevant phenotypic changes in rats compared to concomitant controls.Together with both the previous acute toxicity and the dose range finding study in rats, it was shown that the exposure to the tested GGBS was unable to induce any severe pathogenic responses.

Participation of Tumor-Associated Myeloid Cells in Progression of Amelanotic Melanoma (RMM Tumor Line) in F344 Rats, with Particular Reference to MHC Class II- and CD163-Expressing Cells

Tumor progression is often influenced by infiltration of myeloid cells; depending on the M1- or M2-like activation status, these cells may have either inhibitory or promoting effects on tumor growth. We investigated the properties of tumor-associated myeloid cells in a previously established homotransplantable amelanotic melanoma (RMM tumor line) in F344 rats. RMM tumor nodules were allowed to reach the sizes of 0.5, 1, 2 and 3 cm, respectively. Immunohistochemistry and flow cytometry was performed for macrophage markers CD68 and CD163, and for the antigen-presenting cell marker, MHC class II. Although no significant change was observed in the number of CD68⁺ and CD163⁺ macrophages during RMM progression, the number of MHC class II⁺ antigen-presenting cells was reduced in 3 cm nodules. Real-time RT-PCR of laser microdissection samples obtained from RMM regions rich in MHC class II⁺ cells demonstrated high expressions of M1-like factors: IFN-γ, GM-CSF and IL-12a. Furthermore, fluorescence-activated cell sorting, followed by real-time RT-PCR for CD11b⁺ MHC class II⁺ (myeloid antigen-presenting cells), CD11b⁺ CD163⁺ (M2 type myeloid cells), CD11b⁺ CD80⁺ (M1 type myeloid cells) and CD11b⁺ CD11c⁺ (dendritic cells) cells was performed. Based on the levels of inflammation- and tumor progression-related factors, MHC class II⁺ antigen-presenting cells showed polarization towards M1, while CD163⁺ macrophages, towards M2. CD80⁺ and CD11c⁺ myeloid cells did not show clear functional polarization. Our results provide novel information on tumor-associated myeloid cells in amelanotic melanoma, and may become useful in further research on melanoma immunity.

Modulation of the immune response to respiratory viruses by vitamin D

Background: Vitamin D deficiency has been shown to be independently associated with increased risk of viral acute respiratory infection (ARI) in a number of observational studies, and meta-analysis of clinical trials of vitamin D supplementation for prevention of ARI has demonstrated protective effects. Several cellular studies have investigated the effects of vitamin D metabolites on immune responses to respiratory viruses, but syntheses of these reports are lacking. Scope: In this article, we review the literature reporting results of in vitro experiments investigating immunomodulatory actions of vitamin D metabolites in human respiratory epithelial cells infected with respiratory viruses. Key findings: Vitamin D metabolites do not consistently influence replication or clearance of rhinovirus, respiratory syncytial virus (RSV) or influenza A virus in human respiratory epithelial cell culture, although they do modulate expression and secretion of type 1 interferon, chemokines including CXCL8 and CXCL10 and pro-inflammatory cytokines, such as TNF and IL-6. Future research: More studies are needed to clarify the effects of vitamin D metabolites on respiratory virus-induced expression of cell surface markers mediating viral entry and bacterial adhesion to respiratory epithelial cells.

Asymptomatic HIV-infected individuals on antiretroviral therapy exhibit impaired lung CD4(+) T-cell responses to mycobacteria

RATIONALE

HIV-infected persons on antiretroviral therapy (ART) remain at higher risk of pulmonary tuberculosis (TB) than HIV-uninfected individuals. This increased susceptibility may be caused by impairment of alveolar macrophage (AM) function and/or mycobacteria-specific alveolar CD4(+) T-cell responses observed in HIV-infected ART-naive adults.

OBJECTIVES

To determine whether ART was associated with improvement in both AM function, assessed by phagosomal proteolysis, and alveolar CD4(+) T-cell responses to Mycobacterium in HIV-infected individuals.

METHODS

Peripheral blood was drawn and bronchoalveolar lavage (BAL) performed on healthy, 35 HIV-uninfected, 25 HIV-infected ART-naive, and 50 HIV-infected ART-treated asymptomatic adults. Phagosomal proteolysis of AM was assessed with fluorogenic beads. Mycobacteria-specific CD4(+) T-cell responses were measured by intracellular cytokine staining.

MEASUREMENTS AND MAIN RESULTS

HIV-infected adults on ART exhibited lower plasma HIV viral load and higher blood CD4(+) T-cell count than ART-naive adults. AM proteolysis and total mycobacteria-specific Th1 CD4(+) T-cell responses in individuals on ART for greater than or equal to 4 years were similar to HIV-uninfected control subjects but those on ART for less than 4 years had impaired responses. Total influenza-specific alveolar Th1 CD4(+) T-cell responses were intact in all individuals receiving ART. In contrast, BAL and blood mycobacteria-specific polyfunctional CD4(+) T-cell responses were impaired in adults on ART irrespective of duration.

CONCLUSIONS

AM and mycobacteria-specific alveolar CD4(+) T-cell responses in HIV-infected adults on ART for less than 4 years are impaired and may partly explain the high risk of TB in HIV-infected individuals on ART. Strategies to augment ART to improve lung immune cell function and reduce the high incidence of TB in HIV-infected adults who initiate ART should be investigated.

Pulmonary M. tuberculosis infection delays Th1 immunity via immunoadaptor DAP12-regulated IRAK-M and IL-10 expression in antigen-presenting cells

Interaction of mycobacteria with the host leads to retarded expression of T helper cell type 1 (Th1) immunity in the lung. However, the immune mechanisms remain poorly understood. Using in vivo and in vitro models of Mycobacterium tuberculosis (M. tb) infection, we find the immunoadaptor DAP12 (DNAX-activating protein of 12 kDa) in antigen-presenting cells (APCs) to be critically involved in this process. Upon infection of APCs, DAP12 is required for IRAK-M (interleukin-1 receptor-associated kinase M) expression, which in turn induces interleukin-10 (IL-10) and an immune-suppressed phenotype of APCs, thus leading to suppressed Th1 cell activation. Lack of DAP12 reduces APC IL-10 production and increases their Th1 cell-activating capability, resulting in expedited Th1 responses and enhanced protection. On the other hand, adoptively transferred DAP12-competent APCs suppress Th1 cell activation within DAP12-deficient hosts, and blockade of IL-10 aborts the ability of DAP12-competent APCs to suppress Th1 activation. Our study identifies the DAP12/IRAK-M/IL-10 to be a novel molecular pathway in APCs exploited by mycobacterial pathogens, allowing infection a foothold in the lung.

Diverse macrophage populations mediate acute lung inflammation and resolution

Acute respiratory distress syndrome (ARDS) is a devastating disease with distinct pathological stages. Fundamental to ARDS is the acute onset of lung inflammation as a part of the body's immune response to a variety of local and systemic stimuli. In patients surviving the inflammatory and subsequent fibroproliferative stages, transition from injury to resolution and recovery is an active process dependent on a series of highly coordinated events regulated by the immune system. Experimental animal models of acute lung injury (ALI) reproduce key components of the injury and resolution phases of human ARDS and provide a methodology to explore mechanisms and potential new therapies. Macrophages are essential to innate immunity and host defense, playing a featured role in the lung and alveolar space. Key aspects of their biological response, including differentiation, phenotype, function, and cellular interactions, are determined in large part by the presence, severity, and chronicity of local inflammation. Studies support the importance of macrophages to initiate and maintain the inflammatory response, as well as a determinant of resolution of lung inflammation and repair. We will discuss distinct roles for lung macrophages during early inflammatory and late resolution phases of ARDS using experimental animal models. In addition, each section will highlight human studies that relate to the diverse role of macrophages in initiation and resolution of ALI and ARDS.

An innovative approach to induce cross-protective immunity against porcine reproductive and respiratory syndrome virus in the lungs of pigs through adjuvanted nanotechnology-based vaccination

Porcine reproductive and respiratory syndrome (PRRS) is an economically devastating respiratory disease of pigs. The disease is caused by the PRRS virus (PRRSV), an Arterivirus which is a highly mutating RNA virus. Widely used modified live PRRSV vaccines have failed to prevent PRRS outbreaks and reinfections; moreover, safety of the live virus vaccines is questionable. Though poorly immunogenic, inactivated PRRSV vaccine is safe. The PRRSV infects primarily the lung macrophages. Therefore, we attempted to strengthen the immunogenicity of inactivated/killed PRRSV vaccine antigens (KAg), especially in the pig respiratory system, through: 1) entrapping the KAg in biodegradable poly(lactic-co-glycolic acid) nanoparticles (NP-KAg); 2) coupling the NP-KAg with a potent mucosal adjuvant, whole cell lysate of Mycobacterium tuberculosis (M. tb WCL); and 3) delivering the vaccine formulation twice intranasally to growing pigs. We have previously shown that a single dose of NP-KAg partially cleared the challenged heterologous PRRSV. Recently, we reported that NP-KAg coupled with unentrapped M. tb WCL significantly cleared the viremia of challenged heterologous PRRSV. Since PRRSV is primarily a lung disease, our goal in this study was to investigate lung viral load and various immune correlates of protection at the lung mucosal surfaces and its parenchyma in vaccinated heterologous PRRSV-challenged pigs. Our results indicated that out of five different vaccine-adjuvant formulations, the combination of NP-KAg and unentrapped M. tb WCL significantly cleared detectable replicating infective PRRSV with a tenfold reduction in viral RNA load in the lungs, associated with substantially reduced gross and microscopic lung pathology. Immunologically, strong humoral (enhanced virus neutralization titers by high avidity antibodies) and cell-mediated immune responses (augmented population of interferon-γ secreting CD4(+) and CD8(+) lymphocytes and reduced secretion of immunosuppressive cytokines) in the lungs were observed. In conclusion, combination of NP-KAg and soluble M. tb WCL elicits broadly cross-protective anti-PRRSV immunity in the pig respiratory system.

Regulation of macrophage and dendritic cell function by pathogens and through immunomodulation in the avian mucosa

Macrophages (MPh) and dendritic cells (DC) are members of the mononuclear phagocyte system. In chickens, markers to distinguish MPh from DC are lacking, but whether MPh and DC can be distinguished in humans and mice is under debate, despite the availability of numerous markers. Mucosal MPh and DC are strategically located to ingest foreign antigens, suggesting they can rapidly respond to invading pathogens. This review addresses our current understanding of DC and MPh function, the receptors expressed by MPh and DC involved in pathogen recognition, and the responses of DC and MPh against respiratory and intestinal pathogens in the chicken. Furthermore, potential opportunities are described to modulate MPh and DC responses to enhance disease resistance, highlighting modulation through nutraceuticals and vaccination.

RGD capsid modification enhances mucosal protective immunity of a non-human primate adenovirus vector expressing Pseudomonas aeruginosa OprF

Replication-deficient adenoviral (Ad) vectors of non-human serotypes can serve as Ad vaccine platforms to circumvent pre-existing anti-human Ad immunity. We found previously that, in addition to that feature, a non-human primate-based AdC7 vector expressing outer membrane protein F of P. aeruginosa (AdC7OprF) was more potent in inducing lung mucosal and protective immunity compared to a human Ad5-based vector. In this study we analysed if genetic modification of the AdC7 fibre to display an integrin-binding arginine-glycine-aspartic acid (RGD) sequence can further enhance lung mucosal immunogenicity of AdC7OprF. Intratracheal immunization of mice with either AdC7OprF.RGD or AdC7OprF induced robust serum levels of anti-OprF immunoglobulin (Ig)G up to 12 weeks that were higher compared to immunization with the human vectors Ad5OprF or Ad5OprF.RGD. OprF-specific cellular responses in lung T cells isolated from mice immunized with AdC7OprF.RGD and AdC7OprF were similar for T helper type 1 (Th1) [interferon (IFN)-γ in CD8(+) and interleukin (IL)-12 in CD4(+)], Th2 (IL-4, IL-5 and IL-13 in CD4(+)) and Th17 (IL-17 in CD4(+)). Interestingly, AdC7OprF.RGD induced more robust protective immunity against pulmonary infection with P. aeruginosa compared to AdC7OprF or the control Ad5 vectors. The enhanced protective immunity induced by AdC7OprF.RGD was maintained in the absence of alveolar macrophages (AM) or CD1d natural killer T cells. Together, the data suggest that addition of RGD to the fibre of an AdC7-based vaccine is useful to enhance its mucosal protective immunogenicity.

Differentially imprinted innate immunity by mucosal boost vaccination determines antituberculosis immune protective outcomes, independent of T-cell immunity

Homologous and heterologous parenteral prime-mucosal boost immunizations have shown great promise in combating mucosal infections such as tuberculosis and AIDS. However, their immune mechanisms remain poorly defined. In particular, it is still unclear whether T-cell and innate immunity may be independently affected by these immunization modalities and how it impacts immune protective outcome. Using two virus-based tuberculosis vaccines (adenovirus (Ad) and vesicular stomatitis virus (VSV) vectors), we found that while both homologous (Ad/Ad) and heterologous (Ad/VSV) respiratory mucosal boost immunizations elicited similar T-cell responses in the lung, they led to drastically different immune protective outcomes. Compared with Ad-based boosting, VSV-based boosting resulted in poorly enhanced protection against tuberculosis. Such inferior protection was associated with differentially imprinted innate phagocytes, particularly the CD11c(+)CD11b(+/-) cells, in the lung. We identified heightened type 1 interferon (IFN) responses to be the triggering mechanism. Thus, increased IFN-β severely blunted interleukin-12 responses in infected phagocytes, which in turn impaired their nitric oxide production and antimycobacterial activities. Our study reveals that vaccine vectors may differentially imprint innate cells at the mucosal site of immunization, which can impact immune-protective outcome, independent of T-cell immunity, and it is of importance to determine both T-cell and innate cell immunity in vaccine studies.

Alveolar epithelial cells are critical in protection of the respiratory tract by secretion of factors able to modulate the activity of pulmonary macrophages and directly control bacterial growth

The respiratory epithelium is a physical and functional barrier actively involved in the clearance of environmental agents. The alveolar compartment is lined with membranous pneumocytes, known as type I alveolar epithelial cells (AEC I), and granular pneumocytes, type II alveolar epithelial cells (AEC II). AEC II are responsible for epithelial reparation upon injury and ion transport and are very active immunologically, contributing to lung defense by secreting antimicrobial factors. AEC II also secrete a broad variety of factors, such as cytokines and chemokines, involved in activation and differentiation of immune cells and are able to present antigen to specific T cells. Another cell type important in lung defense is the pulmonary macrophage (PuM). Considering the architecture of the alveoli, a good communication between the external and the internal compartments is crucial to mount effective responses. Our hypothesis is that being in the interface, AEC may play an important role in transmitting signals from the external to the internal compartment and in modulating the activity of PuM. For this, we collected supernatants from AEC unstimulated or stimulated in vitro with lipopolysaccharide (LPS). These AEC-conditioned media were used in various setups to test for the effects on a number of macrophage functions: (i) migration, (ii) phagocytosis and intracellular control of bacterial growth, and (iii) phenotypic changes and morphology. Finally, we tested the direct effect of AEC-conditioned media on bacterial growth. We found that AEC-secreted factors had a dual effect, on one hand controlling bacterial growth and on the other hand increasing macrophage activity.

IL-36α exerts pro-inflammatory effects in the lungs of mice

Interleukin (IL-) 36 cytokines (previously designated as novel IL-1 family member cytokines; IL-1F5- IL-1F10) constitute a novel cluster of cytokines structurally and functionally similar to members of the IL-1 cytokine cluster. The effects of IL-36 cytokines in inflammatory lung disorders remains poorly understood. The current study sought to investigate the effects of IL-36α (IL-1F6) and test the hypothesis that IL-36α acts as a pro-inflammatory cytokine in the lung in vivo. Intratracheal instillation of recombinant mouse IL-36α induced neutrophil influx in the lungs of wild-type C57BL/6 mice and IL-1αβ(-/-) mice in vivo. IL-36α induced neutrophil influx was also associated with increased mRNA expression of neutrophil-specific chemokines CXCL1 and CXCL2 in the lungs of C57BL/6 and IL-1αβ(-/-) mice in vivo. In addition, intratracheal instillation of IL-36α enhanced mRNA expression of its receptor IL-36R in the lungs of C57BL/6 as well as IL-1αβ(-/-) mice in vivo. Furthermore, in vitro incubation of CD11c(+) cells with IL-36α resulted in the generation of neutrophil-specific chemokines CXCL1, CXCL2 as well as TNFα. IL-36α increased the expression of the co-stimulatory molecule CD40 and enhanced the ability of CD11c(+) cells to induce CD4(+) T cell proliferation in vitro. Furthermore, stimulation with IL-36α activated NF-κB in a mouse macrophage cell line. These results demonstrate that IL-36α acts as a pro-inflammatory cytokine in the lung without the contribution of IL-1α and IL-1β. The current study describes the pro-inflammatory effects of IL-36α in the lung, demonstrates the functional redundancy of IL-36α with other agonist cytokines in the IL-1 and IL-36 cytokine cluster, and suggests that therapeutic targeting of IL-36 cytokines could be beneficial in inflammatory lung diseases.

Virus-like particle-induced protection against MRSA pneumonia is dependent on IL-13 and enhancement of phagocyte function

The importance of the priming of the lung environment by past infections is being increasingly recognized. Exposure to any given antigen can either improve or worsen the outcome of subsequent lung infections, depending on the immunological history of the host. Thus, an ability to impart transient alterations in the lung environment in anticipation of future insult could provide an important novel therapy for emerging infectious diseases. In this study, we show that nasal administration of virus-like particles (VLPs) before, or immediately after, lethal challenge with methicillin-resistant Staphylococcus aureus (MRSA) of mice i) ensures complete recovery from lung infection and near absolute clearance of bacteria within 12 hours of challenge, ii) reduces host response-induced lung tissue damage, iii) promotes recruitment and efficient bacterial clearance by neutrophils and CD11c⁺ cells, and iv) protects macrophages from MRSA-induced necrosis. VLP-mediated protection against MRSA relied on innate immunity. Complete recovery occurred in VLP-dosed mice with severe combined immunodeficiency, but not in wild-type mice depleted of either Ly6G⁺ or CD11c⁺ cells. Early IL-13 production associated with VLP-induced CD11c⁺ cells was essential for VLP-induced protection. These results indicate that VLP-induced alteration of the lung environment protects the host from lethal MRSA pneumonia by enhancing phagocyte recruitment and killing and by reducing inflammation-induced tissue damage via IL-13–dependent mechanisms.

Understanding delayed T-cell priming, lung recruitment, and airway luminal T-cell responses in host defense against pulmonary tuberculosis

Mycobacterium tuberculosis (M.tb), the causative bacterium of pulmonary tuberculosis (TB), is a serious global health concern. Central to M.tb effective immune avoidance is its ability to modulate the early innate inflammatory response and prevent the establishment of adaptive T-cell immunity for nearly three weeks. When compared with other intracellular bacterial lung pathogens, such as Legionella pneumophila, or even closely related mycobacterial species such as M. smegmatis, this delay is astonishing. Customarily, the alveolar macrophage (AM) acts as a sentinel, detecting and alerting surrounding cells to the presence of an invader. However, in the case of M.tb, this may be impaired, thus delaying the recruitment of antigen-presenting cells (APCs) to the lung. Upon uptake by APC populations, M.tb is able to subvert and delay the processing of antigen, MHC class II loading, and the priming of effector T cell populations. This delay ultimately results in the deferred recruitment of effector T cells to not only the lung interstitium but also the airway lumen. Therefore, it is of upmost importance to dissect the mechanisms that contribute to the delayed onset of immune responses following M.tb infection. Such knowledge will help design the most effective vaccination strategies against pulmonary TB.

Pulmonary mycobacterial granuloma increased IL-10 production contributes to establishing a symbiotic host-microbe microenvironment

The granuloma, a hallmark of host defense against pulmonary mycobacterial infection, has long been believed to be an active type 1 immune environment. However, the mechanisms regarding why granuloma fails to eliminate mycobacteria even in immune-competent hosts, have remained largely unclear. By using a model of pulmonary Mycobacterium bovis Bacillus Calmette-Guerin (BCG) infection, we have addressed this issue by comparing the immune responses within the airway luminal and granuloma compartments. We found that despite having a similar immune cellular profile to that in the airway lumen, the granuloma displayed severely suppressed type 1 immune cytokine but enhanced chemokine responses. Both antigen-presenting cells (APCs) and T cells in granuloma produced fewer type 1 immune molecules including tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), and nitric oxide. As a result, the granuloma APCs developed a reduced capacity to phagocytose mycobacteria and to induce T-cell proliferation. To examine the molecular mechanisms, we compared the levels of immune suppressive cytokine IL-10 in the airway lumen and granuloma and found that both granuloma APCs and T cells produced much more IL-10. Thus, IL-10 deficiency restored type 1 immune activation within the granuloma while having a minimal effect within the airway lumen. Hence, our study provides the first experimental evidence that, contrary to the conventional belief, the BCG-induced lung granuloma represents a symbiotic host-microbe microenvironment characterized by suppressed type 1 immune activation.

Murine airway luminal antituberculosis memory CD8 T cells by mucosal immunization are maintained via antigen-driven in situ proliferation, independent of peripheral T cell recruitment

RATIONALE

The airway luminal memory CD8 T cells induced by respiratory mucosal immunization in a murine model have been found to be critical to antituberculosis immunity. However, the mechanisms of their maintenance on airway mucosal surface still remain poorly understood.

OBJECTIVES

Using a model of adenovirus-based intranasal immunization we investigated the immune property and the mechanisms of maintenance of airway luminal CD8 T cells.

METHODS

Immune properties of airway luminal Mycobacterium tuberculosis antigen-specific CD8 T cells were examined. Proliferation of airway luminal CD8 T cells was determined by in vivo T cell-labeling techniques. The role of peripheral T cell recruitment in maintaining airway luminal CD8 T cells was investigated by blocking lymphocyte trafficking from lymphoid and peripheral tissues. The requirement of M. tuberculosis antigens for in situ T cell proliferation was evaluated using a T cell transfer approach. An airway M. tuberculosis challenge model was used to study the relationship between CD8 T cell-mediated protection and peripheral T cell recruitment.

MEASUREMENTS AND MAIN RESULTS

Intranasal immunization leads to elicitation of persisting M. tuberculosis antigen-specific CD8 T cells in the airway lumen, which display an activated effector memory phenotype different from those in peripheral tissues. Airway luminal T cells continuously proliferate in an antigen-dependent manner, and can be maintained even in the absence of peripheral T cell recruitment. The lungs equipped with such CD8 T cells are protected from airway M. tuberculosis challenge independent of both peripheral T cell supply and CD4 T cells.

CONCLUSIONS

Vaccine-inducible airway luminal antituberculosis memory CD8 T cells are self-renewable in an antigen-dependent manner, and can be maintained independent of peripheral T cell supply.

Immunological response to (1,4)-alpha-D-glucan in the lung and spleen of endotoxin-stimulated juvenile rats

We investigated the effects of (1,4)-alpha-D-glucan (alpha-DG), a novel immune stimulatory drug from Tinospora cordifolia, on the concentration of pro- and anti-inflammatory cytokines (interleukin [IL]-1beta, IL-6, tumour necrosis factor-alpha [TNF-alpha], gamma-interferon [IFN-gamma] and IL-10) in the lung and spleen of endotoxin-stimulated juvenile rats. Experimental groups (n = 16/group) included controls with an intraperitoneal injection of saline, endotoxaemic rats with a non-lethal dose of 10 mg/kg Escherichia coli endotoxin, and endotoxaemic rats treated with two doses of 10 mg/kg alpha-DG, intraperitoneally, 2 and 4 hr after endotoxin injection. At 24 hr of treatment, rats were euthanized and lungs and spleen were removed for cytokines determination and lung injury. Endotoxaemia increased IL-1beta concentration by fivefold in both organs, while creating a moderate pulmonary hypercellularity (demonstrated by about 11% increase in the alveolar-septal thickening and 11% decrease in the alveolar-interstitial space ratio). In the lung, alpha-DG treatment reduced concentrations of IL-1beta by 30% (p > 0.05), IL-6 by 43% (p < 0.01), IFN-gamma by 46% (p < 0.01) and the anti-inflammatory cytokine, IL-10, by 31% (p > 0.05) compared to endotoxaemia. In the spleen, alpha-DG treatment decreased the ratio of IL-1beta to IL-10 by 55% (p < 0.05), demonstrating an anti-inflammatory trend. These data suggest that alpha-DG differentially modulates cytokine response in the lung and spleen and modifies the pro- and anti-inflammatory balance during an early period of endotoxaemia in juvenile rats.

Intranasal mucosal boosting with an adenovirus-vectored vaccine markedly enhances the protection of BCG-primed guinea pigs against pulmonary tuberculosis

Background

Recombinant adenovirus-vectored (Ad) tuberculosis (TB) vaccine platform has demonstrated great potential to be used either as a stand-alone or a boost vaccine in murine models. However, Ad TB vaccine remains to be evaluated in a more relevant and sensitive guinea pig model of pulmonary TB. Many vaccine candidates shown to be effective in murine models have subsequently failed to pass the test in guinea pig models.

Methods and Findings

Specific pathogen-free guinea pigs were immunized with BCG, AdAg85A intranasally (i.n), AdAg85A intramuscularly (i.m), BCG boosted with AdAg85A i.n, BCG boosted with AdAg85A i.m, or treated only with saline. The animals were then infected by a low-dose aerosol of M. tuberculosis (M.tb). At the specified times, the animals were sacrificed and the levels of infection in the lung and spleen were assessed. In separate studies, the long-term disease outcome of infected animals was monitored until the termination of this study. Immunization with Ad vaccine alone had minimal beneficial effects. Immunization with BCG alone and BCG prime-Ad vaccine boost regimens significantly reduced the level of M.tb infection in the tissues to a similar extent. However, while BCG alone prolonged the survival of infected guinea pigs, the majority of BCG-immunized animals succumbed by 53 weeks post-M.tb challenge. In contrast, intranasal or intramuscular Ad vaccine boosting of BCG-primed animals markedly improved the survival rate with 60% of BCG/Ad i.n- and 40% of BCG/Ad i.m-immunized guinea pigs still surviving by 74 weeks post-aerosol challenge.

Conclusions

Boosting, particularly via the intranasal mucosal route, with AdAg85A vaccine is able to significantly enhance the long-term survival of BCG-primed guinea pigs following pulmonary M.tb challenge. Our results thus support further evaluation of this viral-vectored TB vaccine in clinical trials.