Mediator responses of alveolar macrophages and kinetics of mononuclear phagocyte subset recruitment during acute primary and secondary mycobacterial infections in the lungs of mice

A nod to the bond between NOD2 and mycobacteria

Mycobacteria are responsible for several human and animal diseases. NOD2 is a pattern recognition receptor that has an important role in mycobacterial recognition. However, the mechanisms by which mutations in NOD2 alter the course of mycobacterial infection remain unclear. Herein, we aimed to review the totality of studies directly addressing the relationship between NOD2 and mycobacteria as a foundation for moving the field forward. NOD2 was linked to mycobacterial infection at 3 levels: (1) genetic, through association with mycobacterial diseases of humans; (2) chemical, through the distinct NOD2 ligand in the mycobacterial cell wall; and (3) immunologic, through heightened NOD2 signaling caused by the unique modification of the NOD2 ligand. The immune response to mycobacteria is shaped by NOD2 signaling, responsible for NF-κB and MAPK activation, and the production of various immune effectors like cytokines and nitric oxide, with some evidence linking this to bacteriologic control. Absence of NOD2 during mycobacterial infection of mice can be detrimental, but the mechanism remains unknown. Conversely, the success of immunization with mycobacteria has been linked to NOD2 signaling and NOD2 has been targeted as an avenue of immunotherapy for diseases even beyond mycobacteria. The mycobacteria-NOD2 interaction remains an important area of study, which may shed light on immune mechanisms in disease.

Neutrophilic Pleuritis Is a Severe Complication of Klebsiella pneumoniae Pneumonia in Old Mice

The pathomechanisms underlying the frequently observed fatal outcome of Klebsiella pneumoniae pneumonia in elderly patients are understudied. In this study, we examined the early antibacterial immune response in young mice (age 2-3 mo) as compared with old mice (age 18-19 mo) postinfection with K. pneumoniae. Old mice exhibited significantly higher bacterial loads in lungs and bacteremia as early as 24 h postinfection compared with young mice, with neutrophilic pleuritis nearly exclusively developing in old but not young mice. Moreover, we observed heavily increased cytokine responses in lungs and pleural spaces along with increased mortality in old mice. Mechanistically, Nlrp3 inflammasome activation and caspase-1-dependent IL-1β secretion contributed to the observed hyperinflammation, which decreased upon caspase-1 inhibitor treatment of K. pneumoniae-infected old mice. Irradiated old mice transplanted with the bone marrow of young mice did not show hyperinflammation or early bacteremia in response to K. pneumoniae. Collectively, the accentuated lung pathology observed in K. pneumoniae-infected old mice appears to be due to regulatory defects of the bone marrow but not the lung, while involving dysregulated activation of the Nlrp3/caspase-1/IL-1β axis.

The Upregulation of Cathepsin G Is Associated with Resistance to Bovine Paratuberculosis

An in silico genomic-transcriptomic combined approach allowed the identification of a polymorphism (cis-eQTL-rs41976219) in the Bos taurus genome associated with the CTSG mRNA expression in bovine blood samples, which suggests that individual genetic variation might modulate the CTSG transcriptional response. In the current study, a sandwich ELISA is used to measure the CTSG protein levels in supernatants of monocyte-derived macrophages (MDMs) isolated from cows with the AA (n = 5) and AC (n = 11) genotypes for the rs41976219 and infected ex vivo with MAP. Cows with the AC genotype have significantly higher CTSG protein levels (1.85 ng/mL) in the supernatants of enriched CD14+-MDMs after 2 h of infection when compared with infected CD14+-MDMs from cows with the AA genotype (1.68 ng/mL). Statistically significant differences in the intracellular MAP load at 7 d p.i. are observed between animals with the AA (2.16 log CFUs) and AC (1.44 log CFUs) genotypes. Finally, the association between the rs41976219 allelic variants and resistance to PTB is tested in a larger cattle population (n = 943) classified according to the presence (n = 442) or absence (n = 501) of PTB-associated lesions. The presence of the two minor alleles in the rs41976219 (CC) is more frequent among healthy cows than in cows with PTB-associated lesions in gut tissues (2.2% vs. 1.4%, OR = 0.61). In agreement with this, the CTSG levels in plasma samples of cows without lesions in gut tissues and with the CC (n = 8) genotype are significantly higher than in the plasmas of cows with the AA + AC (n = 36) genotypes.

A place for neutrophils in the beneficial pathogen-agnostic effects of the BCG vaccine

The BCG vaccine has long been recognized for reducing the risk to suffer from infectious diseases unrelated to its target disease, tuberculosis. Evidence from human trials demonstrate substantial reductions in all-cause mortality, especially in the first week of life. Observational studies have identified an association between BCG vaccination and reduced risk of respiratory infectious disease and clinical malaria later in childhood. The mechanistic basis for these pathogen-agnostic benefits, also known as beneficial non-specific effects (NSE) of BCG have been attributed to trained immunity, or epigenetic reprogramming of hematopoietic cells that give rise to innate immune cells responding more efficiently to a broad range of pathogens. Furthermore, within trained immunity, the focus so far has been on enhanced monocyte function. However, polymorphonuclear cells, namely neutrophils, are not only major constituents of the hematopoietic compartment but functionally as well as numerically represent a prominent component of the immune system. The beneficial NSEs of the BCG vaccine on newborn sepsis was recently demonstrated to be driven by a BCG-mediated numeric increase of neutrophils (emergency granulopoiesis (EG)). And experimental evidence in animal models suggest that BCG can modulate neutrophil function as well. Together, these findings suggest that neutrophils are crucial to at least the immediate beneficial NSE of the BCG vaccine. Efforts to uncover the full gamut of mechanisms underpinning the broad beneficial effects of BCG should therefore include neutrophils at the forefront.

Acidic Calcium-Independent Phospholipase A2 Regulates Eosinophil-Mediated Pathology during Filarial Manifestation of Tropical Pulmonary Eosinophilia

Eosinophils mediate pathological manifestations during tropical pulmonary eosinophilia (TPE), a potentially fatal complication of lymphatic filariasis, by mechanisms that are incompletely understood. Using two-dimensional gel electrophoresis, mass spectrometry, flow cytometry, and pharmacological and functional studies, we identified acidic calcium-independent phospholipase A2 (aiPLA2) as the master regulator of TPE pathogenesis. FACS-sorted lung eosinophils from TPE mice exhibited aiPLA2-dependent activation characterized by heavy calcium influx, F-actin polymerization, increased degranulation, and heightened reactive oxygen species generation. Interestingly, aiPLA2 also promoted alternative activation in lung macrophages and regulated the release of inflammatory intermediates from them. Treatment of TPE mice with MJ33, a nontoxic pharmacological inhibitor of aiPLA2, lowered eosinophil counts in the bronchoalveolar lavage fluid, reduced eosinophil peroxidase and β-hexosaminidase activity, increased airway width, improved lung endothelial barrier, and lowered the production of inflammatory lipid intermediates, which significantly improved the pathological condition of the lungs. Importantly, ex vivo reconstitution of arachidonic acid to eosinophils from MJ33-treated TPE mice increased eosinophil degranulation and inflammatory lipid intermediates underlining the pivotal role of aiPLA2 in arachidonic acid metabolism. Mechanistically, phosphorylation of JNK-1 regulated phospholipase activity of aiPLA2, whereas IgG cross-linking mediated pathological activation of eosinophils. Taken together, ours is the first study, to our knowledge, to report hitherto undocumented role of aiPLA2 in regulating TPE pathogenesis.

Cathepsins in Bacteria-Macrophage Interaction: Defenders or Victims of Circumstance?

Macrophages are the first encounters of invading bacteria and are responsible for engulfing and digesting pathogens through phagocytosis leading to initiation of the innate inflammatory response. Intracellular digestion occurs through a close relationship between phagocytic/endocytic and lysosomal pathways, in which proteolytic enzymes, such as cathepsins, are involved. The presence of cathepsins in the endo-lysosomal compartment permits direct interaction with and killing of bacteria, and may contribute to processing of bacterial antigens for presentation, an event necessary for the induction of antibacterial adaptive immune response. Therefore, it is not surprising that bacteria can control the expression and proteolytic activity of cathepsins, including their inhibitors – cystatins, to favor their own intracellular survival in macrophages. In this review, we summarize recent developments in defining the role of cathepsins in bacteria-macrophage interaction and describe important strategies engaged by bacteria to manipulate cathepsin expression and activity in macrophages. Particularly, we focus on specific bacterial species due to their clinical relevance to humans and animal health, i.e., Mycobacterium, Mycoplasma, Staphylococcus, Streptococcus, Salmonella, Shigella, Francisella, Chlamydia, Listeria, Brucella, Helicobacter, Neisseria, and other genera.

Overexpression of Macrophage-Inducible C-Type Lectin Mincle Aggravates Proinflammatory Responses to Streptococcus pneumoniae with Fatal Outcome in Mice

Macrophage-inducible C-type lectin (Mincle)-dependent sensing of pathogens triggers proinflammatory immune responses in professional phagocytes that contribute to protecting the host against pathogen invasion. In this study, we examined whether overexpression of Mincle that is designed to improve early pathogen sensing by professional phagocytes would improve lung-protective immunity against Streptococcus pneumoniae in mice. Proteomic profiling of alveolar macrophages of Mincle transgenic (tg) mice stimulated with the Mincle-specific pneumococcal ligand glucosyl-diacylglycerol (Glc-DAG) revealed increased Nlrp3 inflammasome activation and downstream IL-1β cytokine release that was not observed in Glc-DAG-stimulated Mincle knockout or Nlrp3 knockout macrophages. Along this line, Mincle tg mice also responded with a stronger Nlrp3 expression and early proinflammatory cytokine release after challenge with S. pneumoniae, ultimately leading to fatal pneumonia in the Mincle tg mice. Importantly, Nlrp3 inhibitor treatment of Mincle tg mice significantly mitigated the observed hyperinflammatory response to pneumococcal challenge. Together, we show that overexpression of the pattern recognition receptor Mincle triggers increased Glc-DAG-dependent Nlrp3 inflammasome activation in professional phagocytes leading to fatal pneumococcal pneumonia in mice that is amenable to Nlrp3 inhibitor treatment. These data show that ectopic expression of the Mincle receptor confers increased susceptibility rather than resistance to S. pneumoniae in mice, thus highlighting the importance of an inducible Mincle receptor expression in response to microbial challenge.

Mycobacterium tuberculosis Reactivates HIV-1 via Exosome-Mediated Resetting of Cellular Redox Potential and Bioenergetics

The synergy between Mycobacterium tuberculosis and human immunodeficiency virus-1 (HIV-1) interferes with therapy and facilitates the pathogenesis of both human pathogens. Fundamental mechanisms by which M. tuberculosis exacerbates HIV-1 infection are not clear. Here, we show that exosomes secreted by macrophages infected with M. tuberculosis, including drug-resistant clinical strains, reactivated HIV-1 by inducing oxidative stress. Mechanistically, M. tuberculosis-specific exosomes realigned mitochondrial and nonmitochondrial oxygen consumption rates (OCR) and modulated the expression of host genes mediating oxidative stress response, inflammation, and HIV-1 transactivation. Proteomics analyses revealed the enrichment of several host factors (e.g., HIF-1α, galectins, and Hsp90) known to promote HIV-1 reactivation in M. tuberculosis-specific exosomes. Treatment with a known antioxidant-N-acetyl cysteine (NAC)-or with inhibitors of host factors-galectins and Hsp90-attenuated HIV-1 reactivation by M. tuberculosis -specific exosomes. Our findings uncover new paradigms for understanding the redox and bioenergetics bases of HIV-M. tuberculosis coinfection, which will enable the design of effective therapeutic strategies.IMPORTANCE Globally, individuals coinfected with the AIDS virus (HIV-1) and with M. tuberculosis (causative agent of tuberculosis [TB]) pose major obstacles in the clinical management of both diseases. At the heart of this issue is the apparent synergy between the two human pathogens. On the one hand, mechanisms induced by HIV-1 for reactivation of TB in AIDS patients are well characterized. On the other hand, while clinical findings clearly identified TB as a risk factor for HIV-1 reactivation and associated mortality, basic mechanisms by which M. tuberculosis exacerbates HIV-1 replication and infection remain poorly characterized. The significance of our research is in identifying the role of fundamental mechanisms such as redox and energy metabolism in catalyzing HIV-M. tuberculosis synergy. The quantification of redox and respiratory parameters affected by M. tuberculosis in stimulating HIV-1 will greatly enhance our understanding of HIV-M. tuberculosis coinfection, leading to a wider impact on the biomedical research community and creating new translational opportunities.

Characterisation of a New Human Alveolar Macrophage-Like Cell Line (Daisy)

Purpose

There is currently no true macrophage cell line and in vitro experiments requiring these cells currently require mitogenic stimulation of a macrophage precursor cell line (THP-1) or ex vivo maturation of circulating primary monocytes. In this study, we characterise a human macrophage cell line, derived from THP-1 cells, and compare its phenotype to the THP-1 cells.

Methods

THP-1 cells with and without mitogenic stimulation were compared to the newly derived macrophage-like cell line (Daisy) using microscopy, flow cytometry, phagocytosis assays, antigen binding assays and gene microarrays.

Results

We show that the cell line grows predominantly in an adherent monolayer. A panel of antibodies were chosen to investigate the cell surface phenotype of these cells using flow cytometry. Daisy cells expressed more CD11c, CD80, CD163, CD169 and CD206, but less CD14 and CD11b compared with mitogen-stimulated THP-1 cells. Unlike stimulated THP-1 cells which were barely able to bind immune complexes, Daisy cells showed large amounts of immune complex binding. Finally, although not statistically significant, the phagocytic ability of Daisy cells was greater than mitogen-stimulated THP-1 cells, suggesting that the cell line is more similar to mature macrophages.

Conclusions

The observed phenotype suggests that Daisy cells are a good model of human macrophages with a phenotype similar to human alveolar macrophages.

Extended cleavage specificity of human neutrophil cathepsin G: A low activity protease with dual chymase and tryptase-type specificities

Human neutrophils express at least four active serine proteases, cathepsin G, N-elastase, proteinase 3 and neutrophil serine protease 4 (NSP4). They have all been extensively studied due to their importance in neutrophil biology and immunity. However, their extended cleavage specificities have never been determined in detail. Here we present a detailed cleavage specificity analysis of human cathepsin G (hCG). The specificity was determined by phage display analysis and the importance of individual amino acids in and around the cleavage site was then validated using novel recombinant substrates. To provide a broader context to this serine protease, a comparison was made to the related mast cell protease, human chymase (HC). hCG showed similar characteristics to HC including both the primary and extended specificities. As expected, Phe, Tyr, Trp and Leu were preferred in the P1 position. In addition, both proteases showed a preference for negatively charged amino acids in the P2´ position of substrates and a preference for aliphatic amino acids both upstream and downstream of the cleavage site. However, overall the catalytic activity of hCG was ~10-fold lower than HC. hCG has previously been reported to have a dual specificity consisting of chymase and tryptase-type activities. In our analysis, tryptase activity against substrates with Lys in P1 cleavage position was indeed only 2-fold less efficient as compared to optimal chymase substrates supporting strong dual-type specificity. We hope the information presented here on extended cleavage specificities of hCG and HC will assist in the search for novel in vivo substrates for these proteases as well as aid in the efforts to better understand the role of hCG in immunity and bacterial defence.

Infective Larvae of Brugia malayi Induce Polarization of Host Macrophages that Helps in Immune Evasion

Filarial parasites suppress, divert, or polarize the host immune response to aid their survival. However, mechanisms that govern the polarization of host MΦs during early filarial infection are not completely understood. In this study, we infected BALB/c mice with infective larvae stage-3 of Brugia malayi (Bm-L3) and studied their effect on the polarization of splenic MΦs. Results showed that MΦs displayed M2-phenotype by day 3 p.i. characterized by upregulated IL-4, but reduced IL-12 and Prostaglandin-D2 secretion. Increased arginase activity, higher arginase-1 but reduced NOS2 expression and poor phagocytic and antigen processing capacity was also observed. M2 MΦs supported T-cell proliferation and characteristically upregulated p-ERK but downregulated NF-κB-p65 and NF-κB-p50/105. Notably, Bm-L3 synergized with host regulatory T-cells (Tregs) and polarized M2 MΦs to regulatory MΦs (Mregs) by day 7 p.i., which secreted copious amounts of IL-10 and prostaglandin-E2. Mregs also showed upregulated expression levels of MHC-II, CD80, and CD86 and exhibited increased antigen-processing capacity but displayed impaired activation of NF-κB-p65 and NF-κB-p50/105. Neutralization of Tregs by anti-GITR + anti-CD25 antibodies checked the polarization of M2 MΦs to Mregs, decreased accumulation of regulatory B cells and inflammatory monocytes, and reduced secretion of IL-10, but enhanced IL-4 production and percentages of eosinophils, which led to Bm-L3 killing. In summary, we report hitherto undocumented effects of early Bm-L3 infection on the polarization of splenic MΦs and show how infective larvae deftly utilize the functional plasticity of host MΦs to establish themselves inside the host.

Towards the use of breath for detecting mycobacterial infection: a case study in a murine model

In the present research, the potential of breath analysis by comprehensive two-dimensional gas chromatography coupled to mass spectrometry (GC×GC-MS) was investigated for the discrimination between healthy and infected mice. A pilot study employing a total of 16 animals was used to develop a method for breath analysis in a murine model for studying Mycobacterium tuberculosis complex (MTBC) using the M. bovis bacillus Calmette-Guérin. Breath was collected in Tedlar bags and concentrated onto thermal desorption tubes for subsequent analysis by GC×GC-MS. Immunological test and bacterial cell count in bronchoalveolar lavage fluid and mice lung homogenate confirmed the presence of bacteria in the infected group. From the GC×GC-MS analysis, 23 molecules were found to mainly drive the separation between control and infected mice and their tentative identification is provided.This study shows that the overall used methodology is able to differentiate breath between healthy and infected animals, and the information herein can be used to further develop the mouse breath model to study MTBC pathogenesis, evaluate pre-clinical drug regimen efficacy, and to further develop the concept of breath-based diagnostics.

Adenoviral vector-mediated GM-CSF gene transfer improves anti-mycobacterial immunity in mice - role of regulatory T cells

Granulocyte macrophage-colony stimulating factor (GM-CSF) is a hematopoietic growth factor involved in differentiation, survival and activation of myeloid and non-myeloid cells with important implications for lung antibacterial immunity. Here we examined the effect of pulmonary adenoviral vector-mediated delivery of GM-CSF (AdGM-CSF) on anti-mycobacterial immunity in M. bovis BCG infected mice. Exposure of M. bovis BCG infected mice to AdGM-CSF either applied on 6h, or 6h and 7days post-infection substantially increased alveolar recruitment of iNOS and IL-12 expressing macrophages, and significantly increased accumulation of IFNγ^pos T cells and particularly regulatory T cells (Tregs). This was accompanied by significantly reduced mycobacterial loads in the lungs of mice. Importantly, diphtheria toxin-induced depletion of Tregs did not influence mycobacterial loads, but accentuated immunopathology in AdGM-CSF-exposed mice infected with M. bovis BCG. Together, the data demonstrate that AdGM-CSF therapy improves lung protective immunity against M. bovis BCG infection in mice independent of co-recruited Tregs, which however critically contribute to limit lung immunopathology in BCG-infected mice. These data may be relevant to the development of immunomodulatory strategies to limit immunopathology-based lung injury in tuberculosis in humans.

Effect of Liuweibuqi capsules on the balance between MMP-9 and TIMP1 and viability of alveolar macrophages in COPD

The present study aims to investigate the effect of Liuweibuqi (LWBQ) capsules on the expression of matrix metalloproteinase (MMP)-9 and TIMP1 and cell viability of alveolar macrophages (AMs) in chronic obstructive pulmonary disease (COPD). Rats were randomly divided into normal control (NC) group, model control (MC) group, Jinshuibao (JSB) group, spleen aminopeptidase (PAT) group, and low dose of LWBQ (LWBQ low), mid dose of LWBQ (LWBQ mid), and high dose of LWBQ (LWBQ high) group (n=10). Lung function was measured with a spirometer. Serum cytokines including tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) were detected using ELISA. The expressions of MMP-9 and TIMP1 were detected by quantitative real-time PCR (qRT-PCR) and Western blot. MTT assay and flow cytometry were used to measure cell viability and apoptosis. Compared with the NC group, body weight and lung function were reduced in the MC group. In addition, the serum levels of IL-6 and TNF-α were higher in the MC group than those in the NC group. The expression of MMP-9 protein in the AMs from rats was higher, and TIMP1 protein was lower in the MC group compared with the NC group. After LWBQ capsules treatment, compared with the MC group, the expression of inflammatory cytokines and MMP-9 were lower and TIMP1 was higher. Moreover, after LWBQ-medicated serum treatment, the release of inflammatory cytokines was reduced from AMs. Besides, LWBQ-medicated serum decreased the expression of MMP-9 and increased the expression of TIMP1 and cell viability compared with those in MC group. In conclusion, LWBQ capsules can inhibit the release of inflammatory cytokines, promote cell viability in AMs, and regulate the expression of MMP-9 and TIMP1.

In vivo neutralization of α4 and β7 integrins inhibits eosinophil trafficking and prevents lung injury during tropical pulmonary eosinophilia in mice

Integrins regulate leukocyte trafficking during homeostasis and inflammatory conditions. However, the role of α4 and β7 integrins in guiding eosinophil transmigration into the lungs during filarial manifestation of Tropical Pulmonary Eosinophilia (TPE) has not been explored. In this study, mice exhibiting TPE manifestations were administered with in vivo neutralizing antibodies against integrins α4 and β7 or their combination and immuno-pathological parameters were evaluated. Results show an intact lung barrier, significantly lower lung inflammation and reduced eosinophil counts in the Bronchoalveolar lavage fluid and lungs of mice receiving anti-α4⁺ β7 treatment. Reduced eosinophil peroxidase and β-hexosaminidase activity, downregulation of inflammatory genes, lower production of inflammatory lipid intermediates like prostaglandins E2 and D2, leukotriene B4 and cysteinyl leukotrienes were also noted in anti-α4⁺ β7 treated mice. Reduced accumulation of central memory, effector memory, regulatory T cells and lower production of IL-4, IL-5, and TGF-β were other cardinal features of anti-α4⁺ β7 treated mice lungs. Flow cytometry-sorted lung eosinophils from anti-α4⁺ β7 treated mice showed higher apoptotic potential, downregulated anti-apoptotic gene Bcl-2, and exhibited reduced F-actin polymerization and calcium influx as compared to IgG controls. In summary, neutralization of α4⁺ β7 integrins impairs the transmigration, activation and survival of eosinophils and reduces TPE induced pathology in mice lungs.

Functional Impairment of Murine Dendritic Cell Subsets following Infection with Infective Larval Stage 3 of Brugia malayi

Filarial parasites cause functional impairment of host dendritic cells (DCs). However, the effects of early infection on individual DC subsets are not known. In this study, we infected BALB/c mice with infective stage 3 larvae of the lymphatic filarial parasite Brugia malayi (Bm-L3) and studied the effect on fluorescence-activated cell sorter (FACS)-sorted DC subsets. While myeloid DCs (mDCs) accumulated by day 3 postinfection (p.i.), lymphoid DCs (LDCs) and CD8⁺ plasmacytoid DCs (pDCs) peaked at day 7 p.i. in the spleens and mesenteric lymph nodes (mLNs) of infected mice. Increased tumor necrosis factor alpha (TNF-α) but reduced interleukin 12 (IL-12) and Toll-like receptor 4 (TLR4), -6, and -9 and reciprocal secretion of IL-4 and IL-10 were also observed across all DC subsets. Interestingly, Bm-L3 increased the expression of CD80 and CD86 across all DC subsets but decreased that of major histocompatibility complex class II (MHC-II) on mDCs and pDCs, resulting in their impaired antigen uptake and presentation capacities, but maximally attenuated the T-cell proliferation capacity of only mDCs. Furthermore, Bm-L3 increased phosphorylated p38 (p-p38), but not p-ERK, in mDCs and LDCs but downregulated them in pDCs, along with differential modulation of protein tyrosine phosphatases SHP-1, TCPTP, PTEN, and PTP1B across all DC subsets. Taken together, we report hitherto undocumented effects of early Bm-L3 infection on purified host DC subsets that lead to their functional impairment and attenuated host T-cell response.

Host lung immunity is severely compromised during tropical pulmonary eosinophilia: role of lung eosinophils and macrophages

Eosinophils play a central role in the pathogenesis of tropical pulmonary eosinophilia, a rare, but fatal, manifestation of filariasis. However, no exhaustive study has been done to identify the genes and proteins of eosinophils involved in the pathogenesis of tropical pulmonary eosinophilia. In the present study, we established a mouse model of tropical pulmonary eosinophilia that mimicked filarial manifestations of human tropical pulmonary eosinophilia pathogenesis and used flow cytometry-assisted cell sorting and real-time RT-PCR to study the gene expression profile of flow-sorted, lung eosinophils and lung macrophages during tropical pulmonary eosinophilia pathogenesis. Our results show that tropical pulmonary eosinophilia mice exhibited increased levels of IL-4, IL-5, CCL5, and CCL11 in the bronchoalveolar lavage fluid and lung parenchyma along with elevated titers of IgE and IgG subtypes in the serum. Alveolar macrophages from tropical pulmonary eosinophilia mice displayed decreased phagocytosis, attenuated nitric oxide production, and reduced T-cell proliferation capacity, and FACS-sorted lung eosinophils from tropical pulmonary eosinophilia mice upregulated transcript levels of ficolin A and anti-apoptotic gene Bcl2,but proapoptotic genes Bim and Bax were downregulated. Similarly, flow-sorted lung macrophages upregulated transcript levels of TLR-2, TLR-6, arginase-1, Ym-1, and FIZZ-1 but downregulated nitric oxide synthase-2 levels, signifying their alternative activation. Taken together, we show that the pathogenesis of tropical pulmonary eosinophilia is marked by functional impairment of alveolar macrophages, alternative activation of lung macrophages, and upregulation of anti-apoptotic genes by eosinophils. These events combine together to cause severe lung inflammation and compromised lung immunity. Therapeutic interventions that can boost host immune response in the lungs might thus provide relief to patients with tropical pulmonary eosinophilia.

Arginase 1 activity worsens lung-protective immunity against Streptococcus pneumoniae infection

Type 2 helper cell (Th2) dominated chronic lung diseases such as asthma are characterized by an increased risk for bacterial lung infections. However, the underlying mechanisms are poorly defined. Arginase 1 (Arg1) has been suggested to play an important role in the pathophysiology of asthma, and is rapidly induced in lung macrophages by Th2 cytokines, thereby limiting macrophage-derived antimicrobial nitric oxide (NO) production. Here we examined the effect of Th2 cytokine induced upregulation or lung myeloid cell specific conditional knockdown of Arg1 on lung resistance against Streptococcus pneumoniae (Spn) in mice. Lung macrophages responded with a profound induction of Arg1 mRNA and protein to treatment with IL-13 both in vitro and in vivo. IL-13-induced Arg1 activity in the lungs of mice led to significantly attenuated lung-protective immunity against Spn, while conditional Arg1 knockdown had no effect on lung-protective immunity against Spn. Collectively, the data show that Th2 cytokine induced increased Arg1 activity worsens lung-protective immunity against Spn, and interventions to block Th2 cytokine induced lung Arg1 activity may thus be a novel immunomodulatory strategy to lower the risk of bacterial infections in asthmatic patients.

Macrophage-inducible C-type lectin Mincle-expressing dendritic cells contribute to control of splenic Mycobacterium bovis BCG infection in mice

The macrophage-inducible C-type lectin Mincle has recently been identified to be a pattern recognition receptor sensing mycobacterial infection via recognition of the mycobacterial cell wall component trehalose-6',6-dimycolate (TDM). However, its role in systemic mycobacterial infections has not been examined so far. Mincle-knockout (KO) mice were infected intravenously with Mycobacterium bovis BCG to mimic the systemic spread of mycobacteria under defined experimental conditions. After intravenous infection with M. bovis BCG, Mincle-KO mice responded with significantly higher numbers of mycobacterial CFU in spleen and liver, while reduced granuloma formation was observed only in the spleen. At the same time, reduced Th1 cytokine production and decreased numbers of gamma interferon-producing T cells were observed in the spleens of Mincle-KO mice relative to the numbers in the spleens of wild-type (WT) mice. The effect of adoptive transfer of defined WT leukocyte subsets generated from bone marrow cells of zDC(+/DTR) mice (which bear the human diphtheria toxin receptor [DTR] under the control of the classical dendritic cell-specific zinc finger transcription factor zDC) to specifically deplete Mincle-expressing classical dendritic cells (cDCs) but not macrophages after diphtheria toxin application on the numbers of splenic and hepatic CFU and T cell subsets was then determined. Adoptive transfer experiments revealed that Mincle-expressing splenic cDCs rather than Mincle-expressing macrophages contributed to the reconstitution of attenuated splenic antimycobacterial immune responses in Mincle-KO mice after intravenous challenge with BCG. Collectively, we show that expression of Mincle, particularly by cDCs, contributes to the control of splenic M. bovis BCG infection in mice.

TNF-related apoptosis-inducing ligand (TRAIL) exerts therapeutic efficacy for the treatment of pneumococcal pneumonia in mice

Apoptotic death of alveolar macrophages observed during lung infection with Streptococcus pneumoniae is thought to limit overwhelming lung inflammation in response to bacterial challenge. However, the underlying apoptotic death mechanism has not been defined. Here, we examined the role of the TNF superfamily member TNF-related apoptosis-inducing ligand (TRAIL) in S. pneumoniae-induced macrophage apoptosis, and investigated the potential benefit of TRAIL-based therapy during pneumococcal pneumonia in mice. Compared with WT mice, Trail(-/-) mice demonstrated significantly decreased lung bacterial clearance and survival in response to S. pneumoniae, which was accompanied by significantly reduced apoptosis and caspase 3 cleavage but rather increased necrosis in alveolar macrophages. In WT mice, neutrophils were identified as a major source of intraalveolar released TRAIL, and their depletion led to a shift from apoptosis toward necrosis as the dominant mechanism of alveolar macrophage cell death in pneumococcal pneumonia. Therapeutic application of TRAIL or agonistic anti-DR5 mAb (MD5-1) dramatically improved survival of S. pneumoniae-infected WT mice. Most importantly, neutropenic mice lacking neutrophil-derived TRAIL were protected from lethal pneumonia by MD5-1 therapy. We have identified a previously unrecognized mechanism by which neutrophil-derived TRAIL induces apoptosis of DR5-expressing macrophages, thus promoting early bacterial killing in pneumococcal pneumonia. TRAIL-based therapy in neutropenic hosts may represent a novel antibacterial treatment option.

FMS-like tyrosine kinase 3 ligand treatment of mice aggravates acute lung injury in response to Streptococcus pneumoniae: role of pneumolysin

FMS-like tyrosine kinase-3 ligand (Flt3L) is a dendritic cell (DC) growth and differentiation factor with potential in antitumor therapies and antibacterial immunization strategies. However, the effect of systemic Flt3L treatment on lung-protective immunity against bacterial infection is incompletely defined. Here, we examined the impact of deficient (in Flt3L knockout [KO] mice), normal (in wild-type [WT] mice), or increased Flt3L availability (in WT mice pretreated with Flt3L for 3, 5, or 7 days) on lung DC subset profiles and lung-protective immunity against the major lung-tropic pathogen, Streptococcus pneumoniae. Although in Flt3L-deficient mice the numbers of DCs positive for CD11b (CD11b(pos) DCs) and for CD103 (CD103(pos) DCs) were diminished, lung permeability, a marker of injury, was unaltered in response to S. pneumoniae. In contrast, WT mice pretreated with Flt3L particularly responded with increased numbers of CD11b(pos) DCs and with less pronounced numbers of CD103(pos) DCs and impaired bacterial clearance and with increased lung permeability following S. pneumoniae challenge. Notably, infection of Flt3L-pretreated mice with S. pneumoniae lacking the pore-forming toxin, pneumolysin (PLY), resulted in substantially less lung CD11b(pos) DCs activation and reduced lung permeability. Collectively, this study establishes that Flt3L treatment enhances the accumulation of proinflammatory activated lung CD11b(pos) DCs which contribute to acute lung injury in response to PLY released by S. pneumoniae.

Role of Mincle in alveolar macrophage-dependent innate immunity against mycobacterial infections in mice

The role of macrophage-inducible C-type lectin Mincle in lung innate immunity against mycobacterial infection is incompletely defined. In this study, we show that wild-type (WT) mice responded with a delayed Mincle induction on resident alveolar macrophages and newly immigrating exudate macrophages to infection with Mycobacterium bovis bacillus Calmette-Guérin (BCG), peaking by days 14-21 posttreatment. As compared with WT mice, Mincle knockout (KO) mice exhibited decreased proinflammatory mediator responses and leukocyte recruitment upon M. bovis BCG challenge, and they demonstrated increased mycobacterial loads in pulmonary and extrapulmonary organ systems. Secondary mycobacterial infection on day 14 after primary BCG challenge led to increased cytokine gene expression in sorted alveolar macrophages of WT mice, but not Mincle KO mice, resulting in substantially reduced alveolar neutrophil recruitment and increased mycobacterial loads in the lungs of Mincle KO mice. Collectively, these data show that WT mice respond with a relatively late Mincle expression on lung sentinel cells to M. bovis BCG infection. Moreover, M. bovis BCG-induced upregulation of C-type lectin Mincle on professional phagocytes critically shapes antimycobacterial responses in both pulmonary and extrapulmonary organ systems of mice, which may be important for elucidating the role of Mincle in the control of mycobacterial dissemination in mice.

Cathepsin G and neutrophil elastase contribute to lung-protective immunity against mycobacterial infections in mice

The neutrophil serine proteases cathepsin G (CG) and neutrophil elastase (NE) are involved in immune-regulatory processes and exert antibacterial activity against various pathogens. To date, their role and their therapeutic potential in pulmonary host defense against mycobacterial infections are poorly defined. In this work, we studied the roles of CG and NE in the pulmonary resistance against Mycobacterium bovis bacillus Calmette-Guérin (BCG). CG-deficient mice and even more pronounced CG/NE-deficient mice showed significantly impaired pathogen elimination to infection with M. bovis BCG in comparison to wild-type mice. Moreover, granuloma formation was more pronounced in M. bovis BCG-infected CG/NE-deficient mice in comparison to CG-deficient and wild-type mice. A close examination of professional phagocyte subsets revealed that exclusively neutrophils shuttled CG and NE into the bronchoalveolar space of M. bovis BCG-infected mice. Accordingly, chimeric wild-type mice with a CG/NE-deficient hematopoietic system displayed significantly increased lung bacterial loads in response to M. bovis BCG infection. Therapeutically applied human CG/NE encapsulated in liposomes colocalized with mycobacteria in alveolar macrophages, as assessed by laser scanning and electron microscopy. Importantly, therapy with CG/NE-loaded liposomes significantly reduced mycobacterial loads in the lungs of mice. Together, neutrophil-derived CG and NE critically contribute to deceleration of pathogen replication during the early phase of antimycobacterial responses. In addition, to our knowledge, we show for the first time that liposomal encapsulated CG/NE exhibit therapeutic potential against pulmonary mycobacterial infections. These findings may be relevant for novel adjuvant approaches in the treatment of tuberculosis in humans.

Inhibition of the Plasma-Membrane-Associated Serine Protease Cathepsin G by Mycobacterium tuberculosis Rv3364c Suppresses Caspase-1 and Pyroptosis in Macrophages

Tuberculosis is a disease associated with the infection of a great part of the world’s population and is responsible for the death of two to three million people annually. Mycobacterium tuberculosis infects macrophages and subverts its mechanisms of killing. The pathogen suppresses macrophage apoptosis by many different mechanisms. We describe that, upon uptake by macrophages, M. tuberculosis overexpresses an operon Rv3361c-Rv3365c and secretes Rv3364c. The Rv3365c knockout strain is deficient in apoptosis inhibition. The Rv3364c protein binds to the serine protease cathepsin G on the membrane, inhibiting its enzymatic activity and the downstream activation of caspase-1-dependent apoptosis. In summary, M. tuberculosis prevents macrophage pyroptosis by a novel mechanism involving cytoplasmic surveillance proteins.

Local delivery of GM-CSF protects mice from lethal pneumococcal pneumonia

The growth factor GM-CSF has an important role in pulmonary surfactant metabolism and the regulation of antibacterial activities of lung sentinel cells. However, the potential of intra-alveolar GM-CSF to augment lung protective immunity against inhaled bacterial pathogens has not been defined in preclinical infection models. We hypothesized that transient overexpression of GM-CSF in the lungs of mice by adenoviral gene transfer (Ad-GM-CSF) would protect mice from subsequent lethal pneumococcal pneumonia. Our data show that intra-alveolar delivery of Ad-GM-CSF led to sustained increased pSTAT5 expression and PU.1 protein expression in alveolar macrophages during a 28-d observation period. Pulmonary Ad-GM-CSF delivery 2-4 wk prior to infection of mice with Streptococcus pneumoniae significantly reduced mortality rates relative to control vector-treated mice. This increased survival was accompanied by increased inducible NO synthase expression, antibacterial activity, and a significant reduction in caspase-3-dependent apoptosis and secondary necrosis of lung sentinel cells. Importantly, therapeutic treatment of mice with rGM-CSF improved lung protective immunity and accelerated bacterial clearance after pneumococcal challenge. We conclude that prophylactic delivery of GM-CSF triggers long-lasting immunostimulatory effects in the lung in vivo and rescues mice from lethal pneumococcal pneumonia by improving antibacterial immunity. These data support use of novel antibiotic-independent immunostimulatory therapies to protect patients against bacterial pneumonias.

Resistance to mycobacterial infection: a pattern of early immune responses leads to a better control of pulmonary infection in C57BL/6 compared with BALB/c mice

In this study, we have compared the immunological responses associated with early pulmonary mycobacterial infection in two mouse strains, BALB/c and C57BL/6 known to exhibit distinct differences in susceptibility to infection with several pathogens. We infected mice via the intranasal route. We have demonstrated that BALB/c was less able to control mycobacterial growth in the lungs during the early phase of pulmonary infection. Our results showed that during the early phase (day 3 to week 1), BALB/c mice exhibited a delay in the production of TNF and IFN-gamma in the lungs compared to C57BL/6 mice. Levels of IL-12 and soluble TNF receptors (sTNFR) were comparable between the mouse strains. The cellular subset distribution in these mice before and after infection showed a higher increase in CD11b+ cells in the lungs of C57BL/6, compared to BALB/c as early as day 3 postinfection. At early time points, higher levels of monocyte chemoattractant protein (MCP)-1 and macrophage inflammatory protein 1 (MIP)-alpha were detected in C57BL/6 than BALB/c mice. In vitro, BCG-infected bone marrow derived macrophages (BMM) from both mouse strains displayed similar capacities to either phagocytose bacteria or produce soluble mediators such as TNF, IL-12 and nitric oxide (NO). Although IFN-gamma stimulation of infected BMM in both mouse strains resulted in the induction of antimycobacterial activity, BALB/c mice had a reduced capacity to kill ingested bacteria. The above observations indicate that the chain of early, possibly innate immunological events occurring during pulmonary mycobacterial infection may directly impact on increased susceptibility or resistance to infection.

Important role for CC chemokine ligand 2-dependent lung mononuclear phagocyte recruitment to inhibit sepsis in mice infected with Streptococcus pneumoniae

The monocyte chemoattractant CCL2 is of major importance in inflammatory monocyte recruitment to the lungs in response to bacterial infection. Streptococcus pneumoniae is the most prevalent pathogen in community-acquired pneumonia causing significant morbidity and mortality worldwide. In the current study, we examined the role of CCL2 in lung-protective immunity against two strains of S. pneumoniae exhibiting different virulence profiles. Both wild-type mice and CCL2 knockout (KO) mice became septic within 24 h of infection with serotype 3 S. pneumoniae and died of infection by day 4 after challenge. In contrast, wild-type mice challenged with serotype 19 S. pneumoniae did not become septic or succumb to pneumococcal pneumonia, whereas CCL2 KO mice showed an early bacterial outgrowth in their lungs and sepsis starting by day 2 after infection, finally resulting in approximately 50% decreased survival compared with wild-type mice. This phenotype was not due to impaired lung neutrophil recruitment in the KO mice, but was characterized by a significantly reduced recruitment of lung exudate macrophages and conventional lung dendritic cells, suggesting that these two phagocyte subsets critically regulate protection against septic disease progression in mice. In conclusion, we show here a differential role for CCL2-dependent lung exudate macrophage and conventional dendritic cell recruitment that critically contributes to lung protective immunity against S. pneumoniae.

Mycobacterium bovis Bacillus Calmette-Guérin (BCG)-induced activation of PI3K/Akt and NF-kB signaling pathways regulates expression of CXCL10 in epithelial cells

CXCL10 production is a critical step in limiting mycobacterial infection. Although induction of this chemokine by mycobacteria in epithelial cells has been reported, it is still unclear how CXCL10 is regulated in Mycobacterium bovis BCG-infected epithelial cells. In this study, we demonstrate that phosphatidylinoditol 3-kinase (PI3K)/Akt and the nuclear factor kB (NF-kB) signaling pathways play an important role in CXCL10 expression at the protein and mRNA level in A549 cells. We demonstrate that treatment of A549 cells with LY294002 and wortmannin, two PI3K inhibitors, inhibited M. bovis BCG-induced CXCL10 expression. In addition, treatment of A549 cells with an Akt inhibitor significantly blocked M. bovis BCG-induced CXCL10 production. Moreover, our data show that treatment of epithelial cells with CAPE, BAY 11-7082, and PDTC three selective inhibitors of NF-kB, significantly reduced the effect of M. bovis BCG on induced CXCL10 mRNA expression (74%, 69% and 83% inhibition by 8microM CAPE, 10microM BAY 11-7082 and 3microM PDTC as assessed by real-time PCR, respectively). In accordance with the gene induction, the production of CXCL10 was also significantly reduced by these inhibitors. Finally, the inhibition of PI3K affect NF-kB activation in M. bovis BCG-infected cells, indicating that PI3K activity is required for the M. bovis BCG-induced activation of NF-kB. The functional association between PI3K/Akt and NF-kB demonstrates another mechanism in the regulation of M. bovis BCG-induced CXCL10 in A549 cells.

Mice that overexpress CC chemokine ligand 2 in their lungs show increased protective immunity to infection with Mycobacterium bovis bacille Calmette-Guérin

BACKGROUND

The acute phase of mycobacterial lung infection is characterized by a nearly exponential outgrowth of mycobacteria in the alveolar airspace and lung parenchymal tissue, suggesting insufficient early protective immunity against mycobacterial challenge. In the current study, we tested the hypothesis that a CC chemokine ligand 2 (CCL2)-dependent increased mononuclear phagocyte subset accumulation in distal airspaces would improve the lungs' protective immunity to infection with Mycobacterium bovis bacille Calmette-Guérin (hereafter, "M. bovis BCG").

METHODS

Wild-type mice and CCL2-overexpressing mice that exhibited increased pools of alveolar and lung mononuclear phagocytes-due to the lung-specific overexpression of human CCL2 in type-II alveolar epithelial cells-were infected intratracheally with M. bovis BCG and the developing lung inflammatory response was analyzed.

RESULTS

CCL2-overexpressing mice demonstrated significantly decreased mycobacterial loads in the bronchoalveolar space, lung parenchymal tissue, and spleen compared with wild-type mice, when both groups of mice were infected with M. bovis BCG. Moreover, in M. bovis BCG-infected mice, later-developing, accelerated resolution of lung granuloma formation was noted, particularly in CCL2-overexpressing mice as compared with wild-type mice. In addition, CCL2-overexpressing mice demonstrated an increased trafficking of mycobacteria-loaded dendritic cells towards lung-draining lymph nodes that was found to coincide with increased mycobacterial loads in this compartment.

CONCLUSIONS

The data of the current study suggest that CCL2-dependent amplification of endogenous host-defense programs in the lung may improve the lungs' protective immunity against mycobacterial infections.

CX3CL1 up-regulation is associated with recruitment of CX3CR1+ mononuclear phagocytes and T lymphocytes in the lungs during cigarette smoke-induced emphysema

CX3CR1 is expressed on monocytes, dendritic cells, macrophages, subsets of T lymphocytes, and natural killer cells and functions in diverse capacities such as leukocyte adhesion, migration, and cell survival on ligand binding. Expression of the CX3CL1 gene, whose expression product is the sole ligand for CX3CR1, is up-regulated in human lungs with chronic cigarette smoke-induced obstructive lung disease. At present, it is unknown whether CX3CL1 up-regulation is associated with the recruitment and accumulation of immune cells that express CX3CR1. We show that mice chronically exposed to cigarette smoke up-regulate CX3CL1 gene expression, which is associated with an influx of CX3CR1+ cells in the lungs. The increase in CX3CR1+ cells is primarily comprised of macrophages and T lymphocytes and is associated with the development of emphysema. In alveolar macrophages, cigarette smoke exposure increased the expression of both CX3CR1 and CX3CL1 genes. The inducibility of CX3CR1 expression was not solely dependent on a chronic stimulus because lipopolysaccharide up-regulated CX3CR1 in RAW264.7 cells in vitro and in mononuclear phagocytes in vivo. Our findings suggest a mechanism by which macrophages amplify and promote CX3CR1+ cell accumulation within the lungs during both acute and chronic inflammatory stress. We suggest that one function of the CX3CR1-CX3CL1 pathway is to recruit and sustain divergent immune cell populations implicated in the pathogenesis of cigarette smoke-induced emphysema.

Distinct chemokine and cytokine gene expression pattern of murine dendritic cells and macrophages in response to Mycobacterium tuberculosis infection

In this study, the early innate cytokine and chemokine response of murine dendritic cells (DCs) and macrophages to Mycobacterium tuberculosis infection was compared. The findings indicate a dissimilar gene expression pattern between the two cell types. The expression of IL-12 and IL-23, important for promoting Th1 and Th17 cells, respectively, was up-regulated only in DCs. In addition, expression of CCL1 and CCL17, which are important in recruitment of T regulatory cells, was DC-specific, as was the expression of the immunosuppressive cytokine IL-10. Macrophages, in contrast, exhibited enhanced expression for CCL2 and CXCL10, chemokines that recruit cells to sites of inflammation, and for mycobactericidal molecules NO synthase 2 and TNF. Together, the findings suggest that a component of the innate DC response is not only programmed toward Th1 priming but is also for controlling the magnitude of the Th1 response, and part of the macrophage response is intended for recruiting cells to the lung and for mycobactericidal functions.

Overexpression of cathepsin K in mice decreases collagen deposition and lung resistance in response to bleomycin-induced pulmonary fibrosis

Background

Lung fibrosis is a devastating pulmonary disorder characterized by alveolar epithelial injury, extracellular matrix deposition and scar tissue formation. Due to its potent collagenolytic activity, cathepsin K, a lysosomal cysteine protease is an interesting target molecule with therapeutic potential to attenuate bleomycin-induced pulmonary fibrosis in mice. We here tested the hypothesis that over-expression of cathepsin K in the lungs of mice is protective in bleomycin-induced pulmonary fibrosis.

Methods

Wild-type and cathepsin K overexpressing (cathepsin K transgenic; cath K tg) mice were challenged intratracheally with bleomycin and sacrificed at 1, 2, 3 and 4 weeks post-treatment followed by determination of lung fibrosis by estimating lung collagen content, lung histopathology, leukocytic infiltrates and lung function. In addition, changes in cathepsin K protein levels in the lung were determined by immunohistochemistry, real time RT-PCR and western blotting.

Results

Cathepsin K protein levels were strongly increased in alveolar macrophages and lung parenchymal tissue of mock-treated cathepsin K transgenic (cath K tg) mice relative to wild-type mice and further increased particularly in cath K tg but also wild-type mice in response to bleomycin. Moreover, cath K tg mice responded with a lower collagen deposition in their lungs, which was accompanied by a significantly lower lung resistance (R_L) compared to bleomycin-treated wild-type mice. In addition, cath K tg mice responded with a lower degree of lung fibrosis than wild-type mice, a process that was found to be independent of inflammatory leukocyte mobilization in response to bleomycin challenge.

Conclusion

Over-expression of cathepsin K reduced lung collagen deposition and improved lung function parameters in the lungs of transgenic mice, thereby providing at least partial protection against bleomycin-induced lung fibrosis.

Expression of CXC and CC type of chemokines and its receptors in tuberculous and non-tuberculous effusions

Chemokines mediate their biological functions by transmigration of various immune cells to the site of infection. Tuberculous pleurisy provides an effective model to study the role of chemokines in the recruitment of immune cells to the pleura. Our aim was to understand the cumulative effect of chemokines (IP-10, MIG, IL-8, MCP-1, MIP-1alpha and RANTES) and its receptors (CXCR2, CXCR3, CCR1, CCR2, CCR5 and CCR7) in the recruitment of CD4(+) T cells obtained from blood (BL) and pleural fluid (PF) of tuberculous (TB) and non-tuberculous (NTB) patients. We observed significant increase in CD4(+) T cells in TB PF indicating lymphocytic rich effusion. All chemokines except RANTES were significantly high in PF compared to BL in TB group, whereas IL-8 and MCP-1 showed significant increase only in NTB PF. The significantly high levels of IFN-gamma and TauNuF-alpha in TB PF and their positive correlation with IP-10 and MIP-1alpha indicated their synergistic action to elicit a strong protective Th1 response. In spite of high levels of Th1 cytokines and chemokines in TB PF, significantly lower levels of RANTES indicated its limited role at the site. The CXC receptors in PF of both the groups and CC receptors except CCR5 in TB PF were significantly high compared to BL. Only CXCR2, CCR5 and CCR7 showed significant increase in TB compared to NTB. Thus a selective concentration of chemokines, cytokines and abundant expression of chemokine receptors confirm the accumulation of activated and memory T cells at the site of infection and help in polarizing Th1 immune response.

FMS-like tyrosine kinase 3 ligand aggravates the lung inflammatory response to Streptococcus pneumoniae infection in mice: role of dendritic cells

Pretreatment of mice with the hemopoietic growth factor, FMS-like tyrosine kinase 3 ligand (Flt3L), has been shown to increase monocyte-derived myeloid dendritic cells (DC) in lung parenchymal tissue, with possible implications for protective immunity to lung bacterial infections. However, whether Flt3L treatment improves lung innate immunity of mice to challenge with Streptococcus pneumoniae has not been investigated previously. Mice pretreated with Flt3L exhibited a peripheral monocytosis and a strongly expanded lung myeloid DC pool, but responded with a similar proinflammatory cytokine release (TNF-alpha, IL-6, keratinocyte derived cytokine, MIP-2, CCL2) and neutrophilic alveolitis upon infection with S. pneumoniae as did control mice with a normal lung DC pool. Unexpectedly, however, Flt3L-pretreated mice, but not control mice, infected with S. pneumoniae developed vasculitis and increased lung permeability by days 2-3 postinfection, and florid pneumonia accompanied by sustained increased bacterial loads by days 3-4 postinfection. This was associated with an overall increased mortality of approximately 35% by day 4 after pneumococcal challenge. Application of anti-CCR2 Ab MC21 to block inflammatory monocyte-dependent lung mononuclear phagocyte mobilization significantly reduced the lung leakage, but not vasculitis in Flt3L-pretreated mice infected with S. pneumoniae, without affecting the intra-alveolar cytokine liberation or the concomitantly developing neutrophilic alveolitis. Together, the data demonstrate that previous Flt3L-induced lung DC accumulation is not protective in lung innate immunity to challenge with S. pneumoniae, and support the concept that CCR2-dependent mononuclear phagocyte as opposed to neutrophil recruitment contributes to increased lung leakage in Flt3L-pretreated mice challenged with S. pneumoniae.

Macrophage Turnover Kinetics in the Lungs of Mice Infected with Streptococcus pneumoniae

Streptococcus pneumoniae is the most prevalent cause of community-acquired pneumonia and is known to induce apoptosis and necrosis in macrophages in vivo. We analyzed the kinetics of alveolar and lung parenchymal macrophage replacement by newly recruited exudate macrophages in vehicle-treated and S. pneumoniae-challenged bone marrow chimeric CD45.1 mice. After lethal irradiation, CD45.1 alloantigen-expressing recipient mice were transplanted with bone marrow cells from CD45.2 alloantigen-expressing donor mice. After only 24 hours of low-dose S. pneumoniae infection, approximately 60% of CD45.1(pos) recipient-type alveolar macrophages (AM) were replaced by CD45.2(pos) donor-type exudate AM in bronchoalveolar lavage fluid, and this increased to more than 80% on Day 7 of infection. In contrast, lung parenchymal macrophages of S. pneumoniae-infected chimeric CD45.1 mice were replaced by only about 10% by 24 hours, although this increased to over 80% by Days 3 to 7 of infection. This dramatic macrophage turnover was accompanied by early induction of apoptosis/necrosis in donor-type exudate AM peaking at 6 hours after infection, whereas peak apoptosis/necrosis induction in recipient-type AM was delayed until Day 7. Collectively, these data for the first time demonstrate that S. pneumoniae infection of the lung triggers a brisk turnover of both resident and recruited mononuclear phagocyte subsets, and suggest an important role of exudate but not resident macrophages in re-establishing alveolar and lung homeostasis.

Lung-specific overexpression of CC chemokine ligand (CCL) 2 enhances the host defense to Streptococcus pneumoniae infection in mice: role of the CCL2-CCR2 axis

Mononuclear phagocytes are critical components of the innate host defense of the lung to inhaled bacterial pathogens. The monocyte chemotactic protein CCL2 plays a pivotal role in inflammatory mononuclear phagocyte recruitment. In this study, we tested the hypothesis that increased CCL2-dependent mononuclear phagocyte recruitment would improve lung innate host defense to infection with Streptococcus pneumoniae. CCL2 transgenic mice that overexpress human CCL2 protein in type II alveolar epithelial cells and secrete it into the alveolar air space showed a similar proinflammatory mediator response and neutrophilic alveolitis to challenge with S. pneumoniae as wild-type mice. However, CCL2 overexpressing mice showed an improved pneumococcal clearance and survival compared with wild-type mice that was associated with substantially increased lung mononuclear phagocyte subset accumulations upon pneumococcal challenge. Surprisingly, CCL2 overexpressing mice developed bronchiolitis obliterans upon pneumococcal challenge. Application of anti-CCR2 Ab MC21 to block the CCL2-CCR2 axis in CCL2 overexpressing mice, though completely abrogating bronchiolitis obliterans, led to progressive pneumococcal pneumonia. Collectively, these findings demonstrate the importance of the CCL2-CCR2 axis in the regulation of both the resolution/repair and remodelling processes after bacterial challenge and suggest that overwhelming innate immune responses may trigger bronchiolitis obliterans formation in bacterial lung infections.

A caspase-independent pathway mediates macrophage cell death in response to Mycobacterium tuberculosis infection

Macrophages can undergo apoptosis after infection with Mycobacterium tuberculosis. This macrophage response deprives the bacillus of its niche cell and supports the host response through better antigen presentation. The intracellular pathways of apoptosis that elaborate this macrophage response are not well understood. To address this issue, we investigated the contribution of various apoptosis pathways to M. tuberculosis-induced macrophage cell death. We found that macrophages die in a caspase-independent manner after infection with M. tuberculosis (at multiplicities of infection ranging from 1 to 20). There was evidence for the involvement of both the mitochondria (cleavage of Bid) and the lysosomes (cathepsin-mediated DNA fragmentation) in this cell death pathway. Dying macrophages displayed several features typical of apoptosis, including DNA fragmentation, nuclear condensation, and exposure of phosphatidylserine on the plasma membrane. However, nuclear fragmentation was not observed, which suggests that M. tuberculosis-induced cell death differs in some respects from classical apoptosis. This novel mechanism of cell death was blocked by serine protease inhibitors. A better understanding of this protective macrophage response may direct new vaccine and treatment options.