Cathepsin G in Experimental Tuberculosis: Relevance for Antibacterial Protection and Potential for Immunotherapy.

Neutrophil serine proteases, such as cathepsin G (CG) and neutrophil elastase (NE), have been implicated in the protective response against infections, including experimental mycobacterial infections. The goal of this study was to explore the role of CG in immunocompetent mice challenged aerogenically with Mycobacterium tuberculosis. We used genetically CG- or CG/NE-deficient mice to define the importance of these neutrophil serine proteases for antibacterial protection, granulomatous response, and survival. In addition, we explored the effect of intratracheally delivered liposomally encapsulated CG/NE as a therapeutic approach early during M. tuberculosis infection. Our data show that the presence of CG or CG/NE prolongs survival in M. tuberculosis-infected mice. However, CG is not directly involved in antibacterial defenses, and exogenous intratracheal administration of CG combined with NE does not reduce bacterial loads in the lungs of M. tuberculosis-infected 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.

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.

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.

Cathepsin G and neutrophil elastase play critical and nonredundant roles in lung-protective immunity against Streptococcus pneumoniae in mice.

Neutrophil serine proteases cathepsin G (CG), neutrophil elastase (NE), and proteinase 3 (PR3) have recently been shown to contribute to killing of Streptococcus pneumoniae in vitro. However, their relevance in lung-protective immunity against different serotypes of S. pneumoniae in vivo has not been determined so far. Here, we examined the effect of CG and CG/NE deficiency on the lung host defense against S. pneumoniae in mice. Despite similar neutrophil recruitment, both CG knockout (KO) mice and CG/NE double-KO mice infected with focal pneumonia-inducing serotype 19 S. pneumoniae demonstrated a severely impaired bacterial clearance, which was accompanied by lack of CG and NE but not PR3 proteolytic activity in recruited neutrophils, as determined using fluorescence resonance energy transfer (FRET) substrates. Moreover, both CG and CG/NE KO mice but not wild-type mice responded with increased lung permeability to infection with S. pneumoniae, resulting in severe respiratory distress and progressive mortality. Both neutrophil depletion and ablation of hematopoietic CG/NE in bone marrow chimeras abolished intra-alveolar CG and NE immunoreactivity and led to bacterial outgrowth in the lungs of mice, thereby identifying recruited neutrophils as the primary cellular source of intra-alveolar CG and NE. This is the first study showing a contribution of neutrophil-derived neutral serine proteases CG and NE to lung-protective immunity against focal pneumonia-inducing serotype 19 S. pneumoniae in mice. These data may be important for the development of novel intervention strategies to improve lung-protective immune mechanisms in critically ill patients suffering from severe pneumococcal pneumonia.

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.

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 (RL) 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.

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

Little is known about the activation programme induced in alveolar macrophages upon phagocytosis of mycobacteria and the concomitant mononuclear phagocyte migratory responses that shape the acute phase of mycobacterial infection. Using high-speed cell sorting in conjunction with real-time RT-PCR analysis, we show that sorted alveolar macrophages of transgenic CX3CR1+/GFP mice infected with red fluorescent-labelled Mycobacterium bovis BCG exhibited weak transcriptional changes of lysosomal cathepsins B, L, D, K and S, whereas antimicrobial cathepsin G was strongly induced upon infection. Moreover, mRNA levels of pattern recognition receptors TLR2, TLR4 and NOD2 were downregulated as were neutrophil chemoattractants KC, MIP-2 and IP-10, whereas highly upregulated mRNA levels of the monocyte chemoattractant CCL2 were observed. M. bovis BCG infection of the mice elicited the alveolar accumulation of highly CX3CR1-positive alveolar dendritic cells but not neutrophils within the alveolar compartment, whereas no increased accumulation of CX3CR1high lung parenchymal dendritic cells (lung DC) or CX3CR1neg lung macrophages compared with controls was noted. In contrast, CX3CR1+/GFP mice previously immunized with M. bovis BCG rapidly responded with increased accumulations of both CX3CR1high alveolar and lung parenchymal DC and CX3CR1neg lung macrophages upon intratracheal M. bovis BCG challenge. Moreover, alveolar and lung macrophages and lung DC were found to contribute to early uptake of M. bovis BCG. Together, acute mycobacterial infection triggers both rapid changes in gene expression profiles in infected alveolar macrophages and a compartment-specific accumulation of mononuclear phagocyte subsets contributing to M. bovis BCG uptake in vivo.