Cytokine kinetics and other host factors in response to pneumococcal pulmonary infection in mice

Avian reovirus sigma C enhances the mucosal and systemic immune responses elicited by antigen-conjugated lactic acid bacteria

Mucosal surfaces are common sites of pathogen colonization/entry. Effective mucosal immunity by vaccination should provide protection at this primary infection site. Our aim was to develop a new vaccination strategy that elicits a mucosal immune response. A new strain of Enterococcus faecium, a non pathogenic lactic acid bacteria (LAB) with strong cell adhesion ability, was identified and used as a vaccine vector to deliver two model antigens. Specifically, sigma (σ) C protein of avian reovirus (ARV), a functional homolog of mammalian reovirus σ1 protein and responsible for M-cell targeting, was administered together with a subfragment of the spike protein of infectious bronchitis virus (IBV). Next, the effect of immunization route on the immune response was assessed by delivering the antigens via the LAB strain. Intranasal (IN) immunization induced stronger humoral responses than intragastic (IG) immunization. IN immunization produced antigen specific IgA both systemically and in the lungs. A higher IgA titer was induced by the LAB with ARV σC protein attached. Moreover, the serum of mice immunized with LAB displaying divalent antigens had much stronger immune reactivity against ARV σC protein compared to IBV-S1. Our results indicate that ARV σC protein delivered by LAB via the IN route elicits strong mucosal immunity. A needle-free delivery approach is a convenient and cost effective method of vaccine administration, especially for respiratory infections in economic animals. Furthermore, ARV σC, a strong immunogen of ARV, may be able to serve as an immunoenhancer for other vaccines, especially avian vaccines.

Neutralizing antibodies elicited by a novel detoxified pneumolysin derivative, PlyD1, provide protection against both pneumococcal infection and lung injury

Streptococcus pneumoniae pneumolysin (PLY) is a virulence factor that causes toxic effects contributing to pneumococcal pneumonia. To date, deriving a PLY candidate vaccine with the appropriate detoxification and immune profile has been challenging. A pneumolysin protein that is appropriately detoxified and that retains its immunogenicity is a desirable vaccine candidate. In this study, we assessed the protective efficacy of our novel PlyD1 detoxified PLY variant and investigated its underlying mechanism of protection. Results have shown that PlyD1 immunization protected mice against lethal intranasal (i.n.) challenge with pneumococci and lung injury mediated by PLY challenge. Protection was associated with PlyD1-specific IgG titers and in vitro neutralization titers. Pretreatment of PLY with PlyD1-specific rat polyclonal antiserum prior to i.n. delivery of toxin reduced PLY-mediated lung lesions, interleukin-6 (IL-6) production, and neutrophil infiltration into lungs, indicating that protection from lung lesions induced by PLY is antibody mediated. Preincubation of PLY with a neutralizing monoclonal PLY antibody also specifically reduced the cytotoxic effects of PLY after i.n. inoculation in comparison to nonneutralizing monoclonal antibodies. These results indicate that the induction of neutralizing antibodies against PLY can contribute to protection against bacterial pneumonia by preventing the development of PLY-induced lung lesions and inflammation. Our detoxified PlyD1 antigen elicits such PLY neutralizing antibodies, thus serving as a candidate vaccine antigen for the prevention of pneumococcal pneumonia.

Osteopathic lymphatic pump techniques to enhance immunity and treat pneumonia

Pneumonia is a common cause of morbidity and mortality worldwide. While antibiotics are generally effective for the treatment of infection, the emergence of resistant strains of bacteria threatens their success. The osteopathic medical profession has designed a set of manipulative techniques called lymphatic pump techniques (LPT), to enhance the flow of lymph through the lymphatic system. Clinically, LPT is used to treat infection and oedemaand might be an effective adjuvant therapy in patients with pneumonia.The immune system uses the lymphatic and blood systems to survey to rid the body of pathogens; however, only recently have the effects of LPT on the lymphatic and immune systems been investigated. This short review highlightsclinical and basic science research studies that support the use of LPT to enhance the lymphatic and immune systems and treat pneumonia, and discusses the potential mechanisms by which LPT benefits patients with pneumonia.

Regulation of normal and cystic fibrosis airway epithelial repair processes by TNF-α after injury

Chronic infection and inflammation have been associated with progressive airway epithelial damage in patients with cystic fibrosis (CF). However, the effect of inflammatory products on the repair capacity of respiratory epithelia is unclear. Our objective was to study the regulation of repair mechanisms by tumor necrosis factor-α (TNF-α), a major component of inflammation in CF, in a model of mechanical wounding, in two bronchial cell lines, non-CF NuLi and CF CuFi. We observed that TNF-α enhanced the NuLi and CuFi repair rates. Chronic exposure (24–48 h) to TNF-α augmented this stimulation as well as the migration rate during repair. The cellular mechanisms involved in this stimulation were then evaluated. First, we discerned that TNF-α induced metalloproteinase-9 release, epidermal growth factor (EGF) shedding, and subsequent EGF receptor transactivation. Second, TNF-α-induced stimulation of the NuLi and CuFi wound-closure rates was prevented by GM6001 (metalloproteinase inhibitor), EGF antibody (to titrate secreted EGF), and EGF receptor tyrosine kinase inhibitors. Furthermore, we recently reported a relationship between the EGF response and K+channel function, both controlling bronchial repair. We now show that TNF-α enhances KvLQT1 and KATPcurrents, while their inhibition abolishes TNF-α-induced repair stimulation. These results indicate that the effect of TNF-α is mediated, at least in part, through EGF receptor transactivation and K+channel stimulation. In contrast, cell proliferation during repair was slowed by TNF-α, suggesting that TNF-α could exert contrasting actions on repair mechanisms of CF airway epithelia. Finally, the stimulatory effect of TNF-α on airway wound repair was confirmed on primary airway epithelial cells, from non-CF and CF patients.

Endothelial cells are central orchestrators of cytokine amplification during influenza virus infection

Cytokine storm during viral infection is a prospective predictor of morbidity and mortality, yet the cellular sources remain undefined. Here, using genetic and chemical tools to probe functions of the S1P₁ receptor, we elucidate cellular and signaling mechanisms that are important in initiating cytokine storm. Whereas S1P₁ receptor is expressed on endothelial cells and lymphocytes within lung tissue, S1P₁ agonism suppresses cytokines and innate immune cell recruitment in wild-type and lymphocyte-deficient mice, identifying endothelial cells as central regulators of cytokine storm. Furthermore, our data reveal immune cell infiltration and cytokine production as distinct events that are both orchestrated by endothelial cells. Moreover, we demonstrate that suppression of early innate immune responses through S1P₁ signaling results in reduced mortality during infection with a human pathogenic strain of influenza virus. Modulation of endothelium with a specific agonist suggests that diseases in which amplification of cytokine storm is a significant pathological component could be chemically tractable.

Characterization of a new mouse model of empyema and the mechanisms of pleural invasion by Streptococcus pneumoniae

Although empyema affects more than 65,000 people each year in the United States and in the United Kingdom, there are limited data on the pathogenesis of pleural infection. We investigated the pathogenesis of empyema using animal and cell culture models of Streptococcus pneumoniae infection. The pathological processes during the development of empyema associated with murine pneumonia due to S. pneumoniae (strain D39) were investigated. Lungs were examined using histology, and pleural fluid and blood bacterial colony-forming units, cytokine levels, and cellular infiltrate were determined over time. Bacterial migration across mesothelial monolayers was investigated using cell culture techniques, flow cytometry, and confocal microscopy. After intranasal inoculation with 10(7) S. pneumoniae D39 strain, mice developed pneumonia associated with rapid bacterial invasion of the pleural space; raised intrapleural IL-8, VEGF, MCP-1, and TNF-α levels; and caused significant intrapleural neutrophilia followed by the development of fibrinous pleural adhesions. Bacterial clearance from the pleural space was poor, and in vitro assays demonstrated that S. pneumoniae crossed mesothelial layers by translocation through cells rather than by a paracellular route. This study describes key events during the development of S. pneumoniae empyema using a novel murine model of pneumonia-associated empyema that closely mimics human disease. The model allows for future assessment of molecular mechanisms involved in the development of empyema and evaluation of potential new therapies. The data suggest that transmigration of bacteria through mesothelial cells could be important in empyema development. Furthermore, upon entry the pleural cavity offers a protected compartment for the bacteria.

Suppression of cytokine storm with a sphingosine analog provides protection against pathogenic influenza virus

Human pandemic H1N1 2009 influenza virus rapidly infected millions worldwide and was associated with significant mortality. Antiviral drugs that inhibit influenza virus replication are the primary therapy used to diminish disease; however, there are two significant limitations to their effective use: (i) antiviral drugs exert selective pressure on the virus, resulting in the generation of more fit viral progeny that are resistant to treatment; and (ii) antiviral drugs do not directly inhibit immune-mediated pulmonary injury that is a significant component of disease. Here we show that dampening the host's immune response against influenza virus using an immunomodulatory drug, AAL-R, provides significant protection from mortality (82%) over that of the neuraminidase inhibitor oseltamivir alone (50%). AAL-R combined with oseltamivir provided maximum protection against a lethal challenge of influenza virus (96%). Mechanistically, AAL-R inhibits cellular and cytokine/chemokine responses to limit immunopathologic damage, while maintaining host control of virus replication. With cytokine storm playing a role in the pathogenesis of a wide assortment of viral, bacterial, and immunologic diseases, a therapeutic approach using sphingosine analogs is of particular interest.

The integrins Mac-1 and alpha4beta1 perform crucial roles in neutrophil and T cell recruitment to lungs during Streptococcus pneumoniae infection

Neutrophils and T cells play an important role in host protection against pulmonary infection caused by Streptococcus pneumoniae. However, the role of the integrins in recruitment of these cells to infected lungs is not well understood. In this study we used the twin approaches of mAb blockade and gene-deficient mice to investigate the relative impact of specific integrins on cellular recruitment and bacterial loads following pneumococcal infection. We find that both Mac-1 (CD11b/CD18) and α(4)β(1) (CD49d/CD29) integrins, but surprisingly not LFA-1 (CD11a/CD18), contribute to two aspects of the response. In terms of recruitment from the circulation into lungs, neutrophils depend on Mac-1 and α(4)β(1), whereas the T cells are entirely dependent on α(4)β(1). Second, immunohistochemistry results indicate that adhesion also plays a role within infected lung tissue itself. There is widespread expression of ICAM-1 within lung tissue. Use of ICAM-1(-/-) mice revealed that neutrophils make use of this Mac-1 ligand, not for lung entry or for migration within lung tissue, but for combating the pneumococcal infection. In contrast to ICAM-1, there is restricted and constitutive expression of the α(4)β(1) ligand, VCAM-1, on the bronchioles, allowing direct access of the leukocytes to the airways via this integrin at an early stage of pneumococcal infection. Therefore, integrins Mac-1 and α(4)β(1) have a pivotal role in prevention of pneumococcal outgrowth during disease both in regulating neutrophil and T cell recruitment into infected lungs and by influencing their behavior within the lung tissue itself.

Mathematical model of a three-stage innate immune response to a pneumococcal lung infection

Pneumococcal pneumonia is a leading cause of death and a major source of human morbidity. The initial immune response plays a central role in determining the course and outcome of pneumococcal disease. We combine bacterial titer measurements from mice infected with Streptococcus pneumoniae with mathematical modeling to investigate the coordination of immune responses and the effects of initial inoculum on outcome. To evaluate the contributions of individual components, we systematically build a mathematical model from three subsystems that describe the succession of defensive cells in the lung: resident alveolar macrophages, neutrophils and monocyte-derived macrophages. The alveolar macrophage response, which can be modeled by a single differential equation, can by itself rapidly clear small initial numbers of pneumococci. Extending the model to include the neutrophil response required additional equations for recruitment cytokines and host cell status and damage. With these dynamics, two outcomes can be predicted: bacterial clearance or sustained bacterial growth. Finally, a model including monocyte-derived macrophage recruitment by neutrophils suggests that sustained bacterial growth is possible even in their presence. Our model quantifies the contributions of cytotoxicity and immune-mediated damage in pneumococcal pathogenesis.

Pneumolysin activates the NLRP3 inflammasome and promotes proinflammatory cytokines independently of TLR4

Pneumolysin (PLY) is a key Streptococcus pneumoniae virulence factor and potential candidate for inclusion in pneumococcal subunit vaccines. Dendritic cells (DC) play a key role in the initiation and instruction of adaptive immunity, but the effects of PLY on DC have not been widely investigated. Endotoxin-free PLY enhanced costimulatory molecule expression on DC but did not induce cytokine secretion. These effects have functional significance as adoptive transfer of DC exposed to PLY and antigen resulted in stronger antigen-specific T cell proliferation than transfer of DC exposed to antigen alone. PLY synergized with TLR agonists to enhance secretion of the proinflammatory cytokines IL-12, IL-23, IL-6, IL-1β, IL-1α and TNF-α by DC and enhanced cytokines including IL-17A and IFN-γ by splenocytes. PLY-induced DC maturation and cytokine secretion by DC and splenocytes was TLR4-independent. Both IL-17A and IFN-γ are required for protective immunity to pneumococcal infection and intranasal infection of mice with PLY-deficient pneumococci induced significantly less IFN-γ and IL-17A in the lungs compared to infection with wild-type bacteria. IL-1β plays a key role in promoting IL-17A and was previously shown to mediate protection against pneumococcal infection. The enhancement of IL-1β secretion by whole live S. pneumoniae and by PLY in DC required NLRP3, identifying PLY as a novel NLRP3 inflammasome activator. Furthermore, NLRP3 was required for protective immunity against respiratory infection with S. pneumoniae. These results add significantly to our understanding of the interactions between PLY and the immune system.

Inhibition of T cells provides protection against early invasive pneumococcal disease

Infections caused by Streptococcus pneumoniae are major causes of morbidity and mortality, which are in part mediated by immune cell-dependent mechanisms. Yet, the specific contributions of individual cell types to immunopathology are only partially understood. T cells are well characterized with respect to their function in protective humoral immune responses; however, their roles during early stages of infection and invasive pneumococcal disease (IPD) are less well defined. Using a mouse model of pneumococcal sepsis, we found that CD4(+) T cells were recruited to the lung as early as 12 h after intranasal infection. Recruitment was accompanied by upregulation of CD69 and B7-H1, reflecting T-cell activation. Unexpectedly, major histocompatibility complex (MHC) class II-deficient mice, which lack CD4(+) T cells, displayed an increased survival despite comparable bacterial titers in the blood, spleen, and lung. The higher survival correlated with a lower cytokine and chemokine response upon S. pneumoniae challenge in MHC class II-deficient mice, suggesting that inflammation may contribute to the mortality of IPD. Comparable to the case for MHC class II-deficient mice, antibody-mediated depletion of CD4(+) T cells and drug-induced inhibition of T-cell function with cyclosporine, or interference with T-cell activation using CTLA4-immunoglobulin (Abatacept), led to significant increases in survival during IPD. Our results reveal an important and adverse role of CD4(+) T cells in the pathogenesis of IPD and suggest that modulation of T-cell activation during early phases of S. pneumoniae invasive infection may provide a therapeutic option.

The MerR/NmlR family transcription factor of Streptococcus pneumoniae responds to carbonyl stress and modulates hydrogen peroxide production

The NmlR(sp) transcription factor of Streptococcus pneumoniae is shown to induce adhC (alcohol dehydrogenase) expression in the presence of both formaldehyde and methylglyoxal. nmlR(sp) and adhC mutant strains display altered and opposite aerobic growth phenotypes. The nmlR(sp) strain exhibits increased resistance to high oxygen tension, attributable to decreased H(2)O(2) production, which correlated with downregulation of carbamoyl phosphate synthase (carB). This indicates a possible role for AdhC in aldehyde metabolism and a broader role for NmlR(sp) in the regulation of carbon metabolism.

Enhanced immune response to pneumococcal infection in malnourished mice nasally treated with heat-killed Lactobacillus casei

The present study analyzed whether nasal administration of viable and non-viable Lactobacillus casei CRL 431 to immunocompromised mice was capable of increasing resistance against Streptococcus pneumoniae. Weaned mice were malnourished after consuming a PFD for 21 days. Malnourished mice were fed a BCD for 7 days or BCD for 7 days with viable or non-viable L. casei nasal treatments on day 6 and day 7 (BCD+LcV and BCD+LcN, respectively). The MNC group received PFD whereas the WNC mice consumed BCD. MNC mice showed greater lung colonization, more severe lung injuries, impaired leukocyte recruitment and reduced antibodies and cytokine production when compared with WNC mice. Administration of L. casei increased the resistance of malnourished mice to the infection. Both BCD+LcV and BCD+LcN treatments prevented the dissemination of the pathogen to the blood and induced its lung clearance. BCD+LcV or BCD+LcN groups showed improved production of TNF-alpha and activity of phagocytes in the respiratory tract, an effect that was not observed in the BCD control group. In addition, IL-4 and IL-10 were significantly increased in BCD+LcV and BCD+LcN groups, which correlated with the increase in the levels of specific respiratory IgA. The nasal treatments with L. casei were also effective at stimulating the production of specific IgG at both the systemic and the respiratory levels. The comparative study between the viable and the non-viable bacteria demonstrated that viability would be an important factor to achieve maximum protective effects. However, the results from this study suggest that heat-killed lactic acid bacteria are also effective in the immunomodulation of the systemic and respiratory immune system.

Neutrophils and macrophages work in concert as inducers and effectors of adaptive immunity against extracellular and intracellular microbial pathogens

Emerging data suggest new facets of the concerted participation of neutrophils and macrophages in antimicrobial immunity. The classical view is that DCs and macrophages are the inducers of adaptive antimicrobial immunity, but there is evidence for neutrophil participation in this task as cytokine and chemokine producers and APCs. On the other hand, the concept that the T(H)1 response is only associated with control of infections by intracellular pathogens through activation of macrophages by IFN-gamma, and the T(H)17/IL-17 axis is only involved in protection against extracellular pathogens through mobilization and activation of neutrophils is simplistic: There is evidence suggesting that T(H)1 and T(H)17 responses, separately or in parallel, may use macrophages and neutrophils against infections by extracellular and intracellular microbial pathogens. Opsonization by pathogen-specific Igs enhances the antimicrobial capabilities of neutrophils and macrophages in infections by extracellular and intracellular microbes. The functional partnership between macrophages and neutrophils as inducers and effectors of adaptive antimicrobial immunity conforms to their affiliation with the myeloid phagocyte system and reveals a strategy based on the concurrent use of the two professional phagocytes in the adaptive defense mechanisms. Starting from a common myeloid precursor in the bone marrow, macrophages and neutrophils split during differentiation but come together at the infectious foci for a cooperative strategy that uses modulator and effector activities to attack invading microbial pathogens.

A mathematical model of pulmonary gas exchange under inflammatory stress

During a severe local or systemic inflammatory response, immune mediators target lung tissue. This process may lead to acute lung injury and impaired diffusion of gas molecules. Although several mathematical models of gas exchange have been described, none simulate acute lung injury following inflammatory stress. In view of recent laboratory and clinical progress in the understanding of the pathophysiology of acute lung injury, such a mathematical model would be useful. We first derived a partial differential equations model of gas exchange on a small physiological unit of the lung ( approximately 25 alveoli), which we refer to as a respiratory unit (RU). We next developed a simple model of the acute inflammatory response and implemented its effects within a RU, creating a single RU model. Linking multiple RUs with various ventilation/perfusion ratios and taking into account pulmonary venous blood remixing yielded our lung-scale model. Using the lung-scale model, we explored the predicted effects of inflammation on ventilation/perfusion distribution and the resulting pulmonary venous partial pressure oxygen level during systemic inflammatory stresses. This model represents a first step towards the development of anatomically faithful models of gas exchange and ventilation under a broad range of local and systemic inflammatory stimuli resulting in acute lung injury, such as infection and mechanical strain of lung tissue.

Of mice and men: innate immunity in pneumococcal pneumonia

Pneumococcal pneumonia is characterised by an intense inflammatory response induced mainly by cell wall components of the bacterium. Recognition of cell wall components by Toll-like receptors (TLRs) induces intracellular signalling pathways that culminate in the activation of pro-inflammatory genes through nuclear factor kappaB (NF-kappaB). Tumour necrosis factor-alpha (TNFalpha) is one of the earliest mediators produced and induces a second wave of pro- and anti-inflammatory cytokines that orchestrate the immune response. The magnitude of this response in patients with pneumococcal pneumonia is a complex network and many factors must be considered in the analysis of the cytokine production pattern. First, bacterial growth and the inflammatory response are dynamic processes, produced initially as a local phenomenon with a late systemic extension. Second, host characteristics, such as different cytokine gene polymorphisms, can cause a distinct immune response. Finally, other microorganism determinants and even the immunomodulatory effect of antimicrobials may play a role in cytokine production. Recent data on innate immunity against Streptococcus pneumoniae gathered from the murine model of pneumonia, from studies of human genetic polymorphisms associated with increased susceptibility to pneumococcal infection, and from human clinical trials are discussed. Special emphasis has been placed on the description of the chronology of the complex network of innate immunity triggered by pneumococcal infection.

Cigarette smoke exposure impairs pulmonary bacterial clearance and alveolar macrophage complement-mediated phagocytosis of Streptococcus pneumoniae

Cigarette smoke exposure increases the risk of pulmonary and invasive infections caused by Streptococcus pneumoniae, the most commonly isolated organism from patients with community-acquired pneumonia. Despite this association, the mechanisms by which cigarette smoke exposure diminishes host defense against S. pneumoniae infections are poorly understood. In this study, we compared the responses of BALB/c mice following an intratracheal challenge with S. pneumoniae after 5 weeks of exposure to room air or cigarette smoke in a whole-body exposure chamber in vivo and the effects of cigarette smoke on alveolar macrophage phagocytosis of S. pneumoniae in vitro. Bacterial burdens in cigarette smoke-exposed mice were increased at 24 and 48 h postinfection, and this was accompanied by a more pronounced clinical appearance of illness, hypothermia, and increased lung homogenate cytokines interleukin-1beta (IL-1beta), IL-6, IL-10, and tumor necrosis factor alpha (TNF-alpha). We also found greater numbers of neutrophils in bronchoalveolar lavage fluid recovered from cigarette smoke-exposed mice following a challenge with heat-killed S. pneumoniae. Interestingly, overnight culture of alveolar macrophages with 1% cigarette smoke extract, a level that did not affect alveolar macrophage viability, reduced complement-mediated phagocytosis of S. pneumoniae, while the ingestion of unopsonized bacteria or IgG-coated microspheres was not affected. This murine model provides robust additional support to the hypothesis that cigarette smoke exposure increases the risk of pneumococcal pneumonia and defines a novel cellular mechanism to help explain this immunosuppressive effect.

The virulence variability of different Acinetobacter baumannii strains in experimental pneumonia

OBJECTIVES

Our objective was to compare the virulence of 5 strains of Acinetobacter baumannii by using a mouse model of pneumonia.

METHODS

Six-week old female C3H/HeN mice were used. The pneumonia was inducted by intra-tracheal inoculation of 5.10(6) bacteria. Spontaneous outcome was evaluated by mortality, mice weight variations, and a clinical score. Bacterial counts in lungs, spleen and blood, and inflammatory response in lungs (dosages of tumor necrosis factor-alpha and macrophage inflammatory protein-2) were also measured. Lastly, a histological examination of lungs was performed for 3 strains, giving a histological score.

RESULTS

Global mortality varied from 13% to 79% (P<10(-4)). Bacterial counts in lungs within the 4 days following inoculation varied significantly according to different strains. The evolution curves of bacterial counts were also different. There was a significant correlation between the clinical score and mortality (P<0.05) but not between bacterial counts in lungs and mortality. The increase of pro-inflammatory mediator production in lungs and the histological score also varied according to strains.

CONCLUSIONS

These results demonstrate the variability of the virulence between strains, and suggest that bacterial proliferation is not the only virulence factor responsible for the pathogenesis in A. baumannii pneumonia.

EFFECTS OF SPECIFIC NEUTROPHIL ELASTASE INHIBITOR, SIVELESTAT SODIUM HYDRATE, IN MURINE MODEL OF SEVERE PNEUMOCOCCAL PNEUMONIA

An excessive amount of neutrophil elastase (NE) released from neutrophils accumulated in the lung can cause tissue damage, despite its importance to host defense against microbial pathogens in severe pneumonia. Therefore, NE inhibitors may reduce tissue damage in lungs with severe pneumonia. In this study, the efficacy of a specific NE inhibitor, sivelestat sodium hydrate (sivelestat), was examined using a murine model of severe pneumonia with Streptococcus pneumoniae. Male mice (CBA/JNCrj, aged 5 weeks) were inoculated intranasally with penicillin-susceptible S. pneumonia (1.0 x 10(5) CFU/mouse). Sivelestat (3 mg/kg) or physiological saline was administered every 12 hours beginning at 12 hours after inoculation. Survival was primarily evaluated. Bronchoalveolar lavage fluid (BALF) and blood were collected at 30 hours after inoculation. Thus, cell counts in BALF and numbers of viable bacteria in blood were determined. Histopathological analysis was also performed. Sivelestat significantly prolonged survival when compared with the control group (P < .05), although all animals died within 4 days. Cell count and histopathological analysis indicated that sivelestat prevented the progression of lung inflammation, such as alveolar neutrophil infiltration and hemorrhage. Furthermore, the number of viable bacteria in blood was significantly lower in the sivelestat group than in the control group (5.69 +/- 0.27 and 6.75 +/- 0.32 log CFU/mL, respectively; mean +/- SEM, P < .01). Sivelestat prolonged survival in this model. A possible explanation for the improved survival is that sivelestat prevents tissue damage by inhibiting NE activity in the lung. Therefore, NE inhibitors may be useful for treating with patients with severe pneumonia.

Cellular effectors mediating Th17-dependent clearance of pneumococcal colonization in mice

Microbial colonization of mucosal surfaces may be an initial event in the progression to disease, and it is often a transient process. For the extracellular pathogen Streptococcus pneumoniae studied in a mouse model, nasopharyngeal carriage is eliminated over a period of weeks and requires cellular rather than humoral immunity. Here, we demonstrate that primary infection led to TLR2-dependent recruitment of monocyte/macrophages into the upper airway lumen, where they engulfed pneumococci. Pharmacologic depletion of luminal monocyte/macrophages by intranasal instillation of liposomal clodronate diminished pneumococcal clearance. Efficient clearance of colonization required TLR2 signaling to generate a population of pneumococcal-specific IL-17-expressing CD4+ T cells. Depletion of either IL-17A or CD4+ T cells was sufficient to block the recruitment of monocyte/macrophages that allowed for effective late pneumococcal clearance. In contrast with naive mice, previously colonized mice showed enhanced early clearance that correlated with a more robust influx of luminal neutrophils. As for primary colonization, these cellular responses required Th17 immunity. Our findings demonstrate that monocyte/macrophages and neutrophils recruited to the mucosal surface are key effectors in clearing primary and secondary bacterial colonization, respectively.

Animal models of Streptococcus pneumoniae disease

SUMMARY

Streptococcus pneumoniae is a colonizer of human nasopharynx, but it is also an important pathogen responsible for high morbidity, high mortality, numerous disabilities, and high health costs throughout the world. Major diseases caused by S. pneumoniae are otitis media, pneumonia, sepsis, and meningitis. Despite the availability of antibiotics and vaccines, pneumococcal infections still have high mortality rates, especially in risk groups. For this reason, there is an exceptionally extensive research effort worldwide to better understand the diseases caused by the pneumococcus, with the aim of developing improved therapeutics and vaccines. Animal experimentation is an essential tool to study the pathogenesis of infectious diseases and test novel drugs and vaccines. This article reviews both historical and innovative laboratory pneumococcal animal models that have vastly added to knowledge of (i) mechanisms of infection, pathogenesis, and immunity; (ii) efficacies of antimicrobials; and (iii) screening of vaccine candidates. A comprehensive description of the techniques applied to induce disease is provided, the advantages and limitations of mouse, rat, and rabbit models used to mimic pneumonia, sepsis, and meningitis are discussed, and a section on otitis media models is also included. The choice of appropriate animal models for in vivo studies is a key element for improved understanding of pneumococcal disease.

Enhanced immediate inflammatory response to Streptococcus pneumoniae in the lungs of mice with pulmonary emphysema

BACKGROUND AND OBJECTIVE

Pulmonary emphysema is associated with frequent respiratory infections but little is known about the reasons for this susceptibility to bacterial infection. We previously demonstrated an impaired inflammatory response to Streptococcus pneumoniae in an experimental emphysema mouse model at 24 h, or longer following bacterial inoculation. Toll-like receptors (TLR) have been recognized as regulators in the inflammatory response. We examined the expression of TLR on alveolar macrophages in experimental emphysema mice and evaluated the immediate inflammatory response of the emphysematous lung to streptococcal infection.

METHODS

Elastase was administered once into mice trachea to induce pulmonary emphysema. Three weeks later, expression of TLR-2 and TLR-4 in the BAL cells was examined by immunostaining. Following the intratracheal inoculation of Streptococcus pneumoniae, pro-inflammatory cytokine concentrations were measured in the BAL fluids of the control and emphysema mice.

RESULTS

The expression of TLR-2 and TLR-4 was significantly elevated in the alveolar macrophages of emphysema mice. Six hours after infection, neutrophils in the BAL fluid of emphysema mice were significantly increased, and the levels of tumour necrosis factor-alpha, IL-1beta and IL-6 were significantly elevated, compared with the control mice. At 3 h post inoculation, macrophage inflammatory protein-2 levels were significantly elevated.

CONCLUSIONS

The immediate inflammatory response in the emphysematous lung is significantly enhanced in response to streptococcal infection. This may be partly attributed to the increased expression of TLR in the alveolar macrophages of emphysema mice.

Effect of high dose oral zinc in mice with severe infection with Streptococcus pneumoniae

Zinc is important for normal function of the immune system and inflammation increases the demand for zinc. We hypothesized that high doses of zinc given during acute pneumococcal illness would alter the severity of infection. 24 six-week-old BALB/c mice were anaesthetized and infected intranasally with Streptococcus pneumoniae. Zinc intake was controlled by administering zinc through an intragastric tube. One group was given normal doses (5 microg/d) and the other group high doses of zinc (225 microg/d). We counted the number of bacteria from venous blood at 24 and 48 h, and from heart puncture and nasal wash at 72 h after intranasal challenge. Mice given excess zinc had 2.65 micromol/l, i.e. 25% higher (p= 0.05) mean plasma zinc concentration compared to those given normal amounts. 75% of mice in both groups developed pneumococcal bacteraemia. There were no differences in the numbers of S. pneumoniae colony forming units (CFUs) in blood or nasal wash between the groups. Thus, high doses of zinc did not alter the severity of systemic pneumococcal infection in mice.

Induction of beta defensin 2 by NTHi requires TLR2 mediated MyD88 and IRAK-TRAF6-p38MAPK signaling pathway in human middle ear epithelial cells

Background

All mucosal epithelia, including those of the tubotympanium, are secreting a variety of antimicrobial innate immune molecules (AIIMs). In our previous study, we showed the bactericidal/bacteriostatic functions of AIIMs against various otitis media pathogens. Among the AIIMs, human β-defensin 2 is the most potent molecule and is inducible by exposure to inflammatory stimuli such as bacterial components or proinflammatory cytokines. Even though the β-defensin 2 is an important AIIM, the induction mechanism of this molecule has not been clearly established. We believe that this report is the first attempt to elucidate NTHi induced β-defensin expression in airway mucosa, which includes the middle ear.

Methods

Monoclonal antibody blocking method was employed in monitoring the TLR-dependent NTHi response. Two gene knock down methods – dominant negative (DN) plasmid and small interfering RNA (siRNA) – were employed to detect and confirm the involvement of several key genes in the signaling cascade resulting from the NTHi stimulated β-defensin 2 expression in human middle ear epithelial cell (HMEEC-1). The student's t-test was used for the statistical analysis of the data.

Results

The experimental results showed that the major NTHi-specific receptor in HMEEC-1 is the Toll-like receptor 2 (TLR2). Furthermore, recognition of NTHi component(s)/ligand(s) by TLR2, activated the Toll/IL-1 receptor (TIR)-MyD88-IRAK1-TRAF6-MKK3/6-p38 MAPK signal transduction pathway, ultimately leading to the induction of β-defensin 2.

Conclusion

This study found that the induction of β-defensin 2 is highest in whole cell lysate (WCL) preparations of NTHi, suggesting that the ligand(s) responsible for this up-regulation may be soluble macromolecule(s). We also found that this induction takes place through the TLR2 dependent MyD88-IRAK1-TRAF6-p38 MAPK pathway, with the primary response occurring within the first hour of stimulation. In combination with our previous studies showing that IL-1α-induced β-defensin 2 expression takes place through a MyD88-independent Raf-MEK1/2-ERK MAPK pathway, we found that both signaling cascades act synergistically to up-regulate β-defensin 2 levels. We propose that this confers an essential evolutionary advantage to the cells in coping with infections and may serve to amplify the innate immune response through paracrine signaling.

Systemic expression of cytokine production in patients with severe pneumococcal pneumonia: effects of treatment with a beta-lactam versus a fluoroquinolone

Bacterial alveolar invasion is followed by an inflammatory response. A systemic extension of the compartmentalized immune response has been described in patients with severe pneumonia. The data suggest that some antimicrobials may induce a differential release of cytokines. We conducted a prospective, randomized study in adult patients with severe pneumococcal pneumonia to measure the effects of ceftriaxone and levofloxacin in the systemic cytokine expression over time. Demographic, clinical characteristics, and severity scores were recorded. The serum concentrations of tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), IL-6, IL-8, IL-10, and IL-1 receptor agonist were measured at 0, 24, 72, and 120 h. A total of 32 patients were included in the study. Both groups were homogeneous in terms of age, comorbidities, severity of disease, and corticosteroid or statin use. With the single exception of IL-1beta, all cytokines were detected in venous blood. All of the cytokines studied showed a similar pattern of progressive decrease over time. No significant differences in the concentrations of any of the cytokines studied were found, with the exception of TNF-alpha, for which lower concentrations were obtained at 120 h in the levofloxacin group (P = 0.014). Basal oxygen saturation (P = 0.034) and heart rate (P = 0.029) returned to normal values earlier in the levofloxacin arm. We demonstrated that in patients with severe pneumococcal pneumonia pro- and anti-inflammatory responses could be detected in venous blood, representing a systemic extension of the compartmentalized response. Treatment with a beta-lactam agent or a fluoroquinolone has different effects on cytokine production and its systemic expression, impacting the clinical course of the disease.

Pneumococcal virulence gene expression and host cytokine profiles during pathogenesis of invasive disease

Pneumococcal disease continues to account for significant morbidity and mortality worldwide. For the development of novel prophylactic and therapeutic strategies against the disease spectrum, a complete understanding of pneumococcal behavior in vivo is necessary. We evaluated the expression patterns of the proven and putative virulence factor genes adcR, cbpA, cbpD, cbpG, cpsA, nanA, pcpA, piaA, ply, psaA, pspA, and spxB after intranasal infection of CD1 mice with serotype 2, 4, and 6A pneumococci by real-time reverse transcription-PCR. Simultaneous gene expression patterns of selected host immunomodulatory molecules, CCL2, CCL5, CD54, CXCL2, interleukin-6, and tomor necrosis factor alpha, were also investigated. We show that pneumococcal virulence genes are differentially expressed in vivo, with some genes demonstrating niche- and serotype-specific differential expression. The in vivo expression patterns could not be attributed to in vitro differences in expression of the genes in transparent and opaque variants of the three strains. The host molecules were significantly upregulated, especially in the lungs, blood, and brains of mice. The pneumococcal-gene expression patterns support their ascribed roles in pathogenesis, providing insight into which protein combinations might be more appropriate as vaccine antigens against invasive disease. This is the first simultaneous comparison of bacterial- and host gene expression in the same animal during pathogenesis. The strategy provides a platform for prospective evaluation of interaction kinetics between invading pneumococci and human patients in culture-positive cases and should be feasible in other infection models.

Serum amyloid P aids complement-mediated immunity to Streptococcus pneumoniae

The physiological functions of the acute phase protein serum amyloid P (SAP) component are not well defined, although they are likely to be important, as no natural state of SAP deficiency has been reported. We have investigated the role of SAP for innate immunity to the important human pathogen Streptococcus pneumoniae. Using flow cytometry assays, we show that SAP binds to S. pneumoniae, increases classical pathway–dependent deposition of complement on the bacteria, and improves the efficiency of phagocytosis. As a consequence, in mouse models of infection, mice genetically engineered to be SAP-deficient had an impaired early inflammatory response to S. pneumoniae pneumonia and were unable to control bacterial replication, leading to the rapid development of fatal infection. Complement deposition, phagocytosis, and control of S. pneumoniae pneumonia were all improved by complementation with human SAP. These results demonstrate a novel and physiologically significant role for SAP for complement-mediated immunity against an important bacterial pathogen, and provide further evidence for the importance of the classical complement pathway for innate immunity.

Serum amyloid P (SAP) is a protein that is found in high concentrations in the blood, the exact function(s) of which are not clear. However, no known natural state of SAP deficiency has been identified, which suggests that SAP does have a vital role in human health. SAP can bind to molecular patterns found on the surface of bacteria, and it has been proposed that this may mark bacteria for attack by the immune system. We have investigated whether SAP helps protect against an important bacterial pathogen, Streptococcus pneumoniae. We show that SAP binds to different strains of S. pneumoniae, and that this leads to activation of an important component of the immune response called the complement system. Complement is particularly important for defence against S. pneumoniae infections, and using animal models of infection, we demonstrate that loss of SAP makes mice more susceptible to S. pneumoniae pneumonia. These results suggest that SAP helps the immune system to recognise invasion by bacteria and describe a new mechanism required for control of S. pneumoniae infections. This study may help the design of new therapeutic strategies to prevent or treat important bacterial diseases.

Experimental severe Pseudomonas aeruginosa pneumonia and antibiotic therapy in piglets receiving mechanical ventilation

BACKGROUND

Little is known about the general and local consequences of severe pneumonia under mechanical ventilation (SPMV) and how these are resolved with antibiotic therapy (ABT).

OBJECTIVES

To investigate the physiologic, biological, microbiological, and pathologic changes produced by experimental SPMV in a porcine model, and to evaluate the effect of ABT.

METHODS

Pseudomonas aeruginosa was inoculated in 12 large white-Landrace piglets receiving mechanical that were killed after 72 h if death did not occur before. Vital signs, serum and BAL cytokines, serum C-reactive protein (CRP), and graded postmortem lung pathology and cultures (blood and quantitative BAL and lung) were evaluated. Six piglets received inappropriate ABT (no ABT or ceftriaxone), and six piglets received appropriate ABT (ciprofloxacin).

MEASUREMENTS AND MAIN RESULTS

Pathologic and microbiological evidence of infection were present in all the animals in both groups. SPMV produced significant oxygenation and lung compliance worsening, increased serum CRP, and reduced BAL fluid tumor necrosis factor (TNF)-alpha. Arterial thrombosis in lung pathology was associated with higher temperature, hypoxemia and low lung compliance, higher initial serum CRP and TNF-alpha concentrations, and increased serum interleukin (IL)-6 and BAL IL-6 and TNF-alpha. Reduced ABT reduced body temperature and culture positivity.

CONCLUSIONS

This model resembles VAP and has been used for studying pulmonary infection and inflammation related to mechanical ventilation. ABT reduced fever and bacterial burden in SPMV but had no effect on cytokine or CRP concentrations, oxygenation, or lung mechanics. Pulmonary artery thrombosis was associated with worse response to infection.

Leptin improves pulmonary bacterial clearance and survival in ob/ob mice during pneumococcal pneumonia

The adipocyte-derived hormone leptin is an important regulator of appetite and energy expenditure and is now appreciated for its ability to control innate and adaptive immune responses. We have reported previously that the leptin-deficient ob/ob mouse exhibited increased susceptibility to the Gram-negative bacterium Klebsiella pneumoniae. In this report we assessed the impact of chronic leptin deficiency, using ob/ob mice, on pneumococcal pneumonia and examined whether restoring circulating leptin to physiological levels in vivo could improve host defences against this pathogen. We observed that ob/ob mice, compared with wild-type (WT) animals, exhibited enhanced lethality and reduced pulmonary bacterial clearance following Streptococcus pneumoniae challenge. These impairments in host defence in ob/ob mice were associated with elevated levels of lung tumour necrosis factor (TNF)-alpha, macrophage inflammatory peptide (MIP)-2 [correction added after online publication 28 September 2007: definition of MIP corrected], prostaglandin E(2) (PGE(2)), lung neutrophil polymorphonuclear leukocyte (PMN) counts, defective alveolar macrophage (AM) phagocytosis and PMN killing of S. pneumoniae in vitro. Exogenous leptin administration to ob/ob mice in vivo improved survival and greatly improved pulmonary bacterial clearance, reduced bacteraemia, reconstituted AM phagocytosis and PMN H(2)O(2) production and killing of S. pneumoniae in vitro. Our results demonstrate, for the first time, that leptin improves pulmonary bacterial clearance and survival in ob/ob mice during pneumococcal pneumonia. Further investigations are warranted to determine whether there is a potential therapeutic role for this adipokine in immunocompromised patients.

In Silico Modeling in Infectious Disease

Infectious disease has witnessed the emergence of mathematical modeling a tool of synthesizing data of growing complexity now available to clinicians and basic scientists alike. The purpose of this review is to introduce mathematical tools commonly used to model infectious disease. We will illustrate the use of equation-based, agent-based or statistical modeling approaches to a variety of examples pertaining to acute inflammation, bacterial dynamics, viral dynamics, and signaling pathways, focusing of host-pathogen interactions rather than population models. We will discuss the strengths and weaknesses of these approaches and offer future perspectives for this rapidly evolving field.

Trevor Trust – AstraZeneca R&D Boston, 35 Gatehouse Drive, Waltham, MA 02451, USA

Differential contribution of bacterial N-formyl-methionyl-leucyl- phenylalanine and host-derived CXC chemokines to neutrophil infiltration into pulmonary alveoli during murine pneumococcal pneumonia

Despite the development of new potent antibiotics, Streptococcus pneumoniae remains the leading cause of death from bacterial pneumonia. Polymorphonuclear neutrophil (PMN) recruitment into the lungs is a primordial step towards host survival. Bacterium-derived N-formyl peptides (N-formyl-methionyl-leucyl-phenylalanine [fMLP]) and host-derived chemokines (KC and macrophage inflammatory protein 2 [MIP-2]) are likely candidates among chemoattractants to coordinate PMN infiltration into alveolar spaces. To investigate the contribution of each in the context of pneumococcal pneumonia, CD1, BALB/c, CBA/ca, C57BL/6, and formyl peptide receptor (FPR)-knockout C57BL/6 mice were infected with 10(6) or 10(7) CFU of penicillin/erythromycin-susceptible or -resistant serotype 3 or 14 S. pneumoniae strains. Antagonists to the FPR, such as cyclosporine H (CsH) and chenodeoxycholic acid, or neutralizing antibodies to KC and MIP-2 were injected either 1 h before or 30 min after infection, and then bronchoalveolar lavage fluids were obtained for quantification of bacteria, leukocytes, and chemokines. CsH was effective over a short period after infection with a high inoculum, while anti-CXC chemokine antibodies were effective after challenge with a low inoculum. CsH prevented PMN infiltration in CD1 mice infected with either serotype 3 or 14, whereas antichemokine antibodies showed better efficacy against the serotype 3 strain. When different mouse strains were challenged with serotype 3 bacteria, CsH prevented PMN migration in the CD1 mice only, whereas the antibodies were effective against CD1 and C57BL/6 mice. Our results suggest that fMLP and chemokines play important roles in pneumococcal pneumonia and that these roles vary according to bacterial and host genetic backgrounds, implying redundancy among chemoattractant molecules.

Direct examination and cultures of bronchoalveolar lavage in pneumonia diagnosis: a comparative experimental study

OBJECTIVE

To assess the accuracy of direct examination and quantitative cultures of BAL to diagnose pneumonia with or without antibiotic treatment.

DESIGN

Experimental rat models.

INTERVENTIONS

Pneumonia was induced by intratracheal inoculation of S. pneumoniae (10(9) cfu/ml) or P. aeruginosa (10(8)cfu/ml). Controls (n = 10) received sterile inoculum. Study animals received penicillin (n = 19) or saline (n = 18) (pneumococcal model); amikacin (n = 13), ceftazidime (n = 11), or saline (n = 13) (Pseudomonas model). BAL was assessed 48 h after infection. The animals were killed for histopathological analysis.

RESULTS

All study animals developed pneumonia, which was more extensive in the pneumococcal than in the Pseudomonas model. In pneumococcal pneumonia the sensitivity of BAL cultures (10(3) cfu/ml or higher) was 77.8% with saline and 21.0% with penicillin. In the Pseudomonas ceftazidime group all specimens were negative, precluding diagnosis. The sensitivity of cultures with amikacin was 23.1% vs. 30.8% with saline. In the pneumococcal model intracellular organism (ICO) count of 2% or higher had a sensitivity of 100% for detecting pneumonia with saline and 57.9% with penicillin. In the Pseudomonas model the sensitivity of ICO was 69.2% with both amikacin and saline and 36.3% with ceftazidime. The sensitivity of neutrophil count above 50% in pneumococcal pneumonia was 77.8% and 64.7% with saline and penicillin, respectively, and 69.2%, 61.5%, and 81.8% with saline, amikacin, and ceftazidime, respectively, in Pseudomonas pneumonia.

CONCLUSIONS

BAL-positive intracellular organisms were more accurate than cultures for the diagnosis of recent pneumonia, and were less affected by antibiotic treatment.

Pulmonary stromal-derived factor-1 expression and effect on neutrophil recruitment during acute lung injury

The severe and protracted inflammation that characterizes acute lung injury (ALI) is driven by the ongoing recruitment of neutrophils to the lung. Although much of the cytokine signaling responsible for the initial phase of ALI has been elaborated, relatively little is known about the mechanisms governing the recruitment of neutrophils from the bone marrow to the lung in the later period of this disease. Given its previously described chemoattractant effects on marrow neutrophils, we investigated whether stromal-derived factor-1 (SDF-1) (CXCL12) might participate in this later phase of recruitment. Using immunohistochemistry to examine both banked human lung specimens from patients with ALI and lungs from mice with LPS-induced pneumonitis, we found that pulmonary SDF-1 expression increases during ALI. We further determined that both lung SDF-1 protein expression and mRNA expression rise in a delayed but sustained pattern in this mouse model and that the major source of the increase in expression appears to be the lung epithelium. Lastly, we found that expression of the SDF-1 receptor CXCR4 rises in a similar temporal pattern on neutrophils in both the blood and airspace of LPS-injured mice and that Ab-mediated SDF-1 blockade significantly attenuates late but not early pulmonary neutrophilia in this model. These results implicate SDF-1 in neutrophil recruitment to the lung in the later period of acute lung injury and suggest a novel role for this cytokine in coordinating the transition from the inflammatory response to the initiation of tissue repair.

High pneumococcal DNA loads are associated with mortality in Malawian children with invasive pneumococcal disease

BACKGROUND

In bacteremia owing to Streptococcus pneumoniae, high bacterial counts at presentation have been shown to be predictive of the development of serious invasive disease. Using real-time PCR, we aimed to determine pneumococcal DNA loads in blood and CSF, and their relationship to cytokine concentrations, clinical presentation and outcome.

METHODS

Children with confirmed meningitis (n = 82) or pneumonia (n = 13) were prospectively recruited, and blood and CSF samples taken for pneumococcal bacterial DNA loads and cytokine determination.

RESULTS

At the time of admission, the median bacterial load in blood was 1.6 x 10 DNA copies/mL (range 0.00-1.54 x 10) and in CSF it was 5.77 x 10 DNA copies/mL (range 4.42 x 10 to 6.15 x 10). Median blood and CSF bacterial loads (log DNA copies/mL) were significantly higher in nonsurvivors than in survivors; blood (3.80 vs. 2.97, P = 0.003), CSF (8.17 vs. 7.50, P = 0.03). In HIV-infected children (n = 59), blood and CSF loads and plasma tumor necrosis factor-alpha, interleukin-1beta (IL-1beta), IL-6 and IL-10 were all significantly higher in nonsurvivors than in survivors, but in HIV-uninfected children (n = 36) this difference was not significant. Blood bacterial loads and plasma cytokine concentrations were significantly associated, and were all significantly higher in children with meningitis than in those with pneumonia. In children with meningitis, median CSF cytokine concentrations were significantly higher than median plasma cytokine concentrations (P < 0.001) and CSF bacterial loads were significantly associated with CSF IL-1beta (P = 0.002) and IL-10 (P = 0.001) concentrations.

CONCLUSIONS

Pneumococcal DNA loads are associated with plasma cytokine concentrations, and are higher in meningitis than in pneumonia. High blood and CSF pneumococcal DNA loads are associated with a fatal outcome.

Modulation of adherence, invasion, and tumor necrosis factor alpha secretion during the early stages of infection by Streptococcus pneumoniae ClpL

Heat shock proteins (HSPs) play a pivotal role as chaperones in the folding of native and denatured proteins and can help pathogens penetrate host defenses. However, the underlying mechanism(s) of modulation of virulence by HSPs has not been fully determined. In this study, the role of the chaperone ClpL in the pathogenicity of Streptococcus pneumoniae was assessed. A clpL mutant adhered to and invaded nasopharyngeal or lung cells much more efficiently than the wild type adhered to and invaded these cells in vitro, as well as in vivo, although it produced the same amount of capsular polysaccharide. However, the level of secretion of tumor necrosis factor alpha (TNF-alpha) from macrophages infected with the clpL mutant was significantly lower than the level of secretion elicited by the wild type during the early stages of infection. Interestingly, treatment of the human lung epithelial carcinoma A549 and murine macrophage RAW 264.7 cell lines with cytochalasin D, an inhibitor of actin polymerization, increased adherence of the mutant to the host cells. In contrast, cytochalasin D treatment of RAW 264.7 cells decreased TNF-alpha secretion after infection with either the wild type or the mutant. However, pretreatment of cell lines with the actin polymerization activator jasplakinolide reversed these phenotypes. These findings indicate, for the first time, that the ClpL chaperone represses adherence of S. pneumoniae to host cells and induces secretion of TNF-alpha via a mechanism dependent upon actin polymerization during the initial infection stage.

Influence of neutropenia on the course of serotype 8 pneumococcal pneumonia in mice

Polymorphoneutrophils (PMNs) are important effector cells in host defense against pneumonia. However, PMNs can also induce inflammation and tissue damage. To investigate the contribution of PMNs to host defense against pneumococcal pneumonia, we determined the effect of the PMN-depleting rat monoclonal antibody RB6-8C5 (RB6) on survival and inflammatory and cellular response in the lungs to a lethal intranasal infection with a serotype 8 pneumococcus in BALB/c mice. Control mice received rat immunoglobulin G (rIgG). Strikingly, the survival of RB6-treated mice was significantly prolonged compared to that of rIgG-treated mice. Although the numbers of CFU in the lungs were statistically similar in both groups 4, 24, and 32 h after infection, rIgG-treated mice developed higher levels of bacteremia, and histopathological examination of the lungs of infected mice revealed marked differences between RB6- and rIgG-treated mice. RB6-treated mice had focal, perivascular lesions without accompanying parenchymal inflammation, and rIgG-treated mice had diffuse, interstitial parenchymal inflammation. Lung homogenates from the rIgG-treated mice had more leukocytes and significantly more total and apoptotic PMNs as determined by fluorescence-activated cell sorter analysis with Annexin V and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling staining of lung tissue samples. Studies with a pneumolysin-deficient mutant of the serotype 8 strain we used also demonstrated the prolonged survival of RB6- compared to rIgG-treated mice. Taken together, our findings suggest that PMNs enhance the likelihood of early death and alter the pathological response to pneumococcal lung infection in BALB/c mice with serotype 8 pneumonia without significantly affecting bacterial clearance or the cytokine response.

Contributions of pneumolysin, pneumococcal surface protein A (PspA), and PspC to pathogenicity of Streptococcus pneumoniae D39 in a mouse model

Successful colonization of the upper respiratory tract by Streptococcus pneumoniae is an essential first step in the pathogenesis of pneumococcal disease. However, the bacterial and host factors that provoke the progression from asymptomatic colonization to invasive disease are yet to be fully defined. In this study, we investigated the effects of single and combined mutations in genes encoding pneumolysin (Ply), pneumococcal surface protein A (PspA), and pneumococcal surface protein C (PspC, also known as choline-binding protein A) on the pathogenicity of Streptococcus pneumoniae serotype 2 (D39) in mice. Following intranasal challenge with D39, stable colonization of the nasopharynx was maintained over a 7-day period at a level of approximately 10(5) bacteria per mouse. The abilities of the mutant deficient in PspA to colonize the nasopharynx and to cause lung infection and bacteremia were significantly reduced. Likewise, the PspC mutant and, to a lesser extent, the Ply mutant also had reduced abilities to colonize the nasopharynx. As expected, the double mutants colonized less well than the parent to various degrees and had difficulty translocating to the lungs and blood. A significant additive attenuation was observed for the double and triple mutants in pneumonia and systemic disease models. Surprisingly, the colonization profile of the derivative lacking all three proteins was similar to that of the wild type, indicating virulence gene compensation. These findings further demonstrate that the mechanism of pneumococcal pathogenesis is highly complex and multifactorial but ascribes a role for each of these virulence proteins, alone or in combination, in the process.

Beneficial immunomodulatory activity of Lactobacillus casei in malnourished mice pneumonia: effect on inflammation and coagulation

OBJECTIVE

The effect of Lactobacillus casei CRL 431 immunomodulatory activity on inflammation and coagulation during pneumococcal pneumonia was investigated in malnourished mice.

METHODS

Weaned mice were malnourished after they consumed a protein-free diet for 21 d. Malnourished mice were treated for 7 d with a balanced conventional diet (BCD) with L. casei supplementation (BCD+Lc) or without it. The malnourished control group received only a protein-free diet whereas well-nourished control (WNC) mice consumed BCD ad libitum. Mice were challenged by the intranasal route with pneumococci at the end of each dietary treatment. Lung injury, leukocyte recruitment, cytokine production, coagulation tests, and fibrin(ogen) deposition in lungs were evaluated.

RESULTS

Malnourished control mice showed impaired leukocyte recruitment and cytokine production, and more severe lung injuries when compared with WNC mice. Coagulation tests were significantly impaired in malnourished control group versus WNC group. Repletion with BCD or BCD+Lc improved these parameters, but only BCD+Lc mice achieved the values of WNC mice. In addition, the interleukin-10 level was higher in the BCD+Lc group than in the WNC group.

CONCLUSION

Repletion with supplemental L. casei accelerated recovery of the defense mechanisms against pneumococci by inducing different cytokine profiles. These cytokines would be involved in the improvement of the immune response and in the induction of a more efficient regulation of the inflammatory process, limiting the injury caused by infection.

Decreased Alveolar Macrophage Apoptosis Is Associated with Increased Pulmonary Inflammation in a Murine Model of Pneumococcal Pneumonia

Regulation of the inflammatory infiltrate is critical to the successful outcome of pneumonia. Alveolar macrophage apoptosis is a feature of pneumococcal infection and aids disease resolution. The host benefits of macrophage apoptosis during the innate response to bacterial infection are incompletely defined. Because NO is required for optimal macrophage apoptosis during pneumococcal infection, we have explored the role of macrophage apoptosis in regulating inflammatory responses during pneumococcal pneumonia, using inducible NO synthase (iNOS)-deficient mice. iNOS(-/-) mice demonstrated decreased numbers of apoptotic macrophages as compared with wild-type C57BL/6 mice following pneumococcal challenge, greater recruitment of neutrophils to the lung and enhanced expression of TNF-alpha. Pharmacologic inhibition of iNOS produced similar results. Greater pulmonary inflammation was associated with greater levels of early bacteremia, IL-6 production, lung inflammation, and mortality within the first 48 h in iNOS(-/-) mice. Labeled apoptotic alveolar macrophages were phagocytosed by resident macrophages in the lung and intratracheal instillation of exogenous apoptotic macrophages decreased neutrophil recruitment in iNOS(-/-) mice and decreased TNF-alpha mRNA in lungs and protein in bronchial alveolar lavage, as well as chemokines and cytokines including IL-6. These changes were associated with a lower probability of mice becoming bacteremic. This demonstrates the potential of apoptotic macrophages to down-regulate the inflammatory response and for the first time in vivo demonstrates that clearance of apoptotic macrophages decreases neutrophil recruitment and invasive bacterial disease during pneumonia.

Differential role of CbpA and PspA in modulation of in vitro CXC chemokine responses of respiratory epithelial cells to infection with Streptococcus pneumoniae

Respiratory epithelial cells play an active part in the host response to respiratory pathogens, such as Streptococcus pneumoniae, by releasing chemokines responsible for neutrophil recruitment. In order to investigate the role of specific pneumococcal virulence factors in eliciting CXC chemokine responses, type II pneumocytes (A549) and nasopharyngeal cells (Detroit-562) were infected with S. pneumoniae D39 or mutants lacking choline-binding protein A (CbpA), pneumococcal surface protein A (PspA), or specific domains thereof. In response to wild-type D39, both A549 and Detroit-562 cells showed a significant increase in CXC chemokine mRNA and interleukin-8 protein. This response was increased twofold when a cbpA deletion mutant (DeltaCbpA) was used, suggesting that CbpA inhibits CXC chemokine induction. All three N-terminal domains of CbpA are required for this effect, as in-frame deletion of the respective region of cbpA had the same effect on the CXC chemokine response as deletion of cbpA altogether. Infection with a pspA deletion mutant (DeltaPspA) led to a twofold decrease in the CXC chemokine response of A549 but not Detroit-562 cells, compared to infection with D39 at 2 h. Thus, PspA appears to have the ability to stimulate early CXC chemokine release from A549 cells. Deletion of the region of pspA encoding the first N-terminal alpha-helical domain reduced the ability of S. pneumoniae to elicit a chemokine response to the same degree as deletion of pspA altogether. Thus, the N termini of CbpA and PspA exert differential effects on CXC chemokine induction in epithelial cells infected with S. pneumoniae.