Pulmonary interleukin-23 gene delivery increases local T-cell immunity and controls growth of Mycobacterium tuberculosis in the lungs

Interleukin-23 (IL-23) is a heterodimeric cytokine that shares IL-12 p40 but contains a unique p19 subunit similar to IL-12 p35. Previous studies indicate a greater importance for intact IL-12/23 p40 expression than IL-12 p35 for immunity against Mycobacterium tuberculosis, suggesting a role for IL-23 in host defense. The effects of IL-23 on the outcome of pulmonary infection with M. tuberculosis have not been described. Here, we show that local delivery of replication-defective adenovirus vectors encoding IL-23 (AdIL-23) greatly stimulated expression of both gamma interferon (IFN-gamma) and IL-17 in lung tissues of otherwise normal mice. When given 72 h prior to infection with M. tuberculosis, AdIL-23 significantly reduced the bacterial burden at 14, 21, and 28 days. Markedly lower levels of lung inflammation were observed at 28 days than in control mice pretreated with control adenovirus (AdNull) or vehicle controls. AdIL-23 pretreatment resulted in increased numbers of CD4(+) CD25(+) activated T cells in lungs and draining lymph nodes compared to control groups and more CD4(+) T cells bearing surface memory markers in lung lymph nodes. IL-23 gene delivery also significantly enhanced host anti-mycobacterial T-cell responses, as shown by elevated levels of IFN-gamma and IL-17 secreted in vitro following restimulation with M. tuberculosis purified protein derivative. Overall, our data show that transient IL-23 gene delivery in the lung is well tolerated, and they provide the initial demonstration that this factor controls mycobacterial growth while augmenting early pulmonary T-cell immunity.     

Cyclic di-GMP stimulates protective innate immunity in bacterial pneumonia

Innate immunity is the primary mechanism by which extracellular bacterial pathogens are effectively cleared from the lung. We have previously shown that cyclic di-GMP (c-di-GMP [c-diguanylate]) is a novel small molecule immunomodulator and immunostimulatory agent that triggers protective host innate immune responses. Using a murine model of bacterial pneumonia, we show that local intranasal (i.n.) or systemic subcutaneous (s.c.) administration of c-di-GMP prior to intratracheal (i.t.) challenge with Klebsiella pneumoniae stimulates protective immunity against infection. Specifically, i.n. or s.c. administration of c-di-GMP 48 and 24 h prior to i.t. K. pneumoniae challenge resulted in significantly increased survival. Pretreatment with c-di-GMP resulted in a 5-fold reduction in bacterial CFU in the lung (P < 0.05) and an impressive >1,000-fold decrease in CFU in the blood (P < 0.01). c-di-GMP administration stimulated a robust innate response to bacterial challenge, characterized by enhanced accumulation of neutrophils and alphabeta T cells, as well as activated NK and alphabeta T lymphocytes, which was associated with earlier and more vigorous expression of chemokines and type I cytokines. Moreover, lung macrophages recovered from Klebsiella-infected mice pretreated with c-di-GMP expressed greater quantities of inducible nitric oxide synthase and nitric oxide ex vivo than did macrophages isolated from infected mice pretreated with the control, c-GMP. These findings demonstrate that c-di-GMP delivered in either a compartmentalized or systemic fashion stimulates protective innate immunity in the lung and protects mice against bacterial invasion. We propose that the cyclic dinucleotide c-di-GMP may be used clinically as an effective immunomodulator, immune enhancer, and vaccine adjuvant to protect against respiratory infection and pneumonia in humans and animals.     

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.     

LPS-binding protein-deficient mice have an impaired defense against Gram-negative but not Gram-positive pneumonia

LPS-binding protein (LBP) can facilitate the transfer of cell wall components of both Gram-negative bacteria (LPS) and Gram-positive bacteria (lipoteichoic acid) to inflammatory cells. Although LBP is predominantly produced in the liver, recent studies have indicated that this protein is also synthesized locally in the lung by epithelial cells. To determine the role of LBP in the immune response to pneumonia, LBP gene-deficient (-/-) and normal wild-type (WT) mice were intra-nasally infected with either Streptococcus pneumoniae or Klebsiella pneumoniae, common Gram-positive and Gram-negative pathogens, respectively. Pneumococcal pneumonia was associated with a 7-fold rise in LBP concentrations in bronchoalveolar lavage fluid of WT mice; LBP-/- mice infected with S. pneumoniae showed a similar survival and a similar bacterial burden in their lungs 48 h post-infection. In Klebsiella pneumonia, however, LBP-/- mice demonstrated a diminished survival together with an enhanced bacterial outgrowth in their lungs. These data suggest that LBP is important for a protective immune response in Klebsiella pneumonia, but does not contribute to an effective host response in pneumococcal pneumonia.     

Immunostimulation with macrophage-activating lipopeptide-2 increased survival in murine pneumonia

Community-acquired pneumonia (CAP) is associated with high morbidity and mortality, and Streptococcus pneumoniae is the most prevalent causal pathogen identified in CAP. Impaired pulmonary host defense increases susceptibility to pneumococcal pneumonia. S. pneumoniae may up-regulate Toll-like receptor (TLR)-2 expression and activate TLR-2, contributing to pneumococcus-induced immune responses. In the current study, the course of severe murine pneumococcal pneumonia after pulmonary TLR-2-mediated immunostimulation with synthetic macrophage-activating lipopeptide-2 (MALP-2) was examined. Intratracheal MALP-2 application evoked enhanced proinflammatory cytokine and chemokine release, resulting in recruitment of polymorphonuclear neutrophils (PMN), macrophages, and lymphocytes into the alveolar space in WT, but not in TLR-2-deficient mice. In murine lungs as well as in human alveolar epithelial cells (A549), MALP-2 increased TLR-2 expression at both mRNA and protein level. Blood leukocyte numbers and populations remained unchanged. MALP-2 application 24 hours before intranasal pneumococcal infection resulted in increased levels of CCL5 associated with augmented leukocyte recruitment, and decreased levels of anti-inflammatory IL-10 in bronchoalveolar lavage fluid. Clinically, MALP-2-treated as compared with untreated mice showed increased survival, reduced hypothermia, and increased body weight. MALP-2 also reduced bacteremia and improved bacterial clearance in lung parenchyma, as examined by immunohistochemistry. In conclusion, pulmonary immunostimulation with MALP-2 before infection with S. pneumoniae improved local host defense and increased survival in murine pneumococcal pneumonia.     

Tumor necrosis factor mediates lung antibacterial host defense in murine Klebsiella pneumonia.

Tumor necrosis factor (TNF) is a proinflammatory cytokine which has recently been shown to have beneficial effects in the setting of acquired host immunity. However, the role of TNF in innate immune responses, as in the setting of bacterial pneumonia, has been incompletely characterized. To determine the role of TNF in gram-negative bacterial pneumonia, CBA/J mice were challenged with 10(2) CFU of Klebsiella pneumoniae intratracheally, resulting in the time-dependent expression of TNF MRNA and protein within the lung. Passive immunization of animals with a soluble TNF receptor-immunoglobulin (Ig) construct (sTNFR:Fc) intraperitoneally 2 h prior to K. pneumoniae inoculation resulted in a significant reduction in bronchoalveolar lavage neutrophils, but not macrophages, at 48 h, as compared with animals receiving control IgG1. Furthermore, treatment with sTNFR:Fc resulted in 19.6- and 13.5-fold increases in K. pneumoniae CFU in lung homogenates and plasma, respectively, as compared with animals receiving control IgG1. Finally, treatment of Klebsiella-infected mice with sTNFR:Fc markedly decreased both short- and long-term survival of these animals. In conclusion, our studies indicate that endogenous TNF is a critical component of antibacterial host defense in murine Klebsiella pneumonia.     

Role of lung epithelial cells in defense against Klebsiella pneumoniae pneumonia

The airway epithelium represents a primary site for the entry of pathogenic bacteria into the lungs. It has been suggested for many respiratory pathogens, including Klebsiella pneumoniae, that adhesion and invasion of the lung epithelial cells is an early stage of the pneumonia process. We observed that poorly encapsulated K. pneumoniae clinical isolates and an isogenic unencapsulated mutant invaded lung epithelial cells more efficiently than highly encapsulated strains independent of the K type. By contrast, the unencapsulated mutant was completely avirulent in a mouse model of pneumonia, unlike the wild-type strain, which produced pneumonia and systemic infection. Furthermore, the unencapsulated mutant bound more epithelially produced complement component C3 than the wild-type strain. Our results show that lung epithelial cells play a key role as a host defense mechanism against K. pneumoniae pneumonia, using two different strategies: (i) ingestion and control of the microorganisms and (ii) opsonization of the microorganisms. Capsular polysaccharide avoids both mechanisms and enhances the virulence of K. pneumoniae.     

The role of CD44 in the acute and resolution phase of the host response during pneumococcal pneumonia

Streptococcus pneumoniae is the most prevalent pathogen causing community-acquired pneumonia. CD44 is a transmembrane adhesion molecule, expressed by a wide variety of cell types, that has several functions in innate and adaptive immune responses. In this study, we tested the hypothesis that CD44 is involved in the host response during pneumococcal pneumonia. On intranasal infection with a lethal dose of S. pneumoniae CD44-knockout (KO) mice showed a prolonged survival when compared with wild-type mice, which was accompanied by a diminished pulmonary bacterial growth and reduced dissemination to distant body sites. Whereas, proinflammatory cytokine responses and lung pathology were not affected, CD44 deficiency resulted in increased early neutrophil influx into the lung. In separate experiments, we confirmed a detrimental role of CD44 in host defense against pneumococci during sublethal pneumonia, as demonstrated by an improved capacity of CD44 KO mice to clear a low infectious dose. In addition, CD44 appeared important for the resolution of lung inflammation during sublethal pneumonia, as shown by histopathology of lung tissue slides. In conclusion, we show here that CD44 facilitates bacterial outgrowth and dissemination during pneumococcal pneumonia, which in lethal infection results in a prolonged survival of CD44 KO mice. Moreover, during sublethal pneumonia CD44 contributes to the resolution of the inflammatory response.     

Divergent role of gamma interferon in a murine model of pulmonary versus systemic Klebsiella pneumoniae infection

Klebsiella pneumoniae is a leading cause of both community-acquired and nosocomial gram-negative-bacterial pneumonia. A further clinical complication of pulmonary K. pneumoniae infection is dissemination of bacteria from the lung into the peripheral blood, resulting in bacteremia concurrent with the localized pulmonary infection. Here, we report studies detailing the divergent role of gamma interferon (IFN-gamma) in pulmonary versus systemic K. pneumoniae infection. Intratracheal inoculation of IFN-gamma knockout mice resulted in significantly increased mortality compared to that observed for wild-type infected animals. Increased mortality correlated with a 100-fold increase in pulmonary bacteria within 2 days postinfection and upregulation of lung-associated interleukin-10 (IL-10) mRNA. Interestingly, IFN-gamma knockout mice had a twofold reduction in plasma aminospartate transferase activity, indicating diminished liver injury following peripheral blood bacterial dissemination. To study the host response towards blood-borne bacteria in the absence of the ongoing pulmonary infection, intravenous inoculation studies were initiated. IFN-gamma knockout mice were no more susceptible to intravenous infection than their wild-type counterparts. The consistent observation in IFN-gamma knockout mice was for improved survival correlating with increased clearance of blood- and liver-associated bacteria. Intravenous inoculation resulted in a two- to threefold increase in hepatic IL-10 production 24 and 48 h postinfection. Liver injury was also significantly reduced in IFN-gamma knockout mice. These data indicate that IFN-gamma secretion is a critical mediator in the resolution of localized gram-negative pulmonary pneumonia. Surprisingly, host responses towards systemic infection with the same bacteria appear to be IFN-gamma independent.     

NLRC4 suppresses IL-17A-mediated neutrophil-dependent host defense through upregulation of IL-18 and induction of necroptosis during Gram-positive pneumonia

Gram-positive pathogens, including Staphylococcus aureus, cause necrotizing pneumonia. The central feature of S. aureus pneumonia is toxin-induced necroptosis of immune and resident cells, which impedes host defense. However, the role of the NLRC4 in the lung following S. aureus infection remains elusive. Here, we demonstrate that S. aureus activates the NLRC4 to drive necroptosis and IL-18 production, which impaired IL-17A-dependent neutrophil-mediated host susceptibility. In particular, Nlrc4^−/− mice exhibit reduced necroptosis, enhanced neutrophil influx into the lungs, decreased bacterial burden, and improved host survival. Loss of NLRC4 signaling in both hematopoietic and non-hematopoietic cells contributes to the host protection against S. aureus pneumonia. Secretion of IL-17A by γδ T cells is essential for neutrophil recruitment into the lungs of Nlrc4^−/− mice following infection. Moreover, treatment of wild-type mice with necroptosis inhibitors or genetic ablation of MLKL and IL-18 improves host defense against S. aureus infection, which is associated with increased IL-17A+γδ T cells and neutrophils. Taken together, these novel findings reveal that S. aureus activates the NLRC4 to dampen IL-17A-dependent neutrophil accumulation through induction of necroptosis and IL-18. Thus, modulating the function of the NLRC4 may be an attractive therapeutic approach for treating S. aureus infections.     

白细胞介素22及其受体在大鼠肺炎克雷伯菌肺炎中的表达

目的 探讨白细胞介素22(IL-22)及IL-22受体IL-10R2在大鼠肺炎克雷伯菌肺炎发病过程中表达的意义。方法 50只SPF级SD大鼠按随机数字法分为肺炎组(n=25)和对照组(n=25)。肺炎组通过气管内注射肺炎克雷伯菌建立大鼠肺炎克雷伯菌肺炎模型,对照组则滴入等体积无菌生理盐水。造模后4h、1、2、3、4d通过观察大鼠的一般情况、肺组织大体和病理切片、肺组织细菌菌落计数对肺炎模型进行评价。采用实时荧光定量PCR和ELISA分别检测肺炎组和对照组大鼠造模后4h、1、2、3、4d肺组织IL-10R2 mRNA、外周血IL-22的表达水平。应用直线相关方法分析菌落计数与IL-22及其受体的相关性。结果肺炎组大鼠造模后4h出现活动度下降、聚集成团、竖毛现象;大体肺组织明显充血水肿,显微镜下肺泡结构破坏、肺泡腔及间质显著的充血及水肿、显著的中性粒细胞浸润。肺炎组大鼠肺组织均可培养出细菌,造模后4h细菌菌落计数最高[(0.94±0.02)×105 CFU/g],之后逐渐降低,至4d时降至最低[(0.07±0.00)×105 CFU/g],证实肺炎模型制备成功。与对照组比较,肺炎组IL- 10R2mRNA的表达量于造模后4h开始升高,于第3天达峰值（12.95±0.65比0.31±0.31,P＜0.05）,其后开始下降。肺炎组外周血中IL-22均低于同时间点对照组。肺炎组外周血中IL-22自造模后第3天较4h开始明显升高且随时间的延长逐渐升高。肺炎组中IL-10R2 mRNA、外周血IL-22的表达水平均与同时间点肺组织菌落计数呈负相关（r=-0.64,P=0.01;r=-0.59,P=0.00）。结论 IL-10R2在肺炎克雷伯菌肺炎中高表达,而外周血中IL-22可能由于消耗导致降低,但可随肺炎的好转回升。IL-22是肺炎克雷伯茵肺炎早期的炎性反应因子,在体内具有清除细菌的作用。     

Role of inflammatory mediators in resistance and susceptibility to pneumococcal infection

Variations in the host response during pneumonia caused by Streptococcus pneumoniae in susceptible (CBA/Ca) and resistant (BALB/c) inbred mouse strains were investigated. Significant differences were detected in survival time, core body temperature, lung-associated and systemic bacterial loads, mast cell numbers, magnitude and location of cytokine production, lung disruption, and ability of isolated lung cells to release the cytokine tumor necrosis factor (TNF) alpha in vitro. Overall, the results indicate that the reduced capacity of CBA/Ca mice to induce rapid TNF activity within the airways following infection with S. pneumoniae may be a factor in their elevated susceptibility to pneumococcal pneumonia.     

Molecular analysis of the contribution of the capsular polysaccharide and the lipopolysaccharide O side chain to the virulence of Klebsiella pneumoniae in a murine model of pneumonia

Klebsiella pneumoniae is a common cause of gram-negative bacterial nosocomial pneumonia. Two surface polysaccharides, lipopolysaccharide (LPS) O side chain and capsular polysaccharide (CPS), are critical for the microorganism in causing sepsis, but little is known about their role in pneumonia. To investigate their contribution in the pathogenesis of K. pneumoniae pneumonia, we characterized the host response to bacterial challenge with a highly virulent clinical isolate or with isogenic insertion-duplication mutants deficient in CPS or LPS O side chain in a murine model of pneumonia. Animals challenged intratracheally with the wild-type or LPS O side chain-deficient strain developed pneumonia and became bacteremic before death. Extensive lung lesions as well as pleuritis, vasculitis, and edema were observed by histopathological examination, and polymorphonuclear infiltration was also demonstrated. In contrast, none of the animals challenged with the unencapsulated strain developed pneumonia or bacteremia. Examination of tissue from this group did not identify lung lesions, and none of the infected animals died. Analysis of the early host defense mechanisms that contributed to the clearance of the unencapsulated mutant showed that the levels of C3 deposited on the unencapsulated mutant surface were threefold higher than those for the wild-type and LPS O side chain-deficient strains. Furthermore, phagocytosis of the unencapsulated mutant by human alveolar macrophages (AM) was more efficient than that of the wild-type and LPS O side chain-deficient strains. We conclude that CPS, but not LPS O side chain, is essential for Klebsiella pneumonia because it modulates the deposition of C3 and protects the microorganisms against human AM phagocytosis.     

Interleukin-12 promotes gamma interferon-dependent neutrophil recruitment in the lung and improves protection against respiratory Streptococcus pneumoniae infection

The ability of exogenous interleukin-12 (IL-12) to elicit protective innate immune responses against the extracellular pathogen Streptococcus pneumoniae was tested by infecting BALB/c mice intranasally (i.n.) with S. pneumoniae after i.n. administration of IL-12. It was found that administration of IL-12 resulted in lower bacterial burdens in the infected mice and significantly improved survival rates. All IL-12-treated mice contained higher levels of pulmonary gamma interferon (IFN-gamma) after infection and significantly more neutrophils than infected mice not treated with IL-12. IFN-gamma was found to be essential for IL-12-induced resistance and for neutrophil influx into the lungs, and the observed changes correlated with increased levels of the IL-8 homologue keratinocyte-derived chemokine (KC). In addition, in vitro tumor necrosis factor alpha (TNF-alpha) production by alveolar macrophages stimulated with heat-killed pneumococci was enhanced by IFN-gamma, and TNF-alpha in turn could enhance production of KC by lung cells. Finally, IL-12-induced protection was dependent upon the presence of neutrophils and the KC receptor CXCR2. Taken together, the results indicate that exogenous IL-12 can improve innate defense in the lung against S. pneumoniae by inducing IFN-gamma production, which in turn enhances chemokine expression, and promotes pulmonary neutrophil recruitment into the infected lung. The findings show that IL-12 and IFN-gamma can mediate a protective effect against respiratory infection caused by extracellular bacterial pathogens.     

Spontaneous release of granulocyte colony-stimulating factor (G-CSF) by alveolar macrophages in the course of bacterial pneumonia and sarcoidosis: endotoxin-dependent and endotoxin-independent G-CSF release by cells recovered by bronchoalveolar lavage.

Because granulocyte colony-stimulating factor (G-CSF) is known to induce granulopoiesis and activate mature neutrophils, this factor could be important in determining the number and functional activity of neutrophils at sites of lung disease. The purpose of this study was to evaluate the ability of lung immune and inflammatory cells to produce G-CSF, and to seek evidence for the spontaneous production of this factor by cells recovered by lavage from controls and patients with lung diseases in which neutrophils may play a pathogenetic role. Lavage cells from controls produced little G-CSF spontaneously. Alveolar macrophages (AM), but not lymphocytes, produced large amounts following endotoxin stimulation. Lavage cells from patients with respiratory failure associated with bacterial pneumonia, but not those with respiratory failure from noninfectious causes, spontaneously released G-CSF (32 +/- 24 and less than 1 U/10(6) AM, respectively). Lavage cells from five of 15 patients with sarcoidosis and one of five patients with diffuse pulmonary fibrosis also spontaneously released G-CSF, which could not be explained by endotoxin exposure. The release of G-CSF by endotoxin-dependent and -independent mechanisms could play a role in the recruitment and activation of neutrophils in bacterial pneumonia and participate in the pathogenesis of some interstitial lung diseases.     

Differential activation of the immune system by virulent Streptococcus pneumoniae strains determines recovery or death of the host

Streptococcus pneumoniae infection may result in asymptomatic carriage, mucosal or invasive disease. We hypothesize that self-limiting or fatal disease outcome follows infection with S. pneumoniae differential activation of the host immune response. BALB/c and C57BL/6 mice were inoculated intranasally with S. pneumoniae serotype 3 strain WU2 and serotype 14 strain DW14 and mortality, bacterial load, pathological changes in the lungs and cytokines mRNA levels in the spleen were analysed. No differences between the C57BL/6 and the BALB/c inbred mice were observed except for the severity of their lung pathology and IL-4 expression. Infection of the two mouse strains with S. pneumoniae WU2 resulted in sepsis and death that occurred within 4 days post-inoculation. This death was preceded, in both mouse strains, in an increase over time of the lung bacterial load and bacteraemia. The lung pathology was characterized by diffuse pneumonia with marked congestion of the lungs. Analysis of mRNA expression of cytokines in the spleen revealed no alterations in tumour necrosis factor (TNF)-alpha, transforming growth factor (TGF)-beta, interleukin (IL)-12 and interferon (IFN)-gamma and induction of IL-10 and IL-4. The two strains of mice survived infection with S. pneumoniae DW14. This was accompanied by a reduction over time of lung bacterial load and bacteraemia. The lung pathology was characterized by focal lymphocyte infiltration and preserved architecture of the organ. Analysis of mRNA expression of cytokines in the spleen revealed a significant decrease in the levels of TNF-alpha, TGF-beta, IL-12 and IFN-gamma mRNA expression, which usually precedes cytokine protein expression. Interestingly, a significant increase in the levels of IL-4 mRNA expression was found in BALB/c mice only. This study suggests that differential activation or evasion of cytokine expression by S. pneumoniae virulent strains determines disease outcome regardless of the host's immunogenetic background.     

Novel protective mechanism for interleukin-33 at the mucosal barrier during influenza-associated bacterial superinfection

Influenza A is a highly contagious respiratory virus that causes seasonal epidemics and occasional worldwide pandemics. The primary cause of influenza-related mortality is bacterial superinfection. There are numerous mechanisms by which preceding influenza infection attenuates host defense, allowing for increased susceptibility to bacterial pneumonia. Herein, we demonstrate that influenza inhibits Staphylococcus aureus-induced production of interleukin-33 (IL-33). Restoration of IL-33 during influenza A and methicillin-resistant S. aureus superinfection enhanced bacterial clearance and improved mortality. Innate lymphoid Type 2 cells and alternatively activated macrophages are not required for IL-33-mediated protection during superinfection. We show that IL-33 treatment resulted in neutrophil recruitment to the lung, associated with improved bacterial clearance. These findings identify a novel role for IL-33 in antibacterial host defense at the mucosal barrier.     

Pathogenesis of pneumococcal pneumonia in cyclophosphamide-induced leukopenia in mice

Streptococcus pneumoniae pneumonia frequently occurs in leukopenic hosts, and most patients subsequently develop lung injury and septicemia. However, few correlations have been made so far between microbial growth, inflammation, and histopathology of pneumonia in specific leukopenic states. In the present study, the pathogenesis of pneumococcal pneumonia was investigated in mice rendered leukopenic by the immunosuppressor antineoplastic drug cyclophosphamide. Compared to the immunocompetent state, cyclophosphamide-induced leukopenia did not hamper interleukin-1 (IL-1), IL-6, macrophage inflammatory protein-1 (MIP-1), MIP-2, and monocyte chemotactic protein-1 secretion in infected lungs. Leukopenia did not facilitate bacterial dissemination into the bloodstream despite enhanced bacterial proliferation into lung tissues. Pulmonary capillary permeability and edema as well as lung injury were enhanced in leukopenic mice despite the absence of neutrophilic and monocytic infiltration into their lungs, suggesting an important role for bacterial virulence factors and making obvious the fact that neutrophils are ultimately not required for lung injury in this model. Scanning and transmission electron microscopy revealed extensive disruption of alveolar epithelium and a defect in surfactant production, which were associated with alveolar collapse, hemorrhage, and fibrin deposits in alveoli. These results contrast with those observed in immunocompetent animals and indicate that leukopenic hosts suffering from pneumococcal pneumonia are at a higher risk of developing diffuse alveolar damage.     

Intranasal vaccination with pneumococcal surface protein A and interleukin-12 augments antibody-mediated opsonization and protective immunity against Streptococcus pneumoniae infection

Streptococcus pneumoniae is a major pathogen in humans that enters the host primarily through the respiratory tract. Targeting mucosal surfaces directly may therefore be an optimal approach for vaccination to prevent bacterial colonization and invasive disease. We have previously demonstrated the effectiveness of interleukin-12 (IL-12) delivered intransally (i.n.) as an antiviral respiratory adjuvant. In this study, we examined the effects of i.n. IL-12 treatment on induction of protective humoral immunity against S. pneumoniae. Immunization i.n. with pneumococcal surface protein A (PspA) and IL-12 resulted in enhanced lung IL-10 mRNA expression and marked augmentation of respiratory and systemic immunoglobulin G1 (IgG1), IgG2a, and IgA antibody levels compared to those in animals receiving PspA alone. In addition, i.n. vaccination with PspA and IL-12 provided increased protection against nasopharyngeal carriage. Flow cytometric analysis revealed a threefold increase in antibody-mediated, complement-independent opsonic activity in the sera of PspA- and IL-12-treated animals, which was mainly contributed by IgG2a and, to a lesser extent, IgA. Passive transfer of these immune sera conferred complete protection from death upon systemic pneumococcal challenge. These findings demonstrate the effectiveness of combining PspA and IL-12 at mucosal sites to achieve optimal antibody-mediated opsonization and killing of S. pneumoniae.