Wan C. Tsai

MCP-1 protects mice in lethal endotoxemia.

The overzealous production of proinflammatory cytokines in sepsis can result in shock, multiorgan dysfunction, and even death. In this study, we assessed the role of monocyte chemoattractant protein-1 (MCP-1) as a mediator of sepsis in endotoxin-challenged mice. Intraperitoneal administration of LPS to CD-1 mice induced a substantial time-dependent increase in MCP-1 in plasma, lung, and liver. The passive immunization of mice with rabbit antimurine MCP-1 antiserum 2 h before endotoxin administration resulted in a striking increase in LPS-induced mortality from 10% in control animals to 65% in anti-MCP-1-treated animals. Importantly, the administration of anti-MCP-1 antibodies to endotoxin-challenged mice resulted in increases in peak TNF-alpha and IL-12 levels, and also in a trend toward decreased serum levels of IL-10. Conversely, the administration of recombinant murine MCP-1 intraperitoneally significantly protected mice from endotoxin-induced lethality, and resulted in an increase in IL-10 levels, a decrease in IL-12 levels, and a trend toward decreased levels of TNF. In conclusion, our findings indicate that MCP-1 is a protective cytokine expressed in murine endotoxemia, and does so by shifting the balance in favor of antiinflammatory cytokine expression in endotoxin-challenged animals.

CXC Chemokine Receptor CXCR2 Is Essential for Protective Innate Host Response in Murine Pseudomonas aeruginosa Pneumonia

ABSTRACT Pulmonary infection due to Pseudomonas aeruginosa has emerged as a leading cause of mortality. A vigorous host response is required to effectively clear the organisms from the lungs. This host defense is dependent on the recruitment and activation of neutrophils and macrophages. A family of chemotactic cytokines (chemokines) has been shown to participate in this protective response. In this study, we assessed the role of the ELR+ (glutamic acid-leucine-arginine motif positive) CXC chemokines and their CXC chemokine receptor (CXCR2) in lung antibacterial host defense. The intratracheal administration of Pseudomonas to mice resulted in the time-dependent influx of neutrophils to the lung, peaking at 12 to 24 h after inoculation. The influx of neutrophils was associated with a similar time-dependent expression of the ELR+ CXC chemokines, KC, macrophage inflammatory protein 2 (MIP-2), and lipopolysaccharide-induced CXC chemokine (LIX). Selective neutralization of MIP-2 or KC resulted in modest changes in neutrophil influx but no change in bacterial clearance or survival. However, neutralization of CXCR2 resulted in a striking increase in mortality, which was associated with a marked decrease in neutrophil recruitment and bacterial clearance. Conversely, the site-specific transgenic expression of KC resulted in enhanced clearance of bacteria after Pseudomonas challenge. This study indicates that ELR+ CXC chemokines are critical mediators of neutrophil-mediated host defense in Pseudomonas pneumonia.

Chemokine-dependent neutrophil recruitment in a murine model of Legionella pneumonia: Potential role of neutrophils as immunoregulatory cells

ABSTRACT The roles of CXC chemokine-mediated host responses were examined with an A/J mouse model of Legionella pneumophilapneumonia. After intratracheal inoculation of 106 CFU ofL. pneumophila, the bacterial numbers in the lungs increased 10-fold by day 2; this increase was accompanied by the massive accumulation of neutrophils. Reverse transcription-PCR data demonstrated the up-regulation of CXC chemokines, such as keratinocyte-derived chemokine, macrophage inflammatory protein 2 (MIP-2), and lipopolysaccharide-induced CXC chemokine (LIX). Consistent with these data, increased levels of KC, MIP-2, and LIX proteins were observed in the lungs and peaked at days 1, 2, and 2, respectively. Although the administration of anti-KC or anti–MIP-2 antibody resulted in an approximately 20% decrease in neutrophil recruitment on day 2, no increase in mortality was observed. In contrast, the blockade of CXC chemokine receptor 2 (CXCR2), a receptor for CXC chemokines, including KC and MIP-2, strikingly enhanced mortality; this effect coincided with a 67% decrease in neutrophil recruitment. Interestingly, anti-CXCR2 antibody did not affect bacterial burden by day 2, even in the presence of a lethal challenge of bacteria. Moreover, a significant decrease in interleukin-12 (IL-12) levels, in contrast to the increases in KC, MIP-2, and LIX levels, was demonstrated for CXCR2-blocked mice. These data indicated that CXCR2-mediated neutrophil accumulation may play a crucial role in host defense against L. pneumophilapneumonia in mice. The increase in lethality without a change in early bacterial clearance suggested that neutrophils may exert their protective effect not through direct killing but through more immunomodulatory actions in L. pneumophila pneumonia. We speculate that a decrease in the levels of the protective cytokine IL-12 may explain, at least in part, the high mortality in the setting of reduced neutrophil recruitment.

Human Rhinovirus 1B Exposure Induces Phosphatidylinositol 3-Kinase-dependent Airway Inflammation in Mice

RATIONALE Infection with rhinovirus (RV) triggers exacerbations of asthma and chronic obstructive lung disease. OBJECTIVES We sought to develop a mouse model of RV employing RV1B, a minor group serotype that binds to the low-density lipoprotein receptor. METHODS C57BL/6 mice were inoculated intranasally with RV1B, replication-deficient ultraviolet (UV)-irradiated RV1B, or RV39, a major group virus. MEASUREMENTS AND MAIN RESULTS Viral RNA was present in the lungs of RV1B-treated mice, but not in those exposed to UV-irradiated RV1B or RV39. Lung homogenates of RV-treated mice contained infectious RV 4 days after inoculation. RV1B exposure induced neutrophilic and lymphocytic airway inflammation, as well as increased lung expression of KC, macrophage-inflammatory protein-2, and IFN-alpha and IFN-beta. RV1B-exposed mice showed airway hyperresponsiveness 1 and 4 days after inoculation. UV-irradiated RV1B induced modest neutrophilic airway inflammation and hyperresponsiveness 1 day after exposure. Both RV1B and UV-irradiated RV1B, but not RV39, increased lung phosphorylation of Akt. Confocal immunofluorescence showed colocalization of RV1B and phospho-Akt in the airway epithelium. Finally, pretreatment with the phosphatidylinositol 3-kinase inhibitor LY294002 attenuated chemokine production and neutrophil infiltration. CONCLUSIONS We conclude that RV1B induces airway inflammation in vivo. Evidence is presented that viral replication occurs in vivo and is required for maximal responses. On the other hand, viral replication was not required for a subset of RV-induced responses, including neutrophilic inflammation, airway hyperresponsiveness, and Akt phosphorylation. Finally, phosphatidylinositol 3-kinase/Akt signaling is required for maximal RV1B-induced airway neutrophilic inflammation, likely via its essential role in virus internalization.

Rhinovirus Infection of Allergen-Sensitized and -Challenged Mice Induces Eotaxin Release from Functionally Polarized Macrophages

Human rhinovirus is responsible for the majority of virus-induced asthma exacerbations. To determine the immunologic mechanisms underlying rhinovirus (RV)-induced asthma exacerbations, we combined mouse models of allergic airways disease and human rhinovirus infection. We inoculated OVA-sensitized and challenged BALB/c mice with rhinovirus serotype 1B, a minor group strain capable of infecting mouse cells. Compared with sham-infected, OVA-treated mice, virus-infected mice showed increased lung infiltration with neutrophils, eosinophils and macrophages, airway cholinergic hyperresponsiveness, and increased lung expression of cytokines including eotaxin-1/CCL11, IL-4, IL-13, and IFN-γ. Administration of anti–eotaxin-1 attenuated rhinovirus-induced airway eosinophilia and responsiveness. Immunohistochemical analysis showed eotaxin-1 in the lung macrophages of virus-infected, OVA-treated mice, and confocal fluorescence microscopy revealed colocalization of rhinovirus, eotaxin-1, and IL-4 in CD68-positive cells. RV inoculation of lung macrophages from OVA-treated, but not PBS-treated, mice induced expression of eotaxin-1, IL-4, and IL-13 ex vivo. Macrophages from OVA-treated mice showed increased expression of arginase-1, Ym-1, Mgl-2, and IL-10, indicating a shift in macrophage activation status. Depletion of macrophages from OVA-sensitized and -challenged mice reduced eosinophilic inflammation and airways responsiveness following RV infection. We conclude that augmented airway eosinophilic inflammation and hyperresponsiveness in RV-infected mice with allergic airways disease is directed in part by eotaxin-1. Airway macrophages from mice with allergic airways disease demonstrate a change in activation state characterized in part by altered eotaxin and IL-4 production in response to RV infection. These data provide a new paradigm to explain RV-induced asthma exacerbations.

Anti-interleukin-12 therapy protects mice in lethal endotoxemia but impairs bacterial clearance in murine Escherichia coli peritoneal sepsis

The overzealous production of proinflammatory cytokines in sepsis can result in shock, multiorgan dysfunction, and even death. In this study we assessed the role of endogenously produced interleukin (IL)-12 in murine models of endotoxemia and Gram-negative peritoneal sepsis. Initial studies indicated that intraperitoneal lipopolysaccharide (LPS) administration to mice induced a significant time-dependent increase in plasma, lung, and liver IL-12 levels. Passive immunization with anti-IL-12 serum intraperitoneally before LPS resulted in a marked reduction in plasma levels of tumor necrosis factor and interferon-γ. Furthermore, we observed an increase in endotoxin-induced mortality in mice transiently overexpressing murine IL-12 using a recombinant adenoviral vector (Ad5 mIL-12) administered intraperitoneally. Neutralization of tumor necrosis factor or interferon-γ in animals overexpressing IL-12 resulted in significant reductions in LPS-induced mortality, suggesting that the mechanism whereby IL-12 increases LPS-induced mortality is primarily mediated by the enhancement of these cytokines. In contrast, we observed no survival benefit in animals passively immunized with anti-IL-12 serum before the intraperitoneal administration of 2 x 108 live Escherichia coli. Interestingly, there was an approximately 70-fold increase in peritoneal fluid E. coli colony-forming units and the early onset of bacteremia in animals treated with anti-IL-12 serum, as compared with control animals. These results indicate that IL-12 is produced in response to LPS exposure, and the neutralization of this cytokine improves survival in endotoxin-challenged animals. However, IL-12 represents an essential component of antibacterial host defense, as anti-IL-12 therapy results in significant impairment in the hosts ability to clear Gram-negative bacterial infection.

CXCR2 Is Required for Neutrophilic Airway Inflammation and Hyperresponsiveness in a Mouse Model of Human Rhinovirus Infection

Human rhinovirus (RV) infection is responsible for the majority of virus-induced asthma exacerbations. Using a mouse model of human RV infection, we sought to determine the requirement of CXCR2, the receptor for ELR-positive CXC chemokines, for RV-induced airway neutrophilia and hyperresponsiveness. Wild-type and CXCR2−/− mice were inoculated intranasally with RV1B or sham HeLa cell supernatant. Following RV1B infection, CXCR2−/− mice showed reduced airway and lung neutrophils and cholinergic responsiveness compared with wild-type mice. Similar results were obtained in mice treated with neutralizing Ab to Ly6G, a neutrophil-depleting Ab. Lungs from RV-infected, CXCR2−/− mice showed significantly reduced production of TNF-α, MIP-2/CXCL2, and KC/CXCL1 and lower expression of MUC5B compared with RV-treated wild-type mice. The requirement of TNF-α for RV1B-induced airway responses was tested using TNFR1−/− mice. TNFR1−/− animals displayed reduced airway responsiveness to RV1B, even when exogenous MIP-2 was added to the airways. We conclude that CXCR2 is required for RV-induced neutrophilic airway inflammation and that neutrophil TNF-α release is required for airway hyperresponsiveness.

STAT4 is a critical mediator of early innate immune responses against pulmonary Klebsiella infection.

Bacterial pneumonia is a leading cause of morbidity and mortality in the U.S. An effective innate immune response is critical for the clearance of bacteria from the lungs. IL-12, a key T1 cytokine in innate immunity, signals through STAT4. Thus, understanding how STAT4 mediates pulmonary immune responses against bacterial pathogens will have important implications for the development of rational immunotherapy targeted at augmenting innate immunity. We intratracheally administered Klebsiella pneumoniae to wild-type BALB/c and STAT4 knockout (STAT4−/−) mice. Compared with wild-type controls, STAT4−/− mice had decreased survival following intratracheal Klebsiella administration, which was associated with a higher lung and blood bacterial burden. STAT4−/− animals also displayed impaired pulmonary IFN-γ production and decreased levels of proinflammatory cytokines, including the ELR− CXC chemokines IFN-γ-inducible protein-10 and monokine induced by IFN-γ. Although total lung leukocyte populations were similar between STAT4−/− and wild-type animals following infection, alveolar macrophages isolated from infected STAT4−/− mice had decreased production of proinflammatory cytokines, including IFN-γ, compared with infected wild-type mice. The intrapulmonary overexpression of IFN-γ concomitant with the systemic administration of IFN-γ partially reversed the immune deficits observed in STAT4−/− mice, resulting in improved bacterial clearance from the blood. Collectively, these studies demonstrate that STAT4 is required for the generation of an effective innate host defense against bacterial pathogens of the lung.

Immunomodulatory effects of macrolides in the lung: lessons from in-vitro and in-vivo models.

Macrolide antibiotics appear to play a role in the management of diseases of chronic airway inflammation, distinctly separate from their antibactericidal activity. In the last fifteen years, their success in human clinical trials has prompted both in-vitro and in-vivo investigations to determine the mechanisms by which this family of antibiotics modulate the immune response. A large body of evidence suggests that macrolides directly target multiple components of the inflammatory cascade that occur independent of bactericidal/bacteriostatic effects. We will review the existing data in support of immunomodulatory effects of macrolides on activated leukocytes at the site of lung inflammation, on pulmonary host cells, and in animal models of lung disease.

Intrapulmonary expression of macrophage inflammatory protein 1α (CCL3) induces neutrophil and NK cell accumulation and stimulates innate immunity in murine bacterial pneumonia

ABSTRACT Macrophage inflammatory protein 1α (MIP-1α) (CCL3) is an important mediator of leukocyte recruitment and activation in a variety of inflammatory states, including infection. A recombinant human type 5 adenovirus containing the murine MIP-1α cDNA (AdMIP-1α) was constructed to determine the effect of transient intrapulmonary expression of MIP-1α on leukocyte recruitment, activation, and bacterial clearance in a murine model of Klebsiella pneumoniae pneumonia. The intratracheal administration of AdMIP-1α resulted in both time- and dose-dependent expression of MIP-1α mRNA and protein within the lung. Importantly, the intrapulmonary overexpression of MIP-1α resulted in a maximal 35- and 100-fold reduction in lung and blood bacterial burden, respectively, in animals cochallenged with K. pneumoniae, which was associated with a significant increase in neutrophil and activated NK cell accumulation. Furthermore, the transgenic expression of MIP-1α during bacterial pneumonia resulted in enhanced expression of gamma interferon mRNA, compared to that observed in Klebsiella-challenged animals pretreated with control vector. These findings indicate an important role for MIP-1α in the recruitment and activation of selected leukocyte populations in vivo and identify this cytokine as a potential immunoadjuvant to be employed in the setting of localized bacterial infection.