Modulating airway defenses against microbes

Neutrophil dysfunction in the pathogenesis of cystic fibrosis

Polymorphonuclear neutrophils (PMNs) figure prominently in host defense against infection and in noninfectious inflammation. Mobilized early in an inflammatory response, PMNs mediate immediate cellular defense against microbes and orchestrate events that culminate in cessation of inflammation and restoration of homeostasis. Failure to terminate the inflammatory response and its causes can fuel exuberant inflammation characteristic of many human diseases, including cystic fibrosis (CF), an autosomal recessive genetic disease caused by mutations in the CF transmembrane conductance regulator. CF affects multiple end organs, with persistent bacterial infection and chronic neutrophilic inflammation in airways predominating the clinical picture. To match the diverse microbial challenges that they may encounter, PMNs possess a variety of antimicrobial systems to slow or kill invading microorganisms confined in their phagosomes. Prominent among PMN defense systems is their ability to generate hypochlorous acid, a potent microbicide, by reacting oxidants generated by the NADPH oxidase with myeloperoxidase (MPO) released from azurophilic granules in the presence of chloride (Cl-). Products of the MPO-H2O2-Cl system oxidize susceptible biomolecules and support robust antimicrobial action against many, but not all, potential human pathogens. Underscoring that the MPO-H2O2-Cl system is integral to optimal host defense and proper regulation of inflammation, individuals with defects in any component of this system, as seen in chronic granulomatous disease or MPO deficiency, incur increased rates or severity of infection and signs of dysregulated inflammatory responses. We focus attention in this review on the molecular basis for and the clinical consequences of defects in the MPO-H2O2-Cl system because of the compromised Cl transport seen in CF. We will discuss first how the MPO-H2O2-Cl system in healthy PMNs participates in host defense and resolution of inflammation and then review how a defective MPO-H2O2-Cl system contributes to the increased susceptibility to infection and dysregulated inflammation associated with the clinical manifestations of CF.

Secondary streptococcal infection following influenza

Secondary bacterial infection following influenza A virus (IAV) infection is a major cause of morbidity and mortality during influenza epidemics. Streptococcus pneumoniae has been identified as a predominant pathogen in secondary pneumonia cases that develop following influenza. Although IAV has been shown to enhance susceptibility to the secondary bacterial infection, the underlying mechanism of the viral-bacterial synergy leading to disease progression is complex and remains elusive. In this review, cooperative interactions of viruses and streptococci during co- or secondary infection with IAV are described. IAV infects the upper respiratory tract, therefore, streptococci that inhabit or infect the respiratory tract are of special interest. Since many excellent reviews on the co-infection of IAV and S. pneumoniae have already been published, this review is intended to describe the unique interactions between other streptococci and IAV. Both streptococcal and IAV infections modulate the host epithelial barrier of the respiratory tract in various ways. IAV infection directly disrupts epithelial barriers, though at the same time the virus modifies the properties of infected cells to enhance streptococcal adherence and invasion. Mitis group streptococci produce neuraminidases, which promote IAV infection in a unique manner. The studies reviewed here have revealed intriguing mechanisms underlying secondary streptococcal infection following influenza. This article is protected by copyright. All rights reserved.

Glucagon-like peptide-1 receptor (GLP-1R) signaling ameliorates dysfunctional immunity in COPD patients

Background

The glucagon-like peptide-1 receptor (GLP-1R) agonist – liraglutide (LIR) – is an insulin secretagogue for the treatment of diabetes and has been proven to have therapeutic potential in the treatment of COPD. Evidence suggested that activating GLP-1R signaling might have immunomodulating and anti-inflammatory effects. COPD is characterized by dysregulation of immunity, oxidative stress, and excessive inflammation responses. The aim of this study was to investigate whether GLP-1R signaling had a regulatory role in COPD immunity.

Patients and methods

Fifty-seven COPD patients in a stable condition and 51 age-, sex-, and smoking history-matched non-COPD subjects provided blood samples for isolation of peripheral blood mononuclear cells (PBMCs). GLP-1R expression was measured, and its association with clinical parameters and plasma cytokines was analyzed. T cell function was assessed at baseline and after regulating GLP-1R expression.

Results

GLP-1R expression decreased in circulating PBMCs of COPD patients, which was associated with decreased interferon (IFN)-γ expression. Reduced IFN-γ production stimulated by phytohemagglutinin (PHA) and increased programmed cell death protein 1 (PD-1) expression on T cells were observed in COPD patients compared with non-COPD subjects. Treatment with LIR could upregulate the GLP-1R expression, and this was observed to restore the antigen-stimulated IFN-γ production and downregulate PD-1 expression in T cells.

Conclusion

PBMCs of COPD patients showed defective GLP-1R signaling and functional T-lymphocyte abnormalities that could be rescued by LIR treatment.

Highly differentiated human airway epithelial cells: a model to study host cell-parasite interactions in pertussis

BACKGROUND

Bordetella pertussis colonizes the human respiratory mucosa. Most studies on B. pertussis adherence have relied on cultured mammalian cells that lack key features present in differentiated human airway cells or on animal models that are not natural hosts of B. pertussis. The objectives of this work were to evaluate B. pertussis infection in highly differentiated human airway cells in vitro and to show the role of B. pertussis fimbriae in cell adherence.

METHODS

Primary human airway epithelial (PHAE) cells from human bronchi and a human bronchial epithelial (HBE) cell line were grown in vitro under air-liquid interface conditions.

RESULTS

PHAE and HBE cells infected with B. pertussis wild-type strain revealed bacterial adherence to the apical surface of cells, bacteria-induced cytoskeleton changes, and cell detachment. Mutations in the major fimbrial subunits Fim2/3 or in the minor fimbrial adhesin subunit FimD affected B. pertussis adherence to predominantly HBE cells. This cell model recapitulates the morphologic features of the human airway infected by B. pertussis and confirms the role of fimbriae in B. pertussis adherence. Furthermore, HBE cells show that fimbrial subunits, and specifically FimD adhesin, are critical in B. pertussis adherence to airway cells.

CONCLUSIONS

The relevance of this model to study host-parasite interaction in pertussis lies in the striking physiologic and morphologic similarity between the PHAE and HBE cells and the human airway ciliated and goblet cells in vivo. These cells can proliferate in vitro, differentiate, and express the same genetic profile as human respiratory cells in vivo.

Pulmonary vaccine delivery

This review will discuss developments in the field of pulmonary vaccine delivery. The possibilities of adopting aerosol-generation technology and specific pharmaceutical formulations for the purpose of pulmonary immunization are described. Aerosol-generation systems might offer advantages with respect to vaccine stability and antigenicity. Adjuvants and their inclusion in vaccine-delivery systems are described. Other formulation components, such as surfactants, particulate systems and dispersion of the aerosols are detailed in this paper. The noninvasive, relatively safe and low-cost nature of pulmonary delivery may provide great benefits to the public health vaccination campaign.

Response of Differentiated Human Airway Epithelia to Alcohol Exposure and Klebsiella Pneumoniae Challenge

Alcohol abuse has been associated with increased susceptibility to pulmonary infection. It is not fully defined how alcohol contributes to the host defense compromise. Here primary human airway epithelial cells were cultured at an air-liquid interface to form a differentiated and polarized epithelium. This unique culture model allowed us to closely mimic lung infection in the context of alcohol abuse by basolateral alcohol exposure and apical live bacterial challenge. Application of clinically relevant concentrations of alcohol for 24 hours did not significantly alter epithelial integrity or barrier function. When apically challenged with viable Klebsiella pneumoniae, the cultured epithelia had an enhanced tightness which was unaffected by alcohol. Further, alcohol enhanced apical bacterial growth, but not bacterial binding to the cells. The cultured epithelium in the absence of any treatment or stimulation had a base-level IL-6 and IL-8 secretion. Apical bacterial challenge significantly elevated the basolateral secretion of inflammatory cytokines including IL-2, IL-4, IL-6, IL-8, IFN-γ, GM-CSF, and TNF-α. However, alcohol suppressed the observed cytokine burst in response to infection. Addition of adenosine receptor agonists negated the suppression of IL-6 and TNF-α. Thus, acute alcohol alters the epithelial cytokine response to infection, which can be partially mitigated by adenosine receptor agonists.

Alternaria inhibits double-stranded RNA-induced cytokine production through Toll-like receptor 3

BACKGROUND

Fungi may be involved in asthma and chronic rhinosinusitis (CRS). Peripheral blood mononuclear cells from CRS patients produce interleukin (IL)-5, IL-13 and interferon (IFN)-γ in the presence of Alternaria. In addition, Alternaria produces potent Th2-like adjuvant effects in the airway. Therefore, we hypothesized that Alternaria may inhibit Th1-type defense mechanisms against virus infection.

METHODS

Dendritic cells (DCs) were generated from mouse bone marrow. The functional responses were assessed by expression of cell surface molecules by FACS (MHC class II, CD40, CD80, CD86 and OX40L). Production of IL-6, chemokine CXCL10 (IP-10), chemokine CXCL11 (I-TAC) and IFN-β was measured by ELISA. Toll-like receptor 3 (TLR3) mRNA and protein expression was detected by quantitative real-time PCR and Western blot.

RESULTS

Alternaria and polyinosinic-polycytidylic acid (poly I:C) enhanced cell surface expression of MHC class II, CD40, CD80, CD86 and OX40L, and IL-6 production in a concentration-dependent manner. However, Alternaria significantly inhibited production of IP-10, I-TAC and IFN-β, induced by viral double-stranded RNA (dsRNA) mimic poly I:C. TLR3 mRNA expression and protein production by poly I:C were significantly inhibited by Alternaria. These reactions are likely caused by heat-stable factor(s) in Alternaria extract with >100 kDa molecular mass.

CONCLUSION

These findings suggest that the fungus Alternaria may inhibit production of IFN-β and other cytokines by DCs by suppressing TLR3 expression. These results indicate that Alternaria may inhibit host innate immunity against virus infection.

Type I IFN triggers RIG-I/TLR3/NLRP3-dependent inflammasome activation in influenza A virus infected cells

Influenza A virus (IAV) triggers a contagious and potentially lethal respiratory disease. A protective IL-1β response is mediated by innate receptors in macrophages and lung epithelial cells. NLRP3 is crucial in macrophages; however, which sensors elicit IL-1β secretion in lung epithelial cells remains undetermined. Here, we describe for the first time the relative roles of the host innate receptors RIG-I (DDX58), TLR3, and NLRP3 in the IL-1β response to IAV in primary lung epithelial cells. To activate IL-1β secretion, these cells employ partially redundant recognition mechanisms that differ from those described in macrophages. RIG-I had the strongest effect through a MAVS/TRIM25/Riplet-dependent type I IFN signaling pathway upstream of TLR3 and NLRP3. Notably, RIG-I also activated the inflammasome through interaction with caspase 1 and ASC in primary lung epithelial cells. Thus, NS1, an influenza virulence factor that inhibits the RIG-I/type I IFN pathway, strongly modulated the IL-1β response in lung epithelial cells and in ferrets. The NS1 protein derived from a highly pathogenic strain resulted in increased interaction with RIG-I and inhibited type I IFN and IL-1β responses compared to the least pathogenic virus strains. These findings demonstrate that in IAV-infected lung epithelial cells RIG-I activates the inflammasome both directly and through a type I IFN positive feedback loop.

The influence of cigarette smoking on viral infections: translating bench science to impact COPD pathogenesis and acute exacerbations of COPD clinically

COPD is a complex syndrome that poses a serious health threat to >1.1 billion smokers worldwide. The stable disease is punctuated by episodes of acute exacerbation, which are predominantly the result of viral and bacterial infections. Despite their devastating health impact, mechanisms underlying disease exacerbations remain poorly understood. Mounting evidence suggests that cigarette smoke profoundly affects the immune system, compromising the host's ability to mount appropriate immune and inflammatory responses against microbial agents. This review highlights recent advances in our understanding of the impact of cigarette smoke on type 1 interferon and IL-1 signaling cascades. The immune defects caused by cigarette smoke on these two key pathways contribute to the seemingly contradictory nature of cigarette smoke as both a damaging and a proinflammatory factor as well as an immunosuppressive factor. Understanding the impact of cigarette smoke on the immune system may unravel novel targets for therapies that could affect acute exacerbations and COPD pathogenesis.

Suppression of adenosine-activated chloride transport by ethanol in airway epithelia

Alcohol abuse is associated with increased lung infections. Molecular understanding of the underlying mechanisms is not complete. Airway epithelial ion transport regulates the homeostasis of airway surface liquid, essential for airway mucosal immunity and lung host defense. Here, air-liquid interface cultures of Calu-3 epithelial cells were basolaterally exposed to physiologically relevant concentrations of ethanol (0, 25, 50 and 100 mM) for 24 hours and adenosine-stimulated ion transport was measured by Ussing chamber. The ethanol exposure reduced the epithelial short-circuit currents (I(SC)) in a dose-dependent manner. The ion currents activated by adenosine were chloride conductance mediated by cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP-activated chloride channel. Alloxazine, a specific inhibitor for A(2B) adenosine receptor (A(2B)AR), largely abolished the adenosine-stimulated chloride transport, suggesting that A(2B)AR is a major receptor responsible for regulating the chloride transport of the cells. Ethanol significantly reduced intracellular cAMP production upon adenosine stimulation. Moreover, ethanol-suppression of the chloride secretion was able to be restored by cAMP analogs or by inhibitors to block cAMP degradation. These results imply that ethanol exposure dysregulates CFTR-mediated chloride transport in airways by suppression of adenosine-A(2B)AR-cAMP signaling pathway, which might contribute to alcohol-associated lung infections.

Microbes and asthma: the missing cellular and molecular links

PURPOSE OF REVIEW

In this review, we describe the 'state-of-the-art' in our knowledge of asthma and what gaps exist, which can be exploited in the future for effective translation of our knowledge from the bench or population studies to diagnosis and therapy.

RECENT FINDINGS

The advent of microbiome research has expanded the potential role of microbes in asthma. There has been a significant increase in our understanding of the pathologic, genetic, cellular and molecular mechanisms of asthma. Nonetheless, the contribution of microbes to the genesis, exacerbation and treatment of asthma are poorly understood.

SUMMARY

Asthma is a complex chronic disease of the lung whose incidence is growing at all ages despite the progress that has been made in the areas of diagnosis and treatment of asthma. The complexity is partly due to the environmental insults such as allergens and microbial infections that play differential roles in the pathogenesis of childhood vis-à-vis elderly asthma. Microbes may play important roles in the exacerbation of asthma and hence in the comorbidities due to asthma, and also in the causation of asthma.

Epithelial cells from smokers modify dendritic cell responses in the context of influenza infection

Epidemiologic evidence suggests that cigarette smoking is a risk factor for infection with influenza, but the mechanisms underlying this susceptibility remain unknown. To ascertain if airway epithelial cells from smokers demonstrate a decreased ability to orchestrate an influenza-induced immune response, we established a model using differentiated nasal epithelial cells (NECs) from nonsmokers and smokers, co-cultured with peripheral blood monocyte-derived dendritic cells (mono-DCs) from nonsmokers. NEC/mono-DC co-cultures were infected with influenza A virus and analyzed for influenza-induced immune responses 24 hours after infection. We observed that NECs from smokers, as well as mono-DCs co-cultured with NECs from smokers, exhibited suppressed influenza-induced, interferon-related proteins interferon regulatory factor-7, Toll-like receptor-3, and retinoic acid inducible gene-1, likely because of the suppressed production of IFNα from the NECs of smokers. Furthermore, NEC/mono-DC co-cultures using NECs from smokers exhibited suppressed concentrations of T-cell/natural killer cell chemokine interferon gamma-induced protein 10 (IP-10) after infection with influenza, indicating that NECs from smokers may skew early influenza-induced Th1 responses. In contrast, NEC/mono-DC co-cultures using NEC from smokers contained increased influenza-induced concentrations of the Th2 chemokine thymic stromal lymphopoeitin (TSLP). In addition, NECs from smokers cultured alone had increased influenza-induced concentrations of the Th2 chemokine thymus and activation-regulated chemokine (TARC). Using this model, we demonstrated that in the context of infection with influenza, NECs obtained from smokers create an overall cytokine microenvironment that suppresses the interferon-mediated Th1 response and enhances the TSLP-TARC-mediated Th2 response, with the potential to modify the responses of DCs. Smoking-induced alterations in the Th1/Th2 balance may play a role in developing underlying susceptibilities to respiratory viral infections, and may also promote the likelihood of acquiring Th2 proallergic diseases.

Double-stranded RNA exacerbates pulmonary allergic reaction through TLR3: implication of airway epithelium and dendritic cells

Respiratory viral infections have been implicated in exacerbations of allergic asthma, characterized by a Th2-biased immune response. Respiratory viruses target airway epithelial cells and dendritic cells (DCs). Their activation is, at least in part, mediated by the TLR3-dependent recognition of virus-derived dsRNA. To elucidate the role of epithelial cells and DCs and the implication of TLR3/Toll/IL-1R domain-containing adaptor-inducing IFN-beta (TRIF) pathway, we developed a mouse model of lung allergic exacerbation. The effect of intranasal administration of dsRNA in OVA-sensitized wild-type mice and TRIF(-/-) mice was evaluated on airway hyperresponsiveness and pulmonary inflammation. Our data demonstrated that treatment with dsRNA significantly increased the airway hyperresponsiveness, the lung inflammation, and the OVA-specific Th2 response. This was associated with an infiltrate of eosinophils, myeloid DCs, and T lymphocytes. TRIF activation was required for the development of dsRNA-induced exacerbation of the allergic reaction. Intratracheal transfer of IL-4/dsRNA/OVA-pretreated DCs also triggered exacerbation of the allergic reaction, whereas cells primed with dsRNA/OVA had a more limited effect. dsRNA-induced production of CCL20 by airway epithelium was associated with DC recruitment. In vivo and in vitro treatment with dsRNA amplified airway epithelial production of the pro-Th2 chemokines CCL11 and CCL17, their secretion being enhanced by Th2 cytokines. In conclusion, dsRNA derived from respiratory viruses trigger exacerbation of the pulmonary allergic reaction through TLR3/TRIF-dependent pathway. Moreover, Th2 cytokines participate in this process by modulating the response of airway epithelium and DCs to dsRNA.

Beneficial and Harmful Interactions of Antibiotics with Microbial Pathogens and the Host Innate Immune System

In general antibiotics interact cooperatively with host defences, weakening and decreasing the virulence of microbial pathogens, thereby increasing vulnerability to phagocytosis and eradication by the intrinsic antimicrobial systems of the host. Antibiotics, however, also interact with host defences by several other mechanisms, some harmful, others beneficial. Harmful activities include exacerbation of potentially damaging inflammatory responses, a property of cell-wall targeted agents, which promotes the release of pro-inflammatory microbial cytotoxins and cell-wall components. On the other hand, inhibitors of bacterial protein synthesis, especially macrolides, possess beneficial anti-inflammatory/cytoprotective activities, which result from interference with the production of microbial virulence factors/cytotoxins. In addition to these pathogen-directed, anti-inflammatory activities, some classes of antimicrobial agent possess secondary anti-inflammatory properties, unrelated to their conventional antimicrobial activities, which target cells of the innate immune system, particularly neutrophils. This is a relatively uncommon, potentially beneficial property of antibiotics, which has been described for macrolides, imidazole anti-mycotics, fluoroquinolones, and tetracyclines. Although of largely unproven significance in the clinical setting, increasing awareness of the pro-inflammatory and anti-inflammatory properties of antibiotics may contribute to a more discerning and effective use of these agents.

Present status of bronchoalveolar lavage in interstitial lung disease

PURPOSE OF REVIEW

Sampling the detachable cells and acellular lining secretions of the human respiratory tract by bronchoalveolar lavage (BAL) is a means of obtaining relevant components from the airways and alveolar areas for research use and clinical analysis in normals (controls) and patients with a wide spectrum of interstitial lung diseases (ILDs). This review attempts to discuss recent findings from BAL studies that provide insight into pathogenic mechanisms of ILDs and/or assist in diagnosing disease activity.

RECENT FINDINGS

BAL analysis and usefulness are reviewed for the major forms of ILDs. In addition, some perspective about this sampling method is given and the context for BAL is provided for the respective disease, either for diagnosis or research use.

SUMMARY

Whereas BAL findings continue to impact on understanding disease pathogenesis and this may be its major use now, BAL fluid components, cells in particular, are not correlated well with activity of disease nor for monitoring disease progress or response to treatment. For a few rarer ILDs, BAL fluid characteristics may strongly support a diagnosis.

Cigarette smoke suppresses type I interferon-mediated antiviral immunity in lung fibroblast and epithelial cells

The objective of this study was to investigate the impact of cigarette smoke on innate antiviral defense mechanisms; specifically, we examined the effects of cigarette smoke on the induction of type I interferon (IFN). We observed a dose-dependent decrease in the ability of human lung fibroblast and epithelial cells to elicit an antiviral response against a viral double-strand RNA (dsRNA) mimic, polyI:C, in the presence of cigarette smoke-conditioned medium (SCM). Mechanistically, SCM decreases the expression of IFN-stimulated gene 15 (ISG15) and IFN regulatory factor-7 (IRF-7) transcripts and suppresses the nuclear translocation of key transcription factors, nuclear factor-kappaB (NF-kappaB) and IRF-3, after polyI:C stimulation. Furthermore, we provide evidence that the intercellular defense strategy against viral infection is also impaired. We observed a decrease in the ability of fibroblasts to elicit an antiviral state in response to IFN-beta stimulation. This was associated with decreased nuclear translocation of phosphorylated Stat1 in response to IFN-beta treatment. The effects elicited by SCM are reversible and are almost entirely abrogated in the presence of an antioxidant, such as glutathione. Our findings suggest that cigarette smoke affects the immediate-early, inductive, and amplification phases of the type I IFN response.

Enterobacterial 38-kDa outer membrane protein is an age-dependent molecular marker of innate immunity and immunoglobulin deficiency as results from its reactivity with IgG and IgA antibody

In earlier studies on an animal model we observed protective properties of outer membrane proteins (OMPs) of Shigella, Hafnia, and Escherichia coli strains. In order to investigate human sera for reactivity with OMPs we subjected these proteins to immunoblotting with umbilical cord plasma and sera from children and adults. The IgG and IgA antibodies interacted primarily with a 38-kDa protein, in similar way for several enterobacterial strains, but different for Pseudomonas aeruginosa. This observation prompted us to determine the reactivity with the purified 38-kDa OMP in the sera of several groups of children. The reactivity of the protein from Shigella flexneri serotype 3a with sera in ELISA was age dependent, increasing from low reactivity in infants to the adult antibody level. The IgG and IgA antibody specific response thus revealed the normal pattern of immunity. The level of IgA and IgG antibody was significantly low in child patients with IgA and/or IgG immunoglobulin deficiencies, but was at the healthy control level in children with recurrent respiratory tract inflammation. These data correlated with total IgA and IgG levels in immunoglobulin-deficient children. The results indicate that this protein may serve as an immunodiagnostic marker, but also as an antigen carrier in vaccines.

Surfactant protein A2 (SP-A2) variants expressed in CHO cells stimulate phagocytosis of Pseudomonas aeruginosa more than do SP-A1 variants

Surfactant protein A (SP-A) enhances phagocytosis of Pseudomonas aeruginosa. Two functional genes, SP-A1 and SP-A2, encode human SP-A. As we showed before, baculovirus-mediated insect cell-expressed SP-A2 enhances the association of P. aeruginosa with rat alveolar macrophages (rAMs) more than does SP-A1. However, true phagocytosis (internalization) was not shown, and insect cell derived proteins lack or are defective in certain mammalian posttranslational modifications that may be important for SP-A1 and SP-A2 activity and specificity. Here we used SP-A1 (6A(2), 6A(4)) and SP-A2 (1A(0), 1A(1)) allele variants expressed by CHO (Chinese hamster ovary) mammalian cells to study their effect on association and/or internalization of P. aeruginosa by rAMs and/or human AMs (hAMs) and to study if phagocytosis can be modulated differentially and/or more effectively by CHO cell-expressed SP-A variants than by insect-cell expressed SP-A variants. For cell association and internalization assessments, light microscopy and fluorescence-activated cell sorter analyses were used, respectively. We found the following for the first time. (i) SP-A2 variants enhanced phagocytosis (cell association and/or internalization) of P. aeruginosa more than SP-A1 variants did, and the cell association correlated with internalization. (ii) Differences in the activities of SP-A variants were observed in the following order: 1A(1)>1A(0)>6A(2)>6A(4). (iii) rAMs, although more active than hAMs, are an appropriate model, as SP-A2 variants exhibited activity higher than that seen for SP-A1 variants with either rAMs or hAMs. (iv) CHO cell-expressed SP-A was considerably more active than insect cell-expressed variants. We conclude that SP-A2 variants stimulate phagocytosis of P. aeruginosa more effectively than SP-A1 variants and that posttranslational modifications positively influence the phagocytic activity of SP-A.

Cigarette smoke impacts immune inflammatory responses to influenza in mice

RATIONALE

Studies have shown that cigarette smoke impacts respiratory host defense mechanisms; however, it is poorly understood how these smoke-induced changes impact the overall ability of the host to deal with pathogenic agents.

OBJECTIVE

The objective of this study was to investigate the impact of mainstream cigarette smoke exposure on immune inflammatory responses and viral burden after respiratory infection with influenza A.

METHODS

C57BL/6 mice were sham- or smoke-exposed for 3 to 5 mo and infected with either 2.5 x 10(3) pfu (low dose) or 2.5 x 10(5) pfu (high dose) influenza virus.

MEASUREMENTS AND MAIN RESULTS

Although smoke exposure attenuated the airway's inflammatory response to low-dose infection, we observed increased inflammation in smoke-exposed compared with sham-exposed mice after infection with high-dose influenza, despite a similar rate of viral clearance. The heightened inflammatory response was associated with increased expression of tumor necrosis factor-alpha, interleukin-6, and type 1 IFN in the airway, and increased mortality. Importantly, smoke exposure did not interfere with the development of influenza-specific memory responses; sham- and smoke-exposed animals were equally protected upon viral rechallenge.

CONCLUSION

Our study suggests that, in mice, cigarette smoke affects primary antiviral immune-inflammatory responses, whereas secondary immune protection remains intact.

Treatment With AM3 Restores Defective T-Cell Function in COPD Patients

BACKGROUND

Lymphocyte alterations have been associated with an increased prevalence of acute respiratory infections in COPD patients. AM3 is an oral immunomodulator that normalizes the defective functions of peripheral blood natural killer and phagocytic cells in COPD patients and improves their health-related quality of life.

OBJECTIVES

To characterize putative systemic abnormalities of the T-cell compartment in COPD patients, and to investigate whether AM3 can restore such abnormalities.

DESIGN

The study was a randomized, prospective, double-blind, placebo-controlled trial in a cohort of COPD patients. The results were also compared to those of nonsmoker and ex-smoker healthy control subjects.

SETTING

Outpatient departments of four hospitals.

PATIENTS

Seventy COPD patients were randomized to receive either AM3 or a placebo orally for 90 consecutive days. Populations of 36 healthy nonsmokers and 36 healthy ex-smokers were used as control subjects.

MEASUREMENTS

Peripheral blood mononuclear cell (PBMC) proliferation and production of interleukin (IL)-2, IL-4, IL-12p40, tumor necrosis factor-alpha, and interferon (IFN)-gamma proteins in response to the T-cell polyclonal mitogens were assessed at baseline and at the end of treatment.

RESULTS

The proliferative response was significantly decreased in COPD patients. Decreased production of IFN-gamma was the only defect in the profiles of the cytokine measures, and was selectively observed in COPD patients, but not in nonsmoker and ex-smoker healthy control subjects. Treatment with AM3 significantly restored the PBMC proliferative response to polyclonal mitogens and significantly promoted stimulated IFN-gamma production in these patients. The normalization of these proliferative responses was not related to significant variations in the numbers of peripheral blood monocytes, CD3+, CD4+, CD8+ cells or of any major naïve/memory/activated T-cell subset. The increased IFN-gamma production in the AM3 study arm was associated with an increase in the mean of number of IFN-gamma molecules produced per CD8+ T cells.

CONCLUSIONS

PBMCs of COPD patients showed clear functional T-lymphocyte abnormalities that are rescued by AM3 treatment.

Early interaction of Yersinia pestis with APCs in the lung

Despite the importance of pneumonic plague, little is known of the early pulmonary immune responses that occur following inhalation of Yersinia pestis. Therefore, we conducted studies to identify the early target cells for uptake of Y. pestis in the lungs following intratracheal or i.v. inoculation. Following intratracheal inoculation, Y. pestis was rapidly internalized primarily by a distinctive population of CD11c+DEC-205+CD11b- cells in the airways, whereas i.v. inoculation resulted in uptake primarily by CD11b+CD11c- macrophages and granulocytes in lung tissues. The airway cells internalized and were infected by Y. pestis, but did not support active replication of the organism. Intratracheal inoculation of Y. pestis resulted in rapid activation of airway CD11c+ cells, followed within 24 h by the selective disappearance of these cells from the airways and lungs and the accumulation of apoptotic CD11c+ cells in draining lymph nodes. When CD11c+ cells in the airways were depleted using liposomal clodronate before infection, this resulted in a significantly increased replication of Y. pestis in the lungs and dissemination to the spleen and draining lymph nodes. These findings suggest that CD11c+ cells in the airways play an important role in suppressing the initial replication and dissemination of inhaled Y. pestis, although these results will also require confirmation using fully virulent strains of Y. pestis. Depletion of these airway cells by Y. pestis may therefore be one strategy the organism uses to overcome pulmonary defenses following inhalation of the organism.

Bordetella bronchiseptica adherence to cilia is mediated by multiple adhesin factors and blocked by surfactant protein A

In the virulent state (Bvg+), Bordetella bronchiseptica expresses adhesins and toxins that mediate adherence to the upper airway epithelium, an essential early step in pathogenesis. In this study, we used a rabbit tracheal epithelial cell binding assay to test how specific host or pathogen factors contribute to ciliary binding. The host antimicrobial agent surfactant protein A (SP-A) effectively reduced ciliary binding by Bvg+ B. bronchiseptica. To evaluate the relative contributions of bacterial adhesins and toxins to ciliary binding, we used mutant strains of B. bronchiseptica in the binding assay. When compared to Bvg+ or Bvg- phase-locked B. bronchiseptica strains, single-knockout strains lacking one of the known adhesins (filamentous hemagglutinin, pertactin, or fimbriae) displayed an intermediate ciliary binding capacity throughout the coincubation. A B. bronchiseptica strain deficient in adenylate cyclase-hemolysin toxin also displayed an intermediate level of adherence between Bvg+ and Bvg- strains and had the lowest ciliary affinity of any of the Bvg+ phase strains tested. A B. bronchiseptica strain that was missing dermonecrotic toxin also displayed intermediate binding; however, this strain displayed ciliary binding significantly higher than most of the adhesin knockouts tested. Taken together, these findings suggest that virulent-state B. bronchiseptica expresses multiple adhesins with overlapping contributions to ciliary adhesion and that host production of SP-A can provide innate immunity by blocking bacterial adherence to the ciliated epithelium.

Involvement of toll-like receptor 3 in the immune response of lung epithelial cells to double-stranded RNA and influenza A virus

Influenza A is a highly contagious single-stranded RNA virus that infects both the upper and lower respiratory tracts of humans. The host innate immune Toll-like receptor (TLR) 3 was shown previously in cells of myeloid origin to recognize the viral replicative, intermediate double-stranded RNA (dsRNA). Thus, dsRNA may be critical for the outcome of the infection. Here we first compared the activation triggered by either influenza A virus or dsRNA in pulmonary epithelial cells. We established that TLR3 is constitutively expressed in human alveolar and bronchial epithelial cells, and we describe its intracellular localization. Expression of TLR3 was positively regulated by the influenza A virus and by dsRNA but not by other inflammatory mediators, including bacterial lipopolysaccharide, the cytokines tumor necrosis factor-alpha and interleukin (IL)-1beta, and the protein kinase C activator phorbol 12-myristate 13-acetate. We also demonstrated that TLR3 contributes directly to the immune response of respiratory epithelial cells to influenza A virus and dsRNA, and we propose a molecular mechanism by which these stimuli induce epithelial cell activation. This model involves mitogen-activated protein kinases, phosphatidylinositol 3-kinase/Akt signaling, and the TLR3-associated adaptor molecule TRIF but not MyD88-dependent activation of the transcription factors NF-kappaB or interferon regulatory factor/interferon-sensitive response-element pathways. Ultimately, this signal transduction elicits an epithelial response that includes the secretion of the cytokines IL-8, IL-6, RANTES (regulated on activation normal T cell expressed and secreted), and interferon-beta and the up-regulation of the major adhesion molecule ICAM-1.

Pneumococcal infections in HIV infected adults--clinical features, reasons behind the association and future hopes for prevention

Streptococcus pneumoniae is the most important bacterial cause of pneumonia and meningitis among adults world wide. It is a particularly common cause of these infections and also bacteraemia among HIV infected adults with rates of disease increasing to more than 100 times the normal as HIV infection progresses to AIDS. This article briefly describes the common presentations and outcomes of pneumococcal disease (PD) in HIV infected adult inpatients in Malawi. Factors underlying susceptibility to pneumococcal infection in HIV infected adults are then reviewed, along with the effectiveness of current vaccines. Finally, novel approaches that will be needed to combat PD in HIV afflicted parts of the world are suggested.

[Pulmonary anti-Aspergillus defences]

The lung, constantly exposed to inhaled infectious particles, uses a very efficient immune system to insure sterility of the airways. It has to be tightly regulated for the tissues to be kept from its potentially deleterious effects. Pulmonary anti-Aspergillus defences are based upon the concurrent action of innate immunity, non specific but rapidly mobilisable, and of adaptative immunity. The former first consists in natural barriers, namely the respiratory epithelium and its antimicrobial peptides (complement, defensins, collectins). Then come the phagocytic cells (macrophages and neutrophils), but also the dendritic cells, able to stimulate adaptative responses through the presentation of antigens they have phagocytised ans processed. The Toll-like receptors are among the key ones involved in the recognition of fungal components. Chemokines have a crucial role for the recruitment, maturation and activation of neutrophils, while anti-inflammatory cytokines tightly influence T lymphocytes functional differentiation. These latter, cornerstones of the adaptative immunity, differentiate into two mutually exclusive pathways according to the type of cytokines which they produce. The Th1 one is largely protective in the context of Aspergillus, while the Th2 one is deleterious. However, a good cooperation between these 2 pathways is required for an efficient protection. Pulmonary anti-Aspergillus defences are multifactorial. Innate immunity is crucial but a capacity of the host to generate specific responses is also warranted.

Protozoan predation, diversifying selection, and the evolution of antigenic diversity in Salmonella

Extensive population-level genetic variability at the Salmonella rfb locus, which encodes enzymes responsible for synthesis of the O-antigen polysaccharide, is thought to have arisen through frequency-dependent selection (FDS) by means of exposure of this pathogen to host immune systems. The FDS hypothesis works well for pathogens such as Haemophilus influenzae and Neisseria meningitis, which alter the composition of their O-antigens during the course of bloodborne infections. In contrast, Salmonella remains resident in epithelial cells or macrophages during infection and does not have phase variability in its O-antigen. More importantly, Salmonella shows host-serovar specificity, whereby strains bearing certain O-antigens cause disease primarily in specific hosts; this behavior is inconsistent with FDS providing selection for the origin or maintenance of extensive polymorphism at the rfb locus. Alternatively, selective pressure may originate from the host intestinal environment itself, wherein diversifying selection mediated by protozoan predation allows for the continued existence of Salmonella able to avoid consumption by host-specific protozoa. This selective pressure would result in high population-level diversity at the Salmonella rfb locus without phase variation. We show here that intestinal protozoa recognize antigenically diverse Salmonella with different efficiencies and demonstrate that differences solely in the O-antigen are sufficient to allow for prey discrimination. Combined with observations of the differential distributions of both serotypes of bacterial species and their protozoan predators among environments, our data provides a framework for the evolution of high genetic diversity at the rfb locus and host-specific pathogenicity in Salmonella.