Cytokine responses to group B streptococci induce nitric oxide production in respiratory epithelial cells

An opportunistic pathogen under stress: how Group B Streptococcus responds to cytotoxic reactive species and conditions of metal ion imbalance to survive

Group B Streptococcus (GBS; also known as Streptococcus agalactiae) is an opportunistic bacterial pathogen that causes sepsis, meningitis, pneumonia, and skin and soft tissue infections in neonates and healthy or immunocompromised adults. GBS is well-adapted to survive in humans due to a plethora of virulence mechanisms that afford responses to support bacterial survival in dynamic host environments. These mechanisms and responses include counteraction of cell death from exposure to excess metal ions that can cause mismetallation and cytotoxicity, and strategies to combat molecules such as reactive oxygen and nitrogen species that are generated as part of innate host defence. Cytotoxicity from reactive molecules can stem from damage to proteins, DNA, and membrane lipids, potentially leading to bacterial cell death inside phagocytic cells or within extracellular spaces within the host. Deciphering the ways in which GBS responds to the stress of cytotoxic reactive molecules within the host will benefit the development of novel therapeutic and preventative strategies to manage the burden of GBS disease. This review summarizes knowledge of GBS carriage in humans and the mechanisms used by the bacteria to circumvent killing by these important elements of host immune defence: oxidative stress, nitrosative stress, and stress from metal ion intoxication/mismetallation.

Suppression of pulmonary group B streptococcal proliferation and translocation by surfactants in ventilated near-term newborn rabbits

BACKGROUND

The pathogenesis of neonatal group B Streptococcus (GBS) lung infection may be associated with surfactant dysfunction or deficiency. This study aimed to investigate the efficacy of surfactants on early postnatal GBS infection in ventilated newborn rabbit lungs.

METHODS

A near-term newborn rabbit model was established by intratracheal GBS instillation immediately at birth, followed by mechanical ventilation. At postnatal 1 h, a porcine surfactant was given intratracheally at 100 or 200 mg/kg. After 6 h, animals were euthanized, and lung and blood samples were collected for bacterial counting. Lung histopathology and messenger RNA (mRNA) expression of inflammatory mediators, surfactant proteins, and growth factors in lung tissue were assessed.

RESULTS

The surfactants significantly suppressed (by >50%) pulmonary bacterial proliferation and systemic translocation, alleviated lung inflammatory injury, and improved alveolar expansion by morphometry, in favor of high-dose surfactants. Though the survival rate and lung mechanics were not improved, the surfactants significantly suppressed mRNA expression of proinflammatory mediators, while that for surfactant proteins and growth factors was differentially expressed, compared to the control and GBS infection groups.

CONCLUSION

Exogenous surfactants may provide a therapeutic alternative for neonatal lung infection by suppressing pulmonary GBS proliferation and translocation into systemic circulation, alleviating inflammatory injury and regulating growth factor expression.

The Host Cytokine Responses and Protective Immunity in Oropharyngeal Candidiasis

Over the last three decades, the prevalence of oropharyngeal fungal infections has increased enormously, mainly due to an increasing population of immunocompromised patients, including individuals with HIV infection, transplant recipients, and patients receiving cancer therapy. The vast majority of these infections are caused by Candida species. The presence of cytokines in infected tissues ultimately dictates the host defense processes that are specific to each pathogenic organism. During oral infection with Candida, a large number of pro-inflammatory and immunoregulatory cytokines are generated in the oral mucosa. The main sources of these cytokines are oral epithelial cells, which maintain a central role in the protection against fungal organisms. These cytokines may drive the chemotaxis and effector functions of innate and/or adaptive effector cells, such as infiltrating neutrophils and T-cells in immunocompetent hosts, and CD8+ T-cells in HIV+ hosts. Epithelial cells also have direct anti- Candida activity. Several studies have provided a potential link between lower levels of certain pro-inflammatory cytokines and susceptibility to oral C. albicans infection, suggesting that such cytokines may be involved in immune protection. The exact role of these cytokines in immune protection against oropharyngeal candidiasis is still incompletely understood and requires further investigation. Identification of such cytokines with the ability to enhance anti-fungal activities of immune effector cells may have therapeutic implications in the treatment of this oral infection in the severely immunocompromised host.

LPS-treated macrophage cytokines repress surfactant protein-B in lung epithelial cells

In the mouse lung, Escherichia coli LPS can decrease surfactant protein-B (SFTPB) mRNA and protein concentrations. LPS also regulates the expression, synthesis, and concentrations of a variety of gene and metabolic products that inhibit SFTPB gene expression. The purpose of the present study was to determine whether LPS acts directly or indirectly on pulmonary epithelial cells to trigger signaling pathways that inhibit SFTPB expression, and whether the transcription factor CCAAT/enhancer binding protein (C/EBP)-β (CEBPB) is a downstream inhibitory effector. To investigate the mechanism of SFTPB repression, the human pulmonary epithelial cell lines NCI-H441 (H441) and NCI-H820 (H820) and the mouse macrophage-like cell line RAW264.7 were treated with LPS. Whereas LPS did not decrease SFTPB transcripts in H441 or H820 cells, the conditioned medium of LPS-treated RAW264.7 cells decreased SFTPB transcripts in H441 and H820 cells, and inhibited SFTPB promoter activity in H441 cells. In the presence of neutralizing anti-tumor necrosis factor (TNF) antibodies, the conditioned medium of LPS-treated RAW264.7 cells did not inhibit SFTPB promoter activity. In H441 cells treated with recombinant TNF protein, SFTPB transcripts decreased, whereas CEBPB transcripts increased and the transient coexpression of CEBPB decreased SFTPB promoter activity. Further, CEBPB short, interfering RNA increased basal SFTPB transcripts and countered the decrease of SFTPB transcripts by TNF. Together, these findings suggest that macrophages participate in the repression of SFTPB expression by LPS, and that macrophage-released cytokines (including TNF) regulate the transcription factor CEBPB, which can function as a downstream transcriptional repressor of SFTPB gene expression in pulmonary epithelial cells.

Synergistic effect of interleukin 1 alpha on nontypeable Haemophilus influenzae-induced up-regulation of human beta-defensin 2 in middle ear epithelial cells

Background

We recently showed that beta-defensins have antimicrobial activity against nontypeable Haemophilus influenzae (NTHi) and that interleukin 1 alpha (IL-1 alpha) up-regulates the transcription of beta-defensin 2 (DEFB4 according to new nomenclature of the Human Genome Organization) in human middle ear epithelial cells via a Src-dependent Raf-MEK1/2-ERK signaling pathway. Based on these observations, we investigated if human middle ear epithelial cells could release IL-1 alpha upon exposure to a lysate of NTHi and if this cytokine could have a synergistic effect on beta-defensin 2 up-regulation by the bacterial components.

Methods

The studies described herein were carried out using epithelial cell lines as well as a murine model of acute otitis media (OM). Human cytokine macroarray analysis was performed to detect the released cytokines in response to NTHi exposure. Real time quantitative PCR was done to compare the induction of IL-1 alpha or beta-defensin 2 mRNAs and to identify the signaling pathways involved. Direct activation of the beta-defensin 2 promoter was monitored using a beta-defensin 2 promoter-Luciferase construct. An IL-1 alpha blocking antibody was used to demonstrate the direct involvement of this cytokine on DEFB4 induction.

Results

Middle ear epithelial cells released IL-1 alpha when stimulated by NTHi components and this cytokine acted in an autocrine/paracrine synergistic manner with NTHi to up-regulate beta-defensin 2. This synergistic effect of IL-1 alpha on NTHi-induced beta-defensin 2 up-regulation appeared to be mediated by the p38 MAP kinase pathway.

Conclusion

We demonstrate that IL-1 alpha is secreted by middle ear epithelial cells upon exposure to NTHi components and that it can synergistically act with certain of these molecules to up-regulate beta-defensin 2 via the p38 MAP kinase pathway.

Moxifloxacin inhibits cytokine-induced MAP kinase and NF-kappaB activation as well as nitric oxide synthesis in a human respiratory epithelial cell line

BACKGROUND

We previously demonstrated that the quinolone moxifloxacin prevents Candida albicans pneumonitis and epithelial nuclear factor kappaB (NF-kappaB) nuclear translocation in immunosuppressed mice.

OBJECTIVES

To explore the anti-inflammatory effects of moxifloxacin directly on a lung epithelial cell line.

METHODS

We studied the effect of clinically relevant concentrations of moxifloxacin (2.5-10 mg/L) on cytokine-induced activation of nitric oxide (NO) secretion, inducible NO synthase (iNOS) expression and the activation of signal transduction pathways of inflammation, NF-kappaB and the mitogen-activated protein kinases [extracellular signal-regulated kinases (ERK1/2) and C-Jun N-terminal kinase (JNK)], in the A549 lung epithelial cell line.

RESULTS

Stimulation with the cytokines interleukin-1beta(IL-1beta)/interferon-gamma (IFN-gamma) increased NO up to 3.3-fold and moxifloxacin inhibited this up to 68% (P < 0.05). Similarly, the increase in iNOS levels was inhibited in cells pre-treated with moxifloxacin by up to 62%. IL-1beta stimulated a rapid increase in the activities of early intracellular signalling molecules, ERK1/2 and JNK. Moxifloxacin inhibited ERK1/2 by up to 100% and p-JNK activation by 100%. NF-kappaB, as measured by electrophoretic mobility shift assay, was inhibited up to 72% by moxifloxacin. Western-blot analysis revealed that IL-1beta enhanced NF-kappaB p65 and p50 proteins by 1.7- and 3.6-fold, respectively, whereas moxifloxacin inhibited the proteins by up to 60%.

CONCLUSIONS

Moxifloxacin inhibits intracellular signalling, iNOS expression and NO secretion in a lung epithelial cell line. Future studies may uncover a primary site of quinolone immunomodulation, either upstream or at the cell membrane. Eventually, this quinolone might become an important therapy for inflammatory lung diseases.

In vitro-generated respiratory mucosa: a new tool to study inhalational anthrax

We generated a three-dimensional (3-D) model of human airway tissues in order to study initiation of inhalational form of anthrax infection. The system was designed to model the air-blood barrier of the respiratory tract represented by epithelial cells and macrophages. When grown on collagen/fibronectin gel support at an air-liquid interface, airway epithelial cells formed cell layers morphologically resembling those in vivo. These preformed epithelial cell cultures were further supplemented with monocytes/macrophages isolated from human blood. After 2-5 days of co-culture, monocytes differentiated into a phenotype of resident macrophages, which was evaluated by the expression of specific cell surface markers. This model allowed sorting out the role of each type of cell found at the air surface of the lung. The interdependence of macrophages and epithelial cells in the clearance of anthrax spores from airways and the capacity of the airway epithelial cells to protect from anthrax infection was demonstrated.

Modulation of human beta-defensin-2 transcription in pulmonary epithelial cells by lipopolysaccharide-stimulated mononuclear phagocytes via proinflammatory cytokine production

Human beta-defensin (hBD)-2, a cationic antimicrobial peptide primarily induced in epithelial cells in response to inflammatory stimuli, plays an important role in host defense. To elucidate the expression mechanism of hBD-2 in the lung, we investigated the modulation of hBD-2 transcription in pulmonary epithelial cells by mononuclear phagocytes stimulated with LPS. Coculture of A549 pulmonary epithelial cells with Mono-Mac-6 monocytic cells in the presence of Escherichia coli LPS markedly up-regulated hBD-2 promoter activity, whereas A549 alone did not respond to LPS to activate the hBD-2 promoter. Furthermore, IL-1beta and TNF-alpha in the culture supernatants from LPS-stimulated monocytic cells activated the hBD-2 promoter in A549 cells. Of note, IL-1beta was more potent than TNF-alpha in this effect. In addition, a mutation of the NF-kappaB site at -200 (pkappaB1 site) completely abolished this IL-1beta- and TNF-alpha-induced hBD-2 promoter activation, whereas NF-kappaB inhibitors (MG-132 and helenalin) strongly suppressed it. Moreover, electrophoretic mobility shift assay suggested that NF-kappaB, consisting of p65-p50 heterodimer, could bind to the pkappaB1 site in cytokine-stimulated A549 cells. Interestingly, flow cytometric analysis revealed that A549 cells expressed CD14 but lacked Toll-like receptor 4, which may account for the hyporesponsiveness of A549 cells to LPS. Taken together, these results suggest that hBD-2 expression in pulmonary epithelial cells is modulated by NF-kappaB via the actions of IL-1beta and TNF-alpha produced by LPS-stimulated mononuclear phagocytes.

Effect of nitric oxide donation on mucin production in vitro

Otitis media with effusion (OME) is characterized by the accumulation of a viscous fluid rich in mucins in the middle ear cleft. There is increasing evidence that this fluid is the result of an inflammatory reaction and that nitric oxide (NO) is an important mediator in this reaction. The goblet cell line HT29-MTX produces principally MUC5AC, an important mucin in middle ear effusions, and thus is a good model for the study of mucus-secreting epithelia. Confluent cell cultures were trypsinized, subcultured and incubated with isosorbide dinitrate (ISDN), a NO donor, for 0.5, 1 and 2 h at a concentration of 1 mm and in concentrations of 0.01, 0.1, 0.5, 1 and 2 mm for 1 h. Experiments were performed four times. Mucin production was detected by a slot blot ELISA assay, using a monoclonal mouse antibody to human MUC5AC mucin. Statistical significance was tested using a one-way analysis of variance. NO donation by ISDN caused a consistent rise in mucin production above control. Maximal mucin production of 35% above control occurred at 1 h with 1 mm ISDN. Mucin production increased from 12% above control with 0.1 mm ISDN dinitrate to 45% above baseline with 2 mm ISDN. NO donation by ISDN results in an increase in mucus production, which is both dose and time related. This adds further evidence to an inflammatory model for mucus secretion in OME.