Inhibition of neutrophil elastase attenuates gut mucosal injury evoked by acute alveolar hypoxia in rabbits

Hypoxia and sterile inflammation in cystic fibrosis airways: mechanisms and potential therapies

Cystic fibrosis is one of the most common autosomal recessive genetic diseases in Caucasian populations. Diagnosisvianewborn screening and targeted nutritional and antibiotic therapy have improved outcomes, however respiratory failure remains the key cause of morbidity and mortality. Progressive respiratory disease in cystic fibrosis is characterised by chronic neutrophilic airway inflammation associated with structural airway damage leading to bronchiectasis and decreased lung function. Mucus obstruction is a characteristic early abnormality in the cystic fibrosis airway, associated with neutrophilic inflammation often in the absence of detectable infection. Recent studies have suggested a link between hypoxic cell death and sterile neutrophilic inflammation in cystic fibrosis and other diseasesviathe IL-1 signalling pathway. In this review, we consider recent evidence regarding the cellular responses to respiratory hypoxia as a potential driver of sterile neutrophilic inflammation in the lung, current knowledge on hypoxia as a pathogenic mechanism in cystic fibrosis and the potential for current and future therapies to alleviate hypoxia-driven sterile inflammation.

Essential role for neutrophils in pathogenesis and adaptive immunity in Chlamydia caviae ocular infections

Trachoma, the world's leading cause of preventable blindness, is produced by chronic ocular infection with Chlamydia trachomatis, an obligate intracellular bacterium. While many studies have focused on immune mechanisms for trachoma during chronic stages of infection, less research has targeted immune mechanisms in primary ocular infections, events that could impact chronic responses. The goal of this study was to investigate the function of neutrophils during primary chlamydial ocular infection by using the guinea pig model of Chlamydia caviae inclusion conjunctivitis. We hypothesized that neutrophils help modulate the adaptive response and promote host tissue damage. To test these hypotheses, guinea pigs with primary C. caviae ocular infections were depleted of neutrophils by using rabbit antineutrophil antiserum, and immune responses and immunopathology were evaluated during the first 7 days of infection. Results showed that neutrophil depletion dramatically decreased ocular pathology, both clinically and histologically. The adaptive response was also altered, with increased C. caviae-specific IgA titers in tears and serum and decreased numbers of CD4(+) and CD8(+) T cells in infected conjunctivae. Additionally, there were changes in conjunctival chemokines and cytokines, such as increased expression of IgA-promoting interleukin-5 and anti-inflammatory transforming growth factor β, along with decreased expression of T cell-recruiting CCL5 (RANTES). This study, the first to investigate the role of neutrophils in primary chlamydial ocular infection, indicates a previously unappreciated role for neutrophils in modulating the adaptive response and suggests a prominent role for neutrophils in chlamydia-associated ocular pathology.

Neutrophil elastase inhibitor restores gut ischemia reperfusion-induced impairment of gut immunity with reduced plasma interleukin-6 concentrations in mice

BACKGROUND AND PURPOSE

Gut-associated lymphoid tissue (GALT) is regarded as central mucosa-associated lymphoid tissue that influences systemic mucosal immunity. Our previous study revealed that gut ischemia and reperfusion (I/R) reduces GALT lymphocyte numbers. Because gut hypoperfusion frequently occurs in trauma, shock, and surgery patients, establishment of a therapeutic method to preserve GALT mass after gut I/R may be important for the prevention of infections. We examined the effects of sivelestat sodium hydrate, a selective inhibitor of neutrophil elastase, on GALT mass and plasma cytokine concentrations in a murine gut I/R model.

METHODS

Seventy male ICR mice were randomized to the control (n = 34) or the sivelestat (n = 36) group. After intravenous cannulation of the animals, the superior mesenteric artery was occluded for 60 min. After reperfusion, physiologic saline or sivelestat 5 mg/kg hourly was infused for 24 h. Sixteen mice in the control and 22 in the sivelestat group were alive at 24 h. Twenty-six mice (n = 13 in each group) were chosen randomly for harvest of the small intestine. Lymphocytes from Peyer patches (PP), the intraepithelial space (IE), and the lamina propria (LP) were counted; and their phenotypes (αβT-cell receptor (TCR), γδTCR, CD4, CD8, B cell) were determined by flow cytometry. Cytokine concentrations (interleukin [IL]-6, IL-1β, IL-10) in the plasma and bronchoalveolar lavage fluid were measured by enzyme-linked immunosorbent assay.

RESULTS

Sivelestat treatment did not improve survival but increased PP and IE lymphocyte numbers significantly and reduced the LP CD8(+) cell percentage and plasma IL-6 concentration compared with controls. There were no significant differences between the two groups in other cell phenotypes or cytokine concentrations.

CONCLUSION

Sivelestat treatment after gut I/R may be useful for maintaining gut immunity and preventing systemic inflammatory responses.

Hypoxia selectively inhibits respiratory burst activity and killing of Staphylococcus aureus in human neutrophils

Neutrophils play a central role in the innate immune response and a critical role in bacterial killing. Most studies of neutrophil function have been conducted under conditions of ambient oxygen, but inflamed sites where neutrophils operate may be extremely hypoxic. Previous studies indicate that neutrophils sense and respond to hypoxia via the ubiquitous prolyl hydroxylase/hypoxia-inducible factor pathway and that this can signal for enhanced survival. In the current study, human neutrophils were shown to upregulate hypoxia-inducible factor (HIF)-1α-dependent gene expression under hypoxic incubation conditions (3 kPa), with a consequent substantial delay in the onset of apoptosis. Despite this, polarization and chemotactic responsiveness to IL-8 and fMLP were entirely unaffected by hypoxia. Similarly, hypoxia did not diminish the ability of neutrophils to phagocytose serum-opsonized heat-killed streptococci. Of the secretory functions examined, IL-8 generation was preserved and elastase release was enhanced by hypoxia. Hypoxia did, however, cause a major reduction in respiratory burst activity induced both by the soluble agonist fMLP and by ingestion of opsonized zymosan, without affecting expression of the NADPH oxidase subunits. Critically, this reduction in respiratory burst activity under hypoxia was associated with a significant defect in the killing of Staphylococcus aureus. In contrast, killing of Escherichia coli, which is predominantly oxidase independent, was fully preserved under hypoxia. In conclusion, these studies suggest that although the NADPH oxidase-dependent bacterial killing mechanism may be compromised by hypoxia, neutrophils overall appear extremely well adapted to operate successfully under severely hypoxic conditions.