40 research outputs found
Toll-like receptor (TLR)-based networks regulate neutrophilic inflammation in respiratory disease
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A cardinal role for cathepsin D in co-ordinating the host-mediated apoptosis of macrophages and killing of pneumococci
No full textThe bactericidal function of macrophages against pneumococci is enhanced by their apoptotic demise, which is controlled by the anti-apoptotic protein Mcl-1. Here, we show that lysosomal membrane permeabilization (LMP) and cytosolic translocation of activated cathepsin D occur prior to activation of a mitochondrial pathway of macrophage apoptosis. Pharmacological inhibition or knockout of cathepsin D during pneumococcal infection blocked macrophage apoptosis. As a result of cathepsin D activation, Mcl-1 interacted with its ubiquitin ligase Mule and expression declined. Inhibition of cathepsin D had no effect on early bacterial killing but inhibited the late phase of apoptosis-associated killing of pneumococci in vitro. Mice bearing a cathepsin D-/- hematopoietic system demonstrated reduced macrophage apoptosis in vivo, with decreased clearance of pneumococci and enhanced recruitment of neutrophils to control pulmonary infection. These findings establish an unexpected role for a cathepsin D-mediated lysosomal pathway of apoptosis in pulmonary host defense and underscore the importance of apoptosis-associated microbial killing to macrophage function
Monocytes regulate the mechanism of T-cell death by inducing Fas-mediated apoptosis during bacterial infection.
No full textMonocytes and T-cells are critical to the host response to acute bacterial infection but monocytes are primarily viewed as amplifying the inflammatory signal. The mechanisms of cell death regulating T-cell numbers at sites of infection are incompletely characterized. T-cell death in cultures of peripheral blood mononuclear cells (PBMC) showed 'classic' features of apoptosis following exposure to pneumococci. Conversely, purified CD3(+) T-cells cultured with pneumococci demonstrated necrosis with membrane permeabilization. The death of purified CD3(+) T-cells was not inhibited by necrostatin, but required the bacterial toxin pneumolysin. Apoptosis of CD3(+) T-cells in PBMC cultures required 'classical' CD14(+) monocytes, which enhanced T-cell activation. CD3(+) T-cell death was enhanced in HIV-seropositive individuals. Monocyte-mediated CD3(+) T-cell apoptotic death was Fas-dependent both in vitro and in vivo. In the early stages of the T-cell dependent host response to pneumococci reduced Fas ligand mediated T-cell apoptosis was associated with decreased bacterial clearance in the lung and increased bacteremia. In summary monocytes converted pathogen-associated necrosis into Fas-dependent apoptosis and regulated levels of activated T-cells at sites of acute bacterial infection. These changes were associated with enhanced bacterial clearance in the lung and reduced levels of invasive pneumococcal disease
Approaching intelligent infection diagnostics: Carbon fibre sensor for electrochemical pyocyanin detection
No full textPyocyanin is produced by Ps. aeruginosa as a result of quorum sensing during wound colonisation increasing bacterial virulence and damaging host physiology, both of which contribute to an increased risk of infection. The use of carbon fibre tow as an electrochemical sensing matrix for assessing pyocyanin production is evaluated. Prototype sensor assemblies have been developed and response characteristics towards pyocyanin are detailed. The sensitive and linear quantification of pyocyanin is presented (r2 = 0.998) across the biomedically relevant concentration range (1–100 µM). Precise electrochemical measurements of pyocyanin by square wave voltammetry are established using carbon fibre assemblies (coefficient of variance = 1.2 and 1.4% for 10 and 50 µM pyocyanin, respectively). Further testing of the sensors in bacterial cultures shows the ability to monitor pyocyanin production by Ps. aeruginosa in agreement with the chloroform-acid/photometric method and in the presence of other bacterially derived pigments and metabolites. The proposed small and inexpensive sensor assembly is suggested for use in monitoring Ps. aeruginosa growth
Diagnostic and treatment behaviour in children with chronic respiratory symptoms: relationship with socioeconomic factors
No full textBackground: The prevalence and severity of asthma is believed to increase with increasing socioeconomic
deprivation. The relationship between asthma diagnosis, symptoms, diagnostic accuracy, and
socioeconomic deprivation as determined by Townsend scores was determined in Sheffield schoolchildren.
Methods: All 6021 schoolchildren aged 8–9 years in one school year in Sheffield were given a parent
respondent survey based on International Survey of Asthma and Allergies in Childhood (ISAAC)
questions.
Results: 5011/6021 (83.2%) questionnaires were returned. Postcode data were available in 4131
replies (82.4%) and were used to assign a composite deprivation score (Townsend score). Scores were
divided into five quintiles, with group 1 being least and group 5 being most deprived. A positive trend
was observed from group 1 to group 5 for the prevalence of wheeze in the previous 12 months,
wheeze attacks >4/year, nocturnal wheeze and cough (all p<0.001), cough and/or wheeze “most
times” with exertion (p<0.03), current asthma (p<0.001), and significant asthma symptoms (p<0.001).
No significant trend was observed for lifetime wheeze or attacks of speech limiting wheeze. There were
no significant trends in the prevalence of current asthmatic children without significant symptoms (overdiagnosis)
or children with significant asthma symptoms but no current asthma diagnosis (underdiagnosis)
across the social groups. There was a significant negative trend in the ratio of asthma medication
to asthma diagnosis from least to most deprived groups (p<0.001).
Conclusions: Asthma morbidity and severity increase according to the level of socioeconomic deprivation.
This may be due to differences in environment, asthma management, and/or symptom reporting.
Diagnostic accuracy does not vary significantly across deprivation groups but children living in
areas of least deprivation and taking asthma medication are less likely to be labelled as having
asthma, suggesting diagnostic labelling bias
Increasing prevalence of asthma diagnosis and symptoms in children is confined to mild symptoms
No full textBACKGROUND: The prevalence of childhood asthma is increasing but few studies have investigated trends in asthma severity. We investigated trends in asthma diagnosis and symptom morbidity between an eight year time period in a paired prevalence study.
METHODS: All children in one single school year aged 8-9 years in the city of Sheffield were given a parent respondent questionnaire in 1991 and 1999 based on questions from the International Survey of Asthma and Allergy in Children (ISAAC). Data were obtained regarding the prevalence of asthma and wheeze and current (12 month) prevalences of wheeze attacks, speech limiting wheeze, nocturnal cough and wheeze, and exertional symptoms.
RESULTS: The response rates in 1991 and 1999 were 4580/5321 (85.3%) and 5011/6021 (83.2%), respectively. There were significant increases between the two surveys in the prevalence of asthma ever (19.9% v 29.7%, mean difference 11.9%, 95% confidence interval (CI) 10.16 to 13.57, p<0.001), current asthma (10.3% v 13.0%, mean difference 2.7%, 95% CI 1.44 to 4.03, p<0.001), wheeze ever (30.3% v 35.8%, mean difference 5.7%, 95% CI 3.76 to 7.56, p<0.001), wheeze in the previous 12 months (17.0% v 19.4%, mean difference 2.5, 95% CI 0.95 to 4.07, p<0.01), and reporting of medication use (16.9% v 20%, mean difference 3.0%, 95% CI 1.46 to 4.62, p<0.001). There were also significant increases in reported hayfever and eczema diagnoses.
CONCLUSIONS: Diagnostic labelling of asthma and lifetime prevalence of wheeze has increased. The current 12 month point prevalence of wheeze has increased but this is confined to occasional symptoms. The increased medication rate may be responsible for the static prevalence of severe asthma symptoms. The significant proportion of children receiving medication but reporting no asthma symptoms identified from our 1999 survey suggests that some children are being inappropriately treated or overtreated
A method for the in vivo measurement of zebrafish tissue neutrophil lifespan
No full textNeutrophil function is thought to be regulated, in large part, by limitation of lifespan by apoptosis. A number of studies suggest that circulating neutrophils have a half-life of approximately 6 hours, although contradictory evidence exists. Measuring tissue neutrophil lifespan, however, is more problematic. It is thought that tissue neutrophils survive longer, perhaps with a half-life in the order of 3-5 days, but this has never been directly measured. Zebrafish are an emerging model organism, with several advantages for the study of vertebrate immunity. In zebrafish, neutrophils constitutively assume tissue locations allowing their direct study in vivo. Using a transgenic approach, neutrophils were labelled with a photoconvertible pigment, Kaede. Photoconversion parameters were optimised and the stability of the Kaede confirmed. Individual neutrophils were photoconverted by scanning a confocal 405 nm laser specifically over each cell and their survival monitored for 48 hours, revealing an in vivo half-life for zebrafish tissue neutrophils of around 120 hours (117.7 hrs, 95% CI 95.67-157.8). Laser energy did not extend neutrophil lifespan, and we conclude that this represents a lower bound for the lifespan of a resting tissue neutrophil in the developing zebrafish larva. This is the first direct measurement of the lifespan of an in vivo tissue neutrophil.</p
