Animal and translational models of SARS-CoV-2 infection and COVID-19.

COVID-19 is causing a major once-in-a-century global pandemic. The scientific and clinical community is in a race to define and develop effective preventions and treatments. The major features of disease are described but clinical trials have been hampered by competing interests, small scale, lack of defined patient cohorts and defined readouts. What is needed now is head-to-head comparison of existing drugs, testing of safety including in the background of predisposing chronic diseases, and the development of new and targeted preventions and treatments. This is most efficiently achieved using representative animal models of primary infection including in the background of chronic disease with validation of findings in primary human cells and tissues. We explore and discuss the diverse animal, cell and tissue models that are being used and developed and collectively recapitulate many critical aspects of disease manifestation in humans to develop and test new preventions and treatments.

Obese asthmatics are characterized by altered adipose tissue macrophage activation.

BACKGROUND: Adipose tissue-derived inflammation is linked to obesity-related comorbidities. This study aimed to quantify and immuno-phenotype adipose tissue macrophages (ATMs) from obese asthmatics and obese non-asthmatics and to examine associations between adipose tissue, systemic and airway inflammation. METHODS: Visceral (VAT) adipose tissue and subcutaneous (SAT) adipose tissue were collected from obese adults undergoing bariatric surgery and processed to obtain the stromovascular fraction. Pro-inflammatory (M1) and anti-inflammatory (M2) macrophages were quantified by flow cytometry. Cytospins of induced sputum were stained for differential cell counts. Plasma C-reactive protein (CRP) and CD163 were measured by ELISA. RESULTS: VAT contained a higher number of ATMs compared to SAT. A higher percentage of M1 ATMs was observed in VAT of obese asthmatics compared to obese non-asthmatics. The M1:M2 ratio in VAT was negatively associated with FEV1 %. Sputum macrophage count was correlated positively with M1 ATMs and negatively with M2 ATMs in VAT. In obese asthmatics, CRP was positively associated with M1:M2 ratio in VAT. There were no associations with CD163. An elevated ratio of M1:M2 ATMs was observed in VAT of obese asthmatics with increased disease severity. CONCLUSIONS AND CLINICAL RELEVANCE: Visceral inflammation with increased pro-inflammatory macrophages (M1) occurs in obese asthma and may be a determinant of systemic inflammation and asthma severity.

Targeting PP2A and proteasome activity ameliorates features of allergic airway disease in mice.

BACKGROUND: Asthma is an allergic airway disease (AAD) caused by aberrant immune responses to allergens. Protein phosphatase-2A (PP2A) is an abundant serine/threonine phosphatase with anti-inflammatory activity. The ubiquitin proteasome system (UPS) controls many cellular processes, including the initiation of inflammatory responses by protein degradation. We assessed whether enhancing PP2A activity with fingolimod (FTY720) or 2-amino-4-(4-(heptyloxy) phenyl)-2-methylbutan-1-ol (AAL(S) ), or inhibiting proteasome activity with bortezomib (BORT), could suppress experimental AAD. METHODS: Acute AAD was induced in C57BL/6 mice by intraperitoneal sensitization with ovalbumin (OVA) in combination with intranasal (i.n) exposure to OVA. Chronic AAD was induced in mice with prolonged i.n exposure to crude house dust mite (HDM) extract. Mice were treated with vehicle, FTY720, AAL(S) , BORT or AAL(S) +BORT and hallmark features of AAD assessed. RESULTS: AAL(S) reduced the severity of acute AAD by suppressing tissue eosinophils and inflammation, mucus-secreting cell (MSC) numbers, type 2-associated cytokines (interleukin (IL)-33, thymic stromal lymphopoietin, IL-5 and IL-13), serum immunoglobulin (Ig)E and airway hyper-responsiveness (AHR). FTY720 only suppressed tissue inflammation and IgE. BORT reduced bronchoalveolar lavage fluid (BALF) and tissue eosinophils and inflammation, IL-5, IL-13 and AHR. Combined treatment with AAL(S) +BORT had complementary effects and suppressed BALF and tissue eosinophils and inflammation, MSC numbers, reduced the production of type 2 cytokines and AHR. AAL(S) , BORT and AAL(S) +BORT also reduced airway remodelling in chronic AAD. CONCLUSION: These findings highlight the potential of combination therapies that enhance PP2A and inhibit proteasome activity as novel therapeutic strategies for asthma.

Grandmaternal smoke exposure reduces female fertility in a murine model, with great-grandmaternal smoke exposure unlikely to have an effect.

STUDY QUESTION: What effect does multigenerational (F2) and transgenerational (F3) cigarette smoke exposure have on female fertility in mice? SUMMARY ANSWER: Cigarette smoking has a multigenerational effect on female fertility. WHAT IS KNOWN ALREADY: It has been well established that cigarette smoking decreases female fertility. Furthermore, a growing body of evidence suggests that smoking during pregnancy decreases the fertility of daughters and increases cancer and asthma incidence in grandchildren and great-grandchildren. STUDY DESIGN, SIZE, DURATION: Six-week-old C57BL/6 female mice were exposed nasally to cigarette smoke or room air (controls) for 5 weeks prior to being housed with males. Females continued to be exposed to smoke throughout pregnancy and lactation until pups were weaned. A subset of F1 female pups born to these smoke and non-smoke exposed females were bred to create the F2 grandmaternal exposed generation (multigenerational). Finally, a subset of F2 females were bred to create the F3 great-grandmaternal exposed generation (transgenerational). The reproductive health of F2 and F3 females was examined at 8 weeks and 9 months. PARTICIPANTS/MATERIALS, SETTING, METHODS: Ovarian and oocyte quality was examined in smoke exposed and control animals. A small-scale fertility trial was performed before ovarian changes were examined using ovarian histology and immunofluorescence and/or immunoblotting analysis of markers of apoptosis (TUNEL) and proliferation (proliferating cell nuclear antigen (PCNA) and anti-Mullerian hormone (AMH)). Oocyte quality was examined using immunocytochemistry to analyze the metaphase II spindle and ploidy status. Parthenogenetic activation of oocytes was used to investigate meiosis II timing and preimplantation embryo development. Finally, diestrus hormone serum levels (FSH and LH) were quantified. MAIN RESULTS AND THE ROLE OF CHANCE: F2 smoke exposed females had no detectable change in ovarian follicle quality at 8 weeks, although by 9 months ovarian somatic cell proliferation was reduced (P = 0.0197) compared with non-smoke exposed control. Further investigation revealed changes between control and smoke exposed F2 oocyte quality, including altered meiosis II timing at 8 weeks (P = 0.0337) and decreased spindle pole to pole length at 9 months (P = 0.0109). However, no change in preimplantation embryo development was observed following parthenogenetic activation. The most noticeable effect of cigarette smoke exposure was related to the subfertility of F2 females; F2 smoke exposed females displayed significantly increased time to conception (P = 0.0042) and significantly increased lag time between pregnancies (P = 0.0274) compared with non-smoke exposed F2 females. Conversely, F3 smoke exposed females displayed negligible oocyte and follicle changes up to 9 months of age, and normal preimplantation embryo development. LARGE SCALE DATA: None. LIMITATIONS, REASONS FOR CAUTION: This study focused solely on a mouse model of cigarette smoke exposure to simulate human exposure. WIDER IMPLICATIONS OF THE FINDINGS: Our results demonstrate that grandmaternal cigarette smoke exposure reduces female fertility in mice, highlighting the clinical need to promote cessation of cigarette smoking in pregnant women. STUDY FUNDING/COMPETING INTEREST(S): This study was funded by the Australian Research Council, National Health and Medical Research Council, Hunter Medical Research Institute, Newcastle Permanent Building Society Charitable Trust, and the University of Newcastle Priory Research Centers in Chemical Biology, Healthy Lungs and Grow Up Well. The authors declare no conflict of interest.

The inhibitor of semicarbazide-sensitive amine oxidase, PXS-4728A, ameliorates key features of chronic obstructive pulmonary disease in a mouse model.

BACKGROUND AND PURPOSE: Chronic obstructive pulmonary disease (COPD) is a major cause of illness and death, often induced by cigarette smoking (CS). It is characterized by pulmonary inflammation and fibrosis that impairs lung function. Existing treatments aim to control symptoms but have low efficacy, and there are no broadly effective treatments. A new potential target is the ectoenzyme, semicarbazide-sensitive mono-amine oxidase (SSAO; also known as vascular adhesion protein-1). SSAO is elevated in smokers' serum and is a pro-inflammatory enzyme facilitating adhesion and transmigration of leukocytes from the vasculature to sites of inflammation. EXPERIMENTAL APPROACH: PXS-4728A was developed as a low MW inhibitor of SSAO. A model of COPD induced by CS in mice reproduces key aspects of human COPD, including chronic airway inflammation, fibrosis and impaired lung function. This model was used to assess suppression of SSAO activity and amelioration of inflammation and other characteristic features of COPD. KEY RESULTS: Treatment with PXS-4728A completely inhibited lung and systemic SSAO activity induced by acute and chronic CS-exposure. Daily oral treatment inhibited airway inflammation (immune cell influx and inflammatory factors) induced by acute CS-exposure. Therapeutic treatment during chronic CS-exposure, when the key features of experimental COPD develop and progress, substantially suppressed inflammatory cell influx and fibrosis in the airways and improved lung function. CONCLUSIONS AND IMPLICATIONS: Treatment with a low MW inhibitor of SSAO, PXS-4728A, suppressed airway inflammation and fibrosis and improved lung function in experimental COPD, demonstrating the therapeutic potential of PXS-4728A for this debilitating disease.

A pathogenic role for tumor necrosis factor-related apoptosis-inducing ligand in chronic obstructive pulmonary disease.

Chronic obstructive pulmonary disease (COPD) is a life-threatening inflammatory respiratory disorder, often induced by cigarette smoke (CS) exposure. The development of effective therapies is impaired by a lack of understanding of the underlining mechanisms. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a cytokine with inflammatory and apoptotic properties. We interrogated a mouse model of CS-induced experimental COPD and human tissues to identify a novel role for TRAIL in COPD pathogenesis. CS exposure of wild-type mice increased TRAIL and its receptor messenger RNA (mRNA) expression and protein levels, as well as the number of TRAIL(+)CD11b(+) monocytes in the lung. TRAIL and its receptor mRNA were also increased in human COPD. CS-exposed TRAIL-deficient mice had decreased pulmonary inflammation, pro-inflammatory mediators, emphysema-like alveolar enlargement, and improved lung function. TRAIL-deficient mice also developed spontaneous small airway changes with increased epithelial cell thickness and collagen deposition, independent of CS exposure. Importantly, therapeutic neutralization of TRAIL, after the establishment of early-stage experimental COPD, reduced pulmonary inflammation, emphysema-like alveolar enlargement, and small airway changes. These data provide further evidence for TRAIL being a pivotal inflammatory factor in respiratory diseases, and the first preclinical evidence to suggest that therapeutic agents that target TRAIL may be effective in COPD therapy.

Mucosal production of uric acid by airway epithelial cells contributes to particulate matter-induced allergic sensitization.

Exposure to particulate matter (PM), a major component of air pollution, contributes to increased morbidity and mortality worldwide. PM induces innate immune responses and contributes to allergic sensitization, although the mechanisms governing this process remain unclear. Lung mucosal uric acid has also been linked to allergic sensitization. The links among PM exposure, uric acid, and allergic sensitization remain unexplored. We therefore investigated the mechanisms behind PM-induced allergic sensitization in the context of lung mucosal uric acid. PM10 and house dust mite exposure selectively induced lung mucosal uric acid production and secretion in vivo, which did not occur with other challenges (lipopolysaccharide, virus, bacteria, or inflammatory/fibrotic stimuli). PM10-induced uric acid mediates allergic sensitization and augments antigen-specific T-cell proliferation, which is inhibited by uricase. We then demonstrate that human airway epithelial cells secrete uric acid basally and after stimulation through a previously unidentified mucosal secretion system. Our work discovers a previously unknown mechanism of air pollution-induced, uric acid-mediated, allergic sensitization that may be important in the pathogenesis of asthma.

Avian influenza in Australia: a summary of 5 years of wild bird surveillance.

BACKGROUND: Avian influenza viruses (AIVs) are found worldwide in numerous bird species, causing significant disease in gallinaceous poultry and occasionally other species. Surveillance of wild bird reservoirs provides an opportunity to add to the understanding of the epidemiology of AIVs. METHODS: This study examined key findings from the National Avian Influenza Wild Bird Surveillance Program over a 5-year period (July 2007-June 2012), the main source of information on AIVs circulating in Australia. RESULTS: The overall proportion of birds that tested positive for influenza A via PCR was 1.9 ± 0.1%, with evidence of widespread exposure of Australian wild birds to most low pathogenic avian influenza (LPAI) subtypes (H1-13, H16). LPAI H5 subtypes were found to be dominant and widespread during this 5-year period. CONCLUSION: Given Australia's isolation, both geographically and ecologically, it is important for Australia not to assume that the epidemiology of AIV from other geographic regions applies here. Despite all previous highly pathogenic avian influenza outbreaks in Australian poultry being attributed to H7 subtypes, widespread detection of H5 subtypes in wild birds may represent an ongoing risk to the Australian poultry industry.

Damaging legacy: maternal cigarette smoking has long-term consequences for male offspring fertility.

STUDY QUESTION: What are the effects on fertility of cigarette smoke-induced toxicity on male offspring exposed during the gestational/weaning period? SUMMARY ANSWER: Maternal cigarette smoke exposure during the gestational/weaning period causes long-term defects in male offspring fertility. WHAT IS KNOWN ALREADY: Cigarette smoke is a well-known reproductive toxicant which is particularly harmful to both fetal and neonatal germ cells. However, recent studies suggest a significant portion of young mothers in the developed world still smoke during pregnancy. In the context of male reproductive health, our understanding of the effects of in utero exposure on offspring fertility is limited. STUDY DESIGN, SIZE, DURATION: In this study, 27 C57BL/6 5-week-old female mice were exposed via the nose-only to cigarette smoke (treatment) or 27 were exposed to room air (control) for 6 weeks before being housed with stud males to produce litters. In the treatment group, smoke exposure continued throughout mating, pregnancy and lactation until weaning of pups at 21 days post birth. Male offspring were examined at post-natal days 3, 6, 12, 21 and 98 (adult). PARTICIPANTS/MATERIALS, SETTING, METHODS: Approximately 108 maternal smoke-exposed C57BL/6 offspring and controls were examined. Spermatogenesis was examined using testicular histology and apoptosis/DNA damage was assessed using caspase immunohistochemistry and TUNEL. Sertoli cell morphology and fluctuations in the spermatogonial stem cell population were also examined using immunohistochemistry. Microarray and QPCR analysis were performed on adult testes to examine specific long-term transcriptomic alteration as a consequence of maternal smoke exposure. Sperm counts and motility, zona/oolemma binding assays, COMET analysis and mitochondrial genomic sequencing were also performed on spermatozoa obtained from adult treated and control mice. Fertility trials using exposed adult male offspring were also performed. MAIN RESULTS AND THE ROLE OF CHANCE: Maternal cigarette smoke exposure caused increased gonocyte and meiotic spermatocyte apoptosis (P < 0.01) as well as germ cell depletion in the seminiferous tubules of neonatal and juvenile offspring. Aberrant testicular development characterized by abnormal Sertoli and germ cell organization, a depleted spermatogonial stem cell population (P < 0.01), atrophic seminiferous tubules and increased germ cell DNA damage (P < 0.01) persisted in adult offspring 11 weeks after exposure. Microarray analysis of adult offspring testes associated these defects with meiotic germ cell development, sex hormone metabolism, oxidative stress and Sertoli cell signalling. Next generation sequencing also revealed a high mitochondrial DNA mutational load in the testes of adult offspring (P < 0.01). Adult maternal smoke-exposed offspring also had reduced sperm counts with spermatozoa exhibiting morphological abnormalities (P < 0.01), affecting motility and fertilization potential. Odf2, a spermatozoa flagellum component required for coordinated ciliary beating, was also significantly down-regulated (P < 0.01) in maternal smoke-exposed adult offspring, with aberrant localization along the spermatozoa flagellum. Adult maternal smoke-exposed offspring took significantly longer to impregnate control females and had a slight but significant (P < 0.01) reduction in litter size. LIMITATIONS, REASONS FOR CAUTION: This study examined only one species (mouse) using a smoking model which only simulates human cigarette smoke exposure. WIDER IMPLICATIONS OF THE FINDINGS: This study represents the first comprehensive animal model of maternal smoking on male offspring reproductive function, suggesting that exposure during the gestational/weaning period causes long-term defects in male offspring fertility. This is due to a compromised spermatogonial stem cell population resulting from gonocyte apoptosis and impaired spermatogenic development. This results in significant germ cell damage and Sertoli cell dysfunction, impacting germ cell number, tubule organization, DNA damage and spermatozoa in adult offspring. This study strengthens the current literature suggesting that maternal exposure impairs male offspring fertility, which is currently debated due to conflicting studies. STUDY FUNDING/COMPETING INTERESTS: This study was funded by the Australian Research Council, Hunter Medical Research Institute, National Health and Medical Research Council of Australia and the Newcastle Permanent Building Society Charitable Trust. The authors declare no conflict of interest.

Contribution of epithelial innate immunity to systemic protection afforded by prolyl hydroxylase inhibition in murine colitis.

Pharmacological stabilization of hypoxia-inducible factor (HIF) through prolyl hydroxylase (PHD) inhibition limits mucosal damage associated with models of murine colitis. However, little is known about how PHD inhibitors (PHDi) influence systemic immune function during mucosal inflammation or the relative importance of immunological changes to mucosal protection. We hypothesized that PHDi enhances systemic innate immune responses to colitis-associated bacteremia. Mice with colitis induced by trinitrobenzene sulfonic acid were treated with AKB-4924, a new HIF-1 isoform-predominant PHDi, and clinical, immunological, and biochemical endpoints were assessed. Administration of AKB-4924 led to significantly reduced weight loss and disease activity compared with vehicle controls. Treated groups were pyrexic but did not become subsequently hypothermic. PHDi treatment augmented epithelial barrier function and led to an approximately 50-fold reduction in serum endotoxin during colitis. AKB-4924 also decreased cytokines involved in pyrogenesis and hypothermia, significantly reducing serum levels of interleukin (IL)-1ß, IL-6, and tumor necrosis factor (TNF)-α while increasing IL-10. Treatment offered no protection against colitis in epithelial-specific HIF-1α-deficient mice, strongly implicating epithelial HIF-1α as the tissue target for AKB-4924-mediated protection. Taken together, these results indicate that inhibition of prolyl hydroxylase with AKB-4924 enhances innate immunity and identifies that the epithelium is a central site of inflammatory protection afforded by PHDi in murine colitis.

Tumor necrosis factor-related apoptosis-inducing ligand translates neonatal respiratory infection into chronic lung disease.

Respiratory infections in early life can lead to chronic respiratory disease. Chlamydia infections are common causes of respiratory disease, particularly pneumonia in neonates, and are linked to permanent reductions in pulmonary function and the induction of asthma. However, the immune responses that protect against early-life infection and the mechanisms that lead to chronic lung disease are incompletely understood. Here we identify novel roles for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in promoting Chlamydia respiratory infection-induced pathology in early life, and subsequent chronic lung disease. By infecting TRAIL-deficient neonatal mice and using neutralizing antibodies against this factor and its receptors in wild-type mice, we demonstrate that TRAIL is critical in promoting infection-induced histopathology, inflammation, and mucus hypersecretion, as well as subsequent alveolar enlargement and impaired lung function. This suggests that therapeutic agents that target TRAIL or its receptors may be effective treatments for early-life respiratory infections and associated chronic lung disease.

Scrambled and fried: cigarette smoke exposure causes antral follicle destruction and oocyte dysfunction through oxidative stress.

Cigarette smoke is a reproductive hazard associated with pre-mature reproductive senescence and reduced clinical pregnancy rates in female smokers. Despite an increased awareness of the adverse effects of cigarette smoke exposure on systemic health, many women remain unaware of the adverse effects of cigarette smoke on female fertility. This issue is compounded by our limited understanding of the molecular mechanisms behind cigarette smoke induced infertility. In this study we used a direct nasal exposure mouse model of cigarette smoke-induced chronic obstructive pulmonary disease to characterise mechanisms of cigarette-smoke induced ovotoxicity. Cigarette smoke exposure caused increased levels of primordial follicle depletion, antral follicle oocyte apoptosis and oxidative stress in exposed ovaries, resulting in fewer follicles available for ovulation. Evidence of oxidative stress also persisted in ovulated oocytes which escaped destruction, with increased levels of mitochondrial ROS and lipid peroxidation resulting in reduced fertilisation potential. Microarray analysis of ovarian tissue correlated these insults with a complex mechanism of ovotoxicity involving genes associated with detoxification, inflammation, follicular activation, immune cell mediated apoptosis and membrane organisation. In particular, the phase I detoxifying enzyme cyp2e1 was found to be significantly up-regulated in developing oocytes; an enzyme known to cause molecular bioactivation resulting in oxidative stress. Our results provide a preliminary model of cigarette smoke induced sub-fertility through cyp2e1 bioactivation and oxidative stress, resulting in developing follicle depletion and oocyte dysfunction.

Constitutive production of IL-13 promotes early-life Chlamydia respiratory infection and allergic airway disease.

Deleterious responses to pathogens during infancy may contribute to infection and associated asthma. Chlamydia respiratory infections in early life are common causes of pneumonia and lead to reduced lung function and asthma. We investigated the role of interleukin-13 (IL-13) in promoting early-life Chlamydia respiratory infection, infection-induced airway hyperresponsiveness (AHR), and severe allergic airway disease (AAD). Infected infant Il13(-/-) mice had reduced infection, inflammation, and mucus-secreting cell hyperplasia. Surprisingly, infection of wild-type (WT) mice did not increase IL-13 production but reduced IL-13Rα2 decoy receptor levels compared with sham-inoculated controls. Infection of WT but not Il13(-/-) mice induced persistent AHR. Infection and associated pathology were restored in infected Il13(-/-) mice by reconstitution with IL-13. Stat6(-/-) mice were also largely protected. Neutralization of IL-13 during infection prevented subsequent infection-induced severe AAD. Thus, early-life Chlamydia respiratory infection reduces IL-13Rα2 production, which may enhance the effects of constitutive IL-13 and promote more severe infection, persistent AHR, and AAD.

Effect of neonatal respiratory infection on adult BALB/c hippocampal glucocorticoid and mineralocorticoid receptors.

The current study investigated the effects of neonatal infection with Chlamydia muridarum bacteria on glucocorticoid (GR) and mineralocorticoid (MR) receptors in the adult mouse hippocampus. In male adults infected at birth, circulating corticosterone was significantly increased when compared to same sex controls; while neonatal infection resulted in female adults with significantly increased GR mRNA compared to same sex controls. When comparing males and females after neonatal infection, males had significantly less GR protein than females. Interestingly, after control treatment, males had significantly more GR mRNA, MR mRNA, and GR protein with significantly lower corticosterone than females. Neonatal respiratory infection significantly impacts adult hippocampal GR and MR, and circulating corticosterone in a sex-specific manner potentially altering stress responsivity.

Pulmonary-intestinal cross-talk in mucosal inflammatory disease.

Chronic obstructive pulmonary disease (COPD) and inflammatory bowel diseases (IBDs) are chronic inflammatory diseases of mucosal tissues that affect the respiratory and gastrointestinal tracts, respectively. They share many similarities in epidemiological and clinical characteristics, as well as in inflammatory pathologies. Importantly, both conditions are accompanied by systemic comorbidities that are largely overlooked in both basic and clinical research. Therefore, consideration of these complications may maximize the efficacy of prevention and treatment approaches. Here, we examine both the intestinal involvement in COPD and the pulmonary manifestations of IBD. We also review the evidence for inflammatory organ cross-talk that may drive these associations, and discuss the current frontiers of research into these issues.

Programming of the lung by early-life infection.

Many important human diseases, such as asthma, have their developmental origins in early life. Respiratory infections in particular may alter the course of asthma and may either protect against or promote the development of this disease. It is likely that the nature of the effects depends on the type and age of infection and is determined by the impact of infection on the immune and respiratory systems. Immunity in early life is plastic and can be moulded by antigen encounter, which may enhance or reinforce the asthmatic phenotype of early life, or induce protective responses. Chlamydial respiratory infections have specific effects and may increase asthma severity in early life by promoting systemic interleukin 13 responses and causing permanent changes in lung structure. Respiratory viral infections, such as those of respiratory syncytial virus and rhinovirus, promote pro-asthmatic responses in early life that contribute to the induction of asthma. By contrast, probiotics or infection or exposure to certain bacteria, such as Streptococcus pneumoniae, may have protective effects in asthma by increasing the numbers and activity of regulatory T cells. Here, we review the impact of infections on the developmental origins of asthma. Understanding these effects may lead to new therapeutic approaches for asthma that either target deleterious infections or utilize beneficial ones.

Neonatal respiratory infection and adult re-infection: effect on glucocorticoid and mineralocorticoid receptors in the hippocampus in BALB/c mice.

Stressful events during the perinatal period in both humans and animals have long-term consequences for the development and function of physiological systems and susceptibility to disease in adulthood. One form of stress commonly experienced in the neonatal period is exposure to bacterial and viral infections. The current study investigated the effects of live Chlamydia muridarum bacterial infection at birth followed by re-infection in adulthood on hippocampal glucocorticoid receptors (GR) and mineralocorticoid receptors (MR) and stress response outcomes. Within 24 h of birth, neonatal mice were infected intranasally with C. muridarum (400 inclusion-forming units [ifu]) or vehicle. At 42 days, mice were re-infected (100 ifu) and euthanized 10 days later. In males, infection in adulthood alone had the most impact on the parameters measured with significant increases in GR protein compared to adult infection alone; and significant increases MR protein and circulating corticosterone compared to other treatment groups. Neonatal infection alone induced the largest alterations in the females with results showing reciprocal patterns for GR protein and TH protein. Perinatal infection resulted in a blunted response following adult infection for both males and females across all parameters. The present study demonstrates for the first time that males and females respond differently to infection based on the timing of the initial insult and that there is considerable sex differences in the hippocampal phenotypes that emerge in adulthood after neonatal infection.

Early life infection alters adult BALB/c hippocampal gene expression in a sex specific manner.

During the perinatal period, the developing brain is sensitive to environmental events. Deleterious programing resulting from infection, dietary restriction, or psychological stress has been observed and affects adult immune and endocrine systems as well as behavior. In this study, we determined whether neonatal infection permanently alters immune and glucocorticoid receptor signaling pathways in the adult hippocampus. A Chlamydia muridarum respiratory infection was induced in male and female mice at birth. Mice were allowed to recover and microarray analysis was conducted on RNA from adult hippocampal tissue. In males, neonatal infection induced an up-regulation of genes associated with cellular development, nervous system development and function, such as cyclin-dependent kinase inhibitor 1A. After neonatal infection, adult females exhibited a T-helper 2 immune bias with genes such as major histocompatibility complex, class II, DQ beta 1 up-regulated. Expression of prolactin, vasopressin, hypocretin, corticotrophin-releasing hormone-binding protein, and oxytocin were confirmed by quantitative real-time polymerase chain reaction. This study shows that neonatal infection differentially alters the gene expression profiles of both female and male mice along immune and neuroendocrine pathways.

Streptococcus pneumoniae infection suppresses allergic airways disease by inducing regulatory T-cells.

An inverse association exists between some bacterial infections and the prevalence of asthma. We investigated whether Streptococcus pneumoniae infection protects against asthma using mouse models of ovalbumin (OVA)-induced allergic airway disease (AAD). Mice were intratracheally infected or treated with killed S. pneumoniae before, during or after OVA sensitisation and subsequent challenge. The effects of S. pneumoniae on AAD were assessed. Infection or treatment with killed S. pneumoniae suppressed hallmark features of AAD, including antigen-specific T-helper cell (Th) type 2 cytokine and antibody responses, peripheral and pulmonary eosinophil accumulation, goblet cell hyperplasia, and airway hyperresponsiveness. The effect of infection on the development of specific features of AAD depended on the timing of infection relative to allergic sensitisation and challenge. Infection induced significant increases in regulatory T-cell (Treg) numbers in lymph nodes, which correlated with the degree of suppression of AAD. Tregs reduced T-cell proliferation and Th2 cytokine release. The suppressive effects of infection were reversed by anti-CD25 treatment. Respiratory infection or treatment with S. pneumoniae attenuates allergic immune responses and suppresses AAD. These effects may be mediated by S. pneumoniae-induced Tregs. This identifies the potential for the development of therapeutic agents for asthma from S. pneumoniae.