Neonatal chlamydial pneumonia induces altered respiratory structure and function lasting into adult life

Mechanisms and treatments for severe, steroid-resistant allergic airway disease and asthma

Severe, steroid-resistant asthma is clinically and economically important since affected individuals do not respond to mainstay corticosteroid treatments for asthma. Patients with this disease experience more frequent exacerbations of asthma, are more likely to be hospitalized, and have a poorer quality of life. Effective therapies are urgently required, however, their development has been hampered by a lack of understanding of the pathological processes that underpin disease. A major obstacle to understanding the processes that drive severe, steroid-resistant asthma is that the several endotypes of the disease have been described that are characterized by different inflammatory and immunological phenotypes. This heterogeneity makes pinpointing processes that drive disease difficult in humans. Clinical studies strongly associate specific respiratory infections with severe, steroid-resistant asthma. In this review, we discuss key findings from our studies where we describe the development of representative experimental models to improve our understanding of the links between infection and severe, steroid-resistant forms of this disease. We also discuss their use in elucidating the mechanisms, and their potential for developing effective therapeutic strategies, for severe, steroid-resistant asthma. Finally, we highlight how the immune mechanisms and therapeutic targets we have identified may be applicable to obesity-or pollution-associated asthma.

Programmed Death Ligand 1 Promotes Early-Life Chlamydia Respiratory Infection-Induced Severe Allergic Airway Disease

Chlamydia infections are frequent causes of respiratory illness, particularly pneumonia in infants, and are linked to permanent reductions in lung 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. In the current study, we investigated the role of programmed death (PD)-1 and its ligands PD-L1 and PD-L2 in promoting early-life Chlamydia respiratory infection, and infection-induced airway hyperresponsiveness (AHR) and severe allergic airway disease in later life. Infection increased PD-1 and PD-L1, but not PD-L2, mRNA expression in the lung. Flow cytometric analysis of whole lung homogenates identified monocytes, dendritic cells, CD4(+), and CD8(+) T cells as major sources of PD-1 and PD-L1. Inhibition of PD-1 and PD-L1, but not PD-L2, during infection ablated infection-induced AHR in later life. Given that PD-L1 was the most highly up-regulated and its targeting prevented infection-induced AHR, subsequent analyses focused on this ligand. Inhibition of PD-L1 had no effect on Chlamydia load but suppressed infection-induced pulmonary inflammation. Infection decreased the levels of the IL-13 decoy receptor in the lung, which were restored to baseline levels by inhibition of PD-L1. Finally, inhibition of PD-L1 during infection prevented subsequent infection-induced severe allergic airways disease in later life by decreasing IL-13 levels, Gob-5 expression, mucus production, and AHR. Thus, early-life Chlamydia respiratory infection-induced PD-L1 promotes severe inflammation during infection, permanent reductions in lung function, and the development of more severe allergic airway disease in later life.

Guinea pig genital tract lipidome reveals in vivo and in vitro regulation of phosphatidylcholine 16:0/18:1 and contribution to Chlamydia trachomatis serovar D infectivity

INTRODUCTION

Chlamydia trachomatis (Ct), is the leading cause of sexually transmitted infections worldwide. Host transcriptomic- or proteomic profiling studies have identified key molecules involved in establishment of Ct infection or the generation of anti Ct-immunity. However, the contribution of the host metabolome is not known.

OBJECTIVES

The objective of this study was to determine the contribution of host metabolites in genital Ct infection.

METHODS

We used high-performance liquid chromatography-mass spectrometry, and mapped lipid profiles in genital swabs obtained from female guinea pigs at days 3, 9, 15, 30 and 65 post Ct serovar D intravaginal infection.

RESULTS

Across all time points assessed, 13 distinct lipid species including choline, ethanolamine and glycerol were detected. Amongst these metabolites, phosphatidylcholine (PC) was the predominant phospholipid detected from animals actively shedding bacteria i.e., at 3, 9, and 15 days post infection. However, at days 30 and 65 when the animals had cleared the infection, PC was observed to be decreased compared to previous time points. Mass spectrometry analyses of PC produced in guinea pigs (in vivo) and 104C1 guinea pig cell line (in vitro) revealed distinct PC species following Ct D infection. Amongst these, PC 16:0/18:1 was significantly upregulated following Ct D infection (p < 0.05, >twofold change) in vivo and in vitro infection models investigated in this report. Exogenous addition of PC 16:0/18:1 resulted in significant increase in Ct D in Hela 229 cells.

CONCLUSION

This study demonstrates a role for host metabolite, PC 16:0/18:1 in regulating genital Ct infection in vivo and in vitro.

IgA modulates respiratory dysfunction as a sequela to pulmonary chlamydial infection as neonates

Neonatal Chlamydia lung infections are associated with serious sequelae such as asthma and airway hyper-reactivity in children and adults. Our previous studies demonstrated the importance of Th-1 type cytokines, IL-12 and IFN-γ in protection against neonatal pulmonary chlamydial challenge; however, the role of the humoral arm of defense has not been elucidated. We hypothesized that B-cells and IgA, the major mucosal antibody, play a protective role in newborns against development of later life respiratory sequelae to Chlamydia infection. Our studies using neonatal mice revealed that all WT and IgA-deficient (IgA(-/-)) animals survived a sublethal pulmonary Chlamydia muridarum challenge at one day after birth with similar reduction in bacterial burdens over time. In contrast, all B-cell-deficient (μMT) mice succumbed to infection at the same challenge dose correlating to failure to control bacterial burdens in the lungs. Although IgA may not be important for bacterial clearance, we observed IgA(-/-) mice displayed greater respiratory dysfunction 5 weeks post challenge. Specifically, comparative respiratory functional analyses revealed a significant shift upward in P-V loops, and higher dynamic resistance in IgA(-/-) animals. This study provides insight(s) into the protective role of IgA in neonates against pulmonary chlamydial infection induced respiratory pathological sequelae observed later in life.

Pulmonary immunity during respiratory infections in early life and the development of severe asthma

Asthma affects 10% of the population in Westernized countries, being most common in children. It is a heterogeneous condition characterized by chronic allergic airway inflammation, mucus hypersecretion, and airway hyperresponsiveness (AHR) to normally innocuous antigens. Combination therapies with inhaled corticosteroids and bronchodilators effectively manage mild to moderate asthma, but there are no cures, and patients with severe asthma do not respond to these treatments. The inception of asthma is linked to respiratory viral (respiratory syncytial virus, rhinovirus) and bacterial (Chlamydia, Mycoplasma) infections. The examination of mouse models of early-life infections and allergic airway disease (AAD) provides valuable insights into the mechanisms of disease inception that may lead to the development of more effective therapeutics. For example, early-life, but not adult, Chlamydia respiratory infections in mice permanently modify immunity and lung physiology. This increases the severity of AAD by promoting IL-13 expression, mucus hypersecretion, and AHR. We have identified novel roles for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and IL-13 in promoting infection-induced pathology in early life and subsequent chronic lung disease. Genetic deletion of TRAIL or IL-13 variously protected against neonatal infection-induced inflammation, mucus hypersecretion, altered lung structure, AHR, and impaired lung function. Therapeutic neutralization of these factors prevented infection-induced severe AAD. Other novel mechanisms and avenues for intervention are also being explored. Such studies indicate the immunological mechanisms that may underpin the association between early-life respiratory infections and the development of more severe asthma and may facilitate the development of tailored preventions and treatments.

The need to differentiate between adults and children when treating severe asthma

Severe asthma at all ages is heterogeneous incorporating several phenotypes that are distinct in children and adults, however, there are also numerous similar features including the limitation that they may not remain stable longitudinally. Severe asthma in both children and adults is characterized by eosinophilic airway inflammation and evidence of airway remodeling. In adults, targeting eosinophilia with anti-IL-5 antibody therapy is very successful, resulting in the recommendation that sputum eosinophils should be used to guide treatment. In contrast, data for the efficacy of blocking IL-5 remain unavailable in children. However, its effectiveness is uncertain since many children with severe asthma have normal blood eosinophils and the dominance of Th2-mediated inflammation is controversial. Approaches that have revealed gene signatures and biomarkers such as periostin that are specific to adult disease now need to be adopted in children to identify effective pediatric specific therapeutics and minimize the extrapolation of adult therapeutics to children.

The clinical characteristics and genotype distribution of Chlamydia trachomatis infection in infants less than six months of age hospitalized with pneumonia

BACKGROUND

Chlamydia trachomatis is a common sexually-transmitted bacterial pathogen. As no routine screening is performed during pregnancy, neonates and infants are at high risk for C. trachomatis infection. The objective of this study was to investigate the morbidity, clinical characteristics and genotype distribution of C. trachomatis pneumonia in infants less than six months of age.

METHODS

Clinical manifestations and laboratory results were recorded. Respiratory sputum specimens were tested using RT-PCR targeting C. trachomatis cryptic plasmid. Simultaneously, respiratory virus antigens were detected by direct immunofluorescence and bacterial pathogens were examined by culture in all sputum samples. Positive C. trachomatis samples were further genotyped using a multiplex PCR reverse line blot assay. The relationship between genotype and pneumonia severity was explored.

RESULTS

Of 1408 infants, 101 (7.2%) were infected with C. trachomatis. Sixteen of 101 (15.8%) were assessed as severe pneumonia. These severe cases had a higher proportion of viral co-infection (37.5%) compared to mild pneumonia cases (9.4%, P<0.05).Infants with tachypnea (OR 9.2) and wheezing (OR 3.5) were more likely to be classified as severe pneumonia (P<0.05). Amongst 66 C. trachomatis specimens for which a genotyping result was available, seven genotypes were detected, and 39.4% of these specimens contained two or three genotypes. Overall, genotype E (48.5%) was the most frequent, followed by genotype F (42.4%), J (31.8%), D (12.1%), K (10.6%), G (4.5%) and H (3.0%). There were no significant correlations of particular genotypes with severity of disease, although there was a weak indication that more severe pneumonia might be associated with having certain mixed genotypes of C. trachomatis.

CONCLUSIONS

The prevalence of C. trachomatis in the population of young hospitalized infants with pneumonia in Shenzhen was very high. The relationship between genotype distribution and severity of pneumonia was not clear based on this study due to small sample size. Further in-depth investigation correlating genotype and disease severity based on a larger population is needed.

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 immunology: responses to pathogenic microorganisms and epigenetics reveal an "immunodiverse" developmental state

Neonatal animals have heightened susceptibility to infectious agents and are at increased risk for the development of allergic diseases, such as asthma. Experimental studies using animal models have been quite useful for beginning to identify the cellular and molecular mechanisms underlying these sensitivities. In particular, results from murine neonatal models indicate that developmental regulation of multiple immune cell types contributes to the typically poor responses of neonates to pathogenic microorganisms. Surprisingly, however, animal studies have also revealed that responses at mucosal surfaces in early life may be protective against primary or secondary disease. Our understanding of the molecular events underlying these processes is less well developed. Emerging evidence indicates that the functional properties of neonatal immune cells and the subsequent maturation of the immune system in ontogeny may be regulated by epigenetic phenomena. Here, we review recent findings from our group and others describing cellular responses to infection and developmentally regulated epigenetic processes in the newborn.

Chlamydia muridarum infection associated host MicroRNAs in the murine genital tract and contribution to generation of host immune response

PROBLEM

Chlamydia trachomatis (CT) is the leading sexually transmitted bacterial infection in humans and is associated with reproductive tract damage. However, little is known about the involvement and regulation of microRNAs (miRs) in genital CT.

METHODS

We analyzed miRs in the genital tract (GT) following C. muridarum (murine strain of CT) challenge of wild type (WT) and CD4(+) T-cell deficient (CD4(-/-)) C57BL/6 mice at days 6 and 12 post-challenge.

RESULTS

At day 6, miRs significantly downregulated in the lower GT were miR-125b-5p, -16, -214, -23b, -135a, -182, -183, -30c, and -30e while -146 and -451 were significantly upregulated, profiles not exhibited at day 12 post-bacterial challenge. Significant differences in miR-125b-5p (+5.06-fold change), -135a (+4.9), -183 (+7.9), and -182 (+3.2) were observed in C. muridarum-infected CD4(-/-) compared to WT mice. In silico prediction and mass spectrometry revealed regulation of miR-135a and -182 and associated proteins, that is, heat-shock protein B1 and alpha-2HS-glycoprotein.

CONCLUSION

This study provides evidence on regulation of miRs following genital chlamydial infection suggesting a role in pathogenesis and host immunity.

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.

Evaluation of pulmonary dysfunctions and acid-base imbalances induced by Chlamydia psittaci in a bovine model of respiratory infection

Background

Chlamydia psittaci (Cp) is a respiratory pathogen capable of inducing acute pulmonary zoonotic disease (psittacosis) or persistent infection. To elucidate the pathogenesis of this infection, a translational large animal model was recently introduced by our group. This study aims at quantifying and differentiating pulmonary dysfunction and acid–base imbalances induced by Cp.

Methods

Forty-two calves were grouped in (i) animals inoculated with Cp (n = 21) and (ii) controls sham-inoculated with uninfected cell culture (n = 21). For pulmonary function testing, impulse oscillometry, capnography, and FRC (functional residual capacity) measurement were applied to spontaneously breathing animals. Variables of acid–base status were assessed in venous blood using both (i) traditional Henderson-Hasselbalch and (ii) strong ion approach.

Results

Both obstructive and restrictive pulmonary disorders were induced in calves experimentally inoculated with Cp. Although disorders in respiratory mechanics lasted for 8–11 days, the pattern of spontaneous breathing was mainly altered in the period of acute illness (until 4 days post inoculation, dpi). Expiration was more impaired than inspiration, resulting in elevated FRC. Ventilation was characterised by a reduction in tidal volume (−25%) combined with an increased percentage of dead space volume and a significant reduction of alveolar volume by 10%. Minute ventilation increased significantly (+50%) due to a compensatory doubling of respiratory rate. Hyperventilatory hypocapnia at 2–3 dpi resulted in slightly increased blood pH at 2 dpi. However, the acid–base equilibrium was additionally influenced by metabolic components, i.e. the systemic inflammatory response, all of which were detected with help of the strong ion theory. Decreased concentrations of albumin (2–10 dpi), a negative acute-phase marker, resulted in a decrease in the sum of non-volatile weak acids (A_tot), revealing an alkalotic effect. This was counterbalanced by acidic effects of decreased strong ion difference (SID), mediated by the interplay between hypochloraemia (alkalotic effect) and hyponatraemia (acidic effect).

Conclusions

This bovine model was found to be suitable for studying pathophysiology of respiratory Cp infection and may help elucidating functional host-pathogen interactions in the mammalian lung.

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.

Murine models of infectious exacerbations of airway inflammation

Airway inflammation underpins the pathogenesis of the major human chronic respiratory diseases. It is now well recognized that respiratory infections with bacteria and viruses are important in the induction, progression and exacerbation of these diseases. There are no effective therapies that prevent or reverse these events. The development and use of mouse models are proving valuable in understanding the role of infection in disease pathogenesis. They have recently been used to show that infections in early life alter immune responses and lung structure to increase asthma severity, and alter immune responses in later life to induce steroid resistance. Infection following smoke exposure or in experimental chronic obstructive pulmonary disease exacerbates inflammation and remodeling, and worsens cystic fibrosis. Further exploration of these models will facilitate the identification of new therapeutic approaches and the testing of new preventions and treatments.

Vaginal chlamydial clearance following primary or secondary infection in mice occurs independently of TNF-α

The role of TNF-α in chlamydial clearance is uncertain. Antibody-mediated depletion of TNF-α in mice and guinea pigs has been shown not to significantly affect chlamydial clearance, whereas production of TNF-α in addition to IFN-γ from T cells has been shown to correlate with enhanced clearance. The aim of our study is to evaluate the mechanistic role of TNF-α in clearance of primary and secondary chlamydial infection from the genital tract (GT) using C57BL/6 TNF-α deficient (TNF-α^−/−) and wild type (WT) mice. Chlamydial shedding from the lower GT was evaluated following primary and secondary intravaginal challenge. Also, antibody and antigen specific cytokine responses were analyzed from the infected GT and spleens, and oviduct pathology determined to analyze the role of TNF-α in upper GT pathological sequelae. MHC II^−/− mice, known to display muted adaptive immune responses and failure to resolve genital chlamydial infections, were used as a negative control. Following both primary and secondary genital chlamydial infection, TNF-α^−/− mice exhibited elevated granzyme B production, but similar IFN-γ and antibody responses. Importantly, absence of TNF-α did not significantly alter the resolution of infection. However, TNF-α^−/− mice displayed significantly reduced upper genital tract (UGT) pathology compared to WT mice. This study demonstrates mechanistically that optimal chlamydial clearance following primary and secondary chlamydial genital infection can occur in the complete absence of TNF-α, and considered with the reduction of upper GT pathology in TNF-α^−/− mice, suggests that targeted induction of anti-chlamydial TNF-α responses by vaccination may be unnecessary, and moreover could be potentially pathogenic.

Chlamydia muridarum lung infection in infants alters hematopoietic cells to promote allergic airway disease in mice

BACKGROUND

Viral and bacterial respiratory tract infections in early-life are linked to the development of allergic airway inflammation and asthma. However, the mechanisms involved are not well understood. We have previously shown that neonatal and infant, but not adult, chlamydial lung infections in mice permanently alter inflammatory phenotype and physiology to increase the severity of allergic airway disease by increasing lung interleukin (IL)-13 expression, mucus hyper-secretion and airway hyper-responsiveness. This occurred through different mechanisms with infection at different ages. Neonatal infection suppressed inflammatory responses but enhanced systemic dendritic cell:T-cell IL-13 release and induced permanent alterations in lung structure (i.e., increased the size of alveoli). Infant infection enhanced inflammatory responses but had no effect on lung structure. Here we investigated the role of hematopoietic cells in these processes using bone marrow chimera studies.

METHODOLOGY/PRINCIPAL FINDINGS

Neonatal (<24-hours-old), infant (3-weeks-old) and adult (6-weeks-old) mice were infected with C. muridarum. Nine weeks after infection bone marrow was collected and transferred into recipient age-matched irradiated naïve mice. Allergic airway disease was induced (8 weeks after adoptive transfer) by sensitization and challenge with ovalbumin. Reconstitution of irradiated naïve mice with bone marrow from mice infected as neonates resulted in the suppression of the hallmark features of allergic airway disease including mucus hyper-secretion and airway hyper-responsiveness, which was associated with decreased IL-13 levels in the lung. In stark contrast, reconstitution with bone marrow from mice infected as infants increased the severity of allergic airway disease by increasing T helper type-2 cell cytokine release (IL-5 and IL-13), mucus hyper-secretion, airway hyper-responsiveness and IL-13 levels in the lung. Reconstitution with bone marrow from infected adult mice had no effects.

CONCLUSIONS

These results suggest that an infant chlamydial lung infection results in long lasting alterations in hematopoietic cells that increases the severity of allergic airway disease in later-life.

TLR2, but not TLR4, is required for effective host defence against Chlamydia respiratory tract infection in early life

Chlamydia pneumoniae commonly causes respiratory tract infections in children, and epidemiological investigations strongly link infection to the pathogenesis of asthma. The immune system in early life is immature and may not respond appropriately to pathogens. Toll-like receptor (TLR)2 and 4 are regarded as the primary pattern recognition receptors that sense bacteria, however their contribution to innate and adaptive immunity in early life remains poorly defined. We investigated the role of TLR2 and 4 in the induction of immune responses to Chlamydia muridarum respiratory infection, in neonatal wild-type (Wt) or TLR2-deficient (^−/−), 4^−/− or 2/4^−/− BALB/c mice. Wt mice had moderate disease and infection. TLR2^−/− mice had more severe disease and more intense and prolonged infection compared to other groups. TLR4^−/− mice were asymptomatic. TLR2/4^−/− mice had severe early disease and persistent infection, which resolved thereafter consistent with the absence of symptoms in TLR4^−/− mice. Wt mice mounted robust innate and adaptive responses with an influx of natural killer (NK) cells, neutrophils, myeloid (mDCs) and plasmacytoid (pDCs) dendritic cells, and activated CD4⁺ and CD8⁺ T-cells into the lungs. Wt mice also had effective production of interferon (IFN)γ in the lymph nodes and lung, and proliferation of lymph node T-cells. TLR2^−/− mice had more intense and persistent innate (particularly neutrophil) and adaptive cell responses and IL-17 expression in the lung, however IFNγ responses and T-cell proliferation were reduced. TLR2/4^−/− mice had reduced innate and adaptive responses. Most importantly, neutrophil phagocytosis was impaired in the absence of TLR2. Thus, TLR2 expression, particularly on neutrophils, is required for effective control of Chlamydia respiratory infection in early life. Loss of control of infection leads to enhanced but ineffective TLR4-mediated inflammatory responses that prolong disease symptoms. This indicates that TLR2 agonists may be beneficial in the treatment of early life Chlamydia infections and associated diseases.