Chlamydia trachomatis Cellular Exit Alters Interactions with Host Dendritic Cells.

The strategies utilized by pathogens to exit host cells are an area of pathogenesis which has received surprisingly little attention, considering the necessity of this step for infections to propagate. Even less is known about how exit through these pathways affects downstream host-pathogen interactions and the generation of an immune response. Chlamydia trachomatis exits host epithelial cells through two equally active mechanisms: lysis and extrusion. Studies have characterized the outcome of interactions between host innate immune cells, such as dendritic cells and macrophages, and free, extracellular Chlamydia bacteria, such as those resulting from lysis. Exit via extrusion generates a distinct, host-membrane-bound compartment of Chlamydia separate from the original infected cell. In this study, we assessed the effect of containment within extrusions upon the interaction between Chlamydia and host dendritic cells. Extrusion dramatically affected the outcome of Chlamydia-dendritic cell interactions for both the bacterium and the host cell. Dendritic cells rapidly underwent apoptosis in response to engulfment of an extrusion, while uptake of an equivalent dose of free Chlamydia had no such effect. Containment within an extrusion also prolonged bacterial survival within dendritic cells and altered the initial innate immune signaling by the dendritic cell.

Lack of broad functional differences in immunity in fully vaccinated vs. unvaccinated children.

BACKGROUND: Concerns have been raised that with an increase in the number of vaccines administered early in life, immune development could be altered, leading to either increased or decreased immune reactivity. METHODS: We investigated the impact of vaccination on immune status, contrasting the immune response to general, nonantigen-specific stimuli in a cohort of entirely unvaccinated vs. fully vaccinated children at 3-5 y of age. Innate immunity was assessed by quantifying bulk and cell-type-specific cytokine production in response to stimulation with pathogen associated microbial patterns. Adaptive immune status was characterized by assessing lymphocyte proliferation and cytokine production in response to generic T cell stimuli. RESULTS: Our investigations failed to reveal a broadly evident alteration of either innate or adaptive immunity in vaccinated children. Equivalently robust innate and adaptive responses to pathogen associated microbial patterns and generic T cell stimulants were observed in both groups. CONCLUSION: Although our sample size was small, our data suggest that standard childhood vaccinations do not lead to long-lasting gross alterations of the immune system.

Age-dependent differences in systemic and cell-autonomous immunity to L. monocytogenes.

Host defense against infection can broadly be categorized into systemic immunity and cell-autonomous immunity. Systemic immunity is crucial for all multicellular organisms, increasing in importance with increasing cellular complexity of the host. The systemic immune response to Listeria monocytogenes has been studied extensively in murine models; however, the clinical applicability of these findings to the human newborn remains incompletely understood. Furthermore, the ability to control infection at the level of an individual cell, known as "cell-autonomous immunity," appears most relevant following infection with L. monocytogenes; as the main target, the monocyte is centrally important to innate as well as adaptive systemic immunity to listeriosis. We thus suggest that the overall increased risk to suffer and die from L. monocytogenes infection in the newborn period is a direct consequence of age-dependent differences in cell-autonomous immunity of the monocyte to L. monocytogenes. We here review what is known about age-dependent differences in systemic innate and adaptive as well as cell-autonomous immunity to infection with Listeria monocytogenes.

Hypoxia: a window into Mycobacterium tuberculosis latency.

Tuberculosis is a massive public health problem on a global scale and the success of Mycobacterium tuberculosis is linked to its ability to persist within humans for long periods without causing any overt disease symptoms. Hypoxia is predicted to be a key host-induced stress limiting growth of the pathogen in vivo. However, multiple studies in vitro and in vivo indicate that M. tuberculosis adapts to oxygen limitation by entering into a metabolically altered state, while awaiting the opportunity to reactivate. Molecular signatures of bacteria adapted to hypoxia in vitro are accumulating, although correlations to human disease are only now being established. Similarly, defining the mechanisms that control this adaptation is an active area of research. In this review we discuss the historical precedents linking hypoxia and latency, and the gathering knowledge of M. tuberculosis hypoxic responses. We also examine the role of these responses in tuberculosis latency, and identify promising avenues for future studies.

Rosiglitazone inhibits acyl-CoA synthetase activity and fatty acid partitioning to diacylglycerol and triacylglycerol via a peroxisome proliferator-activated receptor-gamma-independent mechanism in human arterial smooth muscle cells and macrophages.

Rosiglitazone is an insulin-sensitizing agent that has recently been shown to exert beneficial effects on atherosclerosis. In addition to peroxisome proliferator-activated receptor (PPAR)-gamma, rosiglitazone can affect other targets, such as directly inhibiting recombinant long-chain acyl-CoA synthetase (ACSL)-4 activity. Because it is unknown if ACSL4 is expressed in vascular cells involved in atherosclerosis, we investigated the ability of rosiglitazone to inhibit ACSL activity and fatty acid partitioning in human and murine arterial smooth muscle cells (SMCs) and macrophages. Human and murine SMCs and human macrophages expressed Acsl4, and rosiglitazone inhibited Acsl activity in these cells. Furthermore, rosiglitazone acutely inhibited partitioning of fatty acids into phospholipids in human SMCs and inhibited fatty acid partitioning into diacylglycerol and triacylglycerol in human SMCs and macrophages through a PPAR-gamma-independent mechanism. Conversely, murine macrophages did not express ACSL4, and rosiglitazone did not inhibit ACSL activity in these cells, nor did it affect acute fatty acid partitioning into cellular lipids. Thus, rosiglitazone inhibits ACSL activity and fatty acid partitioning in human and murine SMCs and in human macrophages through a PPAR-gamma-independent mechanism likely to be mediated by ACSL4 inhibition. Therefore, rosiglitazone might alter the biological effects of fatty acids in these cells and in atherosclerosis.

Listeria monocytogenes: a promising vehicle for neonatal vaccination.

Vaccination as a medical intervention has proven capable of greatly reducing the suffering from childhood infectious disease. However, newborns and infants in particular are age groups for whom adequate vaccine-mediated protection is still largely lacking. With the challenges that the neonatal immune system faces and the required highest level of stringency for safety, designing vaccines for early life in general and the newborn in particular poses great difficulty. Nevertheless, recent advances in our understanding of neonatal immunity and its responses to vaccines and adjuvants suggest that neonatal vaccination is a task fully within reach. Among the most promising developments in neonatal vaccination is the use of Listeria monocytogenes (Lm) as a delivery platform. In this review, we will outline key properties of Lm that make it such an ideal neonatal and early life vaccine vehicle, and also discuss potential constraints of Lm as a vaccine delivery platform.

Perinatal Immunization With Vaccine-Grade Listeria monocytogenes Provides Protection Against Murine Th2 Airway Inflammation.

PURPOSE: Asthma is a chronic respiratory disorder that leads to inflammation and narrowing of the airways. Its global prevalence has attained epidemic levels and treatment options that reach beyond temporary relief of symptoms are urgently needed. Since the processes leading to clinically symptomatic asthma start early in life, we set out to systematically evaluate a neonatal immunotherapeutic based on Listeria monocytogenes (Lm) for the control of allergic sensitization. METHODS: We modified Lm to express the model allergen, ovalbumin (OVA), and tested the ability of neonatal immunization with this strain to control allergic sensitization in a mouse model of OVA-induced asthma. Mice were immunized as newborns with live or heat killed LmOVA or live Lm, followed 6 weeks later by allergic sensitization with OVA. In order to determine whether the TH1-polarizing effect of this vaccine vector inadvertently may exacerbate development of certain TH1-driven allergic diseases, mice immunized as newborns were assessed in a model of adult hypersensitivity pneumonitis (HP). RESULTS: Both LmOVA and Lm-control vaccines were highly effective in providing long-lasting protection from airway inflammation after only one immunization given perinatally. Serum antibody levels and lung cytokine production suggest that this prophylactic strategy is associated with an allergen specific TH1-dominated response. Specifically, LmOVA vaccinated mice displayed significantly elevated OVA-specific serum IgG2a, but no difference in anti-OVA IgE antibodies and only slightly decreased anti-OVA IgG1 antibodies. Importantly, Lm-based neonatal vaccination did not exacerbate Th1/Th17 driven HP, arguing against broad spectrum immune skewing. CONCLUSIONS: Our findings highlight the promise of early life Lm-based immunomodulatory interventions as a prophylactic strategy for allergic asthma.

Characterization of a Clp protease gene regulator and the reaeration response in Mycobacterium tuberculosis.

Mycobacterium tuberculosis (MTB) enters a non-replicating state when exposed to low oxygen tension, a condition the bacillus encounters in granulomas during infection. Determining how mycobacteria enter and maintain this state is a major focus of research. However, from a public health standpoint the importance of latent TB is its ability to reactivate. The mechanism by which mycobacteria return to a replicating state upon re-exposure to favorable conditions is not understood. In this study, we utilized reaeration from a defined hypoxia model to characterize the adaptive response of MTB following a return to favorable growth conditions. Global transcriptional analysis identified the approximately 100 gene Reaeration Response, induced relative to both log-phase and hypoxic MTB. This response includes chaperones and proteases, as well as the transcription factor Rv2745c, which we characterize as a Clp protease gene regulator (ClgR) orthologue. During reaeration, genes repressed during hypoxia are also upregulated in a wave of transcription that includes genes crucial to transcription, translation and oxidative phosphorylation and culminates in bacterial replication. In sum, this study defines a new transcriptional response of MTB with potential relevance to disease, and implicates ClgR as a regulator involved in resumption of replication following hypoxia.