Infection and apoptosis as a combined inflammatory trigger

The roles of vitamin C in infectious diseases: A comprehensive review

Vitamin C is a versatile nutrient with essential antioxidant properties and roles in amino acid metabolism, collagen promotion, and hormone synthesis. It has long been regarded as benefitting infectious disease management, although its specific roles remain uncertain. The dominant view is that this efficacy not only stems from its redox regulation in the body but also from its profound impact on the immune system. This review provides a comprehensive overview of Vitamin C's effects on redox regulation and shows how the vitamin influences various immune cells and cell-intrinsic innate immunity signaling pathways, thereby updating and expanding our previous perspectives. Clinically, though some studies and case series have suggested potential benefits of Vitamin C in preventing and (or) treating respiratory tract infections and sepsis and septic shock, the evidence remains controversial. The current data is insufficient to support the routine clinical use of Vitamin C in managing these diseases and requires further rigorous evaluation to establish definitive efficacy and safety profiles. This review thoroughly examines current clinical research progress on Vitamin C, summarizes the primary controversies and their underlying causes, and proposes directions for future clinical research. Furthermore, preclinical evidence shows potential roles for Vitamin C in the supplementary treatment of the "Big Three" infectious diseases: acquired immunodeficiency syndrome (AIDS), tuberculosis, and malaria; however, systematic clinical studies in these areas are lacking. We examine related in vitro and animal studies, as well as clinical trials, and discuss potential roles for Vitamin C as a treatment and (or) adjuvant therapy.

Different bacterial cargo in apoptotic cells drive distinct macrophage phenotypes

The removal of dead cells (efferocytosis) contributes to the resolution of the infection and preservation of the tissue. Depending on the environment milieu, macrophages may show inflammatory (M1) or anti-inflammatory (M2) phenotypes. Inflammatory leukocytes are recruited during infection, followed by the accumulation of infected and non-infected apoptotic cells (AC). Efferocytosis of non-infected AC promotes TGF-β, IL-10, and PGE2 production and the polarization of anti-inflammatory macrophages. These M2 macrophages acquire an efficient ability to remove apoptotic cells that are involved in tissue repair and resolution of inflammation. On the other hand, the impact of efferocytosis of infected apoptotic cells on macrophage activation profile remains unknown. Here, we are showing that the efferocytosis of gram-positive Streptococcus pneumoniae-AC (Sp-AC) or gram-negative Klebsiella pneumoniae-AC (Kp-AC) promotes distinct gene expression and cytokine signature in macrophages. Whereas the efferocytosis of Kp-AC triggered a predominant M1 phenotype in vitro and in vivo, the efferocytosis of Sp-AC promoted a mixed M1/M2 activation in vitro and in vivo in a model of allergic asthma. Together, these findings suggest that the nature of the pathogen and antigen load into AC may have different impacts on inducing macrophage polarization.

Inflammatory and pathological changes in Escherichia coli infected mice

Purpose

Understanding the inflammation and histopathological changes in vivo caused by Escherichia coli infection is of great significance for scientific research and clinical diagnosis.

Methods

Mice were randomly divided into 6 groups (N = 10) after adaptive feeding, and it challenged by intraperitoneal injection with different concentrations of E. coli ATCC25922. The survival situation within 7 days was recorded, and the half-lethal dose (LD₅₀) was calculated by Karber's method. After the end, the blood, heart, liver, spleen, lung, and kidney of the mice were collected. We detected the concentration of inflammatory cytokines (IL-6, IL-β, and TNF-α) and inducible nitric oxide synthase (iNOS) in serum by ELSIA. Organs were observed by histopathological staining and electron microscope observation.

Results

The LD₅₀ of mice infected with E. coli was 1.371∗10⁶ CFU/kg. The concentrations of IL-6, IL-β, and TNF-α increased with time after infection in mice, reaching the highest concentration on the 7th day. iNOS was significantly increased on the 1st day of infection, and then decreased over time (P < 0.01). Within a week after infection, the colony counts of the heart, liver, spleen, lung and kidney showed a first decrease, and then reached a surge on the 7th day. Pathological results showed that a small amount of mitochondrial swelling and autophagy were seen in the spleen, lung and kidney tissues of the infected group; and a small amount of secondary lysosomes and autophagy were also seen; but no pathological changes were found in the liver and heart.

Conclusion

Escherichia coli can cause inflammation and oxidative stress in mice, causing different degrees of damage to the spleen, lung, and kidney tissues, which provides theoretical support for inflammatory and pathological changes caused by Escherichia coli infection in vivo.

The TLR-NF-kB axis contributes to the monocytic inflammatory response against a virulent strain of Lichtheimia corymbifera, a causative agent of invasive mucormycosis

Invasive mucormycosis (IM) is a life-threatening infection caused by the fungal order Mucorales, its diagnosis is often delayed, and mortality rates range from 40-80% due to its rapid progression. Individuals suffering from hematological malignancies, diabetes mellitus, organ transplantations, and most recently COVID-19 are particularly susceptible to infection by Mucorales. Given the increase in the occurrence of these diseases, mucormycosis has emerged as one of the most common fungal infections in the last years. However, little is known about the host immune response to Mucorales. Therefore, we characterized the interaction among L. corymbifera—one of the most common causative agents of IM—and human monocytes, which are specialized phagocytes that play an instrumental role in the modulation of the inflammatory response against several pathogenic fungi. This study covered four relevant aspects of the host-pathogen interaction: i) The recognition of L. corymbifera by human monocytes. ii) The intracellular fate of L. corymbifera. iii) The inflammatory response by human monocytes against the most common causative agents of mucormycosis. iv) The main activated Pattern-Recognition Receptors (PRRs) inflammatory signaling cascades in response to L. corymbifera. Here, we demonstrate that L. corymbifera exhibits resistance to intracellular killing over 24 hours, does not germinate, and inflicts minimal damage to the host cell. Nonetheless, viable fungal spores of L. corymbifera induced early production of the pro-inflammatory cytokine IL-1β, and late release of TNF-α and IL-6 by human monocytes. Moreover, we revealed that IL-1β production predominantly depends on Toll-like receptors (TLRs) priming, especially via TLR4, while TNF-α is secreted via C-type lectin receptors (CTLs), and IL-6 is produced by synergistic activation of TLRs and CTLs. All these signaling pathways lead to the activation of NF-kB, a transcription factor that not only regulates the inflammatory response but also the apoptotic fate of monocytes during infection with L. corymbifera. Collectively, our findings provide new insights into the host-pathogen interactions, which may serve for future therapies to enhance the host inflammatory response to L. corymbifera.

Evaluation of Enterococcus faecalis, Lactobacillus acidophilus, and Lactobacillus plantarum in Biopsy Samples of Colorectal Cancer and Polyp Patients Compared to Healthy People

Background: Colorectal cancer (CRC) is one of the leading causes of death in both men and women worldwide. According to different studies, infectious agents or microbiota dysbiosis can play a role in CRC progression. Objective: This study aimed to evaluate the prevalence of Enterococcus faecalis, Lactobacillus acidophilus, and Lactobacillus plantarum in people with polyps or CRC compared to healthy individuals. Methods: In this study, 60 biopsy samples were collected from three groups, including patients with CRC, polyps, and healthy people. The genomic DNA was extracted from the collected samples and amplified by polymerase chain reaction (PCR) to detect E. faecalis, L. acidophilus, and L. plantarum. In the next step, quantitative Real-Time PCR was used to evaluate the copy number of the bacteria in the studied groups. Results: There was no statistically significant difference between the studied groups regarding age and gender (P > 0.05). The mean number of E. faecalis was higher in patients with CRC than in patients with polyps and healthy individuals (P < 0.05). Also, the mean numbers of L. acidophilus and L. plantarum were higher in healthy individuals than in patients with polyps and CRC (P < 0.05). Conclusions: Our findings indicate that L. acidophilus and L. plantarum in people with a family history of CRC and patients with polyps may effectively prevent or reduce CRC progression.

Adipose-derived stem cells decolonize skin Staphylococcus aureus by enhancing phagocytic activity of peripheral blood mononuclear cells in the atopic rats

Staphylococcus aureus (S. aureus) is known to induce apoptosis of host immune cells and impair phagocytic clearance, thereby being pivotal in the pathogenesis of atopic dermatitis (AD). Adipose-derived stem cells (ASCs) exert therapeutic effects against inflammatory and immune diseases. In the present study, we investigated whether systemic administration of ASCs restores the phagocytic activity of peripheral blood mononuclear cells (PBMCs) and decolonizes cutaneous S. aureus under AD conditions. AD was induced by injecting capsaicin into neonatal rat pups. ASCs were extracted from the subcutaneous adipose tissues of naïve rats and administered to AD rats once a week for a month. Systemic administration of ASCs ameliorated AD-like symptoms, such as dermatitis scores, serum IgE, IFN-γ⁺/IL-4⁺ cell ratio, and skin colonization by S. aureus in AD rats. Increased FasL mRNA and annexin V⁺/7-AAD⁺ cells in the PBMCs obtained from AD rats were drastically reversed when co-cultured with ASCs. In contrast, both PBMCs and CD163⁺ cells bearing fluorescent zymosan particles significantly increased in AD rats treated with ASCs. Additionally, the administration of ASCs led to an increase in the mRNA levels of antimicrobial peptides, such as cathelicidin and β-defensin, in the skin of AD rats. Our results demonstrate that systemic administration of ASCs led to decolonization of S. aureus by attenuating apoptosis of immune cells in addition to restoring phagocytic activity. This contributes to the improvement of skin conditions in AD rats. Therefore, administration of ASCs may be helpful in the treatment of patients with intractable AD.

Fabrication and functionalization of biocompatible carboxymethyl chitosan/gelatin membranes via anodic electrophoretic deposition

A biocompatible CMC/G membrane for titanium substrates has been fabricated in an eco-friendly manner and could be a promising carrier for negatively charged agents.

Overexpression of Apolipoprotein C1 (APOC1) in Clear Cell Renal Cell Carcinoma and Its Prognostic Significance

Background

The aims of this study included 3 aspects: 1) assessing the expression of Apolipoprotein C1 (APOC1) in clear cell renal cell carcinoma (ccRCC) and normal groups; 2) evaluating the prognostic significance of APOC1 expression in the overall survival (OS) of ccRCC patients; and 3) exploring APOC1-related signaling pathways.

Material/Methods

The APOC1 expression value and clinical data of ccRCC patients were obtained from the cBioPortal database. We then evaluated the association of APOC1 expression with clinical characteristics of ccRCC patients. We also assessed the correlation between APOC1 expression and clinical outcome using Kaplan-Meier method. Our work then verified the independent prognostic factors of ccRCC by Cox regression analysis. Finally, the potential role of genes co-expressed with APOC1 was revealed via functional enrichment analysis.

Results

Bioinformatic data revealed that APOC1 was expressed at higher levels in ccRCC tissue than in the normal group (all P<0.05). The high expression of APOC1 was associated with unfavorable prognosis of female patients (P<0.01), but not of male patients. APOC1 high expression also shortened the survival time of ccRCC patients age ≥60 years old (P<0.05). Cox regression analysis further indicated that APOC1 expression was an independent prognostic factor for OS of ccRCC patients. Additionally, we found that APOC1 expression was significantly associated with sex, grade, clinical stage, and T stage. Finally, enrichment analysis suggested that APOC1-associated pathways were involved in tumor growth and metastasis.

Conclusions

The current study indicated that APOC1 was highly expressed in ccRCC and was significantly associated with key clinical features. APOC1 appears to be an independent prognostic factor in patients with ccRCC. Importantly, APOC1 might be a potential therapeutic target for ccRCC via regulating pathways involved in cell growth and metastasis.

The Coming Decade of Cell Death Research: Five Riddles

Active cell death, in its many forms, is a fundamental biological process. Studies over the past several decades have explored the functions and consequences of cellular demise and elucidated several of the key cell death pathways. Here, I pose five questions, or riddles, that might provide a guide to the next decade of cell death research. Focusing mainly on four types of active cell death (apoptosis, necroptosis, pyroptosis, and ferroptosis) mainly in mammals, this Perspective explores the possible research directions that might answer these riddles, or at least prompt new ones.

Nerolidol inhibits the LOX-1 / IL-1β signaling to protect against the Aspergillus fumigatus keratitis inflammation damage to the cornea

PURPOSE

Nerolidol, a naturally occurring sesquiterpene has both anti-microbial and anti-inflammatory properties. The current study aims to investigate the antifungal and the anti-inflammatory effects of nerolidol against mouse Aspergillus fumigatus (A. fumigatus) keratitis.

METHODS

The minimum inhibitory concentration (MIC) and cytotoxicity tests were used to study the antifungal ability. For in vivo and in vitro studies, the mouse corneas and the human corneal epithelial cells (HCECs) infected with A. fumigatus spores were intervented with nerolidol or phosphate buffer saline (PBS). Thereafter, the effect of the nerolidol on the response against inflammation was analyzed using the following parameters: recruitment of the neutrophils or macrophages and the expression of the lectin-type oxidized low density lipoprotein receptor-1 (LOX-1) and interleukin 1β (IL-1β). Techniques used were the slit lamp, immunofluorescence, myeloperoxidase (MPO) detection, quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot.

RESULTS

Nerolidol directly inhibits the growth of A. fumigatus. The administration of nerolidol reduced the severity of fungal keratitis with infiltration of fewer inflammatory cells and reduced levels of the LOX-1, as well the anti-inflammatory cytokines such as IL-1β were reduced compared with the PBS group. Additionally, in vitro studies showed that treatment with nerolidol inhibited the production of the LOX-1 / IL-1β levels in A. fumigatus stimulated HCECs.

CONCLUSION

Nerolidol attenuated the A. fumigatus keratitis inflammatory response by inhibiting the growth of A. fumigatus, reducing the recruitment of the neutrophils and the macrophages, and inhibiting the LOX-1/ IL-1β signaling.

EV71 infection induces cell apoptosis through ROS generation and SIRT1 activation

Several studies have substantiated the correlation between reactive oxygen species (ROS) and Sirtuin 1 (SIRT1). Normally, enterovirus 71 (EV71) is associated with severe clinical manifestations and death. However, the effect of EV71 on the induction of cellular death and the interplay between ROS/SIRT1 in cell death has not been confirmed yet. In the current study, an increase in the number of apoptotic cells was observed as soon as the EV71 infection was initiated in cells and mice. Furthermore, EV71 infection also promoted a rise in the levels of three commonly known proinflammatory cytokines, interleukin 1β (IL-1β), IL-6, and tumor necrosis factor-α. During EV71-induced apoptosis in the different cell lines, ROS generation and SIRT1 downregulation were observed. Further investigations showed that the administration of ROS inhibitor, N-acetyl- l-cysteine (NAC), reduced the level of apoptosis and inflammation, reduced EV71 propagation, and increased SIRT1 expression in EV71-infected cells. In addition, combined administration of NAC and EX527 (SIRT1 inhibitor) restored apoptosis in the EV71-infected cells, which was reduced due to NAC. This data demonstrated that ROS generation is positively associated with EV71-induced apoptosis and inflammation, while this effect could be reversed by SIRT1 inhibition. Collectively, we have shown that EV71 induces apoptosis and inflammation by promoting ROS generation and reducing SIRT1 expression.

Osteopontin contributes to effective neutrophil recruitment, IL-1β production and apoptosis in Aspergillus fumigatus keratitis

Fungal keratitis is a major cause of corneal ulcers, resulting in significant visual impairment and blindness. A phosphorylated glycoprotein secreted by immunocompetent cells, osteopontin (OPN) mediates cluster formation of the host fungal receptors and enhances the phagocytosis and clearance of pathogenic fungi. However, whether OPN production and function occurs in fungal keratitis is unknown. OPN expression in Aspergillus fumigatus keratitis patient corneas was assessed by quantitative polymerase chain reaction (qRT-PCR) and immunofluorescence. Human neutrophils, THP-1 macrophages and corneal epithelial cells (HCECs) stimulated with A. fumigatus were utilized for in vitro experiments. Mouse models of A. fumigatus keratitis were developed by intrastromal injection for in vivo experiments. Using siRNAs, neutralizing antibodies, recombinant proteins and inhibitors, the production and role of OPN in A. fumigatus infection was assessed by clinical evaluation, qRT-PCR, immunofluorescence, western blotting and bioluminescence image acquisition. We observed increased corneal OPN expression in A. fumigatus keratitis patients and mouse models compared to controls. OPN production in response to A. fumigatus infection was dependent on LOX-1 and Erk1/2. Compared to controls, OPN knockdown impaired proinflammatory cytokine IL-1β production, which was dependent on 4E-BP1. OPN knockdown decreased myeloperoxidase levels, and resulted in decreased neutrophil recruitment, higher fungal load and increased apoptosis in mouse A. fumigatus keratitis. Our results indicate that OPN is a critical component of the antifungal immune response and is essential for effective neutrophil recruitment, inflammatory cytokine production and apoptosis in A. fumigatus keratitis.

The Multirole of Liposomes in Therapy and Prevention of Infectious Diseases

Liposomes are closed bilayer structures spontaneously formed by hydrated phospholipids that are widely used as efficient delivery systems for drugs or antigens, due to their capability to encapsulate bioactive hydrophilic, amphipathic, and lipophilic molecules into inner water phase or within lipid leaflets. The efficacy of liposomes as drug or antigen carriers has been improved in the last years to ameliorate pharmacokinetics and capacity to release their cargo in selected target organs or cells. Moreover, different formulations and variations in liposome composition have been often proposed to include immunostimulatory molecules, ligands for specific receptors, or stimuli responsive compounds. Intriguingly, independent research has unveiled the capacity of several phospholipids to play critical roles as intracellular messengers in modulating both innate and adaptive immune responses through various mechanisms, including (i) activation of different antimicrobial enzymatic pathways, (ii) driving the fusion–fission events between endosomes with direct consequences to phagosome maturation and/or to antigen presentation pathway, and (iii) modulation of the inflammatory response. These features can be exploited by including selected bioactive phospholipids in the bilayer scaffold of liposomes. This would represent an important step forward since drug or antigen carrying liposomes could be engineered to simultaneously activate different signal transduction pathways and target specific cells or tissues to induce antigen-specific T and/or B cell response. This lipid-based host-directed strategy can provide a focused antimicrobial innate and adaptive immune response against specific pathogens and offer a novel prophylactic or therapeutic option against chronic, recurrent, or drug-resistant infections.

Dectin-1 is essential for IL-1β production through JNK activation and apoptosis in Aspergillus fumigatus keratitis

PURPOSE

To investigate the role of phosphorylated JNK in Dectin-1-induced IL-1β production and the role of Dectin-1 in apoptosis in mouse Aspergillus fumigatus (A. fumigatus) keratitis.

METHODS

Mice corneas were pretreated with Dectin-1 siRNA or SP600125 (the inhibitor of JNK) before A. fumigatus infection. THP-1 macrophages were preincubated with SP600125 before the stimulation of A. fumigatus conidia. Dectin-1, IL-1β, JNK, Bax, Bcl-2, cytochrome-c (cyt-c), caspase-9, caspase-8 and caspase-3 expressions were tested by PCR, Western blot, or Immunofluorescence staining.

RESULTS

Pretreatment with Dectin-1 siRNA significantly decreased A. fumigatus-induced IL-1β production and JNK phosphorylation compared with scrambled control in C57BL/6 mice corneas. SP600125 treatment before infection significantly inhibited IL-1β production compared with DMSO control both in mice corneas and THP-1 macrophages. Furthermore, Dectin-1 deficiency resulted in increased ratio of Bax/Bcl-2, release of cyt-c, activation of caspase-9 and caspase-3 in mouse A. fumigatus keratitis. However, Dectin-1 deficiency didn't affect the activation of caspase-8.

CONCLUSIONS

Being an important inflammatory PRR to mediate host inflammatory response, Dectin-1 induced IL-1β production is JNK dependent in mouse A. fumigatus keratitis, and suppressed apoptosis mediated anti-inflammatory response.

RIPK1-dependent apoptosis bypasses pathogen blockade of innate signaling to promote immune defense

RIPK1 regulates cytokine signaling and cell death during infection and inflammation. Peterson et al. show that RIPK1 kinase activity triggers apoptosis in response to bacterial pathogen blockade of innate immune signaling and that this pathway of effector-triggered immunity is critical for a successful antibacterial response.

Many pathogens deliver virulence factors or effectors into host cells in order to evade host defenses and establish infection. Although such effector proteins disrupt critical cellular signaling pathways, they also trigger specific antipathogen responses, a process termed “effector-triggered immunity.” The Gram-negative bacterial pathogen Yersinia inactivates critical proteins of the NF-κB and MAPK signaling cascade, thereby blocking inflammatory cytokine production but also inducing apoptosis. Yersinia-induced apoptosis requires the kinase activity of receptor-interacting protein kinase 1 (RIPK1), a key regulator of cell death, NF-κB, and MAPK signaling. Through the targeted disruption of RIPK1 kinase activity, which selectively disrupts RIPK1-dependent cell death, we now reveal that Yersinia-induced apoptosis is critical for host survival, containment of bacteria in granulomas, and control of bacterial burdens in vivo. We demonstrate that this apoptotic response provides a cell-extrinsic signal that promotes optimal innate immune cytokine production and antibacterial defense, demonstrating a novel role for RIPK1 kinase–induced apoptosis in mediating effector-triggered immunity to circumvent pathogen inhibition of immune signaling.

CD73 regulates anti-inflammatory signaling between apoptotic cells and endotoxin-conditioned tissue macrophages

The phagocytosis of apoptotic cells (efferocytosis) shifts macrophages to an anti-inflammatory state through a set of still poorly understood soluble and cell-bound signals. Apoptosis is a common feature of inflamed tissues, and efferocytosis by tissue macrophages is thought to promote the resolution of inflammation. However, it is not clear how the exposure of tissue macrophages to inflammatory cues (e.g., PAMPs, DAMPs) in the early stages of inflammation affects immune outcomes of macrophage-apoptotic cell interactions occurring at later stages of inflammation. To address this, we used low-dose endotoxin conditioning (LEC, 1 ng/ml LPS 18 h) of mouse resident peritoneal macrophages (RPMФ) to model the effects of suboptimal (i.e., non-tolerizing), antecedent TLR activation on macrophage inflammatory responses to apoptotic cells. Compared with unconditioned macrophages (MФ), LEC-MФ showed a significant enhancement of apoptotic cell-driven suppression of many inflammatory cytokines (e.g., TNF, MIP-1β, MCP-1). We then found that enzymatic depletion of adenosine or inhibition of the adenosine receptor A2a on LEC-MФ abrogated apoptotic cell suppression of TNF, and this suppression was entirely dependent on the ecto-enzyme CD73 (AMPadenosine) but not CD39 (ATPAMP), both of which are highly expressed on RPMФ. In addition to a requirement for CD73, we also show that Adora2a levels in macrophages are a critical determinant of TNF suppression by apoptotic cells. LEC treatment of RPMФ led to a ~3-fold increase in Adora2a and a ~28-fold increase in adenosine sensitivity. Moreover, in RAW264.7 cells, ectopic expression of both A2a and CD73 was required for TNF suppression by apoptotic cells. In mice, mild, TLR4-dependent inflammation in the lungs and peritoneum caused a rapid increase in macrophage Adora2a and Adora2b levels, and CD73 was required to limit neutrophil influx in this peritonitis model. Thus immune signaling via the CD73-A2a axis in macrophages links early inflammatory events to subsequent immune responses to apoptotic cells.

Efferocytosis of Pathogen-Infected Cells

The prompt and efficient clearance of unwanted and abnormal cells by phagocytes is termed efferocytosis and is crucial for organism development, maintenance of tissue homeostasis, and regulation of the immune system. Dying cells are recognized by phagocytes through pathways initiated via "find me" signals, recognition via "eat me" signals and down-modulation of regulatory "don't eat me" signals. Pathogen infection may trigger cell death that drives phagocytic clearance in an immunologically silent, or pro-inflammatory manner, depending on the mode of cell death. In many cases, efferocytosis is a mechanism for eliminating pathogens and pathogen-infected cells; however, some pathogens have subverted this process and use efferocytic mechanisms to avoid innate immune detection and assist phagocyte infection. In parallel, phagocytes can integrate signals received from infected dying cells to elicit the most appropriate effector response against the infecting pathogen. This review focuses on pathogen-induced cell death signals that drive infected cell recognition and uptake by phagocytes, and the outcomes for the infected target cell, the phagocyte, the pathogen and the host.

Positive Feedback Cycle of TNFα Promotes Staphylococcal Enterotoxin B-Induced THP-1 Cell Apoptosis

Staphylococcal enterotoxin B (SEB) has been demonstrated to be of importance in Staphylococcus aureus related diseases, such as atopic dermatitis (AD). Dysregulated apoptosis in AD is remarkable, and SEB can induce apoptosis of various cell types. However, the mechanisms by which SEB induces apoptosis and influences disease processes remain unclear. In this study, the recombinant SEB-induced THP-1 monocyte apoptosis was demonstrated in the absence of preliminary cell activation in a time- and dose-dependent manner. SEB could up-regulate the expression of tumor necrosis factor alpha (TNFα) in THP-1 cells and induce apoptosis via an extrinsic pathway. TNFα could in turn increase the expression of HLA-DRa, the SEB receptor on the cell surface. As a result, a positive feedback cycle of TNFα was established. TNFα expression and SEB-induced apoptosis were decreased by knocking down the expression of either HLA-DRa or TNFR1. Therefore, the feedback cycle of TNFα is crucial for SEB functions. This work provides insights into the mechanisms of SEB-induced monocyte apoptosis and emphasizes the major role of TNFα in future related studies.

Epstein-Barr Virus BZLF1-Mediated Downregulation of Proinflammatory Factors Is Essential for Optimal Lytic Viral Replication

Elevated secretion of inflammatory factors is associated with latent Epstein-Barr virus (EBV) infection and the pathology of EBV-associated diseases; however, knowledge of the inflammatory response and its biological significance during the lytic EBV cycle remains elusive. Here, we demonstrate that the immediate early transcriptional activator BZLF1 suppresses the proinflammatory factor tumor necrosis factor alpha (TNF-α) by binding to the promoter of TNF-α and preventing NF-κB activation. A BZLF1Δ207-210 mutant with a deletion of 4 amino acids (aa) in the protein-protein binding domain was not able to inhibit the proinflammatory factors TNF-α and gamma interferon (IFN-γ) and reduced viral DNA replication with complete transcriptional activity during EBV lytic gene expression. TNF-α depletion restored the viral replication mediated by BZLF1Δ207-210. Furthermore, a combination of TNF-α- and IFN-γ-neutralizing antibodies recovered BZLF1Δ207-210-mediated viral replication, indicating that BZLF1 attenuates the antiviral response to aid optimal lytic replication primarily through the inhibition of TNF-α and IFN-γ secretion during the lytic cycle. These results suggest that EBV BZLF1 attenuates the proinflammatory responses to facilitate viral replication.

IMPORTANCE

The proinflammatory response is an antiviral and anticancer strategy following the complex inflammatory phenotype. Latent Epstein-Barr virus (EBV) infection strongly correlates with an elevated secretion of inflammatory factors in a variety of severe diseases, while the inflammatory responses during the lytic EBV cycle have not been established. Here, we demonstrate that BZLF1 acts as a transcriptional suppressor of the inflammatory factors TNF-α and IFN-γ and confirm that BZLF1-facilitated escape from the TNF-α and IFN-γ response during the EBV lytic life cycle is required for optimal viral replication. This finding implies that the EBV lytic cycle employs a distinct strategy to evade the antiviral inflammatory response.

Death-defining immune responses after apoptosis

Apoptosis is a programmed form of cell death whereby characteristic internal cellular dismantling is accompanied by the preservation of plasma membrane integrity. Maintaining this order during apoptosis prevents the release of cellular contents and ensures a noninflammatory death. Here, we consider examples of apoptosis in different contexts and discuss how the same form of cell death could have different immunological consequences. Multiple parameters such as cell death as a result of microbial infection, the nature of the inflammatory microenvironment, the type of responding phagocytic cells and the genetic background of the host organism all differentially influence the immunological consequences of apoptosis.

Insights into phagocytosis-coupled activation of pattern recognition receptors and inflammasomes

A decade of work shows that the core function of phagocytosis in engulfment and destruction of microorganisms is only a small facet of the full spectrum of roles for phagocytosis in the immune system. The regulation of phagocytosis and its outcomes by inflammatory pattern recognition receptors (PRRs) is now followed by new studies strengthening this concept and adding further complexity to the relationship between phagocytosis and innate immune signaling. Phagocytosis forms the platform for activation of distinct members of the Toll-like receptor family, and even dictates their signaling outcomes. In many cases, phagocytosis is a necessary precedent to the activation of cytosolic PRRs and assembly of canonical and non-canonical inflammasomes, leading to strong pro-inflammatory responses and inflammatory cell death.

Periodontal disease immunology: 'double indemnity' in protecting the host

During the last two to three decades our understanding of the immunobiology of periodontal disease has increased exponentially, both with respect to the microbial agents triggering the disease process and the molecular mechanisms of the host engagement maintaining homeostasis or leading to collateral tissue damage. These foundational scientific findings have laid the groundwork for translating cell phenotype, receptor engagement, intracellular signaling pathways and effector functions into a 'picture' of the periodontium as the host responds to the 'danger signals' of the microbial ecology to maintain homeostasis or succumb to a disease process. These findings implicate the chronicity of the local response in attempting to manage the microbial challenge, creating a 'Double Indemnity' in some patients that does not 'insure' health for the periodontium. As importantly, in reflecting the title of this volume of Periodontology 2000, this review attempts to inform the community of how the science of periodontal immunology gestated, how continual probing of the biology of the disease has led to an evolution in our knowledge base and how more recent studies in the postgenomic era are revolutionizing our understanding of disease initiation, progression and resolution. Thus, there has been substantial progress in our understanding of the molecular mechanisms of host-bacteria interactions that result in the clinical presentation and outcomes of destructive periodontitis. The science has embarked from observations of variations in responses related to disease expression with a focus for utilization of the responses in diagnosis and therapeutic outcomes, to current investigations using cutting-edge fundamental biological processes to attempt to model the initiation and progression of soft- and hard-tissue destruction of the periodontium. As importantly, the next era in the immunobiology of periodontal disease will need to engage more sophisticated experimental designs for clinical studies to enable robust translation of basic biologic processes that are in action early in the transition from health to disease, those which stimulate microenvironmental changes that select for a more pathogenic microbial ecology and those that represent a rebalancing of the complex host responses and a resolution of inflammatory tissue destruction.

Understanding resolvin signaling pathways to improve oral health

The discovery of resolvins has been a major breakthrough for understanding the processes involved in resolution of inflammation. Resolvins belong to a family of novel lipid mediators that possess dual anti-inflammatory and pro-resolution actions. Specifically, they protect healthy tissue during immune-inflammatory responses to infection or injury, thereby aiding inflammation resolution and promoting tissue healing. One of the major concerns in modern medicine is the management and treatment of oral diseases, as they are related to systemic outcomes impacting the quality of life of many patients. This review summarizes known signaling pathways utilized by resolvins to regulate inflammatory responses associated with the oral cavity.

Revisiting the old link between infection and autoimmune disease with commensals and T helper 17 cells

Genetic composition and major histocompatibility complex polymorphisms unequivocally predispose to autoimmune disease, but environmental factors also play a critical role in precipitating disease in susceptible individuals. Notorious among these has been microbial infection. Older studies describing associations between microbial infection and autoimmune disease are now followed by new studies demonstrating correlations between susceptibility to autoimmune disease and commensal colonization of the intestinal tract. T helper 17 (T(H)17) cells have gained a prominent role in autoimmune disease, and notably, their development within the intestine has been linked to colonization with specific commensal bacteria. Here, we consider current views on how microbes, T(H)17 cells, and autoimmunity are connected. We speculate on how the intricate relationships among commensal, pathogen, and the host might ultimately determine susceptibility to autoimmune disease.

Effects of aging on apoptosis gene expression in oral mucosal tissues

Apoptotic processes are important for physiologic renewal of an intact epithelial barrier and contribute some antimicrobial resistance for bacteria and viruses, as well as anti-inflammatory effects that benefits the mucosa. The oral cavity presents a model of host-bacterial interactions at mucosal surfaces, in which a panoply of microorganisms colonizes various niches in the oral cavity and creates complex multispecies biofilms that challenge the gingival tissues. This report details gene expression in apoptotic pathways that occur in oral mucosal tissues across the lifespan, using a nonhuman primate model. Macaca mulatta primates from 2 to 23 years of age (n = 23) were used in a cross-sectional study to obtain clinical healthy gingival tissues specimens. Further, mRNA was prepared and evaluated using the Affymetrix Rhesus GeneChip and 88 apoptotic pathway genes were evaluated. The results identified significant positive correlations with age in 12 genes and negative correlations with an additional five genes. The gene effects were predicted to alter apoptosis receptor levels, extrinsic apoptotic pathways through caspases, cytokine effects on apoptotic events, Ca(+2)-induced death signaling, cell cycle checkpoints, and potential effects of survival factors. Both the positively and negatively correlated genes within the apoptotic pathways provided evidence that healthy tissues in aging animals exhibit decreased apoptotic potential compared to younger animals. The results suggested that decreased physiologic apoptotic process in the dynamic septic environment of the oral mucosal tissues could increase the risk of aging tissues to undergo destructive disease processes through dysregulated inflammatory responses to the oral microbial burden.

The recombinant tuberculosis vaccine rBCG ΔureC::hly(+) induces apoptotic vesicles for improved priming of CD4(+) and CD8(+) T cells

BACKGROUND

The recombinant BCG ΔureC::hly(+) (rBCG) vaccine candidate is more efficient than parental BCG (pBCG) against tuberculosis (TB) in preclinical models. Evidence exists for superior CD4 and CD8 T cell stimulation. Although the responsible immune mechanisms are incompletely understood, crosspriming of CD8 T cells has been proposed as a major mechanism underlying better protection of rBCG over pBCG. The present study investigates the role of apoptotic vesicles from pBCG- and rBCG-infected macrophages in crosspriming.

METHODS

Apoptotic vesicles were isolated from pBCG- and rBCG-infected mouse macrophages. The priming potential of the isolated vesicles was evaluated in terms of dendritic cell activation and specific T cell stimulation.

RESULTS

Apoptotic vesicles from both pBCG- and rBCG-infected macrophages activated dendritic cells but to a different degree. Overall, rBCG-infected apoptotic vesicles induced more profound CD4 and CD8 T cell responses as compared to pBCG.

CONCLUSIONS

These data support the notion that the improved vaccine efficacy of rBCG rests on enhanced crosspriming as a consequence of stronger apoptosis.

Apoptosis and apoptotic mimicry in Leishmania: an evolutionary perspective

Apoptotic death and apoptotic mimicry are defined respectively as a non-accidental death and as the mimicking of an apoptotic-cell phenotype, usually by phosphatidylserine (PS) exposure. In the case of the murine infection by Leishmania spp, apoptotic death has been described in promastigotes and apoptotic mimicry in amastigotes. In both situations they are important events of the experimental murine infection by this parasite. In the present review we discuss what features we need to consider if we want to establish if a behavior shown by Leishmania is altruistic or not: does the behavior increases the fitness of organisms other than the one showing it? Does this behavior have a cost for the actor? If we manage to show that a given behavior is costly for the actor and beneficial for the recipient of the action, we will be able to establish it as altruistic. From this perspective, we can argue that apoptotic-like death and apoptotic mimicry are both altruistic with the latter representing a weaker altruistic behavior than the former.

Information processing during phagocytosis

Phagocytosis - the process by which macrophages, dendritic cells and other myeloid phagocytes internalize diverse particulate targets - is a key mechanism of innate immunity. The molecular and cellular events that underlie the binding of targets to a phagocyte and their engulfment into phagosomes have been extensively studied. More recent data suggest that the process of phagocytosis itself provides information to myeloid phagocytes about the nature of the targets they are engulfing and that this helps to tailor inflammatory responses. In this Review, we discuss how such information is acquired during phagocytosis and how it is processed to coordinate an immune response.

From tumor cell metabolism to tumor immune escape

Tumorigenesis implies adaptation of tumor cells to an adverse environment. First, developing tumors must acquire nutrients to ensure their rapid growth. Second, they must escape the attack from the host immune system. Recent studies suggest that these phenomena could be related and that tumor cell metabolism may propel tumor immune escape. Tumor cell metabolism tends to avoid mitochondrial activity and oxidative phosphorylation (OXPHOS), and largely relies on glycolysis to produce energy. This specific metabolism helps tumor cells to avoid the immune attack from the host by blocking or avoiding the immune attack. By changing their metabolism, tumor cells produce or sequester a variety of amino acids, lipids and chemical compounds that directly alter immune function therefore promoting immune evasion. A second group of metabolism-related modification targets the major histocompatibility complex-I (MHC-I) and related molecules. Tumor MHC-I presents tumor-associated antigens (TAAs) to cytotoxic T-cells (CTLs) and hence, sensitizes cancer cells to the cytolytic actions of the anti-tumor adaptive immune response. Blocking tumor mitochondrial activity decreases expression of MHC-I molecules at the tumor cell surface. And peroxynitrite (PNT), produced by tumor-infiltrating myeloid cells, chemically modifies MHC-I avoiding TAA expression in the plasma membrane. These evidences on the role of tumor cell metabolism on tumor immune escape open the possibility of combining drugs designed to control tumor cell metabolism with new procedures of anti-tumor immunotherapy. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

Inhalation of sulfur mustard causes long-term T cell-dependent inflammation: possible role of Th17 cells in chronic lung pathology

Sulfur mustard (SM) is a highly toxic chemical warfare agent that remains a threat to human health. The immediate symptoms of pulmonary distress may develop into chronic lung injury characterized by progressive lung fibrosis, the major cause of morbidity among the surviving SM victims. Although SM has been intensely investigated, little is known about the mechanism(s) by which SM induces chronic lung pathology. Increasing evidence suggests that IL-17(+) cells are critical in fibrosis, including lung fibrotic diseases. In this study we exposed F344 rats and cynomolgus monkeys to SM via inhalation and determined the molecular and cellular milieu in their lungs at various times after SM exposure. In rats, SM induced a burst of pro-inflammatory cytokines/chemokines within 72 h, including IL-1β, TNF-α, IL-2, IL-6, CCL2, CCL3, CCL11, and CXCL1 that was associated with neutrophilic infiltration into the lung. At 2 wks and beyond (chronic phase), lymphocytic infiltration and continued elevated expression of cytokines/chemokines were sustained. TGF-β, which was undetectable in the acute phase, was strongly upregulated in the chronic phase; these conditions persisted until the animals were sacrificed. The chronic phase was also associated with myofibroblast proliferation, collagen deposition, and presence of IL-17(+) cells. At ≥30 days, SM inhalation promoted the accumulation of IL-17(+) cells in the inflamed areas of monkey lungs. Thus, SM inhalation causes acute and chronic inflammatory responses; the latter is characterized by the presence of TGF-β, fibrosis, and IL-17(+) cells in the lung. IL-17(+) cells likely play an important role in the pathogenesis of SM-induced lung injury.

Identification of common biological pathways and drug targets across multiple respiratory viruses based on human host gene expression analysis

BACKGROUND

Pandemic and seasonal respiratory viruses are a major global health concern. Given the genetic diversity of respiratory viruses and the emergence of drug resistant strains, the targeted disruption of human host-virus interactions is a potential therapeutic strategy for treating multi-viral infections. The availability of large-scale genomic datasets focused on host-pathogen interactions can be used to discover novel drug targets as well as potential opportunities for drug repositioning.

METHODS/RESULTS

In this study, we performed a large-scale analysis of microarray datasets involving host response to infections by influenza A virus, respiratory syncytial virus, rhinovirus, SARS-coronavirus, metapneumonia virus, coxsackievirus and cytomegalovirus. Common genes and pathways were found through a rigorous, iterative analysis pipeline where relevant host mRNA expression datasets were identified, analyzed for quality and gene differential expression, then mapped to pathways for enrichment analysis. Possible repurposed drugs targets were found through database and literature searches. A total of 67 common biological pathways were identified among the seven different respiratory viruses analyzed, representing fifteen laboratories, nine different cell types, and seven different array platforms. A large overlap in the general immune response was observed among the top twenty of these 67 pathways, adding validation to our analysis strategy. Of the top five pathways, we found 53 differentially expressed genes affected by at least five of the seven viruses. We suggest five new therapeutic indications for existing small molecules or biological agents targeting proteins encoded by the genes F3, IL1B, TNF, CASP1 and MMP9. Pathway enrichment analysis also identified a potential novel host response, the Parkin-Ubiquitin Proteasomal System (Parkin-UPS) pathway, which is known to be involved in the progression of neurodegenerative Parkinson's disease.

CONCLUSIONS

Our study suggests that multiple and diverse respiratory viruses invoke several common host response pathways. Further analysis of these pathways suggests potential opportunities for therapeutic intervention.

Regulation of Immunity via Multipotent Mesenchymal Stromal Cells

Immune cells responsible for inflammation development are involved in tissue damage caused by wounding and various pathologies. Control of immune cell activation could be of significant benefit for regenerative medicine and the treatment of patients with autoimmune and degenerative diseases. It is a proven fact that MCSs (multipotent mesenchymal stromal cells) are capable of suppressing immune responses via the inhibition of dendritic cell maturation and via the restraining of the T, B, and NK cell function in the course of autoimmune diseases and various forms of inflammation. MSCs can be isolated easily from almost every type of tissue or organ and subsequently expandedin vitro. These cells are self-renewable and can be differentiated into various cell types of mesenchymal lineage. The current review contains a collection and critical analysis of data regarding the molecular mechanisms responsible for cross-talk between immune cells and MSCs. Some of these mechanisms can be used for the development of new practical approaches for the treatment of autoimmune diseases.

The role of innate immune-stimulated epithelial apoptosis during gastrointestinal inflammatory diseases

The maintenance of mucosal barrier equilibrium in the intestine requires a delicate and dynamic balance between enterocyte loss by apoptosis and the generation of new cells by proliferation from stem cell precursors at the base of the intestinal crypts. When the balance shifts towards either excessive or insufficient apoptosis, a broad range of gastrointestinal diseases can manifest. Recent work from a variety of laboratories has provided evidence in support of a role for receptors of the innate immune system, including Toll-like receptors 2, 4, and 9 as well as the intracellular pathogen recognition receptor NOD2/CARD15, in the initiation of enterocyte apoptosis. The subsequent induction of enterocyte apoptosis in response to the activation of these innate immune receptors plays a key role in the development of various intestinal diseases, including necrotizing enterocolitis, Crohn's disease, ulcerative colitis, and intestinal cancer. This review will detail the regulatory pathways that govern enterocyte apoptosis, and will explore the role of the innate immune system in the induction of enterocyte apoptosis in gastrointestinal disease.

Mycobacterium tuberculosis infection induces non-apoptotic cell death of human dendritic cells

Background

Dendritic cells (DCs) connect innate and adaptive immunity, and are necessary for an efficient CD4⁺ and CD8⁺ T cell response after infection with Mycobacterium tuberculosis (Mtb). We previously described the macrophage cell death response to Mtb infection. To investigate the effect of Mtb infection on human DC viability, we infected these phagocytes with different strains of Mtb and assessed viability, as well as DNA fragmentation and caspase activity. In parallel studies, we assessed the impact of infection on DC maturation, cytokine production and bacillary survival.

Results

Infection of DCs with live Mtb (H37Ra or H37Rv) led to cell death. This cell death proceeded in a caspase-independent manner, and without nuclear fragmentation. In fact, substrate assays demonstrated that Mtb H37Ra-induced cell death progressed without the activation of the executioner caspases, 3/7. Although the death pathway was triggered after infection, the DCs successfully underwent maturation and produced a host-protective cytokine profile. Finally, dying infected DCs were permissive for Mtb H37Ra growth.

Conclusions

Human DCs undergo cell death after infection with live Mtb, in a manner that does not involve executioner caspases, and results in no mycobactericidal effect. Nonetheless, the DC maturation and cytokine profile observed suggests that the infected cells can still contribute to TB immunity.

TGF-beta-exposed plasmacytoid dendritic cells participate in Th17 commitment

TGF-β is required for both Foxp3(+) regulatory T cell (Treg) and Th17 commitment. Plasmacytoid DCs (pDC) have been shown to participate to both Treg and Th17 commitment as well. However, few studies have evaluated the direct effect of TGF-β on pDC, and to our knowledge, no study has assessed the capacity of TGF-β-exposed pDC to polarize naive CD4(+) T cells. In this paper, we show that TGF-β-treated pDC favor Th17 but not Treg commitment. This process involves a TGF-β/Smad signal, because TGF-β treatment induced Smad2 phosphorylation in pDC and blockade of TGF-β signaling with the SD208 TGF-βRI kinase inhibitor abrogated Th17 commitment induced by TGF-β-treated pDC. Moreover, TGF-β mRNA synthesis and active TGF-β release were induced in TGF-β-treated pDC and anti-TGF-β Ab blocked Th17 commitment. Unexpectedly, TGF-β treatment also induced increased IL-6 production by pDC, which serves as the other arm for Th17 commitment driven by TGF-β-exposed pDC, because elimination of IL-6-mediated signal with either IL-6- or IL-6Rα-specific Abs prevented Th17 commitment. The in vivo pathogenic role of TGF-β-treated pDC was further confirmed in the Th17-dependent collagen-induced arthritis model in which TGF-β-treated pDC injection significantly increased arthritis severity and pathogenic Th17 cell accumulation in the draining lymph nodes. Thus, our data reveal a previously unrecognized effect of TGF-β-rich environment on pDC ability to trigger Th17 commitment. Such findings have implications in the pathogenesis of autoimmune diseases or immune responses against mucosal extracellular pathogens.

Apoptotic genes are differentially expressed in aged gingival tissue

Cellular and molecular changes of the periodontium associated with a higher prevalence of oral diseases (e.g., chronic periodontitis) in aged populations have received little attention. Since impaired apoptosis during aging appears to be related to chronic inflammatory disorders, we hypothesized that the expression of genes associated with apoptotic processes are altered in aged healthy and periodontitis-affected gingival tissue. Ontology analysis of 88 genes related to apoptotic pathways was performed in gingival biopsies of healthy and periodontitis sites from young, adult, and aged non-human primates (Macaca mulatta), using the GeneChip® Rhesus Macaque Genome Array. Lower expression of anti-apoptotic and higher expression of pro-apoptotic genes were associated with healthy gingival tissue from young compared with aged animals. Few differences in gene expression were observed in healthy gingival tissue between adult and aged animals. Comparison between healthy and periodontitis gingival tissues showed that the up- or down-regulated apoptotic genes in diseased gingival tissue are different in adults compared with aged animals. These results suggest that apoptotic events normally occurring in gingival tissues could be reduced in aging,and unique aspects of apoptotic pathways are potentially involved in the pathophysiology of periodontal disease in adult vs. aged gingival tissues.

The unexpected link between infection-induced apoptosis and a TH17 immune response

Microbial pathogens can initiate MOMP in host cells and as such, initiate the mitochondrial pathway of apoptosis. Innate immune recognition of cells dying in this way by infection-induced apoptosis would involve recognition of ligands derived from the apoptotic host cell simultaneously with those derived from the infecting pathogen. The resultant signal transduction pathways engaged direct DCs to concomitantly synthesize TGF-β and IL-6, two cytokines that subsequently favor the differentiation of naïve CD4 T cells into T(h)17 cells. Citrobacter rodentium is one rodent pathogen that targets mitochondria and induces apoptosis, and blockade of apoptosis during enteric Citrobacter infection impairs the characteristic T(h)17 response in the intestinal LP. Here, we review these original findings. We discuss microbial infections other than Citrobacter that have been shown to induce T(h)17 responses, and we examine what is known about the ability of those pathogens to induce apoptosis. We also consider types of cell death other than apoptosis that can be triggered by microbial infection, and we highlight how little we know about the impact of various forms of cell death on the ensuing adaptive immune response.

A model to die for: signaling to apoptotic cell removal in worm, fly and mouse

Programmed cell death is used during developmental morphogenesis to eliminate superfluous cells or cells with inappropriate developmental potential (e.g., self-reactive immune cells, tumorigenic cells). Recent work in genetic models has led to a number of key observations, revealing signal transduction pathways and identifying new roles for genes previously studied in corpse removal (e.g., removal of broken synapses in the nervous system). Further, studies using mouse models have suggested a role for removal of apoptotic cells in the establishment or maintenance of immune tolerance. In this review, we survey current knowledge of phagocytic pathways derived from studies in the nematode (Caenorhabditis elegans), the fly (Drosophila melanogaster), and mouse (Mus musculus) model systems.

Cell death in the neighbourhood: direct microenvironmental effects of apoptosis in normal and neoplastic tissues

Here we consider the impact of the physiological cell-death programme on normal tissue homeostasis and on disease pathogenesis, with particular reference to evolution and progression of neoplasia. We seek to describe the direct contributions played by apoptosis in creating the microenvironments of normal and malignant tissues and to discuss the molecular mechanisms underlying the elements of the '3Rs' that define the meaning of apoptosis: recognition, response, and removal. Apoptotic cells elicit responses in other cell types-both phagocytic and non-phagocytic-through short- and long-range signalling modes that range from direct contact to intercellular communication via membrane-bound microparticles. Such cellular responses include migration, proliferation, and differentiation, as well as production of immunomodulatory and anti-inflammatory mediators together with, in the case of phagocytes, engulfment, and breakdown of apoptotic cells. In normal tissues, the removal of apoptotic cells is rapid and typically non-phlogistic. We discuss the importance of this clearance process in tissue homeostasis and the consequences of its failure in disease pathogenesis. Using the typical cell culture environment in vitro as an illustrative example in which apoptosis occurs commonly in the absence of the removal mechanisms, we also discuss the inhibitory effects of persistent apoptotic cells on their otherwise viable neighbours. Since apoptosis is a common and sustained event in high-grade malignancies, we hypothesize on its purposeful role in conditioning the tumour microenvironment. We propose that apoptosis subserves several pro-tumour functions-trophic, anti-inflammatory, and immunomodulatory-and we identify strategies targeting host responses to apoptotic cells as promising modes of future therapies that could be applied to multiple cancer types in which tumour-cell apoptosis is active.

Dendritic cells continue to capture and present antigens after maturation in vivo

Dendritic cell (DC) maturation is critical for the regulation of T cell responses. The downregulation of endocytosis on maturation is considered a key adaptation that dissociates prior Ag capture by DCs from subsequent T cell engagement. To study the dynamics of Ag capture and presentation in situ, we studied the capacity for Ag uptake by DCs matured in their natural tissue environment. We found that after maturation in vivo, mouse DCs retained a robust capacity to capture soluble Ags. Furthermore, Ags internalized by mature DCs were efficiently presented on MHC class II and cross-presented on MHC class I. These results suggest that under inflammatory conditions, mature DCs may contribute to T cell stimulation without exclusively relying on prior exposure to Ags as immature DC precursors.

Inflammatory effects of inhaled sulfur mustard in rat lung

Inhalation of sulfur mustard (SM), a bifunctional alkylating agent that causes severe lung damage, is a significant threat to both military and civilian populations. The mechanisms mediating its cytotoxic effects are unknown and were investigated in the present studies. Male rats Crl:CD(SD) were anesthetized, and then intratracheally intubated and exposed to 0.7-1.4mg/kg SM by vapor inhalation. Animals were euthanized 6, 24, 48h or 7days post-exposure and bronchoalveolar lavage fluid (BAL) and lung tissue collected. Exposure of rats to SM resulted in rapid pulmonary toxicity, including focal ulceration and detachment of the trachea and bronchial epithelia from underlying mucosa, thickening of alveolar septal walls and increased numbers of inflammatory cells in the tissue. There was also evidence of autophagy and apoptosis in the tissue. This was correlated with increased BAL protein content, a marker of injury to the alveolar epithelial lining. SM exposure also resulted in increased expression of markers of inflammation including cyclooxygenase-2 (COX-2), tumor necrosis factor-α (TNFα), inducible nitric oxide synthase (iNOS), and matrix metalloproteinase-9 (MMP-9), each of which has been implicated in pulmonary toxicity. Whereas COX-2, TNFα and iNOS were mainly localized in alveolar regions, MMP-9 was prominent in bronchial epithelium. In contrast, expression of the anti-oxidant hemeoxygenase, and the anti-inflammatory collectin, surfactant protein-D, decreased in the lung after SM exposure. These data demonstrate that SM-induced oxidative stress and injury are associated with the generation of cytotoxic inflammatory proteins which may contribute to the pathogenic response to this vesicant.