Background: Endorepellin inhibits angiogenesis by simultaneously binding the ␣21 integrin and VEGFR2, attenuating the PI3K/Akt/mTOR and PKC/JNK/AP1 signaling pathways. Results: Endorepellin evokes autophagy by inducing Beclin 1 and LC3 downstream of VEGFR2 in a Peg3-dependent manner. Conclusion: Endorepellin causes endothelial cell autophagy through VEGFR2 independent of the ␣21 integrin. Significance: Endorepellin-evoked endothelial cell autophagy represents a promising strategy for angiostatic-based therapeutics.
Secondary infections arise as a consequence of previous or concurrent conditions and occur in the community or in the hospital setting. The events allowing secondary infections to gain a foothold have been studied for many years and include poor nutrition, anxiety, mental health issues, underlying chronic diseases, resolution of acute inflammation, primary immune deficiencies, and immune suppression by infection or medication. Children, the elderly and the ill are particularly susceptible. This review is concerned with secondary bacterial infections of the lung that occur following viral infection. Using influenza virus infection as an example, with comparisons to rhinovirus and respiratory syncytial virus infection, we will update and review defective bacterial innate immunity and also highlight areas for potential new investigation. It is currently estimated that one in 16 National Health Service (NHS) hospital patients develop an infection, the most common being pneumonia, lower respiratory tract infections, urinary tract infections and infection of surgical sites. The continued drive to understand the mechanisms of why secondary infections arise is therefore of key importance.
Pulmonary immune control is crucial for protection against pathogens. Here we identify a pathway that promotes host responses during pulmonary bacterial infection; the expression of CD200 receptor (CD200R), which is known to dampen pulmonary immune responses, promotes effective clearance of the lethal intracellular bacterium Francisella tularensis . We show that depletion of CD200R in mice increases in vitro and in vivo infectious burden. In vivo, CD200R deficiency leads to enhanced bacterial burden in neutrophils, suggesting CD200R normally limits the neutrophil niche for infection. Indeed, depletion of this neutrophil niche in CD200R −/− mice restores F. tularensis infection to levels seen in wild-type mice. Mechanistically, CD200R-deficient neutrophils display significantly reduced reactive oxygen species production (ROS), suggesting that CD200R-mediated ROS production in neutrophils is necessary for limiting F. tularensis colonisation and proliferation. Overall, our data show that CD200R promotes the antimicrobial properties of neutrophils and may represent a novel antibacterial therapeutic target.
SapM is a secreted virulence factor from Mycobacterium tuberculosis critical for pathogen survival and persistence inside the host. Its full potential as a target for tuberculosis treatment has not yet been exploited because of the lack of potent inhibitors available. By screening over 1500 small molecules, we have identified new potent and selective inhibitors of SapM with an uncompetitive mechanism of inhibition. The best inhibitors share a trihydroxy-benzene moiety essential for activity. Importantly, the inhibitors significantly reduce mycobacterial burden in infected human macrophages at 1 µM, and they are selective with respect to other mycobacterial and human phosphatases. The best inhibitor also reduces intracellular burden of Francisella tularensis, which secretes the virulence factor AcpA, a homologue of SapM, with the same mechanism of catalysis and inhibition. Our findings demonstrate that inhibition of SapM with small molecule inhibitors is efficient in reducing intracellular mycobacterial survival in host macrophages and confirm SapM as a potential therapeutic target. These initial compounds have favourable physico-chemical properties and provide a basis for exploration towards the development of new tuberculosis treatments. The efficacy of a SapM inhibitor in reducing Francisella tularensis intracellular burden suggests the potential for developing broad-spectrum antivirulence agents to treat microbial infections.
Alveolar macrophages reside in the airway lumen, where they are thought to remain. However, in this issue of Cell Host & Microbe,Cohen et al. (2018) show that Mycobacterium tuberculosis may induce their translocation into the lung interstitium, potentially acting as a Trojan horse for bacillary dissemination to other phagocytes.
Lung-resident macrophages are crucial to the maintenance of health and in the defence against lower respiratory tract infections. Macrophages adapt to local environmental cues that drive their appropriate function; however, this is often dysregulated in many inflammatory lung pathologies. In mucosal tissues, neuro-immune interactions enable quick and efficient inflammatory responses to pathogenic threats. Although a number of factors that influence the antimicrobial response of lung macrophages are known, the role of neuronal factors is less well understood. Here, we show an intricate circuit involving the neurotrophic factor, neurturin (NRTN) on human lung macrophages that dampens pro-inflammatory cytokine release and modulates the type of matrix metalloproteinases produced in response to viral stimuli. This circuit involves type 1 interferon–induced up-regulation of RET that when combined with the glial cell line-derived neurotrophic factor (GDNF) receptor α2 (GFRα2) allows binding to epithelial-derived NRTN. Our research highlights a non-neuronal immunomodulatory role for NRTN and a novel process leading to a specific antimicrobial immune response by human lung-resident macrophages.
A rapid immune response to pathogen re-exposure underpins immunological memory, with protection against divergent pathogens such as heterologous or novel viral strains requiring cross-reactive memory T cells. Understanding the pathways that control memory T cell function is therefore important for the rational design of viral vaccines and will aid the discovery of therapies to boost anti-viral immunity. Here, we identify a sub-population of memory T cells that limit secondary immune responses to viral re-infection, which is crucial in preventing host tissue damage. We show that a population of CD4+effector memory T (TEM) cells activate the important immunoregulatory cytokine TGFβ, via expression of an integrin, αvβ8. Integrin αvβ8 expression marks a transcriptionally distinct sub-population of CD4+TEM, enriched for anti-inflammatory pathways. Loss of integrin αvβ8 on murine CD4+TEM, but not Foxp3+regulatory T cells (TREG), led to exacerbated virus-specific CD8+T cell responses following secondary influenza A virus (IAV) infection, which was associated with enhanced viral clearance. However, although accelerating clearance, loss of integrin αvβ8 expression on CD4+TEMresulted in enhanced lung pathology following secondary IAV infection, which was completely reversed by adoptive transfer of αvβ8+CD4+TEMcells. These data highlight a new pathway by which a distinct CD4+memory T cell subset restrains anti-viral immunity to prevent host tissue damage during secondary viral infection. Such pathways could be targeted therapeutically to either boost memory T-cell-mediated immunity or restrain host tissue damage during viral infection.
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