Background & Aims Immune responses in the intestine are controlled by regulatory T cells (Tregs), which prevent inflammation in response to commensal bacteria. A specific population of intestinal ...dendritic cells (DCs), marked by expression of CD103, generate Tregs more efficiently than other DC populations through mechanisms that involve retinoic acid and transforming growth factor (TGF)-β. However, it is not clear how CD103+ DCs are specialized for this function. We investigated the ability of CD103+ DCs to promote Treg generation through activation of TGF-β and the role of integrins with the αv subunit in this process. Methods Naïve T cells were cultured with purified DCs from mesenteric lymph nodes (MLNs) or intestines of wild-type and αv conditional knockout mice to assess generation of Tregs. Antigens were administered orally to mice, and antigen-specific generation of Tregs was measured in intestinal tissues. Expression of the integrin αv subunit was measured in purified subpopulations of DCs by quantitative polymerase chain reaction and immunoblot analyses. Results In vitro, CD103+ DCs generated more Tregs in the presence of latent TGF-β than other MLN DCs. Efficient generation of Tregs required expression of the integrin αv subunit by DCs; mice that lacked αv in immune cells did not convert naïve T cells to intestinal Tregs in response to oral antigen. CD103+ DCs derived from the MLNs selectively expressed high levels of integrin αvβ8 compared with other populations of DCs. Conclusions Expression of αvβ8 is required for CD103+ DCs to become specialized and activate latent TGF-β and generate Tregs during the induction of tolerance to intestinal antigens in mice.
Background & Aims Induction of oral immune tolerance (OT) blocks proinflammatory responses to orally administered antigens and might be used to treat autoimmune conditions. We investigated whether ...gut-tropic T cells that express the integrin α4β7 and the chemokine receptor CCR9 are required for OT. Methods Skin delayed-type hypersensitivity and experimental autoimmune encephalomyelitis were used to monitor OT in mice. To assess the role of receptors that mediate localization of lymphocytes to the gut (gut-homing receptors) in induction of OT, we studied CCR9 −/− and β7 −/− mice and also blocked the α4β7 ligand MAdCAM-1 in wild-type mice. We used DEREG and Scurfy mice to assess the role of Foxp3+ regulatory T cells (Treg) and IL-10 −/− and IL-10Rβ −/− mice to examine the role of interleukin (IL)-10 in induction of OT. Results OT could not be induced in CCR9 −/− or β7 −/− mice, or when MAdCAM-1 was blocked in wild-type mice, indicating that gut-homing receptors are required for oral tolerization. Consistent with the role of all-trans retinoic acid in inducing gut-homing T cells, OT could not be induced in mice depleted of vitamin A. OT was rescued in CCR9 −/− mice following adoptive transfer of wild-type T cells, but not CCR9 −/− or β7 −/− T cells. Gut-homing T cells are therefore necessary and sufficient to induce OT. Wild-type Treg and IL-10 were required to restore OT to CCR9 −/− mice, indicating that homing and functional differentiation of IL-10–producing Treg in the gut is required for OT. Conversely, transfer of CCR9 −/− or β7 −/− T cells to wild-type mice partially inhibited OT. Conclusions Expression of CCR9 and α4β7 on T cells and their subsequent localization to the gut is required for induction of OT in mice. Therapies designed to block gut-homing receptors might, under some conditions, interfere with normal tolerogenic mechanisms in the intestinal mucosa.
Recent outbreaks of Ebola virus (EBOV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have exposed our limited therapeutic options for such diseases and our poor understanding of ...the cellular mechanisms that block viral infections. Using a transposon-mediated gene-activation screen in human cells, we identify that the major histocompatibility complex (MHC) class II transactivator (CIITA) has antiviral activity against EBOV. CIITA induces resistance by activating expression of the p41 isoform of invariant chain CD74, which inhibits viral entry by blocking cathepsin-mediated processing of the Ebola glycoprotein. We further show that CD74 p41 can block the endosomal entry pathway of coronaviruses, including SARS-CoV-2. These data therefore implicate CIITA and CD74 in host defense against a range of viruses, and they identify an additional function of these proteins beyond their canonical roles in antigen presentation.
Phagosomes form during engulfment of large particles and become increasingly acidic and proteolytic, ultimately fusing with lysosomes, in a process termed "phagosome maturation." In this issue, Yin ...et al. (2017.
https://doi.org/10.1083/jcb.201610001) identify GOP-1 as essential for the maturation of phagosomes containing apoptotic cells, through recruitment of the Rab GTPase UNC108.
In atherosclerosis and Alzheimer's disease, deposition of the altered self components oxidized low-density lipoprotein (LDL) and amyloid-beta triggers a protracted sterile inflammatory response. ...Although chronic stimulation of the innate immune system is believed to underlie the pathology of these diseases, the molecular mechanisms of activation remain unclear. Here we show that oxidized LDL and amyloid-beta trigger inflammatory signaling through a heterodimer of Toll-like receptors 4 and 6. Assembly of this newly identified heterodimer is regulated by signals from the scavenger receptor CD36, a common receptor for these disparate ligands. Our results identify CD36-TLR4-TLR6 activation as a common molecular mechanism by which atherogenic lipids and amyloid-beta stimulate sterile inflammation and suggest a new model of TLR heterodimerization triggered by coreceptor signaling events.
In the mammalian gut CD103+ve myeloid DCs are known to suppress inflammation threatened by luminal bacteria, but stimuli driving DC precursor maturation towards this beneficial phenotype are ...incompletely understood. We isolated CD11+ve DCs from mesenteric lymph nodes (MLNs) of healthy mice; CD103+ve DCs were 8–24 fold more likely than CD103-ve DCs to exhibit extensive of prior phagocytosis of apoptotic intestinal epithelial cells. However, CD103+ve and CD103-ve MLN DCs exhibited similar ex vivo capacity to ingest apoptotic cells, indicating that apoptotic cells might drive immature DC maturation towards the CD103+ve phenotype. When cultured with apoptotic cells, myeloid DC precursors isolated from murine bone marrow and characterised as lineage-ve CD103-ve, displayed enhanced expression of CD103 and β8 integrin and acquired increased capacity to induce T regulatory lymphocytes (Tregs) after 7d in vitro. However, DC precursors isolated from αv-tie2 mice lacking αv integrins in the myeloid line exhibited reduced binding of apoptotic cells and complete deficiency in the capacity of apoptotic cells and/or latent TGF-β1 to enhance CD103 expression in culture, whereas active TGF-β1 increased DC precursor CD103 expression irrespective of αv expression. Fluorescence microscopy revealed clustering of αv integrin chains and latent TGF-β1 at points of contact between DC precursors and apoptotic cells. We conclude that myeloid DC precursors can deploy αv integrin to orchestrate binding of apoptotic cells, activation of latent TGF-β1 and acquisition of the immunoregulatory CD103+ve β8+ve DC phenotype. This implies that a hitherto unrecognised consequence of apoptotic cell interaction with myeloid phagocytes is programming that prevents inflammation.
Cytopenias are an important clinical problem associated with inflammatory disease and infection. We show that specialized phagocytes that internalize red blood cells develop in Toll-like receptor 7 ...(TLR7)-driven inflammation. TLR7 signaling caused the development of inflammatory hemophagocytes (iHPCs), which resemble splenic red pulp macrophages but are a distinct population derived from Ly6C
monocytes. iHPCs were responsible for anemia and thrombocytopenia in TLR7-overexpressing mice, which have a macrophage activation syndrome (MAS)-like disease. Interferon regulatory factor 5 (IRF5), associated with MAS, participated in TLR7-driven iHPC differentiation. We also found iHPCs during experimental malarial anemia, in which they required endosomal TLR and MyD88 signaling for differentiation. Our findings uncover a mechanism by which TLR7 and TLR9 specify monocyte fate and identify a specialized population of phagocytes responsible for anemia and thrombocytopenia associated with inflammation and infection.
Super-resolution optical imaging tools are crucial in microbiology to understand the complex structures and behavior of microorganisms such as bacteria, fungi, and viruses. However, the capabilities ...of these tools, particularly when it comes to imaging pathogens and infected tissues, remain limited. MicroMagnify (µMagnify) is developed, a nanoscale multiplexed imaging method for pathogens and infected tissues that are derived from an expansion microscopy technique with a universal biomolecular anchor. The combination of heat denaturation and enzyme cocktails essential is found for robust cell wall digestion and expansion of microbial cells and infected tissues without distortion. µMagnify efficiently retains biomolecules suitable for high-plex fluorescence imaging with nanoscale precision. It demonstrates up to eightfold expansion with µMagnify on a broad range of pathogen-containing specimens, including bacterial and fungal biofilms, infected culture cells, fungus-infected mouse tone, and formalin-fixed paraffin-embedded human cornea infected by various pathogens. Additionally, an associated virtual reality tool is developed to facilitate the visualization and navigation of complex 3D images generated by this method in an immersive environment allowing collaborative exploration among researchers worldwide. µMagnify is a valuable imaging platform for studying how microbes interact with their host systems and enables the development of new diagnosis strategies against infectious diseases.
Phagocytosis is a fundamental cellular process that is pivotal for immunity as it coordinates microbial killing, innate immune activation and antigen presentation. An essential step in this process ...is phagosome acidification, which regulates many functions of these organelles that allow phagosomes to participate in processes that are essential to both innate and adaptive immunity. Here we report that acidification of phagosomes containing Gram-positive bacteria is regulated by the NLRP3 inflammasome and caspase-1. Active caspase-1 accumulates on phagosomes and acts locally to control the pH by modulating buffering by the NADPH oxidase NOX2. These data provide insight into a mechanism by which innate immune signals can modify cellular defenses and establish a new function for the NLRP3 inflammasome and caspase-1 in host defense.
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