Caspase-11 detection of intracellular lipopolysaccharide (LPS) from invasive Gram-negative bacteria mediates noncanonical activation of the NLRP3 inflammasome. While avirulent bacteria do not invade ...the cytosol, their presence in tissues necessitates clearance and immune system mobilization. Despite sharing LPS, only live avirulent Gram-negative bacteria activate the NLRP3 inflammasome. Here, we found that bacterial mRNA, which signals bacterial viability, was required alongside LPS for noncanonical activation of the NLRP3 inflammasome in macrophages. Concurrent detection of bacterial RNA by NLRP3 and binding of LPS by pro-caspase-11 mediated a pro-caspase-11-NLRP3 interaction before caspase-11 activation and inflammasome assembly. LPS binding to pro-caspase-11 augmented bacterial mRNA-dependent assembly of the NLRP3 inflammasome, while bacterial viability and an assembled NLRP3 inflammasome were necessary for activation of LPS-bound pro-caspase-11. Thus, the pro-caspase-11-NLRP3 interaction nucleated a scaffold for their interdependent activation explaining their functional reciprocal exclusivity. Our findings inform new vaccine adjuvant combinations and sepsis therapy.
A dense mucus layer in the large intestine prevents inflammation by shielding the underlying epithelium from luminal bacteria and food antigens. This mucus barrier is organized around the ...hyperglycosylated mucin MUC2. Here we show that the small intestine has a porous mucus layer, which permitted the uptake of MUC2 by antigen-sampling dendritic cells (DCs). Glycans associated with MUC2 imprinted DCs with anti-inflammatory properties by assembling a galectin-S-Dectin-1-FcyRIIB receptor complex that activated β-catenin. This transcription factor interfered with DC expression of inflammatory but not tolerogenic cytokines by inhibiting gene transcription through nuclear factor κB. MUC2 induced additional conditioning signals in intestinal epithelial cells. Thus, mucus does not merely form a nonspecific physical barrier, but also constrains the immunogenicity of gut antigens by delivering tolerogenic signals.
Protective immunoglobulin A (IgA) responses to oral antigens are usually orchestrated by gut dendritic cells (DCs). Here, we show that lung CD103(+) and CD24(+)CD11b(+) DCs induced IgA class-switch ...recombination (CSR) by activating B cells through T cell-dependent or -independent pathways. Compared with lung DCs (LDC), lung CD64(+) macrophages had decreased expression of B cell activation genes and induced significantly less IgA production. Microbial stimuli, acting through Toll-like receptors, induced transforming growth factor-β (TGF-β) production by LDCs and exerted a profound influence on LDC-mediated IgA CSR. After intranasal immunization with inactive cholera toxin (CT), LDCs stimulated retinoic acid-dependent up-regulation of α4β7 and CCR9 gut-homing receptors on local IgA-expressing B cells. Migration of these B cells to the gut resulted in IgA-mediated protection against an oral challenge with active CT. However, in germ-free mice, the levels of LDC-induced, CT-specific IgA in the gut are significantly reduced. Herein, we demonstrate an unexpected role of the microbiota in modulating the protective efficacy of intranasal vaccination through their effect on the IgA class-switching function of LDCs.
BAFF and APRIL are innate immune mediators that trigger immunoglobulin G (IgG) and IgA class-switch recombination (CSR) in B cells by engaging the receptor TACI. The mechanism that underlies CSR ...signaling by TACI remains unknown. Here we found that the cytoplasmic domain of TACI encompasses a conserved motif that bound MyD88, an adaptor that activates transcription factor NF-kappaB signaling pathways via a Toll-interleukin 1 (IL-1) receptor (TIR) domain. TACI lacks a TIR domain, yet triggered CSR via the DNA-editing enzyme AID by activating NF-kappaB through a Toll-like receptor (TLR)-like MyD88-IRAK1-IRAK4-TRAF6-TAK1 pathway. TACI-induced CSR was impaired in mice and humans lacking MyD88 or the kinase IRAK4, which indicates that MyD88 controls a B cell-intrinsic, TIR-independent, TACI-dependent pathway for immunoglobulin diversification.
Acetaminophen (APAP) abuse is a common public health problem which can cause severe liver damage. However, strategies for dealing with this situation safely and effectively are very limited. The goal ...of the current work was to evaluate the protection and potential molecular mechanisms of an ethanol extract from shoots of the wild vegetable shutou (Crateva unilocularis Buch.) (ECS) against APAP-induced liver damage in mice. Mice orally received ECS for seven days (300 or 600 mg/kg b.w. per day) before being intraperitoneally injected with APAP (250 mg/kg). Results exhibited that ECS obviously decreased the content of alkaline phosphatase, alanine aminotransferase, aspartate transaminase, and malondialdehyde (p < 0.05). Catalase and superoxide dismutase were notably restored (p < 0.05), and the content of reduced glutathione was obviously increased (p < 0.05). Moreover, ECS significantly inhibited the secretion of interleukin-1β and tumor necrosis factor-α (p < 0.05). Further analyses of the mechanisms showed that ECS may alleviate oxidative stress in the liver by increasing the expression of the nuclear factor erythroid-2-related factor 2 and NADH quinone oxidoreductase 1 proteins, and may suppress liver inflammation by inhibiting the expression of the phosphorylated-inhibitor kappa B alpha/inhibitor kappa B alpha, phosphorylated-nuclear factor κB/nuclear factor κB, and cyclooxygenase-2 proteins. Meanwhile, ECS inhibited hepatocyte apoptosis by enhancing B-cell lymphoma gene 2 and suppressing Bcl-2-associated X protein. In summary, ECS may be used as a dietary supplement to prevent the liver damage caused by APAP abuse.
The human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein gp120 is a vaccine immunogen that can signal via several cell surface receptors. To investigate whether receptor biology could ...influence immune responses to gp120, we studied its interaction with human, monocyte-derived dendritic cells (MDDCs) in vitro. Gp120 from the HIV-1 strain JR-FL induced IL-10 expression in MDDCs from 62% of donors, via a mannose C-type lectin receptor(s) (MCLR). Gp120 from the strain LAI was also an IL-10 inducer, but gp120 from the strain KNH1144 was not. The mannose-binding protein cyanovirin-N, the 2G12 mAb to a mannose-dependent gp120 epitope, and MCLR-specific mAbs inhibited IL-10 expression, as did enzymatic removal of gp120 mannose moieties, whereas inhibitors of signaling via CD4, CCR5, or CXCR4 were ineffective. Gp120-stimulated IL-10 production correlated with DC-SIGN expression on the cells, and involved the ERK signaling pathway. Gp120-treated MDDCs also responded poorly to maturation stimuli by up-regulating activation markers inefficiently and stimulating allogeneic T cell proliferation only weakly. These adverse reactions to gp120 were MCLR-dependent but independent of IL-10 production. Since such mechanisms might suppress immune responses to Env-containing vaccines, demannosylation may be a way to improve the immunogenicity of gp120 or gp140 proteins.
Summary This study investigated the effect of water extract (ZTWE) and ethanol extract (ZTEE) from Zijuan tea on the in vitro starch digestibility of bread, as well as the underlying mechanisms. ...Results revealed that the ZTWE and ZTEE could reduce the starch digestibility of bread, especially ZTEE, which may be due to the higher polyphenols contains in ZTEE (TPC: 233.11 mg GAE/g) than ZTWE (TPC: 195.94 mg GAE/g). Furthermore, results of enzyme activity experiments and in silico analyses demonstrated that the main four polyphenols enriched in ZTWE and ZTEE could inhibit the activities of starch digestive enzymes. Additionally, scanning electron microscopy and in silico analyses showed that the predominant polyphenols in ZTWE and ZTEE could interact with the starch molecule to alter its structure, thereby reducing the starch digestibility. These findings may offer a theoretical foundation for the development of Zijuan tea‐based functional products aimed at diabetes management.
Polygonatum kingianum Coll & Hemsl is an important Chinese medicine used for enhancing physical function and anti-fatigue, and polysaccharides (PKPs) are considered as the main bioactive components. ...However, the mechanisms through which PKPs exert their anti-fatigue effects are not fully understood. This study aimed more comprehensively to explore the anti-fatigue mechanisms of PKPs, focusing on metabolism, protein expression, and gut flora, by using exhaustive swimming experiments in mice. Results showed a significant increase in the exhaustive swimming time of the mice treated with PKPs, especially in the high-dose group (200 mg/kg/day). Further studies showed that PKPs remarkably improves several fatigue-related physiological indices. Additionally, 16S rRNA sequence analysis showed that PKPs increased antioxidant bacteria (e.g., g_norank_f_Muribaculaceae) and the production of short-chain fatty acids (SCFAs), while reducing the abundance of harmful bacteria (e.g., g_Escherichia-Shigella and g_Helicobacter). PKPs also mitigated oxidative stress through activating the NRF2/HO-1 signaling pathway, and promoted energy metabolism by upregulating the expression of AMPK/PGC-1α/TFAM signaling pathway proteins. This research may offer theoretical support for incorporating PKPs as a novel dietary supplement in functional foods targeting anti-fatigue properties.
•Polygonatum kingianum Coll & Hemsl polysaccharides (PKPs) can relieve fatigue.•PKPs suppress oxidative stress and upregulate energy metabolism related proteins.•PKPs reduce the abundance of g_Escherichia-Shigella and g_Helicobacter.•PKPs increase levels of short chain fatty acids (SCFAs) in mice.
Bacteria colonize the intestine shortly after birth and thereafter exert several beneficial functions, including induction of protective immunoglobulin A (IgA) antibodies. The distal intestine ...contains IgA2, which is more resistant to bacterial proteases than is IgA1. The mechanism by which B cells switch from IgM to IgA2remains unknown. We found that human intestinal epithelial cells (IECs) triggered IgA2class switching in B cells, including IgA1-expressing B cells arriving from mucosal follicles, through a CD4+T cell-independent pathway involving a proliferation-inducing ligand (APRIL). IECs released APRIL after sensing bacteria through Toll-like receptors (TLRs) and further increased APRIL production by activating dendritic cells via thymic stromal lymphopoietin. Our data indicate that bacteria elicit IgA2class switching by linking lamina propria B cells with IECs through a TLR-inducible signaling program requiring APRIL. Thus, mucosal vaccines should activate IECs to induce more effective IgA2responses.
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