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Toll-like receptors (TLRs) initiate and maintain host defenses and inflammation, and directly contribute to diseases such as atherosclerosis. It is not completely understood in what cell types proatherogenic TLR-induced signaling arises and, particularly, there is uncertainty regarding the potential functional role of TLR2 in endothelial cells (ECs). We determined TLR2 and TLR4 gene expression in four different human and two different murine primary ECs using gene array analysis, RT-PCR, and flow cytometry and confirmed these data by functional studies by stimulating ECs with the corresponding TLR ligands. TLR4 was expressed in all human and murine ECs and these cells responded to stimulation with LPS. Faint expression of TLR2 was observed in human ECs, whereas murine ECs express considerable amounts of TLR2 mRNA. Human ECs failed to respond to TLR2 ligands while murine ECs responded to TLR2 ligands. Furthermore, in murine ECs, TLR2 was located on the cell surface while in human ECs, TLR2 was sequestered in intracellular compartments. After 1FN-γ or IL- 1β stimulation, TLR2 translocated to the cell surface of human ECs. In conclusion, TLR2 is expressed intracellularly in human ECs and, therefore, TLR2 ligands are inaccessible to the receptor. Murine ECs express membrane TLR2 and respond to TLR2 ligands, but human ECs normally will not respond unless they are first primed with inflammatory stimulation, which appears to trigger translocation of TLR2 to the cell surface. [ABSTRACT FROM AUTHOR]

Introduction: The maintenance of intestinal homeostasis depends on a complex interaction between the immune system, intestinal epithelial barrier, and microbiota. Alteration in one of these components could lead to the development of inflammatory bowel diseases (IBD). Variants within the autophagy gene ATG16L1 have been implicated in susceptibility and severity of Crohn's disease (CD). Individuals carrying the risk ATG16L1 T300A variant have higher caspase 3-dependent degradation of ATG16L1 resulting in impaired autophagy and increased cellular stress. ATG16L1-deficiency induces enhanced IL-1β secretion in dendritic cells in response to bacterial infection. Infection of ATG16L1-deficient mice with a persistent strain of murine norovirus renders these mice highly susceptible to dextran sulfate sodium colitis. Moreover, persistent norovirus infection leads to intestinal virus specific CD8 + T cells responses. Both Toll-like receptor 7 (TLR7), which recognizes single-stranded RNA viruses, and ATG16L1, which facilitates the delivery of viral nucleic acids to the autolysosome endosome, are required for anti-viral immune responses., Results and Discussion: However, the role of the enteric virome in IBD is still poorly understood. Here, we investigate the role of TLR7 and ATG16L1 in intestinal homeostasis and inflammation. At steady state, Tlr7 -/- mice have a significant increase in large intestinal lamina propria (LP) granzyme B + tissue-resident memory CD8 + T (T RM ) cells compared to WT mice, reminiscent of persistent norovirus infection. Deletion of Atg16l1 in myeloid ( Atg16l1 ΔLyz2 ) or dendritic cells ( Atg16l1 ΔCd11c ) leads to a similar increase of LP T RM . Furthermore, Tlr7 -/- and Atg16l1 ΔCd11c mice were more susceptible to dextran sulfate sodium colitis with an increase in disease activity index, histoscore, and increased secretion of IFN-γ and TNF-α. Treatment of Atg16l1 ΔCd11c mice with the TLR7 agonist Imiquimod attenuated colonic inflammation in these mice. Our data demonstrate that ATG16L1-deficiency in myeloid and dendritic cells leads to an increase in LP T RM and consequently to increased susceptibility to colitis by impairing the recognition of enteric viruses by TLR7., Conclusion: In conclusion, the convergence of ATG16L1 and TLR7 signaling pathways plays an important role in the immune response to intestinal viruses. Our data suggest that activation of the TLR7 signaling pathway could be an attractive therapeutic target for CD patients with ATG16L1 risk variants., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2024 Hamade, Tsuda, Oshima, Stamps, Wong, Stamps, Thomas, Salumbides, Jin, Nunnelee, Dhall, Targan and Michelsen.)

T helper 9 (T H 9) cells are important for the development of inflammatory and allergic diseases. The T H 9 transcriptional network converges signals from cytokines and antigen presentation but is incompletely understood. Here, we identified TL1A, a member of the TNF superfamily, as a strong inducer of mouse and human T H 9 differentiation. Mechanistically, TL1A induced the expression of the transcription factors BATF and BATF3 and facilitated their binding to the Il9 promoter leading to enhanced secretion of IL-9. BATF- and BATF3-deficiencies impaired IL-9 secretion under T H 9 and T H 9-TL1A-polarizing conditions. In vivo, using a T-cell transfer model, we demonstrated that TL1A promoted IL-9-dependent, T H 9 cell-induced intestinal and lung inflammation. Neutralizing IL-9 antibodies attenuated TL1A-driven mucosal inflammation. Batf3 -/- T H 9-TL1A cells induced reduced inflammation and cytokine expression in vivo compared to WT cells. Our results demonstrate that TL1A promotes T H 9 cell differentiation and function and define a role for BATF3 in T-cell-driven mucosal inflammation.

TL1A contributes to the pathogenesis of several chronic inflammatory diseases, including those of the bowel by enhancing T H 1, T H 17, and T H 2 responses. TL1A mediates a strong costimulation of these T H subsets, particularly of mucosal CCR9 + T cells. However, the signaling pathways that TL1A induces in different T H subsets are incompletely understood. We investigated the function of TL1A on human T H 17 cells. TL1A, together with TGF-β, IL-6, and IL-23, enhanced the secretion of IL-17 and IFN-γ from human CD4 + memory T cells. TL1A induced expression of the transcription factors BATF and T-bet that correlated with the secretion of IL-17 and IFN-γ. In contrast, TL1A alone induced high levels of IL-22 in memory CD4 + T cells and committed T H 17 cells. However, TL1A did not enhance expression of IL-17A in T H 17 cells. Expression of the transcription factor aryl hydrocarbon receptor, which regulates the expression of IL-22 was not affected by TL1A. Transcriptome analysis of T H 17 cells revealed increased expression of IL-9 in response to TL1A. Blocking IL-9 receptor antibodies abrogated TL1A-induced IL-22 secretion. Furthermore, TL1A increased IL-9 production by peripheral T H 17 cells isolated from patients with Crohn's disease. These data suggest that TL1A differentially induces expression of T H 17 effector cytokines IL-17, -9, and -22 and provides a potential target for therapeutic intervention in T H 17-driven chronic inflammatory diseases., (© Society for Leukocyte Biology.)

Background: Extracts of the plant Andrographis paniculata have been used to treat inflammatory diseases in Asian countries. A recent double-blind, placebo-controlled trial of HMPL-004 (A. paniculata extract) has demonstrated its safety and effectiveness for induction of clinical response, remission, and mucosal healing in patients with mild to moderate ulcerative colitis (UC). We aimed to determine if HMPL-004 could prevent the development of T-cell-dependent murine colitis and to define its in vivo mechanism(s) of action., Methods: CD(+)4CD45RB(high) T cells were transferred into Rag1(-/-) mice and gavaged daily with HMPL-004 or methyl cellulose (MC). Severity of colitis was evaluated by weight loss, histology, and cytokine expression., Results: Mice treated with MC developed colitis within 4-7 weeks, as evaluated by weight loss, and severe intestinal inflammation. HMPL-004-treated mice did not lose weight and displayed only very mild intestinal inflammation. Tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, interferon-gamma (IFN-γ), and IL-22 expression were significantly decreased in HMPL-004-treated mice. We observed higher percentages of naïve CD4(+) T cells in the lamina propria of HMPL-004-treated mice. At early timepoints HMPL-004-treated mice have significantly reduced splenic cell counts, reduced CD4(+), and IL-17(+), and IFN-γ T(+) cells. Furthermore, HMPL-004 inhibited the proliferation of CD4 T cells and differentiation into TH1/TH17 cells in vitro., Conclusions: HMPL-004 inhibits the development of chronic colitis by affecting early T-cell proliferation, differentiation, and TH(1)/TH(17) responses in a T-cell-driven model of colitis, presenting a unique mechanism of action. Our data suggest that HMPL-004 could be an attractive herbal therapeutic for inflammatory bowel disease.

Experimental and clinical studies link Chlamydia pneumoniae infection to atherogenesis and atherothrombotic events, but the underlying mechanisms are unclear. We tested the hypothesis that C. pneumoniae-induced acceleration of atherosclerosis in apolipoprotein E (ApoE)(-/-) mice is reciprocally modulated by activation of TLR-mediated innate immune and liver X receptor alpha (LXRalpha) signaling pathways. We infected ApoE(-/-) mice and ApoE(-/-) mice that also lacked TLR2, TLR4, MyD88, or LXRalpha intranasally with C. pneumoniae followed by feeding of a high fat diet for 4 mo. Mock-infected littermates served as controls. Atherosclerosis was assessed in aortic sinuses and in en face preparation of whole aorta. The numbers of activated dendritic cells (DCs) within plaques and the serum levels of cholesterol and proinflammatory cytokines were also measured. C. pneumoniae infection markedly accelerated atherosclerosis in ApoE-deficient mice that was associated with increased numbers of activated DCs in aortic sinus plaques and higher circulating levels of MCP-1, IL-12p40, IL-6, and TNF-alpha. In contrast, C. pneumoniae infection had only a minimal effect on atherosclerosis, accumulation of activated DCs in the sinus plaques, or circulating cytokine increases in ApoE(-/-) mice that were also deficient in TLR2, TLR4, or MyD88. However, C. pneumoniae-induced acceleration of atherosclerosis in ApoE(-/-) mice was further enhanced in ApoE(-/-)LXRalpha(-/-) double knockout mice and was accompanied by higher serum levels of IL-6 and TNF-alpha. We conclude that C. pneumoniae infection accelerates atherosclerosis in hypercholesterolemic mice predominantly through a TLR/MyD88-dependent mechanism and that LXRalpha appears to reciprocally modulate and reduce the proatherogenic effects of C. pneumoniae infection.

The intestinal epithelium serves as a barrier to the intestinal flora. In response to pathogens, intestinal epithelial cells (IEC) secrete proinflammatory cytokines. To aid in defense against bacteria, IEC also secrete antimicrobial peptides, termed defensins. The aim of our studies was to understand the role of TLR signaling in regulation of beta-defensin expression by IEC. The effect of LPS and peptidoglycan on beta-defensin-2 expression was examined in IEC lines constitutively or transgenically expressing TLRs. Regulation of beta-defensin-2 was assessed using promoter-reporter constructs of the human beta-defensin-2 gene. LPS and peptidoglycan stimulated beta-defensin-2 promoter activation in a TLR4- and TLR2-dependent manner, respectively. A mutation in the NF-kappaB or AP-1 site within the beta-defensin-2 promoter abrogated this response. In addition, inhibition of Jun kinase prevents up-regulation of beta-defensin-2 protein expression in response to LPS. IEC respond to pathogen-associated molecular patterns with expression of the antimicrobial peptide beta-defensin-2. This mechanism may protect the intestinal epithelium from pathogen invasion and from potential invaders among the commensal flora.