Description: Activation of TLR4 by the endotoxin LPS is a critical event in the pathogenesis of Gram-negative sepsis. Caveolin-1, the signaling protein associated with caveolae, is implicated in regulating the lung inflammatory response to LPS; however, the mechanism is not understood. In this study, we investigated the role of caveolin-1 in regulating TLR4 signaling in endothelial cells. We observed that LPS interaction with CD14 in endothelial cells induced Src -dependent caveolin-1 phosphorylation at Tyr 14 . Using a TLR4-MD2-CD14–transfected HEK-293 cell line and caveolin-1–deficient ( cav-1 –/– ) mouse lung microvascular endothelial cells, we demonstrated that caveolin-1 phosphorylation at Tyr 14 following LPS exposure induced caveolin-1 and TLR4 interaction and, thereby, TLR4 activation of MyD88, leading to NF-B activation and generation of proinflammatory cytokines. Exogenous expression of phosphorylation-deficient Y14F caveolin-1 mutant in cav-1 –/– mouse pulmonary vasculature rendered the mice resistant to LPS compared with reintroduction of wild-type caveolin-1. Thus, caveolin-1 Y14 phosphorylation was required for the interaction with TLR4 and activation of TLR4-MyD88 signaling and sepsis-induced lung inflammation. Inhibiting caveolin-1 Tyr 14 phosphorylation and resultant inactivation of TLR4 signaling in pulmonary vascular endothelial cells represent a novel strategy for preventing sepsis-induced lung inflammation and injury.

Description: Induction of type I IFN (IFN-I) is essential for host antiviral immune responses. However, IFN-I also plays divergent roles in antibacterial immunity, persistent viral infections, autoimmune diseases, and tumorigenesis. IFN regulatory factor 3 (IRF3) is the master transcription factor that controls IFN-I production via phosphorylation-dependent dimerization in most cell types in response to viral infections and various innate stimuli by pathogen-associated molecular patterns (PAMPs). To monitor the dynamic process of IRF3 activation, we developed a novel IRF3 dimerization reporter based on bimolecular luminescence complementation (BiLC) techniques, termed the IRF3-BiLC reporter. Robust induction of luciferase activity of the IRF3-BiLC reporter was observed upon viral infection and PAMP stimulation with a broad dynamic range. Knockout of TANK-binding kinase 1, the critical upstream kinase of IRF3, as well as the mutation of serine 386, the essential phosphorylation site of IRF3, completely abolished the luciferase activity of IRF3-BiLC reporter, confirming the authenticity of IRF3 activation. Taken together, these results demonstrated that the IRF3-BiLC reporter is a highly specific, reliable, and sensitive system to measure IRF3 activity. Using this reporter system, we further observed that the temporal pattern and magnitude of IRF3 activation induced by various PAMPs are highly complex with distinct cell type–specific characteristics, and IRF3 dimerization is a direct regulatory node for IFN-α/β receptor–mediated feed-forward regulation and crosstalk with other pathways. Therefore, the IRF3-BiLC reporter has multiple potential applications, including mechanistic studies as well as the identification of novel compounds that can modulate IRF3 activation.

Description: Helicobacter pylori infection causes chronic gastritis and peptic ulceration. H. pylori –initiated chronic gastritis is characterized by enhanced expression of many NF-B–regulated inflammatory cytokines. Brd4 has emerged as an important NF-B regulator and regulates the expression of many NF-B–dependent inflammatory genes. In this study, we demonstrated that Brd4 was not only actively involved in H. pylori –induced inflammatory gene mRNA transcription but also H. pylori –induced inflammatory gene enhancer RNA (eRNA) synthesis. Suppression of H. pylori –induced eRNA synthesis impaired H. pylori –induced mRNA synthesis. Furthermore, H. pylori stimulated NF-B–dependent recruitment of Brd4 to the promoters and enhancers of inflammatory genes to facilitate the RNA polymerase II–mediated eRNA and mRNA synthesis. Inhibition of Brd4 by JQ1 attenuated H. pylori –induced eRNA and mRNA synthesis for a subset of NF-B–dependent inflammatory genes. JQ1 also inhibited H. pylori –induced interaction between Brd4 and RelA and the recruitment of Brd4 and RNA polymerase II to the promoters and enhancers of inflammatory genes. Finally, we demonstrated that JQ1 suppressed inflammatory gene expression, inflammation, and cell proliferation in H. pylori –infected mice. These studies highlight the importance of Brd4 in H. pylori –induced inflammatory gene expression and suggest that Brd4 could be a potential therapeutic target for the treatment of H. pylori –triggered inflammatory diseases and cancer.

Description: IgG autoantibodies mediate pathology in systemic lupus patients and lupus-prone mice. In this study, we showed that the class-switched IgG autoantibody response in MRL/ Fas lpr/lpr and C57/ Sle1Sle2Sle2 mice was blocked by the CID 1067700 compound, which specifically targeted Ras-related in brain 7 (Rab7), an endosome-localized small GTPase that was upregulated in activated human and mouse lupus B cells, leading to prevention of disease development and extension of lifespan. These were associated with decreased IgG-expressing B cells and plasma cells, but unchanged numbers and functions of myeloid cells and T cells. The Rab7 inhibitor suppressed T cell–dependent and T cell–independent Ab responses, but it did not affect T cell–mediated clearance of Chlamydia infection, consistent with a B cell–specific role of Rab7. Indeed, B cells and plasma cells were inherently sensitive to Rab7 gene knockout or Rab7 activity inhibition in class switching and survival, respectively, whereas proliferation/survival of B cells and generation of plasma cells were not affected. Impairment of NF-B activation upon Rab7 inhibition, together with the rescue of B cell class switching and plasma cell survival by enforced NF-B activation, indicated that Rab7 mediates these processes by promoting NF-B activation, likely through signal transduction on intracellular membrane structures. Thus, a single Rab7-inhibiting small molecule can target two stages of B cell differentiation to dampen the pathogenic autoantibody response in lupus.

Description: Autoimmunity has been implicated in the pathogenesis of idiopathic pulmonary fibrosis (IPF); however, the repertoire of autoantigens involved in this disease and the clinical relevance of these autoimmune responses are still being explored. Our initial discovery assays demonstrated that circulating and intrapulmonary vimentin levels are increased in IPF patients. Subsequent studies showed native vimentin induced HLA-DR–dependent in vitro proliferation of CD4 T cells from IPF patients and enhanced the production of IL-4, IL-17, and TGF-β1 by these lymphocytes in contrast to normal control specimens. Vimentin supplementation of IPF PBMC cultures also resulted in HLA-DR–dependent production of IgG with anti-vimentin specificities. Circulating anti-vimentin IgG autoantibody levels were much greater in IPF subjects from the University of Alabama at Birmingham ( n = 102) and the University of Pittsburgh (U. Pitt., n = 70) than in normal controls. Anti-vimentin autoantibody levels in IPF patients were HLA biased and inversely correlated with physiological measurements of lung function (i.e., forced expiratory volumes and diffusing capacities). Despite considerable intergroup differences in transplant-free survival between these two independent IPF cohorts, serious adverse outcomes were most frequent among the patients within each population that had the highest anti-vimentin autoantibody levels (University of Alabama at Birmingham: hazard ratio 2.5, 95% confidence interval 1.2–5.3, p = 0.012; University of Pittsburgh: hazard ratio 2.7, 95% confidence interval 1.3–5.5, p = 0.006). These data show that anti-vimentin autoreactivity is prevalent in IPF patients and is strongly associated with disease manifestations. These findings have implications with regard to the pathogenesis of this enigmatic disease and raise the possibility that therapies specifically directed at these autoimmune processes could have therapeutic efficacy.

Description: The emergence of adaptive immunity in jawed vertebrates depended on the appearance of variable immune receptors, BCRs and TCRs, which exhibit variable-J–constant (V J -C)–type Ig superfamily folds. Hitherto, however, the structures of IgV-J-IgC–type molecules had never been characterized in invertebrates, leaving the origin of BCR/TCR-type molecules unknown. Using x-ray crystallography, the structure of a V J -C2 molecule, named AmpIgV J -C2, was determined in amphioxus ( Branchiostoma floridae ). The first domain shows typical V folding, including the hydrophobic core, CDR analogs, and eight conserved residues. The second domain is a C2-type Ig superfamily domain, as defined by its short length and the absence of β-strand D- and C1-typical motifs. AmpIgV J -C2 molecules form homodimers, using "three-layer packing dimerization," as described for TCRs and BCRs. The AmpIgV J -C2 V domain harbors a diglycine motif in β-strand G and forms a β-bulge structure participating in V–V intermolecular interaction. By immunohistochemistry, AmpIgV J -C2 molecules were primarily found in mucosal tissues, whereas PCR and sequence analysis indicated considerable genetic variation at the single-gene level; these findings would be consistent with an immune function and a basic ability to adapt to binding different immune targets. Our results show a BCR/TCR-ancestral like molecule in amphioxus and help us to understand the evolution of the adaptive immune system.

Description: Genetically engineered pig organs could provide transplants to all patients with end-stage organ failure, but Ab-mediated rejection remains an issue. This study examines the class II swine leukocyte Ag (SLA) as a target of epitope-restricted Ab binding. Transfection of individual α- and β-chains into human embryonic kidney cells resulted in both traditional and hybrid class II SLA molecules. Sera from individuals on the solid organ transplant waiting list were tested for Ab binding and cytotoxicity to this panel of class II SLA single-Ag cells. A series of elution studies from an SLA-DQ cell line were performed. Our results indicate that human sera contain Abs specific for and cytotoxic against class II SLA. Our elution studies revealed that sera bind the SLA-DQ molecule in an epitope-restricted pattern. Site-specific mutation of one of these epitopes resulted in statistically decreased Ab binding. Humans possess preformed, specific, and cytotoxic Abs to class II SLA that bind in an epitope-restricted fashion. Site-specific epitope mutagenesis may decrease the Ab binding of highly sensitized individuals to pig cells.

Description: IL-35 is a member of the IL-12 family of cytokines that is comprised of an IL-12 p35 subunit and an IL-12 p40-related protein subunit, EBV-induced gene 3 (EBI3). IL-35 functions through IL-35R and has a potent immune-suppressive activity. Although IL-35 was demonstrated to be produced by regulatory T cells, gene-expression analysis revealed that it is likely to have a wider distribution, including expression in cancer cells. In this study, we demonstrated that IL-35 is produced in human cancer tissues, such as large B cell lymphoma, nasopharyngeal carcinoma, and melanoma. To determine the roles of tumor-derived IL-35 in tumorigenesis and tumor immunity, we generated IL-35–producing plasmacytoma J558 and B16 melanoma cells and observed that the expression of IL-35 in cancer cells does not affect their growth and survival in vitro, but it stimulates tumorigenesis in both immune-competent and Rag1/2-deficient mice. Tumor-derived IL-35 increases CD11b + Gr1 + myeloid cell accumulation in the tumor microenvironment and, thereby, promotes tumor angiogenesis. In immune-competent mice, spontaneous CTL responses to tumors are diminished. IL-35 does not directly inhibit tumor Ag–specific CD8 + T cell activation, differentiation, and effector functions. However, IL-35–treated cancer cells had increased expression of gp130 and reduced sensitivity to CTL destruction. Thus, our study indicates novel functions for IL-35 in promoting tumor growth via the enhancement of myeloid cell accumulation, tumor angiogenesis, and suppression of tumor immunity.

Description: MicroRNAs are known to control TLR activation in phagocytes. We have shown that leukotriene (LT) B 4 (LTB 4 ) positively regulates macrophage MyD88 expression by decreasing suppressor of cytokine signaling-1 (SOCS-1) mRNA stability. In this study, we investigated the possibility that LTB 4 control of MyD88 expression involves the generation of microRNAs. Our data show that LTB 4 , via its receptor B leukotriene receptor 1 (BLT1) and Gαi signaling, increased macrophage expression of inflammatory microRNAs, including miR-155, miR-146b, and miR-125b. LTB 4 -mediated miR-155 generation was attributable to activating protein-1 activation. Furthermore, macrophage transfection with antagomirs against miR-155 and miR-146b prevented both the LTB 4 -mediated decrease in SOCS-1 and increase in MyD88. Transfection with miR-155 and miR-146b mimics decreased SOCS-1 levels, increased MyD88 expression, and restored TLR4 responsiveness in both wild type and LT-deficient macrophages. To our knowledge, our data unveil a heretofore unrecognized role for the GPCR BLT1 in controlling expression of microRNAs that regulate MyD88-dependent activation of macrophages.

Description: IL-37 is a potent inhibitor of innate immunity by shifting the cytokine equilibrium away from excessive inflammation. Psoriasis is thought to be initiated by abnormal interactions between the cutaneous keratinocytes and systemic immune cells, triggering keratinocyte hyperproliferation. In the current study, we assessed IL-37 in two well-known psoriasis models: a human keratinocyte cell line (HaCaT) and the keratin 14 VEGF-A–transgenic mouse model. First, we used the HaCaT cell line, which was transiently transfected with an overexpressing IL-37 vector, and tested the effect of IL-37 on these cells using a mixture of five proinflammatory cytokines. IL-37 was effective in suppressing the production of CXCL8, IL-6, and S100A7, which were highly upregulated by the mixture of five proinflammatory cytokines. Keratin 14 VEGF-A–transgenic mice were treated with plasmid coding human IL-37 sequence–formulated cationic liposomes, and we observed potent immunosuppressive effects over the 18-d period. In this model, we observed reduced systemic IL-10 levels, local IFN- gene transcripts, as well as mild mast cell infiltration into the psoriatic lesions of the mice. Immunohistochemical analysis indicated that IL-37 was expressed by effector memory T cells, as well as macrophages, in human psoriatic plaques. In conclusion, our studies strongly indicate that IL-37 plays a potent immunosuppressive role in the pathogenesis of both experimental psoriasis models in vitro and in vivo by downregulating proinflammatory cytokines. Importantly, our findings highlight new therapeutic strategies that can be designed to use this immunosuppressive anti-inflammatory cytokine in psoriasis and other inflammatory cutaneous diseases.