Publications

Individual Toll-like receptor (TLR) recognizes distinct components derived from pathogens, and triggers inflammatory and immune responses including production of cytokines and chemokines as well as activation of dendritic cells. TLR recruits IL-1 receptor associated kinase (IRAK) via adaptor MyD88, and finally induces activation of NF-κB and MAP kinases. Although MyD88 is essential for the responses to all TLR ligands except for TLR3 ligand, the TLR3- and TLR4-mediated signaling possesses a MyD88-independent pathway, which is activated by another adaptor molecule, TRIF. The TRIF-dependent pathway activates IRF3 phosphorylation via TBK1/IKKi complex, which causes translocation of IRF3 from the cytoplasm to the nucleus, and finally induction of interferon-beta (IFN-β). TLR3 recognizes double-stranded RNA (dsRNA), however, TLR3-deficient cells still responded to dsRNA, indicating the presence of TLR3-independent recognition of dsRNA. Recently retinoic acid-inducible gene-I (RIG-I), a DExD/H box RNA helicase has been suggested to be involved in antiviral responses by recognizing dsRNA in the cytoplasm. We have generated RIG-I knock-out (KO) mice, and found that RIG-I is essential for induction of type I interferons (IFNs) after infection with RNA viruses in fibroblasts and myeloid dendritic cells (DCs). RIG-I induces type I IFNs by activating IRF3 via IkB kinase related kinases. In contrast, plasmacytoid DCs, which produce a vast amount of IFN-α after viral infection, use the TLR system rather than RIG-I for viral detection. Taken together, RIG-I and the TLR system exert antiviral responses in a cell type specific manner.

Induction of resting B cell growth and differentiation requires a complex series of temporally coordinated signals that are initiated on contact with activated helper T cells. These signals complement one another, each rendering the B cell susceptible to factors supporting progressive activation. Here, we demonstrate that soluble CD14 (sCD14) bypasses the physiological sequelae of events that limit B cell activation. B cell growth and differentiation in vitro is induced by both native and recombinant forms of sCD14 at nanomolar concentrations. sCD14-mediated cellular activation does not require membrane CD14 expression, depends on a region of CD14 that is not involved in lipopolysaccharide binding, and requires functional Toll-like receptor 4. Consistent with biological activity of sCD14 in vitro , its administration to neonatal mice enhances Ig secretion. The results presented establish sCD14 as a naturally occurring soluble B cell mitogen of mammalian origin.

Atopic dermatitis (AD) is a pruritic inflammatory skin disease. Because IL-18 directly stimulates T cells and mast cells to release AD-associated molecules, Th2 cytokines, and histamine, we investigated the capacity of IL-18 to induce AD-like inflammatory skin disease by analyzing KIL-18Tg and KCASP1Tg, which skin-specifically overexpress IL-18 and caspase-1, respectively. They spontaneously developed relapsing dermatitis with mastocytosis and Th2 cytokine accumulation accompanied by systemic elevation of IgE and histamine. Stat6-deficient KCASP1Tg displayed undetectable levels of IgE but manifested the same degree of cutaneous changes, whereas IL-18-deficient KCASP1Tg evaded the dermatitis, suggesting that IL-18 causes the skin changes in the absence of IgE/stat6. KIL-18Tg and IL-1-deficient KCASP1Tg took longer to display the lesion than KCASP1Tg. Thus, AD-like inflammation is initiated by overrelease of IL-18 and accelerated by IL-1. Our present study might provide insight into understanding the pathogenesis of and establishing therapeutics for chronic inflammatory skin diseases including AD.

Background & Aims : We tested whether the attenuation of experimental colitis by live probiotic bacteria is due to their immunostimulatory DNA, whether toll-like receptor (TLR) signaling is required, and whether nonviable probiotics are effective. Methods : Methylated and unmethylated genomic DNA isolated from probiotics (VSL-3), DNAse-treated probiotics and Escherichia coli (DH5α) genomic DNA were administered intragastricly (i.g.) or subcutaneously (sc) to mice prior to the induction of colitis. Viable or γ-irradiated probiotics were administered i.g. to wild-type mice and mice deficient in different TLR or in the adaptor protein MyD88, 10 days prior to administration of dextran sodium sulfate (DSS) to their drinking water and for 7 days thereafter. Results : ntragastric and sc administration of probiotic and E. coli DNA ameliorated the severity of DSS-induced colitis, whereas methylated probiotic DNA, calf thymus DNA, and DNase-treated probiotics had no effect. The colitis severity was attenuated to the same extent by i.g. delivery of nonviable γ-irradiated or viable probiotics. Mice deficient in MyD88 did not respond to γ-irradiated probiotics. The severity of DSS-induced colitis in TLR2 and TLR4 deficient mice was significantly decreased by i.g. administration of γ-irradiated probiotics, whereas, in TLR9-deficient mice, γ-irradiated probiotics had no effect. Conclusions : The protective effects of probiotics are mediated by their own DNA rather than by their metabolites or ability to colonize the colon. TLR9 signaling is essential in mediating the anti-inflammatory effect of probiotics, and live microorganisms are not required to attenuate experimental colitis because nonviable probiotics are equally effective.

Experimental autoimmune myocarditis (EAM) is a CD4+ T-cell-mediated mouse model of postviral cardiomyopathy. Activation of interleukin-1 type 1 and Toll-like receptors that share the common downstream adaptor molecule MyD88 is required for disease induction. The specific role of MyD88 in myocarditis, however, is not known.In contrast to control littermates, MyD88(-/-) mice were protected from myocarditis after immunization with alpha-myosin heavy chain-derived peptide (MyHC-alpha) and complete Freund's adjuvant. Disease resistance of MyD88(-/-) mice resulted from impaired expansion of heart-specific CD4+ T cells after immunization. Intrinsic defects of MyD88(-/-) CD4+ T cells were excluded. In contrast, MyD88(-/-) but not MyD88(+/+) primary antigen presenting dendritic cells (DCs) were defective in their capacity to prime CD4+ T cells. This defect mainly resulted from the inability of MyD88(-/-) DCs to release tumor necrosis factor-alpha. The critical role of MyD88 signaling in DCs in the peripheral lymphatic compartments was finally proven by repetitive injection of activated, MyHC-alpha-loaded MyD88(+/+) DCs that fully restored T-cell expansion and myocarditis in MyD88(-/-) mice.Autoimmune myocarditis induction depends on MyD88 signaling in self-antigen presenting cells in the peripheral compartments. We conclude that MyD88 might become a target for prevention of heart-specific autoimmunity and cardiomyopathy.

Eicosanoid production by macrophages is an early response to microbial infection that promotes acute inflammation. The intracellular pathogen Listeria monocytogenes stimulates arachidonic acid release and eicosanoid production from resident mouse peritoneal macrophages through activation of group IVA cytosolic phospholipase A2 (cPLA2alpha). The ability of wild type L. monocytogenes (WTLM) to stimulate arachidonic acid release is partially dependent on the virulence factor listeriolysin O; however, WTLM and L. monocytogenes lacking listeriolysin O (DeltahlyLM) induce similar levels of cyclooxygenase 2. Arachidonic acid release requires activation of MAPKs by WTLM and DeltahlyLM. The attenuated release of arachidonic acid that is observed in TLR2-/- and MyD88-/- macrophages infected with WTLM and DeltahlyLM correlates with diminished MAPK activation. WTLM but not DeltahlyLM increases intracellular calcium, which is implicated in regulation of cPLA2alpha. Prostaglandin E2, prostaglandin I2, and leukotriene C4 are produced by cPLA2alpha+/+ but not cPLA2alpha-/- macrophages in response to WTLM and DeltahlyLM. Tumor necrosis factor (TNF)-alpha production is significantly lower in cPLA2alpha+/+ than in cPLA2alpha-/- macrophages infected with WTLM and DeltahlyLM. Treatment of infected cPLA2alpha+/+ macrophages with the cyclooxygenase inhibitor indomethacin increases TNFalpha production to the level produced by cPLA2alpha-/- macrophages implicating prostaglandins in TNFalpha down-regulation. Therefore activation of cPLA2alpha in macrophages may impact immune responses to L. monocytogenes.

Acute lung injury syndromes remain common causes of morbidity and mortality in adults and children. Cellular and physiologic mechanisms maintaining pulmonary homeostasis during lung injury remain poorly understood. In the present study, the Stat-3 gene was selectively deleted in respiratory epithelial cells by conditional expression of Cre-recombinase under control of the surfactant protein C gene promoter. Cell-selective deletion of Stat-3 in respiratory epithelial cells did not alter prenatal lung morphogenesis or postnatal lung function. However, exposure of adult Stat-3–deleted mice to 95% oxygen caused a more rapidly progressive lung injury associated with alveolar capillary leak and acute respiratory distress. Epithelial cell injury and inflammatory responses were increased in the Stat-3–deleted mice. Surfactant proteins and lipids were decreased or absent in alveolar lavage material. Intratracheal treatment with exogenous surfactant protein B improved survival and lung histology in Stat-3–deleted mice during hyperoxia. Expression of Stat-3 in respiratory epithelial cells is not required for lung formation, but plays a critical role in maintenance of surfactant homeostasis and lung function during oxygen injury.

No abstract is provided for this article.

Modulation of intracellular signaling using cell-permeable polypeptides is a promising technology for future clinical applications. To develop a novel approach to activate innate immune signaling by synthetic polypeptides, we characterized several different polypeptides derived from the caspase recruitment domain (CARD) of IFN-β promoter stimulator 1, each of which localizes to a different subcellular compartment. Of particular interest was, N′-CARD, which consisted of the nuclear localization signal of histone H2B and the IFN-β promoter stimulator 1CARD and which localized to the nucleus. This polypeptide led to a strong production of type I IFNs and molecular and genetic analyses showed that nuclear DNA helicase II is critically involved in this response. N′-CARD polypeptide fused to a protein transduction domain (N′-CARD-PTD) readily transmigrated from the outside to the inside of the cell and triggered innate immune signaling. Administration of N′-CARD-PTD polypeptide elicited production of type I IFNs, maturation of bone marrow-derived dendritic cells, and promotion of vaccine immunogenicity by enhancing Ag-specific Th1-type immune responses, thereby protecting mice from lethal influenza infection and from outgrowth of transplanted tumors in vivo. Thus, our results indicate that the N′-CARD-PTD polypeptide belongs to a new class of vaccine adjuvant that directly triggers intracellular signal transduction by a distinct mechanism from those engaged by conventional vaccine adjuvants, such as TLR ligands.

Viral infection and stimulation with lipopolysaccharide (LPS) or double stranded RNA (dsRNA) induce phosphorylation of interferon (IFN) regulatory factor (IRF)-3 and its translocation to the nucleus, thereby leading to the IFN-β gene induction. Recently, two IκB kinase (IKK)–related kinases, inducible IκB kinase (IKK-i) and TANK-binding kinase 1 (TBK1), were suggested to act as IRF-3 kinases and be involved in IFN-β production in Toll-like receptor (TLR) signaling and viral infection. In this work, we investigated the physiological roles of these kinases by gene targeting. TBK1-deficient embryonic fibroblasts (EFs) showed dramatic decrease in induction of IFN-β and IFN-inducible genes in response to LPS or dsRNA as well as after viral infection. However, dsRNA-induced expression of these genes was residually detected in TBK1-deficient cells and intact in IKK-i–deficient cells, but completely abolished in IKK-i/TBK1 doubly deficient cells. IRF-3 activation, in response not only to dsRNA but also to viral infection, was impaired in TBK1-deficient cells. Together, these results demonstrate that TBK1 as well as, albeit to a lesser extent, IKK-i play a crucial role in the induction of IFN-β and IFN-inducible genes in both TLR-stimulated and virus-infected EFs.

AM14 B cells are a prototype for those low affinity autoreactive B cells that routinely mature as naïve cells in peripheral lymphoid tissues. These cells express a transgene-encoded receptor specific for IgG2a and can be effectively activated by immune complexes that incorporate either mammalian DNA or mammalian RNA that has been released from dead or dying cells. Activation depends on the ability of the B-cell receptor to deliver antigen to an internal vesicular compartment containing either Toll-like receptor-9 (TLR9) or TLR7. Since TLR9 and TLR7 are thought to recognize microbial DNA and RNA preferentially, it is important to determine under what conditions mammalian DNA and RNA become effective TLR ligands, and whether the determining factor is delivery or structure. This issue has been addressed by using IgG2a mAbs to deliver immune complexes preloaded with defined fragments of DNA or RNA, or by using modified ODNs/ORNs. The data demonstrate that only certain nucleic acid sequences or structures can induce autoreactive B-cell proliferation, even when delivery to the appropriate TLR compartment is facilitated by uptake through the B-cell receptor (BCR).

Abstract Mutations of HFE are associated with hereditary hemochromatosis, but their influence on host susceptibility to infection is incompletely understood. We report that mice lacking one or both Hfe alleles are protected from septicemia with Salmonella Typhimurium, displaying prolonged survival and improved control of bacterial replication. This increased resistance is paralleled by an enhanced production of the enterochelin-binding peptide lipocalin-2 (Lcn2), which reduces the availability of iron for Salmonella within Hfe-deficient macrophages. Accordingly, Hfe −/− Lcn2 −/− macrophages are unable to efficiently control the infection or to withhold iron from intracellular Salmonella. Correspondingly, the protection conferred by the Hfe defect is abolished in Hfe −/− mice infected with enterochelin-deficient Salmonella as well as in Hfe −/− Lcn2 −/− mice infected with wild-type bacteria. Thus, by induction of the iron-capturing peptide Lcn2, absence of functional Hfe confers host resistance to systemic infection with Salmonella, thereby providing an evolutionary advantage which may account for the high prevalence of genetic hemochromatosis.

Epstein-Barr virus (EBV) is associated with several human diseases including infectious mononucleosis and nasopharyngeal carcinoma. EBV-encoded latent membrane protein 1 (LMP1) is oncogenic and indispensable for cellular transformation caused by EBV. Expression of LMP1 in host cells constitutively activates both the c-Jun N-terminal kinase (JNK) and NF-kappaB pathways, which contributes to the oncogenic effect of LMP1. However, the underlying signaling mechanisms are not very well understood. Based mainly on overexpression studies with various dominant-negative constructs, LMP1 was generally thought to functionally mimic members of the tumor necrosis factor (TNF) receptor superfamily in signaling. In contrast to the prevailing paradigm, using embryonic fibroblasts from different knockout mice and the small interfering RNA technique, we find that the LMP1-mediated JNK pathway is distinct from those mediated by either TNF-alpha or interleukin-1. Moreover, we have further elucidated the LMP1-mediated JNK pathway by demonstrating that LMP1 selectively utilizes TNF receptor-associated factor 6, TAK1/TAB1, and c-Jun N-terminal kinase kinases 1 and 2 to activate JNK.

MyD88 is a key adaptor molecule in innate resistance, engaged in most Toll-like receptor, as well as IL-1 and IL-18, signalling. Here, we analyzed the role of MyD88 in innate resistance during infection with vesicular stomatitis virus (VSV) using myd88(-/-) mice. We found an increased susceptibility to VSV in myd88(-/-) mice, which was not explained by reduced type I IFN or neutralizing antibody responses. Susceptibility of myd88(-/-) mice correlated with impaired recruitment of immune cells to the site of infection. In the absence of MyD88 signalling, VSV rapidly spread to the spinal cord and brain causing lethal encephalitis.

In Newman et al., 2008, Figure 2 contained duplicate profiles in Fig 2H and 2 J. The correct Figure 2E to 2J is shown here. This error doesn't have any influence on the data discussed and conclusions drawn in the article. Figure 2 (E–J) FACS profiles of dual staining for Annexin V and propidium iodide to determine apoptosis and necrosis. Early and late passage G1-mTERC +/+ and G1-mTERC −/− MEFs were exposed to sodium arsenite (3.0 µg/ml) for 48 h and subjected to Annexin V staining. (E) Untreated mTERC +/+ MEFs; (F) arsenite-treated mTERC +/+ MEFs; (G) mTERC −/− (EP) MEFs; (H) arsenite-treated mTERC −/− (EP) MEFs; (I) untreated mTERC −/− (LP) MEFs; (J) arsenite-treated mTERC −/− (LP) MEFs. Annexin V staining in early apoptosis and dual staining in the late apoptosis in mTERC −/− (EP) MEFs were higher as compared to the mTERC +/+ MEFs at both early (data not shown) and late passages (F). Arsenite-treated mTERC −/− (EP) MEFs showed greater number of late apoptotic cells when compared to the untreated mTERC −/− (EP) MEFs and mTERC +/+ MEFs (H). Arsenite-treated G1-mTERC −/− (LP) MEFs displayed greater cell death by apoptosis (J).