Fas ligation induces IL-1beta-dependent maturation and IL-1beta-independent survival of dendritic cells: different roles of ERK and NF-kappaB signaling pathways

An MRI-visible immunoadjuvant based on hollow Gd2O3 nanospheres for cancer immunotherapy

Hollow Gd2O3 nanospheres significantly promote the cellular uptake of a tumor antigen by antigen presenting cells, exhibit pH-dependent alteration of the MR signal intensity and markedly enhance the antitumor immunity. Hollow Gd2O3 nanospheres are promising as magnetic resonance imaging (MRI)-visible cancer immunoadjuvants for cancer immunotherapy.

Fas Signaling in Dendritic Cells Mediates Th2 Polarization in HDM-Induced Allergic Pulmonary Inflammation

Fas-Fas ligand (FasL) signaling plays an important role in the development of allergic inflammation, but the cellular and molecular mechanisms are still not well known. By using the bone marrow-derived dendritic cell (BMDC) transfer-induced pulmonary inflammation model, we found that house dust mite (HDM)-stimulated FAS-deficient BMDCs induced higher Th2-mediated allergic inflammation, associated with increased mucus production and eosinophilic inflammation. Moreover, FAS-deficient BMDCs promoted Th2 cell differentiation upon HDM stimulation in vitro. Compared to wild-type BMDCs, the Fas-deficient BMDCs had increased ERK activity and decreased IL-12 production upon HDM stimulation. Inhibition of ERK activity could largely increase IL-12 production, consequently restored the increased Th2 cytokine expression of OT-II CD4⁺ T cells activated by Fas-deficient BMDCs. Thus, our results uncover an important role of DC-specific Fas signaling in Th2 differentiation and allergic inflammation, and modulation of Fas signaling in DCs may offer a useful strategy for the treatment of allergic inflammatory diseases.

Beyond Cell Death: New Functions for TNF Family Cytokines in Autoimmunity and Tumor Immunotherapy

Originally discovered as an inducer of apoptosis, the TNF-family receptor Fas (CD95, APO-1, TNFRSF6) has more recently been found to have functions beyond cell death, including T cell co-stimulation and promoting terminal differentiation of CD4⁺ and CD8⁺ T cells. Other TNF family members also discovered as apoptosis inducers, such as TRAIL (APO-2L, TNFSF10), can promote inflammation through caspase-8. Surprisingly, non-apoptotic signaling through Fas can protect from the autoimmunity seen in Fas deficiency independently from the cell death inducing functions of the receptor. Non-apoptotic Fas signaling can induce tumor cell growth and migration, and impair the efficacy of T cell adoptive immunotherapy. Blocking of non-apoptotic functions of these receptors may be a novel strategy to regulate autoimmunity and inflammation, and enhance antitumor immunity.

Preclinical Development of EBI-005: An IL-1 Receptor-1 Inhibitor for the Topical Ocular Treatment of Ocular Surface Inflammatory Diseases

OBJECTIVE

Topical interleukin (IL)-1 receptor (R)1 blockade is therapeutically active in reducing signs and symptoms of dry eye disease. Herein, we describe in vitro and in vivo nonclinical Investigational New Drug (IND)-enabling studies of EBI-005, a novel protein chimera of IL-1β and IL-1 receptor antagonist (IL-1Ra or anakinra) that potently binds IL-1R1 and blocks signaling. These studies provide an assessment of receptor affinity, drug bioavailability, immunogenic response, safety, and tolerability in mice and rabbits.

METHODS

In vitro and in silico along with Good Laboratory Practices (GLP) and non-GLP in vivo studies in mice and rabbits assessed the topical ocular and systemic immunogenicity and toxicology of EBI-005. Animals were treated with EBI-005 once daily subcutaneously or four times daily by topical ocular administration for up to 6 weeks (with 2-week recovery phase).

RESULTS

EBI-005 has 500 times higher affinity than anakinra to IL-1R1. Predictive immunogenicity testing suggested that EBI-005 is not more immunogenic. Systemic bioavailability of EBI-005 is low (1.4% in mice and 0.2% in rabbits) after topical ocular administration. EBI-005 penetrated into the anterior ocular tissues within 15 min of topical ocular administration. However, it is low or undetectable after 4 hr and does not form a depot after repeated topical ocular administration. EBI-005 was safe and well tolerated, and exposure to drug was maintained despite an antidrug antibody response after systemic administration, based on IND-enabling toxicology and safety pharmacology studies.

CONCLUSIONS

Ocular doses of EBI-005 at 50 mg/mL in mice and rabbits totaling 0.15 mg/eye in mice and 1.5 mg/eye in rabbits, administered 4 times daily, did not produce adverse effects, and demonstrated excellent bioavailability in target tissues with low systemic exposure. In addition, immunogenic response to the drug did not cause adverse effects or diminish the drug's activity in most cases. The results support drug administration of the highest anticipated human clinical study dose of a 20 mg/mL solution (40 μL 3 times daily in each eye).

Glucocorticoids promote apoptosis of proinflammatory monocytes by inhibiting ERK activity

Glucocorticoids (GCs) are potent anti-inflammatory drugs whose mode of action is complex and still debatable. One likely cellular target of GCs are monocytes/macrophages. The role of GCs in monocyte survival is also debated. Although both granulocyte macrophage-colony stimulating factor (GM-CSF) and macrophage-CSF (M-CSF) are important regulators of macrophage lineage functions including their survival, the former is often associated with proinflammatory functions while the latter is important in lineage homeostasis. We report here that the GC, dexamethasone, induces apoptosis in GM-CSF-treated human monocytes while having no impact on M-CSF-induced monocyte survival. To understand how GCs, GM-CSF, and M-CSF are regulating monocyte survival and other functions during inflammation, we firstly examined the transcriptomic changes elicited by these three agents in human monocytes, either acting alone or in combination. Transcriptomic and Ingenuity pathway analyses found that dexamethasone differentially modulated dendritic cell maturation and TREM1 signaling pathways in GM-CSF-treated and M-CSF-treated monocytes, two pathways known to be regulated by ERK1/2 activity. These analyses led us to provide evidence that the GC inhibits ERK1/2 activity selectively in GM-CSF-treated monocytes to induce apoptosis. It is proposed that this inhibition of ERK1/2 activity leads to inactivation of p90 ribosomal-S6 kinase and Bad dephosphorylation leading in turn to enhanced caspase-3 activity and subsequent apoptosis. Furthermore, pharmacological inhibition of GC receptor activity restored the ERK1/2 signaling and prevented the GC-induced apoptosis in GM-CSF-treated monocytes. Increased tissue macrophage numbers, possibly from enhanced survival due to mediators such as GM-CSF, can correlate with inflammatory disease severity; also reduction in these numbers can correlate with the therapeutic benefit of a number of agents, including GCs. We propose that the ERK1/2 signaling pathway promotes survival of GM-CSF-treated proinflammatory monocytes, which can be selectively targeted by GCs as a novel mechanism to reduce local monocyte/macrophage numbers and hence inflammation.

HIF-1α inhibitor echinomycin reduces acute graft-versus-host disease and preserves graft-versus-leukemia effect

BACKGROUND

Acute graft-versus-host disease (aGVHD) remains a major obstacle against favorable clinical outcomes following allogeneic hematopoietic stem cell transplantation (allo-HSCT). T helper cells including Th17 play key roles in aGVHD pathogenesis. Donor regulatory T cell (Tregs) adoptive therapy reduces aGVHD without weakening graft-versus-leukemia effect (GVL) in both mouse and human, although the purification and ex vivo expansion of Tregs in clinical scenarios remain costly and technically demanding. Hypoxia-inducible factor 1 alpha (HIF-1α) is a key molecule switch that attenuates Treg but promotes Th17 development. However, whether pharmacological inhibition of HIF-1α reduces aGVHD via increasing Treg development and diminishing Th17 responses remains unexplored.

METHODS

By using alloantigen-specific mixed lymphocyte culture and murine models of aGVHD and GVL, we evaluated the impacts of HIF-1α inhibition by echinomycin on the alloantigen-specific CD4 T cell responses ex vivo, as well as on aGVHD and GVL effect following allo-HSCT.

RESULTS

Ex vivo echinomycin treatment resulted in increased number of Tregs in the culture as well as reduced alloantigen-specific Th17 and Th1 responses. In vivo echinomycin treatment reduced GVHD scores and prolonged survival of mice following allo-HSCT, which is associated with increased number of donor Tregs and reduced number of Th17 and Th1 in lymphoid tissues. In murine model of leukemia, echinomycin treatment preserved GVL effect and prolonged leukemia free survival following allo-HSCT.

CONCLUSIONS

Echinomycin treatment reduces aGVHD and preserves GVL effect via increasing donor Treg development and diminishing alloantigen-specific Th17 and Th1 responses following allo-HSCT, presumably via direct inhibition of HIF-1α that results in preferential Treg differentiation during alloantigen-specific CD4 T cell responses. These findings highlight pharmacological inhibition of HIF-1α as a promising strategy in GVHD prophylaxis.

IL-36 receptor is expressed by human blood and intestinal T lymphocytes and is dose-dependently activated via IL-36β and induces CD4+ lymphocyte proliferation

We show that IL-36R is expressed by T (CD4+ and CD8+) and B (CD19+) lymphocytes in human blood and also by CD4+ T lymphocytes in the intestinal lamina propria. IL-36R protein was mostly stored in the cytoplasm of CD4 lymphocytes and B cells, during steady state conditions and the greatest expression of IL-36R mRNA was measured in CD4+ (T helper) lymphocytes. IL-36 β, which functions via IL-36R induced rapid and significant (P<0.05) proliferation of CD4+ lymphocytes, within 48h. IL-36R expression was also maintained on the surface of circulating CD4+ lymphocytes which enter the intestinal lamina propria. In conclusion our study is the first to show that (1) all human blood lymphocytes express IL-36R; (2) IL-36R expression is maintained by circulating CD4+ lymphocytes which enter the intestinal lamina propria and (3) IL-36R/IL-36 β induces rapid CD4 lymphocyte proliferation. The possible significance of these results in the context of human disease is discussed.

Use of functional genomics to understand replication deficient poxvirus-host interactions

High-throughput genomics technologies are currently being used to study a wide variety of viral infections, providing insight into which cellular genes and pathways are regulated after infection, and how these changes are related, or not, to efficient elimination of the pathogen. This article will focus on how gene expression studies of infections with non-replicative poxviruses currently used as vaccine vectors provide a global perspective of the molecular events associated with the viral infection in human cells. These high-throughput genomics approaches have the potential to lead to the identification of specific new properties of the viral vector or novel cellular targets that may aid in the development of more effective pox-derived vaccines and antivirals.

Th1 cytokine-based immunotherapy for cancer

Cytokine-based immunotherapy is executed by harnessing cytokines to activate the immune system to suppress tumors. Th1-type cytokines including IL-1, IL-2, IL-12 and granulocyte-macrophage colony-stimulating factor are potent stimulators of Th1 differentiation and Th1-based antitumor response. Many preclinical studies demonstrated the antitumor effects of Th1 cytokines but their clinical efficacy is limited. Multiple factors influence the efficacy of immunotherapy for tumors. For instance immunosuppressive cells in the tumor microenvironment can produce inhibitory cytokines which suppress antitumor immune response. Most studies on cytokine immunotherapy focused on how to boost Th1 response; many studies combined cytokine-based therapy with other treatments to reverse immunosuppression in tumor microenvironment. In addition, cytokines have pleiotropic functions and some cytokines show paradoxical activities under different settings. Better understanding the physiological and pathological functions of cytokines helps clinicians to design Th1-based cancer therapy in clinical practice.

Caspase-8 acts as a molecular rheostat to limit RIPK1- and MyD88-mediated dendritic cell activation

Caspase-8, an executioner enzyme in the death receptor pathway, was shown to initiate apoptosis and suppress necroptosis. In this study, we identify a novel, cell death-independent role for caspase-8 in dendritic cells (DCs): DC-specific expression of caspase-8 prevents the onset of systemic autoimmunity. Failure to express caspase-8 has no effect on the lifespan of DCs but instead leads to an enhanced intrinsic activation and, subsequently, more mature and autoreactive lymphocytes. Uncontrolled TLR activation in a RIPK1-dependent manner is responsible for the enhanced functionality of caspase-8-deficient DCs, because deletion of the TLR-signaling mediator, MyD88, ameliorates systemic autoimmunity induced by caspase-8 deficiency. Taken together, these data demonstrate that caspase-8 functions in a cell type-specific manner and acts uniquely in DCs to maintain tolerance.

Activated cytotoxic lymphocytes promote tumor progression by increasing the ability of 3LL tumor cells to mediate MDSC chemoattraction via Fas signaling

The Fas/FasL system transmits intracellular apoptotic signaling, inducing cell apoptosis. However, Fas signaling also exerts non-apoptotic functions in addition to inducing tumor cell apoptosis. For example, Fas signaling induces lung cancer tumor cells to produce prostaglandin E2 (PGE2) and recruit myeloid-derived suppressor cells (MDSCs). Activated cytotoxic T lymphocytes (CTLs) induce and express high levels of FasL, but the effects of Fas activation initiated by FasL in CTLs on apoptosis-resistant tumor cells remain largely unclear. We purified activated CD8(+) T cells from OT-1 mice, evaluated the regulatory effects of Fas activation on tumor cell escape and investigated the relevant mechanisms. We found that CTLs induced tumor cells to secrete PGE2 and increase tumor cell-mediated chemoattraction of MDSCs via Fas signaling, which was favorable to tumor growth. Our results indicate that CTLs may participate in the tumor immune evasion process. To the best of our knowledge, this is a novel mechanism by which CTLs play a role in tumor escape. Our findings implicate a strategy to enhance the antitumor immune response via reduction of negative immune responses to tumors promoted by CTLs through Fas signaling.

Blockade of Fas signaling in breast cancer cells suppresses tumor growth and metastasis via disruption of Fas signaling-initiated cancer-related inflammation

Mechanisms for cancer-related inflammation remain to be fully elucidated. Non-apoptotic functions of Fas signaling have been proposed to play an important role in promoting tumor progression. It has yet to be determined if targeting Fas signaling can control tumor progression through suppression of cancer-related inflammation. In the current study we found that breast cancer cells with constitutive Fas expression were resistant to apoptosis induction by agonistic anti-Fas antibody (Jo2) ligation or Fas ligand cross-linking. Higher expression of Fas in human breast cancer tissue has been significantly correlated with poorer prognosis in breast cancer patients. To determine whether blockade of Fas signaling in breast cancer could suppress tumor progression, we prepared an orthotopic xenograft mouse model with mammary cancer cells 4T1 and found that blockade of Fas signaling in 4T1 cancer cells markedly reduced tumor growth, inhibited tumor metastasis in vivo, and prolonged survival of tumor-bearing mice. Mechanistically, blockade of Fas signaling in cancer cells significantly decreased systemic or local recruitment of myeloid derived suppressor cells (MDSCs) in vivo. Furthermore, blockade of Fas signaling markedly reduced IL-6, prostaglandin E2 production from breast cancer cells by impairing p-p38, and activity of the NFκB pathway. In addition, administration of a COX-2 inhibitor and anti-IL-6 antibody significantly reduced MDSC accumulation in vivo. Therefore, blockade of Fas signaling can suppress breast cancer progression by inhibiting proinflammatory cytokine production and MDSC accumulation, indicating that Fas signaling-initiated cancer-related inflammation in breast cancer cells may be a potential target for treatment of breast cancer.

Fas signal promotes the immunosuppressive function of regulatory dendritic cells via the ERK/β-catenin pathway

Dendritic cells (DCs) play important roles in the initiation of immune response and also in the maintenance of immune tolerance. Now, many kinds of regulatory DCs with different phenotypes have been identified to suppress immune response and contribute to the control of autoimmune diseases. However, the mechanisms by which regulatory DCs can be regulated to exert the immunosuppressive function in the immune microenvironment remain to be fully investigated. In addition, how T cells, once activated, can feedback affect the function of regulatory DCs during immune response needs to be further identified. We previously identified a unique subset of CD11b(hi)Ia(low) regulatory DCs, differentiated from mature DCs or hematopoietic stem cells under a stromal microenvironment in spleen and liver, which can negatively regulate immune response in a feedback way. Here, we show that CD11b(hi)Ia(low) regulatory DCs expressed high level of Fas, and endothelial stromal cell-derived TGF-β could induce high expression of Fas on regulatory DCs via ERK activation. Fas ligation could promote regulatory DCs to inhibit CD4(+) T cell proliferation more significantly. Furthermore, Fas ligation preferentially induced regulatory DCs to produce IL-10 and IP-10 via ERK-mediated inactivation of GSK-3 and subsequent up-regulation of β-catenin. Interestingly, activated T cells could promote regulatory DCs to secrete more IL-10 and IP-10 partially through FasL. Therefore, our results demonstrate that Fas signal, at least from the activated T cells, can promote the immunosuppressive function of Fas-expressing regulatory DCs, providing a new manner for the regulatory DCs to regulate adaptive immunity.

Fas-mediated inflammatory response in Listeria monocytogenes infection

The molecular mechanisms of Fas (CD95/Apo-1)-mediated apoptosis are increasingly understood. However, the role of Fas-mediated production of proinflammatory cytokines such as IL-18 and IL-1β in bacterial infection is unclear. We demonstrate the importance of Fas-mediated signaling in IL-18/IL-1β production postinfection with Listeria monocytogenes without the contribution of caspase-1 inflammasome. IL-18/IL-1β production in L. monocytogenes-infected peritoneal exudate cells from Fas-deficient mice was lower than those from wild type mice, indicating that Fas signaling contributes to cytokine production. L. monocytogenes infection induced Fas ligand expression on NK cells, which stimulates Fas expressed on the infected macrophages, leading to the production of IL-18/IL-1β. This was independent of caspase-1, caspase-11, and nucleotide-binding domain and leucine-rich repeat-containing receptors (NLRs) such as Nlrp3 and Nlrc4, but dependent on apoptosis-associated speck-like protein containing a caspase recruitment domain. Wild type cells exhibited caspase-8 activation, whereas Fas-deficient cells did not. L. monocytogenes-induced caspase-8 activation was abrogated by inhibitor for intracellular reactive oxygen species, N-acetyl-L-cysteine. L. monocytogenes-infected macrophages produced type-I IFNs such as IFN-β1, which was required for Il18 gene expression. Thus, Fas signaling regulates innate inflammatory cytokine production in L. monocytogenes infection.

Suppressors of cytokine signaling promote Fas-induced apoptosis through downregulation of NF-κB and mitochondrial Bfl-1 in leukemic T cells

Suppressors of cytokine signaling (SOCS) are known as negative regulators of cytokine- and growth factor-induced signal transduction. Recently they have emerged as multifunctional proteins with regulatory roles in inflammation, autoimmunity, and cancer. We have recently reported that SOCS1 has antiapoptotic functions against the TNF-α- and the hydrogen peroxide-induced T cell apoptosis through the induction of thioredoxin, which protects protein tyrosine phosphatases and attenuates Jaks. In this study, we report that SOCS, on the contrary, promote death receptor Fas-mediated T cell apoptosis. The proapoptotic effect of SOCS1 was manifested with increases in Fas-induced caspase-8 activation, truncated Bid production, and mitochondrial dysfunctions. Both caspase-8 inhibitor c-Flip and mitochondrial antiapoptotic factor Bfl-1 were significantly reduced by SOCS1. These proapoptotic responses were not associated with changes in Jak or p38/Jnk activities but were accompanied with downregulation of NF-κB and NF-κB-dependent reporter gene expression. Indeed, p65 degradation via ubiquitination was accelerated in SOCS1 overexpressing cells, whereas it was attenuated in SOCS1 knockdown cells. With high NF-κB levels, the SOCS1-ablated cells displayed resistance against Fas-induced apoptosis, which was abrogated upon siBfl-1 transfection. The results indicate that the suppression of NF-κB-dependent induction of prosurvival factors, such as Bfl-1 and c-Flip, may serve as a mechanism for SOCS action to promote Fas-mediated T cell apoptosis. SOCS3 exhibited a similar proapoptotic function. Because both SOCS1 and SOCS3 are induced upon TCR stimulation, SOCS would play a role in activation-induced cell death by sensitizing activated T cells toward Fas-mediated apoptosis to maintain T cell homeostasis.

Hepatic stellate cells undermine the allostimulatory function of liver myeloid dendritic cells via STAT3-dependent induction of IDO

Hepatic stellate cells (HSCs) are critical for hepatic wound repair and tissue remodeling. They also produce cytokines and chemokines that may contribute to the maintenance of hepatic immune homeostasis and the inherent tolerogenicity of the liver. The functional relationship between HSCs and the professional migratory APCs in the liver, that is, dendritic cells (DCs), has not been evaluated. In this article, we report that murine liver DCs colocalize with HSCs in vivo under normal, steady-state conditions, and cluster with HSCs in vitro. In vitro, HSCs secrete high levels of DC chemoattractants, such as MΙP-1α and MCP-1, as well as cytokines that modulate DC activation, including TNF-α, IL-6, and IL-1β. Culture of HSCs with conventional liver myeloid (m) DCs resulted in increased IL-6 and IL-10 secretion compared with that of either cell population alone. Coculture also resulted in enhanced expression of costimulatory (CD80, CD86) and coinhibitory (B7-H1) molecules on mDCs. HSC-induced mDC maturation required cell-cell contact and could be blocked, in part, by neutralizing MΙP-1α or MCP-1. HSC-induced mDC maturation was dependent on activation of STAT3 in mDCs and, in part, on HSC-secreted IL-6. Despite upregulation of costimulatory molecules, mDCs conditioned by HSCs demonstrated impaired ability to induce allogeneic T cell proliferation, which was independent of B7-H1, but dependent upon HSC-induced STAT3 activation and subsequent upregulation of IDO. In conclusion, by promoting IDO expression, HSCs may act as potent regulators of liver mDCs and function to maintain hepatic homeostasis and tolerogenicity.

CD95 signaling in colorectal cancer

CD95 and its ligand (CD95L) are widely expressed in colorectal tumors, but their role in shaping tumor behavior is unclear. CD95 activation on tumor cells can lead to apoptosis, while CD95L attracts neutrophils, suggesting a function in tumor suppression. However, CD95 can also promote tumorigenesis, at least in part by activating non-apoptotic signaling pathways that stimulate tumor cell proliferation, invasion and survival. In addition, CD95 signaling in stromal cells and tumor-infiltrating inflammatory cells has to be taken into account when addressing the function of CD95 and its ligand in colorectal tumor biology. We present a model in which the tumor-suppressing and tumor-promoting activities of CD95/CD95L together determine colorectal tumor behavior. We also discuss how these multiple activities are changing our view of CD95 and CD95L as potential therapeutic targets in the treatment of colorectal cancer. We conclude that locking CD95 in apoptosis-mode may be a more promising anti-cancer strategy than simply inhibiting or stimulating CD95.

Expression of IL-1Rrp2 by human myelomonocytic cells is unique to DCs and facilitates DC maturation by IL-1F8 and IL-1F9

We report for the first time that expression of the novel IL-1 cytokine receptor IL-1Rrp2 (IL-1R6) is unique to DCs within the human myelomonocytic lineage. IL-1Rrp2 was expressed by monocyte-derived dendritic cells (MDDCs) which was dose-dependently increased by IL-4 and correlated with increased numbers of differentiated MDDCs. Human plasmacytoid DCs also express IL-1Rrp2 but the receptor is not expressed by either myeloid DC type 1 (mDC1) or mDC2 cells. We also show that IL-1F8 or IL-1F9 cytokines, which signal through IL-1Rrp2, induce maturation of MDDCs, as measured by increased expression of HLA-DR and CD83 and decreased expression of CD1a. Furthermore, IL-1F8 stimulated increased CD40 and CD80 expression and IL-18 and IL-12 p70 production by MDDCs, which induced proliferation of IFN-γ-producing CD3(+) lymphocytes (indicative of inflammatory Th1 subsets). IL-1F8 and IL-1F2 were equipotent in their ability to stimulate IL-18 secretion from MDDCs but IL-1F8 was not as potent as IL-1F2 in stimulating secretion of IL-12p70 from MDDCs or inducing lymphocyte proliferation Therefore, IL-1Rrp2 expression by some DC subsets may have an important function in the human immune response in vivo via its role in differentiation of inflammatory Th1 lymphocytes.

The combination of early and rapid type I IFN, IL-1α, and IL-1β production are essential mediators of RNA-like adjuvant driven CD4+ Th1 responses

There is a growing need for novel vaccine adjuvants that can provide safe and potent T-helper type 1 (Th1) activity. RNA-like immune response modifiers (IRMs) are candidate T-cell adjuvants that skew acquired immune responses towards a Th1 phenotype. We set out to delineate the essential signaling pathways by which the RNA-like IRMs, resiquimod (R-848) and polyinosinic:polycytidylic acid (poly I:C), augment CD4+ T-helper 1 (Th1) responses. Highly purified murine conventional dendritic cells (cDCs) and conventional CD4+ T-cells were co-cultured in allogeneic and MHC congenic mixed leukocyte reactions. The activation of CD4+ Th1 cells was examined utilizing cells from mice deficient in specific RNA-sensing pattern recognition receptors and signaling mediators. R-848 and poly I:C stimulation of Type I interferon production and signaling in cDCs was essential but not sufficient for driving CD4+ Th1 responses. The early and rapid production of IL-1α and IL-1β was equally critical for the optimal activation of Th1 CD4+ T-cells. R-848 activation of Toll-like receptor 7/MyD88-dependent signaling in cDCs led to a rapid upregulation of pro-IL-1α and pro-IL-1β production compared to poly I:C activation of MyD88-independent signaling pathways. The in vitro data show that CD4+ T-cell adjuvant activity of RNA-like IRMs is mediated by a critical combination of early and rapid Type I interferon, IL-1α and IL-1β production. These results provide important insights into the key signaling pathways responsible for RNA-like IRM CD4+ Th1 activation. A better understanding of the critical signaling pathways by which RNA-like IRMs stimulate CD4+ Th1 responses is relevant to the rational design of improved vaccine adjuvants.

Inhibition of Fas ligand in NOD mice unmasks a protective role for IL-10 against insulitis development

Type 1 diabetes mellitus (T1D) is an autoimmune disease caused by the destruction of pancreatic insulin-producing β cells by autoreactive T cells early in life. Despite daily insulin injections, patients typically develop cardiovascular and other complications; and intensive efforts are being directed toward identifying therapeutic targets to prevent the disease without directly impinging on the host defense. Fas ligand (FasL) is one potential target. Fas-FasL interactions primarily regulate T-cell homeostasis, not activation. Nevertheless, spontaneous gene mutation of Fas (called lpr mutation) or FasL (called the gld mutation) prevents autoimmune diabetes in nonobese diabetic (NOD) mice, the widely used model for T1D. Furthermore, although homozygous gld mutations cause age-dependent lymphoproliferation, limiting the gld mutation to one allele (NOD-gld/+) or treating NOD-wild-type mice with FasL-neutralizing monoclonal antibody completely prevents the disease development without causing lymphoproliferation or immune suppression. Herein, we show that the heterozygous gld mutation inhibits the accumulation of diabetogenic T cells in the pancreas, without interfering with their proliferation and expansion in the draining pancreatic lymph nodes. Pancreata from NOD-gld/+ mice contained B cells that expressed CD5 and produced IL-10, which was critical for maintenance of the disease resistance because its neutralization with an IL-10 receptor-blocking monoclonal antibody allowed accumulation of CD4 T cells in the pancreas and led to insulitis development. The results provide novel insights into the pathogenesis of T1D that could have important therapeutic implications.

Immunogenic profiling in mice of a HIV/AIDS vaccine candidate (MVA-B) expressing four HIV-1 antigens and potentiation by specific gene deletions

Background

The immune parameters of HIV/AIDS vaccine candidates that might be relevant in protection against HIV-1 infection are still undefined. The highly attenuated poxvirus strain MVA is one of the most promising vectors to be use as HIV-1 vaccine. We have previously described a recombinant MVA expressing HIV-1 Env, Gag, Pol and Nef antigens from clade B (referred as MVA-B), that induced HIV-1-specific immune responses in different animal models and gene signatures in human dendritic cells (DCs) with immunoregulatory function.

Methodology/Principal Findings

In an effort to characterize in more detail the immunogenic profile of MVA-B and to improve its immunogenicity we have generated a new vector lacking two genes (A41L and B16R), known to counteract host immune responses by blocking the action of CC-chemokines and of interleukin 1β, respectively (referred as MVA-B ΔA41L/ΔB16R). A DNA prime/MVA boost immunization protocol was used to compare the adaptive and memory HIV-1 specific immune responses induced in mice by the parental MVA-B and by the double deletion mutant MVA-B ΔA41L/ΔB16R. Flow cytometry analysis revealed that both vectors triggered HIV-1-specific CD4⁺ and CD8⁺ T cells, with the CD8⁺ T-cell compartment responsible for >91.9% of the total HIV-1 responses in both immunization groups. However, MVA-B ΔA41L/ΔB16R enhanced the magnitude and polyfunctionality of the HIV-1-specific CD4⁺ and CD8⁺ T-cell immune responses. HIV-1-specific CD4⁺ T-cell responses were polyfunctional and preferentially Env-specific in both immunization groups. Significantly, while MVA-B induced preferentially Env-specific CD8⁺ T-cell responses, MVA-B ΔA41L/ΔB16R induced more GPN-specific CD8⁺ T-cell responses, with an enhanced polyfunctional pattern. Both vectors were capable of producing similar levels of antibodies against Env.

Conclusions/Significance

These findings revealed that MVA-B and MVA-B ΔA41L/ΔB16R induced in mice robust, polyfunctional and durable T-cell responses to HIV-1 antigens, but the double deletion mutant showed enhanced magnitude and quality of HIV-1 adaptive and memory responses. Our observations are relevant in the immune evaluation of MVA-B and on improvements of MVA vectors as HIV-1 vaccines.

Lipopolysaccharide-induced expression of TRAIL promotes dendritic cell differentiation

Tumour necrosis factor-related apoptosis inducing ligand (TRAIL) is a death-inducing cytokine whose physiological function is not well understood. Here, we show that TRAIL has a role in programming human dendritic cell (DC) differentiation. TRAIL expression was strongly induced in DCs upon stimulation with lipopolysaccharide (LPS) or Polyinosine-polycytidylic acid (poly(I:C)) stimulation. Blockade of TRAIL with neutralizing antibody partially inhibited LPS-induced up-regulation of co-stimulatory molecules and the expression of inflammatory cytokines including interleukin-12 (IL-12) p70. In addition, neutralization of TRAIL in LPS-treated DCs inhibited the DC-driven differentiation of T cells into interferon-gamma (IFN-gamma) -producing effectors. The effects of TRAIL neutralization in poly(I:C)-treated DCs were similar, except that IL-12 production and the differentiation of effector T cells into IFN-gamma producers were not inhibited. Strikingly, TRAIL stimulation alone was sufficient to induce morphological changes resembling DC maturation, up-regulation of co-stimulatory molecules, and enhancement of DC-driven allogeneic T-cell proliferation. However, TRAIL alone did not induce inflammatory cytokine production. We further show that the effects of TRAIL on DC maturation were not the result of the induction of apoptosis, but may involve p38 activation. Hence, our data demonstrate that TRAIL co-operates with other cytokines to facilitate DC functional maturation in response to Toll-like receptor activation.

Tumor-educated CD11bhighIalow regulatory dendritic cells suppress T cell response through arginase I

Tumors can induce generation and accumulation of the immunosuppressive cells such as regulatory T cells in the tumor microenvironment, contributing to tumor escape from immunological attack. Although dendritic cell (DC)-based cancer vaccine can initiate antitumor immune response, regulatory DC subsets involved in the tolerance induction attracted much attention recently. Our previous studies demonstrate that the stromal microenvironment of the spleen, lung, and liver can program generation of CD11c(low)CD11b(high)Ia(low) DCs with regulatory function (CD11b(high)Ia(low) regulatory DCs). However, whether and how the tumor microenvironment can program generation of CD11b(high)Ia(low) regulatory DCs remain to be investigated. In this study, we used the freshly isolated tumor cells to mimic tumor microenvironment to coculture DCs and found that the freshly isolated tumor cells could drive DCs to differentiate into regulatory DCs with a CD11c(low)CD11b(high)Ia(low) phenotype and high expression of IL-10, NO, vascular endothelial growth factor, and arginase I. Tumor-educated CD11b(high)Ia(low) regulatory DCs inhibited CD4(+) T cell proliferation both in vitro and in vivo. 3LL lung cancer-derived TGF-beta and PGE(2) were responsible for the generation of regulatory DCs. PGE(2) was the main inducer of arginase I in regulatory DCs. Arginase I played a major role in the suppression of T cell response by regulatory DCs induced by 3LL lung cancer. A natural counterpart of CD11b(high)Ia(low) DCs was identified in tumor tissue, and CD11b(high)Ia(low) DCs sorted from 3LL lung cancer tissue expressed arginase I and inhibited T cell response. Therefore, tumors can educate DCs to differentiate into a regulatory DC subset, which contributes to constitution of the immunosuppressive tumor microenvironment and promotes tumor immune escape.

Fas signal promotes lung cancer growth by recruiting myeloid-derived suppressor cells via cancer cell-derived PGE2

Fas/FasL system has been extensively investigated with respect to its capacity to induce cellular apoptosis. However, accumulated evidences show that Fas signaling also exhibits nonapoptotic functions, such as induction of cell proliferation and differentiation. Lung cancer is one of cancer's refractory to the immunotherapy, however, the underlying mechanisms remain to be fully understood. In this study, we show that Fas overexpression does not affect in vitro growth of 3LL cells, but promotes lung cancer growth in vivo. However, such tumor-promoting effect is not observed in FasL-deficient (gld) mice, and also not observed in the immune competent mice once inoculation with domain-negative Fas-overexpressing 3LL cells, suggesting the critical role of Fas signal in the promotion of lung cancer growth in vivo. More accumulation of myeloid-derived suppressor cells (MDSC) and Foxp3(+) regulatory T cells is found in tumors formed by inoculation with Fas-overexpressing 3LL cells, but not domain-negative Fas-overexpressing 3LL cells. Accordingly, Fas-ligated 3LL lung cancer cells can chemoattract more MDSC but not regulatory T cells in vitro. Furthermore, Fas ligation induces 3LL lung cancer cells to produce proinflammatory factor PGE(2) by activating p38 pathway, and in turn, 3LL cells-derived PGE(2) contribute to the Fas ligation-induced MDSC chemoattraction. Furthermore, in vivo administration of cyclooxygenase-2 inhibitor can significantly reduce MDSC accumulation in the Fas-overexpressing tumor. Therefore, our results demonstrate that Fas signal can promote lung cancer growth by recruiting MDSC via cancer cell-derived PGE(2), thus providing new mechanistic explanation for the role of inflammation in cancer progression and immune escape.

IL-1 acts directly on CD4 T cells to enhance their antigen-driven expansion and differentiation

IL-1 causes a marked increase in the degree of expansion of naïve and memory CD4 T cells in response to challenge with their cognate antigen. The response occurs when only specific CD4 T cells can respond to IL-1beta, is not induced by a series of other cytokines and does not depend on IL-6 or CD-28. When WT cells are primed in IL-1R1(-/-) recipients, IL-1 increases the proportion of cytokine-producing transgenic CD4 T cells, especially IL-17- and IL-4-producing cells, strikingly increases serum IgE levels and serum IgG1 levels. IL-1beta enhances antigen-mediated expansion of in vitro primed Th1, Th2, and Th17 cells transferred to IL-1R1(-/-) recipients. The IL-1 receptor antagonist diminished responses to antigen plus lipopolysaccharide (LPS) by approximately 55%. These results indicate that IL-1beta signaling in T cells markedly induces robust and durable primary and secondary CD4 responses.

FasL cross-linking inhibits activation of human peripheral T cells

Activation of resting T cells in vitro is triggered by combined TCR and CD28 engagement and can be modulated by simultaneous ligation of various other surface receptors. Although the Fas ligand (FasL) is best known for its capacity to initiate cell death in Fas-bearing cells, it has recently been implicated in the regulation of T cell activation. Thus, a cross-talk between the TCR and FasL is likely, but far from being biochemically elucidated. We now report that FasL engagement by immobilized but not soluble FasFc fusion protein and anti-FasL polyclonal antibody blocks the activation of human peripheral T cells even in the presence of CD28 co-stimulation. The data presented here stress the importance of the Fas/FasL system for signal initiation via the TCR-CD3 complex and provide further arguments for a retrograde signaling capacity of FasL or a crucial role of Fas as a co-stimulatory molecule.

Epithelial cell apoptosis and neutrophil recruitment in acute lung injury-a unifying hypothesis? What we have learned from small interfering RNAs

In spite of protective ventilatory strategies, Acute Lung Injury (ALI) remains associated with high morbidity and mortality. One reason for the lack of therapeutic options might be that ALI is a co-morbid event associated with a diverse family of diseases and, thus, may be the result of distinct pathological processes. Among them, activated neutrophil- (PMN-) induced tissue injury and epithelial cell apoptosis mediated lung damage represent two potentially important candidate pathomechanisms that have been put forward. Several approaches have been undertaken to test these hypotheses, with substantial success in the treatment of experimental forms of ALI. With this in mind, we will summarize these two current hypotheses of ALI briefly, emphasizing the role of apoptosis in regulating PMN and/or lung epithelial cell responses. In addition, the contribution that Fas-mediated inflammation may play as a potential biological link between lung cell apoptosis and PMN recruitment will be considered, as well as the in vivo application of small interfering RNA (siRNA) as a novel approach to the inhibition of ALI and its therapeutic implications.

Trauma-hemorrhage inhibits splenic dendritic cell proinflammatory cytokine production via a mitogen-activated protein kinase process

Although splenic dendritic cell (DC) functions are markedly altered following trauma-hemorrhage, the mechanism(s) responsible for the altered DC functions remains unknown. We hypothesized that trauma-hemorrhage inhibits DC function via suppressing toll-like receptor 4 (TLR4) expression and mitogen-activated protein kinases (MAPKs). To examine this, male C3H/HeN (6–8 wk) mice were randomly assigned to sham operation or trauma-hemorrhage. Trauma-hemorrhage was induced by midline laparotomy and ∼90 min of hypotension [blood pressure (BP) 35 mmHg], followed by fluid resuscitation (4× the shed blood volume in the form of Ringer lactate). Two hours later, mice were euthanized, splenic DCs were isolated, and the changes in their MAPK activation, TLR4-MD-2 expression, and ability to produce cytokines were measured. The results indicate that trauma-hemorrhage downregulated the lipopolysaccharide (LPS)-induced MAPK activation in splenic DCs. In addition to the decrease in MAPK activation, surface expression of TLR4-MD-2 was suppressed following trauma-hemorrhage. Furthermore, LPS-induced cytokine production from splenic DCs was also suppressed following trauma-hemorrhage. These findings thus suggest that the decrease in TLR4-MD-2 and MAPK activation may contribute to the LPS hyporesponsiveness of splenic DCs following trauma-hemorrhage. Hyporesponsiveness of splenic DCs was also found after stimulation with the TLR2 agonist zymosan. Our results may thus explain the profound immunosuppression that is known to occur under those conditions.

Withdrawal: Leptin induces CD40 expression through the activation of Akt in murine dendritic cells

Increasing evidence suggests a regulatory role for leptin, an adipocyte-derived hormone, in immunity. Although recent studies indicated an essential role of leptin signaling in dendritic cell (DC) maturation, the molecular mechanisms by which leptin modulates DC functional maturation remained unclear. In this study, we showed that leptin induced CD40 expression in murine DC and significantly up-regulated their immunostimulatory function in driving T cell proliferation. Moreover, leptin markedly enhanced lipopolysaccharide-mediated DC activation. Using pharmacological inhibitors for Akt, STAT-1alpha, or NF-kappaB and the dominant negative forms of Akt and IkappaB kinase alpha/beta/gamma, as well as small interfering RNA for STAT-1alpha, we showed that Akt, STAT-1alpha, and NF-kappaB were important for the leptinor lipopolysaccharide-induced CD40 expression. Coimmunoprecipitation analysis revealed that leptin promoted immune complex formation between Akt and the IkappaB kinase subunits as well as STAT-1alpha. Blocking the activity of Akt demonstrated a crucial role for Akt in translocation of STAT-1alpha and NF-kappaB to the nucleus and activation of the CD40 promoter. Further analysis with chromatin immunoprecipitation assay confirmed that leptin recruited STAT-1alpha, NF-kappaBp65, and RNA polymerase II to the CD40 promoter and enhanced histone 4 acetylation in a time-dependent manner. Thus, our results have elucidated the molecular mechanisms underlying leptin-induced CD40 expression and DC maturation.

Transcription factors in the control of dendritic cell life cycle

Dendritic cells (DCs) are potent antigen-presenting cells that guard all parts of the body. They have the unique ability to prime T cells and generate primary immune responses. Their journey beginning with the development from precursor cells and ending with their death is controlled by a group of transcription factors. Some of the transcription factors like PU.1 are involved in more than one stage of DC life. Other transcription factors including Ikaros and JAK3 are involved in the development of more than one cell type. For a long time, the cellular and molecular mechanisms underlying the development, differentiation, maturation, and other stages of DC life were not well understood. However, in recent years novel information has been published by many researchers to better understand the molecular mechanisms of the development and function of DCs in immunological diseases such as asthma, cancer, autoimmunity, and transplantation. This review will discuss the various transcription factors and signaling pathways involved in each stage of the life cycle of DCs.

TLR agonists induce regulatory dendritic cells to recruit Th1 cells via preferential IP-10 secretion and inhibit Th1 proliferation

Dendritic cells (DCs) and chemokines are important mediators linking innate and adaptive immunity on activation by Toll-like receptor (TLR) agonists. We previously identified a kind of regulatory DC subset (diffDCs) that differentiated from mature DCs under splenic stroma and that inhibited T-cell proliferation. The responsiveness of such regulatory DCs to TLR agonists and their pattern of chemokine production remain to be determined. Here, we report that the regulatory DCs secrete a higher level of CXCR3 chemokine IFN-gamma-induced protein-10 (IP-10) than immature DCs (imDCs), and more IP-10 is produced after stimulation with TLR-2, -4, -3, and -9 ligands. Blockade of IFN-alpha/beta inhibits IP-10 production by TLR agonist-activated regulatory DCs. We show that the increased IRF-3 and IFN-beta-induced STAT1 activation are responsible for the autocrine IFN-beta-dependent preferential production of IP-10 by regulatory DCs. In addition, stimulation with recombinant mouse IFN-alpha/beta induces more IP-10 production in regulatory DCs than that in imDCs. Moreover, the regulatory DCs selectively recruit more Th1 cells through IP-10 and inhibit Th1 proliferation. Our results demonstrate a new manner for regulatory DCs to down-regulate T-cell response by preferential IP-10 production and inhibition of recruited Th1 cell proliferation.

Endothelial stroma programs hematopoietic stem cells to differentiate into regulatory dendritic cells through IL-10

Regulatory dendritic cells (DCs) have been reported recently, but their origin is poorly understood. Our previous study demonstrated that splenic stroma can drive mature DCs to proliferate and differentiate into regulatory DCs, and their natural counterpart with similar regulatory function in normal spleens has been identified. Considering that the spleen microenvironment supports hematopoiesis and that hematopoietic stem cells (HSCs) are found in spleens of adult mice, we wondered whether splenic microenvironment could differentiate HSCs into regulatory DCs. In this report, we demonstrate that endothelial splenic stroma induce HSCs to differentiate into a distinct regulatory DC subset with high expression of CD11b but low expression of Ia. CD11bhiIalo DCs secreting high levels of TGF-β, IL-10, and NO can suppress T-cell proliferation both in vitro and in vivo. Furthermore, CD11bhiIalo DCs have the ability to potently suppress allo-DTH in vivo, indicating their preventive or therapeutic perspectives for some immunologic disorders. The inhibitory function of CD11bhiIalo DCs is mediated through NO but not through induction of regulatory T (Treg) cells or T-cell anergy. IL-10, which is secreted by endothelial splenic stroma, plays a critical role in the differentiation of the regulatory CD11bhiIalo DCs from HSCs. These results suggest that splenic microenvironment may physiologically induce regulatory DC differentiation in situ.

IL-1beta, but not IL-1alpha, is required for antigen-specific T cell activation and the induction of local inflammation in the delayed-type hypersensitivity responses

As IL-1 expression is augmented in delayed-type hypersensitivity (DTH) responses, we analyzed the role of IL-1 in this response. DTH responses against methyl BSA (mBSA) were significantly suppressed in IL-1beta-deficient (IL-1beta-/-) and IL-1alpha/beta-/- mice, but not in IL-1alpha-/- mice. In contrast, responses in IL-1R antagonist-/- (IL-1Ra-/-) mice were exacerbated. Lymph node cells derived from mBSA-sensitized IL-1beta-/-, IL-1alpha/beta-/- and IL-1R type I (IL-1RI)-/- mice, but not from IL-1alpha-/- mice, exhibited reduced proliferative responses against mBSA, while these from IL-1Ra-/- mice demonstrated augmented responses. DTH responses in wild-type mice following adoptive transfer of CD4+ T cells from mBSA-sensitized IL-1alpha/beta-/- mice were also reduced, while those in mice given cells derived from IL-Ra-/- mice were increased. DTH responses in IL-1RI-/-, but not IL-1alpha/beta-/-, mice were reduced upon transplantation of mBSA-sensitized CD4+ T cells from wild-type mice. The recall response of mBSA-sensitized CD4+ T cells against mBSA decreased upon co-culture with dendritic cells (DCs) from IL-1RI-/- mice, while the responses were normal with DCs from IL-1alpha/beta-/- mice. DTH responses in tumor necrosis factor alpha-/- (TNF-/-) mice were also suppressed; the magnitude of the suppression in IL-1alpha/beta-/-TNF-/- mice, however, was similar to that observed in IL-1alpha/beta-/- mice. These observations indicate that IL-1 possesses dual functions during the DTH response. IL-1beta is necessary for the efficient priming of T cells. In addition, CD4+ T cell-derived IL-1 plays an important role in the activation of DCs during the elicitation phase, resulting in the production of TNF, that activate allergen-specific T cells.

Balance between NF-κB and JNK/AP-1 activity controls dendritic cell life and death

The life cycle of dendritic cells (DCs) must be precisely regulated for proper functioning of adaptive immunity. However, signaling pathways actively mediating DC death remain enigmatic. Here we describe a novel mechanism of hierarchical transcriptional control of DC life and death. Ligation of tumor necrosis factor receptor superfamily (TNFR-SF) members on DCs and cognate contact with T cells resulted in quantitatively balanced nuclear factor-κB (NF-κB) and c-Jun N-terminal kinase (JNK)–mediated activator protein-1 (AP-1) induction and strongly enhanced DC longevity. Specific blockade of NF-κB in DCs induced strongly augmented JNK/AP-1 activity because of elevated levels of reactive oxygen species. In this scenario, DC activation by TNFR-SF members or T cells induced DC apoptosis. Specific inhibition of JNK/AP-1 rescued DCs from this activation-induced cell death program and restored TNFR-SF member- and T-cell–mediated survival. We conclude that JNK/AP-1 activity is under negative feedback control of NF-κB and can execute apoptosis in DCs. Thus, feedback-controlled signaling amplitudes of 2 transcriptional pathways decide the fate of a DC.

Fas signal links innate and adaptive immunity by promoting dendritic-cell secretion of CC and CXC chemokines

Dendritic cells (DCs) and chemokines are important in linking innate and adaptive immunity. We previously reported that Fas ligation induced interleukin 1beta (IL-1beta)-dependent maturation and IL-1beta-independent survival of DCs, with extracellular signal-regulated kinase (ERK) and nuclear factor-kappaB (NF-kappaB) signaling pathways involved, respectively. We describe here that Fas ligation induced DCs to rapidly produce both CXC and CC chemokines, including macrophage inflammatory protein 2 (MIP-2), MIP-1alpha, MIP-1beta, monocyte chemoattractant protein 1 (MCP-1), RANTES (regulated on activation normal T cell expressed and secreted), and TARC (thymus and activation-regulated chemokine), resulting in enhanced chemoattraction of neutrophils and T cells by Fas-ligated DCs in vivo or by its supernatant in vitro. These chemokines work synergistically in chemoattraction of neutrophils and T cells with MIP-2 more important for neutrophils, MIP-1alpha and TARC more important for T cells. Moreover, Fas-ligated DCs increased endocytosis by neutrophils and activation and proliferation of antigen-specific naive T cells. Fas ligation-induced DC secretion of chemokines involves Ras/Raf/mitogen-activated protein kinase kinase (MEK)/ERK activation and is ERK, but not NF-kappaB, dependent. Activation of caspases, including caspase 1, but not IL-1 autocrine action, is involved in this process. These data indicate that Fas signaling provides a key link between innate response and adaptive immunity by promoting DC chemokine production.

A Stress-Induced, Superoxide-Mediated Caspase-1 Activation Pathway Causes Plasma IL-18 Upregulation

Psychological/physical stresses are known to cause relapses of autoimmune and inflammatory diseases. To reveal a mechanism by which noninflammatory stresses affect host defenses, responses to immobilization stress in mice were investigated, focusing on the role of a multifunctional cytokine, interleukin-18 (IL-18). In the adrenal cortex, the stress induced IL-18 precursor proteins (pro-IL-18) via adrenocorticotropic hormone (ACTH) and a superoxide-mediated caspase-1 activation pathway, resulting in conversion of pro-IL-18 to the mature form, which was released into plasma. Inhibitors of caspase-1, reactive oxygen species, and P38 mitogen-activated protein kinase (MAPK) suppressed stress-induced accumulation of plasma IL-18. These inhibitors also blocked stress-induced IL-6 expression. This, together with the observation that IL-6 was not induced in IL-18-deficient mice, showed that IL-6 induction by stress is dependent on IL-18. In stressed organisms, IL-18 may influence pathological and physiological processes. Controlling the caspase-1 activating pathway to suppress IL-18 levels may provide preventative means against stress-related disruption of host defenses.

Downregulation of mitogen-activated protein kinases by the Bordetella bronchiseptica Type III secretion system leads to attenuated nonclassical macrophage activation

Bordetella bronchiseptica utilizes a type III secretion system (TTSS) to establish a persistent infection of the murine respiratory tract. Previous studies have shown that the Bordetella TTSS mediated cytotoxicity in different cell types, inhibition of NF-kappaB in epithelial cells, and differentiation of dendritic cells into a semimature state. Here we demonstrate modulation of mitogen-activated protein kinase (MAPK) signaling pathways and altered cytokine production in macrophages and dendritic cells by the Bordetella TTSS. In macrophages, the MAPKs ERK and p38 were downregulated. This resulted in attenuated production of interleukin- (IL-)6 and IL-10. In contrast, the Th-1-polarizing cytokine IL-12 was produced at very low levels and remained unmodulated by the Bordetella TTSS. In dendritic cells, ERK was transiently activated, but this failed to alter cytokine profiles. These results suggest that the Bordetella TTSS modulates antigen-presenting cells in a cell type-specific manner and the secretion of high levels of IL-6 and IL-10 by macrophages might be important for pathogen clearance.

Heat shock up-regulates TLR9 expression in human B cells through activation of ERK and NF-kappaB signal pathways

Toll-like receptors (TLRs) play a critical role in innate immunity and TLR9 is essential for CpG ODN signaling. As "dangerous signal", heat shock may regulate immune response. However, little is known about TLRs expression and signaling after heat shock. In this study, we investigated regulation of TLR9 expression and function in human B cell line RPMI8226 by heat shock. We demonstrated that TLR9 expression was up-regulated remarkably following heat shock. Coincidently, CpG ODN stimulation significantly increased IL-6 production and up-regulated expressions of MHC I, MHC II and CD86 by heat-shocked B cells. Heat shock activated ERK and NF-kappaB signal pathways, and pretreatment of B cells with specific inhibitors of ERK or NF-kappaB signal pathways inhibited heat shock-induced up-regulation of TLR9 expression. These results demonstrated that heat shock promotes TLR9 expression and signaling through activation of ERK and NF-kappaB signal pathways in B cells, suggesting that heat shock might modulate host immune response by regulating TLR expression.

Bordetella type III secretion and adenylate cyclase toxin synergize to drive dendritic cells into a semimature state

Bordetella bronchiseptica establishes persistent infection of the murine respiratory tract. We hypothesize that long-term colonization is mediated in part by bacteria-driven modulation of dendritic cells (DCs) leading to altered adaptive immune responses. Bone marrow-derived DCs (BMDCs) from C57BL/6 mice infected with live B. bronchiseptica exhibited high surface expression of MHCII, CD86, and CD80. However, B. bronchiseptica-infected BMDCs did not exhibit significant increases in CD40 surface expression and IL-12 secretion compared with BMDCs treated with heat-killed B. bronchiseptica. The B. bronchiseptica type III secretion system (TTSS) mediated the increase in MHCII, CD86, and CD80 surface expression, while the inhibition of CD40 and IL-12 expression was mediated by adenylate cyclase toxin (ACT). IL-6 secretion was independent of the TTSS and ACT. These phenotypic changes may result from differential regulation of MAPK signaling in DCs. Wild-type B. bronchiseptica activated the ERK 1/2 signaling pathway in a TTSS-dependent manner. Additionally, ACT was found to inhibit p38 signaling. These data suggest that B. bronchiseptica drive DC into a semimature phenotype by altering MAPK signaling. These semimature DCs may induce tolerogenic immune responses that allow the persistent colonization of B. bronchiseptica in the host respiratory tract.