TLR Ligands Can Activate Dendritic Cells to Provide a MyD88-Dependent Negative Signal for Th2 Cell Development

The Effects of IL-23/IL-18-Polarized Neutrophils on Renal Ischemia-Reperfusion Injury and Allogeneic-Skin-Graft Rejection in Mice

Neutrophils display heterogeneity and plasticity with different subgroups and immune-regulatory functions under various surrounding conditions. Neutrophils induced by IL-23/IL-18 (referred to N(IL-23+IL-18) neutrophils) have a unique gene-expression profile, with highly expressing IL-17, MHC-II, and costimulatory molecules. The adoptive transfer of N(IL-23+IL-18) neutrophils significantly increased the pathogenesis in a renal ischemia-reperfusion injury mouse model. N(IL-23+IL-18) neutrophils directly and efficiently induced allogeneic T cell proliferation in vitro. N(IL-23+IL-18) neutrophils enhanced the syngeneic T cell response to allogeneic antigens in mixed-lymphocyte reaction assays. The adoptive transfer of the donor or host N(IL-23+IL-18) neutrophils significantly enhanced the antidonor antibody production in an allogeneic-skin-transplanted mouse model, accompanied by increased Tfh cells in the spleens. Therefore, the neutrophil subset induced by IL-23/IL-18 promotes tissue injury and antidonor humoral response in the allogeneic transplantation mouse model.

TRAIL produced by SAM-1-activated CD4+ and CD8+ subgroup T cells induces apoptosis in human tumor cells through upregulation of death receptors

Bacterial superantigens potently activate conventional T-cells to induce massive cytokine production and mediate tumor cell death. To engineer superantigens for immunotherapy against tumors in clinic, we previously generated SAM-1, a staphylococcal enterotoxins C2 (SEC2) mutant, that exhibited significantly reduced toxicity but maintained the superantigen activity in animal models. This present study aimed to investigate whether SAM-1 activates T cells and induces apoptosis in human tumor cells. We found that SAM-1 induced the maturation of dendritic cells (DCs) with upregulating expression of the surface markers CD80, CD86 and HLA-DR, which secreted high levels of IL-12p70 by activating TLR2-NF-κB signaling pathways. SAM-1 could activate human CD4⁺ subgroup T cells and CD8⁺ subgroup T cells in the presence of mature dendritic cells (DCs), leading to the productions of cytokines TRAIL, IL-2, IFN-γ and TNF-α. We observed that TRAIL mediated the apoptosis and S-phase and G2/M-phase arrest in HGC-27 tumor cells via binding to upregulated death receptors DR4 and DR5. Using shRNA knockdown in HGC-27 cells or constitutive overexpression in ES2 cells for DR4 and DR5, we demonstrated the vital requirement of DR4 and DR5 in apoptosis of tumor cells in response to TRAIL secreted from SAM-1-activated T cells. Collectively, our results will facilitate better understanding of SAM-1-based immunotherapies for cancer.

Mechanism by which TRAF6 Participates in the Immune Regulation of Autoimmune Diseases and Cancer

Tumor necrosis factor (TNF) receptor-associated factor 6 (TRAF6), an E3 ubiquitin ligase, is a signal transduction molecule shared by the interleukin-1 receptor (IL-1R)/Toll-like receptor (TLR) family and the TNFR superfamily. TRAF6 has a unique TRAF domain and RING finger domain that mediate intracellular signaling events. In the immune system, TRAF6-mediated signaling has been shown to be critical for the development, homeostasis, and activation of a variety of immune cells, including B cells, T cells, dendritic cells, and macrophages. Although the pathogenesis and etiology of autoimmune diseases and cancer are not fully understood, it is worth noting that existing studies have shown that TRAF6 is involved in the pathogenesis and development of a variety of these diseases. Herein, we reviewed the role of TRAF6 in certain immune cells, as well as the function and potential effect of TRAF6 in autoimmune diseases and cancer. Our review indicates that TRAF6 may be a novel target for autoimmune diseases and cancer.

Dynamic metabolic reprogramming in dendritic cells: An early response to influenza infection that is essential for effector function

Infection with the influenza virus triggers an innate immune response that initiates the adaptive response to halt viral replication and spread. However, the metabolic response fueling the molecular mechanisms underlying changes in innate immune cell homeostasis remain undefined. Although influenza increases parasitized cell metabolism, it does not productively replicate in dendritic cells. To dissect these mechanisms, we compared the metabolism of dendritic cells to that of those infected with active and inactive influenza A virus and those treated with toll-like receptor agonists. Using quantitative mass spectrometry, pulse chase substrate utilization assays and metabolic flux measurements, we found global metabolic changes in dendritic cells 17 hours post infection, including significant changes in carbon commitment via glycolysis and glutaminolysis, as well as mitochondrial respiration. Influenza infection of dendritic cells led to a metabolic phenotype distinct from that induced by TLR agonists, with significant resilience in terms of metabolic plasticity. We identified c-Myc as one transcription factor modulating this response. Restriction of c-Myc activity or mitochondrial substrates significantly changed the immune functions of dendritic cells, such as reducing motility and T cell activation. Transcriptome analysis of inflammatory dendritic cells isolated following influenza infection showed similar metabolic reprogramming occurs in vivo. Thus, early in the infection process, dendritic cells respond with global metabolic restructuring, that is present in inflammatory lung dendritic cells after infection, and this is important for effector function. These findings suggest metabolic switching in dendritic cells plays a vital role in initiating the immune response to influenza infection.

Dendritic cells are critical in mounting an effective immune response to influenza infection by initiating the immune response to influenza and activating the adaptive response to mediate viral clearance and manifest immune memory for protection against subsequent infections. We found dendritic cells undergo a profound metabolic shift after infection. They alter the concentration and location of hundreds of proteins, including c-Myc, facilitating a shift to a highly glycolytic phenotype that is also flexible in terms of fueling respiration. Nonetheless, we found limiting access to specific metabolic pathways or substrates diminished key immune functions. We previously described an immediate, fixed hypermetabolic state in infected respiratory epithelial cells. Here we present data indicating the metabolic response of dendritic cells is increased yet flexible, distinct from what we previously showed for epithelial cells. Additionally, we demonstrate dendritic cells tailor their metabolic response to the pathogen or TLR stimulus. This metabolic reprogramming occurs rapidly in vitro and is sustained in inflammatory dendritic cells in vivo for at least 9 days following influenza infection. These studies introduce the possibility of modulating the immune response to viral infection using customized metabolic therapy to enhance or diminish the function of specific cells.

TLR2/MyD88 pathway-dependent regulation of dendritic cells by dengue virus promotes antibody-dependent enhancement via Th2-biased immunity

Possible risk mediators in primary dengue virus (DenV) infection that favor secondary DenV infection to life-threatening dengue hemorrhagic fever (DHF) and shock syndrome (DSS) via antibody-dependent enhancement (ADE) have not yet been described. Here, DenV infection enhanced the expression of inflammatory mediators and activation molecules in dendritic cells (DCs) through TLR2/MyD88 pathway. TLR2 appeared to facilitate DenV infection in DCs that were less permissive than macrophages for viral replication. In experiments using separate evaluations of DenV-infected and uninfected bystander DCs, infected DCs showed impaired maturation accompanied with TLR2-dependent production of inflammatory cytokines, by which uninfected bystander DCs showed increased expression of co-stimulatory molecules. Differential phosphorylation of MAPK and STAT3 was also detected between DenV-infected and uninfected DCs. Furthermore, DenV infection stimulated Th2-polarized humoral and cellular immunity against foreign and DenV Ag via TLR2/MyD88 pathway, and DenV-infected DCs were revealed to facilitate Th2-biased immune responses in TLR2-dependent manner. TLR2/MyD88-mediated Th2-biased Ab responses to primary DenV infection increased the infectivity of secondary homotypic or heterotypic DenV via ADE. Collectively, these results indicate that TLR2/MyD88 pathway in DC-priming receptors can drive Th2-biased immune responses during primary DenV infection, which could favor secondary DenV infection to DHF/DSS via ADE.

Promoting effects of IL‑23 on myocardial ischemia and reperfusion are associated with increased expression of IL‑17A and upregulation of the JAK2‑STAT3 signaling pathway

Interleukin (IL)-23, as a novel pro-inflammatory cytokine, is important in several inflammatory diseases, including myocardial ischemia and reperfusion (I/R) injury, however, the underlying mechanism remains to be elucidated. The present study was designed to investigate the specific role of IL-23 in myocardial I/R injury, and whether the Janus kinase 2/signal transducer and activator of transcription 3 (JAK2-STAT3) signaling pathway, one of the important downstream signaling pathways of IL-23, and the IL-17A downstream pro-inflammatory cytokine, were involved. Anesthetized rats underwent different treatments with adenovirus (Ad) vectors (Ad-GFP, Ad-IL-23, Anti-IL-23 or Ad-IL-23+AG490) and were then subjected to ischemia for 30 min prior to 4 h reperfusion. The effects of the upregulation and downregulation of IL-23 on myocardial injury, inflammatory responses in myocardial tissue, and myocardial apoptosis were measured accordingly. In addition, the levels of phosphorylated (P-)JAK2 and P-STAT3 were measured to assess the activity of the JAK2-STAT3 signaling pathway. The results demonstrated that there was an increased expression of IL-23 in the myocardial tissue exposed to myocardial I/R injury (P<0.05). The upregulation of IL-23 significantly increased the infarct size and the expression levels of lactate dehydrogenase and creatine kinase (P<0.05). The upregulation of IL-23 significantly increased inflammatory responses, as reflected by the high expression levels of IL-17A, IL-6, tumor necrosis factor-α in the myocardial tissues (P<0.05). Furthermore, the upregulation of IL-23 significantly facilitated the decrease in the B-cell lymphoma 2 (Bcl-2)/Bcl-2-associated X protein ratio, and the increases in the myocardial apoptotic index and expression of caspase-3 induced by myocardial I/R (P<0.05). IL-23 also activated the JAK2-STAT3 signaling pathway, upregulating the expression levels of P-JAK2 and P-STAT3 in the myocardial tissues (P<0.05). Treatment with AG490, an inhibitor of JAK2-STAT3, partially attenuated the pro-inflammatory and pro-apoptotic effects of IL-23 (P<0.05). The results of the present study suggested that IL-23 aggravated myocardial I/R injury by promoting inflammatory responses and myocardial apoptosis, which may be associated with high expression levels of IL-17A and upregulation of the JAK2-STAT3 signaling pathway.

Inhibition of Myeloid Differentiation Factor 88 Reduces Human and Mouse T-Cell Interleukin-17 and IFNγ Production and Ameliorates Experimental Autoimmune Encephalomyelitis Induced in Mice

Myeloid differentiation factor 88 (MyD88) recruits signaling proteins to the intracellular domain of receptors belonging to the toll-like/interleukin-1 (IL-1) receptor superfamily. Mice lacking MyD88 are highly susceptible to infectious diseases, but tend to resist experimentally induced autoimmune diseases such as experimental autoimmune encephalomyelitis (EAE) and manifest diminished allograft rejection. We reasoned that inhibition of MyD88 should influence the cytokine profile of responding T cells by blocking costimulatory molecule expression by antigen-presenting cells (APCs) and by inhibiting T-cell responses to IL-18. We now report that inhibition of MyD88 in human APCs led to decreased IFNγ and IL-17 production and a shift to IL-4 production by responding T cells in a mixed lymphocyte reaction. Direct inhibition of Myd88 in mouse and human T cells also reduced their production of IFNγ in response to IL-12/IL-18 stimulation. Finally, systemic MyD88 antagonism significantly reduced the clinical manifestations of EAE in mice. Thus, MyD88 appears to be a key factor in determining T cell phenotype and represents a potential target for therapeutic intervention.

CpG-ODN Shapes Alum Adjuvant Activity Signaling via MyD88 and IL-10

Aluminum-containing adjuvants usually referred as Alum are considered as T helper type-2 (Th2) adjuvants, while agonists of toll-like receptors (TLRs) are viewed as adjuvants that favor Th1/Th17 immunity. Alum has been used in numerous vaccine formulations; however, its undesired pro-Th2 adjuvant activity constitutes a caveat for Alum-based vaccines. Combining Alum with TLR-dependent, pro-Th1/Th17 adjuvants might dampen the pro-Th2 activity and improve the effectiveness of vaccine formulations. Here, using the ovalbumin (OVA) model of allergic lung inflammation, we found that sensitization with the synthetic TLR9 agonist, which is composed of oligodeoxynucleotides containing CpG motifs adsorbed to Alum, inhibited the development of OVA-induced lung allergic Th2 responses without shifting toward a Th1 pattern. The conversion of T cell immunity from the polarized allergic Th2 response to a non-polarized form by sensitization with OVA/Alum/CpG was dependent on MyD88 signaling in myeloid cells. Notably, sensitization of IL-10-deficient mice with OVA/Alum/CpG resulted in the development of neutrophilic lung inflammation associated with IFNγ production. However, in IL-10/IL-12-deficient mice, it resulted in neutrophilic inflammation dominated by IL-17 production. We conclude that OVA/Alum/CpG sensitization signaling via MyD88 and IL-10 molecules results in non-polarized immunity. Conversely, OVA/Alum/CpG sensitization in presence of MyD88 but absence of IL-10 or IL-10/IL-12 molecules results, respectively, in neutrophilic inflammation associated with IFNγ or IL-17 production. Our work provides novel OVA models of lung inflammation and suggests that Alum/CpG-based formulations might be of potential use in anti-allergic or anti-infectious processes.

Characterization and function analysis of interleukin-1 receptor-associated kinase-1 (IRAK-1) from Fenneropenaeus penicillatus

The interleukin-1 receptor-associated kinase-1 (IRAK-1) is an important adapter protein which links downstream of MyD88, and involved in the complex composed of MyD88 and TRAF6 to activate TLRs signaling pathway. In this study, an IRAK-1 homolog (FpIRAK-1) was cloned from the red tail shrimp Fenneropenaeus penicillatus. The ORF of FpIRAK-1 consisted of 2874 bp encoding a protein of 957 amino acids which contains a death domain (DD) and a catalytic domain of serine/threonine kinases (STKc). Homology analysis revealed that the predicted amino acid sequence of FpIRAK-1 shared 71% similarities with IRAK-1 of Litopenaeus vannamei. Real-time RT-PCR indicated that FpIRAK-1 was constitutively expressed in various tissues of F. penicillatus. The expression level of FpIRAK-1 mRNA was significantly up-regulated and then decreased gradually after white spot syndrome virus (WSSV) and Vibrio alginolyticus challenge. Gene knockdown of FpIRAK-1 enhanced the sensitivity of shrimps to WSSV and V. alginolyticus challenge, suggesting FpIRAK-1 could play a positive role against bacterial and viral pathogens. In conclusion, the results of this study provide some insights into the function of FpIRAK-1 in activating Toll signaling pathway and the host defense against invading pathogens.

Trim32 Deficiency Enhances Th2 Immunity and Predisposes to Features of Atopic Dermatitis

Altered innate immunity is a feature of certain skin inflammatory diseases such as psoriasis and atopic dermatitis (AD). In this study, we provide evidence that deficiency in Trim32 (a tripartite motif [TRIM] protein with innate antiviral activity) contributes to a T helper type 2 biased response and predisposes to features of AD in mice. On treatment with the toll-like receptor 7 agonist imquimod (IMQ), Trim32 knockout mice displayed compromised psoriasiform phenotypes and defective T helper type 17 response. Instead, IMQ treatment of Trim32 knockout mice induced AD-like phenotypes with enhanced skin infiltration of eosinophils and mast cells, elevation of T helper type 2 cytokines/chemokines expression, and reduced expression of filaggrin protein expression. Furthermore, although the induction of phosphorylated Stat3 and RelA was compromised after IMQ treatment in the knockout mice, phosphorylated Stat6 was elevated. CC chemokine ligand 20 induction by tumor necrosis factor-α and IL-17A was reduced in Trim32-deficient keratinocytes, whereas CC chemokine ligand 5 induction by tumor necrosis factor-α and IL-4 was enhanced. In addition, Trim32 protein levels were elevated in mice treated with IMQ. Unlike Trim32 overexpression in psoriasis, TRIM32 levels were low in patients with AD. Based on Trim32 induction by IMQ, the lower levels of TRIM32 in AD skin compared with healthy control and psoriatic skin suggest a defective TRIM32 pathway in AD pathogenesis.

Adsorption of Toll-Like Receptor 4 Agonist to Alum-Based Tetanus Toxoid Vaccine Dampens Pro-T Helper 2 Activities and Enhances Antibody Responses

Aluminum salts gels (alum) are TLR-independent adjuvants and have been used to boost antibody responses in alum-based vaccines such as diphtheria, pertussis, and tetanus toxoid (DPT) triple vaccine. However, the pro-Th2 activity of alum-based vaccine formulations has not been fully appreciated. Here we found that alum-based tetanus toxoid (TT) vaccine was biased toward a Th-2 profile as shown by TT-induced airway eosinophilic inflammation, type 2 cytokine production, and high levels of IgE anaphylactic antibodies. The adsorption into alum of prototypic TLR4 agonists such as lipopolysaccharides (LPS) derived from Escherichia coli consistently dampened TT-induced Th2 activities without inducing IFNγ or Th1-like responses in the lung. Conversely, adsorption of monophosphoryl lipid A (MPLA) extracted from Salmonella minnesota, which is a TIR-domain-containing adapter-inducing interferon-β- (TRIF-) biased TLR4 agonist, was less effective in decreasing Th-2 responses. Importantly, in a situation with antigenic competition (OVA plus TT), TT-specific IgG1 or IgG2a was decreased compared with TT sensitization. Notably, LPS increased the production of IgG1 and IgG2a TT-specific antibodies. In conclusion, the addition of LPS induces a more robust IgG1 and IgG2a TT-specific antibody production and concomitantly decreases Th2-cellular and humoral responses, indicating a potential use of alum/TLR-based vaccines.

Necrostatin-1 inhibits Hmgb1-IL-23/IL-17 pathway and attenuates cardiac ischemia reperfusion injury

Ischemia reperfusion (IR) injury is a major issue in cardiac transplantation and inflammatory processes play a major role in myocardial IR injury. Necrostatin-1 (Nec-1) is a small molecule capable of inhibiting RIP1 kinase activity and attenuates inflammation-mediated tissue injury. In our study, hearts of C57Bl/6 mice were flushed and stored in cold Bretschneider solution for 8 h and then transplanted into syngeneic recipients. We found that Nec-1 decreased cardiomyocyte necrosis and recruitment of neutrophils and macrophages. Troponin T (TnT) production on 24 h after myocardial IR injury was reduced by Nec-1 administration. Cardiac output at 60 mmHg of afterload pressure was significantly increased in hearts with Nec-1 administration and the cardiac allograft survival in Nec-1-treated animals was significantly prolonged (MST = 90 days in IR + Nec-1 group, P < 0.05 as compared with IR group, MST = 83.5 days). Nec-1 treatment attenuated ROS generation and increased expression of NOS2 and COX-2. The expression of Hmgb1, IL-23, and IL-17A were also decreased with Nec-1 administration. Furthermore, the decreased TnT expression induced by Nec-1 was abrogated with exogenous Hmgb1 administration. In conclusion, Nec-1 played a protective role in cardiomyocyte IR injury, and this was associated with inhibited Hmgb1-IL-23/IL-17 pathway.

Paclitaxel-exposed ovarian cancer cells induce cancer‑specific CD4+ T cells after doxorubicin exposure through regulation of MyD88 expression

Ovarian cancer has the highest mortality rate among gynecological malignancies due to high chemoresistance to the combination of platinum with taxane. Immunotherapy against ovarian cancer is a promising strategy to develop from animal-based cancer research. We investigated changes in the immunogenicity of paclitaxel-exposed ovarian cancer cells following exposure to other chemotherapeutic drugs. Murine ovarian surface epithelial cells (MOSECs) showed some resistance to paclitaxel, a first-line therapy for ovarian cancer. However, MOSECs pre-exposed to paclitaxel died through apoptosis after incubation with doxorubicin or cisplatin for 2 h. Injected into mice, the paclitaxel-exposed MOSECs post-treated with doxorubicin induced more MOSEC-specific CD4(+) T cells and extended survival for a greater time than MOSECs treated with paclitaxel alone; and bone marrow-derived dendritic cells (BMDCs) expressed higher levels of co-stimulatory molecules and produced IL-12 after co-culture with paclitaxel-exposed MOSECs treated with doxorubicin. We also observed that in paclitaxel-exposed MOSECs treated with doxorubicin, but not cisplatin, the expression of MyD88 and related target proteins decreased compared to paclitaxel-exposed MOSECs only, while in BMDCs co-cultured with these MOSECs the expression of myeloid differentiation primary response gene 88 (MyD88) increased. These findings suggest that paclitaxel pre-exposed cancer cells treated with doxorubicin can induce significant apoptosis and a therapeutic antitumor immune response in advanced ovarian cancer.

Mechanistic investigation of immunosuppression in patients with condyloma acuminata

Condyloma acuminatum (CA) is a common sexually transmitted disease caused by human papillomavirus (HPV) infection. Previous studies have identified that the occurrence, relapse and cancerization of CA is relevant to immune imbalance caused by immune hypofunction or immunoregulatory dysfunction. However, to date, the specific mechanisms accounting for immune imbalance in CA patients have remained elusive. In the present study, changes in the expression levels of myeloid differentiation factor 88 (MyD88) and toll‑like receptors (TLRs) were determined in lesion tissues and peripheral blood samples obtained from CA patients by fluorescence quantitative PCR and western blot analysis. The results indicated that TLRs and MyD88 expression was upregulated in the lesion tissues only. In addition, the expression of forkhead box P3, a characteristic marker of regulatory T cells (Tregs), transforming growth factor‑β1 and interleukin (IL)‑10, inhibitory factors secreted by Tregs and inhibitory costimulatory molecules, cytotoxic T-lymphocyte antigen 4, glucocorticoid-induced TNFR-related protein and programmed cell death protein 1 was observed to be upregulated, indicating that immunosuppression of Tregs was enhanced significantly. However, the expression levels of NKG2D and NKp46, natural killer (NK) cell activation receptors located on the surface of NK cells, decreased markedly indicating that HPV infection inhibits the activation of NK cells. The secretion levels of various cytokines in the peripheral blood of CA patients were detected by enzyme‑linked immunosorbent assay revealing that IL‑2, IL‑12 and interferon‑γ levels were markedly lower than that of healthy subjects. By contrast, the expression levels of tumor necrosis factor‑α, IL‑4 and IL‑10 were markedly increased in CA samples compared with the control, with the exception of IL‑6. Taken together, these results are consistent with the hypothesis of immunosuppression in CA patients. Increased expression of MyD88 and TLRs is likely to enhance immunosuppression of Tregs, leading to the imbalance of Th1/Th2, cytotoxic T cell type 1 (Tc1)/Tc2 cells and secreted cytokines.

Shrimp MyD88 responsive to bacteria and white spot syndrome virus

The myeloid differentiation factor 88 (MyD88) is an important adapter protein which links members of the toll-like receptor (TLR) to the downstream components to activate related signaling pathways. In the present study, a MyD88 homolog (FcMyD88) was cloned from penaeid shrimp Fenneropenaeus chinensis. The ORF of FcMyD88 consisted of 1434 bp encoding a polypeptide of 477 amino acids which contains a death domain (DD) and a typical TLR and interleukin-1 receptor (IL-1R)-related (TIR) domain. Homology analysis revealed that the predicted amino acid (aa) sequence of FcMyD88 shared high similarities with a variety of previously reported MyD88s. The time-dependent expression patterns of FcMyD88 in cephalothoraxes of shrimp injected with Vibrio anguillarum (Gram-negative bacteria, G(-)), Micrococcus lysodeikticu (Gram-positive bacteria, G(+)) and white syndrome spot virus (WSSV) were analyzed at transcription and protein level by real-time PCR and western blotting, respectively. The expression level of FcMyD88 mRNA was significantly up-regulated at one hour (h), 12 h and 24 h after stimulation with both V. anguillarum and M. lysodeikticu. The expression level of FcMyD88 protein was 2-fold up-regulated at 12 h post injection (hpi) of inactivated V. anguillarum while it didn't change after M. lysodeikticu injection during this period. After WSSV injection, the expression level of FcMyD88 mRNA remained relatively constant, while the FcMyD88 protein was significantly up-regulated at 12 and 24 hpi. These results suggested that the MyD88-dependent signaling pathway could be involved in the defense of both bacteria and WSSV infection.

Th2-Th1 shift with the multiantigenic formulation TERAVAC-HIV-1 in Balb/c mice

In chronic HIV infection a progressive Th1 to Th2/Th0 cytokine-profile shift is related to disease progression. One of the possible benefits of a therapeutic vaccination might be to counterbalance this phenomenon to allow viral replication control under a Th1-type immune response. TERAVAC-HIV-1 is a multiantigenic formulation vaccine candidate against HIV-1 which comprises the recombinant protein CR3 that contains T cell epitopes and the surface and nucleocapsid antigens of Hepatitis B Virus (HBV). Previous studies showed that such virus like particles of the HBV provide a Th1 adjuvant effect. The present studies examined the capacity of TERAVAC to elicit a Th1 response in the presence of an ongoing HIV-specific Th2-type response in Balb/c mice. To examine this issue, we injected subcutaneously the animals with CR3 or viral lysate in alum which resulted in a Th2-type response. The CR3-specific Th2-type response was verified by induction of IL-4 and IL-10 secretion in ex vivo stimulated splenocytes without secretion of IFN-γ and IgG2a antibodies in serum. Further subcutaneous and simultaneous subcutaneous-nasal immunizations of the same mice with TERAVAC promoted IFN-γ secretion and production of IgG2a antibodies in accordance with a Th1-type response. This result suggests a therapeutic benefit of this vaccine candidate in the restoration of the Th1-type HIV-specific cellular response in seropositive patients.

Innate interferons inhibit allergen and microbial specific T(H)2 responses

Several studies provided evidence of innate interferons (IFNs) regulating T(H)2 cytokine production using purified CD4(+) memory cells and T(H)2 polarisation via interleukin-4 (IL-4). Vitally, none of these previous studies examined IFN attenuation of T(H)2 responses to allergen or antigen. This study therefore sought to investigate the abrogation of specific allergen- and antigen-stimulated T(H)2 response in peripheral blood mononuclear cells (PBMC) derived from 12 sensitised individuals by IFN-β and IFN-λ. PBMC were cultured in the presence of house dust mite (HDM) allergen, rhinovirus (RV), influenza vaccine and tetanus toxoid (TT)±either IFN-β or IFN-λ for 3 and 5 days. IFN-γ, IL-5 and IL-13 protein levels were measured by ELISA. Quantitative PCR (qPCR) was used to investigate induction of genes involved in control of T(H)2 cytokines. No alteration in T(H)1 IFN-γ allergen/antigen response was observed with addition of IFN-β or IFN-λ. Consistent abrogation of T(H)2 response to HDM and influenza was observed with IFN-β at both time points; attenuation was observed by day 5 with RV and TT. IFN-λ had no consistent effect on T(H)2 production except in the presence of RV (multiplicity of infection=5); a decrease in IL-5 alone was observed in the presence of trivalent inactivated influenza vaccine. GATA binding protein 3 (GATA3) and suppressors of cytokine signalling3 mRNA were differentially regulated in HDM and influenza-stimulated cultures±IFN-β. We concluded that IFN-β produced a strong and consistent abrogation of T(H)2 cytokine production in the presence of a range of allergen and antigen stimulants.

Expansion of Tfh-like cells during chronic Salmonella exposure mediates the generation of autoimmune hypergammaglobulinemia in MyD88-deficient mice

The role of TLR signaling in linking the innate and adaptive immune systems has been a controversial issue that remains to be solved. Here, we determined whether MyD88-dependent TLR signals are required for the generation of B-cell responses during chronic Salmonella infection. Oral administration of recombinant attenuated Salmonella enterica serovar Typhimurium vaccine (RASV) strain in MyD88(-/-) mice resulted in chronic infection. Infection was accompanied by enlarged germinal centers and hypergammaglobulinemia with anti-double-stranded DNA (dsDNA)-specific Ab in sera, and the deposition of immune complexes in the kidneys, suggesting onset of autoimmunity. CD4(+) T cells expressing PD-1, CXCR5, ICOS, and IL-21 were dramatically increased in chronically infected mice, indicating the expansion of follicular helper T (Tfh)-like cells. Of note, the depletion of CD4(+) T cells completely blocked the generation of polyclonal IgG Ab in sera after oral RASV challenge. Inflammatory myeloid cells expressing CD11b and Gr-1 accumulated in high numbers in the spleen of MyD88(-/-) mice. Interestingly, the blockade of PD-1 or ICOS significantly reduced the hypergammaglobulinemia and dsDNA-specific autoantibody production. Overall, these results suggest that Tfh-like cells in chronic bacterial infection trigger autoimmune hypergammaglobulinemia in a PD-1- and ICOS-dependent manner.

Inactivation of TLR9 by a suppressive oligodeoxynucleotides can ameliorate the clinical signs of EAN

Susceptible-strain animals immunized with P2 peptide could generate the disease of experimental autoimmune neuritis (EAN) with inflammation and demyelination of peripheral nerve. A myriad of transcription factors and inflammatory cytokines have been found to participate in this process; however, the roles of toll-like receptors (TLRs) are poorly understood in EAN. The aim of this study is to explore the role of TLR9 in the pathogenesis of EAN. The EAN was induced in Lewis rat by immunization with P2(53-78) and complete Freund's adjuvant. CpG oligodeoxynucleotides (ODN) (cODN), a suppressive ODN (sODN) and a control non-specific ODN (nODN) were respectively administered to explore the role of TLR9 in EAN both in vivo and vitro. Following immunization up to the peak phase of EAN, EAN rats inoculated with sODN had remarkably better clinical score of EAN and expressed a significantly inhibited TLR9 signaling pathway. Our study suggests that TLR9 may be involved in the pathogenesis of EAN.

TLR4 signaling via MyD88 and TRIF differentially shape the CD4+ T cell response to Porphyromonas gingivalis hemagglutinin B

Recombinant hemagglutinin B (rHagB), a virulence factor of the periodontal pathogen Porphyromonas gingivalis, has been shown to induce protective immunity against bacterial infection. Furthermore, we have demonstrated that rHagB is a TLR4 agonist for dendritic cells. However, it is not known how rHagB dendritic cell stimulation affects the activation and differentiation of T cells. Therefore, we undertook the present study to examine the role of TLR4 signaling in shaping the CD4(+) T cell response following immunization of mice with rHagB. Immunization with this Ag resulted in the induction of specific CD4(+) T cells and Ab responses. In TLR4(-/-) and MyD88(-/-) but not Toll/IL-1R domain-containing adapter inducing IFN-β-deficient (TRIF(Lps2)) mice, there was an increase in the Th2 CD4(+) T cell subset, a decrease in the Th1 subset, and higher serum IgG(1)/IgG(2) levels of HagB-specific Abs compared with those in wild-type mice. These finding were accompanied by increased GATA-3 and Foxp3 expression and a decrease in the activation of CD4(+) T cells isolated from TLR4(-/-) and MyD88(-/-) mice. Interestingly, TLR4(-/-) CD4(+) T cells showed an increase in IL-2/STAT5 signaling. Whereas TRIF deficiency had minimal effects on the CD4(+) T cell response, it resulted in increased IFN-γ and IL-17 production by memory CD4(+) T cells. To our knowledge, these results demonstrate for the first time that TLR4 signaling, via the downstream MyD88 and TRIF molecules, exerts a differential regulation on the CD4(+) T cell response to HagB Ag. The gained insight from the present work will aid in designing better therapeutic strategies against P. gingivalis infection.

Helminth-induced CD19+CD23hi B cells modulate experimental allergic and autoimmune inflammation

Numerous population studies and experimental models suggest that helminth infections can ameliorate immuno-inflammatory disorders such as asthma and autoimmunity. Immunosuppressive cell populations associated with helminth infections include Treg and alternatively-activated macrophages. In previous studies, we showed that both CD4⁺CD25⁺ Treg, and CD4^– MLN cells from Heligmosomoides polygyus-infected C57BL/6 mice were able to transfer protection against allergic airway inflammation to sensitized but uninfected animals. We now show that CD4^–CD19⁺ MLN B cells from infected, but not naïve, mice are able to transfer a down-modulatory effect on allergy, significantly suppressing airway eosinophilia, IL-5 secretion and pathology following allergen challenge. We further demonstrate that the same cell population can alleviate autoimmune-mediated inflammatory events in the CNS, when transferred to uninfected mice undergoing myelin oligodendrocyte glycoprotein_(p35–55)-induced EAE. In both allergic and autoimmune models, reduction of disease was achieved with B cells from helminth-infected IL-10^−/− donors, indicating that donor cell-derived IL-10 is not required. Phenotypically, MLN B cells from helminth-infected mice expressed uniformly high levels of CD23, with follicular (B2) cell surface markers. These data expand previous observations and highlight the broad regulatory environment that develops during helminth infections that can abate diverse inflammatory disorders in vivo.

Excretory-secretory products (ESP) from Fasciola hepatica induce tolerogenic properties in myeloid dendritic cells

Fasciola hepatica is a helminth trematode that migrates through the host tissues until reaching bile ducts where it becomes an adult. During its migration the parasite releases different excretory-secretory products (ESP), which are in contact with the immune system. In this study, we focused on the effect of ESP on the maturation and function of murine bone marrow derived-dendritic cells (DC). We found that the treatment of DC with ESP failed to induce a classical maturation of these cells, since ESP alone did not activate DC to produce any cytokines, although they impaired the ability of DC to be activated by TLR ligands and also their capacity to stimulate an allospecific response. In addition, using an in vitro ovalbumin peptide-restricted priming assay, ESP-treated DC exhibited a capacity to drive Th2 and regulatory T cell (Treg) polarization of CD4(+) cells from DO11.10 transgenic mice. This was characterized by increased IL-4, IL-5, IL-10 and TGF-beta production and the expansion of CD4(+)CD25(+)Foxp3(+) cells. Our results support the hypothesis that ESP from F. hepatica modulate the maturation and function of DC as part of a generalized immunosuppressive mechanism that involves a bias towards a Th2 response and Treg development.

IL-17 produced by neutrophils regulates IFN-gamma-mediated neutrophil migration in mouse kidney ischemia-reperfusion injury

The IL-23/IL-17 and IL-12/IFN-gamma cytokine pathways have a role in chronic autoimmunity, which is considered mainly a dysfunction of adaptive immunity. The extent to which they contribute to innate immunity is, however, unknown. We used a mouse model of acute kidney ischemia-reperfusion injury (IRI) to test the hypothesis that early production of IL-23 and IL-12 following IRI activates downstream IL-17 and IFN-gamma signaling pathways and promotes kidney inflammation. Deficiency in IL-23, IL-17A, or IL-17 receptor (IL-17R) and mAb neutralization of CXCR2, the p19 subunit of IL-23, or IL-17A attenuated neutrophil infiltration in acute kidney IRI in mice. We further demonstrate that IL-17A produced by GR-1+ neutrophils was critical for kidney IRI in mice. Activation of the IL-12/IFN-gamma pathway and NKT cells by administering alpha-galactosylceramide-primed bone marrow-derived DCs increased IFN-gamma production following moderate IRI in WT mice but did not exacerbate injury or enhance IFN-gamma production in either Il17a-/- or Il17r-/- mice, which suggested that IL-17 signaling was proximal to IFN-gamma signaling. This was confirmed by the finding that IFN-gamma administration reversed the protection seen in Il17a-/- mice subjected to IRI, whereas IL-17A failed to reverse protection in Ifng-/- mice. These results demonstrate that the innate immune component of kidney IRI requires dual activation of the IL-12/IFN-gamma and IL-23/IL-17 signaling pathways and that neutrophil production of IL-17A is upstream of IL-12/IFN-gamma. These mechanisms might contribute to reperfusion injury in other organs.

Parasite immunomodulation and polymorphisms of the immune system

Parasites are accomplished evaders of host immunity. Their evasion strategies have shaped every facet of the immune system, driving diversity within gene families and immune gene polymorphisms within populations. New studies published recently in BMC Biology and Journal of Experimental Medicine document parasite-associated immunosuppression in natural populations and suggest that host genetic variants favoring resistance to parasites may be detrimental in the absence of infection.

T-helper 1 and T-helper 2 adjuvants induce distinct differences in the magnitude, quality and kinetics of the early inflammatory response at the site of injection

Vaccine adjuvants activate the innate immune system and thus influence subsequent adaptive T-cell responses. However, little is known about the initial immune mechanisms preceding the adjuvant-induced differentiation of T-helper (Th) cells. The effect of a T-helper 1 (Th1) adjuvant, dimethyldioctadecylammonium liposomes with monophosphoryl lipid-A (DDA/MPL), and a T-helper 2 adjuvant, aluminium hydroxide [Al(OH)(3)], on early, innate chemotactic signals and inflammatory cell influx at the site of injection was therefore investigated. Injection of the adjuvants into the peritoneal cavity of mice demonstrated distinct differences in the magnitude, quality and kinetics of the response. The inflammatory response to DDA/MPL was prominent, inducing high local levels of pro-inflammatory cytokines, chemokines and a pronounced inflammatory exudate consisting of neutrophils, monocytes/macrophages and activated natural killer cells. This was in contrast to the response induced by Al(OH)(3), which, although sharing some of the early chemokine signals, was more moderate and consisted almost exclusively of neutrophils and eosinophils. Notably, Al(OH)(3) specifically induced the release of a significant amount of interleukin (IL)-5, whereas DDA/MPL induced high amounts of tumour necrosis factor-alpha (TNF-alpha), IL-1alpha and IL-6. Finally, a microarray analysis confirmed that the effect of DDA/MPL was broader with more than five times as many genes being specifically up-regulated after injection of DDA/MPL compared with Al(OH)(3). Thus, the adjuvants induced qualitatively distinct local inflammatory signals early after injection.

IFN-lambda1 (IL-29) inhibits GATA3 expression and suppresses Th2 responses in human naive and memory T cells

IFN-lambda1 (IL-29) plays a novel, emerging role in the inhibition of human Th2 responses. Here, we demonstrate that both naive and memory human CD4(+) T cells express mRNA for the IFN-lambda1-specific receptor, IL-28Ralpha, and are responsive to IFN-lambda1. Expression of Th2 cytokines (IL-4 and IL-13) was suppressed in naive and memory CD4(+) T cells by IFN-lambda1, without affecting their proliferation. Further, acquisition of IL-4Ralpha expression after stimulation was inhibited by IFN-lambda1, as was GATA3 expression. Finally, IFN-lambda1 diminished the change in cell-surface phenotype that accompanies differentiation of "central memory" T cells into "effector memory" T cells. Taken together, our data describe unique immunomodulatory effects of IFN-lambda1 and identify novel mechanisms for the reduction of existing Th2 responses and the regulation of new ones, in circulating naive and memory CD4(+) T cells.

Intradermal immunization improves protective efficacy of a novel TB vaccine candidate

We have developed the Mycobacterium tuberculosis (Mtb) fusion protein (ID83), which contains the three Mtb proteins Rv1813, Rv3620 and Rv2608. We evaluated the immunogenicity and protective efficacy of ID83 in combination with several emulsion-formulated toll-like receptor agonists. The ID83 subunit vaccines containing synthetic TLR4 or TLR9 agonists generated a T helper-1 immune response and protected mice against challenge with Mtb regardless of route. The ID83 vaccine formulated with gardiquimod (a TLR7 agonist) also resulted in a protective response when administered intradermally, whereas the same vaccine given subcutaneously failed to provide protection. This highlights the need to explore different routes of immunization based on the adjuvant formulations used.

IL-12 produced by dendritic cells augments CD8+ T cell activation through the production of the chemokines CCL1 and CCL17

IL-12 family members are an important link between innate and adaptive immunity. IL-12 drives Th1 responses by augmenting IFN-gamma production, which is key for clearance of intracellular pathogens. IL-23 promotes the development of IL-17-producing CD4(+) T cells that participate in the control of extracellular pathogens and the induction of autoimmunity. However, recent studies have shown that these cytokines can modulate lymphocyte migration and cellular interactions. Therefore, we sought to determine the individual roles of IL-12 and IL-23 in naive CD8(+) T cell activation by addressing their ability to influence IFN-gamma production and cellular interaction dynamics during priming by Listeria monocytogenes-infected dendritic cells (DC). We found that IL-12 was the major cytokine influencing the level of IFN-gamma production by CD8(+) T cells while IL-23 had little effect on this response. In addition, we observed that IL-12 promoted longer duration conjugation events between CD8(+) T cells and DC. This enhanced cognate interaction time correlated with increased production of the chemokines CCL1 and CCL17 by WT but not IL-12-deficient DC. Neutralization of both chemokines resulted in reduced interaction time and IFN-gamma production, demonstrating their importance in priming naive CD8(+) T cells. Our study demonstrates a novel mechanism through which IL-12 augments naive CD8(+) T cell activation by facilitating chemokine production, thus promoting more stable cognate interactions during priming.

Review series on helminths, immune modulation and the hygiene hypothesis: mechanisms underlying helminth modulation of dendritic cell function

Dendritic cells (DCs) play a central role in activating CD4 T (T helper, Th) cells. As a component of their response to pathogen-associated stimuli, DCs produce cytokines and express surface molecules that provide important cues to modulate the effector functions of responding Th cells. Much is known of how DCs respond to, and influence immune response outcome to, bacterial and viral pathogens. However, relatively little is understood about how DCs respond to helminth parasites. This is an area of considerable interest since it impacts our understanding of the initiation of Th2 responses, which are stereotypically associated with helminth infections, and the regulation of allergic and autoimmune pathologies which evidence suggests are less severe or absent in individuals infected with helminths. This review attempts to summarize our understanding of the effects of helminth products on dendritic cell biology.

Adjuvants LT-K63 and CpG enhance the activation of dendritic cells in neonatal mice

Dendritic cells (DC) play a major role in the priming of T cells and initiating specific immune responses. We assessed the effects of the adjuvants LT-K63 and CpG on neonatal DC in vivo and in vitro. Cytokine levels (IL-10, IL-12p70 and IL-12p40/IL-23p40) were measured and the expression of the activation markers CD86, CD40 and MHCII on CD11c+ DC was analysed by using FACS. The proportion of MHCII high CD11c+ DC was higher in neonatal mice immunized with a pneumococcal conjugate (PncTT) and LT-K63 or CpG compared with that when PncTT was alone. In vitro stimulation with LT-K63 enhanced the expression of CD86 more on CD11c+ DC from spleens of mice immunized as neonates than those immunized as adults, whereas in vitro stimulation with CpG enhanced the expression of CD86 and CD40 on CD11c+ DC similarly in both age groups. CpG stimulation in vitro enhanced IL-10 and IL-12(p70) production in mice immunized as neonates with PncTT and either adjuvant, but not PncTT alone. The adjuvants LT-K63 and CpG enhance the activation of CD11c+ DC in mice immunized as neonates and can thereby overcome one of the limiting factors in the initiation of the immune response to conjugate vaccines in early life. The fact that neonatal DC are more susceptible to stimulation with either adjuvant, LT-K63 or CpG, could imply that neonatal CD11c+ DC are more easily activated than adult CD11c+ DC, and /or be a consequence of the predominance of different DC subsets in neonatal and adult mice.

Th2 differentiation is unaffected by Jagged2 expression on dendritic cells

Expression of the Jagged Notch ligands by dendritic cells (DCs) has been suggested to play a role in instructing Th2 responses. Supporting this hypothesis, we found that Jagged2 but not Jagged1 expression, correlates with the ability of DCs to induce Th2 responses. Jagged2 expression is up-regulated in response to the helminth soluble Schistosoma mansoni egg Ag, which conditions DCs to induce Th2 responses, and is markedly down-regulated following exposure to TLR agonists that generally promote Th1 responses. Conversely, Jagged1 expression is markedly induced by TLR ligation. Despite these correlations, suppression of expression of Jagged2 using retrovirally delivered small interfering RNA failed to affect the ability of DCs to induce Th2 cell differentiation either in vitro or in vivo. Moreover, retrovirally induced expression of Jagged2 did not enhance the ability of DCs to induce Th2 cell responses. Our data indicate that Jagged2 expression by DCs is not sufficient or required for Th2 cell differentiation.

Sex differences in autoimmune disease from a pathological perspective

Autoimmune diseases affect approximately 8% of the population, 78% of whom are women. The reason for the high prevalence in women is unclear. Women are known to respond to infection, vaccination, and trauma with increased antibody production and a more T helper (Th)2-predominant immune response, whereas a Th1 response and inflammation are usually more severe in men. This review discusses the distribution of autoimmune diseases based on sex and age, showing that autoimmune diseases progress from an acute pathology associated with an inflammatory immune response to a chronic pathology associated with fibrosis in both sexes. Autoimmune diseases that are more prevalent in males usually manifest clinically before age 50 and are characterized by acute inflammation, the appearance of autoantibodies, and a proinflammatory Th1 immune response. In contrast, female-predominant autoimmune diseases that manifest during the acute phase, such as Graves' disease and systemic lupus erythematosus, are diseases with a known antibody-mediated pathology. Autoimmune diseases with an increased incidence in females that appear clinically past age 50 are associated with a chronic, fibrotic Th2-mediated pathology. Th17 responses increase neutrophil inflammation and chronic fibrosis. This distinction between acute and chronic pathology has primarily been overlooked, but greatly impacts our understanding of sex differences in autoimmune disease.

Animal shed Bacillus licheniformis spores possess allergy-protective as well as inflammatory properties

BACKGROUND

Numerous epidemiologic studies have demonstrated an allergy-protective effect of farm life early in childhood. It has been hypothesized that environmental exposure to microbes may contribute to this effect. Because of their small size and thereby their potential for deposition in lower airways of small children, bacterial spores may be candidates for such allergy-protective effects.

OBJECTIVE

To investigate immune responses elicited by exposure to Bacillus spores in experimental settings.

METHODS

Animal shed and mattress dusts were analyzed for bacteria and fungi by aerobic and anaerobic growth. Bacillus licheniformis, the most prominent microorganism found in these samples, was investigated with respect to spore specific stimulation of pattern recognition receptors, monocyte-derived dendritic cells and T(H)-cell polarization in vitro as well as to the prevention of asthma development in a mouse model of allergic asthma.

RESULTS

In vitro, B. licheniformis spores activated a T(H)1 cytokine expression profile. In vivo application of these spores resulted in less spore-specific but long-lasting immune activation preventing eosinophilia and goblet cell hyperplasia; however, they provoked an influx of neutrophils in lung tissue of asthmatic mice.

CONCLUSION

Bacterial spores may contribute to the allergy-protective properties of farming environments, but their persistence in the lung causes ongoing immune activation in mouse experiments.

CpG-ODN but not other TLR-ligands restore the antitumor responses in old mice: the implications for vaccinations in the aged

AIM

There is accumulative evidence indicating that targeting antigen presenting cells (APCs) with different types of adjuvants could result in the induction of antitumor immune responses. It has been hypothesized that APCs function may be altered in the elderly contributing to a decline in the immune function. We evaluated whether targeting APCs following injection with Poly I:C, LPS, flagellin, imiquimod and CpG-ODN would induce an antitumor response in the old.

MATERIALS AND METHODS

The immune and antitumor responses induce Poly I:C, LPS, flagellin, imiquimod and CpG-ODN were compared in young (2 month old) and old (18 months) mice.

RESULTS

Our results indicated that only intratumoral (i.t.) injections of CpG-ODN completely rejected the tumor in both young and old mice. Injections of Poly I:C also induced the rejection of tumors in the young but not in the old. Furthermore, i.t. injections of CpG-ODN promoted the development of protective memory responses in the young and the old. Analysis of the immune responses in the old indicated that CpG-ODN but not Poly-I:C induces: a pro-inflammatory Th1 type response; accumulation and activation of CD4+, CD8+ T and, NK cell responses; activation of APCs; and reduction in the number of Tregs. The activation of these immune-parameters positively correlates with the induction of an antitumor response.

CONCLUSIONS

These studies indicate that there are differences in the level of stimulation with TLR-ligands between young and old APCs and that the aged immune responses can be rescued and exploited for the induction of tumor immunity by targeting APCs with specific TLR-ligands. These results have important clinical implications for developing immunization strategies containing TLR-ligands that will be effective in both the young and old.

Suppression of Th2 cell development by Notch ligands Delta1 and Delta4

Notch signaling plays important roles in Th cell activation. We show that in response to TLR ligation, dendritic cells up-regulate expression of Notch ligands Delta1 and Delta4 via a MyD88-dependent pathway. Expression of Delta1 or Delta4 by dendritic cells enhanced their ability to activate naive Th cells and promote Th1 cell development, and allowed them to strongly inhibit Th2 cell development. Promotion of Th1 cell development was dependent on IFN-gamma and T-bet expression by responding Th cells. However, the inhibition of Th2 cell development occurred independently of IFN-gamma or T-bet, and resulted from a block in IL-4-initiated commitment to the Th2 lineage. The promotion of Th1 cell development by Delta is not a reflection of the delivery of pro-Th1 instructional signal, but rather it is the result of a block in the downstream effects initiated by IL-4 signaling.

T-cell fate and function: PKC-theta and beyond

The serine/threonine-specific protein kinase C-theta (PKC-theta) is a core component of the immunological synapse that was shown in vitro to play a central role in the activation of T cells after T cell receptor (TCR) and co-stimulatory molecule engagement. In recent years, a series of in vivo studies have shown that the situation is far more complex; specifically, PKC-theta signaling is differentially required for Th1, Th2, Th17 and CD8+ cytotoxic T-cell responses. These studies highlight the combination of signals that directly regulate T-cell differentiation and effector responses. In this review, we highlight recent in vivo studies investigating PKC-theta function and discuss this in the context of how the integration of extrinsic signals determines T cell fate and function.

MyD88 negatively controls hypergammaglobulinemia with autoantibody production during bacterial infection

A large body of evidence has convincingly shown that Toll-like receptors are necessary sensors for infections with pathogens, but their activation was also suggested to generate autoimmunity. During experimental infections, the lack of these sensors or of their signaling molecules should lead to a deficient immune response. We found out that MyD88, the major adaptor of the Toll/interleukin-1 (Toll/IL-1) receptor signaling pathway, can actually act as a negative regulator of B-cell function in some settings. MyD88-deficient mice infected by Borrelia burgdorferi developed extreme hypergammaglobulinemia compared to wild-type animals, with high levels of immunoglobulin M (IgM) autoantibodies. In vivo, cell transfer experiments and cell blocking assays showed that this phenotype was not linked to the absence of MyD88 in B cells but rather to CD4 T-cell and likely dendritic cell dysfunctions leading to a Th1-to-Th2 cytokine switch. In addition, our results suggest a relative defect in the Ig class switch recombination process, since MyD88 knockout mice developed mostly IgM antibodies. Collectively, these data emphasize the complex role of the Toll/IL-1 receptor pathway in tuning the immune response against infection and avoiding autoimmunity.

Eosinophil-derived neurotoxin acts as an alarmin to activate the TLR2-MyD88 signal pathway in dendritic cells and enhances Th2 immune responses

Eosinophil-derived neurotoxin (EDN) is an eosinophil granule-derived secretory protein with ribonuclease and antiviral activity. We have previously shown that EDN can induce the migration and maturation of dendritic cells (DCs). Here, we report that EDN can activate myeloid DCs by triggering the Toll-like receptor (TLR)2-myeloid differentiation factor 88 signaling pathway, thus establishing EDN as an endogenous ligand of TLR2. EDN activates TLR2 independently of TLR1 or TLR6. When mice were immunized with ovalbumin (OVA) together with EDN or with EDN-treated OVA-loaded DCs, EDN enhanced OVA-specific T helper (Th)2-biased immune responses as indicated by predominant production of OVA-specific interleukin (IL)-5, IL-6, IL-10, and IL-13, as well as higher levels of immunoglobulin (Ig)G1 than IgG2a. Based on its ability to serve as a chemoattractant and activator of DCs, as well as the capacity to enhance antigen-specific immune responses, we consider EDN to have the properties of an endogenous alarmin that alerts the adaptive immune system for preferential enhancement of antigen-specific Th2 immune responses.

Toll-like receptors, Notch ligands, and cytokines drive the chronicity of lung inflammation

Current dogma supports the concept that the expression of a disease-inducing signature cytokine phenotype is important to the maintenance stage of chronic lung disorders. This cytokine phenotype has been characterized as a polarization toward type 2 cytokines, which are profibrotic and immunoregulatory. The biology of this latter activity could mechanistically explain pathogen-induced exacerbation of chronic lung inflammation, as a skewed cytokine profile in the lung alters dendritic cell function, activates fibroblasts, and facilitates a subsequent "second hit" by an infectious pathogen. In this setting, cytokine biology is also linked to Toll-like receptors (TLRs) in the maintenance of lung immunity, as the activity of this receptor-ligand system by both leukocytes and stromal cells is likely an important component of disease chronicity. The participation of dendritic cells via TLRs in chronic lung disease could facilitate communication circuits established between antigen-presenting cells and lymphocytes. Data suggest that TLR activation via myeloid differentiation factor 88 adaptor protein leads to the induction of a Notch ligand known as Delta-like-4 on dendritic cells that activate the Notch receptor on T cells, promoting a helper T-cell type 1 cytokine response. It is likely that the evolution of host defense signals designed to recognize patterns emitted from a hostile microbial environment may now be superimposed on adaptive immunity and provide the underpinning to support the maintenance of chronic lung disease.

Filaria/Wolbachia activation of dendritic cells and development of Th1-associated responses is dependent on Toll-like receptor 2 in a mouse model of ocular onchocerciasis (river blindness)

Toll-like receptors (TLRs) regulate dendritic cell function and activate signals that mediate the nature of the adaptive immune response. The current study examined the role of TLRs in dendritic cell activation and in regulating T cell and antibody responses to antigens from the filarial parasites Onchocerca volvulus and Brugia malayi, which cause river blindness and lymphatic filariasis, respectively. Bone-marrow-derived CD11c(+) cells from C57BL/6 and TLR4(-/-) mice produced high levels of IL-6 and RANTES, and showed elevated surface CD40 expression, whereas CD11c(+) cells from myeloid differentiation factor 88(-/-) (MyD88(-/-)), TLR2(-/-) and TLR2/4(-/-) mice were not activated. Similarly, IFN-gamma production by splenocytes from immunized TLR2(-/-) mice was significantly impaired compared with splenocytes from C57BL/6 and TLR4(-/-) mice. In contrast, there was no difference among these strains in Th2-associated responses including IL-5 production by splenocytes from immunized animals, serum IgE and IgG(1), or eosinophil infiltration into the corneal stroma. Neutrophil recruitment to the cornea and CXC chemokine production was inhibited in immunized TLR2(-/-) mice compared with C57BL/6 and TLR4(-/-) mice. Taken together, these findings demonstrate an essential role for TLR2 in filaria-induced dendritic cell activation, IFN-gamma production and neutrophil migration to the cornea, but does not affect filaria-induced Th2-associated responses.

Notch ligand Delta-like 4 regulates disease pathogenesis during respiratory viral infections by modulating Th2 cytokines

Recent data have indicated that an important instructive class of signals regulating the immune response is Notch ligand–mediated activation. Using quantitative polymerase chain reaction, we observed that only Delta-like 4 (dll4) was up-regulated on bone marrow–derived dendritic cells after respiratory syncytial virus (RSV) infection, and that it was dependent on MyD88-mediated pathways. Using a polyclonal antibody specific for dll4, the development of RSV-induced disease was examined. Animals treated with anti-dll4 had substantially increased airway hyperresponsiveness compared with control antibody-treated animals. When the lymphocytic lung infiltrate was examined, a significant increase in total CD4⁺ T cells and activated (perforin⁺) CD8⁺ T cells was observed. Isolated lung CD4⁺ T cells demonstrated significant increases in Th2-type cytokines and a decrease in interferon γ, demonstrating an association with increased disease pathogenesis. Parellel in vitro studies examining the integrated role of dll4 with interleukin-12 demonstrated that, together, both of these instructive signals direct the immune response toward a more competent, less pathogenic antiviral response. These data demonstrate that dll4-mediated Notch activation is one regulator of antiviral immunity.

Toll-like receptor-dependent activation of antigen-presenting cells affects adaptive immunity to Helicobacter pylori

BACKGROUND & AIMS

Recognition of infection leads to induction of adaptive immunity through activation of antigen-presenting cells (APCs). Among APCs, dendritic cells (DCs) have the unique capacity to deliver antigens from the periphery to T cells in secondary lymphoid organs.

METHODS

We analyzed molecular mechanisms of the Helicobacter pylori-induced APC activation in vitro and investigated the influence of Myd88 signaling on the phenotype of adaptive immunity to H pylori in a murine infection model.

RESULTS

The adaptor protein Myd88 mediates Toll-like receptor (TLR), interleukin (IL)-1, and IL-18 signaling. DCs from wild-type, IL-1R(-/-), and IL-18(-/-) mice responded to H pylori with secretion of proinflammatory cytokines and up-regulation of major histocompatibility complex II and costimulatory molecules. In Myd88(-/-) DCs these processes were impaired profoundly, showing that TLR-dependent H pylori-sensing affects DC activation. Analysis of the H pylori-specific DC transcriptome revealed that large parts of the bacteria-induced transcriptional changes depended on Myd88 signaling, comprising numerous genes involved in crucial steps of immune regulation, such as DC maturation/differentiation, antigen uptake/presentation, and effector cell recruitment/activation. The impaired ability of Myd88(-/-) DCs, B cells, and macrophages to mount a proinflammatory response to H pylori in vitro was reflected in vivo by reduced gastric inflammation and increased bacterial colonization in Myd88-deficient mice. Furthermore, Helicobacter-specific IgG2c/IgG1 ratios were reduced in Myd88(-/-) animals, suggesting the involvement of the Myd88-dependent pathway in the instruction of adaptive immunity toward a T helper cell type 1 phenotype.

CONCLUSIONS

A principal pathway by which DCs sense H pylori and become activated is the TLR-dependent signaling cascade. In vivo, Myd88 signaling affects adaptive immunity to the bacterium.

STAT1 expression in dendritic cells, but not T cells, is required for immunity to Leishmania major

The generation of Th1 responses is important for resistance to intracellular pathogens, including the parasite, Leishmania major. Although IFN-gammaR/STAT1 signaling promotes a Th1 response via the up-regulation of T-bet, the requirement for STAT1 in Th1 cell differentiation remains controversial. Although in some cases Th1 cells develop independently of STAT1, STAT1(-/-) mice fail to develop a Th1 response during L. major infection. However, the interpretation of this result is complicated by the role STAT1 plays in Ag presentation and, more importantly, in elimination of parasites by macrophages, because both defective Ag presentation and increased parasite burden can influence Th cell development. To resolve this issue, we assessed the ability of STAT1(-/-) T cells to become Th1 cells and protect mice against L. major following adoptive transfer into STAT1-sufficient mice. We found that whereas T-bet is critical for the differentiation of protective Th1 cells during L. major infection, IFN-gammaR and STAT1 are dispensable. Given that a STAT1-independent Th1 cell response was generated by STAT1-sufficient APCs, but not by STAT1(-/-) cells, we next addressed whether dendritic cells (DCs) require STAT1 signaling to effectively present Ag. We found that STAT1(-/-) DCs had impaired up-regulation of MHC and costimulatory molecules, and, as a consequence, the absence of STAT1 resulted in reduced Th1 cell priming. Taken together, these results demonstrate that T cell expression of STAT1 is not required for the development of Th1 cells protective against L. major and instead stress the importance of STAT1 signaling in DCs for the optimal induction of Th1 responses.

Echinococcus granulosus antigen B impairs human dendritic cell differentiation and polarizes immature dendritic cell maturation towards a Th2 cell response

Despite inducing a strong host cellular and humoral immune response, the helminth Echinococcus granulosus is a highly successful parasite that develops, progresses, and ultimately causes chronic disease. Although surgery remains the preferred therapeutic option, pharmacological research now envisages antihelminthic strategies. To understand the mechanisms that E. granulosus uses to escape host immunosurveillance and promote chronic infection, we investigated how two hydatid cyst components, purified antigen B (AgB) and sheep hydatid fluid (SHF), act on host dendritic cell (DC) differentiation from monocyte precursors and how they influence maturation of DC that have already differentiated. We evaluated the immunomodulatory potential of these antigens by performing immunochemical and cytofluorimetric analyses of monocyte-derived DCs from healthy human donors. During monocyte differentiation, AgB and SHF downmodulated CD1a expression and upregulated CD86 expression. Compared with immature DCs differentiated in medium alone (iDCs), AgB- and SHF-differentiated cells stimulated with lipopolysaccharide included a significantly lower percentage of CD83(+) cells (P < 10(-4)) and had weaker costimulatory molecule expression. When stimulated with AgB and SHF, iDCs matured and primed lymphocytes towards the Th2 response typical of E. granulosus infection. SHF and particularly AgB reduced the production of interleukin-12p70 (IL-12p70) and tumor necrosis factor alpha in lipopolysaccharide-stimulated iDCs. Anti-IL-10 antibodies increased the levels of IL-12p70 secretion in AgB- and SHF-matured DCs. AgB and SHF induced interleukin-1 receptor-associated kinase phosphorylation and activated nuclear factor-kappaB, suggesting that Toll-like receptors could participate in E. granulosus-stimulated DC maturation. These results suggest that E. granulosus escapes host immunosurveillance in two ways: by interfering with monocyte differentiation and by modulating DC maturation.