A novel role of endothelin-1 in linking Toll-like receptor 7-mediated inflammation to fibrosis in congenital heart block

Autoimmune associated congenital heart block (CHB) may result from pathogenic cross-talk between inflammatory and profibrosing pathways. Incubation of macrophages with immune complexes (IC) composed of Ro60, a target of the pathologic maternal autoantibodies necessary for CHB, hY3 ssRNA, and affinity-purified anti-Ro60 antibody induces the Toll-like receptor 7 (TLR7)-dependent generation of supernatants that provoke a fibrosing phenotype in human fetal cardiac fibroblasts. We show herein that these cells are a major source of TGFβ and that endothelin-1 (ET-1) is one of the key components responsible for the profibrosing effects generated by stimulated macrophages. Supernatants from macrophages incubated with IC induced the fibroblast secretion of TGFβ, which was inhibited by treating the macrophages with an antagonist of TLR7. Under the same conditions, the induced fibroblast secretion of TGFβ was decreased by inhibitors of the ET-1 receptors ETa or ETb or by an anti-ET-1 antibody but not by an isotype control. Exogenous ET-1 induced a profibrosing phenotype, whereas fibroblasts transfected with either ETa or ETb siRNA were unresponsive to the profibrosing effects of the IC-generated macrophage supernatants. Immunohistochemistry of the hearts from two fetuses dying with CHB revealed the presence of ET-1-producing mononuclear cells in the septal region in areas of calcification and fibrosis. In conclusion, these data support a novel role of ET-1 in linking TLR7 inflammatory signaling to subsequent fibrosis and provide new insight in considering therapeutics for CHB.

Autoimmune skin inflammation is dependent on plasmacytoid dendritic cell activation by nucleic acids via TLR7 and TLR9

Lupus-prone mice develop a chronic inflammatory response to cutaneous injury that depends on the production of type I interferon, TLR7, and TLR9.

Recognition of endogenous DNA and RNA by cells expressing TLR7 and TLR9 is an important contributor to the pathogenesis of systemic lupus erythematosus and has been suggested to contribute to cutaneous lupus and to a group of related inflammatory skin diseases termed interface dermatitis. We have developed a mouse model of TLR7- and TLR9-dependent skin inflammation using tape stripping. In normal mice, this resulted in a rapid but transient inflammatory cell infiltration accompanied by induction of type I IFN production by plasmacytoid dendritic cells (PDCs) and release of extracellular traps and proinflammatory cytokines by neutrophils. These responses were strongly reduced in MyD88-deficient mice and in mice treated with a bifunctional inhibitor of TLR7 and TLR9. In contrast, in lupus-prone (NZBxNZW)F₁ mice, tape stripping induced the development of chronic lesions characterized by a persistent type I IFN gene signature and many clinical and histological features of cutaneous lupus. Depletion of PDCs before injury prevented the development of skin lesions, whereas treatment with a bifunctional TLR7/9 inhibitor before tape stripping or after the initial lesion was established led to a significant reduction of the disease. These data suggest that inhibitors of TLR7 and TLR9 signaling have potential therapeutic application for the treatment of interface dermatitis.

Ro60-associated single-stranded RNA links inflammation with fetal cardiac fibrosis via ligation of TLRs: a novel pathway to autoimmune-associated heart block

Activation of TLR by ssRNA after FcgammaR-mediated phagocytosis of immune complexes (IC) may be relevant in autoimmune-associated congenital heart block (CHB) where the obligate factor is a maternal anti-SSA/Ro Ab and the fetal factors, protein/RNA on an apoptotic cardiocyte and infiltrating macrophages. This study addressed the hypothesis that Ro60-associated ssRNAs link macrophage activation to fibrosis via TLR engagement. Both macrophage transfection with noncoding ssRNA that bind Ro60 and an IC generated by incubation of Ro60-ssRNA with an IgG fraction from a CHB mother or affinity purified anti-Ro60 significantly increased TNF-alpha secretion, an effect not observed using control RNAs or normal IgG. Dependence on TLR was supported by the significant inhibition of TNF-alpha release by IRS661 and chloroquine. The requirement for FcgammaRIIIa-mediated delivery was provided by inhibition with an anti-CD16a Ab. Fibrosis markers were noticeably increased in fetal cardiac fibroblasts after incubation with supernatants generated from macrophages transfected with ssRNA or incubated with the IC. Supernatants generated from macrophages with ssRNA in the presence of IRS661 or chloroquine did not cause fibrosis. In a CHB heart, but not a healthy heart, TLR7 immunostaining was localized to a region near the atrioventricular groove at a site enriched in mononuclear cells and fibrosis. These data support a novel injury model in CHB, whereby endogenous ligand, Ro60-associated ssRNA, forges a nexus between TLR ligation and fibrosis instigated by binding of anti-Ro Abs to the target protein likely accessible via apoptosis.

Self-RNA-antimicrobial peptide complexes activate human dendritic cells through TLR7 and TLR8

Dendritic cell (DC) responses to extracellular self-DNA and self-RNA are prevented by the endosomal seclusion of nucleic acid–recognizing Toll-like receptors (TLRs). In psoriasis, however, plasmacytoid DCs (pDCs) sense self-DNA that is transported to endosomal TLR9 upon forming a complex with the antimicrobial peptide LL37. Whether LL37 also interacts with extracellular self-RNA and how this may contribute to DC activation in psoriasis is not known. Here, we report that LL37 can bind self-RNA released by dying cells, protect it from extracellular degradation, and transport it into endosomal compartments of DCs. In pDC, self-RNA–LL37 complexes activate TLR7 and, like self-DNA–LL37 complexes, trigger the secretion of IFN-α without inducing maturation or the production of IL-6 and TNF-α. In contrast to self-DNA–LL37 complexes, self-RNA–LL37 complexes also trigger the activation of classical myeloid DCs (mDCs). This occurs through TLR8 and leads to the production of TNF-α and IL-6, and the differentiation of mDCs into mature DCs. We also found that self-RNA–LL37 complexes are present in psoriatic skin lesions and are associated with mature mDCs in vivo. Our results demonstrate that the cationic antimicrobial peptide LL37 converts self-RNA into a trigger of TLR7 and TLR8 in human DCs, and provide new insights into the mechanism that drives the auto-inflammatory responses in psoriasis.

Development of TLR inhibitors for the treatment of autoimmune diseases

SUMMARY

The innate immune system is a critical element of protection from invading pathogens. The specific receptors that recognize various components of the pathogens trigger signals that result in the production of proinflammatory cytokines as well as the activation of antigen-presenting cells, which activate the adaptive immune system. The discovery of the Toll-like receptors (TLRs) as important components of pathogen recognition has brought new understanding of the key signaling molecules involves in innate immune activation. Interestingly, it appears that most TLRs can recognize self-ligands as well and that mechanisms are required to discriminate between self and non-self ligands. One of these mechanisms is the expression of all the nucleic acid-specific TLR in endosomal compartments and not on the cell surface. Inappropriate activation of TLRs by self-components can result in sterile inflammation or autoimmunity. For example, TLR7 and TLR9 activation by endogenous RNA and DNA, transported to the endosomes in the form of immune complexes or non-covalently associated with cationic peptides, could be an important mechanism involved in promoting diseases such as systemic lupus erythematosus and psoriasis. In this review, we discuss the rationale for self-recognition by TLR7 and TLR9 as an important part of the development of lupus and other autoimmune diseases. We describe novel inhibitors of these receptors and provide evidence to support their use as novel therapeutic agents for autoimmunity.

Strategies for use of IL-10 or its antagonists in human disease

SUMMARY

Interleukin-10 (IL-10) is a cytokine with broad anti-inflammatory properties by its suppression of both macrophage and dendritic cell function, including antigen-presenting cell function and the production of proinflammatory cytokines. This can result subsequently in the feedback regulation of both T-helper 1 (Th1)-type and Th2-type responses. This review discusses the potential use of IL-10 or agents that induce IL-10 as potential anti-inflammatory therapies in inflammatory diseases. Although IL-10-deficient mice develop colitis in the presence of normal gut flora and clear certain intracellular pathogens more efficiently, this is often accompanied by immunopathology, which can be lethal to the host. This reinforces the anti-inflammatory properties of IL-10, although it should be noted that as discussed below, IL-10 can also promote B-cell and other immune responses under particular settings. A penalty of its role to limit the immune and inflammatory responses to pathogens and prevent damage to the host is that high or dysregulated levels of IL-10 may result in chronic infection. Thus, antagonists of IL-10 show great potential as adjuvants in preventative or therapeutic vaccines against chronic infection or cancer. This article reviews basic published studies on IL-10, which may lead to potential uses of IL-10 or its antagonists in human disease.

Signalling pathways leading to IFN-alpha production in human plasmacytoid dendritic cell and the possible use of agonists or antagonists of TLR7 and TLR9 in clinical indications

Plasmacytoid dendritic cells (PDC) are highly specialized immune cells capable of producing large amounts of type I and III IFN in response to viral infection. This response is mediated through TLR7 and TLR9 signalling pathways. In addition, PDC can differentiate into fully mature dendritic cells able to efficiently crosspresent viral antigens, thus playing an important role in adaptive immunity. This dual property of PDC is being used in clinical settings where synthetic TLR7 and TLR9 ligands are currently evaluated in clinical trials for the treatment of viral infections, allergies and cancers. Interestingly, there is evidence suggesting that chronic activation of PDC by endogenous RNA and DNA containing immune complexes maybe an important mechanism of driving autoimmunity and significant efforts to develop bi-functional antagonists of TLR7 and TLR9 are currently underway.

PI3K is critical for the nuclear translocation of IRF-7 and type I IFN production by human plasmacytoid predendritic cells in response to TLR activation

Plasmacytoid predendritic cells (pDCs) are the main producers of type I interferon (IFN) in response to Toll-like receptor (TLR) stimulation. Phosphatidylinositol-3 kinase (PI3K) has been shown to be activated by TLR triggering in multiple cell types; however, its role in pDC function is not known. We show that PI3K is activated by TLR stimulation in primary human pDCs and demonstrate, using specific inhibitors, that PI3K is required for type I IFN production by pDCs, both at the transcriptional and protein levels. Importantly, PI3K was not involved in other proinflammatory responses of pDCs, including tumor necrosis factor α and interleukin 6 production and DC differentiation. pDCs preferentially expressed the PI3K δ subunit, which was specifically involved in the control of type I IFN production. Although uptake and endosomal trafficking of TLR ligands were not affected in the presence of PI3K inhibitors, there was a dramatic defect in the nuclear translocation of IFN regulatory factor (IRF) 7, whereas nuclear factor κB activation was preserved. Thus, PI3K selectively controls type I IFN production by regulating IRF-7 nuclear translocation in human pDCs and could serve as a novel target to inhibit pathogenic type I IFN in autoimmune diseases.

Selective predisposition to bacterial infections in IRAK-4-deficient children: IRAK-4-dependent TLRs are otherwise redundant in protective immunity

Human interleukin (IL) 1 receptor–associated kinase 4 (IRAK-4) deficiency is a recently discovered primary immunodeficiency that impairs Toll/IL-1R immunity, except for the Toll-like receptor (TLR) 3– and TLR4–interferon (IFN)-a/b pathways. The clinical and immunological phenotype remains largely unknown. We diagnosed up to 28 patients with IRAK-4 deficiency, tested blood TLR responses for individual leukocyte subsets, and TLR responses for multiple cytokines. The patients' peripheral blood mononuclear cells (PBMCs) did not induce the 11 non-IFN cytokines tested upon activation with TLR agonists other than the nonspecific TLR3 agonist poly(I:C). The patients' individual cell subsets from both myeloid (granulocytes, monocytes, monocyte-derived dendritic cells [MDDCs], myeloid DCs [MDCs], and plasmacytoid DCs) and lymphoid (B, T, and NK cells) lineages did not respond to the TLR agonists that stimulated control cells, with the exception of residual responses to poly(I:C) and lipopolysaccharide in MDCs and MDDCs. Most patients (22 out of 28; 79%) suffered from invasive pneumococcal disease, which was often recurrent (13 out of 22; 59%). Other infections were rare, with the exception of severe staphylococcal disease (9 out of 28; 32%). Almost half of the patients died (12 out of 28; 43%). No death and no invasive infection occurred in patients older than 8 and 14 yr, respectively. The IRAK-4–dependent TLRs and IL-1Rs are therefore vital for childhood immunity to pyogenic bacteria, particularly Streptococcus pneumoniae. Conversely, IRAK-4–dependent human TLRs appear to play a redundant role in protective immunity to most infections, at most limited to childhood immunity to some pyogenic bacteria.

Toll-like receptor 4-dependent contribution of the immune system to anticancer chemotherapy and radiotherapy

Conventional cancer treatments rely on radiotherapy and chemotherapy. Such treatments supposedly mediate their effects via the direct elimination of tumor cells. Here we show that the success of some protocols for anticancer therapy depends on innate and adaptive antitumor immune responses. We describe in both mice and humans a previously unrecognized pathway for the activation of tumor antigen-specific T-cell immunity that involves secretion of the high-mobility-group box 1 (HMGB1) alarmin protein by dying tumor cells and the action of HMGB1 on Toll-like receptor 4 (TLR4) expressed by dendritic cells (DCs). During chemotherapy or radiotherapy, DCs require signaling through TLR4 and its adaptor MyD88 for efficient processing and cross-presentation of antigen from dying tumor cells. Patients with breast cancer who carry a TLR4 loss-of-function allele relapse more quickly after radiotherapy and chemotherapy than those carrying the normal TLR4 allele. These results delineate a clinically relevant immunoadjuvant pathway triggered by tumor cell death.

Interferon-alpha promotes abnormal vasculogenesis in lupus: a potential pathway for premature atherosclerosis

Individuals with systemic lupus erythematosus (SLE) have a striking increase in premature atherosclerosis of unclear etiology. Accelerated endothelial cell apoptosis occurs in SLE and correlates with endothelial dysfunction. Endothelial progenitor cells (EPCs) and myelomonocytic circulating angiogenic cells (CACs) are crucial in blood vessel repair after vascular damage, and decreased levels or abnormal function of EPCs/CACs are established atherosclerosis risk factors. We investigated if vascular repair is impaired in SLE. We report that SLE patients display abnormal phenotype and function of EPCs/CACs. These abnormalities are characterized by significant decreases in the number of circulating EPCs (310 +/- 50 EPCs/mL of blood in SLE versus 639 +/- 102 in controls) and significant impairments in the capacity of EPCs/CACs to differentiate into mature ECs and synthesize adequate levels of the proangiogenic molecules vascular endothelial growth factor (VEGF) and hepatic growth factor (HGF). These abnormalities are triggered by interferon-alpha (IFN-alpha), which induces EPC and CAC apoptosis and skews myeloid cells toward nonangiogenic phenotypes. Lupus EPCs/CACs have increased IFN-alpha expression and their supernatants promote higher induction of IFN-inducible genes. Importantly, neutralization of IFN pathways restores a normal EPC/CAC phenotype in lupus. SLE is characterized by an imbalance between endothelial cell damage and repair triggered by type I IFNs, which might promote accelerated atherosclerosis.

Therapeutic targeting of innate immunity with Toll-like receptor agonists and antagonists

The identification of the antigen recognition receptors for innate immunity, most notably the Toll-like receptors, has sparked great interest in therapeutic manipulation of the innate immune system. Toll-like receptor agonists are being developed for the treatment of cancer, allergies and viral infections, and as adjuvants for potent new vaccines to prevent or treat cancer and infectious diseases. As recognition grows of the role of inappropriate Toll-like receptor stimulation in inflammation and autoimmunity, significant efforts have begun to develop antagonists to Toll-like receptors as well.

Properties regulating the nature of the plasmacytoid dendritic cell response to Toll-like receptor 9 activation

Human plasmacytoid dendritic cells (PDCs) can produce interferon (IFN)-α and/or mature and participate in the adaptive immune response. Three classes of CpG oligonucleotide ligands for Toll-like receptor (TLR)9 can be distinguished by different sequence motifs and different abilities to stimulate IFN-α production and maturation of PDCs. We show that the nature of the PDC response is determined by the higher order structure and endosomal location of the CpG oligonucleotide. Activation of TLR9 by the multimeric CpG-A occurs in transferrin receptor (TfR)-positive endosomes and leads exclusively to IFN-α production, whereas monomeric CpG-B oligonucleotides localize to lysosome-associated membrane protein (LAMP)-1–positive endosomes and promote maturation of PDCs. However, CpG-B, when complexed into microparticles, localizes in TfR-positive endosomes and induces IFN-α from PDCs, whereas monomeric forms of CpG-A localize to LAMP-1–positive endosomes accompanied by the loss of IFN-α production and a gain in PDC maturation activity. CpG-C sequences, which induce both IFN-α and maturation of PDCs, are distributed in both type of endosomes. Encapsulation of CpG-C in liposomes stable above pH 5.75 completely abrogated the IFN-α response while increasing PDC maturation. This establishes that the primary determinant of TLR9 signaling is not valency but endosomal location and demonstrates a strict compartmentalization of the biological response to TLR9 activation in PDCs.

Nucleic acids of mammalian origin can act as endogenous ligands for Toll-like receptors and may promote systemic lupus erythematosus

Raised serum levels of interferon (IFN)-alpha have been observed in systemic lupus erythematosus (SLE) patients, and these levels are correlated with both disease activity and severity. The origin of this IFN-alpha is still unclear, but increasing evidence suggests the critical involvement of activated plasmacytoid predendritic cells (PDCs). In SLE patients, DNA and RNA viruses, as well as immune complexes (ICs), that consist of autoantibodies specific to self-DNA and RNA protein particles can stimulate production of IFN-alpha. We have developed three series of oligonucleotide (ODN)-based inhibitors of Toll-like receptor (TLR) signaling. These ODNs include inhibitors of TLR9, inhibitors of TLR7 but not TLR9, and sequences that inhibit both TLR7 and TLR9. Specificity of these inhibitors is confirmed by inhibition of IFN-alpha production by PDCs in response to DNA or RNA viruses. We show that mammalian DNA and RNA, in the form of ICs, are potent self-antigens for TLR9 and TLR7, respectively, and induce IFN-alpha production by PDCs. This work suggests that TLRs may have a critical role in the promotion of lupus through the induction of IFN-alpha by PDCs. These inhibitors of TLR signaling thus represent novel therapeutic agents with potential for the treatment of lupus.

Reversing the defective induction of IL-10-secreting regulatory T cells in glucocorticoid-resistant asthma patients

We previously reported that human CD4+ Tregs secrete high levels of IL-10 when stimulated in the presence of dexamethasone and calcitriol (vitamin D3). We now show that following stimulation by allergen, IL-10-secreting Tregs inhibit cytokine secretion by allergen-specific Th2 cells in an IL-10-dependent manner. A proportion of patients with severe asthma fail to demonstrate clinical improvement upon glucocorticoid therapy, and their asthma is characterized as glucocorticoid resistant (SR, abbreviation derived from "steroid resistant"). Dexamethasone does not enhance secretion of IL-10 by their CD4+ T cells. Addition of vitamin D3 with dexamethasone to cultures of SR CD4+ T cells enhanced IL-10 synthesis to levels observed in cells from glucocorticoid-sensitive patients cultured with dexamethasone alone. Furthermore, pretreatment with IL-10 fully restored IL-10 synthesis in these cells in response to dexamethasone. Vitamin D3 significantly overcame the inhibition of glucocorticoid-receptor expression by dexamethasone while IL-10 upregulated glucocorticoid-receptor expression by CD4+ T cells, suggesting potential mechanisms whereby these treatments may overcome poor glucocorticoid responsiveness. We show here that administration of vitamin D3 to healthy individuals and SR asthmatic patients enhanced subsequent responsiveness to dexamethasone for induction of IL-10. This strongly suggests that vitamin D3 could potentially increase the therapeutic response to glucocorticoids in SR patients.

Human TLR-7-, -8-, and -9-mediated induction of IFN-alpha/beta and -lambda Is IRAK-4 dependent and redundant for protective immunity to viruses

Five TLRs are thought to play an important role in antiviral immunity, sensing viral products and inducing IFN-alpha/beta and -lambda. Surprisingly, patients with a defect of IRAK-4, a critical kinase downstream from TLRs, are resistant to common viruses. We show here that IFN-alpha/beta and -lambda induction via TLR-7, TLR-8, and TLR-9 was abolished in IRAK-4-deficient blood cells. In contrast, IFN-alpha/beta and -lambda were induced normally by TLR-3 and TLR-4 agonists. Moreover, IFN-beta and -lambda were normally induced by TLR-3 agonists and viruses in IRAK-4-deficient fibroblasts. We further show that IFN-alpha/beta and -lambda production in response to 9 of 11 viruses tested was normal or weakly affected in IRAK-4-deficient blood cells. Thus, IRAK-4-deficient patients may control viral infections by TLR-3- and TLR-4-dependent and/or TLR-independent production of IFNs. The TLR-7-, TLR-8-, and TLR-9-dependent induction of IFN-alpha/beta and -lambda is strictly IRAK-4 dependent and paradoxically redundant for protective immunity to most viruses in humans.

Inhibitors of TLR-9 act on multiple cell subsets in mouse and man in vitro and prevent death in vivo from systemic inflammation

In parallel with the discovery of the immunostimulatory activities of CpG-containing oligodeoxynucleotides, several groups have reported specific DNA sequences that could inhibit activation by CpG-containing oligodeoxynucleotides in mouse models. We show that these inhibitory sequences, termed IRS, inhibit TLR-9-mediated activation in human as well as mouse cells. This inhibitory activity includes proliferation and IL-6 production by B cells, and IFN-alpha and IL-12 production by plasmacytoid dendritic cells. Our studies of multiple cell types in both mice and humans show the optimal IRS to contain a GGGG motif within the sequence, and the activity to require a phosphorothioate backbone. Although the GGGG motif readily itself leads to formation of a tetrameric oligodeoxynucleotide structure, inhibitory activity resides exclusively in the single-stranded form. When coinjected with a CpG oligodeoxynucleotide in vivo, IRS were shown to inhibit inflammation through a reduction in serum cytokine responses. IRS do not need to be injected at the same site to inhibit, demonstrating that rapid, systemic inhibition of TLR-9 can be readily achieved. IRS can also inhibit a complex pathological response to ISS, as shown by protection from death after massive systemic inflammation induced by a CpG-containing oligodeoxynucleotides.

IL-10-Secreting Regulatory T Cells Do Not Express Foxp3 but Have Comparable Regulatory Function to Naturally Occurring CD4+CD25+ Regulatory T Cells

Regulatory T cells (T(Reg)) control immune responses to self and nonself Ags. The relationship between Ag-driven IL-10-secreting T(Reg) (IL-10-T(Reg)) and naturally occurring CD4(+)CD25(+) T(Reg) is as yet unclear. We show that mouse IL-10-T(Reg) obtained using either in vitro or in vivo regimens of antigenic stimulation did not express the CD4(+)CD25(+) T(Reg)-associated transcription factor Foxp3. However, despite the absence of Foxp3 expression, homogeneous populations of IL-10-T(Reg) inhibited the in vitro proliferation of CD4(+)CD25(-) T cells with a similar efficiency to that of CD4(+)CD25(+) T(Reg). This inhibition of T cell proliferation by IL-10-T(Reg) was achieved through an IL-10-independent mechanism as seen for CD4(+)CD25(+) T(Reg) and was overcome by exogenous IL-2. Both IL-10-T(Reg) and CD4(+)CD25(+) T(Reg) were similar in that they produced little to no IL-2. These data show that Foxp3 expression is not a prerequisite for IL-10-T(Reg) activity in vitro or in vivo, and suggest that IL-10-T(Reg) and naturally occurring CD4(+)CD25(+) T(Reg) may have distinct origins.

IL-10 regulates plasmacytoid dendritic cell response to CpG-containing immunostimulatory sequences

Immunostimulatory sequences (ISS) are short oligonucleotides containing unmethylated cytosine-phosphate-guanine (CpG) dinucleotides that stimulate innate immune responses through Toll-like receptor-9 on B cells and plasmacytoid dendritic cell (PDC) precursors. The anti-inflammatory cytokine interleukin (IL)-10 is predicted to be a potent inhibitor of many of the activities described for ISS, and this may impact the use of ISS in disease states characterized by elevated IL-10. As the activities of ISS on PDCs are central to many clinical applications of ISS, we have studied the effects of IL-10 on PDC stimulation by 3 distinct classes of ISS. IL-10 inhibited cytokine production and survival of ISS-activated PDCs; however, IL-12 induction was much more sensitive to inhibition than interferon (IFN)-alpha induction. Within the PDC population are cells that respond to ISS by producing either IL-12 or IFN-alpha but not both cytokines. IL-12-producing PDCs require costimulation through CD40 and appear more mature than IFN-alpha-producing PDCs. The 3 distinct classes of ISS differed with respect to induction of PDC maturation and T-cell priming capacity. IL-10 regulated PDC activation but did not inhibit the subsequent T-cell-priming ability of PDCs already activated by ISS.

In vitro generation of interleukin 10-producing regulatory CD4(+) T cells is induced by immunosuppressive drugs and inhibited by T helper type 1 (Th1)- and Th2-inducing cytokines

We show that a combination of the immunosuppressive drugs, vitamin D3 and Dexamethasone, induced human and mouse naive CD4(+) T cells to differentiate in vitro into regulatory T cells. In contrast to the previously described in vitro derived CD4(+) T cells, these cells produced only interleukin (IL)-10, but no IL-5 and interferon (IFN)-gamma, and furthermore retained strong proliferative capacity. The development of these IL-10-producing cells was enhanced by neutralization of the T helper type 1 (Th1)- and Th2-inducing cytokines IL-4, IL-12, and IFN-gamma. These immunosuppressive drugs also induced the development of IL-10-producing T cells in the absence of antigen-presenting cells, with IL-10 acting as a positive autocrine factor for these T cells. Furthermore, nuclear factor (NF)-kappaB and activator protein (AP)-1 activities were inhibited in the IL-10-producing cells described here as well as key transcription factors involved in Th1 and Th2 subset differentiation. The regulatory function of these in vitro generated IL-10-producing T cells was demonstrated by their ability to prevent central nervous system inflammation, when targeted to the site of inflammation, and this function was shown to be IL-10 dependent. Generating homogeneous populations of IL-10-producing T cells in vitro will thus facilitate the use of regulatory T cells in immunotherapy.

1alpha,25-Dihydroxyvitamin d3 has a direct effect on naive CD4(+) T cells to enhance the development of Th2 cells

1alpha,25-Dihydroxyvitamin D3 (vitD3) is an immunoregulatory hormone with beneficial effects on Th1 mediated autoimmune diseases. Although the inhibitory effects of vitD3 on macrophages and dendritic cells are well documented, any direct effects of vitD3 on Th cell development are not clearly defined. Using CD4(+)Mel14(+) T cells derived from mice on a BALB/c and a C57BL/6 genetic background we examined the effect of vitD3 on Th cell development. We demonstrated that vitD3 affects Th cell polarization by inhibiting Th1 (IFN-gamma production) and augmenting Th2 cell development (IL-4, IL-5, and IL-10 production). These effects were observed in cultures driven with splenic APC and Ag, as well as with anti-CD3 and anti-CD28 alone, indicating that CD4(+) cells can also be direct targets for vitD3. The enhanced Th2 development by vitD3 was found in both BALB/c and C57BL/6 mice. An increased expression of the Th2-specific transcription factors GATA-3 and c-maf correlated with the increased production of Th2 cytokines after vitD3 treatment. The vitD3-induced effects were largely mediated via IL-4, because neutralization of IL-4 almost completely abrogated the augmented Th2 cell development after vitD3 treatment. These findings suggest that vitD3 acts directly on Th cells and can, in the absence of APC, enhance the development of a Th2 phenotype and augment the expression of the transcription factors c-maf and GATA-3. Our findings suggest that the beneficial effects of vitD3 in autoimmune diseases and transplantation operate through prevention of strong Th1 responses via the action on the APC, while simultaneously directly acting on the T cell to enhance Th2 cell development.

A critical role for interleukin 18 in primary and memory effector responses to Listeria monocytogenes that extends beyond its effects on Interferon gamma production

The stimulation of interferon (IFN)-gamma by interleukin (IL)-12 has been shown to provide protection from intracellular pathogens such as Listeria monocytogenes. Tumor necrosis factor (TNF) is also a major player in the resolution of Listeria infections and is suggested to have more global effects than can be explained by the induction of IFN-gamma alone. Since IL-18 synergizes with IL-12 to induce IFN-gamma production by natural killer and T helper (Th)1 cells, we determined its role in responses to Listeria. IL-18 appeared to be even more potent than either IL-12 or IFN-gamma for protection against this pathogen and IL-18 enhanced bacterial clearance in the complete absence of IFN-gamma. Indeed IL-18 was comparable to TNF in its ability to resolve the infection and showed a lowered protective capacity in the absence of TNF. Moreover, IL-18 induced macrophages to secrete both TNF and nitric oxide after a Listeria infection. IL-18 was also essential for optimal IFN-gamma production by antigen-specific T cells. Therefore, IL-18 operates via its effects on both the innate immune response, including macrophages, as well as on Th1 cells, to protect against Listeria.