The characteristics and functions of CD4+CD25+ regulatory cells have been well defined in murine and human systems. However, the interaction between CD4+CD25+ T cells and dendritic cells (DC) remains unclear. In this study, we examined the effect of human CD4+CD25+ T cells on maturation and function of monocyte-derived DC. We show that regulatory T cells render the DC inefficient as APCs despite prestimulation with CD40 ligand. This effect was marginally reverted by neutralizing Abs to TGF-β. There was an increased IL-10 secretion and reduced expression of costimulatory molecules in DC. Thus, in addition to direct suppressor effect on CD4+ T cells, regulatory T cells may modulate the immune response through DC.

The clinical use of intravenous immunoglobulin (IVIg) based on its immunomodulatory and anti-inflammatory potential remains an ongoing challenge. Fc␥ receptor-mediated effects of IVIg, although well elucidated in certain pathologies, cannot entirely account for its proven benefit in several autoimmune disorders mediated by autoreactive T cells. In this study, we show that prophylactic infusion of IVIg prevents the devel- IntroductionNatural CD4 ϩ CD25 ϩ regulatory T cells (nTreg) expressing the lineage marker Foxp3 are the key players in controlling immune responses and in maintenance of T-cell homeostasis. 1,2 Therapeutic induction of the Treg represents a novel approach in the treatment of autoimmune pathology. 3,4 CD4 ϩ CD25 ϩ Foxp3 ϩ nTreg develop in thymus, in contrast to "adaptive" or "induced" Treg that develop in peripheral lymphoid tissues from CD4 ϩ conventional T cells (Tconv) and are frequently Foxp3 Ϫ . Although studies have highlighted the role of cytokines interleukin-2 (IL-2), transforming growth factor-␤ (TGF-␤), and IL-10 in Treg development, other factors or mechanisms crucial to Treg homeostasis are not elucidated. 5 Intravenous immunoglobulin (IVIg) is an established therapy for several immune disorders. [6][7][8][9] Several mutually nonexclusive mechanisms have been proposed to explain the beneficial effect of IVIg 7,8 ; however, the issue remains debated and an ongoing challenge. For instance, the Fc␥R-mediated effects of IVIg 10-12 cannot entirely account for its proven benefit in several peripheral and central demyelinating diseases such as GuillainBarré syndrome, chronic inflammatory demyelinating polyneuropathy (CIDP), and relapsing-remitting multiple sclerosis (MS), which are primarily mediated by autoreactive T cells. 6,7,13,14 Because the T cells do not express Fc␥R, 15 the observed effects raise certain speculations, that is, if these effects could be attributed to a direct interaction of the variable region of the immunoglobulin (Ig) G molecules with the T cell or an indirect influence via other cell types such as dendritic cells (DC).During the induction phase of experimental autoimmune encephalomyelitis (EAE), myelin reactive proinflammatory CD4 ϩ T cells proliferate in the periphery, infiltrate the central nervous system (CNS) during the effector phase and, in concert with other inflammatory mediators, lead to demyelination characterized by a progressive paralysis. 16 Natural remission and recovery from relapse in EAE is associated with the recruitment or generation of Treg in the CNS. 17,18 We and others have shown that IVIg protects against EAE development only when administered prophylactically. 14,19 We reasoned that IVIg manifests its protective effect in EAE through an early modulation of autoreactive T cells, and therefore we investigated the regulatory mechanisms, particularly the effect of IVIg on regulatory T cells. Methods Animals, antigen, and tissue culture mediumWe purchased C57BL/6J mice (females, 6-8 weeks of age) from Charles River Laboratories (L'Arbresle, F...

No abstract

Normal immunoglobulin G for therapeutic use (intravenous immunoglobulin [IVIg]) is used in an increasing number of immune-mediated conditions, including acute and chronic/relapsing autoimmune diseases, transplantation, and systemic inflammatory disorders. Several mutually nonexclusive mechanisms of action account for the immunoregulatory effects of IVIg. Although IVIg inhibits T-cell proliferation and T-cell cytokine production, it is unclear whether these effects are directly dependent on the effects of IVIg on T cells or they are dependent through the inhibition of antigen-presenting cell activity. Here, we examined the effects of IVIg on differentiation, maturation, and function of dendritic cells (DCs). We show that IVIg inhibits the differentiation and maturation of DCs in vitro and abrogates the capacity of mature DC to secrete interleukin-12 (IL-12) on activation while enhancing IL-10 production. IVIg-induced down-regulation of costimulatory molecules associated with modulation of cytokine secretion resulted in the inhibition of autoreactive and alloreactive T-cell activation and proliferation. Modulation of DC maturation and function by IVIg is of potential relevance to its immunomodulatory effects in controlling specific immune responses in autoimmune diseases, transplantation, and other immune-mediated conditions.

Initially used as a replacement therapy for immunodeficiency diseases, intravenous immunoglobulin (IVIg) is now widely used for a number of autoimmune and inflammatory diseases. Considerable progress has been made in understanding the mechanisms by which IVIg exerts immunomodulatory effects in autoimmune and inflammatory disorders. The mechanisms of action of IVIg are complex, involving modulation of expression and function of Fc receptors, interference with activation of complement and the cytokine network and of idiotype network, regulation of cell growth, and effects on the activation, differentiation, and effector functions of dendritic cells, and T and B cells.

Proinflammatory cytokines are critically involved in the alteration of adipose tissue biology leading to deterioration of glucose homeostasis in obesity. Here we show a pronounced proinflammatory signature of adipose tissue macrophages in type 2 diabetic obese patients, mainly driven by increased NLRP3-dependent interleukin (IL)-1β production. IL-1β release increased with glycemic deterioration and decreased after gastric bypass surgery. A specific enrichment of IL-17- and IL-22-producing CD4+ T cells was found in adipose tissue of type 2 diabetic obese patients. Coculture experiments identified the effect of macrophage-derived IL-1β to promote IL-22 and IL-17 production by human adipose tissue CD4+ T cells. Reciprocally, adipose tissue macrophages express IL-17 and IL-22 receptors, making them sensitive to IL-17 and IL-22. IL-22 increased IL-1β release by inducing pro-IL-1β transcription through activation of C-Jun pathways in macrophages. In sum, these human data identified IL-1β and the T-cell cytokine IL-22 as key players of a paracrine inflammatory pathway previously unidentified in adipose tissue, with a pathological relevance to obesity-induced type 2 diabetes. These results provide an additional rationale for targeting IL-1β in obesity-linked type 2 diabetes and may have important implications for the conception of novel combined anti-IL-1β and anti-IL-22 immunotherapy in human obesity.

IntroductionA role for von Willebrand factor (VWF) as a chaperone molecule for procoagulant factor VIII (FVIII) has been extensively documented. [1][2][3][4] Under physiologic conditions, VWF binds to FVIII after its release in the circulation. VWF protects FVIII from proteolysis by lipid-bound proteases, stabilizes the FVIII heterodimeric structure, modulates its activity by thrombin, and further regulates its elimination by lipoprotein-related receptors. 5,6 Patients with severe hemophilia A lack functional endogenous FVIII. In up to 30% of the patients, injection of exogenous FVIII to treat hemorrhages results in the development of anti-FVIII antibodies that inhibit the therapeutically administered FVIII. In vivo experimental evidence and clinical observations suggest that the presence of VWF in FVIII preparations is associated with reduced FVIII immunogenicity. 7,8 Cellular and molecular mechanisms underlying a putative protective effect of VWF remain, however, unclear.The induction of a primary anti-FVIII immune response requires the administered FVIII to be endocytosed by professional antigen-presenting cells (APCs) and to be presented to FVIIIspecific naive CD4 ϩ T lymphocytes. In previously untreated patients, dendritic cells (DCs) are presumably the only candidate professional APCs. We hypothesized that VWF protects FVIII from being endocytosed by DCs, thus leading to reduced antigen presentation and stimulation of immune effectors. Materials and methodsDCs were generated from circulating monocytes of healthy blood donors on 5-day culture in X-VIVO 15 -1% AB serum or in RPMI-10% FCS, supplemented with rhGM-CSF (1000 UI/10 6 cells; Immunotools, Friesoythe, Germany) and rhIL-4 (500 UI/10 6 cells; R&D Systems, Lille, France). Surface phenotypic expression confirmed their immature status (data not shown).DCs generated in X-VIVO 15 -1% AB serum were incubated with FVIII-FITC (molar ratio, 1:25) alone or in the presence of VWF (Wilfactin) or human serum albumin (HSA). Conjugation of FVIII with FITC did not alter its specific activity (Ͼ 4000 IU/mg) and its interaction with a series of monoclonal anti-FVIII IgG (data not shown) and with VWF ( Figures S1 and S4, available on the Blood website; see the Supplemental Figures link at the top of the online article).DCs from donors with the DRB1*1501/DRB5*01 haplotype, generated in RPMI-10% FCS, were used for T-lymphocyte activation studies. The synthetic FVIII-derived I 2144 -T 2161 peptide (NeoMPS, Strasbourg, France) and human recombinant factor IX (Benefix) were used as controls.For confocal microscopy studies, DCs were fixed with 100% ethanol and mounted on glass slides. Images were acquired using a Leica SP2 confocal microscope (Leica, Mannheim, Germany) coupled to a Leica DMIRE2 inverted microscope (Wetzlar, Germany). The detection wavelength range was 500 to 580 nm for FITC. Results and discussionWe first analyzed the kinetics of internalization of FITC-labeled FVIII by DCs. Incubation of DCs with FVIII-FITC resulted in a dose-dependent labeling of the cells ...

Hemophilia A is an X chromosome-linked recessive disorder resulting in defective or deficient factor VIII (FVIII) molecules, which, in its severe form, is a life-threatening and crippling hemorrhagic disease. Infusion of homologous FVIII to patients with severe hemophilia A results, in 25% of patients, in the emergence of alloantibodies against FVIII (inhibitors)( ref. 1) that inhibit FVIII procoagulant activity by steric hindrance of the interaction of FVIII either with stabilizing molecules, with molecules essential for its activity or with activating molecules. Here, we report on the proteolysis of FVIII by alloantibodies of two patients with severe hemophilia A, demonstrating a previously unknown mechanism by which FVIII inhibitors may prevent the pro-coagulant function of FVIII. The kinetic parameters of FVIII hydrolysis indicate a functional role for the catalytic immune response in the inactivation of FVIII in vivo. The characterization of alloantibodies against FVIII as site-specific proteases may provide new approaches to the treatment of FVIII inhibitors.