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Exogenous Antigens (exogenous + antigen)

Distribution by Scientific Domains

Medical Sciences	100%

Selected Abstracts

Uncompromised generation of a specific H-2DM-dependent peptide-MHC class,II complex from exogenous antigen in Leishmania mexicana -infected dendritic cells

EUROPEAN JOURNAL OF IMMUNOLOGY, Issue 12 2003
Clare
Abstract Leishmania infection inhibits the capacity of macrophages (M,) to present antigens to CD4+ T cells. Relocation of MHC class,II and H-2DM to the parasitophorous vacuole (PV) and their subsequent degradation by the parasite may contribute to this defect. Dendritic cells (DC) are critical for initiation of primary T cell responses. DC can process Leishmania antigen and elicit Leishmania -specific T cells, but it is unknown whether exposure to Leishmania impairs this capacity. In particular, it is not clear whether DC containing live parasites efficiently process and present antigens. We investigated the ability of mouse bone marrow-derived DC infected with L. mexicana to generate pigeon cytochrome,c (PCC) peptide-MHC class II complexes, using the mAb D4, which recognizes PCC89,104 H-2Ek, and the PCC-specific T cell hybridoma 2B4. We show that H-2DM-dependent complex generation is not compromised by infection and that complexes are fully recognized by specific T cells. We further show that in contrast to infected M,, in infected DC cytoplasmic H-2DM is not down-regulated and not relocated to the parasite-containing vacuole. This observation may explain the continued ability of infected DC to present PCC, and also indicates differences in the habitat of these intracellular parasites in DC compared to M,. [source]

Cross-priming utilizes antigen not available to the direct presentation pathway

IMMUNOLOGY, Issue 1 2006
Keri B. Donohue
Summary CD8+ T cells play a crucial role in protective immunity to viruses and tumours. Antiviral CD8+ T cells are initially activated by professional antigen presenting cells (pAPCs) that are directly infected by viruses (direct-priming) or following uptake of exogenous antigen transferred from virus-infected or tumour cells (cross-priming). In order to efficiently target each of these antigen-processing pathways during vaccine design, it is necessary to delineate the properties of the natural substrates for either of these antigen-processing pathways. In this study, we utilized a novel T-cell receptor (TCR) transgenic mouse to examine the requirement for both antigen synthesis and synthesis of other cellular factors during direct or cross-priming. We found that direct presentation required ongoing synthesis of antigen, but that cross-priming favoured long-lived antigens and did not require ongoing antigen production. Even after prolonged blockade of protein synthesis in the donor cell, cross-priming was unaffected. In contrast, direct-presentation was almost undetectable in the absence of antigen neosynthesis and required ongoing protein synthesis. This suggests that the direct- and cross-priming pathways may utilize differing pools of antigen, an observation that has far-reaching implications for the rational design of vaccines aimed at the generation of protective CD8+ T cells. [source]

DEC-205lo Langerinlo neonatal Langerhans' cells preferentially utilize a wortmannin-sensitive, fluid-phase pathway to internalize exogenous antigen

IMMUNOLOGY, Issue 4 2003
Bernadette M. Bellette
Summary Antigen treatment of neonatal epidermis results in antigen-specific immune suppression. Compared with adult counterparts, neonatal Langerhans' cells (LC) demonstrate an impaired ability to transport antigen to the lymph node (LN). As it is possible that neonatal LC have a reduced ability to endocytose antigen, we evaluated the acquisition of endocytic function, the expression of uptake receptors and the internalization of soluble and small particulate antigens in neonatal, juvenile and adult mice. Although LC from 4-day-old mice were weakly positive for the mannose-type receptor, Langerin, they were capable of internalizing fluorescein isothiocyanate (FITC)-dextran, but to a lesser extent than LC from 6-week-old mice. However, when ratio data were calculated to account for variations in fluorescence intensity at 4°, it was demonstrated that neonatal LC continued to internalize antigen over a longer period of time than adult mice and, as the ratios were much higher, that neonatal cells were also relatively more efficient in antigen uptake. When receptors for mannan and mannose were competitively blocked, LC from neonatal mice, but not adult mice, could still efficiently internalize FITC,dextran. Consequently, the uptake of FITC,dextran, in part, occurred via alternative receptors or a receptor-independent fluid-phase pathway. A feasible pathway is macropinocytosis, as LC from 4-day-old mice demonstrated a reduction in FITC,dextran internalization by the macropinocytosis inhibitor, wortmannin. Evidence of a functional macropinocytosis pathway in neonatal LC was further supported by internalization of the soluble tracer Lucifer Yellow (LY). We conclude that neonatal LC preferentially utilize a wortmannin-sensitive, fluid-phase pathway, rather than receptor-mediated endocytosis, to internalize antigen. As neonatal LC are capable of sampling their environment without inducing immunity, this may serve to avoid inappropriate immune responses during the neonatal period. [source]

Processing and presentation of (pro)-insulin in the MHC class II pathway: the generation of antigen-based immunomodulators in the context of type 1 diabetes mellitus

DIABETES/METABOLISM: RESEARCH AND REVIEWS, Issue 4 2010
Timo Burster
Abstract Both CD4+ and CD8+ T lymphocytes play a crucial role in the autoimmune process leading to T1D. Dendritic cells take up foreign antigens and autoantigens; within their endocytic compartments, proteases degrade exogenous antigens for subsequent presentation to CD4+ T cells via MHC class II molecules. A detailed understanding of autoantigen processing and the identification of autoantigenic T cell epitopes are crucial for the development of antigen-based specific immunomodulators. APL are peptide analogues of auto-immunodominant T cell epitopes that bind to MHC class II molecules and can mediate T cell activation. However, APL can be rapidly degraded by proteases occurring in the extracellular space and inside cells, substantially weakening their efficiency. By contrast, protease-resistant APL function as specific immunomodulators and can be used at low doses to examine the functional plasticity of T cells and to potentially interfere with autoimmune responses. Here, we review the latest achievements in (pro)-insulin processing in the MHC class II pathway and the generation of APL to mitigate autoreactive T cells and to activate Treg cells. Copyright © 2010 John Wiley & Sons, Ltd. [source]

CD4+CD25+ regulatory T,cells control the magnitude ofT-dependent humoral immune responses to exogenous antigens

EUROPEAN JOURNAL OF IMMUNOLOGY, Issue 4 2006
Fouad Eddahri
Abstract CD4+CD25+ T,reg cells are critical for peripheral tolerance and prevention of autoimmunity. Here we show that CD4+CD25+ T,reg also regulate the magnitude of humoral responses against a panel of T-dependent antigens of foreign origin during both primary and secondary immune responses. Depletion of CD4+CD25+ T,cells leads to increased antigen-specific antibody production and affinity maturation but does not affect T-independent B,cell responses, suggesting that CD4+CD25+ T,reg exert a feedback mechanism on non-self antigen-specific antibody secretion by dampening the T,cell help for B,cell activation. Moreover, we show that CD4+CD25+ T,reg also suppress in vitro B,cell immunoglobulin production by inhibiting CD4+CD25, T,cell help delivery, and that blockade of TGF-, activity abolishes this suppression. [source]

Recruitment and selection of marginal zone B,cells is independent of exogenous antigens

EUROPEAN JOURNAL OF IMMUNOLOGY, Issue 7 2005
Peter
Abstract Marginal zone B (MZ-B) cells of the spleen contribute significantly to the immunity against invasive infections with polysaccharide-encapsulated bacteria. Recent evidence indicates that recruitment and selection of MZ-B,cells occurs on the basis of positive selection constraints that likely operate via B,cell receptor (BCR) signaling. Previous studies have shown that MZ-B,cells carry relatively shorter immunoglobulin (Ig) heavy (H) chain complementarity-determining region,3 (H-CDR3) sequences and express BCR which are thought to be polyreactive. In this scenario, MZ-B,cell selection proceeds via engagement of the BCR with exogenous (i.e. microbial gut flora-derived) and/or endogenous (self) antigens. Here, we studied the influence of exogenous antigens on the selection process of MZ-B,cells using non-genetically manipulated adult germ-free and conventionally reared infant rats. This study was carried out by H-CDR3 spectratype analysis of VH(PC7183)-encoded Ig VHDJH -, transcripts expressed by purified splenic MZ-B,cells and other B,cell subsets. We show that MZ-B,cells in both adult germ-free and conventionally reared infant (14-day-old) rats are H-CDR3-selected cells, providing strong evidence that recruitment and selection of MZ-B,cells is driven by self antigens. [source]

The extrathymic T-cell differentiation in the murine gut

IMMUNOLOGICAL REVIEWS, Issue 1 2007
Benedita Rocha
Summary:, The gut epithelial border is in continuous contact with exogenous antigens and harbors a distinctive and very abundant CD8,, intraepithelial T-lymphocyte effector population. We describe here the characteristics of these cells that distinguish them from all other T-cell types in the body as well as their functions in local protection. We also describe how these cells differentiate from local precursors present in the gut cryptopatches (CPs) following a pathway of T-cell differentiation unique to the gut wall. Finally, we describe the origin of the precursors of CD8,, T cells, which come from the bone marrow in athymic mice but are first imprinted in the thymus in euthymic mice. Indeed, CD3,CD4,CD8, T-cell-committed precursors can leave the thymus before T-cell receptor rearrangements and then colonize the gut CPs, proceeding with their differentiation within the gut wall. [source]

Interferons as pathogenic effectors in autoimmunity

IMMUNOLOGICAL REVIEWS, Issue 1 2005
Roberto Baccala
Summary:, Interferons (IFNs) type-1 (IFN ,/,) and type-II (IFN-,) are the most pleiotropic molecules in the intricate cytokine network. This dominance arises from three crucial factors: (i) initiation of IFN-,/, and IFN-, production at the inception of most innate immune responses, which primes for the ensuing adaptive immune responses, primarily through the sine qua non upregulation of major histocompatibility complex and costimulatory molecules; (ii) magnification of their production and signaling by cross-talk between themselves, and synergistic or antagonistic effects on other cytokines; and (iii) direct or indirect initiation of transcription of hundreds of immunologically relevant genes. Considering that aberrant immune responses against self-molecules seem to depend on the same constituents and pathways as those against exogenous antigens, it follows that IFNs are also major effectors in the pathogenesis of autoimmunity. Here, we review the diverse biological effects of IFNs on the immune system, discuss findings pertaining to the nature of exogenous and endogenous stimuli that might induce IFN production through the engagement of Toll-like receptors, and summarize the detrimental and, in some instances, beneficial effects of IFNs in systemic and organ-specific autoimmune diseases. [source]

Cross-presentation, dendritic cell subsets, and the generation of immunity to cellular antigens

IMMUNOLOGICAL REVIEWS, Issue 1 2004
William R. Heath
Summary:, Cross-presentation involves the uptake and processing of exogenous antigens within the major histocompatibility complex (MHC) class I pathway. This process is primarily performed by dendritic cells (DCs), which are not a single cell type but may be divided into several distinct subsets. Those expressing CD8, together with CD205, found primarily in the T-cell areas of the spleen and lymph nodes, are the major subset responsible for cross-presenting cellular antigens. This ability is likely to be important for the generation of cytotoxic T-cell immunity to a variety of antigens, particularly those associated with viral infection, tumorigenesis, and DNA vaccination. At present, it is unclear whether the CD8,-expressing DC subset captures antigen directly from target cells or obtains it indirectly from intermediary DCs that traffic from peripheral sites. In this review, we examine the molecular basis for cross-presentation, discuss the role of DC subsets, and examine the contribution of this process to immunity, with some emphasis on DNA vaccination. [source]