Systemic lupus erythematosus sera inhibit antigen presentation by macrophages to T cells

Several reports have demonstrated that systemic lupus erythematosus (SLE) patients have a decreased response to exogenous antigens both in vivo and in vitro. We examined the effects of SLE sera on macrophage (M phi) antigen-presenting functions. M phi from normal donors were pulsed with tetanus toxoid antigen in the presence of SLE or normal human serum (NHS), fixed in paraformaldehyde, and incubated with autologous T cells. Of 16 SLE sera tested, 11 inhibited the T-cell proliferative response (measured by [3H]thymidine uptake) compared to control NHS; mean percentage inhibition was 53 +/- 23%. This inhibition did not result from interference with antigen uptake by M phi and was found in both IgM and IgG fractions of the sera. There was a positive correlation between the amount of inhibition and the cytotoxic reactivity of the SLE sera against M phi as measured by Terasaki assay (r = 0.659, P less than 0.01). However, the presence and the amount of the inhibition did not correlate with serum immune complexes by Clq ELISA, serum anti-DR antibodies, or clinical disease activity of the SLE patients. We conclude that some SLE sera possess IgM and IgG antibodies reactive with M phi which affect M phi antigen-presenting functions, and might relate to decreased antigenic response in SLE patients.     

CD1d-mediated antigen presentation to natural killer T (NKT) cells

CD1d molecules are lipid antigen-presenting molecules. They are involved in presenting these antigens to a unique subpopulation of T cells called natural killer T (NKT) cells, which have the capacity to produce both T helper (Th) 1 and Th2 cytokines. Thus, it is possible that the antigens presented by CD1d and/or the level at which they are presented could have profound effects on the immunoregulation of autoimmune and infectious diseases, as well as cancer. Because of the ability of CD1d-binding ligands to modulate NKT cell responses, targeting CD1d-mediated antigen presentation as a novel approach for new therapies in these and other diseases holds great promise.     

Leishmania-infected macrophages sequester endogenously synthesized parasite antigens from presentation to CD4+ T cells

CD4⁺ T cell lines raised against the protective leishmanial antigens GP46 and P8 were used to study the presentation of endogenously synthesized Leishmania antigens by infected cells. Using two different sources of macrophages, the 14.07 macrophage cell line (H-2^k) which constitutively expresses major histocompatibility complex (MHC) class II molecules, and elicited peritoneal exudate cells, we found that cells infected with Leishmania amastigotes presented little, if any endogenously synthesized parasite antigens to CD4⁺ T cells. In contrast, promastigote-infected macrophages did present endogenous parasite molecules to CD4⁺ T cells, although only for a limited time, with maximal presentation occurring within 24 h of infection and decreasing to minimal antigen presentation at 72 h post-infection. These observations suggest that once within the macrophage, Leishmania amastigote antigens are sequestered from the MHC class II pathway of antigen presentation. This allows live parasites to persist in infected hosts by evading the activation of CD4⁺ T cells, a major and critical anti-leishmanial component of the host immune system. Studies with drugs that modify fusion patterns of phagosomes suggest that the mechanism of this antigen sequestration includes targeted fusion of the parasitophorous vacuole with certain endocytic compartments.     

Saposins facilitate CD1d-restricted presentation of an exogenous lipid antigen to T cells

Members of the CD1 family present antigenic lipids to T lymphocytes. CD1 molecules survey endocytic compartments for lipid antigens that are sorted into these vesicles after incorporation into the membrane bilayer, and extraction from the bilayer is likely to be a critical step for lipid association. We hypothesized that lysosomal saposins, which are cofactors required for sphingolipid degradation, might be involved in this process. Here we show that saposins, although not required for the autoreactive recognition of CD1d by natural killer T cells, are indispensable for the binding of an exogenous lipid antigen, alpha-galactosylceramide, to CD1d in the endocytic pathway. We suggest that saposins mobilize monomeric lipids from lysosomal membranes and facilitate their association with CD1d.     

Bone marrow macrophages induced to antigen presentation by lymphokines interact selectively with distinct T cells

In vitro matured bone marrow-derived macrophages (BMM phi), which represent a pure population of M phi, were shown to act as antigen-presenting cells (APC) to the T cell clone ST2/K.9. This interaction was major histocompatibility complex restricted. Upon long-term culture in macrophage colony-stimulating factor, BMM phi were activated for antigen presentation by a 48-h pulse with lymphokine-containing supernatant of concanavalin A-stimulated rat spleen cells (Con A sup). The capacity of such activated M phi to function as APC decreased upon removal of Con A sup, and could be regenerated by a second pulse. This finding suggests that antigen presentation by mature M phi is a reversible function regulated by T cell factors. When the responsiveness of various T cell lines to antigen presented on BMM phi or spleen cells was compared, distinct activation requirements were observed for different T cells since lymphokine-activated BMM phi were not capable of inducing antigen-specific proliferation of all lines.     

Molecular basis of lipid antigen presentation by CD1d and recognition by natural killer T cells

Together with peptides, T lymphocytes respond to hydrophobic molecules, mostly lipids, presented by the non-classical CD1 family (CD1a–e). These molecules have evolved complex and diverse binding grooves in order to survey different cellular compartments for self and exogenous antigens, which are then presented for recognition to T-cell receptors (TCRs) on the surface of T cells. In particular, most CD1d-presented antigens are recognized by a population of lymphocytes denominated natural killer T (NKT) cells, characterized by a strong immunomodulatory potential. Among NKT cells, two major subsets (type I and type II NKT cells) have been described, based on their TCR repertoire and antigen specificity. Here we review recent structural and biochemical studies that have shed light on the molecular details of CD1d-mediated antigen recognition by type I and II NKT cells, which are in many aspects distinct from what has been observed for peptide major histocompatibility complex-reactive TCRs.     

Adaptor protein-3 in dendritic cells facilitates phagosomal toll-like receptor signaling and antigen presentation to CD4(+) T cells

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Highlights? AP-3 is selectively required for optimal MHC-II presentation of phagocytosed antigen ? AP-3-deficient dendritic cells induce impaired CD4⁺ T cell inflammatory responses ? AP-3 regulates TLR4 delivery to phagosomes and subsequent inflammatory signaling ? AP-3 regulates phagosomal peptide:MHC-II complex delivery to the cell surface     

TGF-beta1 and IFN-gamma stimulate mouse macrophages to express BAFF via different signaling pathways

B cell-activating factor belonging to the TNF family (BAFF) is primarily expressed by macrophages and dendritic cells and stimulates the proliferation, differentiation, and survival of B cells and their Ig production. In the present study, we examined the pathways by which TGF-beta1 and IFN-gamma induce BAFF expression to see if TGF-beta1 and IFN-gamma regulate B cell differentiation via macrophages. We found that TGF-beta1 stimulated mouse macrophages to express BAFF and that a typical TGF-beta signaling pathway was involved. Thus, Smad3 and Smad4 promoted BAFF promoter activity, and Smad7 inhibited it, and the BAFF promoter was shown to contain three Smad-binding elements. Importantly, TGF-beta1 enhanced the expression of membrane-bound and soluble forms of BAFF. IFN-gamma further augmented TGF-beta1-induced BAFF expression. IFN-gamma caused phosphorylation of CREB, and overexpression of CREB increased IFN-gamma-induced BAFF promoter activity. Furthermore, H89, a protein kinase A (PKA) inhibitor, abrogated the promoter activity. Neither Stat1alpha (a well-known transducing molecule of IFN-gamma) nor AG490 (a JAK inhibitor) affected BAFF expression in response to IFN-gamma. Taken together, these results demonstrate that TGF-beta1 and IFN-gamma up-regulate BAFF expression through independent mechanisms, i.e., mainly Smad3/4 and PKA/CREB, respectively.     

Study on pinocytosis and antigen presentation by murine peritoneal macrophages to T cells in vitro after cisplatin treatment

Macrophage monolayers showed significantly increased rate of pinocytosis on incubation with cisplatin (10 micrograms/ml). Further, the rate of pinocytosis was compared with macrophages treated with LPS (10 micrograms/ml). Cisplatin treated macrophages also showed enhanced capacity of antigen presentation to T cells in vitro. The antigen presenting capacity of cisplatin treated macrophages was compared with the antigen presenting capacity to LPS treated macrophages.     

Immunoregulation of encephalitogenic MBP-NAc1-11-reactive T cells by CD4+ TCR-specific T cells involves IL-4, IL-10 and IFN-gamma

The generation of TCR transgenic (Tg) mice expressing a BV8S2 (Vbeta8 subfamily 2) chain specific for the encephalitogenic NAc1-11 region of MBP provides a unique system for evaluating the mechanisms involved in anti-TCR immunoregulation of EAE. In a previous study, we showed that vaccination with BV8S2 protein induced specific T cells that inhibited proliferation responses and encephalitogenic activity of MBP-reactive T cells in vitro, and resulted in a skewed production of Th2 cytokines by the MBP-reactive T cells. These data suggested that regulation of the encephalitogenic T cells was mediated by inhibitory cytokines rather than through a deletional mechanism. In the current study, we have employed the BV8S2 Tg mouse model to address the issue of which cytokines produced by anti-TCR-reactive T cells can regulate the function of encephalitogenic Th1 cells. Utilizing neutralizing anti-cytokine antibodies to reverse inhibitory effects of supernatants from BV8S2-specific T cells, we found that IL-4, IL-10, and to a lesser extent, IFN-gamma and TGF-beta, were the major regulatory cytokines responsible for inhibiting encephalitogenic activity, proliferation, and IFN-gamma secretion of MBP-NAc1-11-reactive Th1 cells. These results indicate that cytokine regulation is the major mechanism through which TCR specific CD4+ T cells regulate encephalitogenic and potentially other bystander Th1 cells.     

Effective antigen presentation to helper T cells by human eosinophils

Although eosinophils are inflammatory cells, there is increasing attention on their immunomodulatory roles. For example, murine eosinophils can present antigen to CD4⁺ T helper (Th) cells, but it remains unclear whether human eosinophils also have this ability. This study determined whether human eosinophils present a range of antigens, including allergens, to activate Th cells, and characterized their expression of MHC class II and co‐stimulatory molecules required for effective presentation. Human peripheral blood eosinophils purified from non‐allergic donors were pulsed with the antigens house dust mite extract (HDM), Timothy Grass extract (TG) or Mycobacterium tuberculosis purified protein derivative (PPD), before co‐culture with autologous CD4⁺ Th cells. Proliferative and cytokine responses were measured, with eosinophil expression of HLA‐DR/DP/DQ and the co‐stimulatory molecules CD40, CD80 and CD86 determined by flow cytometry. Eosinophils pulsed with HDM, TG or PPD drove Th cell proliferation, with the response strength dependent on antigen concentration. The cytokine responses varied with donor and antigen, and were not biased towards any particular Th subset, often including combinations of pro‐ and anti‐inflammatory cytokines. Eosinophils up‐regulated surface expression of HLA‐DR/DP/DQ, CD80, CD86 and CD40 in culture, increases that were sustained over 5 days when incubated with antigens, including HDM, or the major allergens it contains, Der p I or Der p II. Human eosinophils can, therefore, act as effective antigen‐presenting cells to stimulate varied Th cell responses against a panel of antigens including HDM, TG or PPD, an ability that may help to determine the development of allergic disease.     

Human mast cells present antigen to autologous CD4+ T cells

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Delayed allergic reaction to suxamethonium driven by oligoclonal Th1-skewed CD4+CCR4+IFN-gamma+ memory T cells

BACKGROUND: Muscle relaxants represent the drugs most frequently involved in intraoperative anaphylaxis during surgical procedures. Our aim was to report the case of a delayed reaction to suxamethonium and analyze specific T cell lines with regard to their specificity, phenotype and cytokine profile. METHODS: We generated a drug-specific T cell line from a biopsy at the site of positive intradermal reactions and analyzed the immunophenotype, T cell receptor Vbeta domain expression and cytokine profile. RESULTS: T cells isolated from positive intradermal test reactions to suxamethonium showed a strict dose-dependent proliferation in response to drug-pulsed autologous antigen-presenting cells. The drug-specific CD4+ T cells were oligoclonal memory CD3+CD4+ T cells and expressed the skin homing receptors cutaneous lymphocyte antigen (CLA) and CCR4. Furthermore CD4+ suxamethonium-reactive T cell lines were IFN-gamma-positive and synthesized high levels of IFN-gamma and TNF-alpha. CONCLUSION: The study describes a delayed hypersensitivity to suxamethonium, driven by an oligoclonal T helper cell 1-skewed CD4+ memory T cell population, expressing the skin homing receptors CLA and CCR4.     

Antigen presentation to naive CD4 T cells in the lymph node

Although the presentation of peptide-major histocompatibility complex class II (pMHC class II) complexes to CD4 T cells has been studied extensively in vitro, knowledge of this process in vivo is limited. Unlike the in vitro situation, antigen presentation in vivo takes place within a complex microenvironment in which the movements of antigens, antigen-presenting cells (APCs) and T cells are governed by anatomic constraints. Here we review developments in the areas of lymph node architecture, APC subsets and T cell activation that have shed light on how antigen presentation occurs in the lymph nodes.     

Latent TGF-beta1-transduced CD4+ T cells suppress the progression of allergic encephalomyelitis

Systemic injection of small amounts of transforming growth factor-beta (TGF-beta), a cytokine produced by lymphoid and other cells, has a profound effect in protecting mice from the inflammatory demyelinating lesions of experimental allergic encephalomyelitis (EAE; an animal model for multiple sclerosis). However, TGF-beta has side-effects, which might be avoided if the cells producing TGF-beta can be delivered to the affected site in the nervous system to insure its local release in small amounts. Myelin basic protein (MBP)-specific, cloned CD4+ T cells were engineered by retroviral transduction to produce latent TGF-beta. Studies about the spontaneous form of EAE in T cell receptor (TCR)-transgenic recombination-activating gene (RAG)-1(-/-) mice showed that essentially all of the MBP-specific, TCR-transgenic RAG-1(-/-) (BALB/cxB10.PL)F1 mice develop spontaneous EAE by the age of 11 weeks. By 12 weeks, 25-50% of the mice have died from disease. A single injection of TGF-beta1-transduced T helper cell type 1 (Th1) cells significantly protected the mice from EAE, and untransduced Th1 cells did not protect. MBP-specific BALB/c Th2 clones, transduced with TGF-beta1-internal ribosome entry site-green fluorescent protein (GFP) significantly reduced EAE induction by untransduced Th1 cells in RAG-1(-/-) B10.PL mice. Furthermore, the GFP+ TGF-beta1-producing Th2 cells were detectable in the spinal cords of the injected mice.     

Converting antigen-specific diabetogenic CD4 and CD8 T cells to TGF-beta producing non-pathogenic regulatory cells following FoxP3 transduction

Immuno-regulatory defects, including a reduction in the number and function of regulatory T cells, play an important role in the development of autoimmune diabetes in both humans and non-obese diabetic (NOD) mice. In this study we tested the effect of introduction of FoxP3 into antigen non-specific polyclonal and antigen-specific monoclonal T cells on diabetes development in NOD mice. Transduction of FoxP3 into antigen-specific monoclonal (insulin or BDC2.5 mimotope specific) or antigen non-specific polyclonal T cells using retroviral transduction delayed or prevented diabetes development. However, transduced antigen-specific monoclonal T cells were considerably more effective than polyclonal T cells. Regulatory activity was not limited to CD4 T cells as potent diabetogenic CD8 T cells specific for insulin, were also reduced in pathogenicity by FoxP3 induction. The disease suppressive effect, in both CD4 and CD8 cells, was more evident in spontaneously diabetes-prone NOD hosts (non-lymphopenic) than in lymphopenic NOD.scid hosts. We suggest that this strategy of transducing antigen-specific CD4 or CD8 T cells may be a useful therapeutic approach in the prevention of autoimmune diabetes.     

TGF-beta1 production by CD4+ CD25+ regulatory T cells is not essential for suppression of intestinal inflammation

Naturally occurring CD4+ CD25+ regulatory T cells (Treg) are potent suppressors of CD4+ and CD8+ T cell responses in vitro and inhibit several organ-specific autoimmune diseases. While most in vitro studies suggest that CD4+ CD25+ Treg cells adopt a cytokine-independent but cell contact-dependent mode of T cell regulation, their precise mechanism of suppression in vivo remains largely unknown. Here we examine the functional contribution of Treg cell-derived TGF-beta1 and effector T cell responsiveness to TGF-beta in CD4+ CD25+ T cell-mediated suppression of inflammatory bowel disease (IBD). We show that CD4+ CD25+ Treg cells from either TGF-beta1+/+ or neonatal TGF-beta1-/- mice can suppress the incidence and severity of IBD as well as colonic IFN-gamma mRNA expression induced by WT CD4+ CD25- effector T cells. Furthermore, TGF-beta-resistant Smad3-/- CD4+ CD25+ Treg cells are equivalent to WT Treg cells in their capacity to suppress disease induced by either WT or Smad3-/- CD4+ CD25- effector T cells. Finally, anti-TGF-beta treatment exacerbates the colitogenic potential of CD4+ CD25- effector T cells in the absence of CD4+ CD25+ Treg cells. Together, these data demonstrate that in certain situations CD4+ CD25+ T cells are able to suppress intestinal inflammation by a mechanism not requiring Treg cell-derived TGF-beta1 or effector T cell/Treg cell responsiveness to TGF-beta via Smad3.     

CD4+ T cells rely on a cytokine gradient to control intracellular pathogens beyond sites of antigen presentation

Effector T?cells are critical for clearance of pathogens from sites of infection. Like cytotoxic CD8(+) T?cells, CD4(+) helper T?cells have been shown to deliver effector molecules directionally toward the immunological synapse, suggesting that infected cells need to be engaged individually to receive effector signals. In contrast, we show here that CD4(+) T?cells stably contacted a minority of infected cells, yet these interactions triggered intracellular defense mechanisms in bystander cells in?vivo. By using a functional read-out, we provide evidence that this effector bystander activity extends via a gradient of IFN-γ more than 80?μm beyond the site of antigen presentation, promoting pathogen clearance in the absence of immunological synapse formation. Our results thus demonstrate that CD4(+) T?cells can exert their protective activity by engaging a minority of infected cells.