Disparate ability of murine CD8alpha- and CD8alpha+ dendritic cell subsets to traverse endothelium is not determined by differential CD11b expression

Upon Ag uptake and response to maturation stimuli, dendritic cells (DC) are directed through lymphatic or blood vessel endothelium to T cell areas of secondary lymphoid tissues by the constitutively expressed CC chemokines CCL19 and CCL21. We have shown that mature (m) murine CD8alpha+ DC exhibit poorer migratory ability to these chemokines than classic CD8alpha- DC by quantifying their in vitro chemotaxis through unmodified Transwell filters. We hypothesized that lower surface expression (compared to CD8alpha- mDC) of the adhesion molecule CD11b on CD8alpha+ DC might limit their ability to adhere to filter pores in vitro and/or endothelium in vitro/in vivo. To test the role of this and/or other adhesion molecules (CD11a, CD31, CD54 and CD62L) in regulating murine DC subset migration, we used specific mAbs to block their function and quantified their migration through resting or tumour necrosis factor (TNF)-alpha-activated endothelial cell (EC) layered-Transwell filters. Both CD8alpha+ and CD8alpha- subsets migrated through resting EC (albeit less than in the absence of EC) in response to CCL19 and CCL21, and migration through TNF-alpha-activated EC was enhanced. In contrast to reports concerning human DC, transendothelial migration of the murine DC subsets was not dependent on CD11b, CD31, or CD62L expression by these cells. CD54 and CD11a, however, were at least partly involved in DC/EC interactions. This is the first report to examine adhesion molecules involved in transendothelial migration of murine DC subsets.     

The murine beta-chemokine TARC is expressed by subsets of dendritic cells and attracts primed CD4+ T cells.

To investigate specific properties of dendritic cells (DC) which are not shared by other antigen-presenting cells, we compared gene expression patterns of mouse DC and macrophages by differential mRNA display. One of the cDNA identified coded for a murine homolog of the human beta-chemokine, thymus and activation-regulated chemokine (TARC). The gene is expressed in a subset of bone marrow-derived DC and is up-regulated after lipopolysaccharide (LPS) stimulation. In vivo, murine TARC (mTARC) is constitutively expressed by thymic DC, lymphnode DC and CD11c+ cells in the lung. No expression was detected in bone marrow-derived macrophages and LPS-activated B cells. Recombinant mTARC has no chemoattractant activity on naive peripheral CD4+ T cells. In contrast, mTARC induced migration of primed ovalbumin-specific CD4+ T cells with a preference for Th2 cells during the early phase of the T cell response. These observations suggest that mTARC directs migration of antigen-experienced T helper cells to DC in lymphoid as well as in non-lymphoid organs.     

Soluble HLA-G molecules impair natural killer/dendritic cell crosstalk via inhibition of dendritic cells

HLA-G molecules are known to exert immunosuppressive action on DC maturation and on NK cells, and can in consequence inhibit respectively T cell responses and NK cytolysis. In this study, we show that monocyte-derived DC, differentiated in the presence of GM-CSF and IL-4, are sensitive to soluble (s) HLA-G molecules during LPS/IFN-gamma maturation as demonstrated by the decrease of CD80 and HLA-DR expressions and IL-12 secretion. Moreover, DC pretreated with sHLA-G were found to activate NK/DC crosstalk less than non-treated DC. Early activation of NK cells co-cultured with autologous DC was diminished as assessed by CD69 expression. The IFN-gamma production was impaired whereas a slight inhibition of the NK cell cytotoxicity against Daudi cell line was observed. Since sHLA-G is expressed in grafts or sites of tumour proliferation, its indirect action on NK cells via DC could constitute a pathway of early inhibition for both innate and specific immune responses.     

Chemokine programming dendritic cell antigen response: part II – programming antigen presentation to T lymphocytes by partially maintaining immature dendritic cell phenotype

In a companion article to this study,¹ the successful programming of a JAWSII dendritic cell (DC) line's antigen uptake and processing was demonstrated based on pre‐treatment of DCs with a specific ‘cocktail’ of select chemokines. Chemokine pre‐treatment modulated cytokine production before and after DC maturation [by lipopolysaccharide (LPS)]. After DC maturation, it induced an antigen uptake and processing capacity at levels 36% and 82% higher than in immature DCs, respectively. Such programming proffers a potential new approach to enhance vaccine efficiency. Unfortunately, simply enhancing antigen uptake does not guarantee the desired activation and proliferation of lymphocytes, e.g. CD4⁺ T cells. In this study, phenotype changes and antigen presentation capacity of chemokine pre‐treated murine bone marrow‐derived DCs were examined in long‐term co‐culture with antigen‐specific CD4⁺ T cells to quantify how chemokine pre‐treatment may impact the adaptive immune response. When a model antigen, ovalbumin (OVA), was added after intentional LPS maturation of chemokine‐treated DCs, OVA‐biased CD4⁺T‐cell proliferation was initiated from ~ 100% more undivided naive T cells as compared to DCs treated only with LPS. Secretion of the cytokines interferon‐γ, interleukin‐1β, interleukin‐2 and interleukin‐10 in the CD4⁺ T cell : DC co‐culture (with or without chemokine pre‐treatment) were essentially the same. Chemokine programming of DCs with a 7 : 3 ratio of CCL3 : CCL19 followed by LPS treatment maintained partial immature phenotypes of DCs, as indicated by surface marker (CD80 and CD86) expression over time. Results here and in our companion paper suggest that chemokine programming of DCs may provide a novel immunotherapy strategy to obviate the natural endocytosis limit of DC antigen uptake, thus potentially increasing DC‐based vaccine efficiency.     

CD137 ligand reverse signaling has multiple functions in human dendritic cells during an adaptive immune response

T cell activation via dendritic cells (DC) is an important step in the adaptive immune response, which requires DC maturation, migration to lymph nodes and presentation of antigen to T cells. CD137 receptor expressed on activated T cells is a potent costimulatory molecule. Here, we investigated the functions of CD137 ligand (CD137L) in human monocyte-derived DC during an immune response. Cross-linking of CD137L on DC leads to cell maturation in an autocrine fashion, mostly via release of TNF-alpha. Reverse signaling of CD137L also mediates migration of DC via up-regulation of the CCR7 chemokine receptor, demonstrated by an in vivo MIP-3beta-dependent SCID mouse migration model. Finally, CD137L-activated DC induce differentiation of human T cells into potent Th1 effectors. Cocultivation of autologous T cells and CD137L-activated DC in an antigen-specific reaction leads to T cell proliferation and the release of IL-12p70 and IFN-gamma. These findings deliver new insights into the multiple effects of reverse signaling of CD137L in human DC during the initiation of an adaptive immune response, including the key features of DC maturation, migration and, ultimately, antigen-specific T cell differentiation.     

Mesenchymal stem cells alter migratory property of T and dendritic cells to delay the development of murine lethal acute graft-versus-host disease

Due to the potent immunoregulatory capacity, mesenchymal stem cells (MSCs) have been used in clinical trials to treat acute graft-versus-host disease (aGvHD), although the detailed in vivo mechanisms remain elusive. In a murine lethal aGvHD model, MSCs delayed the development of the disease. Interestingly, we found that MSC infusion increased the number of T lymphocytes in the secondary lymphoid organs (SLOs). Since the expression of CD62L and CCR7 is prerequisite for lymphocyte migration into SLOs, the in vitro experiments revealed that in the presence of MSCs, T lymphocytes (including CD4(+)CD25(+) regulatory T cells) preferred to take the naive-like phenotype (CD62L(+)/CCR7(+)) in mixed lymphocyte reaction and maintained the migratory activity elicited by secondary lymphoid tissue chemokine (SLC). Dendritic cells (DCs) are the initiator of immune response. CCR7 expression is pivotal for their maturation and migration into SLOs. However, CCR7 expression and SLC-driven migratory activity of DCs were remarkably suppressed by MSC coculture. The processes above were realized mainly through secretory mechanism. Consistently, MSC infusion maintained T lymphocytes to take CD62L(+)/CCR7(+) phenotype and decreased the CCR7 expression and proportion of DCs in SLOs of aGvHD mice. In conclusion, the altered migratory properties of T cells and DCs might contribute to the immunosuppressive activity of transplanted MSCs in the setting of aGvHD. Disclosure of potential conflicts of interest is found at the end of this article.     

In vitro differentiation of porcine blood CD163- and CD163+ monocytes into functional dendritic cells

Swine monocytes constitute a heterogeneous cell population containing subsets with distinct functional capacities or representing different maturational stages. Based on the expression of CD163, we have recently identified two monocyte subpopulations. In this study, we investigate the ability of both CD163- and CD163+ monocytes to differentiate into dendritic cells (DCs) in the presence of GM-CSF and IL-4. Monocyte differentiation into DC is accompanied by an up-regulation of the expression of swine leukocyte antigen (SLA) I, SLA II and CD80/86 molecules, and a decrease in the expression of CD14, CD16 and CD163. These DC express the pan-myeloid marker SWC3 and display typical dendritic cytoplasmic projections. When monocytes are split into CD163+ and CD163- cells, both subsets give rise to DC. However, compared to CD163- monocyte-derived DC (MoDC), CD163+ MoDC appear to have reached a more advanced stage of maturation, expressing higher levels of SLA II and CD80/86 and inducing more efficiently proliferation of T cells to recall antigens and alloantigens.     

Corticosteroids inhibit the production of inflammatory mediators in immature monocyte-derived DC and induce the development of tolerogenic DC3.

Corticosteroids (CS) are potent immunosuppressive agents that are known to affect T cell-mediated inflammation by the inhibition of proliferation and cytokine production, as well as the immunostimulatory function of monocytes and macrophages. Not much is known of the effect of corticosteroids on dendritic cells (DC), the professional T cell stimulatory antigen-presenting cells. We report that the endogenous CS hydrocortisone and the synthetic CS clobetasol-17-propionate strongly inhibited the production of the inflammatory mediators interleukin (IL)-12 p70, tumor necrosis factor alpha (TNF-alpha), and IL-6 by lipopolysaccharide (LPS)-stimulated monocyte-derived immature DC (iDC) in vitro. In contrast, the stimulatory capacity, antigen uptake, and the expression of costimulatory molecules were not affected. In accordance with the decreased production of IL-12 p70, CS-treated iDC induced less production of the inflammatory Th1 cytokine interferon-y and enhanced levels of the Th2 cytokines IL-10 and IL-5 in staphylococcal enterotoxin B-stimulated CD4+ Th cells. Furthermore, CS inhibited the maturation of iDC as assessed by the lack of expression of CD83 as well as by the prevention of the loss of antigen uptake capacities. These type 3 DC (DC3) matured in the presence of CS produce less IL-12 p70 and have a decreased T cell stimulatory capacity. Moreover, uncommitted T cells that encounter the CS-induced DC3 develop into Th2-biased cells, which may additionally decrease the Th1-mediated tissue damage but, on the other hand, Th2 cytokines may promote undesirable elevation of IgE and eosinophilia. These findings indicate that suppression of T cell-mediated inflammation by CS not only relies on direct effects on T cells, but also on various effects on DC, their professional antigen-presenting cells.     

Differences in the induction of CD8+ T cell responses by subpopulations of dendritic cells from afferent lymph are related to IL-1 alpha secretion

The major subset of dendritic cells (DC) from bovine afferent lymph expresses the SIRP alpha MyD-1 antigen, but not CD11a or the antigen recognized by mAb CC81, and potently stimulates CD4+ and CD8+ T lymphocyte proliferation. The minor subpopulation, that is CD11a+ CC81+ MyD-1-, effectively stimulates CD4+ but not CD8+ T lymphocyte proliferation. CD11a+ CC81+ MyD-1- DC did not induce anergy or death or secrete an inhibitory factor. However, supernatant from cultures of CD8+ T cells with CD11a- CC81- MyD-1+ DC significantly enhanced proliferation of CD8+ T cells in response to CD11a+ CC81+ MyD-1- DC, an effect that was blocked by interleukin (IL)-1alpha, but not IL-1beta, specific mAb. The proliferation of CD8+ T cells with CD11a+ CC81+ MyD-1- DC was also enhanced by adding IL-1alpha. IL-1beta slightly enhanced proliferation, whereas IL-2, IL-6, IL-12, and IL-15 had no effect. We conclude that the failure to stimulate CD8+ T cell proliferation results from the lack of IL-1alpha synthesis by this population, which may have important consequences in vivo.     

Antibody-mediated delivery of antigen to chemokine receptors on antigen-presenting cells results in enhanced CD4+ T cell responses

Here, we have investigated if targeting of T cell epitopes to chemokine receptors results in improved CD4+ T cell responses. Mouse monoclonal antibodies (mAb) with kappaL chains were targeted to various chemokine receptors expressed on human monocytes or immature dendritic cells (DC), and proliferation of cloned human, DR4-restricted CD4+ T cells specific for mouse Ckappa(40-48) was measured. When using monocytes as antigen-presenting cells, mAb specific for CCR1, CCR2, CCR5, and CXCR4 were 100-10,000-fold more efficient at inducing T cell proliferation when compared to isotype-matched control mAb on a per molecule basis. Targeting of immature DC was less effective and was only seen with anti-CCR1 and anti-CXCR4 mAb. Anti-chemokine receptors mAb required to be processed by the conventional endosomal MHC class II presentation pathway. The mAb did not induce signaling through the chemokine receptors as they failed to induce mobilization of cytosolic Ca2+ and actin polymerization. They also failed to induce APC maturation. The results strongly suggest that chemokine receptors channel antigen into the endocytic pathway for presentation on MHC class II molecules. Targeting T cell epitopes to chemokine receptors by recombinant antibody should be a useful vaccine strategy for the induction of strong CD4+ T cell responses.     

Apoptotic cells induce dendritic cell-mediated suppression via interferon-gamma-induced IDO

Dendritic cells (DC) are sensitive to their local environment and are affected by proximal cell death. This study investigated the modulatory effect of cell death on DC function. Monocyte-derived DC exposed to apoptotic Jurkat or primary T cells failed to induce phenotypic maturation of the DC and were unable to support CD4+ allogeneic T-cell proliferation compared with DC exposed to lipopolysaccharide (LPS) or necrotic cells. Apoptotic cells coincubated with LPS- or necrotic cell-induced mature DC significantly suppressed CD80, CD86 and CD83 and attenuated LPS-induced CD4+ T-cell proliferation. Reduced levels of interleukin-12 (IL-12), IL-10, IL-6, tumour necrosis factor-alpha and interferon-gamma (IFN-gamma) were found to be concomitant with the suppressive activity of apoptotic cells upon DC. Furthermore, intracellular staining confirmed IFN-gamma expression by DC in association with apoptotic environments. The specific generation of IFN-gamma by DC within apoptotic environments is suggestive of an anti-inflammatory role by the induction of indoleamine 2,3-dioxygenase (IDO). Both neutralization of IFN-gamma and IDO blockade demonstrated a role for IFN-gamma and IDO in the suppression of CD4+ T cells. Moreover, we demonstrate that IDO expression within the DC was found to be IFN-gamma-dependent. Blocking transforming growth factor-beta (TGF-beta) also produced a partial release in T-cell proliferation. Our study strongly suggests that apoptosis-induced DC suppression is not an immunological null event and two prime mediators underpinning these functional effects are IFN-gamma-induced IDO and TGF-beta.     

Switching from a restricted to an effective CD4 T cell response by activating CD8+ murine dendritic cells with a Toll-like receptor 9 ligand

Freshly isolated quiescent splenic dendritic cell (DC) subtypes differ in their capacity to activate naive CD4 T cells in culture. The CD8+ DC showed a reduced capacity to stimulate T cell proliferation compared to either of the CD8- DC subsets, regardless of antigen and DC dose. In contrast to CD8- DC, the quiescent CD8+ DC did not induce IFN-gamma production from CD4 T cells. The difference between the DC subtypes appeared to be at the level of initial surface molecule interactions, but could not be attributed to differences in expression of MHC class II or B7 family molecules, or to the expression of Fas ligand on DC. However, when activated by inclusion of the Toll-like receptor 9 ligand CpG in culture, CD8+ DC became potent stimulators of both CD4 T cell proliferation and IFN-gamma production. In contrast, similar activation of CD8- DC produced a more modest increase in capacity to stimulate CD4 T cell proliferation and no increase in capacity to stimulate IFN-gamma production. The difference between a quiescent and an activated state is therefore more extreme for CD8+ than for CD8- DC. The especially tight regulation of the activity of CD8+ DC may be essential for the maintenance of self tolerance.     

Intrinsic ability of GM+IL-4 but not Flt3L-induced rat dendritic cells to promote allogeneic T cell hyporesponsiveness

The influence of GM+IL-4 and Flt3 ligand (FL) on phenotype and function of BM-derived DC from Lewis rats was investigated. GM+IL-4-induced DC, despite expression of CD80/CD86, were less stimulatory than FL-induced DC that expressed low CD80/CD86 and were efficient stimulators of allogeneic T cells. GM+IL-4 DC were CD11b+ OX62lo, whereas FL DC were CD11blo OX62+. Following activation, GM+IL-4 DC produced IL-10 and IL-6, but no IL-12p70, and were resistant to further maturation. FL DC produced IL-12p70, IFN-alpha/beta, IL-10 and IL-6 and underwent maturation. Repeated stimulation of T cells with GM+IL-4 DC inhibited proliferation, cytokine production and induced early T cell apoptosis. FL DC-activated T cells produced large amounts of IFN-gamma/IL-10 and exhibited late T cell apoptosis/necrosis. In vivo, GM+IL-4 DC induced alloAg-specific hyporesponsiveness following T cell restimulation. These results demonstrate that GM+IL-4 DC display intrinsic regulatory properties, inducing passive-cell-death in T cells with potential for inactivation/regulation of alloreactive T cells in transplantation.     

Mesenchymal stem cells inhibit the expression of CD25 (interleukin-2 receptor) and CD38 on phytohaemagglutinin-activated lymphocytes

Mesenchymal stem cells (MSC) are immunomodulatory and inhibit lymphocyte proliferation. We studied surface expression of lymphocyte activation markers and secreted cytokines, when lymphocytes were activated in the presence of MSC. MSC suppressed the proliferation of phytohaemagglutinin (PHA)-stimulated CD3+, CD4+ and CD8+ lymphocytes. MSC significantly reduced the expression of activation markers CD25, CD38 and CD69 on PHA-stimulated lymphocytes. Mixed lymphocyte culture (MLC) supernatants containing MSC suppressed proliferation of MLC and PHA-stimulated lymphocytes dose-dependently. MSC secrete osteoprotegerin (OPG), but not hepatocyte growth factor (HGF) or transforming growth factor-beta (TGF-beta). Stromal-cell-derived factor-1 (SDF-1) is not expressed on the cell surface. A recent report suggested that T-cell suppression by MSC is mediated by HGF and TGF-beta. MSC suppression was not restored by the addition of neutralizing antibodies against SDF-1, OPG, HGF or TGF-beta, alone or in combination. Addition of guanosine to PHA-stimulated lymphocyte cultures containing MSC did not affect lymphocyte proliferation. The immunosuppressive effects of cyclosporine and MSC did not interfere, when present in the cultures of PHA-activated lymphocytes. In summary, human MSC suppress proliferation of both CD4+ and CD8+ lymphocyte and decrease the expression of activation markers.     

Flagellin enhances NK cell proliferation and activation directly and through dendritic cell-NK cell interactions

Flagellin, the principal component of bacterial flagella, is a ligand for Toll-like receptor 5 (TLR5) or TLR11 and contributes to systemic inflammation during sepsis through activation of dendritic cells (DCs) and other cells of the innate immune system. Here, we report that flagellin and the TLR4 ligand, lipopolysaccharide (LPS), induced phenotypic and functional maturation of murine bone marrow-derived DCs and enhanced DC accumulation in the draining popliteal lymph node following their footpad injection. It is interesting that flagellin injection enhanced myeloid (CD8alpha(-1)) and plasmacytoid (plasmacytoid DC antigen(+) B220(+)) DC subsets, whereas LPS only increased myeloid DCs in the draining lymph node. In addition, the footpad injection of flagellin or LPS induced significant CD4(+) T cell activation in the draining popliteal lymph node, as judged by increased CD69 or CD25 expression. We illustrate, for the first time, that flagellin also increases natural killer (NK) cell number and activation status in the draining lymph node after footpad injection. Using coculture with enriched carboxy-fluorescein diacetate succinimidyl ester-labeled NK cells, flagellin-treated DCs induce significant NK cell proliferation and activation. In fact, direct treatment of NK cells with flagellin induces a greater increase in cell proliferation than treatment with LPS. In contrast, flagellin treatment of NK cells was not a strong inducer of interferon-gamma (IFN-gamma) production, indicating that NK cell proliferation and IFN-gamma production may be regulated differentially. These data suggest that flagellin is a capable maturation agent for murine myeloid-derived DCs, and flagellin-activated DCs and flagellin itself are potent inducers of NK cell proliferation.     

Naive CD8+ T cell recruitment and proliferation are dependent on stage of dendritic cell maturation

Dendritic cells (DC) play a crucial role in controlling the initiation and orientation of antigen (Ag)‐specific immune responses. It is widely accepted that optimal T cell priming requires mature DC. Although the molecular events associated with DC activation have been extensively studied, little is known about the consequences of DC maturation on recruitment and expansion of naive T cells. In the present study, we used a model tumor Ag to show that the kinetics of human DC maturation drastically affect the induction of Ag‐specific effector CD8⁺ T cells. In absence of exogenous cytokines and CD4 help, only DC at early stages of maturation were able to generate high frequencies of CTL. This expansion resulted from both enhanced recruitment and intense proliferation ofT cell precursors and could lead to an increase of up to 1,000‐fold in the final number of effector T cells compared to non‐matured DC. In our model, larger recruitment of naïve CD8⁺ cells did not modify the overall avidity of the Ag‐specific T cell population.     

Dendritic cell maturation is required for the cross-tolerization of CD8+ T cells

In vivo models have shown that tissue-restricted antigen may be captured by bone marrow-derived cells and cross-presented for the tolerization of CD8+ T cells. Although these studies have shown peripheral tolerization of CD8+ T cells, the mechanism of antigen transfer and the nature of the antigen-presenting cell (APC) remain undefined. We report here the establishment of an in vitro system for the study of cross-tolerance and show that dendritic cells (DCs) phagocytose apoptotic cells and tolerize antigen-specific CD8+ T cells when cognate CD4+ T helper cells are absent. Using this system, we directly tested the "two-signal" hypothesis for the regulation of priming versus tolerance. We found that the same CD83+ myeloid-derived DCs were required for both cross-priming and cross-tolerance. These data suggested that the current model for peripheral T cell tolerance, "signal 1 in the absence of signal 2", requires refinement: the critical checkpoint is not DC maturation, but instead the presence of a third signal, which is active at the DC-CD4+ T cell interface.     

Differential effects of the tryptophan metabolite 3-hydroxyanthranilic acid on the proliferation of human CD8+ T cells induced by TCR triggering or homeostatic cytokines

Production of indoleamine 2,3-dioxygenase (IDO) by tumor cells, leading to tryptophan depletion and production of immunosuppressive metabolites, may facilitate immune tolerance of cancer. IDO gene is also expressed in dendritic cells (DC) upon maturation induced by lipopolysaccarides or IFN. We investigated IDO gene expression in melanoma cell lines and clinical specimens as compared to mature DC (mDC). Furthermore, we explored effects of L-kynurenine (L-kyn) and 3-hydroxyanthranilic acid (3-HAA) on survival and antigen-dependent and independent proliferation of CD8(+) cells. We observed that IDO gene expression in cultured tumor cells and freshly excised samples is orders of magnitude lower than in mDC, providing highly efficient antigen presentation to CD8(+) T cells. Non toxic concentrations of L-kyn or 3-HAA did not significantly inhibit antigen-specific CTL responses. However, 3-HAA, but not L-kyn markedly inhibited antigen-independent proliferation of CD8(+) T cells induced by common receptor gamma-chain cytokines IL-2, -7 and -15. Our data suggest that CD8(+) T cell activation induced by antigenic stimulation, a function exquisitely fulfilled by mDC, is unaffected by tryptophan metabolites. Instead, in the absence of effective T cell receptor triggering, 3-HAA profoundly affects homeostatic proliferation of CD8(+) T cells.     

Glucocorticoids increase the endocytic activity of human dendritic cells.

We have investigated the effect of glucocorticoids (GC) on antigen uptake molecule expression and on endocytic activity of human dendritic cells (DC). Human monocyte-derived DC were differentiated in vitro for 7 days with granulocyte macrophage colony stimulating factor and IL-4 in the presence or absence of dexamethasone 10(-8) M (Dex). Dex-treated DC showed an enhancement of mannose receptor (MR)-mediated endocytosis (measured as uptake of FITC-dextran) and of fluid-phase endocytosis [measured as uptake of Lucifer yellow (LY)] The effect was dose dependent and correlated with the length of exposure to Dex. The expression of receptors involved in antigen capture was investigated by FACS analysis. Dex up-regulates MR, CD16 and CD32 expression on DC. After maturation with tumor necrosis factor-alpha or CD40 ligand in Dex-treated DC, despite a reduction induced by maturation the endocytic activity of FITC-dextran and LY, the expression of MR, CD16 and CD32 remained higher than in control DC. In view of the fact that antigen capture was increased in cells cultured with Dex, we evaluated the ability to present soluble antigen that needs to be taken up and processed. Cells differentiated in the presence of Dex showed much lower efficiency in presenting tetanus toxin to specific autologous T cell lines. In conclusion our data suggest a new mechanism by which GC may influence immune responses. In fact with the increase in endocytic activity, Dex favors the scavenging of antigen from the external milieu, decreasing antigen concentration and availability, and simultaneously inhibiting the capacity to stimulate T cells.