IL-6 regulates in vivo dendritic cell differentiation through STAT3 activation

Dendritic cells (DCs) orchestrate immune responses according to their state of maturation. In response to infection, DCs differentiate into mature cells that initiate immune responses, while in the absence of infection, most of them remain in an immature form that induces tolerance to self Ags. Understanding what controls these opposing effects is an important goal for vaccine development and prevention of unwanted immune responses. A crucial question is what cytokine(s) regulates DC maturation in the absence of infection. In this study, we show that IL-6 plays a major role in maintaining immature DCs. IL-6 knockout (KO) mice had increased numbers of mature DCs, indicating that IL-6 blocks DC maturation in vivo. We examined this effect further in knockin mice expressing mutant versions of the IL-6 signal transducer gp130, with defective signaling through either Src homology region 2 domain-containing phosphatase 2/Gab/MAPK (gp130(F759/F759)) or STAT3 (gp130(FxxQ/FxxQ)), and combined gp130 and IL-6 defects (gp130(F759/F759)/IL-6 KO mice). Importantly, we found STAT3 activation by IL-6 was required for the suppression of LPS-induced DC maturation. In addition, STAT3 phosphorylation in DCs was regulated by IL-6 in vivo, and STAT3 was necessary for the IL-6 suppression of bone marrow-derived DC activation/maturation. DC-mediated T cell activation was enhanced in IL-6 KO mice and suppressed in gp130(F759/F759) mice. IL-6 is thus a potent regulator of DC differentiation in vivo, and IL-6-gp130-STAT3 signaling in DCs may represent a critical target for controlling T cell-mediated immune responses in vivo.     

Pulmonary immunity to viral infection: adenovirus infection of lung dendritic cells renders T cells nonresponsive to interleukin-2

Adenovirus (Ad) infection has been identified as predisposing hosts to the development of pulmonary disease through unknown mechanisms. Lung dendritic cells (DCs) are vital for initiating pulmonary immune responses; however, the effects of Ad infection on primary lung DC have not been studied. In contrast to the effects on bone marrow- and monocyte-derived DCs, the current study shows that Ad infection of murine BALB/c lung DCs in vitro and in vivo suppresses DC-induced T-cell proliferation. The effect of Ad on DCs was not due to a downregulation of major histocompatibility complex or costimulatory molecules. Analysis of the production of interleukin-12 (IL-12), alpha interferon (IFN-alpha), and IFN-gamma by the Ad-infected DCs shows no significant differences over noninfected control lung DCs. Ad-induced suppression was not due to a deficiency of IL-2 or other DC-secreted factors and was dependent on viral protein synthesis, as UV irradiation of Ad abrogated the suppressive effect. Results suggest that Ad-infected DCs induce T cells to be nonresponsive to IL-2 during primary coculture, as the addition of IL-2 in secondary cultures recovered T-cell proliferation. In vivo studies supported in vitro results showing that Ad infection resulted in lung T cells with decreased proliferative ability. This study demonstrates that Ad infection induces local immunoincompetence by altering DC-T-cell interactions.     

Synthesis and surface expression of hyaluronan by dendritic cells and its potential role in antigen presentation

Hyaluronan (HA) is a large glycosaminoglycan consisting of repeating disaccharide units of glucuronic acid and N-acetylglucosamine. HA is known to act as a filling material of extracellular matrices and as an adhesive substrate for cellular migration. Here we report that dendritic cells (DC) express mRNAs for HA synthases and hyaluronidases, actively synthesize HA, and display HA on their surfaces. Interestingly, HA expression levels on DC were not significantly altered by their maturation states. With respect to physiological function, three specific HA inhibitors, i.e., bovine proteoglycan, a 12-mer HA-binding peptide (GAHWQFNALTVR) termed Pep-1, and an oligomeric Pep-1 formulation, all interfered with DC-induced activation of CD4(+) T cells isolated from DO11.10 TCR transgenic mice. For example, Pep-1 oligomer efficiently inhibited DC-dependent cluster formation, IL-2 and IFN-gamma production, and proliferation by DO11.10 T cells in vitro without affecting the viabilities of DC or T cells, DC function to uptake exogenous proteins, or DC-T cell conjugate formation at earlier time points. These observations suggest a paracrine mechanism by which DC-associated HA facilitates some of the late changes in T cell activation. Although T cells constitutively expressed mRNAs for HA synthases and hyaluronidases, their surface HA expression became detectable only after activation. Oligomeric Pep-1 and bovine proteoglycan both inhibited mitogen-triggered T cell activation in the absence of DC, suggesting an autocrine mechanism by which HA expressed by T cells assists their own activation processes. Finally, adoptively transferred DO11.10 T cells showed progressive mitosis when stimulated with Ag-pulsed DC in living animals, and this clonal expansion was inhibited significantly by administration of Pep-1 oligomer. Our findings may introduce a new concept that relatively simple carbohydrate moieties expressed on DC and perhaps T cells play an important immunomodulatory role during Ag presentation.     

Measles virus induces abnormal differentiation of CD40 ligand-activated human dendritic cells

Measles virus (MV) infection induces a profound immunosuppression responsible for a high rate of mortality in malnourished children. MV can encounter human dendritic cells (DCs) in the respiratory mucosa or in the secondary lymphoid organs. The purpose of this study was to investigate the consequences of DC infection by MV, particularly concerning their maturation and their ability to generate CD8+ T cell proliferation. We first show that MV-infected Langerhans cells or monocyte-derived DCs undergo a maturation process similarly to the one induced by TNF-alpha or LPS, respectively. CD40 ligand (CD40L) expressed on activated T cells is shown to induce terminal differentiation of DCs into mature effector DCs. In contrast, the CD40L-dependent maturation of DCs is inhibited by MV infection, as demonstrated by CD25, CD69, CD71, CD40, CD80, CD86, and CD83 expression down-regulation. Moreover, the CD40L-induced cytokine pattern in DCs is modified by MV infection with inhibition of IL-12 and IL-1alpha/beta and induction of IL-10 mRNAs synthesis. Using peripheral blood lymphocytes from CD40L-deficient patients, we demonstrate that MV infection of DCs prevents the CD40L-dependent CD8+ T cell proliferation. In such DC-PBL cocultures, inhibition of CD80 and CD86 expression on DCs was shown to require both MV replication and CD40 triggering. Finally, for the first time, MV was shown to inhibit tyrosine-phosphorylation level induced by CD40 activation in DCs. Our data demonstrate that MV replication modifies CD40 signaling in DCs, thus leading to impaired maturation. This phenomenon could play a pivotal role in MV-induced immunosuppression.     

Short-term activation induces multifunctional dendritic cells that generate potent antitumor T-cell responses in vivo

Dendritic cell (DC) vaccines have emerged as a promising strategy to induce antitumoral cytotoxic T cells for the immunotherapy of cancer. The maturation state of DC is of critical importance for the success of vaccination, but the most effective mode of maturation is still a matter of debate. Whereas immature DC carry the risk of inducing tolerance, extensive stimulation of DC may lead to DC unresponsiveness and exhaustion. In this study, we investigated how short-term versus long-term DC activation with a Toll-like receptor 9 agonist influences DC phenotype and function. Murine DC were generated in the presence of the hematopoietic factor Flt3L (FL-DC) to obtain both myeloid and plasmacytoid DC subsets. Short activation of FL-DC for as little as 4 h induced fully functional DC that rapidly secreted IL-12p70 and IFN-α, expressed high levels of costimulatory and MHC molecules and efficiently presented antigen to CD4 and CD8 T cells. Furthermore, short-term activated FL-DC overcame immune suppression by regulatory T cells and acquired high migratory potential toward the chemokine CCL21 necessary for DC recruitment to lymph nodes. In addition, vaccination with short-term activated DC induced a strong cytotoxic T-cell response in vivo and led to the eradication of tumors. Thus, short-term activation of DC generates fully functional DC for tumor immunotherapy. These results may guide the design of new protocols for DC generation in order to develop more efficient DC-based tumor vaccines.     

Influenza virus evades innate and adaptive immunity via the NS1 protein

Both antibodies and T cells contribute to immunity against influenza virus infection. However, the generation of strong Th1 immunity is crucial for viral clearance. Interestingly, we found that human dendritic cells (DCs) infected with influenza A virus have lower allospecific Th1-cell stimulatory abilities than DCs activated by other stimuli, such as lipopolysaccharide and Newcastle disease virus infection. This weak stimulatory activity correlates with a suboptimal maturation of the DCs following infection with influenza A virus. We next investigated whether the influenza A virus NS1 protein could be responsible for the low levels of DC maturation after influenza virus infection. The NS1 protein is an important virulence factor associated with the suppression of innate immunity via the inhibition of type I interferon (IFN) production in infected cells. Using recombinant influenza and Newcastle disease viruses, with or without the NS1 gene from influenza virus, we found that the induction of a genetic program underlying DC maturation, migration, and T-cell stimulatory activity is specifically suppressed by the expression of the NS1 protein. Among the genes affected by NS1 are those coding for macrophage inflammatory protein 1beta, interleukin-12 p35 (IL-12 p35), IL-23 p19, RANTES, IL-8, IFN-alpha/beta, and CCR7. These results indicate that the influenza A virus NS1 protein is a bifunctional viral immunosuppressor which inhibits innate immunity by preventing type I IFN release and inhibits adaptive immunity by attenuating human DC maturation and the capacity of DCs to induce T-cell responses. Our observations also support the potential use of NS1 mutant influenza viruses as live attenuated influenza virus vaccines.     

IL-1 beta enhances CD40 ligand-mediated cytokine secretion by human dendritic cells (DC): a mechanism for T cell-independent DC activation.

CD40 ligand (CD40L) is a membrane-bound molecule expressed by activated T cells. CD40L potently induces dendritic cell (DC) maturation and IL-12p70 secretion and plays a critical role during T cell priming in the lymph nodes. IFN-gamma and IL-4 are required for CD40L-mediated cytokine secretion, suggesting that T cells are required for optimal CD40L activity. Because CD40L is rapidly up-regulated by non-T cells during inflammation, CD40 stimulation may also be important at the primary infection site. However, a role for T cells at the earliest stages of infection is unclear. The present study demonstrates that the innate immune cell-derived cytokine, IL-1beta, can increase CD40L-induced cytokine secretion by monocyte-derived DC, CD34(+)-derived DC, and peripheral blood DC independently of T cell-derived cytokines. Furthermore, IL-1beta is constitutively produced by monocyte-derived DC and monocytes, and is increased in response to intact Escherichia coli or CD40L, whereas neither CD34(+)-derived DC nor peripheral blood DC produce IL-1beta. Finally, DC activated with CD40L and IL-1beta induce higher levels of IFN-gamma secretion by T cells compared with DC activated with CD40L alone. Therefore, IL-1beta is the first non-T cell-derived cytokine identified that enhances CD40L-mediated activation of DC. The synergy between CD40L and IL-1beta highlights a potent, T cell-independent mechanism for DC activation during the earliest stages of inflammatory responses.     

Interleukin-4 acts at the locus of the antigen-presenting dendritic cell to counter-regulate cytotoxic CD8+ T-cell responses

The mechanism underlying suppression of immune responses by interleukin-4 (IL-4) has remained unexplained. Here we show that the antigen-presenting dendritic cell is central to counter-regulation of autoimmune disease by IL-4. IL-4 acts at the locus of the dendritic cell to decrease the cytolytic T-cell response, preventing autoimmunity. Stimulation of cytotoxic precursors by antigen pulsed dendritic cells induces their differentiation but the process is blocked by IL-4. IL-4-influenced DC produce distinct effects on CD8+ T cells depending on their state of activation. The molecular basis for this regulation is the alteration of the expression ratio of the costimulatory ligands B7.1/B7.2 on dendritic cells. Our findings demonstrate that B7.2 induces expansion of CD8+ T cells and B7.1 governs their acquisition of cytolytic activity. IL-4 influences the dendritic cell to elicit qualitative differences in T-cell responses, providing the basis for counter-regulation mediated by IL-4.     

Polarization of allogeneic T-cell responses by influenza virus-infected dendritic cells

The developing immune response in the lymph nodes of mice infected with influenza virus has both Th1- and Th2-type characteristics. Modulation of the interactions between antigen-presenting cells and T cells is one mechanism that may alter the quality of the immune response. We have previously shown that the ability of dendritic cells (DC) to stimulate the proliferation of alloreactive T cells is changed by influenza virus due to viral neuraminidase (NA) activity. Here we show that DC infected with influenza virus A/PR/8/34 (PR8) stimulate T cells to produce different types of cytokines in a dose-dependent manner. Optimal amounts of the Th1-type cytokines interleukin-2 (IL-2) and gamma interferon (IFN-gamma) were produced from T cells stimulated by DC infected with low doses of PR8, while the Th2-type cytokines IL-4 and IL-10 were produced only in response to DC infected with high doses of PR8. IL-2 and IFN-gamma levels corresponded with T-cell proliferation and were dependent on the activity of viral NA on the DC surface. In contrast, IL-4 secretion required the treatment of T cells with NA. Since viral particles were released only from DC that are infected with high doses of PR8, our results suggest that viral NA on newly formed virus particles desialylates T-cell surface molecules to facilitate a Th2-type response. These results suggest that the activity of NA may contribute to the mixed Th-type response observed during influenza virus infection.     

Suppression of measles virus expression by noncytolytic antibody in an immortalized macrophage cell line.

Immune regulation of measles virus (MV) expression was studied in a persistently infected mouse macrophage cell line. Synthesis of both membrane-associated and internal MV antigens was suppressed when infected macrophages were treated with polyclonal rabbit anti-MV antibody that was specific for MV proteins. Persistently infected macrophages were treated for 3, 5, or 7 days with increasing doses of anti-MV antibody. All MV proteins were down-regulated 2 days after treatment was terminated. One week after treatment was terminated, down-regulation was still evident but to a lesser degree. MV protein synthesis was suppressed whether or not complement components were inactivated by heating all serum supplements and antibodies. However, when complement was active, cell lysis accounted for some of the reduced MV protein synthesis. When lytic destruction of infected cells by antibody and complement was prevented by inactivation of complement, antibody alone reduced the cellular synthesis of viral proteins by noncytolytic mechanisms. The absence of cell death in the absence of complement was confirmed by the lack of 51Cr release from labeled cells, the lack of reduction in cell number, and the lack of a decrease in total protein synthesis when radiolabeled infected cells were treated with antibody. It is noteworthy that low doses of antibody were optimal for suppression in the longer-term experiments and did not cause lysis, even in the presence of active complement. Since infected macrophages disseminate virus in measles infection, noncytolytic regulation of these cells by antibody may supplement viral clearance by cytolytic T cells and other immune mechanisms.     

Folate deficiency affects dendritic cell function and subsequent T helper cell differentiation

Insufficient folate status may be related to the increasing prevalence of immune- or inflammation-related chronic diseases. To investigate the effects of folate on immune regulation, we examined the impact of folate deficiency (FD) on dendritic cell (DC) maturation and function and, thus, T helper (Th) cells differentiation. First, bone marrow-derived DCs (BMDCs) were generated from BALB/c mice bone marrow cells cultured in folate-containing (F-BMDCs) or folate-deficient (FD-BMDCs) medium. FD-BMDC displayed more immature phenotype including reduced levels of major histocompatibility complex class II (MHC II), co-stimulatory molecules and characteristic of higher endocytic activity. FD-BMDC produced less IL-12p70 and proinflammatory cytokines in response to lipopolysaccharide. This aberrant DC maturation due to FD resulted in reduced BMDC-induced Th cell activity and lower IL-2, IFNγ, IL-13 and IL-10 productions. Further in vivo study confirmed significantly lower IFNγ and IL-10 productions by T cells and showed higher splenic naïve Th and lower memory T, effector T and regulatory T cell (Treg) percentages in mice fed with the FD diet for 13 weeks. To investigate the role of DCs on T cell activity, splenic DCs (spDC) from FD mice were cocultured with Th cells. The FD spDC had lower MHC II and CD80 expressions and subsequently impaired DC-induced Th differentiation, shown as decreased cytokine productions. This study demonstrated that folate deficiency impaired DC functions and, thus, Th differentiation and responses, suggesting that folate plays a crucial role in maintaining Th cells homeostasis.     

IL-10 alters DC function via modulation of cell surface molecules resulting in impaired T-cell responses

IL-10 is a potent inhibitor of T-cell activation and has tolerizing effects on these cells. These effects are primarily mediated via modulation of antigen presenting cell function. Here, it is demonstrated that IL-10 completely inhibits LPS-induced DC maturation, resulting in altered DC-T-cell interactions and reduced T-cell responses. IL-10 inhibited LPS-induced upregulation of costimulatory molecules, MHC Class II, and the secretion of IL-12, TNF-alpha, IL-6, and IL-1beta by DCs, although it upregulated the SLAM (CD150) expression at both the mRNA and protein levels. IL-10 pre-treated DC did not respond to subsequent LPS activation and its stimulatory ability for allogeneic and antigen-specific T-cells was severely impaired. Importantly, T-cells derived from co-cultures with Ag-pulsed, IL-10-treated DC were impaired in their responses to subsequent Ag-specific restimulation. Transwell and DC-derived plasma membrane experiments indicated that the capacity of IL-10-treated DC to induce T-cell unresponsiveness results from alterations in the cell surface molecules rather than modulation of cytokine secretion.     

Dose-dependent changes in influenza virus-infected dendritic cells result in increased allogeneic T-cell proliferation at low, but not high, doses of virus

During the acute phase of infection with influenza A virus, the degree of lymphopenia correlates with severity of disease. Factors that contribute to T-cell activation during influenza virus infection may contribute to this observation. Since the immune response is initiated when dendritic cells (DC) interact with T cells, we have established an in vitro system to examine the effects of influenza virus infection on DC function. Our results show that allogeneic T-cell proliferation was dependent on the dose of A/PR/8/34 used to infect DC, with enhanced responses at low, but not high, multiplicities of infection. The lack of enhancement at high virus doses was not primarily due to the increased rate of DC apoptosis, but required viral replication and neuraminidase (NA) activity. Clusters that formed between DC or between DC and T cells were also dependent on the viral dose. This change in cellular interaction may oppose T-cell proliferation in response to DC infected with high doses of PR8, since the increased contact between DC resulted in the exclusion of T cells. The enhanced alloreactive T-cell response was restored by neutralization of transforming growth factor beta1 (TGF-beta1). It is likely that NA present on viral particles released from DC infected with high doses of PR8 activates TGF-beta1. Future studies will determine the mechanism by which TGF-beta1 modifies the in vitro T-cell response and address the contribution of this cytokine to the lymphopenia observed in severe disease.     

Effect of mesenchymal stem cell-derived exosomes on the induction of mouse tolerogenic dendritic cells

Dendritic cells (DCs) orchestrate innate inflammatory responses and adaptive immunity through T-cell activation via direct cell–cell interactions and/or cytokine production. Tolerogenic DCs (tolDCs) help maintain immunological tolerance through the induction of T-cell unresponsiveness or apoptosis, and generation of regulatory T cells. Mesenchymal stromal cells (MSCs) are adult multipotent cells located within the stroma of bone marrow (BM), but they can be isolated from virtually all organs. Extracellular vesicles and exosomes are released from inflammatory cells and act as messengers enabling communication between cells. To investigate the effects of MSC-derived exosomes on the induction of mouse tolDCs, murine adipose-derived MSCs were isolated from C57BL/6 mice and exosomes isolated by ExoQuick-TC kits. BM-derived DCs (BMDCs) were prepared and cocultured with MSCs-derived exosomes (100 μg/ml) for 72 hr. Mature BMDCs were derived by adding lipopolysaccharide (LPS; 0.1μg/ml) at Day 8 for 24 hr. The study groups were divided into (a) immature DC (iDC, Ctrl), (b) iDC + exosome (Exo), (c) iDC + LPS (LPS), and (d) iDC + exosome + LPS (EXO + LPS). Expression of CD11c, CD83, CD86, CD40, and MHCII on DCs was analyzed at Day 9. DC proliferation was assessed by coculture with carboxyfluorescein succinimidyl ester-labeled BALB/C-derived splenocytes p. Interleukin-6 (IL-6), IL-10, and transforming growth factor-β (TGF-β) release were measured by enzyme-linked immunosorbent assay. MSC-derived exosomes decrease DC surface marker expression in cells treated with LPS, compared with control cells ( ≤ .05). MSC-derived exosomes decrease IL-6 release but augment IL-10 and TGF-β release (p ≤ .05). Lymphocyte proliferation was decreased (p ≤ .05) in the presence of DCs treated with MSC-derived exosomes. CMSC-derived exosomes suppress the maturation of BMDCs, suggesting that they may be important modulators of DC-induced immune responses.     

Gamma irradiation of human dendritic cells influences proliferation and cytokine profile of T cells in autologous mixed lymphocyte reaction

Dendritic cells (DC) are the most potent antigen-presenting cells (APC); their ability to induce proliferation of T cells in a mixed lymphocyte reaction (MLR) assay is commonly used for the evaluation of their function. It is a general thought that gamma irradiation of APC does not influence their ability to activate T-cell proliferation, but the data from several studies are controversial. To further determine the mechanisms involved in DC-induced T-cell activation in MLR assay, human DC induced from peripheral blood mononuclear cells (PBMC) were gamma-irradiated and determine their effects on the proliferation and cytokine profiles of T cells in an autologous MLR. DC were induced from the PBMC of 11 multiple sclerosis (MS) patients with RMPI 640 medium containing recombinant human GM-CSF (rhGM-CSF; 800 U/ml) and recombinant human IL-4 (rhIL-4; 500 U/ml). DC harvested on day 7 were divided into two equal parts. One part was not irradiated (naive DC); the other was gamma-irradiated at a dose of 30 Gy. Cell surface molecules were analyzed by flow cytometry. T-cell proliferation was determined using a beta-scintillation counter. The levels of IL-2, IL-4, IL-6 and IL-10 in co-culture supernatants were measured by ELISA. The results indicated that gamma irradiation reduced expression of CD86, CD80 and HLA-DR molecules on DC, especially CD86 (P=0.0072). DC, irradiated or non-irradiated, effectively stimulated autologous T-cell proliferation. Compared to naive DC, irradiated DC showed a markedly lower capacity to promote T-cell proliferation (P=0.0073), and strikingly up-regulated secretion of IL-4 (P=0.0145) and IL-2 (P=0.0323) by autologous T cells. No significant differences were noted in IL-6 and IL-10 production between T cells co-cultured with naive DC and irradiated DC (P>0.05). It is concluded that gamma irradiation of DC not only influences the phenotype of DC but also alters their capacity to stimulate the proliferation and the cytokine profiles of autologous T cells in a MLR.     

Dendritic cells infected with vpr-positive human immunodeficiency virus type 1 induce CD8+ T-cell apoptosis via upregulation of tumor necrosis factor alpha

Human immunodeficiency virus type 1 (HIV-1) viral protein R (Vpr) plays a crucial role in viral replication and pathogenesis by inducing cell cycle arrest, apoptosis, translocation of preintegration complex, potentiation of glucocorticoid action, impairment of dendritic cell (DC) maturation, and T-cell activation. Recent studies involving the direct effects of Vpr on DCs and T cells indicated that HIV-1 containing Vpr selectively impairs phenotypic maturation, cytokine network, and antigen presentation in DCs and dysregulates costimulatory molecules and cytokine production in T cells. Here, we have further investigated the indirect effect of HIV-1 Vpr(+) virus-infected DCs on the bystander CD8(+) T-cell population. Our results indicate that HIV-1 Vpr(+) virus-infected DCs dysregulate CD8(+) T-cell proliferation and induce apoptosis. Vpr-containing virus-infected DC-mediated CD8(+) T-cell killing occurred in part through enhanced tumor necrosis factor alpha production by infected DCs and subsequent induction of death receptor signaling and activation of the caspase 8-dependent pathway in CD8(+) T cells. Collectively, these results provide evidence that Vpr could be one of the important contributors to the host immune escape by HIV-1 through its ability to dysregulate both directly and indirectly the DC biology and T-cell functions.     

Consequences of Fas-mediated human dendritic cell apoptosis induced by measles virus

Mortality from measles virus (MV) infection is caused mostly by secondary infections associated with a pronounced immunosuppression. Dendritic cells (DCs) represent a major target of MV and could be involved in immunosuppression. In this study, human monocyte-derived DCs were used to demonstrate that DC apoptosis in MV-infected DC-T-cell cocultures is Fas mediated, whereas apoptotic T cells could not be rescued by blocking the Fas pathway. Two novel consequences of DC apoptosis after MV infection were demonstrated. (i) Fas-mediated apoptosis of DCs facilitates MV release, while CD40 activation enhances MV replication in DCs. Indeed, detailed studies of infectious MV release and intracellular MV nucleoprotein (NP) showed that inhibition of CD40-CD40L ligand interaction blocks NP synthesis. We conclude that the CD40 ligand expressed by activated T cells first enhances MV replication in DCs, and then Fas ligand produced by activated T cells induces Fas-mediated apoptosis of DCs, thus facilitating MV release. (ii) Not only MV-infected DCs but also bystander uninfected DCs undergo a maturation process confirmed by CD1a, CD40, CD80, CD86, CD83, and major histocompatibility complex type II labeling. The bystander maturation effect results from contact and/or engulfment of MV-induced apoptotic DCs by uninfected DCs. A model is proposed to explain how both a specific immune response and immunosuppression can simultaneously occur after MV infection through Fas-mediated apoptosis and CD40 activation of DCs.     

Contrasting impacts of immunosuppressive agents (rapamycin,FK506, cyclosporin A,and dexamethasone) on bidirectional dendritic cell-T cell interaction during antigen presentation

Rapamycin (RAP), tacrolimus (FK506), cyclosporin A, and glucocorticoids represent modern and classic immunosuppressive agents being used clinically. Although these agents have distinct molecular mechanisms of action and exhibit different immunoregulatory profiles, their direct influences on Ag presentation processes remain relatively unknown. Here we report quantitative and qualitative differences among the above four immunosuppressants in their impact on Ag-specific, bidirectional interaction between dendritic cells (DC) and CD4(+) T cells. In the presence of relevant Ag, bone marrow-derived DC delivered activation signals to CD4(+) T cells isolated from the DO11.10 TCR transgenic mice, leading to clonal expansion; secretion of IFN-gamma, IL-2, and IL-4; and surface expression of CD69. Conversely, DO11.10 T cells delivered maturation signals to DC, leading to IL-6 and IL-12 production and CD40 up-regulation. FK506 (10(-10)-10(-8) M) and cyclosporin A (10(-9)-10(-7) M) each blocked efficiently and uniformly all the changes resulting from intercellular signaling in both DC-->T cell and T cell-->DC directions. Dexamethasone (10(-9)-10(-6) M) suppressed all changes, except for CD69 up-regulation, rather incompletely. Remarkably, RAP (10(-10)-10(-8) M) efficiently inhibited DC-induced T cell proliferation and T cell-mediated CD40 up-regulation by DC without abrogating other changes. Interestingly, T cell-independent DC maturation triggered by LPS stimulation was inhibited by dexamethasone, but not by other agents. Our results demonstrate contrasting pharmacological effects of RAP vs calcineurin inhibitors on Ag presentation, thus forming a conceptual framework for rationale-based selection (and combination) of immunosuppressive agents for clinical application.