Crosstalk between Toll like receptors and C5a receptor in human monocyte derived DCs suppress inflammatory cytokine production

The complement anaphylatoxin, C5a has been implicated in regulation of adaptive immune responses through modulation of APC function as shown mainly in studies in mice. C5a was shown to enhance cytokine production in immature DCs, but the effect of C5a on DC function during DC activation has not been elucidated in human. In this study we investigated the effect of C5a on human monocyte derived DCs when simultaneously stimulated with TLR ligands. While C5a indeed enhanced cytokine production of immature DCs, the addition of C5a inhibited production of IL-12, IL-23 and TNFα induced by various TLR ligands such as LPS, R848 and Pam(3)CSK(4). The inhibitory effect of C5a on LPS induced IL-6 production was less pronounced and LPS induced IL-10 was not affected at all. This indicates that C5aR signaling has a differential effect on human DC differentiation depending on the crosstalk with other receptors. Furthermore we found that C5a affects the LPS induced cytokines in a small time frame, and requires almost concurrent signaling of C5a receptor and TLR4. These data emphasize the complexity of DC regulation by anaphylatoxins. While complement activation may provide proinflammatory signals to immature DCs in the absence of pathogens, the same products may serve to downmodulate or deviate immune responses upon combat against infections. These context depending effects of anaphylatoxins on immune responses may have important implications for the emerging use of complement inhibitors in clinical practic

Inhibition of Dendritic Cell Activation and Modulation of T Cell Polarization by the Platelet Secretome

Platelet transfusions are a frequently administered therapy for especially hemato-oncological patients with thrombocytopenia. Next to their primary function in hemostasis, currently there is increased attention for the capacity of platelets to affect the function of various cells of the immune system. Here, we investigate the capacity of platelets to immuno-modulate monocyte-derived dendritic cells (moDC) as well as primary dendritic cells and effects on subsequent T cell responses. Platelets significantly inhibited pro-inflammatory (IL-12, IL-6, TNFα) and increased anti-inflammatory (IL-10) cytokine production of moDCs primed with toll-like receptor (TLR)-dependent and TLR-independent stimuli. Transwell assays and ultracentrifugation revealed that a soluble factor secreted by platelets, but not microvesicles, inhibited DC activation. Interestingly, platelet-derived soluble mediators also inhibited cytokine production by human ex vivo stimulated myeloid CD1c+ conventional DC2. Moreover, platelets and platelet-derived soluble mediators inhibited T cell priming and T helper differentiation toward an IFNγ+ Th1 phenotype by moDCs. Overall, these results show that platelets are able to inhibit the pro-inflammatory properties of DCs, and may even induce an anti-inflammatory DC phenotype, with decreased T cell priming capacity by the DC. The results of this study provide more insight in the potential role of platelets in immune modulation, especially in the context of platelet transfusions

Expression of the murine CD27 ligand CD70 in vitro and in vivo

The interaction between TNFR family member CD27 and its ligand CD70 promotes lymphocyte expansion and effector cell formation. In humans, control of CD27 function is partly regulated by the restricted expression of CD70. We used newly developed mAbs to characterize murine (m) CD70 expression in vitro and in vivo. On resting lymphocytes and immature dendritic cells (DC), mCD70 is absent. In vitro, Ag receptor triggering induced mCD70 mRNA in T cells, but cell surface protein expression was very low. Activated B cells synthesized much higher levels of mCD70 mRNA than activated T cells and clearly expressed mCD70 at the cell surface. mCD70 cell surface expression could also be induced on the DC line D1 and on in vitro-generated murine DC upon maturation. In lymphoid organs of naive mice, virtually no mCD70-expressing cells were found, with exception of cells in the thymic medulla, which may be epithelial in origin. However, after intranasal infection with influenza virus, lung-infiltrating T cells and T and B cells in draining lymph nodes expressed mCD70 according to immunohistology. In such activated lymphocytes, mCD70 protein is largely retained intracellularly. Plasma membrane expression of mCD70 was only detectable by flow cytometry on a small proportion of lung-infiltrating T cells and peaked at the height of the primary response. Thus, expression of CD70 in the mouse is highly regulated at the transcriptional and posttranslational level. This most likely serves to limit excessive effector cell formation after antigenic stimulatio

Expression of the murine CD27 ligand CD70 in vitro and in vivo

The interaction between TNFR family member CD27 and its ligand CD70 promotes lymphocyte expansion and effector cell formation. In humans, control of CD27 function is partly regulated by the restricted expression of CD70. We used newly developed mAbs to characterize murine (m) CD70 expression in vitro and in vivo. On resting lymphocytes and immature dendritic cells (DC), mCD70 is absent. In vitro, Ag receptor triggering induced mCD70 mRNA in T cells, but cell surface protein expression was very low. Activated B cells synthesized much higher levels of mCD70 mRNA than activated T cells and clearly expressed mCD70 at the cell surface. mCD70 cell surface expression could also be induced on the DC line D1 and on in vitro-generated murine DC upon maturation. In lymphoid organs of naive mice, virtually no mCD70-expressing cells were found, with exception of cells in the thymic medulla, which may be epithelial in origin. However, after intranasal infection with influenza virus, lung-infiltrating T cells and T and B cells in draining lymph nodes expressed mCD70 according to immunohistology. In such activated lymphocytes, mCD70 protein is largely retained intracellularly. Plasma membrane expression of mCD70 was only detectable by flow cytometry on a small proportion of lung-infiltrating T cells and peaked at the height of the primary response. Thus, expression of CD70 in the mouse is highly regulated at the transcriptional and posttranslational level. This most likely serves to limit excessive effector cell formation after antigenic stimulation

Lethal T cell immunodeficiency induced by chronic costimulation via CD27-CD70 interactions

It has been proposed that HIV-1, in addition to directly infecting and killing CD4+ T cells, causes T cell dysfunction and T cell loss by chronic immune activation. We analyzed the effects of chronic immune activation in mice that constitutively expressed CD70, the ligand for the tumor necrosis factor receptor family member CD27, on B cells. CD70 transgenic (CD70 Tg) mice showed a progressive conversion of naive T cells into effector-memory cells, which culminated in the depletion of naive T cells from lymph nodes and spleen. T cell changes depended on continuous CD27-CD70 interactions and T cell antigen receptor stimulation. Despite this hyperactive immune system, CD70 Tg mice died aged 6-8 months from Pneumocystis carinii infection, a hallmark of T cell immunodeficiency. Thus, persistent delivery of costimulatory signals via CD27-CD70 interactions, as may occur during chronic active viral infections, can exhaust the T cell pool and is sufficient to induce lethal immunodeficienc