DC-SIGN and CD150 Have Distinct Roles in Transmission of Measles Virus from Dendritic Cells to T-Lymphocytes

Measles virus (MV) is among the most infectious viruses that affect humans and is transmitted via the respiratory route. In macaques, MV primarily infects lymphocytes and dendritic cells (DCs). Little is known about the initial target cell for MV infection. Since DCs bridge the peripheral mucosal tissues with lymphoid tissues, we hypothesize that DCs are the initial target cells that capture MV in the respiratory tract and transport the virus to the lymphoid tissues where MV is transmitted to lymphocytes. Recently, we have demonstrated that the C-type lectin DC-SIGN interacts with MV and enhances infection of DCs in cis. Using immunofluorescence microscopy, we demonstrate that DC-SIGN+ DCs are abundantly present just below the epithelia of the respiratory tract. DC-SIGN+ DCs efficiently present MV-derived antigens to CD4+ T-lymphocytes after antigen uptake via either CD150 or DC-SIGN in vitro. However, DC-SIGN+ DCs also mediate transmission of MV to CD4+ and CD8+ T-lymphocytes. We distinguished two different transmission routes that were either dependent or independent on direct DC infection. DC-SIGN and CD150 are both involved in direct DC infection and subsequent transmission of de novo synthesized virus. However, DC-SIGN, but not CD150, mediates trans-infection of MV to T-lymphocytes independent of DC infection. Together these data suggest a prominent role for DCs during the initiation, dissemination, and clearance of MV infection

Interaction of Polysialic Acid with CCL21 Regulates the Migratory Capacity of Human Dendritic Cells

Dendritic cells (DCs) are the most potent antigen-presenting cells (APCs). Immature DCs (iDCs) are situated in the periphery where they capture pathogen. Subsequently, they migrate as mature DCs (mDCs) to draining lymph nodes to activate T cells. CCR7 and CCL21 contribute to the migratory capacity of the DC, but it is not completely understood what molecular requirements are involved. Here we demonstrate that monocyte-derived DCs dramatically change ST8Sia IV expression during maturation, leading to the generation of polysialic acid (polySia). PolySia expression is highly upregulated after 2 days Toll-like receptor-4 (TLR4) triggering. Surprisingly, only immunogenic and not tolerogenic mDCs upregulated polySia expression. Furthermore, we show that polySia expression on DCs is required for CCL21-directed migration, whereby polySia directly captures CCL21. Corresponding to polySia, the expression level of CCR7 is maximal two days after TLR4 triggering. In contrast, although TLR agonists other than LPS induce upregulation of CCR7, they achieve only a moderate polySia expression. In situ we could detect polySia-expressing APCs in the T cell zone of the lymph node and in the deep dermis. Together our results indicate that prolonged TLR4 engagement is required for the generation of polySia-expressing DCs that facilitate CCL21 capture and subsequent CCL21-directed migration

Carbohydrate-specific signaling through the DC-SIGN signalosome tailors immunity to Mycobacterium tuberculosis, HIV-1 and Helicobacter pylori

Cooperation between different innate signaling pathways induced by pattern-recognition receptors (PRRs) on dendritic cells (DCs) is crucial for tailoring adaptive immunity to pathogens. Here we show that carbohydrate-specific signaling through the C-type lectin DC-SIGN tailored cytokine production in response to distinct pathogens. DC-SIGN was constitutively associated with a signalosome complex consisting of the scaffold proteins LSP1, KSR1 and CNK and the kinase Raf-1. Mannose-expressing Mycobacterium tuberculosis and human immunodeficiency virus type 1 (HIV-1) induced the recruitment of effector proteins to the DC-SIGN signalosome to activate Raf-1, whereas fucose-expressing pathogens such as Helicobacter pylori actively dissociated the KSR1-CNK-Raf-1 complex from the DC-SIGN signalosome. This dynamic regulation of the signalosome by mannose- and fucose-expressing pathogens led to the enhancement or suppression of proinflammatory responses, respectively. Our study reveals another level of plasticity in tailoring adaptive immunity to pathogen

C-type lectin DC-SIGN modulates Toll-like receptor signaling via Raf-1 kinase-dependent acetylation of transcription factor NF-kappaB

Adaptive immune responses by dendritic cells (DCs) are critically controlled by Toll-like receptor (TLR) function. Little is known about modulation of TLR-specific signaling by other pathogen receptors. Here, we have identified a molecular signaling pathway induced by the C-type lectin DC-SIGN that modulates TLR signaling at the level of the transcription factor NF-kappaB. We demonstrated that pathogens trigger DC-SIGN on human DCs to activate the serine and threonine kinase Raf-1, which subsequently leads to acetylation of the NF-kappaB subunit p65, but only after TLR-induced activation of NF-kappaB. Acetylation of p65 both prolonged and increased IL10 transcription to enhance anti-inflammatory cytokine responses. We demonstrated that different pathogens such as Mycobacterium tuberculosis, M. leprae, Candida albicans, measles virus, and human immunodeficiency virus-1 interacted with DC-SIGN to activate the Raf-1-acetylation-dependent signaling pathway to modulate signaling by different TLRs. Thus, this pathway is involved in regulation of adaptive immunity by DCs to bacterial, fungal, and viral pathogens

C-type lectin DC-SIGN modulates Toll-like receptor signaling via Raf-1 kinase-dependent acetylation of transcription factor NF-kappaB

Adaptive immune responses by dendritic cells (DCs) are critically controlled by Toll-like receptor (TLR) function. Little is known about modulation of TLR-specific signaling by other pathogen receptors. Here, we have identified a molecular signaling pathway induced by the C-type lectin DC-SIGN that modulates TLR signaling at the level of the transcription factor NF-kappaB. We demonstrated that pathogens trigger DC-SIGN on human DCs to activate the serine and threonine kinase Raf-1, which subsequently leads to acetylation of the NF-kappaB subunit p65, but only after TLR-induced activation of NF-kappaB. Acetylation of p65 both prolonged and increased IL10 transcription to enhance anti-inflammatory cytokine responses. We demonstrated that different pathogens such as Mycobacterium tuberculosis, M. leprae, Candida albicans, measles virus, and human immunodeficiency virus-1 interacted with DC-SIGN to activate the Raf-1-acetylation-dependent signaling pathway to modulate signaling by different TLRs. Thus, this pathway is involved in regulation of adaptive immunity by DCs to bacterial, fungal, and viral pathogen

Are infectious agents involved in the pathogenesis of postpartum psychosis?

Background Since postpartum psychosis has been linked to activation of the immune system, it has been hypothesized that infectious agents may be involved in the pathogenesis of this disorder. We therefore investigated whether exposure to pathogens that can infect the central nervous system is increased in patients with postpartum psychosis. Methods We measured the prevalence and titers of immunoglobulin G (IgG) and M (IgM) to herpes simplex virus type 1 (HSV-1) and 2 (HSV-2), Epstein-Barr virus (EBV), cytomegalovirus (CMV) and Toxoplasma Gondii (TG) in a cohort of patients with postpartum psychosis (n = 81) and compared these to matched postpartum controls. Results We did not find significant differences in seroprevalence or antibody titers for any of these pathogens. Limitations Limitations of this study include the indirect measurement of infectious disease and the cross-sectional design. Conclusion Our results do not support the hypothesis that exposure to these neurotropic pathogens is involved in postpartum psychosis

Are infectious agents involved in the pathogenesis of postpartum psychosis?

Background Since postpartum psychosis has been linked to activation of the immune system, it has been hypothesized that infectious agents may be involved in the pathogenesis of this disorder. We therefore investigated whether exposure to pathogens that can infect the central nervous system is increased in patients with postpartum psychosis. Methods We measured the prevalence and titers of immunoglobulin G (IgG) and M (IgM) to herpes simplex virus type 1 (HSV-1) and 2 (HSV-2), Epstein-Barr virus (EBV), cytomegalovirus (CMV) and Toxoplasma Gondii (TG) in a cohort of patients with postpartum psychosis (n = 81) and compared these to matched postpartum controls. Results We did not find significant differences in seroprevalence or antibody titers for any of these pathogens. Limitations Limitations of this study include the indirect measurement of infectious disease and the cross-sectional design. Conclusion Our results do not support the hypothesis that exposure to these neurotropic pathogens is involved in postpartum psychosis

Dectin-1 directs T helper cell differentiation by controlling noncanonical NF-kappaB activation through Raf-1 and Syk

The C-type lectin dectin-1 activates the transcription factor NF-kappaB through a Syk kinase-dependent signaling pathway to induce antifungal immunity. Here we show that dectin-1 expressed on human dendritic cells activates not only the Syk-dependent canonical NF-kappaB subunits p65 and c-Rel, but also the noncanonical NF-kappaB subunit RelB. Dectin-1, when stimulated by the beta-glucan curdlan or by Candida albicans, induced a second signaling pathway mediated by the serine-threonine kinase Raf-1, which integrated with the Syk pathway at the point of NF-kappaB activation. Raf-1 antagonized Syk-induced RelB activation by promoting sequestration of RelB into inactive p65-RelB dimers, thereby altering T helper cell differentiation. Thus, dectin-1 activates two independent signaling pathways, one through Syk and one through Raf-1, to induce immune response