Plasticity of dendritic cell function in response to prostaglandin E2 (PGE2) and interferon-gamma (IFN-gamma).

Current evidence suggests that maturing dendritic cells (DCs) acquire a migratory phenotype to induce T cell responses in lymph nodes or a proinflammatory phenotype to condition the microenvironment at peripheral sites. We show that the interplay of PGE(2) and IFN-gamma generates a more complex pattern of mixed DC phenotypes in response to TLR stimulation. DCs activated by the TLR ligand R-848 in the presence of IFN-gamma and PGE(2) produced high levels of IL-12p70 and IL-23, started migration toward CCL19 within only 10 h, and still continued to secrete IL-12p70 without further restimulation following the migration step. The accelerated onset of migration was a result of PGE(2) and was associated with reduced plastic adherence and lower amounts of activated CD29. In contrast, IFN-gamma by itself enhanced cell adhesion and strongly hindered CCR7-mediated migration in the absence of PGE(2). This suggests a new role for IFN-gamma in the direct regulation of DC migration through enhanced cell adhesion, perhaps to support the development of T cell effector functions at peripheral sites. Together, our data are relevant to the development of DC vaccines, as they demonstrate the existence of dual-functional DCs, which as a result of the simultaneous effects of PGE(2) and IFN-gamma, can migrate rapidly toward lymph node chemokines and carry with them a wave of primary cytokines.

Functional characterization of monocyte-derived dendritic cells generated under serumfree culture conditions.

The culture of human monocyte-derived dendritic cells (DCs) is typically performed in media containing human or fetal calf serum, supplements with the potential to influence the cells phenotype and their functional properties. Published clinical trails based on serumfree cultured DCs reported the use of the commercially available medium AIMV. In this study, we directly compared DCs generated in AIMV medium ("AIMV/sf-DCs") with DCs generated in RPMI supplemented with 2% human serum ("RPMI/HS-DCs") in functional assays of potential relevance for vaccine application. Using TNF-alpha/PGE(2)/IL-1beta/IL-6 as maturation stimulus, AIMV/sf-DCs revealed to be comparable with RPMI/HS-DCs with regard to phenotypic expression of maturation markers, survival in vitro, migratory capacity and stimulation of lymphocyte proliferation except for CD1a which was expressed on a fraction of DCs only when cultured in serumfree AIMV medium. However, IL-12p70 production in response to Toll-like receptor (TLR) stimulating agents plus IFN-gamma was consistently lower in AIMV medium although also under serumfree culture conditions, nanogram quantities of IL-12 were produced. Together, DCs with functional characteristics important for in vivo application can be generated under defined serumfree conditions; however, medium and/or serum conditions appear to have strong influence on the production of relevant T cell differentiating cytokines.

Efficient chemokine-dependent migration and primary and secondary IL-12 secretion by human dendritic cells stimulated through Toll-like receptors.

Recent findings have demonstrated the properties of cell migration and cytokine secretion to be mutually exclusive and linked them to different functional subpopulations of dendritic cells (DCs). We studied human monocyte-derived DCs after stimulation with peptidoglycan (PGN), poly(I:C), lipopolysaccharide (LPS), and R848 (resiquimod) and found the resulting mature DCs to express CCR7, to migrate toward CCL19 and to be efficient primary interleukin (IL)-12 producers. Importantly, the potential for secondary production of large amounts of IL-12p70 in response to CD40 ligation was also preserved after stimulation by all Toll-like receptor (TLR) ligands. Differences between the TLR ligands were seen in the primary secretion of IL-12 and IL-23, in the survival of the DCs and in the expression of CD38. Finally, DCs stimulated by R848 were efficient in expanding peptide-specific CD8-positive T cells capable of peptide-specific target cell lysis. Together, our data suggest that TLR ligands induce the generation of mature DCs that integrate migratory and cytokine secretory capacity as well as cytotoxic T lymphocyte (CTL) stimulatory properties.

HIV-1 Nef mimics an integrin receptor signal that recruits the polycomb group protein Eed to the plasma membrane.

The Nef protein of human and simian immunodeficiency virus (HIV/SIV) is believed to interfere with T cell activation signals by forming a signaling complex at the plasma membrane. Composition and function of the complex are not fully understood. Here we report that Nef recruits the Polycomb Group (PcG) protein Eed, so far known as a nuclear factor and repressor of transcription, to the membrane of cells. The Nef-induced translocation of Eed led to a potent stimulation of Tat-dependent HIV transcription, implying that Eed removal from the nucleus is required for optimal Tat function. Similar to Nef action, activation of integrin receptors recruited Eed to the plasma membrane, also leading to enhanced Tat/Nef-mediated transcription. Our results suggest a link between membrane-associated activation processes and transcriptional derepression and demonstrate how HIV exploits this mechanism.