(1/629) The haemopoietic growth factor, Flt3L, alters the immune response induced by transcutaneous immunization.
Topical application of antigen induces antigen-specific humoral and cellular immune responses. In this study we examined whether expansion of dendritic cells (DC) by Flt3 ligand (Flt3L) treatment influences the induction of immune responses following transcutaneous immunization. Mice were treated intraperitoneally with Flt3L or phosphate-buffered saline (PBS) and immunized transcutaneously with hen egg lysozyme (HEL). Flt3L-treated mice developed lower HEL-specific cellular and humoral immune responses than PBS-treated mice. However, in the presence of cholera toxin (CT), a potent adjuvant for mucosal and transcutaneous immunization, Flt3L-treated mice developed significantly higher cellular and humoral immune responses to HEL when compared to PBS-treated mice. We assessed whether the immunomodulatory effects of CT were a result of activation of epidermal dendritic cells (Langerhans' cells; LC). Our results indicate that within 8-12 hr of topical application of CT, epidermal LC cells lose their dendritic morphology and become rounder in appearance. In addition, we observed enhanced expression of major histocompatibility complex (MHC) class II, and of adhesion molecules CD11c and intracellular adhesion molecule-1 (ICAM-1). Our observations support the concept that the state of activation of DC in the skin is central to the regulation of immune responses. This information is relevant to the design of effective transcutaneous vaccination strategies. (+info)
(2/629) The interplay of dendritic cell subsets in systemic lupus erythematosus.
Dendritic cells (DC) control immunity and tolerance. Hence, we surmised that systemic lupus erythematosus (SLE), a systemic autoimmune disease with autoreactive T and B cells, might be due to DC alterations. Based on our findings, we are proposing a model of SLE where autoimmune responses are driven by unabated activation of myeloid DC through IFN-alpha produced by plasmacytoid DC. Thus, interplay between DC subsets might represent a key component of SLE pathogenesis. (+info)
(3/629) Mouse CD11c(+) B220(+) Gr1(+) plasmacytoid dendritic cells develop independently of the T-cell lineage.
The developmental origin of dendritic cells (DCs) is controversial. In the mouse CD8alpha(+) and CD8alpha(-) DC subsets are often considered to be of lymphoid and myeloid origin respectively, although evidence on this point is conflicting. Very recently a novel CD11c(+) B220(+) DC subset has been identified that appears to be the murine counterpart to interferon alpha (IFNalpha)-producing human plasmacytoid DCs (PDCs). We show here that CD11c(+) B220(+) mouse PDCs, like human PDCs, are present in the thymus and express T lineage markers such as CD8alpha and CD4. However, the intrathymic development of PDCs can be completely dissociated from immature T lineage cells in mixed chimeras established with bone marrow cells from mice deficient for either Notch-1 or T-cell factor 1, two independent mutations that severely block early T-cell development. Our data indicate that thymic PDCs do not arise from a bipotential T/DC precursor. (+info)
(4/629) Myeloid blood CD11c(+) dendritic cells and monocyte-derived dendritic cells differ in their ability to stimulate T lymphocytes.
Dendritic cells (DCs) initiate and direct immune responses. Recent studies have defined different DC populations, therefore we undertook this study comparing 2 types of myeloid DCs: blood CD11c(+) DCs and in vitro monocyte-derived DCs (Mo-DCs), which are both candidates as cellular adjuvants for cancer immunotherapy. Blood CD11c(+) DCs were prepared by cell sorting from peripheral blood mononuclear cells cultured overnight in RPMI 1640 medium supplemented with autologous or pooled AB serum. Mo-DCs were prepared in the same medium using granulocyte macrophage-colony-stimulating factor (GM-CSF)/interleukin 4 (IL-4) and differentiated/activated with lipopolysaccharide or monocyte-conditioned medium (ActMo-DCs). Morphologically, differences between the DC preparations were noted both at a light and and electron microscopic level. Blood CD11c(+) DCs expressed similar levels of HLA-DR, CD40, CD86, and CD83 as Mo-DCs. CD209 was present on Mo-DCs but not on blood CD11c(+) DCs. Blood CD11c(+) DCs generated a lower proliferative mixed leukocyte response (MLR) than Mo-DCs. Blood CD11c(+) DCs loaded with 0.1 microg/mL tetanus toxoid (TT)-generated greater T lymphocyte proliferative responses than did Mo-DCs or ActMo-DCs, but when loaded with higher TT concentrations no difference in T lymphocyte proliferative response was observed. Keyhole limpet hemocyanin (KLH)-loaded blood CD11c(+) DCs generated greater T lymphocyte proliferative responses than Mo-DCs or ActMo-DCs. Allogeneic MLR- or KLH-specific responses induced by blood CD11c(+) DCs generated more Th1 effectors than the responses induced by Mo-DCs or ActMo-DCs. These data establish several differences in the properties of blood CD11c(+) DCs, Mo-DCs, and ActMo-DCs, which suggest that blood DCs merit further consideration as DC preparations for clinical programs are evolved. (+info)
(5/629) Blood dendritic cells interact with splenic marginal zone B cells to initiate T-independent immune responses.
Marginal zone (MZ) and B1 B lymphocytes participate jointly in the early immune response against T-independent (TI) particulate antigens. Here we show that blood-derived neutrophil granulocytes and CD11c(lo) immature dendritic cells (DC) are the primary cells that efficiently capture and transport particulate bacteria to the spleen. In a systemic infection, CD11c(lo) DC, but not neutrophils, provide critical survival signals, which can be inhibited by TACI-Fc, to antigen-specific MZ B cells and promote their differentiation into IgM-secreting plasmablasts. In a local TI response, peritoneal cavity macrophages provide similar support to B1 B-derived Ag-specific blasts. In the absence of soluble TACI ligands, Ag-activated MZ- and B1-derived blasts lack survival signals and undergo apoptosis, resulting in severely impaired antibody responses. (+info)
(6/629) Transient induction of cyclin T1 during human macrophage differentiation regulates human immunodeficiency virus type 1 Tat transactivation function.
The human immunodeficiency virus type 1 (HIV-1) Tat protein is essential for viral replication and stimulates transcription of the integrated provirus by recruiting the kinase complex TAK/P-TEFb, composed of cyclin T1 (CycT1) and Cdk9, to the viral TAR RNA element. TAK/P-TEFb phosphorylates the RNA polymerase II complex and stimulates transcriptional elongation. In this report, we investigated the regulation of TAK/P-TEFb in primary human macrophages, a major target cell of HIV infection. While Cdk9 levels remained constant, CycT1 protein expression in freshly isolated monocytes was very low, increased early during macrophage differentiation, and, unexpectedly, decreased to very low levels after about 1 week in culture. The kinase activity of TAK/P-TEFb paralleled the changes in CycT1 protein expression. RNA analysis indicated that the transient induction of CycT1 protein expression involves a posttranscriptional mechanism. In transient transfection assays, the ability of Tat to transactivate the HIV long terminal repeat (LTR) in the late differentiated macrophages was greatly diminished relative to its ability to transactivate the HIV LTR in early differentiated cells, strongly suggesting that CycT1 is limiting for Tat function in late differentiated macrophages. Interestingly, lipopolysaccharide, a component of the cell wall of gram-negative bacteria, reinduced CycT1 expression late in macrophage differentiation. These results raise the possibility that regulation of CycT1 expression may be involved in establishing latent infection in macrophages and that opportunistic infection may reactivate the virus by inducing CycT1 expression. (+info)
(7/629) MUC1 epithelial mucin (CD227) is expressed by activated dendritic cells.
The MUC1 mucin (CD227) is a cell surface mucin originally thought to be restricted to epithelial tissues. We report that CD227 is expressed on human blood dendritic cells (DC) and monocyte-derived DC following in vitro activation. Freshly isolated murine splenic DC had very low levels of CD227; however, all DC expressed CD227 following in vitro culture. In the mouse spleen, CD227 was seen on clusters within the red pulp and surrounding the marginal zone in the white pulp. Additionally, we confirm CD227 expression by activated human T cells and show for the first time that the CD227 cytoplasmic domain is tyrosine-phosphorylated in activated T cells and DC and is associated with other phosphoproteins, indicating a role in signaling. The function of CD227 on DC and T cells requires further elucidation. (+info)
(8/629) Sezary syndrome patients demonstrate a defect in dendritic cell populations: effects of CD40 ligand and treatment with GM-CSF on dendritic cell numbers and the production of cytokines.
Sezary syndrome (SzS) is an advanced form of cutaneous T-cell lymphoma associated with involvement of the peripheral blood by malignant T cells. The disease is defined by impaired cell-mediated immunity and the production of interferon-gamma (IFN-gamma) and interleukin-2 (IL-2), possibly as a result of deficient IL-12 production. To understand the mechanism of this impairment, we examined the composition and function of dendritic cells and monocytes in the blood of SzS patients with different levels of peripheral blood tumor burden. Consistent with our previous observations, numbers of monocytes in SzS patients were comparable to numbers observed in healthy donors. In contrast, decreased IL-12 production correlated with a decrease in the numbers of CD11c(+) dendritic cells, which was particularly profound among patients with medium (20%-50% circulating malignant T cells) and high (more than 50% circulating malignant T cells) tumor burden. Furthermore, CD123(+) dendritic cells, major producers of IFN-alpha, were significantly diminished in SzS patients, regardless of the level of tumor burden. Granulocyte macrophage-colony-stimulating factor-treated patients experienced an increase in the number of dendritic cells but not in IFN-alpha or IL-12 production. However, in vitro stimulation of peripheral blood mononuclear cells from SzS patients with rCD40L and IFN-gamma significantly increased the production of IL-12. Thus, our results demonstrate a profound defect in circulating dendritic cells in SzS patients that may contribute to the pathogenesis of the cytokine disorders and to the depressed cellular immunity. Importantly, the ability of rCD40L to potently induce IL-12 production from monocytes and residual dendritic cells of SzS patients could potentially serve as an immune-restorative therapeutic agent. (+info)