Plasmacytoid dendritic cell recruitment by immobilized CXCR3 ligands

Abstract Plasmacytoid dendritic cells (pDCs) recognize microbes, viruses in particular, and provide unique means of innate defense against them. The mechanism of pDC tissue recruitment remained enigmatic because the ligands of CXCR3, the cardinal chemokine receptor on pDCs, have failed to induce in vitro chemotaxis of pDCs in the absence of additional chemokines. In this study, we demonstrate that CXCR3 is sufficient to induce pDC migration, however, by a migratory mechanism that amalgamates the features of haptotaxis and chemorepulsion. To mediate “haptorepulsion” of pDCs, CXCR3 requires the encounter of its cognate ligands immobilized, optimally by heparan sulfate, in a form of a negative gradient. This is the first report of the absolute requirement of chemokine immobilization and presentation for its in vitro promigratory activity. The paradigmatic example of pDC haptorepulsion described here may represent a new pathophysiologically relevant migratory mechanism potentially used by other cells in response to other chemokines.</jats:p

CCR9 is a homing receptor for plasmacytoid dendritic cells to the small intestine

Small intestine plasmacytoid dendritic cells (pDC) are poorly characterized. Here, we demonstrate that intestinal pDC show the characteristic plasma cell-like morphology, and are recognized by antibodies against B220, Ly6c, 120G8, and PDCA-1, markers that are typically expressed by pDC. Furthermore, intestinal pDC carry high levels of CCR9 and are largely absent in the intestine, but not in lung, liver, or secondary lymphoid organs of CCR9-deficient animals. Competitive adoptive transfers reveal that CCR9-deficient pDC are impaired in homing to the small intestine after i.v. transfer. In a model of cholera toxin-induced gut inflammation, pDC are recruited to the intestine in WT but not CCR9-deficient animals. Furthermore, after oral application of a Toll-like receptor (TLR) 7/8 ligand, myeloid DC of the lamina propria are rapidly mobilized in WT but not in CCR9-deficient animals. Mobilization of myeloid DC can be completely rescued by adoptively transferred WT pDC to CCR9-deficient mice before oral challenge. Together, our data reveal an essential role for CCR9 in the homing of pDC to the intestine under homeostatic and inflammatory conditions and demonstrate an important role for intestinal pDC for the rapid mobilization of lamina propria DC

Type-A CpG oligonucleotides activate exclusively porcine natural interferon-producing cells to secrete interferon-α, tumour necrosis factor-α and interleukin-12

Natural interferon-producing cells (NIPC), also referred to as immature plasmacytoid dendritic cells (PDC), constitute a small population of leucocytes secreting high levels of type I interferons in response to certain danger signals. Amongst these signals are those from DNA containing unmethylated CpG motifs. The present work demonstrated that the CpG oligonucleotides (CpG-ODN) 2216, D32 and D19 induce high amounts of interferon-α (IFN-α), tumour-necrosis factor-α (TNF-α) and interleukin (IL)-12 in porcine peripheral blood mononuclear cells (PBMCs). Swine workshop cluster 3 (SWC3)(1ow) CD4(high) cells, with high IL-3-binding activity, representing NIPC, were the exclusive cytokine-producing cells responding to the CpG-ODN. These cells did not express CD6, CD8 or CD45RA. Importantly, monocyte-derived DC did not respond to CpG-ODN by secretion of IFN-α or TNF-α or by the up-regulation of costimulatory molecule expression. CpG-ODN up-regulated MHC class II and CD80/86 expression on the NIPC, but were unable to promote NIPC survival. Interestingly, certain CpG-ODN, incapable of inducing NIPC to secrete IFN-α or up-regulate MHC class II and CD80/86, did promote NIPC viability. Taken together, the influence of CpG-ODN on porcine NIPC, monocytes and myeloid DCs relates to that observed with their human equivalents. These results represent an important basis for the application of CpG-ODN as adjuvants for the formulation of novel vaccines and demonstrate the importance of the pig as an alternative animal model for this approach

Systemic Dendritic Cell Mobilization Associated with Administration of FLT3 Ligand to SIV- and SHIV-Infected Macaques

Reports indicate that myeloid and plasmacytoid dendritic cells (mDCs and pDCs), which are key effector cells in host innate immune responses, can be infected with HIV-1 and are reduced in number and function during the chronic phase of HIV disease. Furthermore, it was recently demonstrated that a sustained loss of mDCs and pDCs occurs in SIV-infected macaques. Since loss of functional DC populations might impair innate immune responses to opportunistic microorganisms and neoplastic cells, we explored whether inoculation of naive and SIV- or SHIV-infected pigtailed macaques with the hematopoietic cytokine FLT3-ligand (FLT3-L) would expand the number of mDCs and pDCs in vivo. After the macaques received supraphysiologic doses of FLT3-L, mDCs, pDCs, and monocytes increased up to 45-fold in blood, lymph nodes, and bone marrow (BM), with DC expansion in the BM preceding mobilization in blood and lymphoid tissues. FLT3-L also increased serum levels of IL-12, at least transiently, and elicited higher surface expression of HLA-DR and the activation markers CD25 and CD69 on NK and T cells. During and after treatment of infected animals, APCs increased in number and were activated; however, CD4+ T cell numbers, virion RNA, and anti-SIV/SHIV antibody titers remained relatively stable, suggesting that FLT3-L might be a safe modality to expand DC populations and provide therapeutic benefit during chronic lentivirus infections