DCs (dendritic cells) function as sentinels of the immune system. They traffic from the blood to the tissues where, while immature, they capture antigens. They then leave the tissues and move to the draining lymphoid organs where, converted into mature DC, they prime naive T cells. This suggestive link between DC traffic pattern and functions led us to investigate the chemokine responsiveness of DCs during their development and maturation. DCs were differentiated either from CD34+ hematopoietic progenitor cells (HPCs) cultured with granulocyte/macrophage colony–stimulating factor (GM-CSF) plus tumor necrosis factor (TNF)-α or from monocytes cultured with GM-CSF plus interleukin 4. Immature DCs derived from CD34+ HPCs migrate most vigorously in response to macrophage inflammatory protein (MIP)-3α, but also to MIP-1α and RANTES (regulated on activation, normal T cell expressed and secreted). Upon maturation, induced by either TNF-α, lipopolysaccharide, or CD40L, DCs lose their response to these three chemokines when they acquire a sustained responsiveness to a single other chemokine, MIP-3β. CC chemokine receptor (CCR)6 and CCR7 are the only known receptors for MIP-3α and MIP-3β, respectively. The observation that CCR6 mRNA expression decreases progressively as DCs mature, whereas CCR7 mRNA expression is sharply upregulated, provides a likely explanation for the changes in chemokine responsiveness. Similarly, MIP-3β responsiveness and CCR7 expression are induced upon maturation of monocyte- derived DCs. Furthermore, the chemotactic response to MIP-3β is also acquired by CD11c+ DCs isolated from blood after spontaneous maturation. Finally, detection by in situ hybridization of MIP-3α mRNA only within inflamed epithelial crypts of tonsils, and of MIP-3β mRNA specifically in T cell–rich areas, suggests a role for MIP-3α/CCR6 in recruitment of immature DCs at site of injury and for MIP-3β/CCR7 in accumulation of antigen-loaded mature DCs in T cell–rich areas.

We show here that mouse interferon-alpha (IFN-alpha)-producing cells (mIPCs) are a unique subset of immature antigen-presenting cells (APCs) that secrete IFN-alpha upon stimulation with viruses. mIPCs have a plasmacytoid morphology, can be stained with an antibody to Ly6G and Ly6C (anti-Ly6G/C) and are Ly6C+B220+CD11cloCD4+; unlike other dendritic cell subsets, however, they do not express CD8alpha or CD11b. Although mIPCs undergo apoptosis in vitro, stimulation with viruses, IFN-alpha or CpG oligonucleotides enhanced their survival and T cell stimulatory activity. In vivo, mIPCs were the main producers of IFN-alpha in cytomegalovirus-infected mice, as depletion of Ly6G+/C+ cells abrogated IFN-alpha production. mIPCs produced interleukin 12 (IL-12) in response to viruses and CpG oligodeoxynucleotides, but not bacterial products. Although different pathogens can selectively engage various APC subsets for IL-12 production, IFN-alpha production is restricted to mIPCs' response to viral infection.

In contrast to naive lymphocytes, memory͞effector lymphocytes can access nonlymphoid effector sites and display restricted, often tissue-selective, migration behavior. The cutaneous lymphocyteassociated antigen (CLA) defines a subset of circulating memory T cells that selectively localize in cutaneous sites mediated in part by the interaction of CLA with its vascular ligand E-selectin. Here, we report the identification and characterization of a CC chemokine, cutaneous T cell-attracting chemokine (CTACK). Both human and mouse CTACK are detected only in skin by Southern and Northern blot analyses. Specifically, CTACK message is found in the mouse epidermis and in human keratinocytes, and anti-CTACK mAbs predominantly stain the epithelium. Finally, CTACK selectively attracts CLA ؉ memory T cells. Taken together, these results suggest an important role for CTACK in recruitment of CLA ؉ T cells to cutaneous sites. CTACK is predominantly expressed in the skin and selectively attracts a tissue-specific subpopulation of memory lymphocytes.

A hostile tumor microenvironment interferes with the development and function of the adaptive immune response. Here we report the mechanisms by which large numbers of tumor-infiltrating macrophages and dendritic cells (DC) can be redirected to become potent effectors and activators of the innate and adaptive immunity, respectively. We use adenoviral delivery of the CCL16 chemokine to promote accumulation of macrophages and DC at the site of preestablished tumor nodules, combined with the Toll-like receptor 9 ligand CpG and with anti-interleukin-10 receptor antibody. CpG plus anti-interleukin-10 receptor antibody promptly switched infiltrating macrophages infiltrate from M2 to M1 and triggered innate response debulking large tumors within 16 hours. Tumor-infiltrating DC matured and migrated in parallel with the onset of the innate response, allowing the triggering of adaptive immunity before the diffuse hemorrhagic necrosis halted the communication between tumor and draining lymph nodes. Treatment of B6>CXB6 chimeras implanted with BALB/c tumors with the above combination induced an efficient innate response but not CTL-mediated tumor lysis. In these mice, tumor rejection did not exceed 25%, similarly to that observed in CCR7-null mice that have DC unable to prime an adaptive response. The requirement of CD4 help was shown in CD40-KO, as well as in mice depleted of CD4 T cells, during the priming rather than the effector phase. Our data describe the critical requirements for the immunologic rejection of large tumors: a hemorrhagic necrosis initiated by activated M1 macrophages and a concomitant DC migration to draining lymph nodes for subsequent CTL priming and clearing of any tumor remnants.

Summary: Interleukin‐10 (IL‐10) is a cytokine with broad anti‐inflammatory properties by its suppression of both macrophage and dendritic cell function, including antigen‐presenting cell function and the production of proinflammatory cytokines. This can result subsequently in the feedback regulation of both T‐helper 1 (Th1)‐type and Th2‐type responses. This review discusses the potential use of IL‐10 or agents that induce IL‐10 as potential anti‐inflammatory therapies in inflammatory diseases. Although IL‐10‐deficient mice develop colitis in the presence of normal gut flora and clear certain intracellular pathogens more efficiently, this is often accompanied by immunopathology, which can be lethal to the host. This reinforces the anti‐inflammatory properties of IL‐10, although it should be noted that as discussed below, IL‐10 can also promote B‐cell and other immune responses under particular settings. A penalty of its role to limit the immune and inflammatory responses to pathogens and prevent damage to the host is that high or dysregulated levels of IL‐10 may result in chronic infection. Thus, antagonists of IL‐10 show great potential as adjuvants in preventative or therapeutic vaccines against chronic infection or cancer. This article reviews basic published studies on IL‐10, which may lead to potential uses of IL‐10 or its antagonists in human disease.

Differential expression of Toll-like receptor (TLR) by conventional dendritic cells (cDCs) and plasmacytoid DC (pDCs) has been suggested to influence the type of immune response induced by microbial pathogens. In this study we show that, in vivo, cDCs and pDCs are equally activated by TLR4, -7, and -9 ligands. Type I interferon (IFN) was important for pDC activation in vivo in response to all three TLR ligands, whereas cDCs required type I IFN signaling only for TLR9- and partially for TLR7-mediated activation. Although TLR ligands induced in situ migration of spleen cDC into the T cell area, spleen pDCs formed clusters in the marginal zone and in the outer T cell area 6 h after injection of TLR9 and TLR7 ligands, respectively. In vivo treatment with TLR9 ligands decreased pDC ability to migrate ex vivo in response to IFN-induced CXCR3 ligands and increased their response to CCR7 ligands. Unlike cDCs, the migration pattern of pDCs required type I IFN for induction of CXCR3 ligands and responsiveness to CCR7 ligands. These data demonstrate that mouse pDCs differ from cDCs in the in vivo response to TLR ligands, in terms of pattern and type I IFN requirement for activation and migration.

Dendritic cells (DCs) form a network comprising different populations that initiate and differentially regulate immune responses. Langerhans cells (LCs) represent a unique population of DCs colonizing epithelium, and we present here observations suggesting that macrophage inflammatory protein (MIP)-3α plays a central role in LC precursor recruitment into the epithelium during inflammation. (a) Among DC populations, MIP-3α was the most potent chemokine inducing the selective migration of in vitro–generated CD34+ hematopoietic progenitor cell–derived LC precursors and skin LCs in accordance with the restricted MIP-3α receptor (CC chemokine receptor 6) expression to these cells. (b) MIP-3α was mainly produced by epithelial cells, and the migration of LC precursors induced by the supernatant of activated skin keratinocytes was completely blocked with an antibody against MIP-3α. (c) In vivo, MIP-3α was selectively produced at sites of inflammation as illustrated in tonsils and lesional psoriatic skin where MIP-3α upregulation appeared associated with an increase in LC turnover. (d) Finally, the secretion of MIP-3α was strongly upregulated by cells of epithelial origin after inflammatory stimuli (interleukin 1β plus tumor necrosis factor α) or T cell signals. Results of this study suggest a major role of MIP-3α in epithelial colonization by LCs under inflammatory conditions and immune disorders, and might open new ways to control epithelial immunity.

The nature of dendritic cell(s) (DC[s]) that conditions efficient in vivo priming of CD8+ CTL after immunization via epithelial tissues remains largely unknown. Here, we show that myeloid DCs rapidly recruited by adjuvants into the buccal mucosa or skin are essential for CD8+ T cell crosspriming. Recruitment of circulating DC precursors, including Gr1+ monocytes, precedes the sequential accumulation of CD11c+ MHC class II+ DCs in dermis and epithelium via a CCR6/CCL20-dependent mechanism. Remarkably, a defect in CCR6, local neutralization of CCL20, or depletion of monocytes prevents in vivo priming of CD8+ CTL against an innocuous protein antigen administered with adjuvant. In addition, transfer of CCR6-sufficient Gr1+ monocytes restores CD8+ T cell priming in CCR6( degrees / degrees ) mice via a direct Ag presentation mechanism. Thus, newly recruited DCs likely derived from circulating monocytes are responsible for efficient crosspriming of CD8+ CTL after mucosal or skin immunization.