P-selectin and P-selectin glycoprotein ligand 1 are major determinants for Th1 cell recruitment to nonlymphoid effector sites in the intestinal lamina propria

The recruitment of activated T cell subsets to sites of effector immune responses is mediated by homing receptors induced upon activation in secondary lymphoid tissue. Using an adoptive transfer model, the intestinal recruitment of CD4+ T cells activated with intraperitoneal antigen in complete Freund's adjuvant was examined. The data demonstrate that activated CD4+ T cells recruited to intestinal Peyer's patches (PP) and lamina propria (LP) up-regulate functional P-selectin glycoprotein ligand 1 (PSGL-1). Blockade of IL-12 inhibited functional PSGL-1 expression and reduced PP and LP CD4+ T cell recruitment by >40%. P-selectin blockade reduced LP recruitment of activated cells by 56% without affecting PP recruitment. Studies of mice examined 3 d after adoptive transfer of differentiated T cell subsets revealed that Th1 but not Th2 cells were recruited to small intestine PP and LP. Mucosal addressin cell adhesion molecule blockade reduced Th1 recruitment to PP by 90% and to LP by >72%, whereas P-selectin blockade reduced Th1 recruitment to PP by 18% and Th1 recruitment to LP by 84%. These data suggest that IL-12-induced functional PSGL-1 expression is a major determinant for the recruitment of Th1 effector cells to noninflamed as well as inflamed intestine.     

Migratory properties of naive, effector, and memory CD8(+) T cells

It has been proposed that two different antigen-experienced T cell subsets may be distinguishable by their preferential ability to home to lymphoid organs (central memory cells) or nonlymphoid tissues (effector memory/effector cells). We have shown recently that murine antigen-primed CD8(+) T cells cultured in interleukin (IL)-15 (CD8(IL-15)) resemble central memory cells in phenotype and function. In contrast, primed CD8(+) T cells cultured in IL-2 (CD8(IL-2)) become cytotoxic effector cells. Here, the migratory behavior of these two subsets was investigated. Naive, CD8(IL-15) cells and, to a lesser degree, CD8(IL-2) cells localized to T cell areas in the spleen, but only naive and CD8(IL-15) cells homed to lymph nodes (LNs) and Peyer's patches. Intravital microscopy of peripheral LNs revealed that CD8(IL-15) cells, but not CD8(IL-2) cells, rolled and arrested in high endothelial venules (HEVs). Migration of CD8(IL-15) cells to LNs depended on L-selectin and required chemokines that bind CC chemokine receptor (CCR)7. Both antigen-experienced populations, but not naive T cells, responded to inflammatory chemokines and accumulated at sites of inflammation. However, CD8(IL-2) cells were 12 times more efficient in migrating to inflamed peritoneum than CD8(IL-15) cells. Furthermore, CD8(IL-15) cells proliferated rapidly upon reencounter with antigen at sites of inflammation. Thus, central memory-like CD8(IL-15) cells home avidly to lymphoid organs and moderately to sites of inflammation, where they mediate rapid recall responses, whereas CD8(IL-2) effector T cells accumulate in inflamed tissues, but are excluded from most lymphoid organs.     

Follicular B helper T cells express CXC chemokine receptor 5, localize to B cell follicles, and support immunoglobulin production

Chemokines and their receptors have been identified as major regulators controlling the functional organization of secondary lymphoid organs. Here we show that expression of CXC chemokine receptor 5 (CXCR5), a chemokine receptor required for B cell homing to B cell follicles, defines a novel subpopulation of B helper T cells localizing to follicles. In peripheral blood these cells coexpress CD45RO and the T cell homing CC chemokine receptor 7 (CCR7). In secondary lymphoid organs, CD4(+)CXCR5(+) cells lose expression of CCR7, which allows them to localize to B cell follicles and germinal centers where they express high levels of CD40 ligand (CD40L), a costimulatory molecule required for B cell activation and inducible costimulator (ICOS), a recently identified costimulatory molecule of the CD28 family. Thus, when compared with CD4(+)CD45RO(+)CXCR5(-) cells, CD4(+)CD45RO(+)CXCR5(+) tonsillar T cells efficiently support the production of immunoglobulin (Ig)A and IgG. In contrast, analysis of the memory response revealed that long-lasting memory cells are found within the CD4(+)CD45RO(+)CXCR5(-) population, suggesting that CXCR5(+)CD4 cells represent recently activated effector cells. Based on the characteristic localization within secondary lymphoid organs, we suggest to term these cells "follicular B helper T cells" (T(FH)).     

B Lymphocyte Chemotaxis Regulated in Association with Microanatomic Localization, Differentiation State, and B Cell Receptor Engagement

Migration of mature B lymphocytes within secondary lymphoid organs and recirculation between these sites are thought to allow B cells to obtain T cell help, to undergo somatic hypermutation, to differentiate into effector cells, and to home to sites of antibody production. The mechanisms that direct migration of B lymphocytes are unknown, but there is evidence that G protein–coupled receptors, and possibly chemokine receptors, may be involved. Stromal cell– derived factor (SDF)-1α is a CXC chemokine previously characterized as an efficacious chemoattractant for T lymphocytes and monocytes in peripheral blood. Here we show with purified tonsillar B cells that SDF-1α also attracts naive and memory, but not germinal center (GC) B lymphocytes. Furthermore, GC B cells could be converted to respond to SDF-1α by in vitro differentiation into memory B lymphocytes. Conversely, the migratory response in naive and memory B cells was significantly reduced after B cell receptor engagement and CD40 signaling. The receptor for SDF-1, CXC chemokine receptor 4 (CXCR4), was found to be expressed on responsive as well as unresponsive B cell subsets, but was more rapidly downregulated on responsive cells by ligand. Finally, messenger RNA for SDF-1 was detected by in situ hybridization in a layer of cells surrounding the GC. These findings show that responsiveness to the chemoattractant SDF-1α is regulated during B lymphocyte activation, and correlates with positioning of B lymphocytes within a secondary lymphoid organ.     

Thymus-independent development and negative selection of T cells expressing T cell receptor alpha/beta in the intestinal epithelium: evidence for distinct circulation patterns of gut- and thymus-derived T lymphocytes.

We demonstrate that mouse intestinal intraepithelial lymphocytes (IEL) can be divided into subsets based on the differential expression of functional T cell receptor alpha/beta (TCR-alpha/beta) signaling complexes. Two subsets, CD4+ 8 alpha + beta - and CD8 alpha + beta -, are refractory to stimulation with anti-TCR-alpha/beta and contain high frequencies of potentially self-reactive cells. In contrast, the CD4+ and CD8 alpha + beta + IEL subsets are responsive to anti-TCR-alpha/beta and depleted of potentially self-reactive cells. The analysis of fetal liver radiation chimeras using adult thymectomized recipients demonstrates that the four TCR-alpha/beta + IEL subsets are generated in normal numbers in the absence of the thymus. Moreover, expression of the major histocompatibility complex class II-encoded I-E molecule and Mls1a in the gut of the athymic host results in the negative selection of potentially self-reactive T cells expressing V beta 11 and V beta 6, respectively, from those IEL subsets that express functional TCR-alpha/beta signaling complexes. Neither the spleen nor the Peyer's patches of athymic recipients contain T cells of donor origin. In contrast, normal numbers of phenotypically and functionally mature CD4+ and CD8 alpha + beta + T cells of donor origin are found in the lamina propria of chimeric animals. The phenotypic analysis of lymphocytes obtained from Ly5 congenic parabionts reveals that peripheral T cells migrate rapidly to the Peyer's patches and lamina propria, but not to the intestinal epithelium. Taken together, these results demonstrate that the intestinal epithelium is a thymus-independent site of T lymphopoiesis, where selection of the T cell repertoire involves the deletion of potentially self-reactive cells in situ. Moreover, the appearance of donor-derived, phenotypically mature T cells, exclusively in the lamina propria of athymic radiation chimeras, suggests that mature IEL expressing functional TCR-alpha/beta migrate to this site.     

Expression of mucosal homing receptor alpha4beta7 by circulating CD4+ cells with memory for intestinal rotavirus.

The integrin alpha4beta7 mediates lymphocyte binding to mucosal addressin cell adhesion molecule-1, and its expression defines lymphocytes capable of trafficking through the intestines and the intestinal lymphoid tissues. We examined the ability of discrete alpha4beta7(hi) and alpha4beta7- subsets of circulating memory phenotype (CD45RA-) CD4+ T cells to proliferate in response to rotavirus, a ubiquitous intestinal pathogen. alpha4beta7(hi) memory (CD45RA-) CD4+ T cells displayed much greater reactivity to rotavirus than alpha4beta7- memory or naive (CD45RA+) CD4+ T cells. In contrast, alpha4beta7- memory cells were the predominant population responsive to mumps antigen after intramuscular vaccination. Our results are consistent with the conclusion that natural rotavirus infection, an enteric pathogen, results in a specific circulating memory CD4+ response that is largely limited to the gut-homing alpha4beta7+ subpopulation. This phenotype is not shared with memory cells elicited by intramuscular immunization (shown here) or by skin contact allergens. The results support the hypothesis that gut trafficking memory CD4+ T cells comprise cellular memory for intestinal antigens and suggest that regulated expression of alpha4beta7 helps target and segregate intestinal versus systemic immune response.     

Human macrophage inflammatory protein alpha (MIP-1 alpha) and MIP-1 beta chemokines attract distinct populations of lymphocytes

Lymphocyte trafficking is an essential process in immune and inflammatory functions which can be thought to contain at least two main components: adhesion and migration. Whereas adhesion molecules such as the selections are known to mediate the homing of leukocytes from the blood to the endothelium, the chemoattractant substances responsible for the migration of specific subsets of lymphocytes to sites of infection or inflammation are largely unknown. Here we show that two molecules in the chemokine (for chemoattractant cytokine) superfamily, human macrophage inflammatory protein 1 alpha (MIP-1 alpha) and MIP-1 beta, do not share identical attractant activities for lymphocyte subpopulations. When analyzed in vitro in microchemotaxis experiments, HuMIP-1 beta tends to attract CD4+ T lymphocytes, with some preference for T cells of the naive (CD45RA) phenotype. HuMIP-1 alpha, when tested in parallel with HuMIP-1 beta, is a more potent lymphocyte chemoattractant with a broader range of concentration- dependent chemoattractant specificities. HuMIP-1 alpha at a concentration of 100 pg/ml attracts B cells and cytotoxic T cells, whereas at higher concentrations (10 ng/ml), the migration of these cells appears diminished, and the migration of CD4+ T cells is enhanced. Thus, in this assay system, HuMIP-1 alpha and -1 beta have differential attractant activities for subsets of immune effector cells, with HuMIP-1 alpha having greater effects than HuMIP-1 beta, particularly on B cells.     

CRK proteins selectively regulate T cell migration into inflamed tissues

Effector T cell migration into inflamed sites greatly exacerbates tissue destruction and disease severity in inflammatory diseases, including graft-versus-host disease (GVHD). T cell migration into such sites depends heavily on regulated adhesion and migration, but the signaling pathways that coordinate these functions downstream of chemokine receptors are largely unknown. Using conditional knockout mice, we found that T cells lacking the adaptor proteins CRK and CRK-like (CRKL) exhibit reduced integrin-dependent adhesion, chemotaxis, and diapedesis. Moreover, these two closely related proteins exhibited substantial functional redundancy, as ectopic expression of either protein rescued defects in T cells lacking both CRK and CRKL. We determined that CRK proteins coordinate with the RAP guanine nucleotide exchange factor C3G and the adhesion docking molecule CASL to activate the integrin regulatory GTPase RAP1. CRK proteins were required for effector T cell trafficking into sites of inflammation, but not for migration to lymphoid organs. In a murine bone marrow transplantation model, the differential migration of CRK/CRKL-deficient T cells resulted in efficient graft-versus-leukemia responses with minimal GVHD. Together, the results from our studies show that CRK family proteins selectively regulate T cell adhesion and migration at effector sites and suggest that these proteins have potential as therapeutic targets for preventing GVHD.     

Developmental stage, phenotype, and migration distinguish naive- and effector/memory-like CD4+ regulatory T cells

Regulatory T cells (Tregs) fulfill a central role in immune regulation. We reported previously that the integrin alphaEbeta7 discriminates distinct subsets of murine CD4+ regulatory T cells. Use of this marker has now helped to unravel a fundamental dichotomy among regulatory T cells. alphaE-CD25+ cells expressed L-selectin and CCR7, enabling recirculation through lymphoid tissues. In contrast, alphaE -positive subsets (CD25+ and CD25-) displayed an effector/memory phenotype expressing high levels of E/P-selectin-binding ligands, multiple adhesion molecules as well as receptors for inflammatory chemokines, allowing efficient migration into inflamed sites. Accordingly, alphaE -expressing cells were found to be the most potent suppressors of inflammatory processes in disease models such as antigen-induced arthritis.     

Unique chemotactic response profile and specific expression of chemokine receptors CCR4 and CCR8 by CD4(+)CD25(+) regulatory T cells

Chemokines dictate regional trafficking of functionally distinct T cell subsets. In rodents and humans, a unique subset of CD4(+)CD25(+) cytotoxic T lymphocyte antigen (CTLA)-4(+) regulatory T cells (Treg) has been proposed to control peripheral tolerance. However, the molecular basis of immune suppression and the trafficking properties of Treg cells are still unknown. Here, we determined the chemotactic response profile and chemokine receptor expression of human blood-borne CD4(+)CD25(+) Treg cells. These Treg cells were found to vigorously respond to several inflammatory and lymphoid chemokines. Treg cells specifically express the chemokine receptors CCR4 and CCR8 and represent a major subset of circulating CD4(+) T cells responding to the chemokines macrophage-derived chemokine (MDC)/CCL22, thymus and activation-regulated chemokine (TARC)/CCL17, I-309/CCL1, and to the virokine vMIP-I (ligands of CCR4 and CCR8). Blood-borne CD4(+) T cells that migrate in response to CCL1 and CCL22 exhibit a reduced alloproliferative response, dependent on the increased frequency of Treg cells in the migrated population. Importantly, mature dendritic cells preferentially attract Treg cells among circulating CD4(+) T cells, by secretion of CCR4 ligands CCL17 and CCL22. Overall, these results suggest that CCR4 and/or CCR8 may guide Treg cells to sites of antigen presentation in secondary lymphoid tissues and inflamed areas to attenuate T cell activation.     

Molecular basis for hematopoietic/mesenchymal interaction during initiation of Peyer's patch organogenesis

Mice deficient in lymphotoxin beta receptor (LTbetaR) or interleukin 7 receptor alpha (IL-7Ralpha) lack Peyer's patches (PPs). Deficiency in CXC chemokine receptor 5 (CXCR5) also severely affects the development of PPs. A molecular network involving these three signaling pathways has been implicated in PP organogenesis, but it remains unclear how they are connected during this process. We have shown that PP organogenesis is initiated at sites containing IL-7Ralpha(+) lymphoid cells and vascular cell adhesion molecule (VCAM)-1/intercellular adhesion molecule (ICAM)-1 expressing nonlymphoid elements. Here we characterize these lymphoid and nonlymphoid components in terms of chemokine signals. The lymphoid population expresses CXCR5 and has a strong chemotactic response to B lymphocyte chemoattractant (BLC). Importantly, chemokines produced by VCAM-1(+)ICAM-1(+) nonlymphoid cells mediate the recruitment of lymphoid cells. Furthermore, we show that these VCAM-1(+)ICAM-1(+) cells are mesenchymal cells that are activated by lymphoid cells through the LTbetaR to express adhesion molecules and chemokines. Thus, promotion of PP development relies on mutual interaction between mesenchymal and lymphoid cells.     

Acquisition of selectin binding and peripheral homing properties by CD4(+) and CD8(+) T cells.

Different T cell subsets exhibit distinct capacities to migrate into peripheral sites of inflammation, and this may in part reflect differential expression of homing receptors and chemokine receptors. Using an adoptive transfer approach, we examined the ability of functionally distinct subsets of T cells to home to a peripheral inflammatory site. The data directly demonstrate the inability of naive T cells and the ability of effector cells to home to inflamed peritoneum. Furthermore, interleukin (IL)-12 directs the differentiation of either CD4(+) or CD8(+) T cells into effector populations that expresses functional E- and P-selectin ligand and that are preferentially recruited into the inflamed peritoneum compared with T cells differentiated in the presence of IL-4. Recruitment can be blocked by anti-E- and -P-selectin antibodies. The presence of antigen in the peritoneum promotes local proliferation of recruited T cells, and significantly amplifies the Th1 polarization of the lymphocytic infiltrate. Preferential recruitment of Th1 cells into the peritoneum is also seen when cytokine response gene 2 (CRG-2)/interferon gamma-inducible protein 10 (IP-10) is used as the sole inflammatory stimulus. We have also found that P-selectin binds only to antigen-specific T cells in draining lymph nodes after immunization, implying that both antigen- and cytokine-mediated signals are required for expression of functional selectin-ligand.     

A role for CCR4 in development of mature circulating cutaneous T helper memory cell populations

Expression of the chemokine receptor CCR4 is strongly associated with trafficking of specialized cutaneous memory T helper (Th) lymphocytes to the skin. However, it is unknown whether CCR4 itself participates in the development of cutaneous Th populations. We have addressed this issue via competitive bone marrow (BM) reconstitution assays; equal numbers of BM cells from CCR4(+/+) and CCR4(-/-) donors were allowed to develop side-by-side within RAG-1(-/-) hosts. Cells from both donor types developed equally well into B cells, naive CD8 T cells, naive CD4 T cells, interferon-gamma(+) Th1 cells, and interleukin-4(+) Th2 cells. In marked contrast, circulating cutaneous memory Th cells (i.e., E-selectin ligand(+) [E-lig(+)]) were more than fourfold more likely to be derived from CCR4(+/+) donors than from CCR4(-/-) donors. Most of this effect resides within the CD103(+) subset of the E-lig(+) Th population, in which donor CCR4(+/+) cells can outnumber CCR4(-/-) cells by >12-fold. No similar effect was observed for alpha4beta7(+) intestinal memory Th cells or CD103(+)/E-lig(-) Th cells. We conclude that CCR4 expression provides a competitive advantage to cutaneous Th cells, either by participating in their development from naive Th cells, or by preferentially maintaining them within the memory population over time.     

Lymphocyte CC chemokine receptor 9 and epithelial thymus-expressed chemokine (TECK) expression distinguish the small intestinal immune compartment: Epithelial expression of tissue-specific chemokines as an organizing principle in regional immunity

The immune system has evolved specialized cellular and molecular mechanisms for targeting and regulating immune responses at epithelial surfaces. Here we show that small intestinal intraepithelial lymphocytes and lamina propria lymphocytes migrate to thymus-expressed chemokine (TECK). This attraction is mediated by CC chemokine receptor (CCR)9, a chemoattractant receptor expressed at high levels by essentially all CD4(+) and CD8(+) T lymphocytes in the small intestine. Only a small subset of lymphocytes in the colon are CCR9(+), and lymphocytes from other tissues including tonsils, lung, inflamed liver, normal or inflamed skin, inflamed synovium and synovial fluid, breast milk, and seminal fluid are universally CCR9(-). TECK expression is also restricted to the small intestine: immunohistochemistry reveals that intense anti-TECK reactivity characterizes crypt epithelium in the jejunum and ileum, but not in other epithelia of the digestive tract (including stomach and colon), skin, lung, or salivary gland. These results imply a restricted role for lymphocyte CCR9 and its ligand TECK in the small intestine, and provide the first evidence for distinctive mechanisms of lymphocyte recruitment that may permit functional specialization of immune responses in different segments of the gastrointestinal tract. Selective expression of chemokines by differentiated epithelium may represent an important mechanism for targeting and specialization of immune responses.     

Rules of chemokine receptor association with T cell polarization in vivo

Current concepts of chemokine receptor (CKR) association with Th1 and Th2 cell polarization and effector function have largely ignored the diverse nature of effector and memory T cells in vivo. Here, we systematically investigated the association of 11 CKRs, singly or in combination, with CD4 T cell polarization. We show that Th1, Th2, Th0, and nonpolarized T cells in blood and tissue can express any of the CKRs studied but that each CKR defines a characteristic pool of polarized and nonpolarized CD4 T cells. Certain combinations of CKRs define populations that are markedly enriched in major subsets of Th1 versus Th2 cells. For example, although Th0, Th1, and Th2 cells are each found among blood CD4 T cells coordinately expressing CXCR3 and CCR4, Th1 but not Th2 cells can be CXCR3(+)CCR4(-), and Th2 but only rare Th1 cells are CCR4(+)CXCR3(-). Contrary to recent reports, although CCR7(-) cells contain a higher frequency of polarized CD4 T cells, most Th1 and Th2 effector cells are CCR7(+) and thus may be capable of lymphoid organ homing. Interestingly, Th1-associated CKRs show little or no preference for Th1 cells except when they are coexpressed with CXCR3. We conclude that the combinatorial expression of CKRs, which allow tissue- and subset-dependent targeting of effector cells during chemotactic navigation, defines physiologically significant subsets of polarized and nonpolarized T cells.     

Developmental switches in chemokine response profiles during B cell differentiation and maturation

Developing B cells undergo dramatic changes in their responses to chemoattractant cytokines (chemokines) and in expression of chemokine receptors. Bone marrow pre-pro-B cells (AA4.1(+)/natural killer 1.1(-) Fraction A cells) and cells capable of generating pro-B colonies in the presence of interleukin 7 and flt3 ligand migrate to thymus-expressed chemokine (TECK), a response lost in later stages of B cell development. B cell-attracting chemokine 1 (BCA-1) responses correlate with CXC chemokine receptor (CXCR)5 expression, are first displayed by a pro-B cell subset, are lost in pre-B cells, and then are regained just before and after egress from the marrow. All peripheral B cell subsets, including follicular and germinal center as well as marginal zone and peritoneal B1 B cells, respond to BCA-1, implying that responsiveness to this follicular chemokine is not sufficient to predict follicle localization. Responses to the CC chemokine receptor (CCR)7 ligands secondary lymphoid tissue chemoattractant (SLC) and macrophage inflammatory protein (MIP)-3beta, implicated in homing to lymphoid tissues, are upregulated before B cell exit from the marrow, but increase further in the periphery and are shared by all peripheral B cells. In contrast, responsiveness to MIP-3alpha and expression of CCR6 are acquired only after emigration to the periphery and during maturation into the recirculating B cell pool. Chemotaxis to stromal cell-derived factor 1alpha is observed at all stages of B cell differentiation. Thus, unique patterns of chemokine responses may help define developing B cell populations and direct their maturation in the marrow and migration to the periphery.     

Functional specialization of gut CD103+ dendritic cells in the regulation of tissue-selective T cell homing

Gut-associated lymphoid tissue (GALT) dendritic cells (DCs) display a unique ability to generate CCR9+alpha4beta7+ gut-tropic CD8+ effector T cells. We demonstrate efficient induction of CCR9 and alpha4beta7 on CD8+ T cells in mesenteric lymph nodes (MLNs) after oral but not intraperitoneal (i.p.) antigen administration indicating differential targeting of DCs via the oral route. In vitro, lamina propria (LP)-derived DCs were more potent than MLN or Peyer's patch DCs in their ability to generate CCR9+alpha4beta7+ CD8+ T cells. The integrin alpha chain CD103 (alphaE) was expressed on almost all LP DCs, a subset of MLN DCs, but on few splenic DCs. CD103+ MLN DCs were reduced in number in CCR7-/- mice and, although CD8+ T cells proliferated in the MLNs of CCR7-/- mice after i.p. but not oral antigen administration, they failed to express CCR9 and had reduced levels of alpha4beta7. Strikingly, although CD103+ and CD103- MLN DCs were equally potent at inducing CD8+ T cell proliferation and IFN-gamma production, only CD103+ DCs were capable of generating gut-tropic CD8+ effector T cells in vitro. Collectively, these results demonstrate a unique function for LP-derived CD103+ MLN DCs in the generation of gut-tropic effector T cells.     

CC chemokine receptor (CCR)4 and the CCR10 ligand cutaneous T cell-attracting chemokine (CTACK) in lymphocyte trafficking to inflamed skin.

The chemokine thymus and activation-regulated chemokine (TARC; CCL17) is displayed by cutaneous (but not intestinal) venules, and is thought to trigger vascular arrest of circulating skin homing memory T cells, which uniformly express the TARC receptor CC chemokine receptor (CCR)4. Cutaneous T cell-attracting chemokine (CTACK; CCL27), expressed by skin keratinocytes, also attracts cutaneous memory T cells, and is hypothesized to assist in lymphocyte recruitment to skin as well. Here we show that chronic cutaneous inflammation induces CD4 T cells expressing E-selectin binding activity (a marker of skin homing memory cells) in draining lymph node, and that these E-selectin ligand+ T cells migrate efficiently to TARC and to CTACK. In 24 h in vivo homing assays, stimulated lymph node T cells from wild-type mice or, surprisingly, from CCR4-deficient donors migrate efficiently to inflamed skin; and an inhibitory anti-CTACK antibody has no effect on wild-type lymphocyte recruitment. However, inhibition with anti-CTACK monoclonal antibody abrogates skin recruitment of CCR4-deficient T cells. We conclude that CTACK and CCR4 can both support homing of T cells to skin, and that either one or the other is required for lymphocyte recruitment in cutaneous delayed type hypersensitivity.     

Role of ChemR23 in directing the migration of myeloid and plasmacytoid dendritic cells to lymphoid organs and inflamed skin

Chemerin is a chemotactic agent that was recently identified as the ligand of ChemR23, a serpentine receptor expressed by activated macrophages and monocyte-derived dendritic cells (DCs). This paper shows that blood plasmacytoid and myeloid DCs express functional ChemR23. Recombinant chemerin induced the transmigration of plasmacytoid and myeloid DCs across an endothelial cell monolayer. In secondary lymphoid organs (lymph nodes and tonsils), ChemR23 is expressed by CD123(+) plasmacytoid DCs and by CD1a(+) DC-SIGN(+) DCs in the interfollicular T cell area. ChemR23(+) DCs were also observed in dermis from normal skin, whereas Langerhans cells were negative. Chemerin expression was selectively detected on the luminal side of high endothelial venules in secondary lymphoid organs and in dermal endothelial vessels of lupus erythematosus skin lesions. Chemerin(+) endothelial cells were surrounded by ChemR23(+) plasmacytoid DCs. Thus, ChemR23 is expressed and functional in plasmacytoid DCs, a property shared only by CXCR4 among chemotactic receptors. This finding, together with the selective expression of the cognate ligand on the luminal side of high endothelial venules and inflamed endothelium, suggests a key role of the ChemR23/chemerin axis in directing plasmacytoid DC trafficking.