Differential responsiveness to constitutive vs. inducible chemokines of immature and mature mouse dendritic cells.

Upon exposure to immune or inflammatory stimuli, dendritic cells (DC) migrate from peripheral tissues to lymphoid organs, where they present antigen. The molecular basis for the peculiar trafficking properties of DC is largely unknown. In this study, mouse DC were generated from CD34+ bone marrow precursors and cultured with granulocyte-macrophage-CSF and Flt3 ligand for 9 days. Chemokines active on immature DC include MIP1alpha, RANTES, MIP1beta, MCP-1, MCP-3, and the constitutively expressed SDF1, MDC, and ELC. TNF-alpha-induced DC maturation caused reduction of migration to inducible chemokines (MIP1alpha, RANTES, MIP1beta, MCP-1, and MCP-3) and increased migration to SDF1, MDC, and ELC. Similar results were obtained by CD40 ligation or culture in the presence of bacterial lipopolysaccharide. TNF-alpha down-regulated CC chemokine receptor (CCR)1, CCR2, and CCR5 and up-regulated CCR7 mRNA levels, in agreement with functional data. This study shows that selective responsiveness of mature and immature DC to inducible vs. constitutively produced chemokines can contribute to the regulated trafficking of DC.     

The role of chemokines in the regulation of dendritic cell trafficking.

The immunobiology of dendritic cells (DC) involves localization in tissues and trafficking via the lymph or blood to lymphoid organs. Appropriate assays representative of different steps of DC trafficking (e.g., reverse transmigration) provide the tools to dissect the migratory properties of these cells. Chemokines have emerged as important regulators of DC migration. DC are both the target and the source of chemokines. DC express receptors for and respond to a set of chemoattractants that overlap with, but are distinct from, those active on other leukocytes. Differential expression of the CCR6 receptor reveals heterogeneity among DC populations. Functional maturation is associated with loss of responsiveness to chemokines present at sites of inflammation and acquisition of a receptor repertoire that renders these cells responsive to signals that guide their localization in lymphoid organs. A better understanding of the molecular basis of DC trafficking may provide molecular and conceptual tools to direct and modulate DC traffic as a strategy to up-regulate and orient specific immunity.     

Regulation of dendritic cell trafficking: a process that involves the participation of selective chemokines.

DC 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 to the investigation of the chemokine responsiveness of DC during their development and maturation. These studies have shown that immature and mature DC are not recruited by the same chemokines. Immature DC respond to many CC- and CXC-chemokines (MIP-1alpha, MIP-1beta, MIP-5, MCP-3, MCP-4, RANTES, TECK, and SDF-1) and in particular to MIP-3alpha/LARC, which acts through CCR6, a receptor mainly expressed in DC and lymphocytes. Like most other chemokines acting on immature DC, MIP-3alpha is inducible on inflammatory stimuli. In contrast, mature DC have lost their responsiveness to most of these chemokines through receptor down-regulation or desensitization, but acquired responsiveness to MIP-3beta/ELC and 6Ckine/SLC as a consequence of CCR7 up-regulation. MIP-3alpha mRNA is only detected within inflamed epithelial crypts of tonsils, the site of antigen entry known to be infiltrated by immature DC, whereas MIP-3alpha and 6Ckine are specifically expressed in the T cell-rich areas where mature IDC home. These observations suggest a role for chemokines induced on inflammation such as MIP-3alpha in recruitment of immature DC at the site of injury and a role for MIP-3beta/6Ckine in accumulation of antigen-loaded mature DC in T cell-rich areas of the draining lymph node. A better understanding of the regulation of DC trafficking might offer new opportunities of therapeutic interventions to suppress or stimulate the immune response.     

Chemokines have diverse abilities to form solid phase gradients

Chemokines play critical roles in leukocyte recruitment into sites of inflammation such as rheumatoid arthritis (RA). While chemokines immobilized on endothelium (solid-phase), but not soluble chemokines, direct rolling leukocytes to firmly adhere to endothelium, soluble and solid-phase chemokine gradients may play important roles in leukocyte extravasation into the tissue. In this study, we have sought to determine (1) if chemokines can be immobilized on structures in the extravascular space, (2) the mechanisms by which chemokines may be immobilized, and (3) if different chemokines have similar potentials to form solid-phase gradients. While secreted alkaline phosphatase (SEAP)-tagged chemokines SLC (CCL21), TARC (CCL17), and RANTES (CCL5) bound to mast cells and the extracellular matrix (ECM) in RA synovium under physiologic salt conditions, MCP1 (CCL2), MIP1 alpha (CCL3), MIP1 beta (CCL4), and fractalkine (FKN, CX3CL1) fusion proteins did not detectably bind. Chemokine binding to ECM and mast cells in situ and to immobilized heparin was inhibited by high salt and glycosaminoglycans (GAGs) heparin, heparan sulfate, chondroitin sulfate, and dermatan sulfate, but not by dextran or hyaluronan, indicating that the chemokines bind to highly sulfated GAGs. Chemokine binding to synovial structures correlated strongly with avidity of chemokine binding to heparin (SLC > TARC > RANTES > MIP1 beta > MCP1 > MIP1 alpha > FKN). A RANTES mutant with decreased avidity for heparin was not able to bind to ECM or mast cells. Thus, these data indicate that chemokines can bind to ECM and mast cell granule constituents in situ via interactions with GAGs. Further, only a subset of chemokines were able to bind efficiently to structures in the extravascular space, indicating that chemokines may form different types of gradients based on their GAG binding ability and that chemotactic gradients in tissues may be quite complex.     

Chemokines and Dendritic Cell Traffic

Localization in tissues and migration to lymphoid organs are essential steps in the immunobiology of dendritic cells (DC). Chemokines play an important role in guiding the traffic of DC. Receptor expression and responsiveness to constitutively made chemokines account for the presence of DC in normal tissues. Inflammatory chemokines and nonchemokine attractants promote recruitment and localization of DC at sites of inflammation and infection. Upon exposure to maturation signals, DC undergo a chemokine receptor switch, with down-regulation of inflammatory chemokine receptors followed by induction of CCR7. These temporally coordinated events allow DC to leave tissues and to localize in lymphoid organs by responding to CCR7 agonists. DC are also present in tumors that produce chemokines, but their significance remains to be defined. In addition to responding to chemokines, DC are a major source of certain chemokines such as macrophage-derived chemokine. The interaction of DC with chemokines is essential to the function of these cells in normal and pathological conditions and may provide tools for novel therapeutic strategies.     

Human cytomegalovirus inhibits the migration of immature dendritic cells by down-regulating cell-surface CCR1 and CCR5

Dendritic cells (DC) play a key role in the host immune response to infections. Human cytomegalovirus (HCMV) infection can inhibit the maturation of DC and impair their ability to stimulate T cell proliferation and cytotoxicity. In this study, we assessed the effects of HCMV infection on the migratory behavior of human DC. The HCMV strain TB40/E inhibited the migration of immature monocyte-derived DC in response to inflammatory chemokines by 95% 1 day after infection. This inhibition was mediated by early viral replicative events, which significantly reduced the cell-surface expression of CC chemokine receptor 1 (CCR1) and CCR5 by receptor internalization. HCMV infection also induced secretion of the inflammatory chemokines CC chemokine ligand 3 (CCL3)/macrophage inflammatory protein-1alpha (MIP-1alpha), CCL4/MIP-1beta, and CCL5/regulated on activation, normal T expressed and secreted (RANTES). Neutralizing antibodies for these chemokines reduced the effects of HCMV on chemokine receptor expression and on DC migration by approximately 60%. Interestingly, the surface expression of the lymphoid chemokine receptor CCR7 was not up-regulated after HCMV infection on immature DC, and immature-infected DC did not migrate in response to CCL19/MIP-3beta. These findings suggest that blocking the migratory ability of DC may be a potent mechanism used by HCMV to paralyze the early immune response of the host.     

Differential migration behavior and chemokine production by myeloid and plasmacytoid dendritic cells

The existence of dendritic cell (DC) subsets is firmly established, but their trafficking properties are still largely unknown. We have indicated that myeloid dendritic cells (M-DCs) and plasmacytoid dendritic cells (P-DCs) isolated from human blood differ widely in the capacity to migrate to chemotactic stimuli. The pattern of chemokine receptors expressed ex vivo by both subsets is similar, but P-DCs display, compared with M-DCs, higher levels of CC chemokine receptor (CCR)5, CCR7, and CXCR3. Intriguingly, most chemokine receptors of P-DCs, in particular those specific for inflammatory chemokines and classical chemotactic agonists, are not functional in circulating cells. Following maturation induced by cluster designation (CD)40 ligation, the receptors for inflammatory chemokines are downregulated and CCR7 on P-DCs becomes coupled to migration. The drastically impaired capacity of blood P-DCs to migrate in response to inflammatory chemotactic signals contrasts with the response to lymph node-homing chemokines, indicating a propensity to migrate to secondary lymphoid organs rather than to sites of inflammation. The distinct migration behavior of DC subsets is accompanied by a different profile of chemokine production. In contrast to the high production by M-DCs, the homeostatic CC chemokine ligand (CCL)17/ thymus- and activation-regulated chemokine (TARC) is not produced by PDCs in response to any stimulus tested and their production of CCL22/MDC is minimal, if any, compared with M-DCs. Thus, stimulated M-DCs, but not P-DCs, are able to produce high levels of chemokines recruiting T-helper 2 cells (Th2) and T-regulatory cells. Conversely, the proinflammatory chemokine CCL3/macrophage inflammatory protein (MIP)-1 is predominantly produced by P-DCs. Therefore, P-DCs appear to produce preferentially proinflammatory chemokines, but to respond selectively to homeostatic ones, whereas the reverse is true for M-DCs, highlighting not only the different migratory properties of these DC subsets, but also their capacity to recruit different cell types at inflammation sites.     

CD8+ and CD45RA+ human peripheral blood lymphocytes are potent sources of macrophage inflammatory protein 1α, interleukin-8 and RANTES

The chemokines macrophage inflammatory protein 1α (MIP 1α), interleukin-8 (IL-8) and RANTES are potent regulators of leukocyte trafficking. Examination of chemokine secretion by human peripheral blood lymphocytes after stimulation with anti-CD3 or phorbol 12, 13 myristate acetate and ionomycin showed CD8⁺ cells were the dominant source of MIP 1α and RANTES. Although production of MIP 1α and IL-8 were similar in pharmacologically stimulated CD4⁺ CD45RA⁺, CD4⁺ CD45RO⁺, and CD8⁺ CD45RA⁺ cells, the largest amounts of MIP 1α and RANTES were secreted by CD8⁺ CD45RO⁺ lymphocytes. A parallel pattern of prolonged chemokine mRNA expression for at least 18 h after activation was observed in the T cell subsets. These results confirm that human T lymphocytes have a unique capacity for secretion of these three chemokines. In addition, CD8⁺ cells have an unrecognized role in recruiting cells to sites of inflammation, and adult human CD45RA⁺ cells have a physiologically significant secretory capacity.     

Upon dendritic cell (DC) activation chemokines and chemokine receptor expression are rapidly regulated for recruitment and maintenance of DC at the inflammatory site.

Dendritic cells (DC) are highly motile antigen-presenting cells that are recruited to sites of infection and inflammation to antigen uptake and processing. Then, to initiate T cell-dependent immune responses, they migrate from non-lymphoid organs to lymph nodes and the spleen. Since chemokines have been involved in human DC recruitment, we investigated the role of chemokines on mouse DC migration using the mouse growth factor-dependent immature DC line (D1). In this study, we characterized receptor expression, responsiveness to chemoattractants and chemokine expression of D1 cells during the maturation process induced by lipopolysaccharide (LPS). MIP-1alpha and MIP-5 were found to be the most effective chemoattractants, CCR1 was the main receptor expressed and modulated during LPS treatment, and MIP-2, RANTES, IP-10 and MCP-1 were the chemokines modulated during DC maturation. Thus, murine DC respond to a unique set of CC and CXC chemokines, and the maturational stage determines the program of chemokine receptors and chemokines that are expressed. Since CCR1 is modulated during the early phases of DC maturation, our results indicate that the CCR1 receptor may participate in the recruitment and maintenance of DC at the inflammatory site.     

CXC and CC chemokines induced in human renal epithelial cells by inflammatory cytokines

Human renal epithelial cells might play an important role during the allograft rejection by producing chemokines in response to proinflammatory cytokines such as tumor necrosis factor (TNF)‐α and interleukin (IL)‐1β produced by endothelial and epithelial cells early after transplantation. The production of chemokines allows inflammatory cells to be drawn into the kidney graft and therefore plays a critical role in the pathophysiologic processes that lead to the rejection of renal transplant. In this process, two chemokine superfamilies, the CC and the CXC chemokines, are the most important. The CC chemokines target mainly monocytes and T lymphocytes, while most of the CXC chemokines attract neutrophils. We showed in our study that in vitro, in unstimulated cells, basal mRNA expression of CXC chemokines (Groα, Groβ, Groγ, ENA‐78 and GCP‐2, IL‐8) that attract neutrophils was detectable and expression of these genes and chemokine release were increased in TNF‐α‐ and IL‐1β‐induced renal epithelial cells. Most of the CC chemokines [monocyte chemotactic protein‐1 (MCP‐1), macrophage Inflammatory protein 1 beta (MIP‐1β), regulated upon activation, normal T cell expressed and secreted (RANTES) and macrophage inflammatory protein (MIP‐3α)] showed detectable mRNA expression only after stimulation with proinflammatory cytokines and not in control cells. TNF‐α seems to induce preferably the expression of RANTES, MCP‐1, interferon‐inducible protein (IP‐10) and Interferon‐Inducible T‐cell Alpha Chemoattractant (I‐TAC), while IL‐1β induces mainly IL‐8 and epithelial neutrophil‐activating peptide 78 (ENA‐78).     

Cholera toxin induces maturation of human dendritic cells and licences them for Th2 priming

Cholera toxin (CT) is a potent mucosal adjuvant that amplifies B and T cell responses to mucosally co-administered antigens, stimulating predominant Th2-type responses. However, little is known about the mechanism of adjuvanticity of CT and on the influence this toxin may have on Th2 cell development during the priming of an immune response. We analyzed the effect of CT on dendritic cells (DC), which are responsible for the priming of immune responses at the systemic as well as at the mucosal level. We found that CT induces phenotypic and functional maturation of blood monocyte-derived DC. Indeed, CT-treated DC up-regulate expression of HLA-DR molecules, B7. 1 and B7.2 co-stimulatory molecules, and are able to prime naive CD4(+)CD45RA(+) T cells in vitro, driving their polarization towards the Th2 phenotype. Furthermore, CT-matured DC express functional chemokine receptors CCR7 and CXCR4 which may render them responsive to migratory stimuli towards secondary lymphoid organs. Interestingly, the maturation program induced by CT is unique since CT does not induce but rather inhibits cytokine (IL-12p70 and TNF-alpha) and chemokine (RANTES, MIP-1alpha and MIP-1beta) secretion by lipopolysaccharide- or CD40 ligand-activated DC. Our results help to elucidate the mechanism of action of CT as an adjuvant and highlight a new stimulus of bacterial origin that promotes maturation of DC.     

Distinct patterns and kinetics of chemokine production regulate dendritic cell function.

Dendritic cells (DC) have been showed to both produce and respond to chemokines. To understand how this may impact on DC function, we analyzed the kinetics of chemokine production and responsiveness during DC maturation. After stimulation with LPS, TNF-alpha or CD40 ligand, the inflammatory chemokines MIP-1alpha, MIP-1beta and IL-8 were produced rapidly and at high levels, but only for a few hours, while RANTES and MCP-1 were produced in a sustained fashion. The constitutive chemokines TARC, MDC and PARC were expressed in immature DC and were up-regulated following maturation, while ELC was produced only at late time points. Activated macrophages produced a similar spectrum of chemokines, but did not produce TARC and ELC. In maturing DC chemokine production had different impact on chemokine receptor function. While CCR1 and CCR5 were down-regulated by endogenous or exogenous chemokines, CCR7 levels gradually increased in maturing DC and showed a striking resistance to ligand-induced down-regulation, explaining how DC can sustain the response to SLC and ELC throughout the maturation process. The time-ordered production of inflammatory and constitutive chemokines provides DC with the capacity to self-regulate their migratory behavior as well as to recruit other cells for the afferent and efferent limb of the immune response.     

Chemokine gene expression and clonal analysis of B cells in tissues involved by lymphoid interstitial pneumonitis from HIV-infected pediatric patients.

Lymphoid interstitial pneumonitis (LIP), a frequent pulmonary complication in HIV-infected pediatric patients, is characterized histologically by marked infiltration of lymphoid cells. We sought to evaluate the nature and pathogenesis of the lymphoid infiltrates and to examine the relationship of LIP to pulmonary MALT lymphoma that has been described in pediatric HIV positive patients. To examine the potential contribution of chemokines and cytokines to the inflammatory cell recruitment in tissues involved by lymphoid interstitial pneumonitis from HIV-infected pediatric patients, RNA was extracted from paraffin-embedded tissues from five lung biopsies in four pediatric HIV-positive patients and from five control, normal lung biopsies in five HIV-negative patients and was analyzed by semiquantitative RT-PCR for the expression of cytokines (TNF-alpha, GM-CSF, IFN-gamma, IL-4, IL-6, IL-10, and IL-18) and chemokines (IP-10, Mig, regulated upon activation, normal T expressed and secreted [RANTES], and MIP1-alpha and beta) after normalization for G3PDH. Expression of IL-18 was increased, as well as expression of IFN-gamma-inducible chemokines IP-10 and Mig in LIP tissues compared with controls. RANTES and MIP1-alpha and -beta were also increased in pediatric LIP lesions compared with controls. In contrast, expression of TNF-alpha, GM-CSF, IL-10, and IL-6 was variable in LIP tissues and controls. In addition, clonality of the B-cell population was evaluated by VDJ-PCR. A polyclonal B-cell population was shown in all five biopsies from five patients with LIP; and in one patient with concurrent LIP and MALT lymphoma, a band of increased intensity was observed in the LIP biopsy that was identical in size to the monoclonal band in the concurrent MALT lymphoma biopsy. These results provide evidence of high-level expression of certain chemokines in lymphoid interstitial pneumonitis tissues and suggest that chemokines and cytokines may play an important role in the recruitment of inflammatory cell infiltrates into these tissues. In addition, LIP may represent an early stage of MALT lymphoma or an immunologic response to a chronic antigenic stimulus that may provide a milieu or microenvironment for the evolution of a monoclonal B-cell population.     

Adhesion of dendritic cells derived from CD34+ progenitors to resting human dermal microvascular endothelial cells is down-regulated upon maturation and partially depends on CD11a-CD18, CD11b-CD18 and CD36

DC are sentinels of the immune system. In order to reach the skin, bone-marrow-derived DC precursors need to bind and migrate through microvascular endothelial cells. Binding of DC toprimary endothelial cells of the skin has not been investigated. We therefore determined adhesion of DC at different stages of development to human dermal microvascular endothelial cells (HDMEC). DC were derived from CD34+ progenitors in cord blood. To enhance DC maturation, a defined cocktail of IL-1beta+IL-6+TNF-alpha+PGE2 was applied. Adhesion was quantified by fluorimetric and phase-contrast microscopical assays. Significantly more DC precursors (tested on day 5 after isolation) than mature DC (spontaneously matured or cytokine-cocktail-matured and tested on day 13) bound to unstimulated HDMEC. In contrast, the maturation stage of DC had no influence on their binding to human umbilical vein endothelial cells. Pretreatment of HDMEC with TNF-alpha and IFN-gamma resulted in an enhanced attachment of both DC precursors and mature DC. Mature DC lacked expression of CD31, CD36, CD45RA and CLA, and expressed lower levels of CD11a, CD11b and CD49d as compared with precursors tested on day 5. mAb against CD18, CD11a, CD11b, and CD36 markedly inhibited DC binding, whereas anti-CLA, anti-DC-SIGN, anti-CD29 and anti-CD49 mAb did not. Our data support the hypothesis of immunosurveillance with selective recruitment of blood DC precursors to resting and, more so, to inflamed skin. The data have potential relevance for anti-cancer immunotherapy strategies favoring the intracutaneous application of mature DC.     

Disparate ability of murine CD8alpha- and CD8alpha+ dendritic cell subsets to traverse endothelium is not determined by differential CD11b expression

Upon Ag uptake and response to maturation stimuli, dendritic cells (DC) are directed through lymphatic or blood vessel endothelium to T cell areas of secondary lymphoid tissues by the constitutively expressed CC chemokines CCL19 and CCL21. We have shown that mature (m) murine CD8alpha+ DC exhibit poorer migratory ability to these chemokines than classic CD8alpha- DC by quantifying their in vitro chemotaxis through unmodified Transwell filters. We hypothesized that lower surface expression (compared to CD8alpha- mDC) of the adhesion molecule CD11b on CD8alpha+ DC might limit their ability to adhere to filter pores in vitro and/or endothelium in vitro/in vivo. To test the role of this and/or other adhesion molecules (CD11a, CD31, CD54 and CD62L) in regulating murine DC subset migration, we used specific mAbs to block their function and quantified their migration through resting or tumour necrosis factor (TNF)-alpha-activated endothelial cell (EC) layered-Transwell filters. Both CD8alpha+ and CD8alpha- subsets migrated through resting EC (albeit less than in the absence of EC) in response to CCL19 and CCL21, and migration through TNF-alpha-activated EC was enhanced. In contrast to reports concerning human DC, transendothelial migration of the murine DC subsets was not dependent on CD11b, CD31, or CD62L expression by these cells. CD54 and CD11a, however, were at least partly involved in DC/EC interactions. This is the first report to examine adhesion molecules involved in transendothelial migration of murine DC subsets.     

Dendritic cell biology and regulation of dendritic cell trafficking by chemokines

DC (dendritic cells) represent an heterogeneous family of cells which function as sentinels of the immune system. They traffic from the blood to the tissues where, while immature, they capture antigens. Then, following inflammatory stimuli, they leave the tissues and move to the draining lymphoid organs where, converted into mature DC, they prime naive T cells. The key role of DC migration in their sentinel function led to the investigation of the chemokine responsiveness of DC populations during their development and maturation. These studies have shown that immature DC respond to many CC and CXC chemokines (MIP-lα, MIP-lβ, MIP-3α, MIP-5, MCP-3, MCP-4, RANTES, TECK and SDF-1) which are inducible upon inflammatory stimuli. Importantly, each immature DC population displays a unique spectrum of chemokine responsiveness. For examples, Langerhans cells migrate selectively to MIP-3α (via CCR6), blood CD11c⁺ DC to MCP chemokines (via CCR2), monocytes derived-DC respond to MIP-1α/β (via CCR1 and CCR5), while blood CD11c^– DC precursors do not respond to any of these chemokines. All these chemokines are inducible upon inflammatory stimuli, in particular MIP-3α, which is only detected within inflamed epithelium, a site of antigen entry known to be infiltrated by immature DC. In contrast to immature DC, mature DC lose their responsiveness to most of these inflammatory chemokines through receptor down-regulation or desensitization, but acquire responsiveness to ELC/MIP-3β and SLC/6Ckine as a consequence of CCR7 up-regulation. ELC/MIP-3β and SLC/6Ckine are specifically expressed in the T-cell-rich areas where mature DC home to become interdigitating DC. Altogether, these observations suggest that the inflammatory chemokines secreted at the site of pathogen invasion will determine the DC subset recruited and will influence the class of the immune response initiated. In contrast, MIP-3β/6Ckine have a determinant role in the accumulation of antigen-loaded mature DC in T cell-rich areas of the draining lymph node, as illustrated by recent observations in mice deficient for CCR7 or SLC/6Ckine. A better understanding of the regulation of DC trafficking might offer new opportunities of therapeutic interventions to suppress, stimulate or deviate the immune response.     

Selective attraction of naive and memory B cells by dendritic cells

In this study, we investigate whether dendritic cells (DC), known to interact directly with T and B cells, might also contribute to the recruitment of B cells through the production of chemotactic factors. We found that B cells responded to several chemokines (CXCL12, CCL19, CCL20, and CCL21), which can be produced by DC upon activation. In addition, supernatant from DC (SNDC) potently and selectively attracted naive and memory B cells but not germinal center (GC) B cells or other lymphocytes (CD4(+), CD8(+) T cells or NK cells). Production of this activity was restricted to DC and was not increased following DC activation by LPS or CD40 ligand. Surprisingly, the B-cell chemotactic response to SNDC was insensitive to pertussis toxin treatment. In addition, the chemotactic factor(s) appeared resistant to protease digestion and highly sensitive to heat. This suggested that the DC chemotactic factor(s) is different from classical chemoattractants and does not involve G(alpha(i)) proteins on the responding B lymphocytes. It is interesting that SNDC was able to synergize with several chemokines to induce massive migration of B lymphocytes. These observations show that DC spontaneously produce factors that, alone or in cooperation with chemokines, specifically regulate B-cell migration, suggesting a key role of DC in the recruitment or localization of B lymphocytes within secondary lymphoid organs.     

Increased circulating CD11b+CD11c+ dendritic cells (DC) in aged BWF1 mice which can be matured by TNF-alpha into BLC/CXCL13-producing DC

Dendritic cells (DC) play a pivotal role in regulating immune responses. We previously reported aberrant high production of B lymphocyte chemoattractant (BLC/CXCL13) by DC in aged BWF1 mice, amurine model for systemic lupus erythematosus (SLE). We describe here that CD11b+CD11c+ cells were markedly increased in the peripheral blood (PBL-DC) in aged BWF1, but not in similarly aged NZB or NZW mice. Part of PBL-DC showed a typical dendritic morphology and expressed MHC class II molecules, and had a weak, but significant antigen-presenting ability in mixed lymphocytereaction. PBL-DC were chemoattracted to several chemokines in vitro including secondary lymphoid tissue chemokine (SLC), liver and activation-regulated chemokine (LARC), RANTES, macrophage inflammatory protein-1alpha, whereas splenic mature DC from aged BWF1 mice were preferentially chemoattracted towards SLC. BLC production was induced when PBL-DC were cultured in the presence of TNF-alpha for 3 days. BLC expression was also induced in bone marrow-derived DC when they were differentiated into mature DC in the presence of TNF-alpha and IL-1beta, while both IFN-alpha and IFN-gamma failed to induce BLC expression in bone marrow-derived DC. Since TNF-alpha expression is increased in aged BWF1 mice, DC recruitment in the circulation and maturation into BLC-producing DC by TNF-alpha may play a pivotal role in the development of systemic autoimmune diseases.