Chemokines and dendritic cells: a crucial alliance

In vitro induction of a dendritic cell phenotype in primary human acute myelogenous leukemia (AML) blasts alters the chemokine release profile and increases the levels of T cell chemotactic CCL17 and CCL22

Immunotherapy is now considered in acute myelogenous leukemia (AML). A dendritic cell (DC) phenotype can be induced in primary human AML cells by in vitro culture in the presence of various cytokine combinations. The aim was to investigate whether this phenotypic alteration is associated with altered chemokine release. AML cells were cultured according to four protocols that have been characterized in detail for AML-DC induction: (1) granulocyte-macrophage colony-stimulating factor (GM-CSF) + interleukin-4 (IL-4) days 1-14 and tumor necrosis factor-alpha (TNF-alpha) for days 6-14, (2) GM-CSF + IL-4 + TNF-alpha + FMS-like tyrosine kinase 3-ligand (Fl3-L) for 8 days, (3) GM-CSF + IL-4 + TNF-alpha + Flt3-L + stem cell factor (SCF) + transforming growth factor-beta1 (TGF-beta1) for 8 days, and (4) 25 Gy gamma-irradiation combined with culture in the presence of GM-CSF + SCF + IL-3 for 4 days. Significantly increased AML-DC release of CCL17 and CCL22 was observed for protocols 1, 2, and 3, whereas effects on CCL2-5, CXCL8, and CXCL10 differed in all protocols. Neutralization studies using a transwell migration assay demonstrated the increased level of CCL17 and CCL22 release was important for AML-DC chemotaxis of normal T cells. Induction of a dendritic AML cell phenotype is associated with an altered chemokine release profile. Detailed characterization of chemokine release should be included in future studies of AML-DC vaccination.

Dendritic cells--at the front-line of pathogen attack

Efficient immune defence function is dependent on the role played by dendritic cells (DCs), particularly the interaction between conventional DC (cDC) and plasmacytoid DC (pDC), together with other monocytic cells. This functionality of immune defences is open to manipulation by viral pathogens infecting DC, a situation further complicated by the diversity of mechanisms employed by different viruses and the subset of DC involved. The present review uses two virus examples--classical swine fever virus (CSFV) and porcine circovirus type 2 (PCV2)--to demonstrate the complexity of this host-pathogen scenario. CSFV is a monocytotropic RNA virus infecting and replicating in both cDC and pDC. This virus employs its non-structural Npro protein for antagonizing the Type I interferon (IFN) induction pathway. The Npro protein promotes proteasomal degradation of interferon regulatory factor (IRF)3, particularly notable in cDC. In contrast, CSFV infection induces IFNalpha production by pDC, probably due to a lack of interference by the Npro protein with the IRF7 more prominent in pDC. Such ability of the virus to inhibit cDC while augmenting IFNalpha production by pDC might lead to an exaggerated pDC response, relating to the immunopathological characteristics of the disease. PCV2 is an ssDNA containing virus, which in contrast to CSFV is inefficient in its capacity to replicate in DC. Recent evidence suggests that virus replication occurs in endothelial cells, with the DC being more involved through their particularly elevated endocytosis of the virus. PCV2 can accumulate to high levels both in vitro and in vivo, a phenomenon dependent on the virus capsid protein, inferring that the viral capsid or genome impedes DC endocytic degradation of the virus. Nevertheless, the presence of PCV2 in cDC does not interfere with processing of other antigens. The immunoregulatory characteristics of PCV2 are manifest as impairment of "danger" recognition by cells of the innate defences. This varies dependent on the "danger" signal and the cells responding, especially when one compares cDC and pDC. Overall, the PCV2-induced immunomodulation contrasts with that of CSFV in being a property dependent on the viral genome, particularly the dsDNA replicative form, and with immunoregulatory capacity for both cDC and pDC. Moreover, PCV2 compromises immune defence development against other pathogens rather than itself. In conclusion, the DC family represents a critical immune defence element open to modulation by virus infection, with serious consequences for host resistance to disease. The characteristics of the immune modulation depend on the virus and the DC subsets involved. Overall, the roles played by the pDC can be decisive in shaping the outcome of the infection and the characteristics of the virus-induced immunocompromisation.

Dendritic cells in the kidney

Dendritic cells (DC) in nonlymphoid organs function at the crossroads of innate and adaptive immunity, self-tolerance, and tissue homeostasis. This review provides an overview of the study of DC in the kidney, tracing its history leading to the current knowledge of the origins, migration, and function of renal DC. Together, these studies suggest that renal DC play a critical role in the health and disease of the kidney, opening the way to direct targeting of renal DC for therapeutic benefit.

Dynamic alteration of soluble serum biomarkers in healthy aging

Dysbalanced production of inflammatory cytokines is involved in immunosenescence in aging. The age-related changes of the levels of circulating inflammatory mediators and their clinical importance have not been investigated until recently. Still, little is known about the influence of aging on circulating levels of many cytokines, chemokines, growth factors, and angiogenic factors. In the present study, we evaluated the effect of aging on 30 different serum biomarkers involved in pro- and anti-inflammatory responses using multianalyte LabMAP Luminex technology. The simultaneous measurement of serological markers has been done in 397 healthy subjects between 40 and 80 years old. We demonstrated an increase in serum interferon-gamma-inducible chemokines (MIG and IP-10), eotaxin, chemoattractant for eosinophils, and soluble TNFR-II with advancing age. Serum levels of EGFR and EGF, important regulators of cell growth and differentiation, were decreased with age in healthy donors. These data suggest novel pathways, which may be involved in age-associated immunosenescence.

Involvement of intestinal epithelial cells in dendritic cell recruitment during C. parvum infection

Dendritic cells (DCs) play a key role in activating and orientating immune responses. Little is currently known about DC recruitment during Cryptosporidium parvum infection. In the intestine, epithelial cells act as sensors, providing the first signals in response to infection by enteric pathogens. We analyzed the contribution of these cells to the recruitment of DCs during cryptosporidiosis. We found that intestinal epithelial cells produced a broad range of DC-attracting chemokines in vitro in response to C. parvum infection. The supernatant of the infected cells induced the migration of both bone marrow-derived DCs (BMDC) and the SRDC lymphoid dendritic cell line. Chemokine neutralization abolished DC migration in these assays. We next analyzed chemokine mRNA expression in the mucosa of C. parvum-infected neonatal mice and recruitment of the various subsets of DCs. Myeloid (CD11c+ CD11b+) and double-negative DCs (CD11c+ CD11b- CD8alpha-) were the main subsets recruited in the ileum during C. parvum infection, via a mechanism involving IFNgamma. DCs were also recruited and activated in the draining lymph nodes during C. parvum infection, as shown by the upregulation of expression of MHC II and of the costimulation molecules CD40 and CD86.

Expression of CXCR-1 and CXCR-2 chemokine receptors on synovial neutrophils in inflammatory arthritides: Does persistent or increasing expression of CXCR-2 contribute to the chronic inflammation or erosive changes?

OBJECTIVE

To analyze the CXCR-1 and CXCR-2 chemokine receptor expression on peripheral blood neutrophils (PBN) and synovial fluid neutrophils (SFN) of patients with rheumatoid arthritis (RA) and Behçet's disease (BD) (characterized by erosive and non-erosive arthritis, respectively), and to compare them with those of patients with osteoarthritis (OA).

METHODS

We used flow cytometry to investigate the expression of CXCR-1 and CXCR-2 chemokine receptors on PBN and SFN of fifty-five (22 RA, 22 BD and 11 OA) age and sex-matched patients.

RESULTS

In respect to chemokine receptor expression on neutrophils isolated from patients with RA, mean fluorescein intensity (MFI) of CXCR-1 chemokine receptors on PBN from active and inactive RA patients, and SFN from patients with RA were 151 (90-395), 129 (81-539) and 136 (64-220), respectively, and there were not statistically significant difference each other. But MFI of CXCR-2 chemokine receptors on SFN of patients with RA was 18 (10-32), and significantly higher than PBN of active and inactive RA patients (MFI: 10 (6-15) and 12 (7-16), P=0.002 and 0.037, respectively). In respect to chemokine receptor expression on neutrophils isolated from patients with BD, MFI of CXCR-1 chemokine receptors on PBN of active BD patients was 245 (97-844), and higher than PBN of active RA patients and SFN of BD patients (MFI: 151 (90-395) and 134 (61-231), P=0.047 and 0.017, respectively). MFI of CXCR-2 chemokine receptors on PBN of active and inactive BD patients, and SFN of patients BD were 10 (6-14), 10 (2-16), and 12 (8-24), respectively, there were not statistically significant difference each other. MFI of CXCR-1 chemokine receptors on SFN from patients with RA, BD, and OA were 136 (64-220), 134 (61-231), and 114 (60-180), respectively, and there was no difference between the study groups. MFI of CXCR-2 chemokine receptors on SFN of patients with RA was 18 (10-32), and higher than patients with BD and OA (MFI: 12 (8-24) and 11 (9-18), P=0.037 and 0.005, respectively), though there was no difference between last two groups.

CONCLUSION

Our study points that CXCR-1 and CXCR-2 chemokine receptors of SFN may have diverse functions in the course of inflammatory arthritides. These results indicate that CXCR-2 chemokine receptor might play more critical role in long lasting accumulation of neutrophils within the synovial fluid of patients with RA.

Dendritic cells modified to express fractalkine/CX3CL1 in the treatment of preexisting tumors

Fractalkine (CX3CL1) is a unique membrane-bound CX3C chemokine that serves as a potent chemoattractant for lymphocytes. The hypothesis of this study is that dendritic cells (DC) genetically modified ex vivo to overexpress fractalkine would enhance the T cell-mediated cellular immune response with a consequent induction of anti-tumor immunity to suppress tumor growth. To prove this hypothesis, established tumors of different mouse cancer cells (B16-F10 melanoma, H-2b, and Colon-26 colon adenocarcinoma, H-2d) were treated with intratumoral injection of bone marrow-derived DC that had been modified in vitro with an RGD fiber-mutant adenovirus vector expressing mouse fractalkine (Ad-FKN). In both tumor models tested, treatment of tumor-bearing mice with Ad-FKN-transduced DC gave rise to a significant suppression of tumor growth along with survival advantages in the treated mice. Immunohistochemical analysis of tumors treated with direct injection of Ad-FKN-transduced DC demonstrated that the treatment prompted CD8+ T cells and CD4+ T cells to accumulate in the tumor milieu, leading to activation of immune-relevant processes. Consistent with the finding, the intratumoral administration of Ad-FKN-transduced DC evoked tumor-specific cytotoxic T lymphocytes, which ensued from in vivo priming of Th1 immune responses in the treated host. In addition, the anti-tumor effect provided by intratumoral injection of Ad-FKN-transduced DC was completely abrogated in CD4+ T cell-deficient mice as well as in CD8+ T cell-deficient mice. These results support the concept that genetic modification of DC with a recombinant fractalkine adenovirus vector may be a useful strategy for cancer immunotherapy protocols.

Gliadin fragments induce phenotypic and functional maturation of human dendritic cells

Celiac disease is a chronic inflammatory disease developing in genetically predisposed individuals. Ingested gliadin, the triggering agent of the disease, can cross the epithelial barrier and elicit a harmful T cell-mediated immune response. Dendritic cells (DC) are supposed to play a pivotal role in shaping the immune response. The direction of the immune response toward immunity or tolerance depends on the stage of maturation and the functional properties of the DC. DC become fully functional APC upon maturation by various stimuli. We investigated the effect of a peptic digest of gliadin on the maturation of human monocyte-derived DC. Stimulation of cells with gliadin, in contrast with other tested food proteins, led to enhanced expression of maturation markers (CD80, CD83, CD86, and HLA-DR molecules) and increased secretion of chemokines and cytokines (mainly of IL-6, IL-8, IL-10, TNF-alpha, growth-related oncogene, MCP-1, MCP-2, macrophage-derived chemokine, and RANTES). Maturation was accompanied by a greater capacity to stimulate proliferation of allogeneic T cells and significantly reduced endocytic activity. Furthermore, gliadin-induced phosphorylation of members of three MAPK families (ERK1/2, JNK, and p38 MAPK) was demonstrated. The largest contribution of p38 MAPK was confirmed using its inhibitor SB203580, which markedly down-regulated the gliadin-triggered up-regulation of maturation markers and cytokine production. Gliadin treatment also resulted in increased NF-kappaB/DNA binding activity of p50 and p65 subunits. Taken together, gliadin peptides can contribute to overcoming the stage of unresponsiveness of immature DC by inducing phenotypic and functional DC maturation, resulting in more efficient processing and presentation of gliadin peptides to specific T lymphocytes.

Dendritic cell trafficking: More than just chemokines

Dendritic cells (DC) are professional antigen presenting cells. To accomplish their biological function they need to undergo a complex pattern of migration which includes their localization to both peripheral non-lymphoid tissues and secondary lymphoid organs. In the absence of correct tissue localization, DC fail to promote proper immune responses. The first description of chemotactic factors active on DC was published by this group 10 years ago. Since then, it was described that multiple signals are able to regulate the migration of DC in vitro and in vivo. These signals include nonchemokine chemotactic agonists, lipid mediators and membrane proteins. This review summarizes this large body of information and focuses on the complexity of the process of DC trafficking.

Contact sensitizers downregulate the expression of the chemokine receptors CCR6 and CXCR4 in a skin dendritic cell line

Chemokines are involved in the control of dendritic cell (DC) trafficking, which is critical for the immune response, namely in allergic contact dermatitis (ACD). In this work, we investigated by flow cytometry the effect of the contact sensitizers 2,4-dinitrofluorobenzene (DNFB), 1,4-phenylenediamine (PPD) and nickel sulfate (NiSO(4)), on the surface expression of the chemokine receptors CCR6 and CXCR4 in DC. As an experimental model of a DC we used a fetal skin-derived dendritic cell line (FSDC), which has morphological, phenotypical and functional characteristics of skin DC. Our results show that all the skin sensitizers studied decreased the membrane expression of the chemokine receptors CCR6 and CXCR4. In contrast, 2,4-dichloronitrobenzene (DCNB), the inactive analogue of DNFB without contact sensitizing properties, was without effect on the surface expression of these receptors. Lipopolysaccharide (LPS), which induces the maturation of DC, also reduced surface CCR6 and CXCR4 expression.

Involvement of fractalkine/CX3CL1 expression by dendritic cells in the enhancement of host immunity against Legionella pneumophila

Legionnaires' disease is clinically manifested as severe pneumonia caused by Legionella pneumophila. However, the dendritic cell (DC)-centered immunological framework of the host defense against L. pneumophila has not been fully delineated. For this study, we focused on a potent chemoattractant for lymphocytes, fractalkine/CX3CL1, and observed that the fractalkine expression of DCs was somewhat up-regulated when they encountered L. pneumophila. We therefore hypothesized that fractalkine expressed by Legionella-capturing DCs is involved in the induction of T-cell-mediated immune responses against Legionella, which would be enhanced by a genetic modulation of DCs to overexpress fractalkine. In vivo immunization-challenge experiments demonstrated that DCs modified with a recombinant adenovirus vector to overexpress fractalkine (AdFKN) and pulsed with heat-killed Legionella protected immunized mice from a lethal Legionella infection and that the generation of in vivo protective immunity depended on the host lymphocyte subsets, including CD4(+) T cells, CD8(+) T cells, and B cells. Consistent with this, immunization with AdFKN/Legionella/DC induced significantly higher levels of serum anti-Legionella antibodies of several isotypes than those induced by control immunizations. Further analysis of spleen cells from the immunized mice indicated that the AdFKN/Legionella/DC immunization elicited Th1-dominated immune responses to L. pneumophila. These observations suggest that fractalkine may play an important role in the DC-mediated host defense against intracellular pathogens such as L. pneumophila.

Human Tumor Antigen MUC1 Is Chemotactic for Immature Dendritic Cells and Elicits Maturation but Does Not Promote Th1 Type Immunity

The immunostimulatory outcome of the interactions of many pathogens with dendritic cells (DCs) has been well characterized. There are many fewer examples of similar interactions between DCs and self-molecules, especially the abnormal self-proteins such as many tumor Ags, and their effects on DC function and the immune response. We show that human epithelial cell Ag MUC1 mucin is recognized in its aberrantly glycosylated form on tumor cells by immature human myeloid DCs as both a chemoattractant (through its polypeptide core) and a maturation and activation signal (through its carbohydrate moieties). On encounter with MUC1, similar to the encounter with LPS, immature DCs increase cell surface expression of CD80, CD86, CD40, and CD83 molecules and the production of IL-6 and TNF-alpha cytokines but fail to make IL-12. When these DCs are cocultured with allogeneic CD4+ T cells, they induce production of IL-13 and IL-5 and lower levels of IL-2, thus failing to induce a type 1 response. Our data suggest that, in vivo in cancer patients, MUC1 attracts immature DCs to the tumor through chemotaxis and subverts their function by negatively affecting their ability to stimulate type 1 helper T cell responses important for tumor rejection.

Loss of new chemokine CXCL14 in tumor tissue is associated with low infiltration by dendritic cells (DC), while restoration of human CXCL14 expression in tumor cells causes attraction of DC both in vitro and in vivo

Breast and kidney-expressed chemokine (BRAK) CXCL14 is a new CXC chemokine with unknown function and receptor selectivity. The majority of head and neck squamous cell carcinoma (HNSCC) and some cervical squamous cell carcinoma do not express CXCL14 mRNA, as opposed to constitutive expression by normal oral squamous epithelium. In this study, we demonstrate that the loss of CXCL14 in HNSCC cells and at HNSCC primary tumor sites was correlated with low or no attraction of dendritic cell (DC) in vitro, and decreased infiltration of HNSCC mass by DC at the tumor site in vivo. Next, we found that recombinant human CXCL14 and CXCL14-positive HNSCC cell lines induced DC attraction in vitro, whereas CXCL14-negative HNSCC cells did not chemoattract DC. Transduction of CXCL14-negative HNSCC cell lines with the human CXCL14 gene resulted in stimulation of DC attraction in vitro and increased tumor infiltration by DC in vivo in chimeric animal models. Furthermore, evaluating the biologic effect of CXCL14 on DC, we demonstrated that the addition of recombinant human CXCL14 to DC cultures resulted in up-regulation of the expression of DC maturation markers, as well as enhanced proliferation of allogeneic T cells in MLR. Activation of DC with recombinant human CXCL14 was accompanied by up-regulation of NF-kappaB activity. These data suggest that CXCL14 is a potent chemoattractant and activator of DC and might be involved in DC homing in vivo.

CCR and CC chemokine expression in relation to Flt3 ligand-induced renal dendritic cell mobilization

BACKGROUND

We investigated the expression and function of CC chemokine receptors (CCR) on highly-purified kidney and blood dendritic cells isolated from mice in which dendritic cells were mobilized with fms-like tyrosine 3 kinase ligand (Flt3L).

METHODS

CCR and CC chemokine expression were determined by RNase protection assay or flow cytometry, and dendritic cell migratory responses assayed using Transwell chambers. Chemokine production in renal tissue was detected by immunofluorescence staining. Trafficking of fluorochrome-labeled dendritic cells was monitored in vivo.

RESULTS

Freshly-isolated renal dendritic cells expressed mRNA for CCR1, 2, 5, and 7 and CCR1 and 5 protein. They did not migrate to inducible chemokines--CCL3 [macrophage inflammatory protein (MIP)-1alpha], CCL5 [regulated upon activation, normal T cell expressed and secreted (RANTES)], or CCL20 (MIP-3alpha). Following lipopolysaccharide (LPS) stimulation, the dendritic cells down-regulated CCR1, 2, and 5 expression, up-regulated or sustained signals for CCR7, and migrated to the constitutively expressed ligands CCL19 (MIP-3beta) and CCL21 (secondary lymphoid tissue chemokine). Normal kidneys expressed weak message for CCL2, 3, and 4, with stronger signals for CCL5 and 19. Intrarenal CCL5 production was enhanced by Flt3L administration, in association with marked increases in interstitial CD45+ mononuclear cells. Mobilized blood dendritic cells migrated to CCR2 and CCR5 ligands and trafficked to renal intertubular sites following adoptive (intravenous) transfer. Their migration to the CCR5 ligand MIP-1beta (CCL4) and homing to kidneys of Flt3L-treated recipients were inhibited by CCR5 antagonism.

CONCLUSION

These data implicate specific CCR and their ligands in regulation of the dendritic cell constituency of the kidney. CCR5 antagonism inhibits their directed migration and intrarenal accumulation.

Leishmania major modulates chemokine and chemokine receptor expression by dendritic cells and affects their migratory capacity

Dendritic cells (DC) both produce and respond to chemokines. We examined the profiles of chemokines and chemokine receptors expressed by DC and their chemotactic response after interaction with Leishmania major. Expression of the chemokine receptors CCR2 and CCR5 by DC and their responsiveness to the respective ligands, CCL2 and CCL3, were downregulated, while the level of CCR7 and the DC response to its ligand CCL21 were enhanced. These parasite-induced alterations were observed with DC from L. major-resistant and -susceptible mice. In contrast, expression of the chemokine CXCL10 was elicited only in DC from L. major-resistant mice.

T cell costimulation by chemokine receptors

Signals mediated by chemokine receptors may compete with T cell receptor stop signals and determine the duration of T cell-antigen-presenting cell interactions. Here we show that during T cell stimulation by antigen-presenting cells, T cell chemokine receptors coupled to G(q) and/or G(11) protein were recruited to the immunological synapse by a G(i)-independent mechanism. When chemokine receptors were sequestered at the immunological synapse, T cells became insensitive to chemotactic gradients, formed more stable conjugates and finally responded with enhanced proliferation and cytokine production. We suggest that chemokine receptor trapping at the immunological synapse enhances T cell activation by improving T cell-antigen-presenting cell attraction and impeding the 'distraction' of successfully engaged T cells by other chemokine sources.

Dendritic cells acquire tolerogenic properties at the site of sterile granulomatous inflammation

Subcutaneous implantation of polyvinyl sponges represents a suitable model for studying the mechanisms of acute and chronic inflammation, granulomatous foreign-body reaction, as well as wound healing. Using such a model in rats, we studied the phenotypic and functional characteristics of dendritic cells (DC). DC were purified from the sponge exudate using a combination of separation gradients, adherence to plastics, and immunomagnetic sorting. We have shown that the number of DC progressively increased in the sponges, reaching maximal values at day 10 after implantation, followed by their decrease thereafter. Inflammatory DC expressed MHC class II molecules and myeloid markers CD11b, CD11c, and CD68. A subset of DC expressed CD4, R-MC46, DEC-205, R-MC17, and CCR1. Compared to DC isolated in the early phase of inflammation (day 6 DC), DC in the late stage of inflammation (day 14 DC) had a lower capability to stimulate the proliferation of allogeneic lymphocytes and CD4(+) T cells. This finding correlated with the downregulation of CD80, CD86, and CD54 expression and the increased proportion of plasmacytoid MHC class II(+) His 24(+) His 48(+) DC. The suppression of allogeneic lymphocyte proliferation was abrogated by the treatment of DC with lipopolysaccharide. In addition, day 14 DC exerted tolerogenic capability in co-culture with allogenic CD4(+) T cells. These results correlated with the increased levels of IL-10 and TGF-beta in culture supernatants and the sponge exudate.

Suppressive effect of 1alpha,25-dihydroxyvitamin D3 on type I IFN-mediated monocyte differentiation into dendritic cells: impairment of functional activities and chemotaxis

Dendritic cells (DCs) generated by a single-step exposure of human monocytes to type I IFN and GM-CSF (IFN-DCs) are endowed with potent immunostimulatory activities and a distinctive migratory response to specific chemokines. In this study, we evaluated the effects of 1alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), the biologically active metabolite of vitamin D(3), on the DC differentiation/activation induced by type I IFN. We found that 1,25(OH)(2)D(3) prevented the generation of IFN-DCs when added to freshly isolated monocytes, and was capable of redirecting already differentiated IFN-DCs toward a more immature stage, as revealed by their immunophenotype, reduced allostimulatory activity, and impaired LPS-induced production of Th1-polarizing cytokines. Control and 1,25(OH)(2)D(3)-treated IFN-DCs exhibited a similar expression of vitamin D receptor, as well as comparable cell death rates. Furthermore, the chemotactic response of IFN-DCs to CCL4 and CCL19 was markedly reduced or completely abrogated by 1,25(OH)(2)D(3). Despite these changes in the IFN-DC migratory behavior, the expression of CCR5 and CCR7 and the calcium fluxes triggered by CCL4 and CCL19 were not affected. These findings indicate that, in this innovative single-step DC generation model from monocytes, the suppressive effect of 1,25(OH)(2)D(3) is associated with a potent impairment of DC migration in response to inflammatory and lymph node-homing chemokines, thus unraveling a novel mechanism involved in 1,25(OH)(2)D(3)-mediated immunomodulation.

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.

Antigen delivery by dendritic cells

Dendritic cells (DC) link the innate and adaptive arms of the immune system and thus orchestrate the immune response to pathogens. A novel immune intervention strategy to control infectious diseases is based on the use of the potent immunostimulatory properties of DC for vaccination and immunotherapy. Recent advances in our understanding of DC biology and the molecular mechanisms by which DC instruct the development of an appropriate immune response to microorganisms provide means for DC-based approaches to manipulate the immune system. In experimental systems, DC vaccination has been documented to mediate protection against a wide spectrum of infectious diseases caused by viral, bacterial, parasitic and fungal pathogens. The protocols for the generation, stimulation and antigen loading of DC are being optimized, and methods for DC targeting in situ are likely to become available soon, thus paving the way for clinical applications of DC-based vaccines.

Differential roles of CCL2 and CCR2 in host defense to coronavirus infection

The CC chemokine ligand 2 (CCL2, monocyte chemoattractant protein-1) is important in coordinating the immune response following microbial infection by regulating T cell polarization as well as leukocyte migration and accumulation within infected tissues. The present study examines the consequences of mouse hepatitis virus (MHV) infection in mice lacking CCL2 (CCL2(-/-)) in order to determine if signaling by this chemokine is relevant in host defense. Intracerebral infection of CCL2(-/-) mice with MHV did not result in increased morbidity or mortality as compared to either wild type or CCR2(-/-) mice and CCL2(-/-) mice cleared replicating virus from the brain. In contrast, CCR2(-/-) mice displayed an impaired ability to clear virus from the brain that was accompanied by a reduction in the numbers of antigen-specific T cells as compared to both CCL2(-/-) and wild-type mice. The paucity in T cell accumulation within the central nervous system (CNS) of MHV-infected CCR2(-/-) mice was not the result of either a deficiency in antigen-presenting cell (APC) accumulation within draining cervical lymph nodes (CLN) or the generation of virus-specific T cells within this compartment. A similar reduction in macrophage infiltration into the CNS was observed in both CCL2(-/-) and CCR2(-/-) mice when compared to wild-type mice, indicating that both CCL2 and CC chemokine receptor 2 (CCR2) contribute to macrophage migration and accumulation within the CNS following MHV infection. Together, these data demonstrate that CCR2, but not CCL2, is important in host defense following viral infection of the CNS, and CCR2 ligand(s), other than CCL2, participates in generating a protective response.

Immunopathways in giant cell arteritis and polymyalgia rheumatica

Giant cell arteritis (GCA), a vasculitis that targets medium- and large-size arteries, is ranked as a medical emergency because of its potential to cause blindness and stroke. The typical lesions, granulomas in the vessel wall, are formed by IFN-gamma-producing CD4+ T cells and macrophages. CD4+ T cells undergo in situ activation in the adventitia, where they interact with indigenous dendritic cells. Tissue injury is mediated by several distinct sets of macrophages that are committed to diverse effector functions. The dominant tissue injury in the media results from oxidative stress and leads to smooth muscle cell apoptosis and nitration of endothelial cells. Macrophage-derived growth factors are instrumental in driving the response-to-injury program of the artery that causes intimal hyperplasia and vessel occlusion. Clinical manifestations are those of tissue ischemia or a syndrome of exuberant systemic inflammation. The vascular and the systemic components of GCA contribute differentially to the disease, leading to distinct clinical phenotypes of this arteritis. Immunologically most interesting is polymyalgia rheumatica, in which the systemic component is combined with aborted vasculitis, suggesting a role for artery-specific tolerance mechanisms.

Different ELR (+) angiogenic CXC chemokine profiles in synovial fluid of patients with Behçet's disease, familial Mediterranean fever, rheumatoid arthritis, and osteoarthritis

The aim of the present study was to determine synovial levels of ELR (+) CXC chemokines, known to attract mainly neutrophils to inflamed tissues by binding the neutrophil chemokine receptors CXCR1 and CXCR2 and promoting neovascularization in patients with various inflammatory disorders. The study group consisted of 14 patients with Behçet's disease and nine with familial Mediterranean fever. Fourteen patients with rheumatoid arthritis and 16 with osteoarthritis served as controls. Synovial chemokine levels were measured by two-step sandwich enzyme-linked immunosorbent assay, and significant differences were found in the various chemokines studied. In addition to its angiogenic properties, increased synovial levels of interleukin-8 by attraction of more neutrophils to synovial fluids might also be responsible for the acute synovitis in patients with Behçet's disease. However, the absence of chronic changes with the eventual development of pannus and erosions might result from relatively lower expression of interleukin-8 and the transient, short-lived nature of the arthritis observed in these patients.

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.

Local delivery of recombinant vaccinia virus expressing secondary lymphoid chemokine (SLC) results in a CD4 T-cell dependent antitumor response

Secondary lymphoid chemokine (SLC) attracts mature dendritic cells (DCs) and naïve T cells. Co-localization of these cells within local tumor environments may enhance the induction of tumor-specific T cells. However, the presence of danger signals or other DC maturation signals are required to optimize T-cell priming. We hypothesized that expression of SLC in vaccinia virus would provide local chemokine delivery and adjuvant factors. A recombinant vaccinia virus expressing murine SLC (rVmSLC) was constructed and characterized. SLC expression was confirmed by Western blot analysis and functional activity was determined by in vitro chemotaxis assay. Supernatants from rVmSLC-infected cells attracted CD4 T cells, and also induced the migration of CD8 T cells and DCs. Although poxviruses are known to express several chemokine-binding proteins, systemic injection of rVmSLC was well tolerated in mice up to a dose of 1 x 10(7) pfu and did not significantly alter vaccinia-specific T-cell immunity. Local injection of rVmSLC into established tumors derived from the murine colon cancer line, CT26, resulted in enhanced infiltration of CD4 T cells, which correlated with inhibition of tumor growth. The central role of CD4 T cells was further demonstrated by loss of anti-tumor activity in CD4 T-cell depleted mice. Intratumoral delivery of SLC using a poxviral vaccine extends the use of SLC in anti-tumor therapies and may present an effective alternative for improving the immunotherapy of cancer alone or in combination with other anti-tumor agents for clinical therapy.

The CC chemokine ligand 3 regulates CD11c+CD11b+CD8alpha- dendritic cell maturation and activation following viral infection of the central nervous system: implications for a role in T cell activation

The role of CC chemokine ligand 3 (CCL3) in activation of dendritic cells (DCs) following mouse hepatitis virus (MHV) infection of the central nervous system (CNS) was examined. The results indicate that CCL3 participates in an effective host response to MHV infection by contributing to CD11c⁺CD11b⁺CD8α⁻ DC maturation, activation, and migration to cervical lymph nodes (CLN). Diminished CD8α⁻ DC activation correlated with reduced IFN-γ expression by virus-specific T cells accompanied by increased IL-10 production suggesting that CCL3 contributes to an effective host response to viral infection by enhancing the T cell activation potential of DC.

Chemokine regulation of naïve T cell traffic in health and disease

A central feature of the immune response is the precise spatio-temporal convergence of T cells and antigen presenting cells (APC) in particular microenvironments within secondary lymphoid organs (SLO). CCR7 and its ligands CCL19 and CCL21 have been identified as the gatekeepers for both naïve T lymphocytes and dendritic cells (DC) to these defined anatomical compartments. A new perception on the regulation of lymphocyte traffic in lymph nodes (LN) has come from observations that sphingosine-1-phosphate (S1P) receptor agonists affect T cell entry and exit from these organs. Recent developments in intravital microscopy (IVM) techniques reveal unexpected autonomous random motion of lymphocytes within secondary lymphoid tissues, and provoke questions about the mechanisms that guide their compartmental navigation.

Defective dendritic cell migration and activation of adaptive immunity in PI3Kgamma-deficient mice

Gene-targeted mice were used to evaluate the role of the gamma isoform of phosphoinositide 3-kinase (PI3Kgamma) in dendritic cell (DC) migration and induction of specific T-cell-mediated immune responses. DC obtained from PI3Kgamma-/- mice showed a reduced ability to respond to chemokines in vitro and ex vivo and to travel to draining lymph nodes under inflammatory conditions. PI3Kgamma-/- mice had a selective defect in the number of skin Langerhans cells and in lymph node CD8alpha- DC. Furthermore, PI3Kgamma-/- mice showed a defective capacity to mount contact hypersensitivity and delayed-type hypersensitivity reactions. This defect was directly related to the reduced ability of antigen-loaded DC to migrate from the periphery to draining lymph nodes. Thus, PI3Kgamma plays a nonredundant role in DC trafficking and in the activation of specific immunity. Therefore, PI3Kgamma may be considered a new target to control exaggerated immune reactions.

Cancer immunotherapy with chemoattractant peptides

The chemokine/chemokine receptor network is an essential part of an intricate system of immunosurveillance and homeostasis, it promotes or suppresses neovascularization, affects and regulates directly or indirectly growth and metastasis of malignant cells. Numerous studies have been conducted to harness this network as therapeutic agents for cancer to redress the chemokine balance and control angiogenesis and tumour growth and metastasis. Second generation of immunotherapeutics and chemoattractant-based vaccines use chemokines and chemoattractant peptides to elicit antitumor immunity by a specific targeting and modulating subsets of effector leukocytes, including professional antigen presenting cells.

17beta-estradiol (E2) modulates cytokine and chemokine expression in human monocyte-derived dendritic cells

The effects of estrogen on the immune system are still largely unknown. We have investigated the effect of 17beta-estradiol (E(2)) on human monocyte-derived immature dendritic cells (iDCs). Short-term culture in E(2) had no effect on iDC survival or the expression of cell surface markers. However, E(2) treatment significantly increased the secretion of interleukin 6 (IL-6) in iDCs and also increased secretion of osteoprotegerin (OPG) by DCs. Furthermore, E(2) significantly increased secretion of the inflammatory chemokines IL-8 and monocyte chemoattractant protein 1 (MCP-1) by iDCs, but not the production of the constitutive chemokines thymus and activation-regulated chemokine (TARC) and macrophage-derived chemokine (MDC). However, after E(2) pretreatment the lipopolysaccharide (LPS)-induced production of MCP-1, TARC, and MDC by DCs was clearly enhanced. Moreover, mature DCs pretreated with E(2) stimulated T cells better than control cells. Finally, we found that E(2) provides an essential signal for migration of mature DCs toward CCL19/macrophage inflammatory protein 3beta (MIP3beta). In summary, E(2) may affect DC regulation of T-cell and B-cell responses, as well as help to sustain inflammatory responses. This may explain, in part, the reason serum levels of estrogen correlate with the severity of certain autoimmune diseases.

Gene expression changes in peripheral blood-derived dendritic cells following exposure to a contact allergen

A critical step in the induction of allergic contact allergy is the activation and subsequent migration of Langerhans cells (LC), an important antigen presenting dendritic cell (DC) of the skin. As the Langerhans cells migrate, they undergo a maturation process. It has been proposed that contact allergen exposure can induce DC maturation. While changes in DC gene expression profiles induced by various maturation stimuli have been explored, there are no published reports describing genomic-scale analysis of the changes induced by chemical allergen exposure. Therefore, to explore the concept of chemical allergen-induced DC maturation and to identify genes that are regulated by exposure to allergens we examined, at the transcriptional level, the effects of exposure to a contact allergen on DC. Peripheral blood-derived DC were exposed for 24 h to either 1mM or 5 mM dinitrobenzenesulfonic acid (DNBS). Changes in gene expression were analyzed using Affymetrix U95Av2 GeneChip. Comparison of mean signal values from replicate cultures revealed 173 genes that were significantly different (P < or = 0.001) between 1 mM DNBS treated and untreated control DC and 1249 significant gene changes between 5 mM DNBS treated and control DC. Real-time reverse-transcriptase polymerase chain reaction (RT-PCR) was used to evaluate the observed transcript changes for selected genes in DC derived from a second donor. Comparison of the fold-changes in transcript levels between the two platforms and donors revealed a good correlation in both direction and magnitude. RT-PCR analysis was also used to assess the allergen specificity of a selected number of genes in DC derived from a third donor. Many of the gene expression changes were found to be induced only by exposure to the allergen, DNBS, and not by exposure to a structurally similar non-allergen, benzenesulfonic acid. A number of gene expression changes induced by allergen exposure were found to be consistent with what is known of the DC maturation process, and thus provide support for the theory of contact allergen-induced DC maturation. Additionally, it is hoped that some of the transcript changes identified through this approach will be shown to be suitable for use in the development of an in vitro predictive assay for contact sensitization.