Salmonella typhimurium infection triggers dendritic cells and macrophages to adopt distinct migration patterns in vivo

The presence of an anti-bacterial T cell response and evidence of bacterial products in inflamed joints of reactive arthritis patients suggests an antigen transportation role in this disease for macrophages and dendritic cells. We have investigated the functional properties and in vivo migration of macrophages and DC after infection with Salmonella enterica serovar Typhimurium (S. typhimurium). BM-derived macrophages and DC displayed enhanced expression of costimulatory molecules (CD40 and CD86) and increased production of pro-inflammatory cytokines (TNF-alpha, IL-6 and IL-12p40) and nitric oxide after infection. Upon adoptive transfer into mice, infected DC migrated to lymphoid tissues and induced an anti-Salmonella T cell response, whereas infected macrophages did not. Infection of DC with S. typhimurium was associated with strong up-regulation of the chemokine receptor CCR7 and acquisition of responsiveness to chemokines acting through this receptor. Moreover, S. typhimurium-infected CCR7-deficient DC were unable to migrate to lymph nodes after adoptive transfer, although they did reach the spleen. Our data demonstrate distinct roles for macrophages and DC as antigen transporters after S. typhimurium infection and a dependence on CCR7 for migration of DC to lymph nodes after bacterial infection.     

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+CD8alpha- DC maturation, activation, and migration to cervical lymph nodes (CLN). Diminished CD8alpha- DC activation correlated with reduced IFN-gamma 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.     

Salmonella virulence factor SipB induces activation and release of IL-18 in human dendritic cells

Interleukin-18 (IL-18) plays an important role in innate and acquired immunity, in particular against intracellular pathogens. However, little is known about the microbial factors that trigger IL-18 secretion by dendritic cells (DCs). To determine the influence of bacterial virulence factors on the activation and release of IL-18, we infected human monocyte-derived DCs with virulence mutants of the facultative intracellular pathogen Salmonella typhimurium. Our results show that infection by S. typhimurium causes caspase-1-dependent activation of IL-18 and triggers the release of IL-18 in human DCs. The secretion of IL-18 by the DCs was closely correlated with the ability of the S. typhimurium strains to induce apoptosis. We demonstrate that activation and release of IL-18 are blocked by mutations in the Salmonella sipB gene, which encodes a virulence factor that activates caspase-1 to induce apoptosis. These findings indicate that the activation and release of IL-18 induced by bacterial virulence factors may represent one component of innate immunity against the intracellular bacteria.     

IL-21 enhances SOCS gene expression and inhibits LPS-induced cytokine production in human monocyte-derived dendritic cells

Dendritic cells (DCs) play an important role in innate and adaptive immune responses. In addition to their phagocytic activity, DCs present foreign antigens to na?ve T cells and regulate the development of adaptive immune responses. Upon contact with DCs, activated T cells produce large quantities of cytokines such as interferon-gamma (IFN-gamma) and interleukin (IL)-21, which have important immunoregulatory functions. Here, we have analyzed the effect of IL-21 and IFN-gamma on lipopolysaccharide (LPS)-induced maturation and cytokine production of human monocyte-derived DCs. IL-21 and IFN-gamma receptor genes were expressed in high levels in immature DCs. Pretreatment of immature DCs with IL-21 inhibited LPS-stimulated DC maturation and expression of CD86 and human leukocyte antigen class II (HLAII). IL-21 pretreatment also dramatically reduced LPS-stimulated production of tumor necrosis factor alpha, IL-12, CC chemokine ligand 5 (CCL5), and CXC chemokine ligand 10 (CXCL10) but not that of CXCL8. In contrast, IFN-gamma had a positive feedback effect on immature DCs, and it enhanced LPS-induced DC maturation and the production of cytokines. IL-21 weakly induced the expression Toll-like receptor 4 (TLR4) and translation initiation region (TIR) domain-containing adaptor protein (TIRAP) genes, whereas the expression of TIR domain-containing adaptor-inducing IFN-beta (TRIF), myeloid differentiation (MyD88) 88 factor, or TRIF-related adaptor molecule (TRAM) genes remained unchanged. However, IL-21 strongly stimulated the expression of suppressor of cytokine signaling (SOCS)-1 and SOCS-3 genes. SOCS are known to suppress DC functions and interfere with TLR4 signaling. Our results demonstrate that IL-21, a cytokine produced by activated T cells, can directly inhibit the activation and cytokine production of myeloid DCs, providing a negative feedback loop between DCs and T lymphocytes.     

The chemokine CCL2 is required for control of murine gastric Salmonella enterica infection

Salmonella enterica is a gram-negative intracellular pathogen that can cause a variety of diseases ranging from gastroenteritis to typhoid fever. The Typhimurium serotype causes gastroenteritis in humans; however, infection of mice results in an enteric fever that resembles human typhoid fever and has been used as a model for typhoid fever. The present study examined the role of the chemokine CCL2 in the control of Salmonella infection. Upon infection with salmonellae, mucosal expression of CCL2 is rapidly up-regulated, followed by systemic expression in the spleen. CCL2(-/-) mice became moribund earlier and had a higher rate of mortality compared to wild-type C57BL/6 mice. Moreover, CCL2(-/-) mice had significantly higher levels of bacteria in the liver compared to wild-type controls. Mucosal and serum interleukin-6 and tumor necrosis factor alpha levels were elevated in CCL2(-/-) mice compared to wild-type mice. In vitro analysis demonstrated that CCL2(-/-) macrophages infected with salmonellae resulted in dysregulated cytokine production compared to macrophages derived from wild-type mice. These data are the first to directly demonstrate CCL2 as a critical factor for immune responses and survival following S. enterica infection.     

Streptococcus pyogenes and Lactobacillus rhamnosus differentially induce maturation and production of Th1-type cytokines and chemokines in human monocyte-derived dendritic cells

Dendritic cells (DCs) are the most efficient antigen-presenting cells and thus, have a major role in regulating host immune responses. In the present study, we have analyzed the ability of Gram-positive, pathogenic Streptococcus pyogenes and nonpathogenic Lactobacillus rhamnosus to induce the maturation of human monocyte-derived DCs. Stimulation of DCs with S. pyogenes resulted in strong expression of DC costimulatory molecules CD80, CD83, and CD86 accompanied with a T helper cell type 1 (Th1) cytokine and chemokine response. S. pyogenes also induced interleukin (IL)-2 and IL-12 production at mRNA and protein levels. In addition, IL-23 and IL-27 subunits p40, p19, p28, and EBI3 were induced at mRNA level. In contrast, L. rhamnosus-stimulated DCs showed only moderate expression of costimulatory molecules and produced low levels of cytokines and chemokines. Furthermore, no production of IL-2 or IL-12 family cytokines was detected. Bacteria-induced DC maturation and especially cytokine and chemokine production were reduced when bacteria were heat-inactivated. Our results show that human monocyte-derived DCs respond differently to different Gram-positive bacteria. Although pathogenic S. pyogenes induced a strong Th1-type response, stimulation with nonpathogenic L. rhamnosus resulted in development of semi-mature DCs characterized by moderate expression of costimulatory molecules and low cytokine production.     

Asthmatic bronchial epithelium activated by the proteolytic allergen Der p 1 increases selective dendritic cell recruitment

BACKGROUND: Airway dendritic cells (DCs) are crucial for allergen-induced sensitization and inflammation in allergic asthma. After allergen challenge, an increased number of DCs is observed in airway epithelium from patients with allergy. OBJECTIVE: Because Der p 1, a cysteine protease allergen from Dermatophagoides pteronyssinus , induces chemokine production by bronchial epithelial cells (BECs), the purpose of this investigation was to evaluate the capacity of BEC exposed to Der p 1 to recruit DCs. METHODS: Chemotactic activity of BEAS-2B, a bronchial epithelial cell line, and BECs from nonatopic controls and patients with allergic asthma was evaluated on the migration of precursors, immature and mature monocyte-derived DCs (MDDCs), and CD34 + -derived Langerhans cells (LCs). RESULTS: C-C chemokine ligand (CCL)-2, CCL5, and C-X-C chemokine ligand 10 production by BEAS-2B and BEC was increased after Der p 1 exposure, whereas the proenzyme proDer p 1 devoid of enzymatic activity had no effect. Der p 1 stimulation of BEAS-2B and BEC from both groups increased significantly the recruitment of MDDC precursors, depending on CCL2, CCL5, and C-X-C chemokine ligand 10 production. In a reconstituted polarized epithelium, apical application of Der p 1 enhanced MDDC precursor migration into the epithelial layer. Moreover, Der p 1 stimulation of BEC from patients with asthma but not from controls increased the migration of LC precursors, mainly dependent on CCL20 secretion. No migration of immature and mature DCs was observed. CONCLUSION: These data confirmed that BECs participate in the homeostasis of the DC network present within the bronchial epithelium through the secretion of chemokines. In allergic asthma, upregulation of CCL20 production induced LC recruitment, the role of which remains to be determined.     

Interleukin-12 is critical for induction of nitric oxide-mediated immunosuppression following vaccination of mice with attenuated Salmonella typhimurium.

Studies from our laboratory have shown that infection of mice with an attenuated strain of Salmonella typhimurium causes a marked suppression in the capacity of splenocytes to generate an in vitro plaque-forming cell (PFC) response to sheep erythrocytes. The suppression has been shown to be mediated by mature, adherent macrophages (Mphis) and nonadherent, precursor Mphis. Nitric oxide has been identified as the suppressor factor. The present study investigated the role of interleukin-12 (IL-12) in the generation of nitric oxide-mediated immunosuppression in this model. Salmonella inoculation resulted in marked suppression of PFC responses and high levels of nitrite production. When mice were treated with anti-IL-12 prior to inoculation, nitrite levels in splenocyte cultures were reduced by 75% and the suppression of PFC responses was prevented. The nonadherent splenocyte fraction from Salmonella-inoculated mice, which contains precursor Mphis and is weakly immunosuppressive, was treated with IL-12 in vitro. IL-12 augmented the capacity of this fraction to suppress PFC responses by normal splenocytes in a coculture system. Additionally, IL-12 induced nitrite and gamma interferon (IFN-gamma) production in a dose-dependent manner. Treatment with anti-IFN-gamma blocked nitrite production and suppression, indicating that IFN-gamma is an important intermediary in the pathway of IL-12-induced immunosuppression. These results indicate that IL-12 is critical for the induction of nitric oxide-mediated immunosuppression following S. typhimurium inoculation and, through its ability to stimulate IFN-gamma production, can induce nitric oxide-producing suppressor Mphis.     

The Lymphoid Chemokine CCL21 Enhances the Cytotoxic T Lymphocyte‐Inducing Functions of Dendritic Cells

The potential use of lymphoid chemokines to generate a dendritic cell (DC) cancer vaccine is not yet clear. We investigated the effect of lymphoid chemokines on DC function and on the production of effective cytotoxic T lymphocytes (CTLs) for application of cancer vaccine using monocyte‐derived mature DCs (mDCs) prestimulated with lymphoid chemokines. mDCs exposed to a secondary lymphoid organ chemokine (SLC/CCL21) dramatically induced CTL response by increasing cytolytic activity without any significant alterations on expression of cell surface markers (e.g. CD80, CD83, CD86 and CCR7) or on the production of cytokines (e.g. IL‐12p70, IL‐10 and IL‐23). Interestingly, mDCs prestimulated with CCL21 showed higher levels of CXCL10 (IP‐10) production, but not the production of CCL22, compared with untreated mDCs. IP‐10 treatment during CTL generation with DCs dramatically enhanced tumour‐specific CTL response compared with untreated CTLs, and these enhanced CTL‐inducing functions of CCL21‐treated DCs were inhibited by anti‐IP‐10 treatment. Taken together, our data suggested an important role of the lymphoid‐endothelium‐associated chemokine, CCL21, on DCs in the induction of CTL responses.     

Airway epithelial cells release MIP-3alpha/CCL20 in response to cytokines and ambient particulate matter

The initiation and maintenance of airway immune responses in Th2 type allergic diseases such as asthma are dependent on the specific activation of local airway dendritic cells (DCs). The cytokine microenvironment, produced by local cells, influences the recruitment of specific subsets of immature DCs and their subsequent maturation. In the airway, DCs reside in close proximity to airway epithelial cells (AECs). We examined the ability of primary culture human bronchial epithelial cells (HBECs) to synthesize and secrete the recently described CC-chemokine, MIP-3alpha/CCL20. MIP-3alpha/CCL20 is the unique chemokine ligand for CCR6, a receptor with a restricted distribution. MIP-3alpha/CCL20 induces selective migration of DCs because CCR6 is expressed on some immature DCs but not on CD14+ DC precursors or mature DCs. HBECs were stimulated with pro-inflammatory cytokines tumor necrosis factor-alpha and interleukin (IL)-1beta or, because of their critical role in allergic diseases, IL-4 and IL-13. Cells were also exposed to small size-fractions of ambient particulate matter. Each of these stimuli induced MIP-3alpha/CCL20 gene and protein expression. Moreover, these agents upregulated mitogen-activated protein kinase pathways in HBECs. Inhibition of the ERK1/2 pathway or p38 reduced cytokine-induced MIP-3alpha/CCL20 expression. These data suggest a mechanism by which AEC may facilitate recruitment of DC subsets to the airway.     

CpG-C ISS-ODN activation of blood-derived B cells from healthy and chronic immunodeficiency virus-infected macaques

Cytosine-phosphate-guanine class C (CpG-C) immunostimulatory sequence oligodeoxynucleotides (ISS-ODNs) activate human B cells and dendritic cells (DCs), properties that suggest potential use as a novel adjuvant to enhance vaccine efficacy. After demonstrating that the CpG-C ISS-ODN C274 activates macaque DCs, we examined in vitro activation of macaque B cells by C274 as a prelude to evaluation of this molecule as an adjuvant in the testing of candidate human immunodeficiency virus vaccines in the rhesus macaque-simian immunodeficiency virus (SIV) model. C274 induced macaque CD20(+) B cells to proliferate more strongly than CD40 ligand or CpG-B ISS-ODN. C274 enhanced B cell survival; increased viability was most evident after 3-7 days of culture. Increased expression of CD40, CD80, and CD86 by B cells was apparent within 24 h of exposure to C274 and persisted for up to 1 week. C274-stimulated, B cell-enriched and peripheral blood mononuclear cell suspensions from na?ve and immunodeficiency virus-infected monkeys secreted several cytokines [e.g., interleukin (IL)-3, IL-6, IL-12, interferon-alpha] and chemokines [e.g., monocyte chemoattractant protein-1/CC chemokine ligand 2 (CCL2), macrophage-inflammatory protein-1alpha/CCL3, IL-8/CXC chemokine ligand 8]. In comparison, exposure of macaque B cells to SIV had minimal impact on surface phenotype, despite inducing cytokine and chemokine production in cells from infected and uninfected animals. These observations emphasize the need to identify strategies to optimally boost immune function, as immunodeficiency viruses themselves only partially activate B cells and DCs. The ability of C274 to stimulate B cells and DCs in healthy and infected monkeys suggests its possible use as a broad-acting adjuvant to be applied in the rhesus macaque model for the development of preventative and therapeutic vaccines.     

IL-17A is produced by Th17, gammadelta T cells and other CD4- lymphocytes during infection with Salmonella enterica serovar Enteritidis and has a mild effect in bacterial clearance

T(h)17 cells represent a new pro-inflammatory T(h) cell lineage distinct from T(h)1 and T(h)2 cells. T(h)17 cells have been shown to be involved in extracellular bacterial infection but their role in intracellular infection remains unclear. We found antigen-specific IL-17A production during a systemic infection of mice with the facultative intracellular bacterium Salmonella enterica serovar Enteritidis (S. Enteritidis) and examined the function and cellular source of IL-17A during the adaptive immune response to S. Enteritidis. Infected IL-17A-/- mice survived completely after inoculation with the highest infection dose found to be sub-lethal for wild-type (WT) C57BL/6 mice. However, at 20 and 80 days post-infection (d.p.i.), we repeatedly found mildly elevated bacterial burden in spleen and liver of IL-17A-/- mice as compared with WT mice. Overall, IL-17A-/- mice showed reduced clearance of S. Enteritidis. S. Enteritidis-specific IL-17A production was induced in splenocytes and lymph node cells of infected WT mice at both time points, 20 and 80 d.p.i. Classical CD4+ T(h)17 cells developed upon infection with Salmonella. CD4- gammadelta TCR+ and CD4- gammadelta TCR- cells were found to be additional IL-17A-producing cell populations. In infected IL-17A-/- mice, a normal T(h)1 cytokine profile was observed consistent with the overall subtle phenotype. Nevertheless, in the absence of IL-17A, recruitment of neutrophils and delayed-type hypersensitivity (DTH) reactivity was significantly compromised. Our data indicate that IL-17A responses are induced by Salmonella and mildly contribute to protective immunity during S. Enteritidis infection. Thus, IL-17A complements the IL-12/IFN-gamma axis which is essential for protective immunity against salmonellosis in mice and men.     

Novel roles of osteopontin and CXC chemokine ligand 7 in the defence against mycobacterial infection

Granulocyte-macrophage colony-stimulating factor (GM-CSF)-induced human monocyte-derived macrophage (GM-Mphi) or macrophage CSF (M-CSF)-induced human monocyte-derived Mphi (M-Mphi) are distinct in terms of the resistance to Mycobacterium tuberculosis. To elucidate the role of molecules involved in the functional differences between these Mphis, we investigated the gene expression profiles using microarray. After culture of CD14+ monocytes with CSFs, Mphis were cultured with or without bacillus Calmette-Guérin (BCG) (GM-Mphi-BCG and M-Mphi-BCG). The gene expression profiles from these cells were compared. Chemokines highly expressed in M-Mphis were selected and evaluated for anti-mycobacterial activity and superoxide production. FN1 and FCGR2B were the most up-regulated genes in GM-Mphi and M-Mphi, respectively. After stimulation with BCG, three chemokine genes (Osteopontin (SPP1), CXC chemokine ligand 7 (CXCL7) and CC chemokine ligand 11 (CCL11)) were highly expressed in M-Mphi-BCG when compared to those in GM-Mphi-BCG. A significantly increased resistance to M. tuberculosis H37Ra was observed after the stimulation of GM-Mphi with SPP1 or CXCL7. Superoxide production levels of SPP1- or CXCL7-stimulated GM-Mphis were higher than those of GM-Mphis without stimulation. These results indicate that both SPP1 and CXCL7 might have a role in the resistance against mycobacteria, at least in part, through augmenting reactive oxygen intermediate production in Mphis.     

Streptococcus pyogenes activates human plasmacytoid and myeloid dendritic cells

Human peripheral blood contains two major dendritic cell (DC) populations, namely CD11c(-)CD123+ plasmacytoid DCs (PDCs) and CD11c+CD123(-) myeloid DCs (MDCs). Although the activation of these DC types by various TLR ligands has been relatively well-characterized, less is known about the ability of whole live bacteria to induce PDC and MDC activation. In the present report, we have compared the activation of human PDCs and MDCs in response to major human bacterial pathogen Streptococcus pyogenes (group A streptococci) and influenza A virus. S. pyogenes stimulation resulted in the maturation of both DC types, as evidenced by enhanced expression of costimulatory molecules and production of proinflammatory cytokines and chemokines. Furthermore, S. pyogenes-stimulated PDCs and MDCs activated na?ve CD4+ T cells and enhanced their Th1 cytokine production. Influenza A virus infection induced rapid PDC activation, whereas MDCs were extremely sensitive to influenza A virus-induced cell death. The most significant differences between DC types were seen in the production of IL-10 and IL-12, which were only produced by S. pyogenes-stimulated MDCs. Although S. pyogenes was able to induce PDC activation, only influenza A virus infection resulted in detectable IFN-alpha production. Our results show that depending on the infecting microbe, the functions of PDCs and MDCs may be partially overlapping, suggesting a considerable flexibility of the human DC system.     

Salmonella infection of afferent lymph dendritic cells

The interactions of Salmonella enterica subspecies I serotype Abortusovis (S. Abortusovis) with ovine afferent lymph dendritic cells (ALDCs) were investigated for their ability to deliver Maedi visna virus (MVV) GAG p25 antigens to ALDCs purified from afferent lymph. Salmonellae were found to enter ALDC populations by a process of cell invasion, as confirmed by electron and confocal microscopy. This led to phenotypical changes in ALDC populations, as defined by CD1b and CD14 expression. No differences in the clearance kinetics of intracellular aroA-negative Salmonella from CD1b+ CD14lo and CD1b+ CD14(-) ALDC populations were noted over 72 h. ALDCs were also shown to present MVV GAG p25 expressed by aroA-negative S. Abortusovis to CD4+ T lymphocytes. Thus, the poor immune responses that Salmonella vaccines elicited in large animal models compared with mice are neither a result of an inability of Salmonella to infect large animal DCs nor an inability of these DCs to present delivered antigens. However, the low efficiency of infection of ALDC compared with macrophages or monocyte-derived DCs may account for the poor immune responses induced in large animal models.     

Salmonella typhimurium-induced cytokine production and surface molecule expression by murine macrophages.

The influence of Salmonella enterica serovar Typhimurium (S. typhimurium) on co-stimulatory molecule expression, cytokine production and induction of nitric oxide synthase (iNOS) by murine macrophages (Mphi), as well as the influence of the phoP locus on these aspects of S. typhimurium-Mphi interaction, was characterized. Pulsing Mphi with S. typhimurium resulted in increased surface expression of MHC-I, MHC-II, CD86 and CD54. Furthermore, co-incubating S. typhimurium with Mphi resulted in interleukin (IL)-12p40, IL-6 and tumor necrosis factor-alpha production as well as iNOS induction while IL-12p70 was not detectable. Finally, although phoP did not influence the level of surface molecule expression or cytokine production by S. typhimurium-pulsed Mphi phoP did influence the level of iNOS induction. Together these data show that S. typhimurium interaction with Mphi activates these cells in ways that may enhance their ability to productively stimulate Salmonella-specific T cells following phagocytic processing and presentation of Salmonella antigens.     

Tumour-loaded α-type 1-polarized dendritic cells from patients with chronic lymphocytic leukaemia produce a superior NK-, NKT- and CD8+ T cell-attracting chemokine profile

Tumour-loaded dendritic cells (DCs) from patients with chronic lymphocytic leukaemia (CLL) matured using an α-type 1-polarized DC cocktail (IL-1β/TNF-α/IFN-α/IFN-γ/poly-I:C;αDC1) were recently shown to induce more functional CD8(+) T cells against autologous tumour cells in vitro than DCs matured with the 'standard' cocktail (IL-1β/TNF-α/IL-6/PGE(2) ;PGE(2) DCs). However, the ability of vaccine DCs to induce a type 1-polarized immune response in vivo probably relies on additional features, including their ability to induce a CXCR3-dependent recruitment of NK cells into vaccine-draining lymph nodes. Moreover, their guiding of rare tumour-specific CD8(+) T cells to sites of DC-CD4(+) T cell interactions by secretion of CCL3 and CCL4 is needed. We therefore analysed the chemokine profile and the lymphocyte-attracting ability in vitro of monocyte-derived PGE(2) DCs and αDC1s from patients with CLL. αDC1s produced much higher levels of CXCR3 ligands (CXCL9/CXCL10/CXCL11) than PGE(2) DCs. Functional studies further demonstrated that αDC1s were superior recruiters of both NK and NKT cells. Moreover, αDC1s produced higher levels of CCL3/CCL4 upon CD40 ligation. These findings suggest that functional αDC1s, derived from patients with CLL, produce a desirable NK-, NKT- and CD8(+) T cell-attracting chemokine profile which may favour a guided and Th1-deviated priming of CD8(+) T cells, supporting the idea that αDC1-based vaccines have a higher immunotherapeutic potential than PGE(2) DCs.     

Human epithelial cells trigger dendritic cell mediated allergic inflammation by producing TSLP

Whether epithelial cells play a role in triggering the immune cascade leading to T helper 2 (T(H)2)-type allergic inflammation is not known. We show here that human thymic stromal lymphopoietin (TSLP) potently activated CD11c(+) dendritic cells (DCs) and induced production of the T(H)2-attracting chemokines TARC (thymus and activation-regulated chemokine; also known as CCL17) and MDC (macrophage-derived chemokine; CCL22). TSLP-activated DCs primed na?ve T(H) cells to produce the proallergic cytokines interleukin 4 (IL-4), IL-5, IL-13 and tumor necrosis factor-alpha, while down-regulating IL-10 and interferon-gamma. TSLP was highly expressed by epithelial cells, especially keratinocytes from patients with atopic dermatitis. TSLP expression was associated with Langerhans cell migration and activation in situ. These findings shed new light on the function of human TSLP and the role played by epithelial cells and DCs in initiating allergic inflammation.     

Migration of Salmonella typhimurium --harboring bone marrow--derived dendritic cells towards the chemokines CCL19 and CCL21

Macrophages are considered as main cellular target encountered by the facultative intracellular bacterium Salmonella typhimurium. However, in orally infected mice these pathogens are first internalized by dendritic cells (DCs) that are located in the subepithelial dome of Peyer's patches. Moreover, DCs can penetrate the intestinal epithelium to sample bacteria. Here, we examined the interaction of Salmonella with bone marrow-derived DCs (BM-DCs). In order to study the role of DCs as vehicles for the dissemination of Salmonella, an in vitro model was established. In this model, Salmonella -activated BM-DCs enhanced surface expression of MHC class II and co-stimulatory molecules. We found that, upon maturation, BM-DCs upregulated chemokine receptor 7 (CCR7) mRNA and surface molecule expression. Salmonella -exposed DCs as well as mature DCs, but not immature DCs, were recruited towards the CC chemokines CCL19 and CCL21, two ligands of CCR7. The maturation process of DCs did neither require bacterial internalization nor viability. About one third of the migrated BM-DCs harbored intracellular bacteria, whereas the remaining two third did not contain bacteria. Salmonella, but not an apathogenic E. coli laboratory strain was capable to survive within BM-DCs. Taken together, our data implicate that DCs are first activated and subsequently utilized as carriers by Salmonella.