The secretions products from invading cercariae of S. japonicum (0-3hRP) restrain mouse dendritic cells to mature

Schistosomiasis is a water-borne infection caused mainly by human schistosomes including Schistosoma mansoni (S. mansoni) and Schistosoma japonicum (S. japonicum). In the infected host, immune events in the skin appear to have an important initiating role in determining the type, and guiding the magnitude, of the ensuing acquired immune response. The previous studies of S. mansoni showed that dendritic cells (DCs) prime Th2 response after activating with products released by schistosome larvae (material released in the first 3 h after transformation, 0–3hRP). Therefore, it is interesting to know whether 0–3hRP from S. japonicum also activate DC and induce Th2 immune response. Here, we report 0–3hRP of S. japonicum failed to stimulate the maturation of bone marrow-derived DCs (BM-DCs), while soluble antigen of the body of cercariae preparation (SCAP) induced BM-DCs to mature which can be weakened by 0–3hRP. Moreover, using an in vitro ovalbumin peptide-restricted priming assay, DCs treated with 0–3hRP failed to induce T cells to secrete more cytokines than the negative control group by CD4⁺ T cells from DO11.10 transgenic mice, while DCs treated with SCAP upregulated secretions of IFN-γ and IL-17A, but downregulated IL-4. Importantly, BM-DCs treated with 0–3hRP plus SCAP induced BM-DCs selective mature which drive Th2-type polarized response. Our in vitro results agree with the findings of in vivo studies by inoculation of DO11.10 mice with different stimulus-activated DCs pulsed with ovalbumin peptide. Our data demonstrate that the secretions from invading cercariae of S. japonicum (0–3hRP) impaired DCs to mature, which is potentially allowing the parasite to negotiate the immune recognition and attack.     

Tumour necrosis factor-alpha but not lipopolysaccharide enhances preference of murine dendritic cells for Th2 differentiation

Using murine spleen-derived dendritic cells (DC) and DO11.10 T cells specific for ovalbumin (OVA), the influences of maturational condition and antigen dose on the capability of DC to induce helper T-cell (Th) differentiation were analysed. Immature DC (iDC) with high- or low-dose OVA(323-339) predominantly induced Th1 or Th2 responses in DO11.10 T cells, respectively. DC matured by tumour necrosis factor-alpha (TNF/DC) induced a significantly higher Th2 response in the presence of low-dose OVA(323-339) than iDC and DC matured by lipopolysaccharide (LPS) (LPS/DC). In the presence of high-dose OVA(323-339), LPS/DC induced significantly lower levels of Th1 response than iDC. Under these conditions no difference in the Th1 response was noted between TNF/DC and iDC. The enhanced capability of TNF/DC with a low-dose antigen for Th2 polarization and the decreased preference of LPS/DC with a high-dose antigen to Th1 polarization were not related to the amount of IL-12 produced in these cultures. These results demonstrate for the first time that TNF/DC with a low-dose antigen are potent inducers of Th2 differentiation.     

The antigen dose determines T helper subset development by regulation of CD40 ligand

Although the amount of antigen and the strength of T cell stimulation have been suggested to regulate Th1 vs. Th2 polarization, it remains unclear how the antigen dose and the strength of signal is detected by the T cell and translated into differential cytokine production. Using co-cultures of dendritic cells (DC) and ovalbumin (OVA)-specific CD4+ T cells obtained from RAG-2)(-/-) DO11.10 mice, we show here that high-dose antigen induced Th1 development by up-regulation of CD40 ligand (CD40L), whereas low-dose antigen stimulation failed to induce CD40L and promoted Th2 development. CD40-CD40L interaction was essential for IL-12 production by DC. In the absence, de novo IL-4 production by T cells and autocrine Th2 development was induced. Furthermore, our results demonstrate that LFA-1/ ICAM interaction promotes Th1 differentiation by lowering the antigen dose required for CD40L up-regulation. Thus, we propose that (1) peptide-MHC density and (2) accessory molecules such as LFA-1 determine T helper polarization by regulation of CD40L.     

A novel bulk-culture method for generating mature dendritic cells from mouse bone marrow cells

We established a novel culture method for generating dendritic cells (DC) from mouse bone marrow (BM) cells. Unfractionated bulk BM cells were cultured in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) for 5-7 days and a DC population was isolated by gradient centrifugation with 14.5% (w/v) metrizamide. Through this method, 30-40 x 10(6)/mouse DC with 85-95% purity was obtained on day 7; this yield was higher than those of conventional DC generated by Inaba's method either with GM-CSF alone (conventional-GM DC) or GM-CSF and IL-4 (conventional-GM/4 DC). Bulk-cultured DC have a more matured phenotype than both conventional-GM and -GM/4 DC as shown by higher expression of CD86, MHC class II and CD40. Functional analyses reveal that (1) bulk-DC show less ability in endocytosis than conventional-GM DC and are comparable in IL-12 p70 production with conventional-GM and -GM/4 DC. (2) Bulk-DC exhibit stronger stimulatory capacity in allogeneic T-cell proliferation than conventional DC. (3) By using ovalbumin (OVA) and OVA-specific T-cell receptor (TCR) transgenic mice (DO11.10) system, OVA protein-loaded bulk-DC stimulated CD4 T cells of DO11.10 mice more than conventional-GM DC and comparable with conventional-GM/4 DC. (4) Furthermore, OVA peptide-pulsed bulk-DC stimulated CD4 T cells more than conventional-GM and -GM/4 DC. These data indicate that bulk-DC are functionally more mature than conventional DC. Taken together, bulk-culture method is a simple technique for generating functionally mature BM-DC in large quantities and high purity.     

Induction of Th2 cell differentiation in the primary immune response: dendritic cells isolated from adherent cell culture treated with IL-10 prime naive CD4+ T cells to secrete IL-4

A number of observations indicate that exposure to IL-4 is essential for the priming of Th2-type effector T cells and that exposure to IL-12 is essential for the priming of Th1-type effector T cells. However, the initial source of IL-4 in the early immune response has not been clearly identified. Dendritic cells (DC) are the most potent antigen- presenting cells (APC) in priming naive T cells. In this report, we show that DC exposed to IL-10 may play an important role in the priming of IL-4-secreting cells in the early immune response. DC isolated from splenic adherent cell cultures treated with rIL-10 (IL-10-DC) primed naive ovalbumin (OVA)-TCR transgenic T cells to secrete IL-4 upon re- stimulation with OVA and splenic APC. By contrast, DC isolated from rIL- 12, rIL-4 or control treated cultures induced almost exclusively Th1- type effector T cells. IL-4 secretion was detected in the primary cultures of IL-10-DC plus naive CD4+ T cells and the priming of IL-4- secreting T cells by IL-10-DC was dependent on endogenous IL-4 production in the priming culture since anti-IL-4 neutralizing antibody completely abrogated the priming of IL-4-secreting cells. Anti-B7-2 but not anti-B7-1 inhibited the ability of IL-10-DC to prime T cells to secrete IL-4. Furthermore, the ability of IL-10 DC to prime for IL-4- secreting T cells was closely related to the down-regulation of CD40 ligand-mediated IL-12 p70 production by DC in the primary cultures and was markedly reduced by adding exogenous IL-12 to the priming cultures. Thus, our findings indicate that early immunologic events that drive Th2 differentiation involve the effects of IL-10 on DC.      

Th1 cells induce and Th2 inhibit antigen-dependent IL-12 secretion by dendritic cells

Dendritic cells are the most relevant antigen-presenting cells (APC) for presentation of antigens administered in adjuvant to CD4⁺ T cells. Upon interaction with antigen-specific T cells, dendritic cells (DC) expressing appropriate peptide-MHC class II complexes secrete IL-12, a cytokine that drives Th1 cell development. To analyze the T cell-mediated regulation of IL-12 secretion by DC, we have examined their capacity to secrete IL-12 in response to stimulation by antigen-specific Th1 and Th2 DO11.10 TCR-transgenic cells. These cells do not differ either in TCR clonotype or CD40 ligand (CD40L) expression. Interaction with antigen-specific Th1, but not Th2 cells, induces IL-12 p40 and p75 secretion by DC. The induction of IL-12 production by Th1 cells does not depend on their IFN-γ secretion, but requires direct cell-cell contact mediated by peptide/MHC class II-TCR and CD40-CD40L interactions. Th2 cells not only fail to induce IL-12 secretion, but they inhibit its induction by Th1 cells. Unlike stimulation by Th1, inhibition of IL-12 production by Th2 cells is mediated by soluble molecules, as demonstrated by transwell cultures. Among Th2-derived cytokines, IL-10, but not IL-4 inhibit Th1-driven IL-12 secretion. IL-10 produced by Th2 cells appears to be solely responsible for the inhibition of Th1-induced IL-12 secretion, but it does not account for the failure of Th2 cells to induce IL-12 production by DC. Collectively, these results demonstrate that Th1 cells up-regulate IL-12 production by DC via IFN-γ-independent cognate interaction, whereas this is inhibited by Th2-derived IL-10. The inhibition of Th1-induced IL-12 production by Th2 cells with the same antigen specificity represents a novel mechanism driving the polarization of CD4⁺ T cell responses.     

Role of Macrophage Migration Inhibitory Factor in the Th2 Immune Response to Epicutaneous Sensitization

We examined the role of macrophage migration inhibitory factor (MIF) in the generation of the Th2 response using MIF-deficient mice in a model of epicutaneous sensitization to ovalbumin. Lymph node cells from sensitized MIF-deficient mice produce lower levels of Th2 cytokines after antigen challenge when compared to their wild-type counterparts. Sensitized mice lacking MIF show less pulmonary inflammation after intranasal antigen exposure. Mice deficient in CD74, the MIF receptor, also are unable to generate an inflammatory response to epicutaneous sensitization. Examination of the elicitation phase of the atopic response using DO11.10 OVA TCR transgenic animals shows that T cell proliferation and IL-2 production are strongly impaired in MIF-deficient T cells. This defect is most profound when both T cells and antigen-presenting cells are lacking MIF. These data suggest that MIF is crucial both for the sensitization and the elicitation phases of a Th2-type immune response in allergic disease.     

Eradication of Cryptosporidium parvum infection by mice with ovalbumin-specific T cells

CD154 is necessary for mice to clear a Cryptosporidium parvum infection, but whether this ligand has to be expressed on T cells with specificity for C. parvum has not been determined. We infected DO11.10 (ovalbumin specific) T-cell receptor transgenic mice that had been bred to a RAG(-/-) background with C. parvum and found that the infection was cleared within 6 weeks, while RAG(-/-) controls were unable to clear C. parvum infection. Recovery was accompanied by an increase in the number of splenic T cells with the CD44(high) phenotype that characterizes memory cells. To determine whether a C. parvum-infected environment sufficed to activate transgenic T cells, we reconstituted C. parvum-infected BALB/c SCID mice with DO11.10 RAG(-/-) splenocytes. Fecal excretion of C. parvum antigen ceased in the 12 weeks following the adoptive transfer, unless the mice were also injected with tolerizing doses of ovalbumin. DO11.10 T cells were found in the submucosa of C. parvum-infected, but not uninfected, BALB/c SCID hosts within 48 h of injection. The transferred DO11.10 T cells divided and acquired a CD44(high) memory phenotype in C. parvum-infected, but not uninfected, recipients. DO11.10 splenocytes from CD154 knockout donors failed to clear a C. parvum infection, confirming a requirement for CD154 in recovery. In vitro, the DO11.10 cells did not proliferate in response to C. parvum antigen, and a tBlast GenBank search revealed no matches between the ovalbumin peptide and C. parvum DNA sequences. C. parvum-infected SCID mice given RAG(-/-) CD8(+) T cells with a Listeria-specific transgene did not recover from C. parvum infection. Our data suggest that antigen-nonspecific CD4(+) T-cell effector mechanisms in combination with the innate arm of the immune system are sufficient for the eradication of C. parvum infection.     

CD40L-expressing CD8 T cells prime CD8alpha(+) DC for IL-12p70 production

CD8alpha(+) DC are implicated as the principle DC subset for cross-presentation and cross-priming of cytotoxic CD8 T cell responses. In this study, we demonstrate another unique facet of the CD8alpha(+) DC and CD8 T cell relationship, by showing that CD8 T cells reciprocally activate CD8alpha(+) DC, but not CD8alpha(-) DC, for IL-12p70 production, the key Th1-promoting cytokine. This effect was observed during an antigen-specific interaction between DC and activated CD8 T cells, along with secondary TLR stimulation of DC by LPS. Activated CD8 T cells use a combination of IFN-gamma and CD40L, which is rapidly up-regulated post-stimulation, to prime DC for IL-12p70 production during an antigen-specific response. Our results suggest that the interaction between CD8alpha(+) DC and antigen-primed CD8 T cells may form an important component of Th1-mediated immunity through the induction of IL-12p70.     

Regulation of autoimmune diabetes by non-islet-specific T cells - a role for the glucocorticoid-induced TNF receptor

Diabetogenic BDC2.5 CD4 T cells induce diabetes when injected into NOD.scid mice. However, when co-transferred with the OVA-specific DO11.10 CD4 T cells, BDC2.5 T cells failed to cause diabetes. This inhibition depended upon the stimulation of DO11.10 T cells only with soluble OVA, which skewed their differentiation to a Th2-type pattern of cytokine secretion in vivo. However, in vivo neutralization of IL-4, IL-10 or TGF-beta using monoclonal antibodies did not prevent the inhibition whereas treatment with an antibody against the glucocorticoid-induced TNF receptor abrogated the protection from disease. In the protected mice, the diabetogenic T cells could be isolated from their spleens and shown to transfer diabetes when injected into new NOD.scid recipients. Thus, the inhibition took place without the physical or functional elimination of the diabetogenic T cells.     

Interferon-beta mediates opposing effects on interferon-gamma-dependent Interleukin-12 p70 secretion by human monocyte-derived dendritic cells

Interferon-beta (IFN-beta) exposure during tumour necrosis factor-alpha (TNF-alpha)-induced human monocyte-derived dendritic cell (DC) maturation augments the capacity of DC to promote the generation of T helper 1 (Th1) cells, while IFN-beta exposure during naive Th cell stimulation inhibits Th1 cell generation (Nagai et al., J Immunol, 2003 171:5233-43). Investigating these contradictory outcomes of IFN-beta exposure, we find that isolated DC matured with both TNF-alpha and IFN-beta secrete more IL-12 p70 upon CD40L stimulation than DC matured with TNF-alpha alone. mAb blocking studies indicate that the basis for this enhanced IL-12 p70 production is augmentation of two successive CD40-dependent autocrine pathways in the DC: (1) a pathway in which low levels of IL-12 p70, IL-27, IL-18 and, possibly, IL-23 act to mediate autocrine induction of DC IFN-gamma secretion; and (2) an IFN-gamma-initiated autocrine pathway promoting optimal DC IL-12 p70 secretion. In contrast to the IL-12 p70 promoting effects of IFN-beta during DC maturation, IFN-beta pre-treatment before CD40L stimulation was found to inhibit IFN-gamma-mediated enhancement of DC IL-12 p70 secretion. Thus, IFN-beta exposure during TNF-alpha-mediated DC maturation may promote Th1 polarization by increasing DC IL-12 p70 secretion, through enhancement of autocrine-acting IFN-gamma production by the DC. Moreover, IFN-beta exposure during naive Th cell stimulation may inhibit Th1 cell generation by blocking the IFN-gamma-induced signals required for optimal CD40L-induced DC IL-12 p70 secretion. IFN-beta pre-treatment was also observed to inhibit CD40L-induced DC IL-23 secretion. Our findings may account for some of the beneficial effects of IFN-beta therapy in patients with relapsing remitting multiple sclerosis.     

Nontoxic Shiga toxin derivatives from Escherichia coli possess adjuvant activity for the augmentation of antigen-specific immune responses via dendritic cell activation

Shiga toxin (Stx) derivatives, such as the Stx1 B subunit (StxB1), which mediates toxin binding to the membrane, and mutant Stx1 (mStx1), which is a nontoxic doubly mutated Stx1 harboring amino acid substitutions in the A subunit, possess adjuvant activity via the activation of dendritic cells (DCs). Our results showed that StxB1 and mStx1, but not native Stx1 (nStx1), resulted in enhanced expression of CD86, CD40, and major histocompatibility complex (MHC) class II molecules and, to some extent, also enhanced the expression of CD80 on bone marrow-derived DCs. StxB1-treated DCs exhibited an increase in tumor necrosis factor alpha and interleukin-12 (IL-12) production, a stimulation of DO11.10 T-cell proliferation, and the production of both Th1 and Th2 cytokines, including gamma interferon (IFN-gamma), IL-4, IL-5, IL-6, and IL-10. When mice were given StxB1 subcutaneously, the levels of CD80, CD86, and CD40, as well as MHC class II expression by splenic DCs, were enhanced. The subcutaneous immunization of mice with ovalbumin (OVA) plus mStx1 or StxB1 induced high titers of OVA-specific immunoglobulin M (IgM), IgG1, and IgG2a in serum. OVA-specific CD4+ T cells isolated from mice immunized with OVA plus mStx1 or StxB1 produced IFN-gamma, IL-4, IL-5, IL-6, and IL-10, indicating that mStx1 and StxB1 elicit both Th1- and Th2-type responses. Importantly, mice immunized subcutaneously with tetanus toxoid plus mStx1 or StxB1 were protected from a lethal challenge with tetanus toxin. These results suggest that nontoxic Stx derivatives, including both StxB1 and mStx1, could be effective adjuvants for the induction of mixed Th-type CD4+ T-cell-mediated antigen-specific antibody responses via the activation of DCs.     

Schistosome larvae stimulate macrophage cytokine production through TLR4-dependent and -independent pathways

Exposure of the mammalian host to infective larvae of Schistosomamansoni causes an acute inflammatory response in the skin andthe activation of several cell types of the innate immune responseincluding macrophages. Using an in vitro model of macrophageactivation, we show that schistosome larvae possess moleculesthat directly stimulate both thioglycollate-elicited macrophages(tM) and IFN-activated tM in vitro to produce several cytokinesincluding IL-6, IL-12p40 and IL-10. The parasite-derived moleculesare enriched within the material released by the parasite followingtransformation [0- to 3-h released larval preparation (0-3hRP)]but not within soluble preparations of whole larvae. Cytokineproduction was maintained in the presence of polymyxin B, confirmingthat contaminating endotoxin was not responsible. IL-12p40 andIL-10 production was much lower by cells from C3H/HeJ mice,which have defective Toll-like receptor 4 (TLR4), but IL-6 productionwas unaffected. Experiments using TLR4^–/– mice confirmedthat IL-12p40 production by tM in response to 0-3hRP was partlydependent upon functional TLR4, whereas IL-6 production wasentirely independent. In contrast, tM from MyD88^–/–mice failed to secrete either IL-12p40 or IL-6, underlininga pivotal role of TLR signalling in cytokine production by macrophagesin response to stimulation with 0-3hRP. Finally, we show thatglycan components of 0-3hRP are required for optimal cytokineproduction since protease treatment of 0-3hRP had no effecton IL-12p40 production and only a slight effect on IL-6, whilesodium meta-periodate treatment almost completely abolishedproduction of both cytokines.     

Dendritic cells from Chlamydia-infected mice show altered Toll-like receptor expression and play a crucial role in inhibition of allergic responses to ovalbumin

Our previous study has shown that Chlamydia lung infection can inhibit local eosinophilic inflammation induced by allergen sensitization and challenge, which is correlated with altered cytokine production. In the present study, we examined the role played by dendritic cells (DC) in chlamydial infection-mediated modulation of allergic responses. The results showed that DC freshly isolated from Chlamydia-infected mice (iIDC), unlike those from naive control mice (iNDC), could efficiently modulate immune responses to ovalbumin in vitro and in vivo. Co-culture of freshly isolated DC with naive CD4 cells from T cell receptor transgenic mice (DO11.10) showed that iIDC directed Th1-dominant, while iNDC directed Th2-dominant, allergen-specific CD4 T cell responses. Moreover, adoptive transfer of iIDC, but not iNDC, could inhibit systemic and local eosinophilia induced by allergen exposure. The reduction of eosinophilia was associated with a decrease in IL-5 receptor expression on bone marrow cells and the production of IL-5 and IL-13 by T lymphocytes. Analysis of the DC showed that iIDC expressed significantly higher levels of mRNA for Toll-like receptor 9 and produced more IL-12 compared to iNDC. The data demonstrate a critical role played by DC in infection-mediated inhibition of allergic responses.     

High antigen dose and activated dendritic cells enable Th cells to escape regulatory T cell-mediated suppression in vitro

CD4+CD25+ regulatory T cells (Tregs) are critical for peripheral tolerance and prevention of autoimmunity. In vitro coculture studies have revealed that increased costimulation breaks Treg-mediated suppression in response to anti-CD3 or antigen. However, it was unclear whether loss of suppression arose from inactivation of Tregs or whether increased stimulation caused Th cells to escape suppression. We have investigated conditions that allow or override Treg-mediated suppression using DO11.10 TCR-transgenic T cells and chicken ovalbumin peptide 323-339-pulsed antigen-presenting cells. Treg suppression of Th proliferation is broken with potent stimulation, using activated spleen cells and high antigen dose, but is intact at low antigen dose. Costimulation with CD80 and CD86 expressed on activated dendritic cells was essential for Th cell escape from suppression at a high antigen dose. Potently stimulated Tregs were functional since they reduced levels of IL-2, IFN-gamma, IL-4 and Th CD25 expression in cocultures. Furthermore, Tregs responding to high antigen dose and activated splenocytes retained the ability to suppress proliferation, but only of Th cells responding to a sub-optimal dose of independent antigen. Together, our results demonstrate that under conditions of strong antigen-specific stimulation, Tregs remain functional, but Th cells escape Treg-mediated suppression.     

The proteolytic activity of the major dust mite allergen Der p 1 conditions dendritic cells to produce less interleukin-12: allergen-induced Th2 bias determined at the dendritic cell level

BACKGROUND: The proteolytic activity of the house dust mite allergen Der p 1 has recently been shown to bias Th cell subset development in favour of Th2. Apart from its direct effect on T cells, it is conceivable that the proteolytic activity of Der p 1 may induce the generation of dendritic cells (DCs) that favour a Th2 response. OBJECTIVE: To study the effect of the proteolytic activity of Der p 1 on DC functions; namely cell surface phenotype, IL-12 production and ability to favour a Th2 response. METHODS: We have generated immature DCs from peripheral blood monocytes, matured them with LPS in the presence of either proteolytically active or inactive Der p 1 and compared their functions using flow cytometric analysis. RESULTS: Here we demonstrate for the first time that DCs that have been matured in the presence of proteolytically active Der p 1 produce significantly less IL-12, compared to DCs that have been matured in the presence of proteolytically inactive Der p 1. The suppression of IL-12 production was due to the cleavage of CD40 by the proteolytic activity of Der p 1, hence rendering the DCs less responsive to stimulation through the CD40L-CD40 pathway. Furthermore, we demonstrate that DCs that have been matured in the presence of proteolytically active Der p 1 induce the production of significantly less IFN-gamma and more IL-4 by CD4 T cells, compared to DCs that have been matured in the presence of proteolytically inactive Der p 1. CONCLUSIONS: Collectively, our data provide compelling evidence for the role of the proteolytic activity of Der p 1 in directing DCs to induce Th2 subset development.     

Pregnancy-specific glycoprotein 1a activates dendritic cells to provide signals for Th17-, Th2-, and Treg-cell polarization

Because of their plasticity and central role in orchestrating immunity and tolerance, DCs can respond to pregnancy-specific signals, thus promoting the appropriate immune response in order to support pregnancy. Here, we show that pregnancy-specific glycoprotein (PSG1a), the major variant of PSG released into the circulation during pregnancy, targets DCs to differentiate into a subset with a unique phenotype and function. This semi-mature phenotype is able to secrete IL-6 and TGF-β. PSG1a also affected the maturation of DCs, preventing the up-regulation of some costimulatory molecules, and inducing the secretion of TGF-β or IL-10 and the expression of programmed death ligand 1 (PD-L1) in response to TLR-9 or CD40 ligation. In addition, PSG1a-treated DCs promoted the enrichment of Th2-type cytokines, IL-17-producing cells, and Treg cells from CD4(+) T cells from DO11.10 Tg mice. Moreover, in vivo expression of PSG1a promoted the expansion of Ag-specific CD4(+) CD25(+) Foxp3(+) Treg cells and IL-17-, IL-4-, IL-5-, and IL-10-secreting cells able to protect against Listeria monocytogenes infection. Taken together, our data indicate that DCs can be targeted by PSG1a to generate the signals necessary to mount an appropriate, well-balanced, and effective immune response able to protect against invading pathogens while at the same time being compatible with a successful pregnancy.     

IL-33-activated dendritic cells are critical for allergic airway inflammation

IL-33, a new member of the IL-1 family cytokine, is involved in Th2-type responses in a wide range of diseases and signals through the ST2 receptor expressed on many immune cells. Since the effects of IL-33 on DCs remain controversial, we investigated the ability of IL-33 to modulate DC functions in vitro and in vivo. Here, we report that IL-33 activates myeloid DCs to produce IL-6, IL-1b, TNF, CCL17 and to express high levels of CD40, CD80 OX40L and CCR7. Importantly, IL-33-activated DCs prime naive lymphocytes to produce the Th2 cytokines IL-5 and IL-13, but not IL-4. In vivo, IL-33 exposure induces DC recruitment and activation in the lung. Using an OVA-induced allergic lung inflammation model, we demonstrate that the reduced airway inflammation in ST2-deficient mice correlates with the failure in DC activation and migration to the draining LN. Finally, we show that adoptive transfer of IL-33-activated DCs exacerbates lung inflammation in a DC-driven model of allergic airway inflammation. These data demonstrate for the first time that IL-33 activates DCs during antigen presentation and thereby drives a Th2-type response in allergic lung inflammation.     

Selective maturation of dendritic cells by Nippostrongylus brasiliensis-secreted proteins drives Th2 immune responses

Helminth infections at mucosal and tissue sites strongly polarize towards Th2 immune responses, following pathways which have yet to be elucidated. We investigated whether dendritic cells (DC) exposed to gastrointestinal nematodes induce Th2 differentiation and, if so, whether this outcome reflects the absence of DC activation (the default hypothesis). We studied secreted proteins from the parasite Nippostrongylus brasiliensis, which induce Th2 development in vivo without live infection. Murine bone marrow-derived DC pulsed with N. brasiliensis excretory/secretory antigen (NES) can, on transfer to naive recipients, prime mice for Th2 responsiveness. Heat inactivation of NES abolishes both its ability to drive Th2 responses in vivo and its capacity to stimulate DC for Th2 induction. NES, but not heat-inactivated NES, up-regulates DC maturation markers associated with Th2 promotion (CD86 and OX40L), with little change to CD80 and MHC class II. Moreover, DC exposed to NES readily produce IL-6 and IL-12p40, but not IL-12p70. LPS induced high IL-12p70 levels, except in DC that had been pre-incubated with NES. These data contradict the default hypothesis, demonstrating that a helminth product (NES) actively matures DC, selectively up-regulating CD86 and OX40L together with IL-6 production, while blocking IL-12p70 responsiveness in a manner consistent with Th2 generation in vivo.     

Impaired responses to toll-like receptor 4 and toll-like receptor 3 ligands in human cord blood

Toll-like receptor (TLR)-4 signaling pathway plays an essential role in host defense against gram-negative bacteria while TLR-3-mediated signaling is critically involved in anti-viral immunity. To gain insight into the defects responsible for impaired Th1 responses in human newborns, we investigated the responses of human cord blood cells to lipopolysaccharide, LPS, and to polyinosinic-polycytidylic acid, Poly (I:C), ligands of TLR-4 and TLR-3, respectively. Measurement of cytokine levels revealed a profound defect in IL-12 (p70) synthesis and an increased release of IL-10 in cord blood exposed to LPS or Poly (I:C), as compared to adult blood. Moreover, Poly (I:C)-induced IFN-alpha production was found to be significantly impaired in cord blood. Phenotypic maturation of myeloid DC in response to LPS or Poly (I:C) was next compared in cord and adult blood. We observed that neonatal myeloid DC displayed decreased upregulation of CD40, CD80 whereas CD86 and HLA-DR upregulation did not differ significantly between adults and neonates. Taken together, these findings might be relevant to the increased vulnerability of human newborns to intracellular pathogens and to their inability to develop efficient Th1-type responses.