Production of IL-12 by human monocyte-derived dendritic cells is optimal when the stimulus is given at the onset of maturation, and is further enhanced by IL-4

Dendritic cells produce IL-12 both in response to microbial stimuli and to T cells, and can thus skew T cell reactivity toward a Th1 pattern. We investigated the capacity of dendritic cells to elaborate IL-12 with special regard to their state of maturation, different maturation stimuli, and its regulation by Th1/Th2-influencing cytokines. Monocyte-derived dendritic cells were generated with GM-CSF and IL-4 for 7 days, followed by another 3 days +/- monocyte-conditioned media, yielding mature (CD83(+)/dendritic cell-lysosome-associated membrane glycoprotein(+)) and immature (CD83(-)/dendritic cell-lysosome-associated membrane glycoprotein(-)) dendritic cells. These dendritic cells were stimulated for another 48 h, and IL-12 p70 was measured by ELISA. We found the following: 1) Immature dendritic cells stimulated with CD154/CD40 ligand or bacteria (both of which concurrently also induced maturation) secreted always more IL-12 than already mature dendritic cells. Mature CD154-stimulated dendritic cells still made significant levels (up to 4 ng/ml). 2) Terminally mature skin-derived dendritic cells did not make any IL-12 in response to these stimuli. 3) Appropriate maturation stimuli are required for IL-12 production: CD40 ligation and bacteria are sufficient; monocyte-conditioned media are not. 4) Unexpectedly, IL-4 markedly increased the amount of IL-12 produced by both immature and mature dendritic cells, when present during stimulation. 5) IL-10 inhibited the production of IL-12. Our results, employing a cell culture system that is now being widely used in immunotherapy, extend prior data that IL-12 is produced most abundantly by dendritic cells that are beginning to respond to maturation stimuli. Surprisingly, IL-12 is only elicited by select maturation stimuli, but can be markedly enhanced by the addition of the Th2 cytokine, IL-4.     

Final maturation of dendritic cells is associated with impaired responsiveness to IFN-gamma and to bacterial IL-12 inducers: decreased ability of mature dendritic cells to produce IL-12 during the interaction with Th cells

Activation of immature CD83- dendritic cells (DC) in peripheral tissues induces their maturation and migration to lymph nodes. Activated DC become potent stimulators of Th cells and efficient inducers of Th1- and Th2-type cytokine production. This study analyzes the ability of human monocyte-derived CD1a+ DC at different stages of IL-1 beta and TNF-alpha-induced maturation to produce the major Th1-driving factor IL-12. DC at the early stages of maturation (2 and 4 h) produced elevated amounts of IL-12 p70 during interaction with CD40 ligand-bearing Th cells or, after stimulation with the T cell-replacing factors, soluble CD40 ligand and IFN-gamma. The ability to produce IL-12 was strongly down-regulated at later time points, 12 h after the induction of DC maturation, and in fully mature CD83+ cells, at 48 h. In contrast, the ability of mature DC to produce IL-6 was preserved or even enhanced, indicating their intact responsiveness to CD40 triggering. A reduced IL-12-producing capacity of mature DC resulted mainly from their impaired responsiveness to IFN-gamma, a cofactor in CD40-induced IL-12 p70 production. This correlated with reduced expression of IFN-gamma R (CD119) by mature DC. In addition, while immature DC produced IL-12 and IL-6 after stimulation with LPS or Staphylococcus aureus Cowan I strain, mature DC became unresponsive to these bacterial stimuli. Together with the previously described ability of IL-10 and PGE2 to stably down-regulate the ability to produce IL-12 in maturing, but not in fully mature, DC, the current data indicate a general resistance of mature DC to IL-12-modulating factors.     

Quantities of interleukin-12p40 in mature CD8alpha negative dendritic cells correlate with strength of TCR signal and determine Th cell development

Strength of T cell antigen receptor (TCR) signaling drives the development of Th1 and Th2 subsets from naive T helper precursors. The quantity of interleukin-12 (IL-12) from antigen presenting cells (APC) is also profoundly involved in Th development. TCR signal strength and IL-12 production from dendritic cells (DCs) are linked by CD40 ligand (CD40L) expression on activated T cells. CD40L on the activated T cells interacts with CD40 on DC, resulting in induction of IL-12 from DCs. However, the subsets of DC in spleen that produce the IL-12 have not been clearly identified. Purification of DC subsets itself may provide maturation signals to immature DCs. Thus, we used non-purified mouse spleen cells to analyze IL-12 producing cells, near to steady states, during the interaction of naive T cells either with or without agonist. Mature CD86highCD8alpha- DCs in spleen mainly produced IL-12p40 after stimulation of high dose agonist. The ratio of CD40L positive T cells and IL-12p40 secreting CD86high DCs correlated with the concentration of agonist and Th1 development. However, anti-IL-12 did not completely inhibit the Th1 development. Altogether, strength of TCR signaling directs Th cell development by regulating CD40L expression on T cells which determines production of IL-12p40 from CD86high CD8alpha- DC via CD40.     

CD40 ligand promotes priming of fully potent antitumor CD4(+) T cells in draining lymph nodes in the presence of apoptotic tumor cells.

The presence or absence of CD4(+) T cell help can determine the direction of adaptive immune responses toward either cross-priming or cross-tolerance. It has been demonstrated that interactions of CD40-CD40 ligand can replace CD4(+) T cell help and enable dendritic cells to prime cytotoxic T cells. Here, we demonstrate that antitumor reactivity induced in regional lymph nodes (LNs) by s.c. injection of CD40 ligand (CD40L)-transduced tumor (MCA205 CD40L) showed far superior therapeutic efficacy against established brain tumors of a weakly immunogenic fibrosarcoma, MCA205, when adoptively transferred. Coinjection of apoptotic, but not necrotic parental tumor cells with CD40L-expressing tumor cells caused a strong synergistic induction of antitumor reactivity in tumor-draining LNs. Freshly isolated T cells from LNs immunized with apoptotic parental tumor cells and MCA205 CD40L were capable of mediating regression of the parental tumor in vivo. In contrast, T cells derived from LNs immunized without MCA205 CD40L required ex vivo anti-CD3/IL-2 activation to elicit therapeutic activity. On anti-CD3/IL-2 activation, cells from LNs immunized with MCA205 CD40L exhibited superior per cell antitumor reactivity. An in vitro depletion study revealed that either CD4(+) or CD8(+) T cells could mediate therapeutic efficacy but that the antitumor efficacy mediated by CD4(+) T cells was far superior. Cytosolic flow cytometric analyses indicated that priming of CD4(+) cells in LNs draining CD40L-expressing tumors was polarized to the Th1 type. This is the first report that fully potent antitumor CD4(+) T cell priming was promoted by s.c. injection of CD40L-transduced tumor in the presence of apoptotic tumor cells.     

Gangliosides from human melanoma tumors impair dendritic cell differentiation from monocytes and induce their apoptosis

Gangliosides are ubiquitous membrane-associated glycosphingolipids, which are involved in cell growth and differentiation. Most tumor cells synthesize and shed large amounts of gangliosides into their microenvironment, and many studies have unraveled their immunosuppressive properties. In the present study we analyzed the effects of GM3 and GD3 gangliosides, purified from human melanoma tumors, on the differentiation of monocyte-derived dendritic cells (MoDC). At concentrations close to those detected in the sera from melanoma patients, both gangliosides dose-dependently inhibit the phenotypic and functional differentiation of MoDC, as assessed by a strong down-regulation of CD1a, CD54, CD80, and CD40 Ags and impaired allostimulatory function on day 6 of culture. Furthermore, GM3 and GD3 gangliosides decreased the viable cell yield and induced significant DC apoptosis. Finally, addition of GD3 to differentiating DC impaired their subsequent maturation induced by CD154. The resulting DC produced low amounts of IL-12 and large amounts of IL-10, a cytokine pattern that might hamper an efficient antitumor immune response. In conclusion, the results demonstrate that gangliosides impair the phenotypic and functional differentiation of MoDC and induce their apoptosis, which may be an additional mechanism of human melanoma escape.     

Functional dichotomy in CD40 reciprocally regulates effector T cell functions

Activation of T cells requires signals through Ag-specific TCR and costimulatory molecules such as CD40L. Although the use of defined tumor Ags for the induction of protective T cells met with limited success, the CD40-CD40L interaction that was proposed to induce antitumor T cells did not prevent tumor growth completely. Using a model for prostate tumor, a leading cause of tumor-induced mortality in men, we show that the failure is due to a novel functional dichotomy of CD40 whereby it self-limits its antitumor functions by inducing IL-10. IL-10 prevents the CD40-induced CTL and TNF-alpha and IL-12 production, Th1 skewing, and tumor regression. Priming mice with tumor lysate-pulsed IL-10-deficient dendritic cells (DCs) or wild-type DC plus anti-IL-10 Ab establishes antitumor memory T cells that can transfer the protection into syngenic nude mice. Infusion of Ag-pulsed IL-10-deficient but not wild-type DCs back into syngenic mice results in successful therapeutic autovaccination. Thus, we demonstrate the IL-10-sensitive antitumor T cell memory formulating a novel prophylactic and therapeutic principle.     

CD8- dendritic cell activation status plays an integral role in influencing Th2 response development

Whether dendritic cells (DC) play a passive or active role in Th2 response induction is poorly understood. In this study, we show that CD8- DC pulsed with Th2-polarizing Ag (soluble egg Ag (SEA)) from Schistosoma mansoni potently stimulate Th2 responses in vivo and in vitro while failing to undergo a conventional maturation process. Thus, in contrast to DC pulsed with the Th1 response inducing Ag Propionebacterium acnes, SEA-exposed DC exhibit a phenotype that is most similar to that of immature DC, failing to up-regulate expression of CD40, CD54, CD80, CD86, or OX40L; producing no detectable IL-4, IL-10, or IL-12; and displaying only a minor increase in MHC class II expression. Importantly, in vitro derived DC exposed to SEA were phenotypically similar to CD8- DC isolated from active S. mansoni infection. By discriminating between different types of pathogen and responding appropriately, CD8- DC play a major role in the decision process to mount either a Th1 or Th2 response.     

Ascaris lumbricoides pseudocoelomic body fluid induces a partially activated dendritic cell phenotype with Th2 promoting ability in vivo

Dendritic cells (DCs) matured with helminth-derived molecules that promote Th2 immune responses do not follow conventional definitions of DC maturation processes. While a number of models of DC maturation by Th2 stimuli are postulated, further studies are required if we are to clearly define DC maturation processes that lead to Th2 immune responses. In this study, we examine the interaction of Th2-inducing molecules from the parasitic helminth Ascaris lumbricoides with the maturation processes and function of DCs. Here we show that murine bone marrow-derived DCs are partially matured by A. lumbricoides pseudocoelomic body fluid (ABF) as characterised by the production of IL-6, IL-12p40 and macrophage inflammatory protein 2 (MIP-2) but no enhanced expression of cluster of differentiation (CD)-14, T-cell co-stimulatory markers CD80, CD86, CD40, OX40L and major histocompatibility complex class II was observed. Despite these phenotypic characteristics, ABF-stimulated DCs displayed the functional hallmarks of fully matured cells, enhancing DC phagocytosis and promoting Th2-type responses in skin-draining lymph node cells in vivo. ABF activated Th2-associated extracellular signal-regulated kinase-1 and nuclear factor-kB intracellular signalling pathways independently of toll-like receptor 4. Taken together, we believe this is the first paper to demonstrate A. lumbricoides murine DC-Th cell-driven responses shedding further light on DC maturation processes by helminth antigens.     

Antitumor effects and immunoregulation mechanisms of IL-23 gene in mouse mammary cancer mediated by retrovirus

Background: Interleukin (IL)-23, composed of p19 and p40 subunits, has diverse functions in regulating immune systems, enhancing cell-mediated immunity. In the present study, we investigated whether forced expression of the p19-linked p40 gene in murine mammary cancer cells (MA891) produced antitumor effects in vivo. Tumor growth of MA-891 cells expressing IL-23 (IL-23/MA891) in mice was retarded compared with parental and vector DNA-transduced tumors and survival of the mice inoculated with IL-23/MA-891 cells was prolonged. Expressions of the CD4⁺ T cells and CD8⁺ T cells were up-regulated not only in IL-23/MA-891 tumor specimens but also in spleen cells of mice inoculated with IL-23/MA-891 as compared with those of mice inoculated with parental or vector DNA-transduced tumors. Cytotoxic CD8⁺ T lymphocyte (CTL) activity of spleen cells from mice inoculated with IL-23/MA-891 was also significantly higher than the other two groups. Th1-type cytokines such as interferon-γ, TNF-α and IL-12p70 secreted from spleen cells of mice bearing IL-23/MA-891 tumors were increased while Th2-type cytokine IL-4 was negative regulated. Moreover, we have identified that the quantity of DC in spleen cells of mice bearing IL-23/MA-891 tumors was increased as compared with those mice bearing parental or vector DNA-transfected tumors.     

Alterations of costimulatory molecules and instructive cytokines expressed by dendritic cells in the microenvironment of an endogenous mouse lymphoma

Costimulatory surface molecules and instructive cytokines expressed by dendritic cells (DCs) determine the outcome of an immune response. In malignant disease, DCs are often functionally compromised. In most tumors studied so far, the deficient induction of effective T cell responses has been associated with a blockade of DC maturation, but little has been known on DCs infiltrating malignant B cell lymphoma. Here, we investigated for the first time the phenotypic and functional status of DCs in B cell lymphoma, and we analyzed the network of DCs, tumor cells, natural killer (NK) cells and cytokines present in the tumor micromilieu. Therefor, we used an endogenous myc-transgenic mouse lymphoma model, because transplanted tumor cells foster an IFN-γ-driven Th1 antitumor response rather than an immunosuppressive environment, which is observed in autochthonous neoplasias. Lymphoma-infiltrating DCs showed a mature phenotype and a Th2-inducing cytokine pattern. This situation is in contrast to most human malignancies and mouse models described. Cellular contacts between DCs and tumor cells, which involved CD62L on the lymphoma, caused upregulation of costimulatory molecules, whereas IL-10 primarily derived from lymphoma cells induced an IL-12/IL-10 shift in DCs. Thus, alteration of costimulatory molecules and instructive cytokines was mediated by distinct mechanisms. Normal NK cells were able to additionally modulate DC maturation but this effect was absent in the lymphoma environment where IFN-γ production by NK cells was severely impaired. These data are relevant for establishing novel immunotherapeutic approaches against B cell lymphoma.     

CD25+CD4+ cells contribute to Th2 polarization during helminth infection by suppressing Th1 response development

Mice infected with Schistosoma mansoni develop polarized Th2 responses in which Th1 responses are prevented by IL-10-mediated suppression of IL-12 production. We show that dendritic cells from infected mice are primed to make IL-12 in response to CD40 ligation, and that IL-10 acts by inhibiting this process. In infected mice, two subpopulations of CD4(+) cells, separable by their expression of CD25, make IL-10. CD25(+)CD4(+) cells expressed forkhead box P3, inhibited proliferation of CD4(+) T cells, and made IL-10, but little IL-5. In contrast, CD25(-)CD4(+) cells failed to express forkhead box P3 or to inhibit proliferation and accounted for all the IL-5, IL-6, and IL-13 produced by unseparated splenic populations. Thus, CD25(+) and CD25(-) subpopulations could be characterized as regulatory T cells (Treg cells) and Th2 cells, respectively. Consistent with their ability to make IL-10, both CD25(+) and CD25(-)CD4(+) T cells from infected mice were able, when stimulated with egg Ag, to suppress IL-12 production by CD40 agonist-stimulated dendritic cells. Additionally, in adoptive transfer experiments, both CD4(+) subpopulations of cells were able to partially inhibit the development of Th1 responses in egg-immunized IL-10(-/-) mice. The relationship of Treg cells in infected mice to natural Treg cells was strongly suggested by the ability of CD25(+)CD4(+) cells from naive mice to inhibit Th1 response development when transferred into egg-immunized or infected IL-10(-/-) mice. The data suggest that natural Treg cells and, to a lesser extent, Th2 cells play roles in suppressing Th1 responses and ensuring Th2 polarization during schistosomiasis.     

Cholera toxin promotes the induction of regulatory T cells specific for bystander antigens by modulating dendritic cell activation

It has previously been reported that cholera toxin (CT) is a potent mucosal adjuvant that enhances Th2 or mixed Th1/Th2 type responses to coadministered foreign Ag. Here we demonstrate that CT also promotes the generation of regulatory T (Tr) cells against bystander Ag. Parenteral immunization of mice with Ag in the presence of CT induced T cells that secreted high levels of IL-4 and IL-10 and lower levels of IL-5 and IFN-gamma. Ag-specific CD4(+) T cell lines and clones generated from these mice had cytokine profiles characteristic of Th2 or type 1 Tr cells, and these T cells suppressed IFN-gamma production by Th1 cells. Furthermore, adoptive transfer of bone marrow-derived dendritic cells (DC) incubated with Ag and CT induced T cells that secreted IL-4 and IL-10 and low concentrations of IL-5. It has previously been shown that IL-10 promotes the differentiation or expansion of type 1 Tr cells. Here we found that CT synergized with low doses of LPS to induce IL-10 production by immature DC. CT also enhanced the expression of CD80, CD86, and OX40 (CD134) on DC and induced the secretion of the chemokine, macrophage inflammatory protein-2 (MIP-2), but inhibited LPS-driven induction of CD40 and ICAM-I expression and production of the inflammatory cytokines/chemokines IL-12, TNF-alpha, MIP-1alpha, MIP-1beta, and monocyte chemoattractant protein-1. Our findings suggest that CT induces maturation of DC, but, by inducing IL-10, inhibiting IL-12, and selectively affecting surface marker expression, suppresses the generation of Th1 cells and promotes the induction of T cells with regulatory activity.     

One NY-ESO-1-derived epitope that promiscuously binds to multiple HLA-DR and HLA-DP4 molecules and stimulates autologous CD4+ T cells from patients with NY-ESO-1-expressing melanoma

NY-ESO-1 is expressed by a broad range of human tumors and is often recognized by Abs in the sera of cancer patients with NY-ESO-1-expressing tumors. The NY-ESO-1 gene also encodes several MHC class I- and class II-restricted tumor epitopes recognized by T lymphocytes. In this study we report one novel pan-MHC class II-restricted peptide sequence, NY-ESO-1 87-111, that is capable of binding to multiple HLA-DR and HLA-DP4 molecules, including HLA-DRB1*0101, 0401, 0701, and 1101 and HLA-DPB1*0401 and 0402 molecules. We also demonstrate that peptide NY-ESO-1 87-111 stimulates Th1-type and Th-2/Th0-type CD4(+) T cells and clones when presented in the context of these HLA-DR and HLA-DP4 molecules. Both bulk CD4(+) T cells and CD4(+) T cell clones were capable of recognizing not only peptide-pulsed APCs, but also autologous dendritic cells, either loaded with the NY-ESO-1 protein or transfected with NY-ESO-1 cDNAs. Using IFN-gamma and IL-5 ELISPOT assays and PBL from patients with NY-ESO-1-expressing tumors, we observed the existence of Th1-type circulating CD4(+) T cells recognizing peptide NY-ESO-1 87-111 in the context of HLA-DP4 molecules. Taken together, these data represent the first report of an HLA-DR- and HLA-DP-restricted epitope from a tumor Ag. They also support the relevance of cancer vaccine trials with peptides NY-ESO-1 87-111 in the large number of cancer patients with NY-ESO-1-expressing tumors.     

OX40 ligand regulates splenic CD8 dendritic cell-induced Th2 responses in vivo

In mice, splenic conventional dendritic cells (cDCs) can be separated, based on their expression of CD8α into CD8⁻ and CD8⁺ cDCs. Although previous experiments demonstrated that injection of antigen (Ag)-pulsed CD8⁻ cDCs into mice induced CD4 T cell differentiation toward Th2 cells, the mechanism involved is unclear. In the current study, we investigated whether OX40 ligand (OX40L) on CD8⁻ cDCs contributes to the induction of Th2 responses by Ag-pulsed CD8⁻ cDCs in vivo, because OX40–OX40L interactions may play a preferential role in Th2 cell development. When unseparated Ag-pulsed OX40L-deficient cDCs were injected into syngeneic BALB/c mice, Th2 cytokine (IL-4, IL-5, and IL-10) production in lymph node cells was significantly reduced. Splenic cDCs were separated to CD8⁻ and CD8⁺ cDCs. OX40L expression was not observed on freshly isolated CD8⁻ cDCs, but was induced by anti-CD40 mAb stimulation for 24 h. Administration of neutralizing anti-OX40L mAb significantly inhibited IL-4, IL-5, and IL-10 production induced by Ag-pulsed CD8⁻ cDC injection. Moreover, administration of anti-OX40L mAb with Ag-pulsed CD8⁻ cDCs during a secondary response also significantly inhibited Th2 cytokine production. Thus, OX40L on CD8⁻ cDCs physiologically contributes to the development of Th2 cells and secondary Th2 responses induced by Ag-pulsed CD8⁻ cDCs in vivo.     

Enhanced therapeutic anti-tumor immunity induced by co-administration of 5-fluorouracil and adenovirus expressing CD40 ligand

Bystander immune activation by chemotherapy has recently gained extensive interest and provided support for the clinical use of chemotherapeutic agents in combination with immune enhancers. The CD40 ligand (CD40L; CD154) is a potent regulator of the anti-tumor immune response and recombinant adenovirus (RAd)-mediated CD40L gene therapy has been effective in various cancer models and in man. In this study we have assessed the combined effect of local RAd-CD40L and 5-fluorouracil (5-FU) administration on a syngeneic MB49 mouse bladder tumor model. Whereas MB49 cells implanted into immunocompetent mice responded poorly to RAd-CD40L or 5-FU alone, administration of both agents dramatically decreased tumor growth, increased survival of the mice and induced systemic MB49-specific immunity. This combination treatment was ineffective in athymic nude mice, highlighting an important role for T cell mediated anti-tumor immunity for full efficacy. 5-FU up-regulated the expression of Fas and immunogenic cell death markers in MB49 cells and cytotoxic T lymphocytes from mice receiving RAd-CD40L immunotherapy efficiently lysed 5-FU treated MB49 cells in a Fas ligand-dependent manner. Furthermore, local RAd-CD40L and 5-FU administration induced a shift of myeloid-derived suppressor cell phenotype into a less suppressive population. Collectively, these data suggest that RAd-CD40L gene therapy is a promising adjuvant treatment to 5-FU for the management of bladder cancer.     

Dendritic cell differentiation state and their interaction with NKT cells determine Th1/Th2 differentiation in the murine model of Leishmania major infection

Recent reports demonstrated that dendritic cells (DC) sense inflammatory and microbial signals differently, redefining their classical subdivision into an immature endocytic and a mature Ag-presenting differentiation stage. Although both signals induce DC maturation by up-regulating MHC class II and costimulatory molecules, only TLR signals such as LPS are able to trigger proinflammatory cytokine secretion by DCs, including Th1-polarizing IL-12. Here, we explored the murine Leishmania major infection model to examine the CD4(+) T cell response induced by differentially matured DCs. When partially matured TNF-DCs were injected into BALB/c mice before infection, the mice failed to control L. major infection and developed a Th2 response which was dependent on IL-4Ralpha signaling. In contrast, injections of fully matured LPS+CD40-DCs induced a Th1 response controlling the infection. Pulsing DCs with a lysate of L. major did not affect DC maturation with TNF-alpha or LPS+anti-CD40. When the expression of different Notch ligands on DCs was analyzed, we found increased expression of Th2-promoting Jagged2 in TNF-DCs, whereas LPS+CD40-DCs up-regulated the Th1-inducing Delta4 and Jagged1 molecules. The Th2 polarization induced by TNF-DCs required interaction with CD1d-restricted NKT cells. However, NKT cell activation by L. major lysate-pulsed DCs was not affected by blockade of the endogenous glycolipid, suggesting exchange with exogenous parasite-derived CD1 glycolipid Ag. In sum, the differentiation stage of DCs as well as their interaction with NKT cells determines Th1/Th2 differentiation. These results have generic implications for the understanding of DC-driven Th cell responses and the development of improved DC vaccines against leishmaniasis.     

CD40-CD40 ligand costimulation is required for generating antiviral CD4 T cell responses but is dispensable for CD8 T cell responses.

This study documents a striking dichotomy between CD4 and CD8 T cells in terms of their requirements for CD40-CD40 ligand (CD40L) costimulation. CD40L-deficient (-/-) mice made potent virus-specific CD8 T cell responses to dominant as well as subdominant epitopes following infection with lymphocytic choriomeningitis virus. In contrast, in the very same mice, virus-specific CD4 T cell responses were severely compromised. There were 10-fold fewer virus-specific CD4 T cells in CD40L-/- mice compared with those in CD40L+/+ mice, and this inhibition was seen for both Th1 (IFN-gamma, IL-2) and Th2 (IL-4) responses. An in vivo functional consequence of this Th cell defect was the inability of CD40L-/- mice to control a chronic lymphocytic choriomeningitis virus infection. This study highlights the importance of CD40-CD40L interactions in generating virus-specific CD4 T cell responses and in resolving chronic viral infection.     

Effective stimulation for IL-12 p35 mRNA accumulation and bioactive IL-12 production of antigen-presenting cells interacted with Th cells.

Bioactive IL-12 is composed of two subunits, p35 and p40. In the APC-Th cell interaction, p40 mRNA accumulation in APC was shown to be up-regulated by stimulation with CD40 ligand (CD40L) on Th cells. However, the CD40-CD40L interaction scarcely induced p35 mRNA accumulation in APC. In the present experiments, p35 mRNA accumulation was induced in splenic macrophages/dendritic cells by the interaction with paraformaldehyde-fixed Th1 cells in the presence of Ag, and the p35 mRNA accumulation was abrogated by the inclusion of anti-I-A in cultures to block TCR/MHC class II interaction. The accumulation was also induced by the stimulation with agonistic anti-I-A. These results indicate that the interaction of the MHC class II molecule with TCR evokes an activation signal for p35 mRNA accumulation in APC. Furthermore, the production of bioactive IL-12 in macrophages/dendritic cells stimulated with CD40L was enhanced by the inclusion of agonistic anti-I-A. The p35 mRNA accumulation and IL-12 production of macrophages/dendritic cells induced by stimulation with OVA-specific fixed Th1 clone expressing CD40L were also enhanced by adding OVA in cultures. These results indicate that the p35 mRNA accumulation induced by MHC class II stimulation plays a role in bioactive IL-12 production.     

Cytokines regulate the capacity of CD8alpha(+) and CD8alpha(-) dendritic cells to prime Th1/Th2 cells in vivo

Prior studies have shown that subclasses of dendritic cells (DC) direct the development of distinct Th populations in rodents and in humans. In the mouse, we have recently shown that administration of Ag-pulsed CD8alpha(-) DC induces a Th2-type response, whereas injection of CD8alpha(+) DC leads to Th1 differentiation. To define the DC-derived factors involved in the polarization of Th responses, we injected either subset purified from mice genetically deficient for IFN-gamma, IL-4, IL-12, or IL-10 into wild-type animals. In this work, we report that DC-derived IL-12 and IFN-gamma are required for Th1 priming by CD8alpha(+) DC, whereas IL-10 is required for optimal development of Th2 cells by CD8alpha(-) DC. The level of IL-12 produced by the DC appears to determine the Th1/Th2 balance in vivo. We further show that the function of DC subsets displays some flexibility. Treatment of DC with IL-10 in vitro induces a selective decrease in the viability of CD8alpha(+) DC. Conversely, incubation with IFN-gamma down-regulates the Th2-promoting capacities of CD8alpha(-) DC and increases the Th1-skewing properties of both subsets.