Synergistic effects of IL-4 and IL-18 on IL-12-dependent IFN-gamma production by dendritic cells

Mouse splenic dendritic cells (DCs) produce IFN-gamma in response to IL-12. In the present study, we analyzed effects of Th1 and Th2 cytokines on IFN-gamma production by DCs. IL-18 produced by DCs and macrophages acts in an autocrine manner and augments IL-12-induced IFN-gamma production by DCs as also observed in T and NK cells. Surprisingly, IL-4, a Th2 cytokine, also acts synergistically with IL-12 on IFN-gamma production by DCs. In addition, IL-4 markedly enhances IFN-gamma production when DCs are stimulated through CD40 or MHC class II. These results indicate that both Th1 and Th2 cytokines act on DCs during T cell-DC interaction upon Ag presentation. p38 mitogen-activated protein kinase is constitutively activated in mature DCs and is required for IFN-gamma production by DCs. IL-18 but not IL-4 or IL-12 further activates the p38 mitogen-activated protein kinase activity, suggesting that IL-4 and IL-18 enhance IFN-gamma production through distinct intracellular signal transduction pathways in DCs.     

Galectin-9 induces maturation of human monocyte-derived dendritic cells

Maturation of dendritic cells (DCs) is critical for initiation of immune responses and is regulated by various stimulatory signals. We assessed the role of galectin (Gal)-9 in DC maturation. Culture of immature DCs with exogenous Gal-9 markedly increased the surface expression of CD40, CD54, CD80, CD83, CD86, and HLA-DR in a dose-dependent manner, although Gal-9 had no or little effect on differentiation of human monocytes into immature DCs. Gal-9-treated DCs secreted IL-12 but not IL-10, and they elicited the production of Th1 cytokines (IFN-gamma and IL-2) but not that of the Th2 cytokines (IL-4 and IL-5) by allogeneic CD4+ T cells. These effects of Gal-9 on immature DCs were not essentially dependent on its lectin properties, given that they were inhibited only slightly by lactose. We further found that a Gal-9 mutant that lacks beta-galactoside binding activity reproduced the above activities and that an anti-Gal-9 mAb suppressed them. Gal-9 induced phosphorylation of the MAPK p38 and ERK1/2 in DCs, and an inhibitor of p38 signaling, but not inhibitors of signaling by either ERK1/2 or PI3K, blocked Gal-9-induced up-regulation of costimulatory molecule expression and IL-12 production. These findings suggest that Gal-9 plays a role not only in innate immunity but also in acquired immunity by inducing DC maturation and promoting Th1 immune responses.     

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.     

Dendritic cells transduced with SOCS-3 exhibit a tolerogenic/DC2 phenotype that directs type 2 Th cell differentiation in vitro and in vivo

Dendritic cells (DCs) have been suggested to direct a type of Th differentiation through their cytokine profile, e.g., high IL-12/IL-23 for Th1 (named DC1/immunogenic DCs) and IL-10 for Th2 (DC2/tolerogenic DCs). Suppressor of cytokine signaling (SOCS)-3 is a potent inhibitor of Stat3 and Stat4 transduction pathways for IL-23 and IL-12, respectively. We thus hypothesize that an enhanced SOCS-3 expression in DCs may block the autocrine response of IL-12/IL-23 in these cells, causing them to become a DC2-type phenotype that will subsequently promote Th2 polarization of naive T cells. Indeed, in the present study we found that bone marrow-derived DCs transduced with SOCS-3 significantly inhibited IL-12-induced activation of Stat4 and IL-23-induced activation of Stat3. These SOCS-3-transduced DCs expressed a low level of MHC class II and CD86 on their surface, produced a high level of IL-10 but low levels of IL-12 and IFN-gamma, and expressed a low level of IL-23 p19 mRNA. Functionally, SOCS-3-transduced DCs drove naive myelin oligodendrocyte glycoprotein-specific T cells to a strong Th2 differentiation in vitro and in vivo. Injection of SOCS-3-transduced DCs significantly suppressed experimental autoimmune encephalomyelitis, a Th1 cell-mediated autoimmune disorder of the CNS and an animal model of multiple sclerosis. These results indicate that transduction of SOCS-3 in DCs is an effective approach to generating tolerogenic/DC2 cells that then skew immune response toward Th2, thus possessing therapeutic potential in Th1-dominant autoimmune disorders such as multiple sclerosis.     

Modulation of CD4 Th cell differentiation by ganglioside GD1a in vitro

Cell surface gangliosides are shed by tumors into their microenvironment. In this study they inhibit cellular immune responses, including APC development and function, which is critical for Th1 and Th2 cell development. Using human dendritic cells (DCs) and naive CD4(+) T cells, we separately evaluated Th1 and Th2 development under the selective differentiating pressures of DC1-inducing pertussis toxin (PT) and DC2-inducing cholera toxin (CT). High DC IL-12 production after PT exposure and high DC IL-10 production after CT exposure were observed, as expected. However, when DCs were first preincubated with highly purified G(D1a) ganglioside, up-regulation of costimulatory molecules was blunted, and PT-induced IL-12 production was reduced, whereas CT-induced IL-10 production was increased. The combination of these effects could contribute to a block in the Th1 response. In fact, when untreated naive T cells were coincubated with ganglioside-preincubated, Ag-exposed DCs, naive Th cell differentiation into Th effector cells was reduced. Both the subsequent DC1-induced T cell production of IFN-gamma (Th1 marker) and DC2-induced T cell IL-4 production (Th2) were inhibited. Thus, ganglioside exposure of DC impairs, by at least two distinct mechanisms, the ability to induce Th differentiation, which could adversely affect the development of an effective cellular antitumor immune response.     

Sphingosine kinase 1 is a negative regulator of CD4+ Th1 cells

CD4+ Th1 cells produce IFN-gamma, TNF-alpha, and IL-2. These Th1 cytokines play critical roles in both protective immunity and inflammatory responses. In this study we report that sphingosine kinase 1 (SPHK1), but not SPHK2, is highly expressed in DO11.10 Th1 cells. The expression of SPHK1 in Th1 cells requires TCR signaling and new protein synthesis. SPHK1 phosphorylates sphingosine to form sphingosine-1-phosphate. Sphingosine-1-phosphate plays important roles in inhibition of apoptosis, promotion of cell proliferation, cell migration, calcium mobilization, and activation of ERK1/2. When SPHK1 expression was knocked down by SPHK1 short interfering RNA, the production of IL-2, TNF-alpha, and IFN-gamma by Th1 cells in response to TCR stimulation was enhanced. Consistently, overexpression of dominant-negative SPHK1 increased the production of IL-2, TNF-alpha, and IFN-gamma in Th1 cells. Furthermore, overexpression of SPHK1 in Th1 and Th0 cells decreased the expression of IL-2, TNF-alpha, and IFN-gamma. Several chemokines, including Th2 chemokines CCL17 and CCL22, were up-regulated by SPHK1 short interfering RNA and down-regulated by overexpression of SPHK1. We also showed that Th2 cells themselves express CCL17 and CCL22. Finally, we conclude that SPHK1 negatively regulates the inflammatory responses of Th1 cells by inhibiting the production of proinflammatory cytokines and chemokines.     

IL-32gamma induces the maturation of dendritic cells with Th1- and Th17-polarizing ability through enhanced IL-12 and IL-6 production

IL-32, a newly described multifunctional cytokine, has been associated with a variety of inflammatory diseases, including rheumatoid arthritis, vasculitis, and Crohn's disease. In this study, we investigated the immunomodulatory effects of IL-32γ on bone marrow-derived dendritic cell (DC)-driven Th responses and analyzed the underlying signaling events. IL-32γ-treated DCs exhibited upregulated expression of cell-surface molecules and proinflammatory cytokines associated with DC maturation and activation. In particular, IL-32γ treatment significantly increased production of IL-12 and IL-6 in DCs, which are known as Th1- and Th17-polarizing cytokines, respectively. This increased production was inhibited by the addition of specific inhibitors of the activities of phospholipase C (PLC), JNK, and NF-κB. IL-32γ treatment increased the phosphorylation of JNK and the degradation of both IκBα and IκBβ in DCs, as well as NF-κB binding activity to the κB site. The PLC inhibitor suppressed NF-κB DNA binding activity and JNK phosphorylation increased by IL-32γ treatment, thereby indicating that IL-32γ induced IL-12 and IL-6 production in DCs via a PLC/JNK/NF-κB signaling pathway. Importantly, IL-32γ-stimulated DCs significantly induced both Th1 and Th17 responses when cocultured with CD4(+) T cells. The addition of a neutralizing anti-IL-12 mAb abolished the secretion of IFN-γ in a dose-dependent manner; additionally, the blockage of IL-1β and IL-6, but not of IL-21 or IL-23p19, profoundly inhibited IL-32γ-induced IL-17 production. These results demonstrated that IL-32γ could effectively induce the maturation and activation of immature DCs, leading to enhanced Th1 and Th17 responses as the result of increased IL-12 and IL-6 production in DCs.     

IL-10 induces CCR6 expression during Langerhans cell development while IL-4 and IFN-gamma suppress it.

Immune responses are initiated by dendritic cells (DC) that form a network comprising different populations. In particular, Langerhans cells (LC) appear as a unique population of cells colonizing epithelial surfaces. We have recently shown that macrophage-inflammatory protein-3alpha/CCL20, a chemokine secreted by epithelial cells, induces the selective migration of LC among DC populations. In this study, we investigated the effects of cytokines on the expression of the CCL20 receptor, CCR6, during differentiation of LC. We found that both IL-4 and IFN-gamma blocked the expression of CCR6 and CCL20 responsiveness at different stages of LC development. The effect of IL-4 was reversible and most likely due to the transient blockade of LC differentiation. In contrast, IFN-gamma-induced CCR6 loss was irreversible and was concomitant to the induction of DC maturation. When other cytokines involved in DC and T cell differentiation were tested, we found that IL-10, unlike IL-4 and IFN-gamma, maintained CCR6 expression. The effect of IL-10 was reversible and upon IL-10 withdrawn, CCR6 was lost concomitantly to final LC differentiation. In addition, IL-10 induced the expression of CCR6 and responsiveness to CCL20 in differentiated monocytes that preserve their ability to differentiate into mature DC. Finally, TGF-beta, which induces LC differentiation, did not alter early CCR6 expression, but triggered its irreversible down-regulation, in parallel to terminal LC differentiation. Taken together, these results suggest that the recruitment of LC at epithelial surface might be suppressed during Th1 and Th2 immune responses, and amplified during regulatory immune responses involving IL-10 and TGF-beta.     

Effects of liver-derived dendritic cell progenitors on Th1- and Th2-like cytokine responses in vitro and in vivo

There is evidence that donor-derived dendritic cells (DC), particularly those at a precursor/immature stage, may play a role in the immune privilege of liver allografts. Underlying mechanisms are poorly understood. We have examined the influence of in vitro generated mouse liver-derived DC progenitors (DCp) on proliferative, cytotoxic, and Th1/Th2 cytokine responses induced in allogeneic T cells. Liver DCp, propagated in GM-CSF from C57B10 mice (H2b), induced only minimal proliferation, and weak cytotoxic responses in allogeneic (C3H; H2k) T cells compared with mature bone marrow (BM)-derived DC. Flow-cytometric analysis of intracellular cytokine staining revealed that mature BM DC, but not liver DCp, elicited CD4+ T cell production of IFN-gamma. Intracellular expression of IL-10 was very low in both BM DC- and liver DCp-stimulated CD4+ T cells. Only stimulation by liver DCp was associated with IL-10 secretion in primary MLR. Notably, these liver DCp cocultured with allogeneic T cells stained strongly for IL-10. Following local (s.c. ) injection in allogeneic recipients, both BM DC and liver DCp homed to T cell areas of draining lymph nodes and spleen, where they were readily detected by immunohistochemistry up to 2 wk postinjection. Liver DCp induced clusters of IL-10- and IL-4-secreting mononuclear cells, whereas Th2 cytokine-secreting cells were not detected in mice injected with mature BM DC. By contrast, comparatively high numbers of IFN-gamma+ cells were induced by BM DC. Modulation of Th2 cytokine production by donor-derived DCp may contribute to the comparative immune privilege of hepatic allografts.     

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.     

Differential expression of inflammatory chemokines by Th1- and Th2-cell promoting dendritic cells: a role for different mature dendritic cell populations in attracting appropriate effector cells to peripheral sites of inflammation

Protective immunity to pathogens depends on efficient immune responses adapted to the type of pathogen and the infected tissue. Dendritic cells (DC) play a pivotal role in directing the effector T cell response to either a protective T helper type 1 (Th1) or type 2 (Th2) phenotype. Human monocyte-derived DC can be differentiated into Th1-, Th2- or Th1/Th2-promoting DC in vitro upon activation with microbial compounds or cytokines. Host defence is highly dependent on mobile leucocytes and cell trafficking is largely mediated by the interactions of chemokines with their specific receptors expressed on the surface of leucocytes. The production of chemokines by mature effector DC remains elusive. Here we assess the differential production of both inflammatory and homeostatic chemokines by monocyte-derived mature Th1/Th2-, Th1- or Th2-promoting DC and its regulation in response to CD40 ligation, thereby mimicking local engagement with activated T cells. We show that mature Th1- and Th1/Th2-, but not Th2-promoting DC, selectively express elevated levels of the inflammatory chemokines CCL2/MCP-1, CCL3/MIP-1alpha, CCL4/MIP-1beta and CCL5/RANTES, as well as the homeostatic chemokine CCL19/MIP-3beta. CCL21/6Ckine is preferentially expressed by Th2-promoting DC. Production of the Th1-attracting chemokines, CXCL9/Mig, CXCL10/IP-10 and CXCL11/I-TAC, is restricted to Th1-promoting DC. In contrast, expression of Th2-associated chemokines does not strictly correlate with the Th2-promoting DC phenotype, except for CCL22/MDC, which is preferentially expressed by Th2-promoting DC. Because inflammatory chemokines and Th1-associated chemokines are constitutively expressed by mature Th1-promoting DC and CCL22/MDC is constitutively expressed by mature Th2-promoting DC, we propose a novel role for mature DC present in inflamed peripheral tissues in orchestrating the immune response by recruiting appropriate leucocyte populations to the site of pathogen entry.     

Francisella tularensis LVS-induced Interleukin-12 p40 cytokine production mediates dendritic cell migration through IL-12 Receptor β1

Three cytokines use the IL-12p40 cytokine subunit namely: IL-12p70 (IL-12-comprised of IL-12p40 and IL-12p35), IL-23 (comprised of the IL-12p40 and IL-23p19 subunits) and homodimeric IL-12p40 (IL-12(p40)(2)). Following activation, immature dendritic cells (DCs) upregulate the chemokine receptor Chemokine-C-Receptor 7 (CCR7), and migrate in response to homeostatic chemokines such as chemokine (C-C motif) ligand 19 (CCL19). Induction of the cytokine IL-12p40 in response to pathogen-exposure, likely in its homodimeric form, is one of the primary events that mediates migration of DCs in response to CCL19. Here we show that following exposure to Francisella tularensis Live Vaccine Strain (LVS), DCs produce IL-12p40 and promote the migration of DCs to the chemokine CCL19 in an IL-12Rβ1- and IL-12p(40)(2)-dependent manner. Induction of IL-12p40 and resulting chemokine responsiveness in DCs is TLR2-dependent and coincides with the uptake of F. tularensis LVS and activation of DCs. Importantly, we show that IL-12Rβ1 signaling is required for DC migration from the lung to the draining lymph node following F. tularensis LVS exposure and coincides with accumulation of IL-12p40 expressing DCs in the draining lymph nodes. Together, these findings illustrate that IL-12p40 is induced rapidly in response to F. tularensis LVS and is required for DC migration through an IL-12Rβ1-IL-12(p40)(2) dependent mechanism.     

1 Alpha,25-dihydroxyvitamin D3 inhibits differentiation, maturation, activation, and survival of dendritic cells leading to impaired alloreactive T cell activation

1 Alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3), the active form of vitamin D3, is a potent immunomodulatory agent. Here we show that dendritic cells (DCs) are major targets of 1,25(OH)2D3-induced immunosuppressive activity. 1,25(OH)2D3 prevents the differentiation in immature DCs of human monocytes cultured with GM-CSF and IL-4. Addition of 1,25(OH)2D3 during LPS-induced maturation maintains the immature DC phenotype characterized by high mannose receptor and low CD83 expression and markedly inhibits up-regulation of the costimulatory molecules CD40, CD80, and CD86 and of class II MHC molecules. This is associated with a reduced capacity of DCs to activate alloreactive T cells, as determined by decreased proliferation and IFN-gamma secretion in mixed leukocyte cultures. 1, 25(OH)2D3 also affects maturing DCs, leading to inhibition of IL-12p75 and enhanced IL-10 secretion upon activation by CD40 ligation. In addition, 1,25(OH)2D3 promotes the spontaneous apoptosis of mature DCs. The modulation of phenotype and function of DCs matured in the presence of 1,25(OH)2D3 induces cocultured alloreactive CD4+ cells to secrete less IFN-gamma upon restimulation, up-regulate CD152, and down-regulate CD154 molecules. The inhibition of DC differentiation and maturation as well as modulation of their activation and survival leading to T cell hyporesponsiveness may explain the immunosuppressive activity of 1, 25(OH)2D3.     

CCR7 ligand-enhanced phagocytosis of various antigens in mature dendritic cells-time course and antigen distribution different from phagocytosis in immature dendritic cells

CC chemokine receptor 7 (CCR7) is selectively expressed on mature dendritic cells (DC). The CCR7 ligands, CC chemokine ligand (CCL) 19 and CCL21, facilitate migration of mature DC from the peripheral tissues to regional lymph nodes. We previously demonstrated that CCR7 ligands induced rapid receptor-mediated endocytosis of dextran in mature DC. In the present study, we further examined the effects of CCR7 ligands on endocytosis of other kinds of antigen, mannosilated bovine serum albumin (Mann-BSA), Escherichia coli(E. coli), or ovalbumin-containing immune complex (OVA-IC), by mature DC. We found that CCR7 ligands enhanced the endocytosis of Mann BSA, E. coli, and OVA-IC in mature DC but not in immature DC. The endocytosis of BSA was not enhanced by CCR7 ligands. Furthermore, the phagocytosis of OVA-IC was significantly inhibited by anti-Fcgamma receptor III/II antibody. These results demonstrate that CCR7 ligands enhance only receptor-mediated endocytosis by mature DC. When rapidly phagocytosed E. coli were traced in CCL19-treated mature DC, most of the phagocytosed E. coli did not colocalize with the lysosomal marker: lysosome-associated membrane protein-1 (Lamp-1), whereas most of E. coli taken up relatively slowly by immature DC colocalized with Lamp-1. These results suggest that phagocytosis of antigens by immature and mature DC plays different functional roles.     

IL-12 or IL-4 prime human NK cells to mediate functionally divergent interactions with dendritic cells or tumors

In the course of inflammatory responses in peripheral tissues, NK cells may be exposed to cytokines such as IL-12 and IL-4 released by other cell types that may influence their functional activities. In the present study we comparatively analyzed purified human peripheral blood NK cells that had been exposed to either IL-12 or IL-4 during short (overnight) incubation. We show that although IL-12-cultured NK cells produced abundant IFN-gamma, TNF-alpha, and GM-CSF in response to stimuli acting on the NKp46-activating receptor, IL-4-cultured NK cells did not release detectable levels of these cytokines. In contrast, IL-4-cultured NK cells produced significant levels of TNF-alpha and GM-CSF only when stimulated with PMA and ionomycin. In no instance could the production of IL-5 and IL-13 be detected. Importantly, IL-12-cultured, but not IL-4-cultured, NK cells displayed strong cytolytic activity against various tumor cells or immature dendritic cells (DCs). Moreover, only NK cells that had been cultured in IL-12 were able to induce substantial DC maturation. Our data suggest that NK cells exposed to IL-12 for a time interval compatible with in vivo responses may favor the selection of appropriate mature DCs for subsequent Th1 cell priming in secondary lymphoid organs. On the contrary, NK cells exposed to IL-4 do not exert DC selection, may impair efficient Th1 priming, and favor either tolerogenic or Th2-type responses.     

Comparative roles of IL-4, IL-13, and IL-4Ralpha in dendritic cell maturation and CD4+ Th2 cell function

IL-4 and IL-13 play key roles in Th2 immunity and asthma pathogenesis. Although the function of these cytokines is partially linked through their shared use of IL-4Ralpha for signaling, the interplay between these cytokines in the development of memory Th2 responses is not well delineated. In this investigation, we show that both IL-4 and IL-13 influence the maturation of dendritic cells (DC) in the lung and their ability to regulate secretion of IFN-gamma and Th2 cytokines by memory CD4(+) T cells. Cocultures of wild-type T cells with pulmonary DC from allergic, cytokine-deficient mice demonstrated that IL-4 enhanced the capacity of DC to stimulate T cell secretion of Th2 cytokines, whereas IL-13 enhanced the capacity of DC to suppress T cell secretion of IFN-gamma. Because IL-4Ralpha is critical for IL-4 and IL-13 signaling, we also determined how variants of IL-4Ralpha influenced immune cell function. T cells derived from allergic mice expressing a high-affinity IL-4Ralpha variant produced higher levels of IL-5 and IL-13 compared with T cells derived from allergic mice expressing a low-affinity IL-4Ralpha variant. Although DC expressing different IL-4Ralpha variants did not differ in their capacity to influence Th2 cytokine production, they varied in their capacity to inhibit IFN-gamma production by T cells. Thus, IL-4 and IL-13 differentially regulate DC function and the way these cells regulate T cells. The affinity of IL-4Ralpha also appears to be a determinant in the balance between Th2 and IFN-gamma responses and thus the severity of allergic disease.     

Synergistic effect of IL-2, IL-12, and IL-18 on thymocyte apoptosis and Th1/Th2 cytokine expression

In the periphery, IL-18 synergistically induces the expression of the Th1 cytokine IFN-gamma in the presence of IL-12 and the Th2 cytokines IL-5 and IL-13 in the presence of IL-2. Although the expression of these cytokines has been described in the thymus, their role in thymic development and function remains uncertain. We report here that freshly isolated thymocytes from C57BL/6 and BALB/c mice stimulated in vitro with IL-2-plus-IL-18 or IL-12-plus-IL-18 produce large amounts of IFN-gamma and IL-13. Analysis of the thymic subsets, CD4(-)CD8(-) (DN), CD4(+)CD8(+), CD4(+)CD8(-), and CD4(-)CD8(+) revealed that IL-18 in combination with IL-2 or IL-12 induces IFN-gamma and IL-13 preferentially from DN cells. Moreover, DN2 and DN3 thymocytes contained more IFN-gamma(+) cells than cells in the later stage of maturation. Additionally, IL-18 in combination with IL-2 induces CCR4 (Th2-associated) and CCR5 (Th1-associated) gene expression. In contrast, IL-18-plus-IL-12 specifically induced CCR5 expression. The IL-2-plus-IL-18 or IL-12-plus-IL-18 effect on IFN-gamma and IL-13 expression is dependent on Stat4 and NF-kappaB but independent of Stat6, T-bet, or NFAT. Furthermore, IL-12-plus-IL-18 induces significant thymocyte apoptosis when expressed in vivo or in vitro, and this effect is exacerbated in the absence of IFN-gamma. IL-12-plus-IL-18-stimulated thymocytes can also induce IA-IE expression on cortical and medullary thymic epithelial cells in an IFN-gamma-dependent manner. Thus, the combination of IL-2, IL-12, and IL-18 can induce phenotypic and functional changes in thymocytes that may alter migration, differentiation, and cell death of immature T cells inside the thymus and potentially affect the Th1/Th2 bias in peripheral immune compartments.     

Mature dendritic cells infiltrate the T cell-rich region of oral mucosa in chronic periodontitis: in situ, in vivo, and in vitro studies

Previous studies have analyzed the lymphoid and myeloid foci within the gingival mucosa in health and chronic periodontitis (CP); however, the principal APCs responsible for the formation and organizational structure of these foci in CP have not been defined. We show that in human CP tissues, CD1a(+) immature Langerhans cells predominantly infiltrate the gingival epithelium, whereas CD83(+) mature dendritic cells (DCs) specifically infiltrate the CD4(+) lymphoid-rich lamina propria. In vivo evidence shows that exacerbation of CP results in increased levels of proinflammatory cytokines that mediate DC activation/maturation, but also of counterregulatory cytokines that may prevent a Th-polarized response. Consistently, in vitro-generated monocyte-derived DCs pulsed with Porphyromonas gingivalis strain 381 or its LPS undergo maturation, up-regulate accessory molecules, and release proinflammatory (IL-1beta, PGE(2)) and Th (IL-10, IL-12) cytokines. Interestingly, the IL-10:IL-12 ratio elicited from P. gingivalis-pulsed DCs was 3-fold higher than that from Escherichia coli-pulsed DCs. This may account for the significantly (p < 0.05) lower proliferation of autologous CD4(+) T cells and reduced release of IFN-gamma elicited by P. gingivalis-pulsed DCs. Taken together, these findings suggest a previously unreported mechanism for the pathophysiology of CP, involving the activation and in situ maturation of DCs by the oral pathogen P. gingivalis, leading to release of counterregulatory cytokines and the formation of T cell-DC foci.