Murine Peyer's patches favor development of an IL-10-secreting,regulatory T cell population

Peyer's patches (PP) are believed to be the principal sites for induction of tolerance to Ags from food and commensal flora, yet the phenotype of T cells activated within the PP is largely unexplored. We hypothesize that exposure to Ags within the PP promotes differentiation of T cells with immunoregulatory functions. Cytokine production and cell surface marker expression of murine PP mononuclear cells (MC) are compared with those from mesenteric lymph nodes and peripheral lymph nodes (PLN). In response to stimulation through the TCR/CD3 complex, PP MC exhibit vigorous proliferation, modest production of IL-2, and significantly elevated synthesis of IL-10. Exogenous IL-12 enhances both IL-10 and IFN-gamma secretion by activated PP MC. Cell surface marker analysis reveals that PP T cells consist of activated and memory subpopulations compared with the predominantly naive T cells identified in the PLN and mesenteric lymph nodes. Upon stimulation, only CD45RB(low)CD4(+) PP T cells produce IL-10, whereas secretion of IL-2, IL-4, and IFN-gamma was not detected. Furthermore, PP MC, but not PLN MC, stimulated through the TCR/CD3 complex suppress proliferation of purified PLN T cells in vitro, evidence for a regulatory function among PP lymphocytes. We conclude that PP favor differentiation of an IL-10-producing, regulatory CD45RB(low)CD4(+) T cell population and that inhibition of T cell proliferation by activated PP MC may reflect regulatory activity consistent with T regulatory cells.     

Human CD4(+) T cells recognize an epitope within alpha-fetoprotein sequence and develop into TGF-beta-producing CD4(+) T cells

There is limited information on the influence of tumor growth on the expansion of tumor-specific TGF-beta-producing CD4(+) T cells in humans. alpha-Fetoprotein (AFP) is an oncofetal Ag and has intrinsic immunoregulatory properties. In this study, we report the identification and characterization of subsets of CD4(+) T cells that recognize an epitope within the AFP sequence (AFP(46-55)) and develop into TGF-beta-producing CD4(+) T cells. In a peptide-specific and dose-dependent manner, AFP(46-55) CD4(+) T cells produce TGF-beta, GM-CSF, and IL-2 but not Th1-, Th2-, Th17-, or Tr1-type cytokines. These cells express CTLA-4 and glucocorticoid-induced TNR receptor and inhibit T cell proliferation in a contact-dependent manner. In this study, we show that the frequency of AFP(46-55) CD4(+) T cells is significantly higher (p = 001) in patients with hepatocellular carcinoma than in healthy donors, suggesting that these cells are expanded in response to tumor Ag. In contrast, tumor necrosis-inducing treatments that are shown to improve survival rate can shift the Th1/TGF-beta-producing CD4(+) T cell balance in favor of Th1 responses. Our data demonstrate that tumor Ags may contain epitopes which activate the expansion of inducible regulatory T cells, leading to evasion of tumor control.     

Differential requirement for the CD40-CD154 costimulatory pathway during Th cell priming by CD8 alpha+ and CD8 alpha- murine dendritic cell subsets

Dendritic cells (DCs) regulate the development of distinct Th populations and thereby provoke appropriate immune responses to various kinds of Ags. In the present work, we investigated the role CD40-CD154 interactions play during the process of Th cell priming by CD8 alpha(+) and CD8 alpha(-) murine DC subsets, which have been reported to differently regulate the Th response. Adoptive transfer of Ag-pulsed CD8 alpha(+) DCs induced a Th1 response and the production of IgG2a Abs, whereas transfer of CD8 alpha(-) DCs induced Th2 cells and IgE Abs in vivo. Induction of distinct Th populations by each DC subset was also confirmed in vitro. Although interruption of CD80/CD86-CD28 interactions inhibited Th cell priming by both DC subsets, disruption of CD40-CD154 interactions only inhibited the induction of the Th1 response by CD8 alpha(+) DCs in vivo. CD40-CD154 interactions were not required for the proliferation of Ag-specific naive Th cells stimulated by either DC subset, but were indispensable in the production of IL-12 from CD8 alpha(+) DCs and their induction of Th1 cells in vitro. Taken together, in our immunization model of Ag-pulsed DC transfer, CD40-CD154 interactions play an important role in the development of CD8 alpha(+) DC-driven Th1 responses but not CD8 alpha(-) DC-driven Th2 responses to protein Ags.     

Colitis induced by enteric bacterial antigen-specific CD4+ T cells requires CD40-CD40 ligand interactions for a sustained increase in mucosal IL-12

C3H/HeJBir is a mouse substrain that is highly susceptible to colitis. Their CD4+ T cells react to Ags of the commensal enteric bacteria, and the latter can mediate colitis when activated by these Ags and transferred to histocompatible scid recipients. In this study, multiple long-term C3H/HeJBir CD4+ T cell (Bir) lines reactive to commensal enteric bacterial Ags have been generated. All these were Ag specific, pauciclonal, and Th1 predominant; most induced colitis uniformly after transfer to scid recipients. Lesions were focal and marked by increased expression of IL-12p40 and IFN-gamma mRNA and protein. Pathogenic Bir T cell lines expressed CD40 ligand (CD40L) when cultured with Ag-pulsed APCs in vitro. Production of IL-12 was also increased in such cultures, an effect that was Ag- and T cell-dependent and required costimulation by CD40, but not by B7. The two Bir T cell lines that did not induce lesions after transfer failed to significantly express CD40L or increase IL-12 when cultured with Ag-pulsed APCs. Administration of anti-CD40L blocked disease expression induced by pathogenic T cells. We conclude that interactions in the colon mucosa between CD40L-expressing Bir Th1 cells with APCs endogenously loaded with commensal bacterial Ags are critical for sustained increases in local IL-12 production and progression to colitis.     

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.     

Immune modulation in multiple sclerosis patients treated with the pregnancy hormone estriol

The protective effect of pregnancy on putative Th1-mediated autoimmune diseases, such as multiple sclerosis and rheumatoid arthritis, is associated with a Th1 to Th2 immune shift during pregnancy. The hormone estriol increases during pregnancy and has been shown to ameliorate experimental autoimmune encephalomyelitis and collagen-induced arthritis. In addition, estrogens induce cytokine changes consistent with a Th1 to Th2 shift when administered in vitro to human immune cells and in vivo to mice. In a pilot trial, oral estriol treatment of relapsing remitting multiple sclerosis patients caused significant decreases in enhancing lesions on brain magnetic resonance imaging. Here, the immunomodulatory effects of oral estriol therapy were assessed. PBMCs collected longitudinally during the trial were stimulated with mitogens, recall Ags, and glatiramer acetate. Cytokine profiles of stimulated PBMCs were determined by intracellular cytokine staining (IL-5, IL-10, IL-12 p40, TNF-alpha, and IFN-gamma) and cytometric bead array (IL-2, IL-4, IL-5, IL-10, TNF-alpha, and IFN-gamma). Significantly increased levels of IL-5 and IL-10 and decreased TNF-alpha were observed in stimulated PBMC isolated during estriol treatment. These changes in cytokines correlated with reductions of enhancing lesions on magnetic resonance imaging in relapsing remitting multiple sclerosis. The increase in IL-5 was primarily due to an increase in CD4(+) and CD8(+) T cells, the increase in IL-10 was primarily due to an increase in CD64(+) monocytes/macrophages with some effect in T cells, while the decrease in TNF-alpha was primarily due to a decrease in CD8(+) T cells. Further study of oral estriol therapy is warranted in Th1-mediated autoimmune diseases with known improvement during pregnancy.     

IL-12 augments CD8+ T cell development for contact hypersensitivity responses and circumvents anti-CD154 antibody-mediated inhibition.

During sensitization with dinitrofluorobenzene for contact hypersensitivity (CHS) responses, hapten-specific CD8(+) T cells develop into IFN-gamma-producing cells, and CD4(+) T cells develop into IL-4/IL-5-producing cells. Administration of IL-12 during sensitization skews CD4(+) T cell development to IFN-gamma-producing cells, resulting in exaggerated CHS responses. In the current report we tested the role of IL-12 on CD8(+) T cell development during sensitization and elicitation of CHS to dinitrofluorobenzene. Administration of IL-12 during hapten sensitization induced the expression of IL-12Rbeta2 on both CD4(+) and CD8(+) T cells, augmented IFN-gamma production by these T cell populations, and increased the magnitude and duration of the CHS response to hapten challenge. CHS responses were virtually identical in wild-type and IL-12 p40(-/-) mice. Since engagement of CD40 on APC may stimulate IL-12 production, we also tested the role of CD40-CD154 interactions on the development of IFN-gamma-producing CD4(+) and CD8(+) T cells following hapten sensitization. Development of IFN-gamma-producing CD4(+) T cells during hapten sensitization was absent in wild-type mice treated with anti-CD154 mAb or in CD154(-/-) mice. In contrast, the absence of CD40-CD154 signaling had little or no impact on the development of IFN-gamma-producing CD8(+) T cells. These results demonstrate that the development of hapten-specific Th1 effector CD4(+) T cells in CHS requires both CD40-CD154 interactions and IL-12, whereas the development of IFN-gamma-producing effector CD8(+) T cells can occur independently of these pathways.     

Th3 cells in peripheral tolerance. II. TGF-beta-transgenic Th3 cells rescue IL-2-deficient mice from autoimmunity

We developed a transgenic (Tg) mouse that expresses TGF-beta under control of the IL-2 promoter to investigate Th3 cell differentiation both in vitro and in vivo. We previously found that repetitive in vitro Ag stimulation results in constant expression of Foxp3 in TGF-beta-Tg Th3 cells that acquire regulatory function independent of surface expression of CD25. To examine the differentiation and function of Th3 cells in vivo and to compare them with thymic-derived CD4(+)CD25(+) regulatory T cells (Treg), we introduced the TGF-beta transgene into T cells of IL-2-deficient (IL-2(-/-)) mice. We found that the induction, differentiation, and function of TGF-beta-derived Foxp3(+) Th3 cells were independent of IL-2, which differs from thymic Tregs. In an environment that lacks functional CD25(+) thymic-derived Tregs, expression of the TGF-beta transgene in IL-2(-/-) mice led to the induction of distinct CD25(-) regulatory cells in the periphery. These cells expressed Foxp3 and efficiently controlled hyperproliferation of T cells and rescued the IL-2(-/-) mouse from lethal autoimmunity. Unlike IL-2(-/-) animals, TGF-beta/IL-2(-/-) mice had normal numbers of T cells, B cells, macrophages, and dendritic cells and did not have splenomegaly, lymphadenopathy, or inflammation in multiple organs. Accumulation of Foxp3(+) cells over time, however, was dependent on IL-2. Our results suggest that TGF-beta-derived Foxp3(+)CD25(+/-) Th3 regulatory cells represent a different cell lineage from thymic-derived CD25(+) Tregs in the periphery but may play an important role in maintaining thymic Tregs in the peripheral immune compartment by secretion of TGF-beta.     

Cutting edge: regulatory T cells induce CD4+CD25-Foxp3- T cells or are self-induced to become Th17 cells in the absence of exogenous TGF-beta

Recent studies have shown that TGF-beta together with IL-6 induce the differentiation of IL-17-producing T cells (Th17) T cells. We therefore examined whether CD4(+)CD25(+)Foxp3(+) regulatory T cells, i.e., cells previously shown to produce TGF-beta, serve as Th17 inducers. We found that upon activation purified CD25(+) T cells (or sorted GFP(+) T cells obtained from Foxp3-GFP knockin mice) produce high amounts of soluble TGF-beta and when cultured with CD4(+)CD25(-)Foxp3(-) T cells in the presence of IL-6 induce the latter to differentiate into Th17 cells. Perhaps more importantly, upon activation, CD4(+)CD25(+)Foxp3(+)(GFP(+)) T cells themselves differentiate into Th17 cells in the presence of IL-6 (and in the absence of exogenous TGF-beta). These results indicate that CD4(+)CD25(+)Foxp3(+) regulatory T cells can function as inducers of Th17 cells and can differentiate into Th17 cells. They thus have important implications to our understanding of regulatory T cell function and their possible therapeutic use.     

The role of IL-12 in maintaining resistance to Leishmania major

IL-12p40 is required for the maintenance of resistance during Leishmania major infection. In this study, we addressed how IL-12 mediates this function. First, we demonstrated that both subunits of IL-12, p40 and p35, were required for continued resistance to L. major. Second, using IL-12, IL-4 doubly deficient mice, we investigated the possibility that IL-12 inhibits IL-4-induced outgrowth of Th2 cells that might compete with Th1 cells. We found that even in the absence of a Th2 response, IL-12 was still required to maintain resistance. Next, using adoptive transfer of Thy-1 disparate CD4(+) T cells from L. major-healed mice, we were able to show that the loss of a protective response in L. major-infected IL-12-deficient mice is linked with the loss of Th1 cells. In contrast, there was an equal recovery of CD4(+) Th1 cells from wild-type and IL-12-deficient mice when transferred into mice that were not challenged with L. major. The ability of Th1 cells to survive regardless of IL-12 levels in the absence of Ag stimulation was confirmed by adoptive transfer studies of CD4(+) Th1 cells from DO11.10 TCR transgenic mice. Taken together, these results indicate that, rather than modulating Th2 responses or optimizing IFN-gamma production, the critical role for IL-12 in maintaining cell-mediated immunity may be to prevent the loss of Th1 cells during a challenge infection.     

Hepatitis C virus-specific Th17 cells are suppressed by virus-induced TGF-beta

IL-17-secreting T (Th17) cells play a protective role in certain bacterial infections, but they are major mediators of inflammation and are pathogenic in organ-specific autoimmune diseases. However, human Th17 cells appear to be resistant to suppression by CD4(+)CD25(+)FoxP3(+) regulatory T cells, suggesting that they may be regulated by alternative mechanisms. Herein we show that IL-10 and TGF-beta suppressed IL-17 production by anti-CD3-stimulated PBMC from normal individuals. TGF-beta also suppressed IL-17 production by purified CD4(+) T cells, whereas the inhibitory effect of IL-10 on IL-17 production appears to be mediated predominantly by its effect on APC. An examination of patients infected with hepatitis C virus (HCV) demonstrated that Ag-specific Th17 cells are induced during infection and that these cells are regulated by IL-10 and TGF-beta. PBMC from HCV Ab-positive donors secreted IL-17, IFN-gamma, IL-10, and TGF-beta in response to stimulation with the HCV nonstructural protein 4 (NS4). Furthermore, NS4 induced innate TGF-beta and IL-10 expression by monocytes from normal donors and at higher levels from HCV-infected patients. Neutralization of TGF-beta, and to a lesser extent IL-10, significantly enhanced NS4-specific IL-17 and IFN-gamma production by T cells from HCV-infected donors. Our findings suggest that both HCV-specific Th1 and Th17 cells are suppressed by NS4-induced production of the innate anti-inflammatory cytokines IL-10 and TGF-beta. This may represent a novel immune subversion mechanism by the virus to evade host-protective immune responses. Our findings also suggest that TGF-beta and IL-10 play important roles in constraining the function of Th17 cells in general.     

Assessment of cell mediated immunogenicity of Mycobacterium leprae-derived antigens

The antigenicity of Mycobacterium leprae (M. leprae)-derived cell membrane fraction was examined using human dendritic cells (DCs). Immature DCs internalized and processed the cell membrane components, and expressed M. leprae-derived antigens (Ags) on their surface. The expression of MHC class II, CD86, and CD83 Ags on DCs and CD40 ligand (L)-associated IL-12 p70 production from DCs were up-regulated by the membrane Ags. Moreover these stimulated DCs induced significantly higher level of interferon-gamma (IFN-gamma) production by autologous CD4(+) and CD8(+) T cells than those pulsed with equivalent doses of live M. leprae or its cytosol fraction. Both subsets of T cells from tuberculoid leprosy patients also produced several fold more IFN-gamma than those from normal individuals. Furthermore, the intracellular perforin production in CD8(+) T cells was up-regulated in an Ag-dose dependent manner. These results suggest that M. leprae membrane Ags might be useful as the vaccinating agents against leprosy.     

Th3 cells in peripheral tolerance. I. Induction of Foxp3-positive regulatory T cells by Th3 cells derived from TGF-beta T cell-transgenic mice

TGF-beta has been shown to be critical in the generation of CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs). Because Th3 cells produce large amounts of TGF-beta, we asked whether induction of Th3 cells in the periphery was a mechanism by which CD4(+)CD25(+) Tregs were induced in the peripheral immune compartment. To address this issue, we generated a TGF-beta1-transgenic (Tg) mouse in which TGF-beta is linked to the IL-2 promoter and T cells transiently overexpress TGF-beta upon TCR stimulation but produce little or no IL-2, IL-4, IL-10, IL-13, or IFN-gamma. Naive TGF-beta-Tg mice are phenotypically normal with comparable numbers of lymphocytes and thymic-derived Tregs. We found that repeated antigenic stimulation of pathogenic myelin oligodendrocyte glycoprotein (MOG)-specific CD4(+)CD25(-) T cells from TGF-beta Tg mice crossed to MOG TCR-Tg mice induced Foxp3 expression in both CD25(+) and CD25(-) populations. Both CD25 subsets were anergic and had potent suppressive properties in vitro and in vivo. Furthermore, adoptive transfer of these induced regulatory CD25(+/-) T cells suppressed experimental autoimmune encephalomyelitis when administrated before disease induction or during ongoing experimental autoimmune encephalomyelitis. The suppressive effect of TGF-beta on T cell responses was due to the induction of Tregs and not to the direct inhibition of cell proliferation. The differentiation of Th3 cells in vitro was TGF-beta dependent as anti-TGF-beta abrogated their development. Thus, Ag-specific TGF-beta-producing Th3 cells play a crucial role in inducing and maintaining peripheral tolerance by driving the differentiation of Ag-specific Foxp3(+) regulatory cells in the periphery.     

TGF-beta and IL-10 regulation of IFN-gamma produced in Th2-type schistosome granulomas requires IL-12

Interleukin-10 (IL-10) and transforming growth factor-beta (TGF-beta) regulate CD4+ T cell interferon-gamma (IFN-gamma) secretion in schistosome granulomas. The role of IL-12 was determined using C57BL/6 and CBA mice. C57BL/6 IL-4-/- granuloma cells were stimulated to produce IFN-gamma when cultured with IL-10 or TGF-beta neutralizing monoclonal antibody. In comparison, C57BL/6 wild-type (WT) control granuloma cells produced less IFN-gamma. IL-12, IL-18, and soluble egg antigen stimulated IFN-gamma release from C57BL/6 IL-4-/- and WT mice. IFN-gamma production in C57 IL-4-/- and WT granulomas was IL-12 dependent, because IL-12 blockade partly abrogated IFN-gamma secretion after stimulation. All granuloma cells released IL-12 (p70 and p40), and IL-12 production remained constant after anti-TGF-beta, anti-IL-10, recombinant IL-18, or antigen stimulation. C57 WT and IL-4-/- mouse granuloma cells expressed IL-12 receptor (IL-12R) beta1-subunit mRNA but little beta2 mRNA. TGF-beta or IL-10 blockade did not influence beta1 or beta2 mRNA expression. CBA mouse dispersed granuloma cells released no measurable IFN-gamma, produced IL-12 p70 and little p40, and expressed IL-12R beta2 and little beta1 mRNA. In T helper 2 (Th2) granulomas of C57BL/6 WT and IL-4-/- mice, cells produce IL-12 (for IFN-gamma production) and IL-10 and TGF-beta modulate IFN-gamma secretion via mechanisms independent of IL-12 and IL-12R mRNA regulation. We found substantial differences in control of granuloma IFN-gamma production and IL-12 circuitry in C57BL/6 and CBA mice.     

Two phenotypically distinct subsets of spleen dendritic cells in rats exhibit different cytokine production and T cell stimulatory activity

We recently reported that splenic dendritic cells (DC) in rats can be separated into CD4(+) and CD4(-) subsets and that the CD4(-) subset exhibited a natural cytotoxic activity in vitro against tumor cells. Moreover, a recent report suggests that CD4(-) DC could have tolerogenic properties in vivo. In this study, we have analyzed the phenotype and in vitro T cell stimulatory activity of freshly isolated splenic DC subsets. Unlike the CD4(-) subset, CD4(+) splenic DC expressed CD5, CD90, and signal regulatory protein alpha molecules. Both fresh CD4(-) and CD4(+) DC displayed an immature phenotype, although CD4(+) cells constitutively expressed moderate levels of CD80. The half-life of the CD4(-), but not CD4(+) DC in vitro was extremely short but cells could be rescued from death by CD40 ligand, IL-3, or GM-CSF. The CD4(-) DC produced large amounts of the proinflammatory cytokines IL-12 and TNF-alpha and induced Th1 responses in allogeneic CD4(+) T cells, whereas the CD4(+) DC produced low amounts of IL-12 and no TNF-alpha, but induced Th1 and Th2 responses. As compared with the CD4(+) DC that strongly stimulated the proliferation of purified CD8(+) T cells, the CD4(-) DC exhibited a poor CD8(+) T cell stimulatory capacity that was substantially increased by CD40 stimulation. Therefore, as previously shown in mice and humans, we have identified the existence of a high IL-12-producing DC subset in the rat that induces Th1 responses. The fact that both the CD4(+) and CD4(-) DC subsets produced low amounts of IFN-alpha upon viral infection suggests that they are not related to plasmacytoid DC.     

Generation of antigen-specific, Foxp3-expressing CD4+ regulatory T cells by inhibition of APC proteosome function

We tested the hypothesis that immature APC, whose NF-kappaB-signaling pathway and thus maturation was blocked by the proteosome inhibitor benzyloxycarbonyl-isoleucyl-glutamyl(O-tert-butyl)-alanyl-leucinal (PSI), could be a source of Ag-specific regulatory T (Treg) cells. DO11.10 CD4(+) T cells that were incubated with Ag- and PSI-pulsed APC proliferated poorly, produced less IL-2, IFN-gamma, and IL-10 in secondary cultures, and inhibited the response of both naive and memory CD4(+) T cells stimulated by Ag-pulsed APC. The generation of PSI-APC Treg cells required IL-10 production by APC. PSI-APC Treg cell inhibition required cell-cell contact but not IL-10 or TGF-beta. Addition of IL-2 did not reverse, but Ab to CTLA-4 did reverse partially the inhibitory effect. Depletion of CD25(+) T cells before initial culture with PSI-APC did not affect Treg generation. PSI-APC Treg cells expressed high levels of Foxp3, inhibited proliferation of naive DO11.10 T cells in vivo, and abrogated colitis driven by a memory Th1 response to bacterial-associated Ag. We conclude that NF-kappaB-blocked, immature APC are able to induce the differentiation of Treg cells that can function in vitro and in vivo in an Ag-specific manner.     

The pathogenic Th17 cell response to major schistosome egg antigen is sequentially dependent on IL-23 and IL-1β

CBA/J mice infected with the helminth Schistosoma mansoni develop severe CD4 T cell-mediated hepatic granulomatous inflammation against parasite eggs associated with a robust Th17 cell response. We investigated the requisites for Th17 cell development using novel CD4 T cells expressing a transgenic TCR specific for the major Sm-p40 egg Ag, which produce IL-17 when stimulated with live schistosome eggs. Neutralization of IL-23 or blockade of the IL-1 receptor, but not IL-6 neutralization, abrogated egg-induced IL-17 secretion by transgenic T cells, whereas exogenous IL-23 or IL-1β reconstituted their ability to produce IL-17 when stimulated by syngeneic IL-12p40-deficient dendritic cells. Kinetic analysis demonstrated that IL-17 production was initiated by IL-23 and amplified by IL-1β. Significantly, schistosome-infected IL-12p40-deficient or IL-1R antagonist-treated CBA/J mice developed markedly reduced hepatic immunopathology with a dampened egg Ag-specific IL-17 response. These results demonstrate that the IL-23-IL-1-IL-17 axis has a central role in the development of severe schistosome egg-induced immunopathology.     

Immunomodulatory effects of the liver: deletion of activated CD4+ effector cells and suppression of IFN-gamma-producing cells after intravenous protein immunization

The liver is tolerogenic in many situations, including as an allograft and during the response to allogeneic MHC expressed on hepatocytes. The majority of data that address this issue focus on endogenous Ags. Little is known about CD4(+) T cells and their fate under tolerizing conditions, especially with respect to fully differentiated CD4(+) effector T cells. In this study, we used the adoptive transfer of populations of TCR-transgenic CD4(+) T cells, skewed toward the Th1 or Th2 phenotype, to test whether either apoptotic or immune deviation mechanisms apply to cytokine-producing CD4(+) T cells that enter the liver. After transfer, Th1 and Th2 cells could be detected up to 25 days in lymphoid organs and the liver. Intravenous high dose Ag application resulted in accumulation, proliferation, and subsequent deletion of effector cells within the liver. Th1 cells lost their capacity to produce cytokines, whereas IL-4 expression was sustained within Th2 cells from the liver. However, there was no evidence for a deviation of Th1-programmed cells toward a Th2 (IL-4) or regulatory T cell (IL-10) pattern of cytokine expression. We used isolated populations of liver-derived APCs to test whether the liver had the capacity to impose a bias toward IL-4 expression in T cells. These experiments showed that liver sinusoidal endothelial cells selectively suppress the expansion of IFN-gamma-producing cells, yet they promote the outgrowth of IL-4-expressing Th2 cells, creating an immune suppressive milieu within this organ. These data suggest that presentation of Ags in the liver leads to modulation of immune response in terms of quantity and quality.