Interleukin-25 (IL-25 or IL-17E), a member of the structurally related IL-17 family, functions as an important mediator of T helper 2 cell-type (type 2) responses. We examined the cell-type specific role of IL-25-induced Act1-mediated signaling in protective immunity against helminth infection. Targeted Act1 deficiency in epithelial cells resulted in a marked delay in worm expulsion and abolished the expansion of the Lin−c-kit+ innate cell population in the mesenteric lymph node, lung and liver. Th2 cell-inducing cytokines (IL-25 and IL-33) expression were reduced in the intestinal epithelial cells from the infected and IL-25-injected epithelial-specific Act1-deficient mice. Adoptive transfer of Lin−c-kit+ cells or combined injection of IL-25 and IL-33 restored the type 2 responses in these mice. Taken together, these results suggest that epithelial-specific Act1 mediates the expansion of the Lin−c-kit+ innate cell population through the positive feedback loop of IL-25, initiating the type 2 immunity against helminth infection.
Naïve T cells undergo robust proliferation in lymphopenic conditions, while they remain quiescent in steady-state conditions. However, a mechanism by which naïve T cells are kept from proliferating under steady-state conditions remains unclear. Here we report that memory CD4 T cells are able to limit naïve T cell proliferation within lymphopenic hosts by modulating stimulatory functions of DC. The inhibition was mediated by IL-27, which was primarily expressed in CD8+ DC subsets as the result of memory CD4 T cell-DC interaction. IL-27 appeared to be the major mediator of inhibition as naïve T cells deficient in IL-27R were resistant to memory CD4 T cell mediated inhibition. Finally, IL-27-mediated regulation of T cell proliferation was also observed in steady-state conditions as well as during Ag-mediated immune responses. We propose a new model for maintaining peripheral T cell homeostasis via memory CD4 T cells and CD8+ DC-derived IL-27 in vivo.
Within lymphopenic recipients, naïve T cells undergo proliferation that is induced by homeostatic mechanisms. Earlier studies have demonstrated that commensal antigens play a key role in inducing the proliferation. However, a relative contribution of endogenous self antigens in this process has not been formally investigated. In this study, we utilized a pharmacologic inhibitor that blocks T cell egress from the lymphoid tissues, antibiotics, and germ-free animals to examine the role of commensal and self antigens. The results suggest that T cell proliferation under lymphopenic conditions is a heterogeneous process triggered by both exogenous commensal and endogenous self antigens.
homeostasis; T cell; commensal antigen; FTY720; self antigen; lymphopenia
IL-4 production by leukocytes is a key regulatory event that occurs early in the type-2 immune response, which induces allergic reactions and mediates expulsion of parasites. CD4+ T-cells and basophils are thought to be the key cell types that produce IL-4 during a type-2 response. Here, we assessed the relative contribution of both CD4+ T-cell- and basophil-IL-4 production during primary and secondary responses to Nippostrongylus brasiliensis using a murine IL-4-eGFP reporter system. During infection, IL-4 producing basophils were detected systemically and tissue recruitment occurred independent of IL-4/STAT6 signaling. We observed that basophil recruitment to a tissue environment was required for their full activation. Basophil induction in response to secondary infection exhibited accelerated kinetics in comparison to primary infection. However, total basophil numbers were not enhanced, as predicted by previous models of protective immunity. Overall, the induction and migration of IL-4 producing basophils into peripheral tissues was found to be a prominent characteristic of the primary, but not memory responses to N. brasiliensis infection where CD4+ T-cells were identified as the major source of IL-4. While basophils were the major initial producers of IL-4 we determined that normal TH2 differentiation occurs independently of basophils and depletion of basophils led to an enhancement of inflammatory cell recruitment to the site of infection.
Basophils are of interest in immunology due to their ability to produce a Th2-signature cytokine, IL-4, following activation. New understanding of the role of basophils in immunity shows novel functions at a cellular level through which basophils influence adaptive immunity. This review summarizes new advances in basophil biology and discusses new roles for basophils in human disease, especially in the mediation of the pathogenesis of lupus nephritis. Recently, basophils have been shown to contribute to self-reactive antibody production in systemic lupus erythematosus and may enhance pre-existing loss of B cell tolerance, suggesting that basophils, IL-4 and IgE mediate the pathogenesis of lupus nephritis by promoting the Th2 environment and activating autoreactive B cells. In addition to envisaging exciting therapeutic prospects, these novel findings open the way for the study of basophils in other autoimmune and renal diseases.
A proportional balance between αβ and γδ T cell subsets in the periphery is exceedingly well maintained via a homeostatic mechanism. However, a cellular mechanism underlying the regulation remains undefined. We recently reported that a subset of developing γδ T cells spontaneously acquire IL-17-producing capacity even within naïve animals via a TGFβ1-dependent mechanism, thus considered ‘einnate’ IL-17-producing cells. Here we report that γδ T cells generated within αβ T cell (or CD4 T cell)-deficient environments displayed altered cytokine profiles; particularly, ‘einnate’ IL-17 expression was significantly impaired compared to those in wild type mice. Impaired IL-17 production in γδ T cells was directly related to the CD4 T cell deficiency, because depletion of CD4 T cells in wild type mice diminished and adoptive CD4 T cell transfer into TCRβ−/− mice restored IL-17 expression in γδ T cells. CD4 T cell-mediated IL-17 expression required TGFβ1. Moreover, Th17 but not Th1 or Th2 effector CD4 T cells were highly efficient in enhancing γδ T cell IL-17 expression. Taken together, our results highlight a novel CD4 T cell-dependent mechanism that shapes the generation of IL-17+ γδ T cells in naïve settings.
CD4 T cells; γδ T cells; IL-17; TGFβ1
CD4 T cell activation during peripheral infections not only is essential in inducing protective CD8 T cell memory but also promotes CD8 T cell function and survival. However, the contributions of CD4 T cell help to antiviral CD8 T cell immunity during central nervous system (CNS) infection are not well established. Encephalitis induced by the sublethal coronavirus JHMV was used to identify when CD4 T cells regulate CD8 T cell responses following CNS infection. Peripheral expansion of virus-specific CD8 T cells was impaired when CD4 T cells were ablated prior to infection but not at 4 days postinfection. Delayed CD4 T cell depletion abrogated CD4 T cell recruitment to the CNS but only slightly diminished CD8 T cell recruitment. Nevertheless, the absence of CNS CD4 T cells was associated with reduced gamma interferon (IFN-γ) and granzyme B expression by infiltrating CD8 T cells, increased CD8 T cell apoptosis, and impaired control of infectious virus. CD4 T cell depletion subsequent to CD4 T cell CNS migration restored CD8 T cell activity and virus control. Analysis of γc-dependent cytokine expression indicated interleukin-21 (IL-21) as a primary candidate optimizing CD8 T cell activity within the CNS. These results demonstrate that CD4 T cells play critical roles in both enhancing peripheral activation of CD8 T cells and prolonging their antiviral function within the CNS. The data highlight the necessity for temporally and spatially distinct CD4 T cell helper functions in sustaining CD8 T cell activity during CNS infection.
Purpose of review
Mechanisms involved in the development of in-vivo type 2 immunity are poorly defined. Basophils are potent IL-4-producing cells and may contribute to the process of polarizing immune responses.
Although basophils represent fewer than 0.5% of blood leukocytes, their frequency dramatically increases under certain circumstances, particularly Th2-related responses including parasitic infection and allergic inflammation. Recent studies proposed the hypothesis that basophils could contribute to the development of type 2 immunity by providing initial IL-4 important in T cell polarization and by recruiting other effector cells such as eosinophils or neutrophils. Multiple stimuli of IgE-dependent and IgE-independent pathways that lead to release of cytokines and mediators from activated basophils have been identified. In addition, progenitors that differentiate into mature basophils have recently been identified.
The current review revisits basophils with the goal of providing insights into understanding unappreciated roles of basophils in vivo.
basophils; IL-4; parasites; Th2 type immunity
Th17 cells have been implicated in the pathogenesis of colitis; however, a cellular mechanism by which colitogenic Th17 immunity arises in vivo remains unclear. In this study, we report that a subset of IL-17+γδ T cells plays a crucial role in enhancing in vivo Th17 differentiation and T cell-mediated colitis. TCRβ-/- mice were highly susceptible to T cell-mediated colitis, while TCRβδ-/- mice were resistant to the disease. Importantly, cotransfer of IL-17+ but not of IL-17-γδ T cells with CD4 T cells was sufficient to enhance Th17 differentiation and induce full-blown colitis in TCRβδ-/- recipients. Collectively, our results provide a novel function of IL-17+γδ T cell subsets in supporting in vivo Th17 differentiation and possibly in fostering the development of intestinal inflammation.
colitis; γδ T cells; IL-17; Th17 CD4 T cells
In naïve animals, γδ T cells are innate sources of IL-17, a potent proinflammatory cytokine mediating bacterial clearance as well as autoimmunity. However, mechanisms underlying the generation of these cells in vivo remain unclear. Here we show that TGFβ1 plays a key role in the generation of IL-17+ γδ T cells, and that it mainly occurs in the thymus particularly during the postnatal period. Interestingly, IL-17+ γδ TCR+ thymocytes were mainly CD44highCD25low cells, which seem to derive from DN4 γδ TCR+ cells that acquired CD44 and IL-17 expression. Our findings identify a novel developmental pathway during which IL-17-competent γδ T cells arise in the thymus by a TGFβ1-dependent mechanism.
γδ T cells; IL-17; TGFβ
Basophils are recognized as immune modulators through their ability to produce IL-4, a key cytokine required for Th2 immunity. It has also recently been reported that basophils are transiently recruited into the draining LN after allergen immunization and that the recruited basophils promote the differentiation of naïve CD4 T cells into Th2 effector cells. Using IL-3-/- and IL-3Rβ-/- mice, we report here that the IL-3/IL-3R system is absolutely required to recruit circulating basophils into the draining LN following helminth infection. Unexpectedly, the absence of IL-3 or of basophil LN recruitment played little role in helminth-induced Th2 immune responses. Moreover, basophil depletion in infected mice did not diminish the development of IL-4-producing CD4 T cells. Taken together, our results reveal a previously unknown role of IL-3 in recruiting basophils to the LN and demonstrate that basophils are not necessarily associated with the development of Th2 immunity during parasite infection.
basophils; CD4 T cells; IL-3; parasites; Th2 immunity
Basophils are the least abundant granulocytes found in the circulation. Until recently, their functions were poorly understood. In the past few years, the list of basophil functions in the context of immunity has dramatically increased. Thus, the need for basophil-deficient animal models to confirm these findings is imperative. In this issue of the JCI, Wada and colleagues introduce the first mouse model in which basophils are conditionally ablated in vivo. Using this model, they then uncover a nonredundant role for basophils in acquired immunity against tick infection.
Despite the fact that basophils represent less than 0.5% of circulating leukocytes, recent studies have begun to unveil their potent immunoregulatory functions, i.e., induction of Th2 immunity. It is believed that basophils are capable of doing so primarily by secreting key Th2-inducing cytokines, namely IL-4 and Thymic Stromal Lymphopoietin (TSLP), and by functioning as professional antigen presenting cells. However, we have recently demonstrated that Th2 immunity can develop in the absence of basophils or IL-4 during helminth infection. In this review, how basophils may (and may not) contribute to the development of Th2 immunity in vivo is discussed.
basophils; CD4 T cells; IL-3; Nippostrongylus brasiliensis; Th2 immunity
A novel cytokine IL-33, an IL-1 family member, signals via ST2 receptor and promotes T helper type 2 (Th2) responses, through the activation of NFκB and MAP kinases. Previous studies reported that SIGIRR (single immunoglobulin IL-1R-related molecule)/TIR8 (Toll IL-1R8) acts as negative regulator for TLR-IL-1R-mediated signaling. We now found that SIGIRR formed a complex with ST2 upon IL-33 stimulation and specifically inhibited IL-33/ST2-mediated signaling in cell culture model. Furthermore, IL-33-induced Th2 response was enhanced in SIGIRR-deficient mice compared to that in wild-type control mice, suggesting a negative regulatory role of SIGIRR in IL-33/ST2 signaling in vivo. Similar to ST2, SIGIRR was highly expressed in in vitro polarized Th2 cells, but not Th1 cells. SIGIRR-deficient Th2 cells produce higher levels of “Th2 cytokines”, including IL-5, IL-4 and IL-13 than that in wild-type cells. Moreover, SIGIRR-deficient mice developed stronger Th2 immune response in OVA-challenged asthma model. Taken together, our results suggest that SIGIRR plays an important role in the regulation of Th2 response in vivo, possibly through its impact on IL-33-ST2-mediated signaling.
Th1/Th2 Cells; Cytokine receptors; Eosinophils; Lung
Basophils represent potential effector and immunoregulatory cells, as well as a potential source of IL-4, during the immune response elicited by infection with the nematode Nippostrongylus brasiliensis (N.b.), and in other settings. However, the factors which regulate the numbers of blood basophils in mice, or the ability of these cells to produce IL-4, are not fully understood. We found that infection of mice with the nematodes N.b. or Strongyloides venezuelensis (S.v.) induced substantial increases in the numbers of blood basophils (to as high as 18 % of circulating blood leukocytes). Experiments in IL-3−/− vs IL-3+/+ mice, and in IL-3-treated IL-3−/− mice, showed that essentially all of the increases in blood or bone marrow basophils during N.b. or S.v. infection were IL-3-dependent. Many of the blood, bone marrow or liver-derived basophils from IL-3−/− or IL-3+/+ mice expressed intra-cellular IL-4 upon stimulation with anti-IgE in vitro. However, after incubation of the cells with exogenous IgE in vitro, blood- or liver-derived basophils from IL-3+/+ mice exhibited higher levels of intra-cellular IL-4 after stimulation with anti-IgE than did basophils derived from IL-3−/− mice. Thus, IL-3 is a major regulator of the marked increases in blood basophil levels observed during infection of mice with N.b. or S.v. and also can enhance levels of intra-cellular IL-4 upon activation of basophils with anti-IgE in vitro.
Allergy; Cytokines; Immune response; Inflammation; Mast cells; Parasites
Electricity generation from wheat straw hydrolysate and the microbial ecology of electricity-producing microbial communities developed in two-chamber microbial fuel cells (MFCs) were investigated. The power density reached 123 mW/m2 with an initial hydrolysate concentration of 1,000 mg chemical oxygen demand (COD)/liter, while coulombic efficiencies ranged from 37.1 to 15.5%, corresponding to the initial hydrolysate concentrations of 250 to 2,000 mg COD/liter. The suspended bacteria found were different from the bacteria immobilized in the biofilm, and they played different roles in electricity generation from the hydrolysate. The bacteria in the biofilm were consortia with sequences similar to those of Bacteroidetes (40% of sequences), Alphaproteobacteria (20%), Bacillus (20%), Deltaproteobacteria (10%), and Gammaproteobacteria (10%), while the suspended consortia were predominately Bacillus (22.2%). The results of this study can contribute to improving understanding of and optimizing electricity generation in microbial fuel cells.
The physiologic control of cytokine receptor activation is primarily mediated by reciprocal activation of receptor-associated protein tyrosine kinases and protein tyrosine phosphatases (PTPs). Here, we show that immediately following ligand-dependent activation, IL-4 receptor induces an intracellular calcium flux via IRS-PI3K-PLC-γ pathway which, in turn, induces PKC-dependent activation of NAD(P)H oxidase (NOX)5 that generates reactive oxygen species (ROS). IL-4 also induces NOX1-mediated ROS production via IRS-PI3K-RAC1 pathway. ROS, in turn, promote IL-4 receptor activation by oxidatively inactivating PTP1B that physically associates with and deactivates IL-4 receptor. However, ROS are not required for the initiation of IL-4 receptor activation. ROS generated by activated EPO-, TNF-α- or IL-3 receptor also promote IL-4 signaling. These data reveal that inactivation of receptor-associated PTP-activity by cytokine-generated ROS is a physiologic mechanism for the amplification of cytokine receptor activation in both cis and trans, unfolding a novel means of cytokine signaling cross-talk.
In humans, limited T-cell receptor repertoire and lymphopenia are associated with severe eosinophilic inflammatory disease. A model of lymphopenia and reduced T-cell repertoire was created; C57BL/6 Rag2−/− mice received limited (30,000) or large (2 million) numbers of CD4 T-cells. Three to five months post-transfer, mice that had received 30,000 T-cells, but not those that received 2 million, developed fulminant macrophage pneumonia with eosinophilia, Ym1 deposition. methacholine-induced airway hyperresponsiveness, eosinophilic gastritis and esophagitis. These mice had strikingly elevated serum IgE (in CD3ε−/− hosts) and donor-cells were enriched for IL-4, IL-5 and IL-13 producers. Th2 pathology and serum IgE were enhanced when transferred populations were depleted of CD25+ CD4 Tregs, but was more severe when the effector population was derived from limited as compared to the large effector population. Pretreatment of Rag2−/− mice with 300,000 CD25+ CD4 Tregs prior to effector cell transfer prevented disease while pretreatment with 30,000 did not, despite the fact that there were equal numbers of Tregs in the hosts at the time of transfer of effector cells. Limited repertoire complexity of Tregs may lead to a failure to control immunopathologic responses and limited repertoire complexity of conventional cells may be responsible for the Th2 phenotype.
IL-4; IL-13; IgE; alternatively activated macrophages; eosinophils
IRAK4 is a member of IL-1 receptor (IL-1R)–associated kinase (IRAK) family and has been shown to play an essential role in Toll-like receptor (TLR)–mediated signaling. We recently generated IRAK4 kinase-inactive knock-in mice to examine the role of kinase activity of IRAK4 in TLR-mediated signaling pathways. The IRAK4 kinase–inactive knock-in mice were completely resistant to lipopolysaccharide (LPS)- and CpG-induced shock, due to impaired TLR-mediated induction of proinflammatory cytokines and chemokines. Although inactivation of IRAK4 kinase activity did not affect the levels of TLR/IL-1R–mediated nuclear factor κB activation, a reduction of LPS-, R848-, and IL-1–mediated mRNA stability contributed to the reduced cytokine and chemokine production in bone marrow–derived macrophages from IRAK4 kinase–inactive knock-in mice. Both TLR7- and TLR9-mediated type I interferon production was abolished in plasmacytoid dendritic cells isolated from IRAK4 knock-in mice. In addition, influenza virus–induced production of interferons in plasmacytoid DCs was also dependent on IRAK4 kinase activity. Collectively, our results indicate that IRAK4 kinase activity plays a critical role in TLR-dependent immune responses.
Infection with gastrointestinal nematodes exerts profound effects on both immune and physiological responses of the host. Helminth infection induces a hypercontractility of intestinal smooth muscle that is dependent on the Th2 cytokines, IL-4 and IL-13, and may contribute to worm expulsion. Protease-activated receptors (PARs) are expressed throughout the gut, and activation of PAR-1 was observed in asthma, a Th2-driven pathology. In the current study we investigated the physiologic and immunologic regulation of PAR-1 in the murine small intestine, specifically 1) the effect of PAR-1 agonists on small intestinal smooth muscle contractility, 2) the effects of Nippostrongylus brasiliensis infection on PAR-1 responses, 3) the roles of IL-13 and IL-4 in N. brasiliensis infection-induced alterations in PAR-1 responses, and 4) the STAT6 dependence of these responses. We demonstrate that PAR-1 activation induces contraction of murine intestinal smooth muscle that is enhanced during helminth infection. This hypercontractility is associated with an elevated expression of PAR-1 mRNA and protein. N. brasiliensis-induced changes in PAR-1 function and expression were seen in IL-4-deficient mice, but not in IL-13- or STAT6-deficient mice, indicating the dependence of IL-13 on the STAT6 signaling pathway independent of IL-4.
Using mice in which the eGfp gene replaced the first exon of the Il4 gene (G4 mice), we examined production of interleukin (IL)-4 during infection by the intestinal nematode Nippostrongylus brasiliensis (Nb). Nb infection induced green fluorescent protein (GFP)pos cells that were FcɛRIpos, CD49bbright, c-kitneg, and Gr1neg. These cells had lobulated nuclei and granules characteristic of basophils. They were found mainly in the liver and lung, to a lesser degree in the spleen, but not in the lymph nodes. Although some liver basophils from naive mice express GFP, Nb infection enhanced GFP expression and increased the number of tissue basophils. Similar basophil GFP expression was found in infected Stat6−/− mice. Basophils did not increase in number in infected Rag2−/− mice; Rag2−/− mice reconstituted with CD4 T cells allowed significant basophil accumulation, indicating that CD4 T cells can direct both tissue migration of basophils and enhanced IL-4 production. IL-4 production was immunoglobulin independent and only partially dependent on IL-3. Thus, infection with a parasite that induces a “Th2-type response” resulted in accumulation of tissue basophils, and these cells, stimulated by a non-FcR cross-linking mechanism, are a principal source of in vivo IL-4 production.
CD4; T cells; cytokine; green fluorescent protein; Nippostrongylus brasiliensis; liver
Interleukin (IL)-18 synergizes with IL-12 to promote T helper cell (Th)1 responses. Somewhat paradoxically, IL-18 administration alone strongly induces immunoglobulin (Ig)E production and allergic inflammation, indicating a role for IL-18 in the generation of Th2 responses. The ability of IL-18 to induce IgE is dependent on CD4+ T cells, IL-4, and signal transducer and activator of transcription (stat)6. Here, we show that IL-18 fails to induce IgE both in CD1d−/− mice that lack natural killer T (NKT) cells and in class II−/− mice that lack conventional CD4+ T cells. However, class II−/− mice reconstituted with conventional CD4+ T cells show the capacity to produce IgE in response to IL-18. NKT cells express high levels of IL-18 receptor (R)α chain and produce significant amounts of IL-4, IL-9, and IL-13, and induce CD40 ligand expression in response to IL-2 and IL-18 stimulation in vitro. In contrast, conventional CD4+ T cells express low levels of IL-18Rα and poorly respond to IL-2 and IL-18. Nevertheless, conventional CD4+ T cells are essential for B cell IgE responses after the administration of IL-18. These findings indicate that NKT cells might be the major source of IL-4 in response to IL-18 administration and that conventional CD4+ T cells demonstrate their helper function in the presence of NKT cells.
IL-18R; CD4+ NK1.1+ T cells; Th2 cytokines; CD40 ligand; allergy
Several immune-based approaches are being considered for modulation of inflammatory T cells and amelioration of autoimmune diseases. The most recent strategies include simulation of peripheral self-tolerance by injection of adjuvant free antigen, local delivery of cytokines by genetically altered T cells, and interference with the function of costimulatory molecules. Although promising results have been obtained from these studies that define mechanisms of T cell modulation, efficacy, practicality, and toxicity, concerns remain unsolved, thereby justifying further investigations to define alternatives for effective downregulation of aggressive T cells. In prior studies, we demonstrated that an immunoglobulin (Ig) chimera carrying the encephalitogenic proteolipid protein (PLP)1 peptide corresponding to amino acid sequence 139–151 of PLP, Ig-PLP1, is presented to T cells ∼100-fold better than free PLP1. Here, we demonstrate that aggregation endows Ig-PLP1 with an additional feature, namely, induction of interleukin (IL)-10 production by macrophages and dendritic cells, both of which are antigen-presenting cells (APCs). These functions synergize in vivo and drive effective modulation of autoimmunity. Indeed, it is shown that animals with ongoing active experimental allergic encephalomyelitis dramatically reduce the severity of their paralysis when treated with adjuvant free aggregated Ig-PLP1. Moreover, IL-10 displays bystander antagonism on unrelated autoreactive T cells, allowing for reversal of disease involving multiple epitopes. Therefore, aggregated Ig-PLP1 likely brings together a peripheral T cell tolerance mechanism emanating from peptide presentation by APCs expressing suboptimal costimulatory molecules and IL-10 bystander suppression to drive a dual-modal T cell modulation system effective for reversal of autoimmunity involving several epitopes and diverse T cell specificities.
autoimmunity; antigen delivery; bystander downregulation; cytokine antagonism; T cell modulation
Induction of neonatal T cell tolerance to soluble antigens requires the use of incomplete Freund's adjuvant (IFA). The side effects that could be associated with IFA and the ill-defined mechanism underlying neonatal tolerance are setbacks for this otherwise attractive strategy for prevention of T cell–mediated autoimmune diseases. Presumably, IFA contributes a slow antigen release and induction of cytokines influential in T cell differentiation. Immunoglobulins (Igs) have long half-lives and could induce cytokine secretion by binding to Fc receptors on target cells. Our hypothesis was that peptide delivery by Igs may circumvent the use of IFA and induce neonatal tolerance that could confer resistance to autoimmunity. To address this issue we used the proteolipid protein (PLP) sequence 139–151 (hereafter referred to as PLP1), which is encephalitogenic and induces experimental autoimmune encephalomyelitis (EAE) in SJL/J mice. PLP1 was expressed on an Ig, and the resulting Ig–PLP1 chimera when injected in saline into newborn mice confers resistance to EAE induction later in life. Mice injected with Ig–PLP1 at birth and challenged as adults with PLP1 developed T cell proliferation in the lymph node but not in the spleen, whereas control mice injected with Ig–W, the parental Ig not including PLP1, developed T cell responses in both lymphoid organs. The lymph node T cells from Ig–PLP1 recipient mice were deviated and produced interleukin (IL)-4 instead of IL-2, whereas the spleen cells, although nonproliferative, produced IL-2 but not interferon (IFN)-γ. Exogenous IFN-γ, as well as IL-12, restored splenic proliferation in an antigen specific manner. IL-12–rescued T cells continued to secrete IL-2 and regained the ability to produce IFN-γ. In vivo, administration of anti–IL-4 antibody or IL-12 restored disease severity. Therefore, adjuvant-free induced neonatal tolerance prevents autoimmunity by an organ-specific regulation of T cells that involves both immune deviation and a new form of cytokine- dependent T cell anergy.
neonatal tolerance; deviation; anergy; autoimmunity; antigen delivery
T cell receptor (TCR) antagonism is being considered for inactivation of aggressive T cells and reversal of T cell–mediated autoimmune diseases. TCR antagonist peptides silence aggressive T cells and reverse experimental allergic encephalomyelitis induced with free peptides. However, it is not clear whether free antagonist peptides could reverse natural disease where the antigen is presumably available for endocytic processing and peptides gain access to newly synthesized class II MHC molecules. Using an efficient endocytic presentation system, we demonstrate that a proteolipid protein (PLP) TCR antagonist peptide (PLP-LR) presented on an Ig molecule (IgPLP-LR) abrogates the activation of T cells stimulated with free encephalitogenic PLP peptide (PLP1), native PLP, or an Ig containing PLP1 peptide (Ig-PLP1). Free PLP-LR abolishes T cell activation when the stimulator is free PLP1 peptide, but has no measurable effect when the stimulator is the native PLP or Ig-PLP1. In vivo, Ig-PLP1 induces a T cell response to PLP1 peptide. However, when coadministered with Ig-PLP-LR, the response to PLP1 peptide is markedly reduced whereas the response to PLP-LR is normal. Free PLP-LR coadministered with Ig-PLP1 has no effect on the T cell response to PLP1. These findings indicate that endocytic presentation of an antagonist peptide by Ig outcompete both external and endocytic agonist peptides whereas free antagonist hinders external but not endocytic agonist peptide. Direct contact with antagonist ligand and/or trans-regulation by PLP-LR–specific T cells may be the operative mechanism for Ig-PLP-LR–mediated downregulation of PLP1-specific T cells in vivo. Efficient endocytic presentation of antagonist peptides, which is the fundamental event for either mechanism, may be critical for reversal of spontaneous T cell–mediated autoimmune diseases where incessant endocytic antigen processing could be responsible for T cell aggressivity.