Activation of naive CD4(+) T-helper cells results in the development of at least two distinct effector populations, Th1 and Th2 cells. Th1 cells produce cytokines (interferon (IFN)-gamma, interleukin (IL)-2, tumour-necrosis factor (TNF)-alpha and lymphotoxin) that are commonly associated with cell-mediated immune responses against intracellular pathogens, delayed-type hypersensitivity reactions, and induction of organ-specific autoimmune diseases. Th2 cells produce cytokines (IL-4, IL-10 and IL-13) that are crucial for control of extracellular helminthic infections and promote atopic and allergic diseases. Although much is known about the functions of these two subsets of T-helper cells, there are few known surface molecules that distinguish between them. We report here the identification and characterization of a transmembrane protein, Tim-3, which contains an immunoglobulin and a mucin-like domain and is expressed on differentiated Th1 cells. In vivo administration of antibody to Tim-3 enhances the clinical and pathological severity of experimental autoimmune encephalomyelitis (EAE), a Th1-dependent autoimmune disease, and increases the number and activation level of macrophages. Tim-3 may have an important role in the induction of autoimmune diseases by regulating macrophage activation and/or function.

Chronic progression of two T cell-mediated central nervous system (CNS) demyelinating models of multiple sclerosis, relapsing EAE (R-EAE) and Theiler's murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD) is dependent on the activation of T cells to endogenous myelin epitopes (epitope spreading). Using transfer of carboxyfluorescein succinyl ester (CFSE)-labeled T-cell receptor (TCR)-transgenic T cells and mixed bone marrow chimeras, we show that activation of naive proteolipid protein (PLP)139-151-specific T cells in SJL mice undergoing PLP178-191-induced R-EAE or TMEV-IDD occurs directly in the CNS and not in the cervical lymph nodes or other peripheral lymphoid organs. Examination of the antigen-presentation capacity of antigen-presenting cell (APC) populations purified from the CNS of mice with PLP178-191-induced R-EAE shows that only F4/80-CD11c+CD45hi dendritic cells (DCs) efficiently present endogenous antigen to activate naive PLP139-151-specific T cells in vitro. In contrast, DCs as well as F4/80+CD45hi macrophages and F4/80+CD45lo microglia activate a PLP139-151-specific helper T cell line. The data suggest that naive T cells enter the inflamed CNS and are activated by local APCs, possibly DCs, to initiate epitope spreading.

The newly identified TIM family of proteins is associated with regulation of T helper type 1 (T(H)1) and T(H)2 immune responses. TIM-1 is genetically linked to asthma and is a receptor for hepatitis A virus, but the endogenous ligand of TIM-1 is not known. Here we show that TIM-4, which is expressed by antigen-presenting cells, is the ligand for TIM-1. In vivo administration of either soluble TIM-1-immunoglobulin (TIM-1-Ig) fusion protein or TIM-4-Ig fusion protein resulted in hyperproliferation of T cells, and TIM-4-Ig costimulated T cell proliferation mediated by CD3 and CD28 in vitro. These data suggest that the TIM-1-TIM-4 interaction is involved in regulating T cell proliferation.

A central challenge for improving autoimmune therapy is preventing inflammatory pathology without inducing generalized immunosuppression. T helper 17 (TH17) cells, characterized by their production of interleukin-17, have emerged as important and broad mediators of autoimmunity. Here we show that the small molecule halofuginone (HF) selectively inhibits mouse and human TH17 differentiation by activating a cytoprotective signaling pathway, the amino acid starvation response (AAR). Inhibition of TH17 differentiation by HF is rescued by the addition of excess amino acids and is mimicked by AAR activation after selective amino acid depletion. HF also induces the AAR in vivo and protects mice from TH17-associated experimental autoimmune encephalomyelitis. These results indicate that the AAR pathway is a potent and selective regulator of inflammatory T cell differentiation in vivo.

T cells that can respond to self-antigens are present in the peripheral immune repertoire of all healthy individuals. Recently we have found that unmanipulated SJL mice that are highly susceptible to EAE also maintain a very high frequency of T cells responding to an encephalitogenic epitope of a myelin antigen proteolipid protein (PLP) 139-151 in the peripheral repertoire. This is not due to lack of expression of myelin antigens in the thymus resulting in escape of PLP 139-151 reactive cells from central tolerance, but is due to expression of a splice variant of PLP named DM20, which lacks the residues 116-150. In spite of this high frequency, the PLP 139-151 reactive cells remain undifferentiated in the periphery and do not induce spontaneous EAE. In contrast, SJL TCR transgenic mice expressing a receptor derived from a pathogenic T cell clone do develop spontaneous disease. This may be because in normal mice, autoreactive cells are kept in check by an alternate PLP 139-151 reactive nonpathogenic repertoire, which maintains a balance that keeps them healthy. If this is the case, selective activation of one repertoire or the other may alter susceptibility to autoimmune disease. Since T cells are generally cross-reactive, besides responding to nonself-antigens, they also maintain significant responses to self-antigens. Based on the PLP 139-151 system, we propose a model in which activation with foreign antigens can result in the generation of pathogenic memory T cells that mediate autoimmunity. We also outline circumstances under which activation of self-reactive T cells with foreign antigens can generate selective tolerance and thus generate protective/regulatory memory against self while still maintaining significant responses against foreign antigens. This provides a mechanism by which the fidelity and specificity of the immune system against foreign antigens is improved without increasing the potential for developing an autoimmune disease.

Proteolipid protein (PLP)-139 -151 is the dominant encephalitogenic peptide that induces experimental autoimmune encephalomyelitis (EAE) in SJL (H-2 s ) mice. To examine the contribution of T cell receptor (TCR) specificity in the induction of EAE, we generated transgenic mice expressing the rearranged TCR genes from an encephalitogenic or a nonencephalitogenic PLP-139 -151͞I-A s -specific T cell clone. Both types of transgenic lines developed spontaneous EAE, but, remarkably, the lines expressing the TCR from the nonencephalitogenic clone showed increasingly higher frequencies of disease (60 -83%) in progressive SJL backcrosses and could not be propagated on the susceptible background. The T cells from the transgenic mice were not tolerized, because they responded vigorously to the antigen in vitro and mediated EAE when the mice were immunized with antigen. Besides being the only description of a TCR transgenic mice for the PLP-139 -151͞I-A s epitope, the results demonstrate that the TCR from a nonencephalitogenic PLP-specific T cell clone can induce autoimmune disease when expressed appropriately in vivo. Myelin proteolipid protein (PLP) is the major protein of the central nervous system (CNS) myelin. Multiple epitopes of PLP that can induce experimental autoimmune encephalomyelitis (EAE) in several different strains of mice have been identified (1-5). In SJL (H-2 s ) mice, there are two major encephalitogenic epitopes of PLP, 6), each of which binds with a binding affinity of K 50 Ͻ 1 M to I-A s (5), but the immune response to PLP-139-151 is unusually dominant. First, immunization of SJL mice with whole spinal cord homogenate that contains multiple myelin antigens including myelin basic protein (MBP), PLP, and myelin oligodendrocyte glycoprotein results in a T cell response directed entirely to the PLP-139-151 epitope (7). Second, if PLP-139-151-specific T cells are tolerized in SJL mice, disease induction by whole spinal cord homogenate is abrogated (8). In addition to the unique features of this epitope, different H-2 s strains show differences in their susceptibility to EAE. Whereas SJL mice are highly susceptible, B10.S mice are relatively resistant to the development of EAE when they are immunized with PLP-139-151. Thus, these mouse strains provide an opportunity to identify the genetic loci and genes that are responsible for disease susceptibility (9).In this paper, we describe the generation of PLP-139-151-specific TCR-transgenic mice by expressing rearranged TCR ␣ and ␤ chains from an encephalitogenic and a nonencephalitogenic T cell clone derived from SJL mice and that are specific for PLP-139-151. The transgenic mice expressing either the encephalitogenic or the nonencephalitogenic TCR developed spontaneous EAE in specific pathogen-free͞viral antibody-free conditions (SPF͞VAF). More importantly, the two lines of transgenic mice expressing TCR from the nonencephalitogenic clone developed spontaneous EAE with such a high frequency that they could not be maintained on the SJL background. Materials and ...

AU-rich elements within the 3' untranslated region of transcripts of lymphokines and some protooncogenes serve as signal for rapid mRNA degradation. By using an AUUUA matrix, we have affinity-purified a 32-kDa protein, microsequenced it, and cloned the corresponding cDNA. In vitro, the recombinant protein bound specifically to AU-rich transcripts, including those for interleukin 3, granulocyte/macrophage colony-stimulating factor, c-fos, and c-myc. Sequence analysis revealed an unexpected homology to enoylCoA hydratase (EC 4.2.1.17), and the recombinant protein showed a low degree of the enzymatic activity. Thus, this gene, designated AUH, encodes an RNA binding protein with intrinsic enzymatic activity. Protein immobilized on an AUUUA matrix was enzymatically active, suggesting that hydratase and AU-binding functions are located on distinct domains within a single polypeptide.

To date, very few Ag-based regimens have been defined that could expand T regulatory (Treg) cells to reverse autoimmunity. Additional understanding of Treg function with respect to specificity and broad suppression should help overcome these limitations. Ig-proteolipid protein (PLP)1, an Ig carrying a PLP1 peptide corresponding to amino acid residues 139-151 of PLP, displayed potent tolerogenic functions and proved effective against experimental allergic encephalomyelitis (EAE). In this study, we took advantage of the Ig-PLP1 system and the PLP1-specific TCR transgenic 5B6 mouse to define a regimen that could expand Ag-specific Treg cells in vivo and tested for effectiveness against autoimmunity involving diverse T cell specificities. The findings indicate that in vivo exposure to aggregated Ig-PLP1 drives PLP1-specific 5B6 TCR transgenic cells to evolve as Treg cells expressing CD25, CTLA-4, and Foxp3 and producing IL-10. These Treg cells were able to suppress PLP1 peptide-induced EAE in both SJL/J and F1 (SJL/J × C57BL/6) mice. However, despite being effective against disease induced with a CNS homogenate, the Treg cells were unable to counter EAE induced by a myelin basic protein or a myelin oligodendrocyte glycoprotein peptide. Nevertheless, activation with Ag before transfer into the host mice supports suppression of both myelin oligodendrocyte glycoprotein- and myelin basic protein peptide-induced EAE. Thus, it is suggested that activation of Treg cells by the cognate autoantigen is necessary for operation of broad suppressive functions.