Lindsay B. Nicholson

An altered peptide ligand mediates immune deviation and prevents autoimmune encephalomyelitis.

In experimental autoimmune encephalomyelitis (EAE) induced with myelin proteolipid protein (PLP) peptide 139-151, we have previously shown that the disease is mediated by Th1 cells, which recognize tryptophan 144 as the primary TCR contact point. Here we describe an altered peptide ligand (APL), generated by a single amino acid substitution (tryptophan to glutamine) at position 144 (Q144), which inhibits the development of EAE induced with the native PLP 139-151 peptide (W144). We show that the APL induces T cells that are cross-reactive with the native peptide and that these cells produce Th2 (IL-4 and IL-10) and Th0 (IFN gamma and IL-10) cytokines. Adoptive transfer of T cell lines generated with the APL confer protection from EAE. These data show that changing a single amino acid in an antigenic peptide can significantly influence T cell differentiation and suggest that immune deviation may be one of the mechanisms by which APLs can inhibit an autoimmune disease.

Manipulation of the Th1/Th2 balance in autoimmune disease.

Many autoimmune diseases are caused by autopathogenic Th1 cells. Because in vitro Th1 and Th2 cells cross-regulate each other, it is likely that the induction of self-antigen-specific Th2 cells can prevent autoimmune disease. In the past year, investigators have further defined the role of Th1 and Th2 cytokines in the induction and regulation of autoimmunity. Furthermore, the role of MHC-antigen-T-cell avidity (strength of signal) in inducing such protective immune responses has been elucidated.

IL-4, IL-10, IL-13, and TGF-beta from an altered peptide ligand-specific Th2 cell clone down-regulate adoptive transfer of experimental autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) is induced in the SJL/J mouse by adoptive transfer of activated proteolipid protein peptide (PLP) 139-151-specific Th1 cells. T cells responding to altered peptide ligands (APL) of PLP, previously shown to induce Th2 differentiation and regulate disease in PLP-immunized mice, do not transfer EAE. However, the exact mechanism of disease regulation by APL-specific T cells has not been elucidated. In this report, we show that 1F1, a Th2 clone specific for an APL of PLP139-151 can prevent adoptive transfer of EAE when cocultured with PLP-encephalitogenic spleen cells (PLP-spleen). Cytokines from activated 1F1 cells were detected by hybridization of mRNA to oligonucleotide arrays (DNA chip) and by ELISA. The Th2 cytokines found to be present at the highest protein and mRNA levels were evaluated for their role in suppression of adoptive transfer of EAE from PLP-activated spleen cell cultures. Abs to individual cytokines in 1F1 PLP-spleen cocultures suggested that IL-4, IL-13, and TGF-β played a significant role in suppressing EAE. Abs to the combination of IL-4, IL-10, IL-13, and TGF-β completely neutralized the protective effect of 1F1. Addition of Th2 cytokines to PLP-spleen cultures showed that IL-13 and TGF-β were each individually effective and low levels of IL-4 synergized with IL-13 to inhibit disease transfer. IL-5, IL-9, and IL-10 had little or no effect whereas GM-CSF slightly enhanced EAE. Our results demonstrate that Th2 cytokines derived from APL-specific Th2 cells can effectively down-regulate the encephalitogenic potential of PLP-spleen cells if present during their reactivation in culture.

Detection of Autoreactive Myelin Proteolipid Protein 139–151-Specific T Cells by Using MHC II (IAs) Tetramers

Detection of autoreactive T cells using MHC II tetramers is difficult because of the low affinity of their TCR. We have generated a class II tetramer using the IAs class II molecule combined with an autoantigenic peptide from myelin proteolipid protein (PLP; PLP139–151) and used it to analyze myelin PLP139–151-reactive T cells. Using monomers and multimerized complexes labeled with PE, we confirmed the specificity of the reagent by bioassay and flow cytometry. The IAs tetramers stimulated and stained the PLP139–151-specific 5B6 TCR transgenic T cells and a polyclonal cell line specific for PLP139–151, but not a control T cell line specific for PLP178–191. We used this reagent to optimize conditions to detect low affinity autoreactive T cells. We found that high pH (∼8.0) and neuraminidase treatment enhances the staining capacity of PLP139–151 tetramer without compromising specificity. Furthermore, we found that induction of calcium fluxing by tetramers in T cells may be used as a sensitive measure to detect autoreactive T cells with a low affinity. Taken together, the data show that the tetrameric reagent binds and stimulates PLP139–151-reactive T cells with specificity. This tetrameric reagent will be useful in studying the evolution of PLP139–151-specific repertoire in naive mice and its expansion during the autoimmune disease experimental autoimmune encephalomyelitis.

The role of cytokines in experimental autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) is an animal model of the demyelinating disease multiple sclerosis. In EAE cytokines play a critical role in defining the Th1 or Th2 nature of the autoantigen directed immune response, and in propagating and regulating inflammation within the central nervous system. In this review we summarize some of the recent developments in the field of cytokine research that relate to this model of human disease, focusing principally on disease induced with the autoantigens myelin proteolipid protein and myelin oligodendrocyte protein.

T cell tolerance induced by cross-reactive TCR ligands can be broken by superagonist resulting in anti-inflammatory T cell cytokine production.

Cross-reactive activation of potentially autoreactive T cells by high-affinity nonself ligands may be important in breaking self-tolerance in autoimmunity. In a mouse transgenic for a cross-reactive TCR, we have previously shown that a hyperstimulating altered peptide ligand, L144, induced unresponsiveness to the self peptide, proteolipid protein 139–151. In this study, we demonstrate that a superagonist ligand can break T cell tolerance induced by the lower affinity cognate Ag. T cells tolerant to the cognate ligand, Q144, responded to superagonist, L144, by proliferation and the production of mainly IL-4 and IL-10 in vitro. In contrast, T cells that were tolerized to the superagonist were unable to respond to any peptide that cross-reacted with the transgenic TCR. Low-dose immunization with the superagonist L144 was able to break tolerance to the cognate ligand in vivo and resulted in a blunted proliferative response with production of Th2 cytokines.

Cytokines in Autoimmune Disease

Cytokines play an important role in the induction and regulation of autoimmune diseases. They mediate the expansion and differentiation of T helper (Th) cells to generate autoantigen-reactive pathogenic or protective effectors, they help self-reactive B cells to produce autoantibodies, and they also participate in mediating tissue damage in the target organ. Cytokines also control tissue tolerance and “immune-privilege” and prevent the propagation of inflammation in a number of organs. In addition, in concert with the selectin and intergrin molecules, cytokines control the trafficking and homing of self-reactive cells to target organs. Simply put, cytokines form a central coordinating network of soluble effector molecules and this plays a crucial role at every step of development of autoimmune disease: in the generation of pathogenic (or protective) effectors, in the trafficking of pathogenic cells to the target organ, and in mediating tissue damage or tissue tolerance in the target organ.

The Origin and Regulation of Autopathogenic T Cells

A clear understanding of the events surrounding the selection of autoreactive T cells in the thymus and their regulation in the periphery has eluded immunologists for years. However, recent work examining the expression of tissue-specific antigens in the thymus and the biochemistry of disease associated MHC alleles has provided important clues into the generation of the autoreactive T cell repertoire in the thymus. In addition, recent studies focusing on the role of immunoregulatory cytokines and cross-reactive peptide ligands has provided information regarding both the regulation and activation of autoreactive cells in the periphery. An improved understanding of the selection and regulation of autoreactive T cells will undoubtedly aid in the development of strategies for treating autoimmune disease.

Selecting killers: the line between life and death

How do T cells that are specific for pancreatic islet cell antigens cause diabetes? A recent paper in Nature provides evidence from NOD mice that the killer T cells responsible increase their avidity as the disease progresses—removing the high avidity clones prevents disease.

Expansion by self antigen is necessary for the induction of experimental autoimmune encephalomyelitis by T cells primed with a cross-reactive environmental antigen

Cross-reactivity with environmental antigens has been postulated as a mechanism responsible for the induction of autoimmune disease. Experimental autoimmune encephalomyelitis is a T cell-mediated autoimmune disease model inducible in susceptible strains of laboratory animals by immunization with protein constituents of myelin. We used myelin proteolipid protein (PLP) peptide 139-151 and its analogues to define motifs to search a protein database for structural homologues of PLP139-151 and identified five peptides derived from microbial Ags that elicit immune responses that cross-react with this self peptide. Exposure of naive SJL mice to the cross-reactive environmental peptides alone was insufficient to induce autoimmune disease even when animals were treated with Ag-nonspecific stimuli (superantigen or LPS). However, immunization of SJL mice with suboptimal doses of PLP139-151 after priming with cross-reactive environmental peptides consistently induced experimental autoimmune encephalomyelitis. Furthermore, T cell lines from mice immunized with cross-reactive environmental peptides and restimulated in vitro with PLP139-151 could induce disease upon transfer into naive recipients. These data suggest that expansion by self Ag is required to break the threshold to autoimmune disease in animals primed with cross-reactive peptides.