Jayagopala Reddy

Myelin-specific regulatory T cells accumulate in the CNS but fail to control autoimmune inflammation.

Treatment with ex vivo–generated regulatory T cells (T-reg) has been regarded as a potentially attractive therapeutic approach for autoimmune diseases. However, the dynamics and function of T-reg in autoimmunity are not well understood. Thus, we developed Foxp3gfp knock-in (Foxp3gfp.KI) mice and myelin oligodendrocyte glycoprotein (MOG)35–55/IAb (MHC class II) tetramers to track autoantigen-specific effector T cells (T-eff) and T-reg in vivo during experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. MOG tetramer–reactive, Foxp3+ T-reg expanded in the peripheral lymphoid compartment and readily accumulated in the central nervous system (CNS), but did not prevent the onset of disease. Foxp3+ T cells isolated from the CNS were effective in suppressing naive MOG-specific T cells, but failed to control CNS-derived encephalitogenic T-eff that secreted interleukin (IL)-6 and tumor necrosis factor (TNF). Our data suggest that in order for CD4+Foxp3+ T-reg to effectively control autoimmune reactions in the target organ, it may also be necessary to control tissue inflammation.

CD226 is specifically expressed on the surface of Th1 cells and regulates their expansion and effector functions.

Surface molecules that are differentially expressed on Th1 and Th2 cells may be useful in regulating specific immune responses in vivo. Using a panel of mAbs, we have identified murine CD226 as specifically expressed on the surface of differentiated Th1 cells but not Th2 or Th0 cells. Although CD226 is constitutively expressed on CD8 cells, it is up-regulated on CD4 cells upon activation. Th1 differentiation results in enhanced CD226 expression, whereas expression is down-regulated upon Th2 polarization. We demonstrate that CD226 is involved in the regulation of T cell activation; in vivo treatment with anti-CD226 results in significant reduction of Th1 cell expansion and in the induction of APCs that inhibit T cell activation. Furthermore, anti-CD226 treatment delays the onset and reduces the severity of a Th1-mediated autoimmune disease, experimental autoimmune encephalomyelitis. Our data suggest that CD226 is a costimulatory molecule that plays an important role in activation and effector functions of Th1 cells.

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.

IL-10 Plays an Important Role in the Homeostatic Regulation of the Autoreactive Repertoire in Naive Mice

We have previously shown that naive SJL (H-2s) mice, which are highly susceptible to myelin proteolipid protein (PLP)-induced experimental autoimmune encephalomyelitis (EAE), have a very high frequency (1/20,000 CD4 T cells) of PLP139–151-reactive T cells in the naive repertoire. In this study, we examine the function of this endogenous PLP139–151-reactive repertoire in vivo and find that this repertoire encompasses the precursors of pathogenic T cells. Because SJL mice do not develop spontaneous EAE, we have explored the mechanisms that keep this autopathogenic repertoire in check and prevent the development of spontaneous autoimmunity. We crossed IL-4 and IL-10 deficiency onto the SJL background and analyzed the roles of these two immunoregulatory cytokines in regulating the size and effector function of the endogenous PLP139–151-reactive repertoire and development of autoimmune disease. We find that IL-10 is important in the homeostatic regulation of the endogenous PLP139–151-reactive repertoire in that it both limits the size of the repertoire and prevents development of effector autoaggressive T cells. SJL IL-10−/− mice with high numbers of PLP139–151-specific precursors in the repertoire did not develop spontaneous EAE, but when they were injected with pertussis toxin, they showed atypical clinical signs of EAE with small numbers of typical mononuclear cell infiltrates predominantly in the meninges. EAE could be inhibited by prior tolerization of the mice with soluble PLP139–151 peptide. These findings indicate that IL-10 may contribute to the regulation of the endogenous autoimmune repertoire.

Monoclonal antibodies to distinct regions of human myelin proteolipid protein simultaneously recognize central nervous system myelin and neurons of many vertebrate species

Myelin proteolipid protein (PLP), the major protein of mammalian CNS myelin, is a member of the proteolipid gene family (pgf). It is an evolutionarily conserved polytopic integral membrane protein and a potential autoantigen in multiple sclerosis (MS). To analyze antibody recognition of PLP epitopes in situ, monoclonal antibodies (mAbs) specific for different regions of human PLP (50–69, 100–123, 139–151, 178–191, 200–219, 264–276) were generated and used to immunostain CNS tissues of representative vertebrates. mAbs to each region recognized whole human PLP on Western blots; the anti‐100–123 mAb did not recognize DM‐20, the PLP isoform that lacks residues 116–150. All of the mAbs stained fixed, permeabilized oligodendrocytes and mammalian and avian CNS tissue myelin. Most of the mAbs also stained amphibian, teleost, and elasmobranch CNS myelin despite greater diversity of their pgf myelin protein sequences. Myelin staining was observed when there was at least 40% identity of the mAb epitope and known pgf myelin proteins of the same or related species. The pgf myelin proteins of teleosts and elasmobranchs lack 116–150; the anti‐100–123 mAb did not stain their myelin. In addition to myelin, the anti‐178–191 mAb stained many neurons in all species; other mAbs stained distinct neuron subpopulations in different species. Neuronal staining was observed when there was at least approximately 30% identity of the PLP mAb epitope and known pgf neuronal proteins of the same or related species. Thus, anti‐human PLP epitope mAbs simultaneously recognize CNS myelin and neurons even without extensive sequence identity. Widespread anti‐PLP mAb recognition of neurons suggests a novel potential pathophysiologic mechanism in MS patients, i.e., that anti‐PLP antibodies associated with demyelination might simultaneously recognize pgf epitopes in neurons, thereby affecting their functions.

Copolymer effects on microglia and T cells in the central nervous system of humanized mice

The random amino acid copolymers FYAK and VWAK ameliorate EAE in a humanized mouse model expressing both a human transgenic myelin basic protein (MBP)85–99‐specific T cell receptor and HLA‐DR2. Here we show that microglia isolated from the central nervous system (CNS) of humanized mice with EAE induced by MBP85–99 and treated with these copolymers had reduced expression of HLA‐DR, and thus reduced capacity to present MBP85–99 and activate transgenic T cells. In vitro microglia up‐regulated empty HLA‐DR2 upon activation with GM‐CSF with or without LPS or IFN‐γ, but not with IL‐4 or IL‐10. Correspondingly, gene chip arrays showed that the CNS of untreated and YFAK‐treated mice differentially expressed pro‐ and anti‐inflammatory molecules during MBP85–99‐induced EAE. Interestingly, microglia expressed the full‐length γβ and αβ subunits of the tetrameric adaptor protein complexes AP‐1 and AP‐2 respectively, but after treatment with GM‐CSF these complexes were cleaved, as had been found in immature dendritic cells derived from bone marrow. Strikingly, in vivo the perivascular lymphocyte infiltration seen in untreated mice immunized with MBP85–99 was composed of equal numbers of hVβ2+ MPB85–99‐specific transgenic and hVβ2– endogenous T cells, while the much smaller infiltration seen after treatment with YFAK was composed predominantly of hVβ2– endogenous T cells.

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.