Immunodominant T-cell epitopes of MOG reside in its transmembrane and cytoplasmic domains in EAE

Abstract

Objective: Studies evaluating T-cell recognition of myelin oligodendrocyte glycoprotein (MOG) in multiple sclerosis (MS) and its model, experimental autoimmune encephalomyelitis (EAE), have focused mostly on its 117 amino acid (aa) extracellular domain, especially peptide (p) 35-55. We characterized T-cell responses to the entire 218 aa MOG sequence, including its transmembrane and cytoplasmic domains.

Methods: T-cell recognition in mice was examined using overlapping peptides and intact full-length mouse MOG. EAE was evaluated by peptide immunization and by adoptive transfer of MOG epitope-specific T cells. Frequency of epitope-specific T cells was examined by ELISPOT.

Results: Three T-cell determinants of MOG were discovered in its transmembrane and cytoplasmic domains, p119-132, p181-195, and p186-200. Transmembrane MOG p119-132 induced clinical EAE, CNS inflammation, and demyelination as potently as p35-55 in C57BL/6 mice and other H-2(b) strains. p119-128 contained its minimal encephalitogenic epitope. p119-132 did not cause disease in EAE-susceptible non-H-2(b) strains, including Biozzi, NOD, and PL/J. MOG p119-132-specific T cells produced Th1 and Th17 cytokines and transferred EAE to wild-type recipient mice. After immunization with full-length MOG, a significantly higher frequency of MOG-reactive T cells responded to p119-132 than to p35-55, demonstrating that p119-132 is an immunodominant encephalitogenic epitope. MOG p181-195 did not cause EAE, and MOG p181-195-specific T cells could not transfer EAE into wild-type or highly susceptible T- and B-cell-deficient mice.

Conclusions: Transmembrane and cytoplasmic domains of MOG contain immunodominant T-cell epitopes in EAE. A CNS autoantigen can also contain nonpathogenic stimulatory T-cell epitopes. Recognition that a myelin antigen contains multiple encephalitogenic and nonencephalitogenic determinants may have implications for therapeutic development in MS.

Figure 1. Identification of the encephalitogenic MOG determinant, p119-132

(A) Immunization with rMOG 1-117 elicited a recall proliferative response to p35-55 but not to p111-130. (B) Proliferation was detected to MOG p116-130 but not to p111-125 in mice immunized with p111-130. (C) Testing proliferative responses to truncated peptides after immunization with MOG p116-130 identified the core N-terminal boundary, F¹¹⁹. (D) Recall proliferative responses to MOG p119-132 and truncated peptides after immunization with MOG p119-132 identified the core C-terminal boundary, T¹²⁸. The proliferative response was maximal for p119-132. Lymph node cells were harvested 12 days after immunization. Results shown in panels A–D are representative of 3 separate experiments with 4 mice/group. (E) Mice were primed with MOG p119-132. Lymph node cells were isolated on day 10 and restimulated with MOG p119-132 in the presence of anti-MHC class II (M5/114), anti-MHC class I (28-14-8), or isotype control antibodies. Proliferation was evaluated after 72 hours by thymidine incorporation. (F, G) Mice were immunized with MOG p35-55, MOG p119-132, p181-195, and p186-200 for experimental autoimmune encephalomyelitis (EAE) induction. (F) EAE clinical course was similar after immunization with p35-55 and p119-132, but no signs of disease were observed with MOG p181-195 and p186-200. Data are representative of 5 separate experiments (5 mice/group) and represent mean clinical scores ± SEM. (G) Histologic analysis was performed on mice 14 days after immunization. Mice immunized with p35-55 (a, b) and p119-132 (c, d) developed EAE lesions in spinal cord white matter (arrows in a and c). (b, d) Meningeal and parenchymal mononuclear cell inflammation and demyelination were observed at higher magnifications. No evidence of histologic disease was observed in spinal cords of mice immunized with MOG p181-195 (e) or p186-200 (f). Luxol fast blue-hematoxylin & eosin; scale bars 100 μm (a, c, e, and f), 50 μm (b and d). (H) Mice were immunized with p35-55 or p119-132 and CNS-infiltrating cells were isolated 4 days after disease onset. Cells were stained with markers specific for CD4⁺ T cells, CD8⁺ T cells, B cells (CD19⁺B220⁺), monocytes (CD11b⁺, CD45^high), and dendritic cells (CD11c⁺). (I) Adoptive transfer EAE was induced by MOG p119-132–specific and p35-55–specific CD4⁺ T cells but not by p181-195–specific and p186-200–specific T cells. MOG epitope-specific CD4⁺ T cells were isolated from mice primed with individual MOG peptides and adoptively transferred into naïve recipient mice by intraperitoneal injection. Data shown represent mean clinical scores ± SEM of 5 recipient mice/group. EAE incidence was 100% in recipients of MOG p119-132–specific or p35-55–specific T cells. No clinical EAE was detected in recipient mice that received donor MOG p181-195–specific or p186-200–specific T cells. Results are representative of 3 independent experiments. MHC = major histocompatibility complex; MOG = myelin oligodendrocyte glycoprotein.

Figure 2. MOG p119-132 is the immunodominant T-cell determinant of full-length mouse MOG and elicits a proinflammatory bias

(A, B) Mice were immunized with myelin oligodendrocyte glycoprotein (MOG) p35-55, p119-132, p181-195, and p186-200. (A) Fourteen days after immunization with p35-55 and p119-132, spleen cells and CNS-infiltrating cells were isolated and analyzed for interleukin (IL)-17 and interferon (IFN)-γ production by intracellular staining after stimulation with phorbol 12-myristate 13-acetate (PMA)/ionomycin for 5 hours. Results are representative of 2 experiments that tested 4 individual mice for each peptide immunization. (B) Ten days after immunization with p119-132, p181-195, and p185-200, spleen cells were isolated and analyzed for IL-17 and IFN-γ production by intracellular staining after stimulation with PMA/ionomycin for 5 hours. Data summarize 2 experiments that tested 5 individual mice for each peptide immunization. (C) Frequencies of MOG peptide-specific IFN-γ–secreting cells were determined by ELISPOT as described in the methods. Lymph node cells from mice immunized with full-length MOG (left panel) or the extracellular domain of MOG (rMOG 1-117) (right panel) were cultured with the respective antigen used for immunization. Quantification of MOG peptide-specific T cells was performed at the time of restimulation with MOG peptides (25 μg/mL). Results are representative of 3 separate experiments (3 mice/group). (D) Schematic anatomic localization of T-cell epitopes within full-length (218 amino acid) mouse MOG (indicated in red). Amino acid 117, the last residue of extracellular domain, is indicated. T-cell determinants are highlighted in blue.