Arthritogenic T cell epitope in glucose-6-phosphate isomerase-induced arthritis.
BACKGROUND
Arthritis induced by immunisation with glucose-6-phosphate isomerase (GPI) in DBA/1 mice was proven to be T helper (Th) 17 dependent. We undertook this study to identify GPI-specific T cell epitopes in DBA/1 mice (H-2q) and investigate the mechanisms of arthritis generation.


METHODS
For epitope mapping, the binding motif of the major histocompatibility complex (MHC) class II (I-Aq) from DBA/1 mice was identified from the amino acid sequence of T cell epitopes and candidate peptides of T cell epitopes in GPI-induced arthritis were synthesised. Human GPI-primed CD4+ T cells and antigen-presenting cells (APCs) were co-cultured with each synthetic peptide and the cytokine production was measured by ELISA to identify the major epitopes. Synthetic peptides were immunised in DBA/1 mice to investigate whether arthritis could be induced by peptides. After immunisation with the major epitope, anti-interleukin (IL) 17 monoclonal antibody (mAb) was injected to monitor arthritis score. To investigate the mechanisms of arthritis induced by a major epitope, cross-reactivity to mouse GPI peptide was analysed by flow cytometry and anti-GPI antibodies were measured by ELISA. Deposition of anti-GPI antibodies on the cartilage surface was detected by immunohistology.


RESULTS
We selected 32 types of peptides as core sequences from the human GPI 558 amino acid sequence, which binds the binding motif, and synthesised 25 kinds of 20-mer peptides for screening, each containing the core sequence at its centre. By epitope mapping, human GPI325-339 was found to induce interferon (IFN) gamma and IL-17 production most prominently. Immunisation with human GPI325-339 could induce polyarthritis similar to arthritis induced by human GPI protein, and administration of anti-IL-17 mAb significantly ameliorated arthritis (p < 0.01). Th17 cells primed with human GPI325-339 cross-reacted with mouse GPI325-339, and led B cells to produce anti-mouse GPI antibodies, which were deposited on cartilage surface.


CONCLUSIONS
Human GPI325-339 was identified as a major epitope in GPI-induced arthritis, and proved to have the potential to induce polyarthritis. Understanding the pathological mechanism of arthritis induced by an immune reaction to a single short peptide could help elucidate the pathogenic mechanisms of autoimmune arthritis.
Iwanami
Keiichi
K
Department of Clinical Immunology, Doctoral Program in Clinical Sciences, Graduate School of Comprehensive Human Science, University of Tsukuba, Tsukuba, Japan.
Matsumoto
Isao
I
Tanaka
Yoko
Y
Inoue
Asuka
A
Goto
Daisuke
D
Ito
Satoshi
S
Tsutsumi
Akito
A
Sumida
Takayuki
T
D000595:Amino Acid Sequence; D000818:Animals; D001169:Arthritis, Experimental / Q000139:chemically induced / Q000201:enzymology / Q000276:immunology*; D018984:Epitopes, T-Lymphocyte / Q000276:immunology*; D005956:Glucose-6-Phosphate Isomerase / Q000008:administration & dosage / Q000633:toxicity*; D006801:Humans; D051379:Mice; D008811:Mice, Inbred DBA; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000276:immunology; D011485:Protein Binding / Q000276:immunology
D018984:Epitopes, T-Lymphocyte; D010446:Peptide Fragments; D005956:Glucose-6-Phosphate Isomerase