Characterization of autoreactive T-cell clones to myeloperoxidase in patients with microscopic polyangiitis and healthy individuals

Objective. To characterize autoreactive T cells against myeloperoxidase (MPO) by generating antigen-specific T-cell clones from patients with microscopic polyangiitis (MPA) and healthy individuals. Methods. Peripheral blood T cells from five patients with MPA and MPO-anti-neutrophil cytoplasmic antibodies (ANCAs) and from three healthy donors were used to establish MPO-specific T-cell clones by repeated stimulation with recombinant MPO fragments, followed by limiting dilution. The MPO-specific T-cell clones were subjected to analyses for CD4/CD8 phenotype, human leukocyte antigen (HLA) class II restriction, T-cell receptor (TCR) β-chain gene usage, complementarity-determining region 3 (CDR3) amino acid sequences, and cytokine expression profiles. Results. We successfully generated seven MPO-specific T-cell clones, five from the patients and two from healthy donors. Two clones recognized the light chain of MPO and five recognized the heavy chain. All the clones were HLA-DR-restricted CD4⁺CD8^- helper T cells. The T-cell clones shared TCR β CDR3 amino acid motifs, depending on their MPO epitope: AGxxN was used by clones recognizing the light chain and TGxS or QGxE by those recognizing the heavy chain, whether the cells were derived from MPA patients or healthy subjects. However, the cytokine expression profiles of the patients' clones were skewed towards the Th1 phenotype, whereas the healthy individuals' clones remained Th0. Conclusions. We have characterized MPO-reactive T cells in detail. This information may be useful for elucidating the mechanism of ANCA production and for developing selective therapeutic strategies for MPO-ANCA-associated vasculitis.