A Single Microorganism Epitope Attenuates the Development of Murine Autoimmune Arthritis: Regulation of Dendritic Cells via the Mannose Receptor

A single epitope of Leishmania analog of the receptors for activated C kinase (LACK) from Leishmania major, the polypeptide LACK_156-173, is recognized by Vβ4⁺/Vα8⁺ T cells, and activate these cells that drives the subsequent T helper (Th)2 response. This study was undertaken to investigate the therapeutic potential of the LACK_156-173 epitope in murine autoimmune arthritis models. To explore the influence of the LACK_156-173 epitope on murine collagen antibody-induced arthritis, as well as its immunological mechanism, we vaccinated or treated mice with a LACK_156-173 epitope expression plasmid or polypeptide. The effect of LACK_156-173 epitope was then evaluated by clinical scores, histopathology, and quantitative real-time polymerase chain reaction (qRT-PCR) analysis. Using flow cytometry, we measured the subsets and maturity of CD11c⁺ dendritic cells (DCs), as well as T cell polarization, in co-culture experiments. We also measured cytokine gene expression and production. The murine macrophage-like cell line RAW264.7 was used to identify the receptor for the epitope. Vaccination or treatment of the mice with the LACK_156-173 epitope expression plasmid or polypeptide ameliorated the severity of arthritis. qRT-PCR analysis revealed that the LACK_156-173 epitope improved the balance of effector T cells in synovial tissue compared to that in untreated arthritis controls. Toll-like Receptor (TLR) 4 expression was diminished by LACK_156-173. The epitope also influenced T cell polarization by regulating the differentiation, maturation, and functions of CD11c⁺ DCs and upregulating Jagged1 ligand expression. Blocking the Mannose Receptor (MR) significantly attenuated LACK_156-173 epitope-induced macrophage activation. Our data indicate that vaccination or treatment with a single microorganism epitope, LACK_156-173, is a highly efficient therapy for murine autoimmune arthritis. The therapeutic effects are mediated by the regulation of the differentiation, maturation, and functions of DCs via MR, resulting in the upregulation of Jagged1 expression and Th2 cell polarization. Our results demonstrate the therapeutic potential of the LACK_156-173 epitope in rheumatoid arthritis.