The transmembrane activator and calcium modulator and cyclophilin ligand interactor-immunoglobulin (TACI-Ig), a recombinant fusion protein that modulates B and T cells activation by binding and neutralizing B lymphocyte stimulator (BLyS) and a proliferation-inducing ligand (APRIL), has been shown to have a therapeutic effects on autoimmune disorders. The objective of this study was to investigate immunoregulatory efficacy of TACI-Ig on helper T (Th) cells in mesenteric lymph node (MLN) of adjuvant-induced arthritis (AA) in rats. The levels of BLyS, APRIL, interferon (IFN)-γ, interleukin (IL)-4, transforming growth factor beta (TGF)-β1, and IL-17 were measured by enzyme-linked immunosorbent assay. The localization and expression of TACI, B-cell maturation antigen (BCMA) and B cell activating factor-receptor (BAFF-R) were investigated by immunohistochemistry and western blotting analysis in MLN. Administration of TACI-Ig significantly reduced histological changes, along with decreased Th1 and Th17-cell cytokines and increased CD4(+)CD25(+)FOXP3(+) regulatory T cell (Treg) and Th2-cell cytokines in MLN of AA rats. The levels of BLyS and APRIL were decreased in MLN homogenate of AA rats after treatment with TACI-Ig. TACI-Ig inhibited TACI and BCMA expression, and increased BAFF-R expression in MLN with AA rats. Taken together, BLyS/APRIL-receptors signaling are important not only for B cell function but for T cell-mediated immune responses. TACI-Ig might exert its anti-inflammatory and immunoregulatory effects through inducing immune balance of Th1/Th2 and Treg/Th17 in peripheral MLN. The mechanisms of TACI-Ig on BLyS/APRIL-receptors-dependent signaling in MLN lymphocytes may play key roles in the pathogenesis of autoimmune disorders.
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