TLR7 regulates dendritic cell-dependent B-cell responses through BlyS in immune thrombocytopenic purpura

Immune thrombocytopenic purpura (ITP) is an autoimmune disorder in which anti-platelet antibodies induce platelet destruction owing to an imbalanced immune response. Several studies have established that B cells play an important role in the production of anti-platelet antibodies and that dendritic cells (DC) are professional antigen-presenting cells of the immune system that may lead to the development of autoantibody through B cells. We aimed at investigating the role of B cells and DC in the pathogenesis of ITP through B-lymphocyte stimulator (BlyS) and toll-like receptor 7 (TLR7) signals.

Twenty-two patients with ITP and 20 healthy controls were enrolled in this study. Serum BlyS, its mRNA and TLR7 mRNA were measured using ELISA kits or RT-PCR, and CD14(+) or CD19(+) monocytes were investigated for the pathogenesis of ITP with in vitro culture systems.

We demonstrated that serum BlyS levels in patients with ITP were significantly higher than those in healthy controls and that there was a positive correlation between serum BlyS levels and glycoprotein-specific antibody levels in patients with ITP. We found that TLR7 regulates dendritic cell-dependent B-cell responses through BlyS in patients with ITP. Dendritic cells stimulated with R848 (TLR7 ligand) are able to produce vast amounts of BlyS, which is crucial for B-cell survival, proliferation and differentiation, and increase anti-platelet antibodies production in in vitro coculture systems.

These findings provide new insights into the pathogenesis of ITP by which TLR7 regulates DC-dependent B-cell responses through BlyS.