Increased Complement 3a Receptor is Associated with Behcet's disease and Vogt-Koyanagi-Harada disease.

Behcet's disease (BD) and Vogt-Koyanagi-Harada disease (VKH) are systemic and recurrent autoimmune diseases associated with abnormal T cell immune response. Complement 3a receptor (C3aR) and complement 5a receptor (C5aR) have been reported to be involved in T cell mediated autoimmune disease. This study aimed to investigate the role of C3aR and C5aR in these two diseases. The C3aR expression in PBMCs was increased in patients with active BD (aBD) and active VKH (aVKH). No statistical difference was found concerning the expression of C5aR in PBMCs between patients with aBD or aVKH and normal controls. After the intraocular inflammation in BD and VKH patients was controlled, the C3aR expression returned back to normal levels. The serum from patients with aBD and aVKH significantly induced C3aR expression by PBMCs. C3a induced IL-6, IL-1β and TNF-α secretion, while inhibited the production of IL-10 by monocytes. Activation of C3aR in CD4+ T cells could upregulate IL-17 production and inhibit IL-10 production, but had no detectable influence on IFN-γ production. Our data indicates that increased C3aR expression may lead to over activation of the Th17 cell response and may therefore contribute to the pathogenesis of BD and VKH disease.