The stromal component in rheumatoid arthritis: CD55 expression, cell death and beyond

Since 1990, when CD55 expression in synovial tissue was first described, this molecule has become a broadly used marker for detection of intimal lining synovial fibroblasts. In this thesis, we clarify the reason for its high expression and identify a collagen fiber meshwork in the synovial lining. We demonstrate that CD55 cooperates with regulating Fc receptors in controlling immune-complex mediated inflammation of the synovium. Moreover, our research proves for the first time interaction of CD55 with the Adhesion-GPCR CD97 in vivo and shows downregulation of CD97 after contact with CD55 under shear-stress conditions. The last part of this thesis, related to stromal cells biology in arthritis, provides evidence for the existence of a novel mechanism of recognition of intracellular poly(I:C) in FLS, leading to apoptosis. Identification of this sensor and the signaling molecules involved may disclose possibilities for the specific targeting of synovial hyperplasia in RA.