Fibroblast-like synoviocytes from rheumatoid arthritis patients have intrinsic properties of follicular dendritic cells

The production of IgG rheumatoid factors in the inflamed synovium of many p atients with rheumatoid arthritis (RA) implies that local sites exist where plasma cell precursors undergo isotype switching and affinity maturation b y somatic mutation and selection. Lymphonodular infiltrates of the synovium -containing germinal centers (GCs), are candidates to fulfill such function in the rheumatoid patient. It has been suggested that these GCs are organi zed around, obviously ectopic, follicular dendritic cells (FDCs). The prese nt study attempts to find out whether these putative FDCs 1) are specific f or RA, 2) have the same phenotype and functional capacity as FDCs in lympho id organs, and 3) may locally differentiate from fibroblast-like synoviocyt es (FLS), Synovial biopsies from patients with RA versus non-PA, yet arthri tic backgrounds, were compared; Cells with the FDC phenotype were found in both RA and non-PA tissues as well as in single cell suspensions thereof. W hen FLS were cultured in vitro, part of these cell lines could be induced w ith IL-1 beta and TNF-alpha to express the FDC phenotype, irrespective of t heir RA or non-Ri-l background. By contrast, the FDC function, i.e., stable binding of GC B cells and switching off the apoptotic machinery in B cells , appeared to be the prerogative of RA-derived FLS only. The present data i ndicate that FDC function of FLS in RA patients is intrinsic and support th e idea that synovial fibroblast-like cells have undergone some differentiat ion process that is unique for this disease.