APOPTOSIS IN RHEUMATOID-ARTHRITIS SYNOVIUM

RA synovial tissue (ST) was studied to determine if and where apoptosi s occurs in situ, Genomic DNA was extracted from 5 RA and 1 osteoarthr itis ST samples. Agarose gel electrophoresis demonstrated DNA ladders characteristic for apoptosis from each tissue, In situ end labeling (I SEL) was used to identify DNA strand breaks consistent with apoptosis in frozen sections. 12 RA and 4 osteoarthritis ST were studied by ISEL and all were positive, but only 2 of 4 normal tissues were positive, The primary location of apoptotic cells was the synovial lining, Some sublining cells were also positive, but lymphoid aggregate staining wa s conspicuously absent, Immunohistochemistry and ISEL were combined an d showed that the lining cells with DNA strand breaks were mainly macr ophages, although some fibroblastlike cells were also labeled. Sublini ng cells with fragmented DNA included macrophages and fibroblasts, but T cells in lymphoid aggregates, which expressed large amounts of bcl- 2, were spared. DNA strand breaks in cultured fibroblastlike synoviocy tes was assessed using ISEL, Apoptosis could be induced by actinomycin D, anti-fas antibody, IL-1, and TNF-alpha but not by TFN-gamma. Fas e xpression was also detected on fibroblast-like synoviocytes using flow cytometry, Therefore, DNA strand breaks occur in synovium of patients with arthritis. Cytokines regulate this process, and the cytokine pro file in RA (high IL-1/TNP; low IFN-gamma) along with local oxidant inj ury might favor induction of apoptosis.