Proliferation capacity of rheumatoid arthritis synovial fibroblasts (RASFs). (a) Early-cultured RASFs exhibit only a very low proliferation rate in vitro (>2 n DNA equates S phase and G2/M phase, representative histogram). ~2 n DNA (arrow at 200) refers to the normal DNA content of interphase (G0/G1 phase) RASFs . 4 n DNA (arrow at G2/M peak at 400) refers to twice the amount of DNA in G2/M compared with G0/G1 phase. (b) Decrease in proliferation rate in confluent RASFs. (c) Quantitative analysis. Values are mean ± standard deviation as a percentage of early-cultured and confluent RASFs obtained from 11 or 6 individual patients with rheumatoid arthritis. **P < 0.01.