ARG098 binding and cytotoxicity to rheumatoid arthritis (RA) synoviocytes. (A) ARG098 binding activity to RA synoviocytes was assessed by flow cytometory. The white area is stained with human IgM and the black area is stained with ARG098. (B) RA synoviocytes pretreated with anti-Fas neutralizing antibody clone SM1/23. (C) Representative cell viability of RA synoviocytes following ARG098 treatment vs. non-treated condition as measured by the WST assay. Black circles, ARG098; white circles, human IgM. Each point represents mean ± SEM (n = 5). **: p < 0.01 vs. non-treated cells (Dunnett's test). (D) Neutralization of RA synoviocyte viability by SM1/23. The cells were treated with 100 ng/mL of human IgM or ARG098. N, non-treated group. Each bar represents mean ± SEM (n = 5). **: p < 0.01 (Student's t-test). (E) RA synoviocytes were treated with 100 ng/mL of human IgM or ARG098. After stained with PI/annexin-V, the annexin-V positive fluorescent intensity was measured by FACSCalibur 3A. Each bar represents mean ± S.E.M of five data from synoviocytes derived from five different patients with RA.