Figure 5. Induction of apoptosis by biosimilar 1B8 mAb. Human Burkitt’s lymphoma Ramos cells were incubated with 3 µg/mL of biosimilar 1B8 mAb for 24 (A, upper pannels) or 48 h (A, lower panels; B) at 37°C. (A) Early-stage apoptosis was assessed by FITC-labeled annexinV and PI staining. AnnexinV-positive and PI-negative cells were scored as apoptotic cells. (B) Late-stage apoptosis was measured by activation of caspase 3. Upper panels: Ramos cells were incubated with the indicated mAbs alone. Lower panels: A goat anti-human IgG (γ-chain specific) antibody was added. Rituximab and isotype-matched chimeric C5 antibody were used as positive and negative controls, respectively. Results are representative of two independent experiments. NT: non-treated cells.