Autocrine and exogenous IL-6 protects MCL cells from apoptosis. (A) Percentages of apoptotic cells in 48-hour cultures of primary MCL cells of 6 patients (PT1-PT6) in medium with or without addition of IL-6–neutralizing antibodies (α-IL-6; 50 μg/mL) and/or gp130-blocking antibodies (α-gp130; 5 μg/mL) or control IgG1. (B) Proliferation (CPM) of IL-6⁺ MCL SP53 and Granta 519 cells in a 7-day culture in medium in the presence or absence of α-IL-6 (50 μg/mL) and α-gp130 (5 μg/mL) antibodies or control IgG1. (C) Percentages of apoptotic Mino cells in 48-hour cultures in the presence of BTZ (10nM), atiprimod (ATI; 2μM), or cytarabine (Ara-c; 2μM). Mino cells were precultured with rIL-6 (0.5 ng/mL) for 2 hours before the drugs were added. Percentages of apoptotic cells induced by (D) BTZ (10nM) or (E) serum starvation. MCL cell cultures were first added with rIL-6 (50-5000 pg/mL) and 2 hours later were treated with BTZ or serum starvation. (F) Pooled data from 3 patients (PT1-PT3) showing that rIL-6 protected both MCL cell lines and primary MCL cells against BTZ-induced apoptosis. The presence of 50 μg/mL of α-IL-6 and/or 5 μg/mL of α-gp130 antibodies abrogated the protection of rIL-6 against BTZ-induced apoptosis. Results of 3 independent experiments are shown. The P values in the graphs show comparison as indicated. *P < .01.