Induction of telomerase activity in normal B cells. Intrinsic telomerase activity was measured by TRAP assay as described in Materials and Methods. (A) Purified B cells from tonsils were stimulated in vitro with soluble goat antihuman IgM Ab (10 μg/mL), goat antihuman IgM Ab bound to beads (10 μg/mL), anti-CD40 MoAb (10 μg/mL) or soluble anti-IgM Ab plus anti-CD40 MoAb for 2 days. (B) Tonsillar B cells were stimulated with various kinds of cytokines in the presence or absence of soluble anti-IgM Ab (10 μg/mL) for 2 days. TRAP assay was performed using the lysate from cells that showed equivalent proliferation. (C) Telomerase activity was measured at the points of 12, 24, 48, 72, 96, 120, 144, and 168 hours after the stimulation with soluble anti-IgM Ab plus anti-CD40 MoAb.