sCD40L represses Ig secretion by Sm-specific B cells. Sm-specific (2-12H/Vκ8) B cells (1 × 10⁵) were stimulated with LPS (30 μg/mL) and cocultured with CM from C57BL/6 BMMΦs, CM from LPS-activated C57BL/6 BMMΦs, anti-IL-6 (50 μg/mL) or CM from LPS-activated IL-6^−/− BMMΦs (A), LPS-activated IL-6^−/− BMMΦ CM, anti-CD40L (10 μg/mL) or isotype-matched control antibody (10 μg/mL) (B), the indicated concentration of rsCD40L or supernatant from CD40L transfected (m40L2) or untransfected cells (CHO-K1) (C), LPS-activated C57BL/6 BMMΦ CM, anti-IL6 (50 μg/mL), anti-CD40L (10 μg/mL) or isotype-matched control antibodies (10 μg/mL) (D). IgM^a/κ levels were quantitated on day 4 by ELISA. Titrations of CD40L-transfected cell supernatants represent 8.6 pg/mL (1:128), 4.3 pg/mL (1:256), and 2.1 pg/mL (1:512) as determined by ELISA. LPS-stimulated B cells (100%) secreted 1.3-8.5 μg/mL. Statistical analysis was performed using one-sample t test by comparing treated cultures to untreated cultures (control) except in panel D where antibody/C57BL/6 BMMΦ CM-treated cultures were compared with cultures treated with C57BL/6 BMMΦ CM lacking antibody. Data represent triplicate samples in each of 2-4 independent experiments. Error bars represent plus or minus SEM. (*P ≤ .05; **P ≤ .001.)