Repression of Ig secretion by MRL/lpr MΦs is defective coincident with a failure to secrete soluble mediators. Sm-specific B cells (1 × 10⁵) were stimulated with LPS (30 μg/mL) and cocultured with the indicated number of C57BL/6 (n = 5) or MRL/lpr (n = 9) BMMΦs (A) or LPS-activated BMMΦ CM from C57BL/6 (n = 5) or MRL/lpr (n = 9) mice (B) for 4 days. IgM^a/κ was determined by ELISA. LPS-stimulated B cells (100%) secreted 1.2-20 μg/mL. (C) IL-6 levels in LPS-activated BMMΦ CM from C57BL/6 (○) or MRL/lpr (●) MΦs were determined by ELISA. (D) MΦs derived from C57BL/6 and MRL/lpr mice were LPS stimulated (15 μg/mL) for 3 hours then stained with anti-CD40L. The quantitative data from 5 experiments (100 cells/experiment) is shown. The absolute number of LPS-stimulated C57BL/6 MΦs that expressed CD40L averaged 55%. (E) Sm-specific B cells (1 × 10⁵) were stimulated with LPS (30 μg/mL) and cocultured with LPS-activated MΦ CM from ex vivo C57BL/6 (n = 6), C57BL/6.lpr (n = 6), MRL (n = 5), predisease MRL/lpr (n = 5), or postdisease MRL/lpr (n = 6) mice for 4 days. IgM^a/κ was determined by ELISA. LPS-stimulated B cells (100%) secreted 1-4 μg/mL. Each circle represents an individual mouse. The horizontal bars mark the mean secretion. Statistical analysis was performed using the exact Wilcoxon rank-sum test to compare all experimental groups to LPS-stimulated C57BL/6 MΦs (panels A-C) or the one-sample t test to compare unstimulated cultures to stimulated cultures (panel D) or experimental groups to C57BL/6 MΦ CM (panel E) (*P ≤ .05).