Id-specific IgG⁺ B cells are lost irreversibly, but IgM⁺ B cells are unaffected by “helpless” Id antigen. Purified B cells (10⁷) from either suppressed or nonsuppressed donor mice were mixed with 4 × 10⁶ FrC-primed purified CD4⁺ T cells and injected into Rag2KO recipients. One week after transfer, mice in each recipient cohort were divided into 2 groups and one was challenged with 100 μg Id-FrC fusion protein (suppressed, n = 10; nonsuppressed, n = 9). The remaining groups were unchallenged controls. Mice were bled a week later, and sera were analyzed for anti-Id IgG (A) and IgM (B) by ELISA. The horizontal bars represent median values. These are combined data of 2 independent experiments. **Statistical significance (P < .01). n/s indicates not significant.