The effect of “helpless” antigen on NP-specific IgG⁺ and IgM⁺ memory B cells as revealed by adoptive transfer. A total of 5 × 10⁶ purified B cells from either suppressed or nonsuppressed donor mice were transferred into recipients primed with KLH in alum. One week later, the recipient mice were challenged with 20 μg NP-KLH (suppressed, n = 11; nonsuppressed, n = 10), and serum samples were analyzed for IgG (A) and IgM (B) by ELISA after further one week. *Statistical significance (P < .05). n/s indicates not significant. These are combined data of 2 independent experiments.