Characterization of affinity of memory IgG and IgM antibodies. NP-specific antibody affinity was measured by binding to either highly haptenated antigen (NP16; total Ig affinity) or less haptenated antigen (NP4; high-affinity Ig). Sera were mildly treated by 2-mercaptoethanol (2-ME) to reduce pentameric IgM. Mice were primed and boosted with NP-KLH, and affinity was measured with or without 2-ME in pooled sera samples 3 weeks after boost (A-B) or individual samples taken at 1 or 3 weeks after boost (C-D). (A-B) Representative of 2 independent experiments. (C-D) Combined data of 2 independent experiments. (E) Affinity of IgG in suppressed and nonsuppressed groups in samples from the adoptive transfer experiments shown in Figure 5. The samples were taken one week after challenge with NP-KLH after an adoptive transfer one week before challenge. Horizontal bars represent median values. **Statistical significance (P < .01). These are combined data of 2 independent experiments.