Diminished affinity maturation of IgG₁ antibodies in mice treated with FTY720. BM, spleen, and serum samples were collected at day 14 after immunization from control (▪) or FTY720-treated (□) mice. The ratios of NP₅-binding to NP₂₅-binding IgG₁ or IgM AFCs were used as indexes of affinity maturation in the splenic (A) or BM (B) AFC pool during humoral response to NP-CGG. The ratios of NP₅-binding to NP₂₅-binding IgG₁ or IgM serum antibodies were shown as indexes of affinity maturation of serum antibodies (C). The data represent the mean ± SE from 5 individual mice in each group. Similar results were obtained from 2 independent experiments.