The level of B7h on plasma B cells, but not on dendritic cells, regulates high-affinity antibody responses to T cell-dependent antigens. Transgenic B-B7hTg and DC-B7hTg mice on the B7h+/+ background, and non-transgenic B7h+/+ and B7h−/− controls were immunized with NP-CGG in alum, and the affinity of serum anti-NP IgG responses were assessed by ELISA after 21 days. Total NP-specific IgG (captured with NP15BSA; upper panels), high-affinity anti-NP IgG (captured with NP1BSA; middle), and the ratio of high affinity/total NP-specific IgG (lower panels) are shown relative to wild-type responses. Each symbol represents an individual mouse and bars indicate the mean of each group. The data were normalized such that the mean of the wild-type group was equal to 1. P values are shown for comparisons where differences were statistically significant. The data are representative of three independent experiments.