Enhanced basal sera immunoglobulin levels and T-cell–independent immune responses in Dok-3^−/− mice. Wild-type (open circles) and Dok-3^−/− (black circles) mice were analyzed via ELISA for (A) basal serum Ig levels, (B) humoral immune responses to T-cell–independent type I and II antigens NP-LPS and NP-Ficoll, respectively, and (C) humoral immune response to T-cell–dependent antigen, NP-CG. NP-specific antibodies were measured 7 days after immunization for the T-cell–independent immune responses and sera were diluted 2000-fold. For T-cell–dependent immune response, sera were examined at days 7 and 14 for antigen-specific IgM and IgG1 antibodies in the primary response. For secondary immune response, mice were rechallenged 30 days later with the same antigen and examined 5 days thereafter for NP-specific IgG1 antibodies. Sera were diluted as indicated. In all graphs, each data point denoted a single mouse analyzed. Statistical significance was determined by paired 2-tailed Student t test. Horizontal bars indicate the mean responses.