Abnormal responses to immunization with a TD antigen in young DKO female mice. (A and B) 8–10-wk-old female mice (n = 6–7/group) were immunized with NP-KLH emulsified in CFA. Unimmunized control mice received CFA only (not depicted). At day 7 after immunization, spleens were analyzed for the numbers of B220⁺NP⁺ cells (A) and of B220⁺NP⁺PNA⁺ cells (B) by flow cytometry. (C and D) ELISPOT analysis of total (C) and high-affinity (D) IgG1 secretion by splenocytes from NP-KLH–immunized mice at day 14 after immunization. (E and F) Serum responses to NP-KLH immunization in the indicated mice. 14 d after immunization, serum samples were collected and total NP-specific anti-IgG1 (E) and IgG2a (F) antibody titers were determined by ELISA with NP14-BSA as capture antigen. Each dot represents individual mice, and horizontal bar represents mean for each group. Data are representative of two independent experiments. *, P < 0.05; **, P < 0.01; ***, P < 0.005.