(A) WT (n=4; white) and Cebpa KO (n=5; black) mice were immunized with OVA alum (day 0 and day 7) and boosted with OVA on day 14. On day 21, GC B, Tef and PD-1+ Tfh cells were identified by FACS staining in spleen (upper). Frequency of these populations was shown (lower). (B) The sera were isolated from WT and Cebpa KO mice on day 21 after boosting and subjected to a 3-fold serial dilution. The concentration of OVA specific IgG1, IgG2a and IgG2b were determined by ELISA. Data are a representative of three independent experiments with similar results. (C) Total splenocyte was isolated from WT and Cebpa KO mice after immunization. Then, cells were stimulated with indicated concentrations of OVA. IFN-γ was measured after three days of re-stimulation by ELISA (left). The splenocytes were stimulated with 0 or 250 μg/ml OVA. After 24 hrs, IFN-γ was detected in CD4+ cells by ICS (middle). Frequency of IFN-γ+ cells was shown (right). Data are a representative of three independent experiments with similar results.