Loss of OBF-1 but not Oct2 results in loss of GCs and reduction of T_FH during influenza infection. Analysis of GC B cells and T_FH cells in control or OBF-1– or Oct2-deficient mice on day 10 of infection. (A and B) mLN cells were stained with α-B220, α-Fas, and PNA to detect GC B cells. Representative staining is shown in A, and summary of data for all mice is shown in B. (C and D) mLN cells were stained with α-CD4, α-CXCR5, and α–PD-1 to detect T_FH cells. Representative staining is shown in C, and the frequency distribution for all mice is shown in D. (E) Analysis of Bcl6 and Il21 expression in CD4⁺, PD-1⁺, and CXCR5⁺ T_FH sorted from spleens of WT and Obf-1^−/− mice 10 d after influenza infection. Bars and numbers show mean normalized gene expression with ± SEM (n = 3). (F and G) T_FH and GC B cells were analyzed in WT:CD19^−/−, Obf-1^−/−:CD19^−/−, WT:TCRα^−/−, and Obf-1^−/−:TCRα^−/− mixed BM chimeras 10 d after influenza infection. (F) Cells from the mLNs were stained for GC B cells as described in A and B. (G) Cells from the mLNs were stained for T_FH cells, as described for E. Each symbol represents an individual animal. ***, P < 0.001; *, P = 0.01–0.05. Results are from three independent experiments.