FIGURE 1.

CD40 signaling promotes B cell HP. (A–E) B cell HP measured by transfer of splenic B cells into B cell–deficient μMT hosts. Ly5.2 congenically marked WT or CD40 KO B cells were transplanted in Ly5.1 μMT–recipient mice (A) Gating on congenically marked donor B cells (left panel) and proliferating cells by CFSE dilution (right panel). (B) B cell HP measured 5–7 d after transfer of WT B cells to μMT mice. Left panel, Mice receiving WT B cells were treated with either isotype control or CD4-depleting Ab. Right panel, Transfer of WT versus CD40 KO B cells to μMT recipients. (C) Summary of HP data from multiple experiments, data are normalized to either WT B cells or isotype control treated recipients for each individual experiment. (D) Transfer of B cells and/or CD40 sufficient or deficient CD4⁺ T cells into Rag KO recipients. (E) Surface phenotype of WT donor B cells prior to transfer into μMT recipients for HP experiment (left panel) and after HP (middle panel); CD40 KO B cells after HP (right panel). (F) HP experiment using donor B cells from M167-Tg mice, showing proliferation of Id⁻ and Id⁺ cells (left panel) and the frequency of Id⁺ cells in nonproliferating or proliferating cells (right panel). (G) KREC assay on sorted FM and MZ cells from WT, CD40 KO, and CD40L KO mice. (H) Serum BAFF levels measured by ELISA in WT, CD40 KO, and CD40L KO mice. Error bars show SEM. Data representative of at least three experiments. *p < 0.05, **p < 0.005, ***p < 0.0005.