Fig 1: CD45 phosphatase activity is upregulated upon CD40L stimulation and leads to more potent BCR signaling in MBCs(A and B) CD45 phosphatase activity (A) and CD45 surface expression (B) in naive B cells (left panels) and MBCs (right panels), control (CTR) treated (filled histogram) or CD40L (open histograms).(C) CD45 phosphatase activity (upper panel, n = 13), panCD45 surface expression (middle panel, n= 7), and CD45 mRNA levels (lower panel, n = 3) of naive B cells (blue) and MBCs (red), CTR or CD40L treated. Graphs show pCAP-SP1 (upper panel) or CD45 (middle panel) MFI values relative to naive B cells. Lower graph: Quantitative real-time PCR of CD45 mRNA normalized to POLR2A expressed as RQ (relative quantity).(D and F) Activated BCR signaling kinases pSyk (D) and pErk (F) upon BCR cross-linking in naive B cells (left panel) or MBC (right panel) in CTR+vehicle (VEH) (filled histograms), CD40L+VEH (open histograms), or CD40L+CD45 inhibitor (open dotted histograms).(E and G) Graphs show pSyk (n= 9) (E) and pErk (n = 7) (G) MFI values relative to CTR naive B cells.(H and I) Real-time quantitative PCR analysis of SYK (H) and ERK (I) mRNA relative to POLR2A expressed as RQ (n = 3).(J) Purified human B cells were stimulated for 1 h at 37?C before CD45 activity was measured. Graph depicts % CD45 activity+ B cells in CTR or CD40L-stimulated B cells (n= 4).Related to Figure S1. **p < 0.01, ***p < 0.001, ****p < 0.0001.