CD40 and aneurysmal bone cyst: Since ABC-DLBCLs correspond to B-cells arrested in a plasmablast (PB)-like state1,2, we next assessed whether TFH-derived signals that normally drive the differentiation of GC B-cells into plasmablast/plasma cells (PB/PCs), such as CD40 engagement and IL-21, could induce IRF4 phosphorylation.