All the chromogen-conjugated antibodies used in flow cytometry and BD Trucount beads were purchased from BD Biosciences. Fluorescein isothiocyanate (FITC)-conjugated annexin V was purchased from Life Technologies. Goat F(ab′)2 anti-human IgM was purchased from SouthernBiotech. Ibrutinib (PCI-32765) was purchased from Selleck Chemical(12 (link)).