Identification of mouse plasma/plasmablast cells (PCs) with a fluorescent dye specific for the endoplasmic reticulum (ER). (A) Cytology images of mouse lymph node cells stained with anti-mouse IgG (green) and ER-tracker (blue). The arrow indicates the IgGlow ERhigh cells. (B) A representative fluorescence-activated cell sorting (FACS) graph of cells prepared from the lymph nodes of egg albumin-immunized mice. The forward-versus-side-scatter (FSC vs SSC) with gate R1 represents lymphocytes. The R1-gated cells were stained with anti-mouse IgG Dylight 488 and ER-tracker, and the IgGlow ERhigh cells (R2) were further analyzed for CD38-APC versus CD45R-PE surface expression using FACS. The relative number of cells in each region is given as a mean percentage of three separate experiments. (C) FACS-sorted R1-gated, R2-gated and R3-gated cells stained intracellularly with anti-mouse IgG Dylight 488 (green) and 4',6-diamidino-2-phenylindole (DAPI; blue). The numbers indicate the mean percentages of the cells with intense cytoplasmic IgG from three separate experiments.