Flow cytometric analysis of CD20, CD38, and surface Ig expression. HB4C5 cells, HTD8 bulk population, and the new light chain expressing HTD8 subclones (D8-1, D8-2, D8-3, D8-4, and D8-11) were stained with FITC-conjugated anti-human CD20, CD38, or Ig antibodies and analyzed by flow cytometry (shaded histogram). The negative control was established using an irrelevant FITC-conjugated antibody of the same isotype (clear histogram). The fluorescence intensity is shown on the x-axis and the cell number on the y-axis. HB4C5 and HTD8 cells were examined for CD20 and CD38 expression (A). Presence of sIg was assessed for bulk population HB4C5 and HTD8 cells, the same cells after a 4-week culture, as well as for the HTD8 subclones (B). After isolating sIg⁻ HTD8 cells, these cells were examined for sIg expression at day 0, 1, and 4 of culture using FITC-conjugated anti-human μ antibody (C). Numbers in the upper left corners indicate the percentage of cells that are stained negative.