Immunophenotypic identification of peripheral blood B-cell clones in otherwise healthy adults. Top panels (A-D) illustrate the sequential gating strategy used to identify B cells in one representative sample: in a first acquisition step, a gate was drawn on the cell fraction positive for CD19 and/or CD20 (A); information from only those events included in this gate was stored in a second step for more than 5 × 10⁶ total leukocytes (B); finally only those events included in a wide gate drawn on a FSC/SSC and CD45 versus SSC dot plots, corresponding to small and eventually large CD45^hi lymphocytes, were selected as B cells (C-D). Illustrative examples of 3 different samples displaying aberrant/clonal B cells are shown in panels E through G (aberrant/clonal B cells are shown as black dots, and residual polyclonal B cells are shown as gray dots): CLL-like cells present at low frequencies (0.01% of the whole cellularity of the sample and 0.7% of the whole B-cell population) are shown in panel E and CLL-like cells present at very low frequencies (0.0015% of the whole cellularity and 0.1% of the whole B-cell population) are displayed in panel F; non–CLL-like B cells proven to be clonal by polymerase chain reaction are shown in panel G.