CD5/CD20 expression on B-CLL cells, low-grade NHL cells, and normal lymphocytes.

Mononuclear cells were isolated from peripheral blood of B-CLL patients (n = 44); from blood, bone marrow, or fine-needle lymph node aspirates from patients with low-grade NHL (n = 11), and from buffy coats from healthy volunteer blood donors (n = 16). The mononuclear cells (1 × 10⁶/mL) were stained simultaneously with FITC-conjugated anti-CD20 and phycoerythrin-conjugated anti-CD5 monoclonal antibodies, or isotype-matched control antibodies, and analyzed on a FACSort flow cytometer. Normal lymphocytes can be divided into 3 populations: (1) CD5^brightCD20^dim; (2) CD5^dimCD20^bright; and (3) CD5⁻CD20^bright populations (top, right panel). In B-CLL samples, one population of CD5^brightCD20^dim cells can be identified (top, left panel). In NHL samples, one population of CD5⁻CD20^bright cells can be identified (top, middle panel). The mean CD20 fluorescence intensity on B-CLL cells is significantly weaker than that of normal CD5^dim or CD5⁻ B cells or CD5⁻ NHL cells, but not statistically different from that of normal CD20^dimCD5^bright cells, which express CD3, CD4, or CD8, in the absence of B cells, natural-killer (NK) cells, and myeloid-lineage markers (bottom).