CD20 expression by spontaneous mouse primary B-cell lymphomas. (A) Representative CD20 expression by primary B-cell lymphomas isolated from Eµ-cMyc transgenic mice. Cell surface CD20 (open histograms) and isotype-matched control (shaded histograms) immunofluorescence staining were quantified by flow cytometry after brief periods of culture for 24 to 48 hours. The bar graph shows CD20 MFIs with isotype-matched control values subtracted. (B) Representative cell surface phenotype of the BL3750 lymphoma. Histograms show cell surface molecule staining (open histograms) vs isotype-matched control mAb staining (shaded histograms).