Co-expression of CD3 and CD20 on the cell surface is not a staining artifact.

<p>(A) Shown is the presence of CD3^lowCD20⁺ cells after overnight storage of blood samples at 4°C for two representative patients (#1 and #2, left). Staining of blood cells with the respective allophycocyanin (APC)-labeled mouse IgG1 isotype control excludes an artifact caused by the fluorochrome APC (#1 and #2, right). (B) Simultaneous expression of CD20 and CD3 on the surface of MACS-purified CD20⁺ lymphocytes is demonstrated for one representative donor by single cell analysis using confocal laser microscopy. (C) Confirmation of concomitant CD20 (FITC) and CD19 (PE) expression on MACS-purified CD20⁺ B cells served as positive control. Whole blood samples were stored overnight at 4°C before PBMC isolation and MACS analysis.