Flow cytometric profiles of surface CTLA-4 expression in peripheral blood T cells, B cells, stem cells, and cell lines.

Cells were tested before (gray histograms) and after (black histograms) activation for 48 hours as described in “Patients, materials, and methods.” Resting and activated cells were stained with FITC-conjugated anti–CTLA-4 scFv 83 and analyzed by flow cytometry. Results are expressed as fluorescence intensity.