Flow cytometric analysis for quantification of apoptotic cells. MM cells (2 × 10⁵/mL were cultured in RPMI containing 10% FCS (Hyclone Laboratories) and collected after 4 days of exposure to NK4 (100 nM) or anti–HGF-neutralizing monoclonal antibody (19 μg/mL) in the presence or absence of 100 ng/mL HGF; this concentration of HGF was an excess amount sufficient to counteract NK4 or the neutralizing antibody. Cells were stained with FITC-coupled annexin V and propidium iodide. Induction of apoptosis by NK4 was evaluated by flow cytometry. The percentages of early apoptotic cells (annexin V⁺/PI⁻) and late apoptotic cells (annexin V⁺/PI⁺) are indicated in the corresponding quadrants.