The mononuclear blood cells of patient MZL-1 consist predominantly of malignant B lymphocytes. (A) Flow cytometric analysis of peripheral blood cells of patient MZL-1. Mononuclear cells from the blood of patient MZL-1 were analyzed by flow cytometry using a FITC-conjugated anti-CD19 (HD37) antibody in combination with a PE-labeled anti-CD5 (DK23) antibody or with unlabeled anti-IgM (AF6), anti-κ (6E1), anti-CD23 (9P25), anti-CD38 (HB-7), and anti-CD40 (MoAb89) antibodies. The unlabeled MoAbs were visualized by indirect staining with a secondary PE-conjugated goat antimouse antibody. (B) Flow cytometric analysis of peripheral mononuclear cells of a normal individual. The percentage of CD40⁺ B lymphocytes is indicated.