Expression of cell surface and soluble FL in chemotherapy-induced aplasia. (A) Flow cytometric analysis of cell surface FL. PBMC were stained with FITC-conjugated MoAb M5 (shaded area) or with FITC-conjugated control rat IgG2a (broken line). Analysis was performed with 9 patients; representative results for 3 patients are shown. Days of treatment and peripheral leukocyte count are indicated. (B) Serum concentrations of soluble FL (sFL) determined by ELISA. *Below the detection limit of 100 pg/mL. Results refer to the same 3 patients and same days as the FACS data shown in (A). The standard deviation is indicated. Correlation between sFL levels and leukocyte count was −.51 (P < .0001).