Ligation of CD23 increases iNOS expression in B-CLL cells. Purified leukemic B cells from two patients were incubated for 48 hours in the presence of control medium or anti-CD23 135 MoAb (10 μg/mL). FACS analysis was then performed by direct immunofluorescence on permeabilized cells with an FITC-labeled anti-iNOS MoAb (clone 6) (black line), using FITC-IgG2a as an isotypic matched control MoAb (gray line).