CD20 and CD74 labeling by specific fluorescent antibodies. Binding and internalization of CD20 and CD74 in Jeko cells were examined by laser scanning confocal microscopy. Jeko cells were incubated with rhodamine-conjugated rituximab (red) and Alexa Fluor 488-conjugated milatuzumab (green) in the absence (A) or presence (B) of a cross-linking antibody for 2 hours at 37°C. DRAQ5 was used for nuclear staining (blue). Cross-linked milatuzumab forms large aggregates and colocalizes with cross-linked rituximab on the surface of MCL cells. (C) Representative histograms summarizing the percentage of capped cells in the presence or absence of a cross-linking antibody are shown (Jeko cells left and Mino cells right). At least 100 cell/conditions were counted for each of the 3 independent experiments. Anti–Fc indicates anti–Fc cross-linking antibody.