Electron micrographs showing location of acid phosphatase, a lysosomal enzyme.

Micrographs are representative examples of experiments repeated 4 times. Transfectant CHO cells were allowed to internalize IgG-coated EAs and then fixed and stained for acid phosphatase. (A) Internalization via wild-type FcγRIIA (clone 131-3) exhibits strong acid phosphatase activity near the internalized target in 61 of 63 internal targets counted (n = 4 for both lines). (B) However, internalization via tail-minus FcγRIIA (clone 169-23), using CR3 to mediate the phagocytic signal, does not show colocalization of the target with acid phosphatase activity (arrows). When counted, only 9 of 97 internal targets show colocalization with acid phasphatase (original magnification × 6000).