Figure 3.

THP-1 monocytes and COS transfectants extend morphologically similar pseudopods. THP-1 monocytes (A and B) and FcγRIA COS transfectants (C and D) were incubated with IgG-opsonized sheep RBCs at 37°C for 45 min (A and C) or 1 h (B and D). The cells were then fixed, labeled with a WGA–HRP conjugate, and processed for electron microscopy as described in the legend to Fig. 2, A and B. In A, a THP-1 monocyte has extended fine pseudopods around an RBC target in an early phase of the phagocytic process. B shows a later phase of pseudopod extension in which the THP-1 cell has drawn the RBC target almost completely into the cell. In C, an FcγRIA COS transfectant has extended fine pseudopods around the RBC targets in an early phase of the process, whereas D shows a later terminal phase in which the RBC is surrounded by the cell, but not sealed within a phagosome. Bar, 1 μm.