Figure 1.

PMA- or LPS-induced membrane ruffles are associated with C3bi-sRBCs. RAW264.7 mouse macrophages, primary mouse peritoneal macrophages and human monocyte-derived macrophages were isolated and plated as described in Materials and Methods. Macrophages were serum-starved for 3 h before activation with 150 nM PMA for 15 min or 10 μg/ml LPS for 6 h. Cells were exposed to C3bi-sRBCs for 12 min, or directly fixed after activation, before processing for SEM. No visible membrane ruffles or bound C3bi-sRBCs were observed in unstimulated (control) macrophages. In contrast, PMA- and LPS-activated macrophages exhibited broad dorsal ruffles that partially surrounded bound C3bi-sRBCs (arrows). In the absence of C3bi-sRBCs, PMA-, and LPS-stimulated macrophages showed pronounced membrane ruffles, which are lacking in control, unstimulated RAW264.7 cells. Scale bars, 10 μm.