FIG. 2.

Live MCF7 cells exposed to biotinylated aptamers, streptavidin-C1q conjugate, and human serum complement proteins (HSCP). After fixation, cells were labeled with an anti-human C9 antibody and a Cy5-conjugated secondary (magenta) then counterstained with Hoechst nuclear stain (blue). Aptamer-biotin-streptavidin-C1q plus HSCP-treated cells were strongly decorated (A), while the complement control group, in which cells were not exposed to streptavidin-C1q conjugate but did experience HSCP exposure, was only moderately decorated (B). The negative control group, in which cells were not exposed to either streptavidin-C1q or HSCP, appeared devoid of anti-C9 binding (C). Each of the A, B, and, C image panels is a z-stack projection of ten 500-nm-thick optical sections. Panel D shows a transmission electron microscopy image of an immunogold anti-C9 stained ultrathin section of an MCF7 cell treated as described for panel A. The red arrows indicate gold particles on or near the cell surface. The black arrow labeled “TV” indicates a heavily anti-C9 labeled structure in the cytoplasm, possibly a transport vesicle (TV). The black arrow labeled “Mx” indicates a mucin exocytotic structure, characteristic of MCF7 cells. In panel E, the edge portion of an MCF7 cell, treated and stained as in panel D, containing a possible MAC complex is shown. The red arrow points to immunogold anti-C9 labeling in close proximity to the putative membrane attack complex pore as would be expected for authentic MAC pores.