Immunolocalization of B1R and B2R in IMR-90 cells. Ultra-thin sections of unstimulated (A,C) or stimulated with 1% (vol/vol) exudates from monocytes treated with 1% (vol/vol) S aureus supernatant from an overnight culture (B,D). IMR-90 cells were incubated with antibodies against B1R (A-B) or B2R (C-D). Bound antibodies were visualized by secondary antibodies labeled with 10-nm gold particles and processed as described in “Materials and methods.” Examples of intracellular (arrows) and membrane-associated receptors (arrowheads) are indicated. The scale bar indicates 0.5 μm (magnification ×25 000).