Thrombin-activated platelets incubated with S aureus, immunolabeled for fibrinogen (arrowheads).

(A) Platelet pseudopods surround the particle by a process of circumferential adherence. Fibrinogen release in OCS indicates platelet activation. Original magnification, × 37 200. (B) Several α-granules (a) fuse together and their fibrinogen content is released into the engulfing vacuole (v). Original magnification, × 27 900. (C) The α-granule fibrinogen is detected within the engulfing vacuole, in close contact with the bacterium. Original magnification, × 44 950.