Immunogold labeling of thrombin-activated platelets incubated with
S aureus. (A) In platelets containing bacteria (B), αIIbβ3 labeling (arrowheads) is prominent along the plasma membrane (pm) and the OCS membrane. Like OCS, the limiting membrane of the engulfing vacuoles (v) is heavily labeled. Original magnification, × 23 250. Inset: In control platelets, αIIbβ3 is immunodetected along the plasma membrane and the α-granule membrane. Inset original magnification, × 34 100. (B) P-selectin (arrowheads) is consistently detected along the plasma membrane (pm) and the OCS, as expected, following platelet activation. The membrane of the engulfing vacuoles surrounding the bacteria is also labeled for P-selectin. Original magnification, × 23 250. Inset: In control platelets, P-selectin is restricted to the α-granular membrane and is absent from plasma membrane. Inset original magnification, × 34 100. (C) GPIb (arrowheads), which is immunodetected on the OCS membrane, is not found within the membrane of the engulfing vacuoles, showing that this compartment is distinct from the OCS. Noteworthy, GPIb is absent from the plasma membrane (pm), showing its redistribution into the OCS, a distribution pattern that is well established in activated platelets. Original magnification, × 23 250. Inset: In control platelets, GPIb is located mainly on the plasma membrane. Inset original magnification, × 34 100.
