Hypothesis to explain how lack of functional GPIIb/IIIa receptors alters platelet deposition on collagen.

(A) In the presence of functional GPIIb/IIIa receptors, first the vanguard platelet adheres and spreads. A follower platelet that randomly comes to lie above (and potentially overlaps) the vanguard platelet can then tether to the vanguard platelet. Eventually the follower platelet adheres to, and spreads over, the vanguard platelet and the adjacent collagen. (B) In the absence of functional GPIIb/IIIa receptors, platelet-platelet interactions cannot occur; thus, a platelet that comes to lie above (and partially overlaps) an already adherent platelet moves laterally as it approaches the surface and adheres directly to the adjacent collagen.