The
platelet glycoproteins (GPs) Ib,
integrin alpha(2)beta(1), and GPVI are considered central to
thrombus formation. Recently, their relative importance has been re-evaluated based on data from murine knockout models. To examine their relationship during human
thrombus formation on
collagen type I fibers at high shear (1000 s(-1)), we tested a novel antibody against GPVI, an
immunoglobulin single-chain variable fragment, 10B12, together with specific antagonists for GPIb alpha (12G1 Fab(2)) and alpha(2)beta(1) (6F1 mAb or GFOGER-GPP
peptide). GPVI was found to be crucial for aggregate formation, Ca(2+) signaling, and
phosphatidylserine (PS) exposure, but not for primary adhesion, even with more than 97% receptor blockade. Inhibiting alpha(2)beta(1) revealed its involvement in regulating Ca(2+) signaling, PS exposure, and aggregate size. Both GPIb alpha and alpha(2)beta(1) contributed to primary adhesion, showing overlapping function. The coinhibition of receptors revealed synergism in
thrombus formation: the coinhibition of
adenosine diphosphate (
ADP) receptors with
collagen receptors further decreased adhesion and aggregation, and, crucially, the complete eradication of
thrombus formation required the coinhibition of GPVI with either GPIb alpha or alpha(2)beta(1). In summary, human platelet deposition on
collagen depends on the concerted interplay of several receptors: GPIb in synergy with alpha(2)beta(1) mediating primary adhesion, reinforced by activation through GPVI, which further regulates the
thrombus formation.