Glycoprotein Ib also known as CD42,
is a component of the GPIb-V-IX complex on platelets. The GPIb-V-IX complex binds von Willebrand factor

Von Willebrand factor

von Willebrand factor is a blood glycoprotein involved in hemostasis. It is deficient or defective in von Willebrand disease and is involved in a large number of other diseases, including thrombotic thrombocytopenic purpura, Heyde's syndrome, and possibly hemolytic-uremic syndrome...

, allowing platelet adhesion and platelet plug formation at sites of vascular injury.

It is deficient in the Bernard-Soulier syndrome

Bernard-Soulier syndrome

Bernard–Soulier syndrome , also called hemorrhagiparous thrombocytic dystrophy, is a rare autosomal recessive coagulopathy that causes a deficiency of glycoprotein Ib , the receptor for von Willebrand factor, which is important in clot formation.The incidence is estimated to be less than 1 in 1...

. A gain-of-function mutation causes platelet-type von Willebrand's disease.

Autoantibodies against Ib/IX can be produced in immune thrombocytopenic purpura.

Components include GP1BA

GP1BA

Glycoprotein Ib , alpha polypeptide also known as CD42b , is a human gene.-Interactions:GP1BA has been shown to interact with YWHAZ and FLNB.-Further reading:...

 and GP1BB

GP1BB

Glycoprotein Ib , beta polypeptide also known as CD42c , is a human gene.-External links:...

.

It complexes with Glycoprotein IX

Glycoprotein IX

Glycoprotein IX also known as CD42a , is a human gene.-External links:...

.