CD42b (EP409), RMab

CD42b Platelet glycoprotein Ib alpha chain also known as glycoprotein Ib (platelet), alpha polypeptide is a protein that in humans is encoded by the GP1BA gene. The Gp Ib functions as a receptor for von Willebrand factor (VWF), which includes noncovalent association of the alpha and beta subunits with platelet glycoprotein IX and platelet glycoprotein V. The binding of the GP Ib-IX-V complex to VWF facilitates initial platelet adhesion to vascular subendothelium after vascular injury, and also initiates signaling events within the platelet that lead to enhanced platelet activation, thrombosis, and hemostasis. This gene encodes the alpha subunit. Several polymorphisms and mutations have been described in this gene, some of which are the cause of Bernard-Soulier syndromes and platelet-type von Willebrand disease (1).

CD42b antibody is a marker of megakaryocytes and platelets and used in the Diagnosis of AML-M7 to distinguish AML-M7 (CD42b+) from acute myelosis with myelofibrosis (usually CD42b -). Acute megakaryoblastic leukemia has a significantly higher proportion of blasts expressing CD42b (2). Patients with Histoplasma capsulatum infections have been noted with unusual IHC positivity of the platelet associated marker CD42b/GP1b expressed on the surface of this fungal organisms. Evaluation of additional cases demonstrated that a majority of histoplasmosis cases (83%) showed positive staining with CD42b/GP1b, comparable to GMS stain results (3).