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CD Markers

CD42b


Reviewers: Charanjeet Singh, M.D., University of Minnesota (see Reviewers page)
Revised: 8 February 2011, last major update December 2010
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.

General
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● CD42a-d complex is receptor for von Willebrand factor and thrombin

Terminology
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● Also called platelet GPIb alpha, glycoprotein Ib-alpha

Physiology
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● CD42a-d complex (also called glycoprotein Ib-IX-V receptor) is the surface platelet receptor for von Willebrand factor on endothelium (particularly CD42b)
● Endothelial damage exposes vWF, which binds to platelets very quickly despite high shear pressures; this leads to platelet activation, then a change in the platelet GpIIb-IIIa receptor, which allows binding to surface bound fibrinogen and free fibrinogen; this leads to platelet crosslinking and aggregation
● Platelet activation apparently involves disruption of the macromolecular complex of GP-Ib with the platelet glycoprotein IX (GP-IX) and dissociation of GP-Ib from the actin-binding protein
● GPIb alpha (CD42b) and GPIb beta (CD42c) form main part of VWF receptor
● CD42b also binds to thrombospondin-1, a glycoprotein in arteriosclerotic plaques, causing thrombus formation independent of von Willebrand factor (FASEB J 2003;17:1490)
● Platelet receptors are important in understanding thrombus formation (Haematologica 2009;94:700)

Drawings
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CD42a-d complex

Major platelet receptor-ligand interactions

Clinical features
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● Mutations are associated with Bernard-Soulier syndrome (giant platelet syndrome, OMIM 231200, Int J Hematol 2002;76:319), a bleeding disorder with thrombocytopenia, prolonged bleeding time and giant platelets
● CD42b mutations also cause platelet type von Willebrand disease, which is known as pseudo-von Willebrand disease (OMIM 177820)
● Reduced levels are associated with bleeding disorders in AML patients (Saudi Med J 2005;26:1095)
● Aspirin induces shedding of CD42d and CD42b from platelets (J Biol Chem 2005;280:39716)
● Various snake venoms induce platelet aggregation via CD42b, including TVMA (Toxicon 2004;44:649, but see Xenotransplantation 2004;11:203-inhibits platelet aggregation), alboluxin (Thromb Haemost 2002;87:692) and bilinexin (Thromb Haemost 2001;86:1277)
● CD42b physiology is part of bacterial virulence factors: (a) Streptococcus sanguis, an oral bacteria causing infective endocarditis, adheres to platelets and platelet-fibrin vegetations via CD42b (Br J Haematol 2005;129:101); (b) some strains of H. pylori induce platelet activation mediated by H. pylori-bound vWF interacting with CD42b, which may promote peptic ulcer disease and H. pylori-associated cardiovascular disease (Gastroenterology 2003;124:1846)

Case reports
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● Bernard-Soulier disease variant (Arch Pathol Lab Med 2005;129:e214)

Uses for pathologists
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● Marker of megakaryocytes and platelets
● Diagnosis of AML-M7; distinguish AML-M7 (CD42b+) from acute myelosis with myelofibrosis (usually CD42b neg, Mod Path 2005;18:603)

Positive stains - normal
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● Platelets, megakaryocytes, megakaryoblasts

Positive stains - disease
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● Blasts in transient myeloproliferative disorder

Micro images
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CD42b+ megakaryocytes in acute panmyelosis with myelofibrosis (not a typical finding, figure 1d)

AML-M7 (figure 2c)

Flow cytometry images
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Reduced CD42b in Bernard-Soulier patient, normal levels in parents

Additional references
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MIM 606672

End of CD Markers > CD42b


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