PECAM1

PO

WP

Definition: PECAM1 (or CD31) is a member of the immunoglobulin (Ig) superfamily that is expressed on the surface of circulating platelets, monocytes, neutrophils, and particular T-cell subsets. PECAM1 is also a major constituent of the endothelial cell intercellular junction, where up to an estimated 1 million molecules are concentrated.

Functions

Because of this cellular expression pattern, PECAM1 is implicated in several functions, including transendothelial migration of leukocytes, angiogenesis, and integrin activation.

Ig superfamily members are known to mediate cell adhesion, as:
 NCAM1 (MIM.116930)
 ICAM1 (MIM.147840)
 VCAM1 (vascular cell adhesion molecule-1) (MIM.192225)

They also mediate antigen recognition:
 immunoglobulins (IGH, IGL, IGK)
 T-cell receptors (TCRA, TCRB, TCRD, TCRG)
 MHC molecules.

In addition, a subgroup comprising 30 members characterized by the presence of one or more immunoreceptor tyrosine-based inhibitory motifs (ITIMs) within their cytoplasmic domain has also been recognized. PECAM1, which has 6 ITIMs within its cytoplasmic domain, is a member of this subfamily;

Expression in normal cells

 endothelial cells
 macrophages (histiocytes)

• Langerhans cells

Diagnostic use

 endothelial cell markers

• Most sensitive and specific endothelial marker in paraffin sections; stains small and large vessels.
• Confirms vascular origin of tumors, but may also stain nodal sinuses (J Clin Pathol 2003;56:638)
• Identifies/confirms vascular invasion (J Clin Pathol 2003;56:786, Arch Pathol Lab Med 2005;129:354), although D240 may be more sensitive (Am J Clin Pathol 2009;131:92, Am J Surg Pathol 2007;31:1825)
• Assesses tumor microvessel density, a possible prognostic factor, although D240 and endoglin / CD105 (Am J Clin Pathol 2008;129:578) may be more sensitive.
• Potential pitfall: don’t confuse CD31+ macrophages (granular, membranous expression) with a vascular tumor (Am J Surg Pathol 2001;25:1167)