title: Normal and neoplastic cells of brown adipose tissue express the adhesion molecule CD31.
abstract: BACKGROUND
  CD31 (platelet-endothelial cell adhesion molecule-1; PECAM-1), an adhesion molecule involved in the process of angiogenesis, is used as a marker of normal and neoplastic vascularization. During the assessment of angiogenesis and vascular invasion in a thymic carcinoid tumor, we observed unexpected immunostaining for CD31 in perithymic brown fat nests.
  
  
  OBJECTIVE
  To determine whether CD31 is expressed by normal and neoplastic cells of brown fat, a tissue whose thermogenetic activity depends heavily on high perfusion.
  
  
  METHODS
  Formalin-fixed, paraffin-embedded archival tissues were immunostained by the labeled avidin-biotin method using antibodies against CD31 (clones JC70A and 1A10) after retrieval of heat-induced epitopes. Archival tissues included perithymic, periadrenal, axillary, and neck adipose tissue in which were embedded nests of brown fat (n = 15), hibernoma (n = 3), lipoma (n = 6), well-differentiated liposarcoma (n = 4), and myxoid liposarcoma (n = 4).
  
  
  RESULTS
  Invariably, multivacuolated and univacuolated adipocytes of normal brown fat and hibernomas were intensely positive for the CD31 antigen. The immunostaining "decorated" cell membranes and the membranes of intracytoplasmic vacuoles. No expression of CD31 was found in normal adipocytes of white fat, in neoplastic cells of lipomas, or in multivacuolated lipoblasts of well-differentiated and myxoid liposarcomas.
  
  
  CONCLUSIONS
  The spectrum of cell types that express CD31 is expanded to include normal and neoplastic brown fat cells. We speculate that the expression of CD31 may play a role in the development and maintenance of the vascular network characterizing this specialized adipose tissue. Moreover, CD31 may inhibit the Bax-mediated apoptosis of brown fat cells. For practical purposes, CD31 may be used as an immunohistochemical marker for distinguishing between white and brown fat and for diagnosing hibernoma in paraffin sections.
authors.affiliation: From the Department of Pathology, University of Pavia, IRCCS San Matteo Hospital, Pavia, Italy. rosso@unipv.it
authors.forename: Renato
authors.initials: R
authors.lastname: Rosso
authors.forename: Marco
authors.initials: M
authors.lastname: Lucioni
mesh_terms: D017667:Adipocytes / Q000166:cytology / Q000378:metabolism* / Q000473:pathology; D002001:Adipose Tissue, Brown / Q000098:blood supply / Q000166:cytology / Q000378:metabolism*; D005404:Fixatives; D005557:Formaldehyde; D006801:Humans; D007124:Immunoenzyme Techniques; D008067:Lipoma / Q000098:blood supply / Q000378:metabolism* / Q000473:pathology; D018208:Liposarcoma, Myxoid / Q000098:blood supply / Q000378:metabolism* / Q000473:pathology; D009389:Neovascularization, Pathologic; D018919:Neovascularization, Physiologic; D016612:Paraffin Embedding; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000378:metabolism*
chemical_list: D005404:Fixatives; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D005557:Formaldehyde