The 390 mAb reacts with CD31 (PECAM-1), a transmembrane glycoprotein belonging to the immunoglobin superfamily. CD31 is expressed constitutively on endothelial cells and at lower density on platelets, neutrophils, monocytes and a subset of T cells. CD31 mediates hemophilic and heterophilic cell-cell adhesion and is involved in the process of angiogenesis. The 390 mAb can be used for acetone-fixed frozen sections and zinc-fixed paraffin-embedded tissues. This antibody has also demonstrated the ability to block CD31-mediated interactions and has been reported to be useful for immunoprecipitation .