The 3F1 monoclonal antibody specifically binds to CD155, which is also known as Poliovirus receptor (Pvr) or Tumor-associated antigen 1 (Taa1). CD155 is a type I transmembrane glycoprotein that belongs to the Ig supergene family. CD155 is an adhesion receptor that binds to different ligands including nectin-3, CD96, CD226, TIGIT, and the extracellular matrix protein vitronectin. It is highly expressed on double positive thymocytes and variably expressed on mature thymocytes and T cells, including regulatory T cells and NKT cells. CD155 is also differentially expressed on subsets of B cells, plasma cells, dendritic cells, and monocytes. CD155 expression is upregulated by activated T cells, B cells, and dendritic cells. CD155 is involved in forming adherens junctions between adjacent epithelial or endothelial cells. CD155 plays roles in regulating cell growth, adhesion, motility, migration, and cell-mediated cytotoxicity. CD155-deficient mice exhibit impaired secondary humoral immune responses to orally administered antigens.