Anti-Plexin B1 antibodies are used in the immunodetection of the protein encoded by the PLXNB1 gene. In humans, the canonical protein has a reported length of 2135 amino acid residues and a mass of 232.3 kDa. Its subcellular localization is in the cell membrane and is also secreted. Alternative splicing is reported to yield 3 different isoforms for this protein. It is reported to be highly expressed in fetal kidney, and at slightly lower levels in fetal brain, lung and liver. A member of the Plexin protein family, it is a known receptor for SEMA4D. Post-translational modifications have been described, including glycosylation, protein cleavage and phosphorylation. Other names for this target antigen include SEP, plexin 5, semaphorin receptor SEP, and PLXN5.