Anti-Np4 antibodies are protein reagents that detect specific antigens. The Np4 antigen is another term for the human protein proteinase 3, encoded by the PRTN3 gene. The protein is reported to be a serine protease that degrades elastin, fibronectin, laminin, vitronectin, and collagen types I, III, and IV (in vitro). Canonically, it has an amino acid length of 256 residues and a mass of 27.8 kilodaltons. Its subcellular localization is in the cell membrane, cytoplasm, and is secreted. It is reported to be expressed in polymorphonuclear leukocytes. The Np4 protein is a member of the Peptidase S1 protein family. Other alias names for Np4 include ACPA, ACPA, and AGP7. ELISA, Western Blot, Immunocytochemistry, and Immunohistochemistry are common applications for Np4 antibodies.