Anti-PI antibodies are protein reagents that detect specific antigens. The PI antigen is another term for the human protein serpin family A member 1, encoded by the SERPINA1 gene. The protein is known as an inhibitor of serine proteases. Canonically, it has an amino acid length of 418 residues and a mass of 46.7 kilodaltons. Its subcellular localization is in the ER, extracellular matrix, and is secreted. It is ubiquitously expressed across many tissue types. The PI protein is a member of the Serpin protein family.