Anti-defensin alpha 4 antibodies are used in the immunodetection of the protein encoded by the DEFA4 gene. In humans, the canonical protein has a reported length of 97 amino acid residues and a mass of 10.5 kDa. Its subcellular localization is in the cytoplasmic vesicles and is also secreted. It is reported to be expressed in neutrophils. A member of the Alpha-defensin protein family, it is reported to be a host-defense peptide that has antimicrobial activity against Gram-negative bacteria, and to a lesser extent also against Gram-positive bacteria and fungi. Other names for this target antigen include HNP-4, HP-4, HP4, corticostatin, corticostatin HP-4, and DEF4.