Cathelicidin antimicrobial peptide is a family of polypeptides found in lysosomes in polymorphonuclear leukocytes (PMNs).Members of the cathelicidin family of antimicrobial polypeptides are characterized by a highly conserved region (cathelin domain) and a highly variable cathelicidin peptide domain. Cathelicidin peptides have been isolated from many different species of mammals. Cathelicidins were originally found in neutrophils but have since been found in many other cells including epithelial cells and macrophages activated by bacteria, viruses, fungi, or the hormone 1,25-D. The cathelicidin family shares primary sequence homology with the cathepsin family of cysteine proteinase inhibitors, although amino acid residues thought to be important in such protease inhibition are usually lacking.