Defensins in macrophages

Antimicrobial peptides, formerly thought of as specialized products of certain bacteria and fungi, appear to be widespread in the animal kingdom, and have been found in amphibian skin, insect hemolymph, various mucosal secretions and in professional phagocytes (1). Among professional phagocytes, granulocytes (polymorphonuclear leukocytes and eosinophils) are distinguished by a large storage compartment of up to several thousand cytoplasmic ‘granules’ which have proven to be a very rich and highly concentrated source of antimicrobial peptides (2–4). In contrast, macrophages have a modest storage (primary lysosomal) compartment which is continually discharged into phagolysosomes and replenished by protein synthesis. Characterization of microbicidal proteins has relied heavily on the classical techniques of biochemistry: subcellular fractionation, followed by protein purification, bioassay, and amino acid sequencing.