A small antimicrobial peptide made by your immune cells and epithelial surfaces—your body’s natural antibiotic.Defensins are cationic, cysteine-rich antimicrobial peptides of the innate immune system. Alpha-defensins (HNP-1–4 from neutrophils; HD-5, HD-6 from Paneth cells) and beta-defensins (hBD-1–4 from epithelial surfaces) kill pathogens through membrane disruption. Beyond direct antimicrobial activity, defensins function as chemoattractants, promote wound healing, and bridge innate and adaptive immunity. Defensins represent both a natural defense system and a template for antimicrobial drug development.