Which antimicrobial peptide is secreted by epithelial cells and macrophages and targets bacteria and fungi by membrane disruption?

• A. Cathelicidin
• B. Defensins
• C. Bacteriocins
• D. Dermcidin

Answer: (B)

Defensins are small, positively charged peptides released by epithelial cells and macrophages that kill bacteria and fungi by disrupting their membranes. They insert into the microbial lipid bilayer, form pores, and compromise membrane integrity, causing leakage of ions and essential molecules that leads to rapid cell death. This membrane-lysing action at barrier surfaces like the skin, gut, and respiratory tract makes defensins a frontline innate defense. They come in two main groups—alpha-defensins (found in neutrophils and Paneth cells) and beta-defensins (produced by epithelial cells)—highlighting their close association with epithelial and phagocytic cells. While other antimicrobial peptides such as cathelicidin or dermcidin also disrupt membranes, defensins are the classic family described as secreted by epithelial cells and macrophages with membrane-disrupting activity against bacteria and fungi.