Which antimicrobial peptide produced by epithelial cells and macrophages inhibits bacteria and fungi by disrupting membranes and is associated with the skin?

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

Answer: (D)

Defensins are small, cationic antimicrobial peptides that form a key part of the innate defense on barrier surfaces. They’re produced by epithelial cells, including skin keratinocytes, and by macrophages (as well as neutrophils). Their mode of action is to bind to microbial membranes, insert into the lipid bilayer, and create pores, which disrupts membrane integrity and leads to leakage and cell death. This membrane-disrupting, broad-spectrum activity against bacteria and fungi fits the description exactly, and their strong association with the skin makes them a prime example of a peptide that protects the barrier surface. Other peptides like dermcidin, histatins, or cathelicidins also disrupt membranes but have different primary sites of expression and roles (dermcidin mainly from sweat glands, histatins in saliva, cathelicidins more widely expressed), so defensins best match the given clue.