Which peptide secreted by epithelial cells and macrophages provides antimicrobial activity on the skin by disrupting membranes against bacteria and fungi?

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

Answer: (C)

This question centers on antimicrobial peptides produced by skin cells that kill microbes by disrupting their membranes. Cathelicidin, specifically the active form LL-37, is produced by epithelial cells such as keratinocytes in the skin and by macrophages. It is secreted into the skin environment and works by inserting into microbial membranes to form pores, which compromises membrane integrity and leads to death of a broad range of bacteria and fungi. This membrane-disrupting mechanism and the fact that it is produced by both epithelial cells and macrophages make it the best match for the described function. Dermcidin is mainly secreted by sweat glands, defensins are produced by various cells including epithelial cells and neutrophils but aren’t the primary macrophage-epithelial product described here, and histatins are primarily salivary antifungals.