Which antimicrobial substances are released by Paneth cells in the small intestine?

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Paneth cells in the small intestine are specialized for innate immune defense, releasing antimicrobial substances into the gut lumen. Their secretions include defensins and lysozyme. Defensins are small peptides that insert into bacterial membranes to form pores, causing disruption and death of the microbe. Lysozyme targets the bacterial cell wall by breaking the bonds in peptidoglycan, helping to lyse bacteria. Together, these two components provide a rapid, non-specific first line of defense against ingested or resident bacteria in the small intestine.

Mucin is produced mainly by goblet cells and forms the mucus layer that coats the epithelium, not a Paneth cell product. IgA is produced by plasma cells in the lamina propria and transported across the epithelium, so it is not released by Paneth cells. A lysozyme-only option would omit the defensins that Paneth cells also secrete, making it incomplete.