13. Chemical Weapons: Lysozyme, Defensins and Antimicrobial Peptides

Epithelia don't just block microbes: they make chemicals that kill them. This episode covers the chemical barrier: lysozyme and the bacterial cell wall, Gram-positive vs Gram-negative bacteria, Paneth cells, defensins and how they punch pores in membranes, cathelicidins, histatins, RegIII lectins and calprotectin. Episode 13 of Primer on Immunology In this episode • Simple chemistry: stomach acid, bile salts, fatty acids, lysolipids • Peptidoglycan: GlcNAc and MurNAc, cross-linked by peptide bridges • Gram-positive vs Gram-negative cell envelopes, and why it matters • Lysozyme cuts the β-1,4 linkage; secretory phospholipase A2 • Paneth cells at the base of the intestinal crypts • Defensins: short, cationic, amphipathic; how they form a pore • α-, β- and θ-defensins: neutrophil granules, cryptdins, lamellar bodies in skin and lung • Activation by cutting: propeptides and why they are made inactive • Cathelicidins: two granule stores, neutrophil elastase as the key • Histatins in saliva: Candida, Cryptococcus, wound healing • Bactericidal lectins: RegIIIγ and the RegIIIα pore; why LPS blocks it • Calprotectin (S100A8/S100A9), the metal thief • Recognise and kill: innate immunity in its simplest form Chapters 0:00 Welcome 0:14 The epithelium as a chemist 0:34 Four families 0:47 Peptidoglycan 1:12 Gram-positive vs Gram-negative 1:34 Lysozyme 2:08 Paneth cells and phospholipase A2 2:35 Antimicrobial peptides 3:02 Defensins 3:32 How defensins punch holes 4:15 Alpha, beta and theta defensins 5:24 Activation by cutting 6:03 Cathelicidins: two stores, two keys 6:45 Histatins 7:10 Bactericidal lectins: RegIII 7:55 Calprotectin, the metal thief 8:18 Recognise and kill 8:38 The first line of defence in one breath 8:56 Next: complement, and links Next: a microbe slips past the barrier into tissue and blood, and meets the complement system. Everything we make is at rheumatologydigest.org WhatsApp channel (new material first): https://whatsapp.com/channel/0029Vb6P... Icons from Noun Project (CC BY 3.0): Stomach by El Hikami. For educational purposes only. Rheumatology Digest is made for students and clinicians; it is not medical advice. #immunology #innateimmunity #antimicrobialpeptides