Category
Antimicrobial
Host defense peptides and their synthetic analogs studied for direct antimicrobial activity and immune-modulatory signaling. LL-37, the only human cathelicidin, is active against bacteria, fungi, and enveloped viruses through membrane disruption and immune cell recruitment.
4 peptides in this category
What are antimicrobial peptides and how do they kill bacteria?
Antimicrobial peptides (AMPs) are short, positively charged peptides produced by the immune system that kill bacteria by disrupting their cell membranes. Unlike conventional antibiotics that target specific metabolic pathways, AMPs physically insert into microbial membranes and cause structural disruption — a mechanism that is harder for bacteria to develop specific resistance against. LL-37, the only human cathelicidin, kills a broad range of bacteria, fungi, and enveloped viruses while also recruiting immune cells and promoting wound healing. Beta-defensins provide epithelial surface defense in the skin, gut, and airways.
Antimicrobial peptides (AMPs) are components of the innate immune system found in organisms from bacteria to mammals. They typically kill microorganisms by disrupting cell membranes — their cationic and amphipathic structure allows them to insert into microbial lipid bilayers and form pores or cause membrane disintegration, a mechanism that is difficult for bacteria to develop resistance to quickly. In humans, the primary AMP classes are cathelicidins (LL-37 is the only known human cathelicidin) and defensins (alpha-defensins produced by neutrophils and small intestinal Paneth cells; beta-defensins produced by epithelial cells throughout the body).
LL-37 is produced at sites of infection and inflammation, where it kills Gram-positive and Gram-negative bacteria, fungi, and enveloped viruses including influenza and HIV. Beyond direct killing, it chemotactically recruits neutrophils and monocytes, promotes dendritic cell maturation, and stimulates wound healing through keratinocyte migration. Synthetic LL-37 analogs are in development as next-generation antibiotics, and there is particular research interest in AMP-based approaches to drug-resistant infections given the distinct mechanism of action from traditional antibiotics.
Compounds
Peptides in this category
Defensin Alpha
PreclinicalHuman Neutrophil Peptides (HNP-1, HNP-2, HNP-3) · α-defensins
Alpha-defensins are cationic antimicrobial peptides secreted by neutrophils (HNP-1 to 4) and Paneth cells (HD-5, HD-6) in the small intestine. They kill bacteria, fungi, and enveloped viruses through membrane disruption and also function as chemokines, recruiting immune cells and bridging innate and adaptive immunity. Paneth cell alpha-defensins (HD-5, HD-6) play a critical role in shaping intestinal microbiome composition.
Elafin
Phase IITrappin-2 · SKALP
Elafin is an endogenous serine protease inhibitor (serpin-like) peptide produced by epithelial cells at mucosal surfaces. It inhibits neutrophil elastase and proteinase 3, protecting tissues from excessive inflammatory damage, while also exhibiting direct antimicrobial activity against bacteria and fungi. Research focuses on inflammatory bowel disease, cystic fibrosis, ARDS, and vaginal microbiome modulation, where recombinant elafin is in Phase 2 trials.
LL-37
Phase ICathelicidin · hCAP18/LL-37
LL-37 is the only known human cathelicidin antimicrobial peptide, derived from the C-terminus of hCAP18 protein. It exhibits broad-spectrum antimicrobial activity against bacteria, fungi, and viruses by disrupting microbial membranes. Beyond direct killing, LL-37 modulates inflammation, promotes wound healing, and may have anticancer properties. Research focuses on chronic wound care, infection, and skin disorders like rosacea.
Magainin-2
PreclinicalMagainin II
Magainin-2 is a 23-amino-acid cationic antimicrobial peptide (AMP) isolated from the skin of the African clawed frog (Xenopus laevis). It kills bacteria through membrane disruption — forming toroidal pores in bacterial lipid bilayers — while showing low toxicity to mammalian cells due to differences in membrane composition. It is a key model peptide for AMP research and drug design, with a derivative (pexiganan) evaluated in clinical trials for diabetic foot ulcers.
Research applications
What researchers are studying
Broad-spectrum membrane disruption
LL-37 and defensins kill bacteria by inserting into bacterial membranes (which have negatively charged surfaces that attract cationic peptides) and disrupting membrane integrity. This mechanism differs fundamentally from antibiotic targets like cell wall synthesis, protein synthesis, or DNA replication, which means most existing antibiotic resistance mechanisms do not confer resistance to AMPs.
Immune cell recruitment and activation
LL-37 binds the formyl peptide receptor 2 (FPR2) on neutrophils and monocytes, stimulating chemotaxis toward infection sites. It also activates keratinocytes, promotes angiogenesis during wound repair, and modulates TLR signaling on macrophages. This dual antimicrobial-immunomodulatory role means it functions as both a first responder and a coordinator of adaptive immune responses.
Drug-resistant pathogen research
As MRSA, carbapenem-resistant Enterobacteriaceae, and other drug-resistant organisms become increasingly prevalent, AMP research has intensified. Several LL-37 analogs with improved stability and selectivity for bacterial over mammalian membranes have entered preclinical development. Research also examines synergy between AMPs and conventional antibiotics — combinations often show markedly improved activity against resistant strains compared to either agent alone.
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