Cathelicidin antimicrobial peptide (CAMP) is an antimicrobial peptide encoded in the human by the CAMP gene.[5] The active form is LL-37, a 37 amino acid peptide having sequence LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES.[6] In humans, CAMP encodes the peptide precursorCAP-18 (18 kDa), which is processed by proteinase 3-mediated extracellular cleavage into the active form LL-37.[7][5]
The cathelicidin family includes 30 types of which LL-37 is the only cathelicidin in the human.[8] Cathelicidins are stored in the secretory granules of neutrophils and macrophages and can be released following activation by leukocytes.[9] Cathelicidin peptides are dual-natured molecules called amphiphiles: one end of the molecule is attracted to water and repelled by fats and proteins, and the other end is attracted to fat and proteins and repelled by water. Members of this family react to pathogens by disintegrating, damaging, or puncturing cell membranes.
Cathelicidins thus serve a critical role in mammalian innate immune defense against invasive bacterial infection.[10] The cathelicidin family of peptides are classified as antimicrobial peptides (AMPs). The AMP family also includes the defensins. Whilst the defensins share common structural features, cathelicidin-related peptides are highly heterogeneous.[10] Members of the cathelicidin family of antimicrobial polypeptides are characterized by a highly conserved region (cathelin domain) and a highly variable cathelicidin peptide domain.[10]
Cathelicidin peptides have been isolated from many different species of mammals, including marsupials.[11] Cathelicidins are mostly found in neutrophils, monocytes, mast cells, dendritic cells and macrophages[12] after activation by bacteria, viruses, fungi, parasites or the hormone 1,25-D, which is the hormonally active form of vitamin D.[13] They have been found in some other cells, including epithelial cells and human keratinocytes.[14] Some viruses evolved immunomodulatory mechanisms to avoid cathelicidin exposure by downregulating the cellular vitamin D receptor.[15]
Etymology
The term was coined in 1995 from cathelin, due to the characteristic cathelin-like domain present in cathelicidins.[16] The name cathelin itself is coined from cathepsin L inhibitor in 1989.[17]
Mechanism of antimicrobial activity
The general rule of the mechanism triggering cathelicidin action, like that of other antimicrobial peptides, involves the disintegration (damaging and puncturing) of cell membranes of organisms toward which the peptide is active.[9]
Cathelicidins rapidly destroy the lipoprotein membranes of microbes enveloped in phagosomes after fusion with lysosomes in macrophages. Therefore, LL-37 can inhibit the formation of bacterial biofilms.[18]
The pleiotropic properties of LL-37 in relation to the different cells and tissues
Other activities
LL-37 plays a role in the activation of cell proliferation and migration, contributing to the wound closure process.[19] All these mechanisms together play an essential role in tissue homeostasis and regenerative processes. Moreover, it has an agonistic effect on various pleiotropic receptors, for example, formyl peptide receptor like-1 (FPRL-1),[20]purinergic receptor P2X7, epidermal growth factor receptor (EGFR).[21]
Cathelicidins range in size from 12 to 80 amino acid residues and have a wide range of structures.[24] Most cathelicidins are linear peptides with 23-37 amino acid residues, and fold into amphipathic α-helices. Additionally cathelicidins may also be small-sized molecules (12-18 residues) with beta-hairpin structures, stabilized by one or two disulphide bonds. Even larger cathelicidin peptides (39-80 amino acid residues) are also present. These larger cathelicidins display repetitive proline motifs forming extended polyproline-type structures.[10]
In 1995, Gudmundsson et al. assumed that the active antimicrobial peptide is formed of a 39-residue C-terminal domain (termed FALL-39). However, only a year later stated that the matured AMP, now called LL-37, is in reality two amino acids shorter than FALL-39.[25][26]
The cathelicidin family shares primary sequence homology with the cystatin[27] family of cysteine proteinase inhibitors, although amino acid residues thought to be important in such protease inhibition are usually lacking.
Cleavage products
LL-37 is cleaved into a number of smaller fragments which retain anti-microbial and anti-cancer effects but generally have a lower toxicity to human cells. RK-31, KS-30 and KR-20 are naturally occurring fragments, while other related peptides have been made synthetically based on natural fragments of LL-37 during research into cathlicidins, and in some cases have amino acid substitutions.[28]
Cleavage products of LL-37
Code
Fragment
Amino acid sequence
LL-37
1-37
LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES
RK-31
7–37
RKSKEKIGKEFKRIVQRIKDFLRNLVPRTES
KS-30
8–37
KSKEKIGKEFKRIVQRIKDFLRNLVPRTES
KR-20
18–37
KRIVQRIKDFLRNLVPRTES
FK-13
17–29
FKRIVQRIKDFLR
FK-16
17–32
FKRIVQRIKDFLRNLV
KR-12
18–29
KRIVKLIKKWLR
GF-17
16-32
GFKRIVQRIKDFLRNLV
GI-20
12–32
GIKEFKRIVQRIKDFLRNLV
Non-human orthologs
Cathelicidin peptides have been found in humans, monkeys, mice, rats, rabbits, guinea pigs, pandas, pigs, cattle, frogs, sheep, goats, chickens, horses and wallabies.[29] Antibodies to the human LL-37/hCAP-18 have been used to find cathelicidin-like compounds in a marsupial.[30] About 30 cathelicidin family members have been described in mammals, with only one (LL-37) found in humans.[9] Currently identified cathelicidin peptides include the following:[10]
Patients with rosacea have elevated levels of cathelicidin and elevated levels of stratum corneum tryptic enzymes (SCTEs). Cathelicidin is cleaved into the antimicrobial peptide LL-37 by both kallikrein 5 and kallikrein 7 serine proteases. Excessive production of LL-37 is suspected to be a contributing cause in all subtypes of Rosacea.[35] Antibiotics have been used in the past to treat rosacea, but antibiotics may only work because they inhibit some SCTEs.[36]
Lower plasma levels of human cathelicidin antimicrobial protein (hCAP18) appear to significantly increase the risk of death from infection in dialysis patients.[37] The production of cathelicidin is up-regulated by vitamin D.[38][39]
SAAP-148 (a synthetic antimicrobial and antibiofilm peptide) is a modified version of LL-37 that has enhanced antimicrobial activities compared to LL-37. In particular, SAAP-148 was more efficient in killing bacteria under physiological conditions.[40] In addition, SAAP-148 synergises with the repurposed antibiotic halicin against antibiotic-resistant bacteria and biofilms.[41]
LL-37 is thought to play a role in psoriasis pathogenesis (along with other anti-microbial peptides). In psoriasis, damaged keratinocytes release LL-37 which forms complexes with self-genetic material (DNA or RNA) from other cells. These complexes stimulate dendritic cells (a type of antigen presenting cell) which then release interferon α and β which contributes to differentiation of T-cells and continued inflammation.[42] LL-37 has also been found to be a common auto-antigen in psoriasis; T-cells specific to LL-37 were found in the blood and skin in two thirds of patients with moderate to severe psoriasis.[42]
LL-37 binds to the peptide Ab, which is associated with Alzheimer's disease. An imbalance between LL-37 and Ab may be a factor affecting AD-associated fibrils and plaques. Chronic, oral Porphyromonas gingivalis, and herpesvirus (HSV-1) infections may contribute to the progression of Alzheimer's dementia.[43][44]
Applications
Research into the AMP family—particularly in regards to their mechanism of action—has been ongoing for nearly 20 years. Despite sustained interest, treatments derived or utilizing AMPs have not been widely adopted for clinical use for several reasons.[45] One, drug candidates from AMPs have a narrow window of bioavailability, because peptides are quickly broken down by proteases. Two, peptide drugs are more expensive than small molecule drugs to produce, which is problematic since peptide drugs must be given in large doses to counter rapid enzymatic breakdown. These qualities also limit routes of administration, typically to injection, infusion, or slow release therapy.[46] Research into new and improved variations derived from cathelicidin continues.[47]
↑ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
↑ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
1 2 "UniProt". www.uniprot.org. Retrieved 8 February 2024.
↑ Voronko OE, Khotina VA, Kashirskikh DA, Lee AA, Gasanov VAO. Antimicrobial Peptides of the Cathelicidin Family: Focus on LL-37 and Its Modifications. Int J Mol Sci. 2025 Aug 21;26(16):8103. doi:10.3390/ijms26168103{{doi}}: unflagged free DOI (link)PMID40869425
↑ Carman R, Simonian MR, Old JM, Jacques NA, Deane EM (2008). Immunohistochemistry using antibodies to the Cathelicidin LL37/hCAP18 in the tammar wallaby (Macropus eugenii). Tissue and Cell. 40(6), 459-466. DOI: 10.1016/j.tice.2008.05.002
↑ Vandamme D, Landuyt B, Luyten W, Schoofs L (November 2012). "A comprehensive summary of LL-37, the factotum human cathelicidin peptide". Cellular Immunology. 280 (1): 22–35. doi:10.1016/j.cellimm.2012.11.009. PMID23246832.
↑ Voronko OE, Khotina VA, Kashirskikh DA, Lee AA, Gasanov VAO. Antimicrobial Peptides of the Cathelicidin Family: Focus on LL-37 and Its Modifications. Int J Mol Sci. 2025 Aug 21;26(16):8103. doi:10.3390/ijms26168103{{doi}}: unflagged free DOI (link)PMID40869425
↑ Carman RL, Old JM, Baker M, Jacques NA, Deane EM (2009). Identification and expression of a novel marsupial cathelicidin from the tammar wallaby (Macropus eugenii). Veterinary Immunology and Immunopathology. 127(3-4), 269-276. DOI: 10.1016/j.vetimm.2008.10.319
↑ Carman RL, Simonian MR, Old JM, Jacques NA, Deane EM (December 2008). "Immunohistochemistry using antibodies to the cathelicidin LL37/hCAP18 in the tammar wallaby, Macropus eugenii". Tissue & Cell. 40 (6): 459–466. doi:10.1016/j.tice.2008.05.002. PMID18597803.
↑ Hao X, Yang H, Wei L, Yang S, Zhu W, Ma D, Yu H, Lai R (August 2012). "Amphibian cathelicidin fills the evolutionary gap of cathelicidin in vertebrate". Amino Acids. 43 (2): 677–85. doi:10.1007/s00726-011-1116-7. PMID22009138. S2CID2794908.
↑ Yuan Y, Li J, Wei G, Shen Z, Li B, Wu J, Liu J. Exploring the Antimicrobial Potential of LL-37 Derivatives: Recent Developments and Challenges. ACS Biomater Sci Eng. 2025 Jun 9;11(6):3145-3164. doi:10.1021/acsbiomaterials.4c02029PMID40423576
Niyonsaba F, Hirata M, Ogawa H, Nagaoka I (September 2003). "Epithelial cell-derived antibacterial peptides human beta-defensins and cathelicidin: multifunctional activities on mast cells". Current Drug Targets. Inflammation and Allergy. 2 (3): 224–31. doi:10.2174/1568010033484115. PMID14561157.
van Wetering S, Tjabringa GS, Hiemstra PS (April 2005). "Interactions between neutrophil-derived antimicrobial peptides and airway epithelial cells". Journal of Leukocyte Biology. 77 (4): 444–50. doi:10.1189/jlb.0604367. PMID15591123. S2CID8261526.
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