see also:

• innate immunity
• lysozyme (LYZ)

• cathelicidins are a family of antimicrobial peptides characterized by a conserved cathelin domain and a variable antimicrobial peptide domain
• they disrupt bacterial cell membranes, leading to cell death.
• they can modulate the activity of various immune cells and influence inflammatory processes and can also promote wound healing and angiogenesis
• human cathelicidin LL-37 is expressed in various cells and tissues, including neutrophils, epithelial cells, and macrophages
• in contrast, defensins, another family of antimicrobial peptides, are structurally diverse, with different types exhibiting variations in disulfide bond patterns. Cathelicidins have a conserved cathelin domain, with the antimicrobial activity residing in a separate variable domain.
  • defensins are more commonly associated with epithelial cells, while cathelicidins are found in a wider range of cell types.

• cathelicidin genes in mammals and birds likely evolved from a common ancestral gene before the divergence of these lineages
• in eutherian (placental) mammals, cathelicidin genes are typically found as a single gene cluster that is syntenic (conserved in order and location) across species. Most eutherians, such as humans and mice, possess a single cathelicidin gene, while some (e.g., cows, sheep, pigs) have multiple genes due to recent lineage-specific duplications, likely driven by pathogen pressures
• phylogenetic analyses show that mammalian cathelicidins have experienced multiple evolutionary events, including gene duplication, loss, and the derivation of related genes such as Ngp (neutrophil granule protein)
• marsupials (e.g., kangaroos) and monotremes (e.g., platypus) show greater cathelicidin gene diversity. Recent studies identified 130 cathelicidin genes across 14 marsupial species, with gene expansions in all species studied. Marsupials have two cathelicidin gene clusters, and monotremes have three, compared to one in eutherians
• many birds have at least four of these cathelicidin genes: CATHL1, CATHL2, CATHL3 and CATHB1
  • the majority of bird species share a conserved gene order of KLHL18, CATHL2, CATHL3, CATHB1 and TBRG4
  • these genes share similar structures with mammalian cathelicidins, each comprising of four exons, encoding a prepropiece consisting of a signal peptide, the cathelin-like domain (propiece) and the mature peptide.¹⁾