Betadefensin

Betadefensin, commonly referred to as beta-defensin, is a family of small, cationic antimicrobial peptides produced by epithelial cells and neutrophils. They are part of the innate immune system and exhibit broad-spectrum antimicrobial activity. Mature beta-defensins are typically about 36–45 amino acids long and contain six cysteine residues that form three intramolecular disulfide bonds, establishing a characteristic beta-defensin fold.

Genetically, beta-defensins are encoded by a multigene family. In humans, several beta-defensin genes exist, producing different peptides such as human beta-defensin 1 (hBD-1), hBD-2, and hBD-3. hBD-1 is constitutively expressed by many epithelia, whereas hBD-2 and hBD-3 are inducible by microbial products and pro-inflammatory cytokines, leading to increased antimicrobial activity during infection. Expression patterns vary across tissues, including the skin, respiratory tract, gastrointestinal tract, and urogenital tract.

Mechanism and role: Beta-defensins kill microbes primarily by disrupting microbial membranes and interfering with essential cellular processes. Beyond antimicrobial activity, they can modulate immune responses by acting as chemoattractants for dendritic cells and memory T cells through the CCR6 receptor, and they may influence wound healing and inflammation.

Clinical relevance: Altered beta-defensin expression has been linked to various diseases, including chronic inflammatory conditions, periodontal disease, and cystic fibrosis. Due to their antimicrobial properties and immune-modulatory effects, beta-defensins are explored as potential therapeutics for infections and inflammation, though challenges remain in stability, delivery, and potential host toxicity.

Evolution and nomenclature: Beta-defensins constitute one of the defensin families, alongside alpha- and theta-defensins. They are found across mammals and other vertebrates, with gene clusters and copy-number variation contributing to species-specific repertoires.