hBD2

Human beta-defensin 2 (hBD-2) is a small cationic antimicrobial peptide belonging to the defensin family. It is encoded in the DEFB4 gene cluster on chromosome 8p23.1 and is one of several beta-defensins expressed in humans. hBD-2 is inducible and is typically present at low baseline levels in epithelial tissues, but its expression rises in response to infection or inflammation.

Expression and regulation: Epithelial cells of the skin, respiratory, gastrointestinal, and genitourinary tracts produce hBD-2. Its transcription is upregulated by proinflammatory cytokines such as IL-1β and TNF-α and by microbial products that activate Toll-like receptors. Copy number variation at the DEFB4 locus can influence basal and inducible levels of hBD-2.

Structure and function: The mature hBD-2 peptide is about 41 amino acids long and contains six conserved cysteines that form three disulfide bonds, giving it a stable, cationic structure. It has broad-spectrum antimicrobial activity against bacteria (including Staphylococcus aureus and Escherichia coli), fungi such as Candida species, and some enveloped viruses. In addition to direct antimicrobial effects, hBD-2 can act as a chemoattractant for immune cells, interacting with the CCR6 receptor to recruit memory T cells and dendritic cells to sites of infection.

Clinical relevance and research: hBD-2 contributes to barrier defense and wound healing and is studied as a potential therapeutic agent in topical infections. Alterations in hBD-2 expression or DEFB4 gene copy number have been investigated for associations with infectious and inflammatory diseases, including periodontitis and inflammatory lung conditions, though findings are context-dependent.