Antimicrobial proteins (AMP) are a fundamental element of the primary response against pathogens. AMP’s are small endogenous cationic molecules expressed by phagocytic and epithelial cells. The antimicrobial activity of AMP’s is directed towards a broad spectrum of pathogens, like Gram-positive and -negative bacteria, viruses, yeast and fungi. AMP’s aid in innate immunity and adaptive immunity via direct inactivation and by immunomodulatory activity like leukocyte migration. Defensins are the most prominent mammalian AMP’s. Three defensin peptide families are identified, the α-, β-, and θ-defensins. They are characterized by a triple-stranded β-hairpin structure, six disulfide-linked cysteine residues and a positive charge. They are synthesized as preproteins and undergo processing to become a fully active peptide. Defensins are divided in alpha- and beta-defensins depending on their disulfide bridging pattern. Human beta-defensin-2 (hBD-2) is a cystein-rich cationic 41 amino acid antimicrobial peptide of 4-5 kDa. hBDs are localized in epithelial surfaces. Originally, hBD2 was identified in psoriatic scales. Nowadays, hBD-2 has been described as a dynamic component of the local epithelial defense system of the skin, intestinal and respiratory tract, where it functions by protecting surfaces from infection. The hBD2 gene is flanked by several binding sites of NF-kB. Its expression is inducible by proinflammatory molecules like TNFα, IL1α, diverse panel of bacteria, yeasts, IL22 and most of all by IL-17. hBD2 functions best under low ionic strength conditions and is weakened at high salt concentrations. hBD is capable of forming dimers and its microbial activity derives from the mechanism to permeabilize the anionic lipid bilayer, to form pores and the subsequent release of cellular content. HC2140 is a synthetic peptide and has the following sequence: H-GIGDPVTCLKSGAICHPVFCPRRYKQIGTCGLPGTKCCKKP-OH.
Functional studies, Western blot
W: A reduced sample treatment and SDS-Page was used. The band size is ~12 kDa.
FS: Complement activation after incubation with CVF is tested by the lysis of sheep red blood cells.