Human ß-defensin HBD3 binds to immobilized Bla g2 from the German cockroach (Blattella germanica).

Human ß-defensin 3 (HBD3) is a small, well-characterized peptide in mucosal secretions with broad antimicrobial activities and diverse innate immune functions. Among these functions is the ability of HBD3 to bind to antigens. In this study, we hypothesize that HBD3 binds to the allergen Bla g2 from the German cockroach (Blattella germanica). The ability of HBD1 (used as a control ß-defensin) and HBD3 to bind to Bla g2 and human serum albumin (HSA, used as a control ligand) was assessed using the SensíQ Pioneer surface plasmon resonance (SPR) spectroscopy biosensor system. HBD1 was observed to bind weakly to Bla g2, while HBD3 demonstrated a stronger affinity for the allergen. HBD3 was assessed under two buffer conditions using 0.15 M and 0.3 M NaCl to control the electrostatic attraction of the peptide to the chip surface. The apparent K(D) of HBD3 binding Bla g2 was 5.9±2.1 µM and for binding HSA was 4.2±0.7 µM, respectively. Thus, HBD3, found in mucosal secretions has the ability to bind to allergens like Bla g2 possibly by electrostatic interaction, and may alter the ability of Bla g2 to induce localized allergic and/or inflammatory mucosal responses.

Defensins as anti-inflammatory compounds and mucosal adjuvants.

Human neutrophil peptide alpha-defensins and human beta-defensins are small, well-characterized peptides with broad antimicrobial activities. In mixtures with microbial antigens, defensins attenuate proinflammatory cytokine responses by dendritic cells in culture, attenuate proinflammatory cytokine responses in the nasal fluids of exposed mice and enhance antibody responses in the serum of vaccinated mice. Although the exact mechanisms are unknown, defensins first start by binding to microbial antigens and adhesins, often attenuating toxic or inflammatory-inducing capacities. Binding is not generic; it appears to be both defensin-specific and antigen-specific with high affinities. Binding of defensins to antigens may, in turn, alter the interaction of antigens with epithelial cells and antigen-presenting cells attenuating the production of proinflammatory cytokines. The binding of defensins to antigens may also facilitate the delivery of bound antigen to antigen-presenting cells in some cases via specific receptors. These interactions enhance the immunogenicity of the bound antigen in an adjuvant-like fashion. Future research will determine the extent to which defensins can suppress early events in inflammation and enhance systemic antibody responses, a very recent and exciting concept that could be exploited to develop therapeutics to prevent or treat a variety of oral mucosal infections, particularly where inflammation plays a role in the pathogenesis of disease and its long-term sequelae.

Human alpha- and beta-defensins bind to immobilized adhesins from Porphyromonas gingivalis.

Human neutrophil peptide alpha-defensins (HNPs) and human beta-defensins (HBDs) are small well-characterized peptides with broad antimicrobial activities and a diversity of innate immune functions. Although the interactions of defensins with bacteria and their membranes have been well characterized, the interactions of defensins with bacterial adhesins have not. Here we determine if HNPs and HBDs bind to the immobilized adhesins of Porphyromonas gingivalis strain 381, recombinant hemagglutinin B (rHagB) and recombinant fimbrillin A (rFimA), by surface plasmon resonance spectroscopy. Association of HNPs and HBDs with rHagB or rFimA was dose dependent and defensin specific. HBD3, HNP-2, and HNP-1 bound more readily to immobilized rHagB than HBD2 and HBD1 did. HNP-2, HNP-1, and HBD3 bound more readily to immobilized rFimA than HBD1 and HBD2 did. Binding of defensins to adhesins may serve to prevent microbial adherence to tissues, attenuate proinflammatory cytokine responses, and facilitate delivery of bound antigen to antigen-presenting cells with defensin receptors.

Human beta-defensin 3 binds to hemagglutinin B (rHagB), a non-fimbrial adhesin from Porphyromonas gingivalis, and attenuates a pro-inflammatory cytokine response.

Regulatory mechanisms in mucosal secretions and tissues recognize antigens and attenuate pro-inflammatory cytokine responses. Here, we asked whether human beta-defensin 3 (HBD3) serves as an upstream suppressor of cytokine signaling that binds and attenuates pro-inflammatory cytokine responses to recombinant hemagglutinin B (rHagB), a non-fimbrial adhesin from Porphyromonas gingivalis strain 381. We found that HBD3 binds to immobilized rHagB and produces a significantly higher resonance unit signal in surface plasmon resonance spectroscopic analysis, than HBD2 and HBD1 that are used as control defensins. Furthermore, we found that HBD3 significantly attenuates (P<0.05) the interleukin (IL)-6, IL-10, granulocyte macrophage colony stimulating factor (GM-CSF) and tumor-necrosis factor-alpha (TNF-alpha) responses induced by rHagB in human myeloid dendritic cell culture supernatants and the extracellular signal-regulated kinases (ERK 1/2) response in human myeloid dendritic cell lysates. Thus, HBD3 binds rHagB and this interaction may be an important initial step to attenuate a pro-inflammatory cytokine response and an ERK 1/2 response.