Alarmins are a group of structurally diverse host defense
antimicrobial peptides that are important immune activators. In this article, we present a novel role for two potent
alarmins, human β-
defensin 2 and 3 (HBD2 and 3), in promoting IFN-α production by human plasmacytoid dendritic cells. We demonstrate that HBD2 and 3 activate pDCs by enhancing the intracellular uptake of CpG and self
DNA and promote
DNA-induced IFN-α production in a TLR9-dependent manner. Both CpG and host
DNA form aggregates that resemble
DNA nets when combined with HBD2 and 3. Isothermal titration calorimetry studies to elucidate the nature of HBD3/CpG complexes demonstrate involvement of enthalpy-driven interactions, in addition to hydrophobic interactions, with the formation of complexes at a molar ratio of 2:1
defensin/CpG. The i.v. administration of HBD3/CpG complexes induced proinflammatory
cytokines like
IL-12, IFN-γ,
IL-6, IFN-α, and
IL-10 in serum, associated with an increased recruitment of APCs in the spleen.
Subcutaneous injections of these complexes showed enhanced infiltration of inflammatory cells at the injection site, indicating a potential pathophysiological role for
alarmin/
DNA complexes in contributing to
inflammation. Intraperitoneal immunization of HBD3/CpG complexes with OVA enhanced both cellular and humoral responses to OVA, compared with OVA/HBD3 or OVA/CPG alone, indicative of a much more potent adjuvant effect of the HBD3/CpG complexes. Thus, the ability of
defensins to enhance cellular uptake of
nucleic acids can lead to improved
vaccine formulations by promoting their uptake by various cells, resulting in an enhanced immune response.