β-Defensin 2 and 3 Promote the Uptake of Self or CpG DNA, Enhance IFN-α Production by Human Plasmacytoid Dendritic Cells, and Promote Inflammation

Abstract

Alarmins are a group of structurally diverse host defense antimicrobial peptides that are important immune activators. Here we present a novel role of two potent alarmins, human beta defensin 2 and 3 (HBD2 and 3) in promoting IFN-α production by human plasmacytoid DCs (pDCs). 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 (ITC) studies to elucidate the nature of HBD3-CpG complexes demonstrates involvement of enthalpy driven interactions in addition to hydrophobic interactions with the formation of complexes at a molar ratio of 2:1 defensin/CpG. Intravenous 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 antigen presenting cells (APCs) in the spleen. Subcutaneous injections of these complexes showed enhanced infiltration of inflammatory cells at injection site indicating a potential pathophysiological role of alarmin/DNA complexes in contributing to inflammation. Intraperitoneal immunization of HBD3/CpG complexes with OVA enhanced both cellular and humoral responses in response to OVA as compared to 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.

Porcine Cathelicidins Efficiently Complex and Deliver Nucleic Acids to Plasmacytoid Dendritic Cells and Can Thereby Mediate Bacteria-Induced IFN-α Responses

“…Additionally, the cathelicidin-driven IFN-a induction is not restricted to a-helical and proline-rich peptides because comparable results were obtained with PG-1, a disulfide-bridged cysteine-rich cathelicidin. In humans, both b-defensin 2 and 3 have been shown to participate in enhancing IFN-a response in pDC (21). Thus, results obtained with PG-1 structurally relating to defensins support the role of this subclass of peptides in promoting pDC activation with induction of IFN-a in response to free nucleic acids.…”

“…This mechanism has been proposed for the pathogenesis of some autoimmune diseases such as psoriasis and lupus erythematosus (19,20). Similar to what has been observed with LL-37, human b-defensin 2 and 3 have been shown to enhance IFN-a response in pDC (21). However, nothing has been described regarding the effect of porcine cathelicidins in the activation of pDC by microbial nucleic acids.…”

Importance of Endosomal Cathelicidin Degradation To Enhance DNA-Induced Chicken Macrophage Activation

“…One of their previously described functions is the enhancement of DNA-induced IFN-a production in pDCs (18,29). To our knowledge, this study is the first description of enhancement of DNA-induced immune activation by cathelicidins in a nonmammalian species.…”

“…This also appears to be the case in other studies investigating the role of HDPs on TLR9 activation (18,28,29). Nevertheless, very little is known about the intracellular stability of HDP-DNA complexes and how this influences endosomal TLR activation.…”

Mechanisms of NDV-3 vaccine efficacy in MRSA skin versus invasive infection

“…In humans, host defense peptides including β-defensins 2 and 3 can enhance adaptive immunity (e.g., dendritic cell or lymphocyte function) (70) and potentiate opsonophagocytosis and intracellular killing of pathogens by granulocytes (71). Likewise, complementary or compensatory mechanisms including Th1 responses (41)(42)(43)(44), functional antibodies, as well as complement fixation (72) may also contribute to NDV-3 efficacy.…”