Human β-defensin 2 plays a regulatory role in innate antiviral immunity and is capable of potentiating the induction of antigen-specific immunity

Abstract

BackgroundAntimicrobial peptides (AMPs) are primarily known for their innate immune defense against invading microorganisms, including viruses. In addition, recent research has suggested their modulatory activity in immune induction. Given that most subunit vaccines require an adjuvant to achieve effective immune induction through the activation of innate immunity, AMPs are plausible candidate molecules for stimulating not only innate immune but also adaptive immune responses.ResultsIn this study, we investigated the ability of human β-defensin (HBD) 2 to promote antiviral immunity in vitro and in vivo using a receptor-binding domain (RBD) of Middle East respiratory syndrome-coronavirus (MERS-CoV) spike protein (S RBD) as a model antigen (Ag). When HBD 2-conjugated S RBD was used to treat THP-1 human monocytic cells, the expression levels of antiviral (IFN-β, IFN-γ, MxA, PKR, and RNaseL) and primary immune-inducing (NOD2, TNF-α, IL-1β, and IL-6) molecules were enhanced compared to those expressed after treatment with S RBD only. The expression of chemokines capable of recruiting leukocytes, including monocytes/macrophages, natural killer cells, granulocytes, T cells, and dendritic cells, was also increased following HBD 2-conjugated S RBD treatment. More important, immunization of mice with HBD 2-conjugated S RBD enhanced the immunogenicity of the S RBD and elicited a higher S RBD-specific neutralizing antibody response than S RBD alone.ConclusionsWe conclude that HBD 2 activates the primary antiviral innate immune response and may also mediate the induction of an effective adaptive immune response against a conjugated Ag.

Human β-defensin 2 is involved in CCR2-mediated Nod2 signal transduction, leading to activation of the innate immune response in macrophages

“…We next focused on endosomal and/or cytoplasmic signal transmediators involved in HBD 2-mediated activation of primary antiviral responses. In our previous report, a proinflammatory cytokine response, which requires the activation of NF-κB, was induced by HBD 2 (Kim et al, 2018). Additionally, early stimulation of an innate immune response is dependent on Toll-like receptor (TLR) 4 and/or Nod2-triggered NF-κB signaling (Tsai et al, 2011).…”

“…Briefly, the gene encoding S RBD was synthesized with codon optimization based on the MERS-CoV S protein sequence (GenBank AKL59401.1; GenScript, Piscataway, NJ, USA). The S RBD gene with the HBD 2 gene at its 3′ terminus was amplified by polymerase chain reaction (PCR) using forward and reverse primers reported previously (Kim et al, 2018). The amplified genes were cloned into the pColdII Escherichia coli expression vector (TaKaRa Bio, Shiga, Japan).…”

“…To assess the viral loads and the expression levels of target genes in MERS-CoV-infected cells, MERS-CoV was passaged six times in Vero E6 cells and transferred to THP-1 cells (2 × 10 6 /well) in a tissue culture plate. After incubation for 24 h, we extracted total RNA and performed quantitative real-time RT-PCR using the primers in Table 1 to measure the expression levels of MERS-CoV upE and target genes (Kim et al, 2018).…”

“…Due to their location, macrophages detect viral Ags first and promote an antiviral innate immune response as well as an Ag-specific adaptive immune response by presenting Ags to T-cells (Manicassamy et al, 2010). We previously reported that HBD 2 promotes an antiviral innate immune response in macrophage-like THP-1 cells and elicits an enhanced Ag-specific and virus-neutralizing antibody (Ab) response in vivo using the receptor binding domain (RBD) of MERS-CoV spike protein (S RBD) as a model Ag (Kim et al, 2018). Moreover, the type I IFN response and the production of primary antiviral molecules such as Nod2 were enhanced by S RBD-HDB 2 treatment of THP-1 cells (Kim et al, 2018).…”

“…We previously reported that HBD 2 promotes an antiviral innate immune response in macrophage-like THP-1 cells and elicits an enhanced Ag-specific and virus-neutralizing antibody (Ab) response in vivo using the receptor binding domain (RBD) of MERS-CoV spike protein (S RBD) as a model Ag (Kim et al, 2018). Moreover, the type I IFN response and the production of primary antiviral molecules such as Nod2 were enhanced by S RBD-HDB 2 treatment of THP-1 cells (Kim et al, 2018). Consequently, we assumed that modulation of Nod2 signaling by HBD 2 would prevent infection by viruses that suppress innate antiviral immunity.…”