Beta-defensins activate macrophages and synergize in pro-inflammatory cytokine expression induced by TLR ligands

Our previous studies indicated that mouse beta defensin 14 (mBD14, Defb14), a newly identified member of the beta-defensin super family, interacts with the chemokine receptors CCR2 and CCR6. In this study we report that pre-stimulation of primary mouse macrophages with mBD14 results in a synergistic, enhanced expression of pro-inflammatory cytokines and chemokines induced by TLR ligand re-stimulation. Experiments using specific inhibitors of Gi-protein-coupled receptor signaling provide evidence that this effect seems to be mediated by a Gi-protein-coupled receptor expressed on bone marrow derived macrophages. However, using primary macrophages derived from CCR6- and CCR2-deficient mice clearly demonstrated that the enhanced pro-inflammatory cytokine and chemokine expression is independent of the chemokine receptors CCR6 and CCR2. Additionally, signaling pathway analysis indicated that mBD14 is capable of inducing MAPK ERK1/2 phosphorylation and the induction of CD86 and F4/80 expression in bone marrow-derived macrophages after mBD14 stimulation. Collectively, our data indicate that β-defensins activate primary macrophages and enhance pro-inflammatory responses by using GiPCRs in order to support inflammatory reactions induced by TLR ligands.