Novel role of zinc homeostasis in IL-23 regulation and host defense following bacterial infection

Abstract

Abstract Zinc homeostasis is crucial for immune cell activation and intracellular zinc is tightly regulated by zinc transporters. Zinc deficiency is associated with increased prevalence of respiratory bacterial infections. Although the association between zinc and immunity is well established, the mechanisms by which zinc protects against bacteria remain to be elucidated. In human monocytes the zinc transporter Zip8 regulates inflammation in a zinc-dependent manner after LPS exposure. Given the critical role of APCs (macrophages and dendritic cells) in guiding the immune response against bacteria, we sought to determine the role of Zip8 in coordinating the immune response after bacterial exposure. In a novel myeloid-specific Zip8KO mouse model we observed that intranasal instillation of S. pneumoniae resulted in a significant increase of infiltrating neutrophils in the airways of Zip8KO mice when compared to WT counterparts. Analysis of BAL fluid revealed elevated levels of CXCL1 and IL-23 in the Zip8KO mice. To determine whether dendritic cells potentially play a role in the observed response, BMDCs were generated from Zip8KO and WT mice. LPS stimulation produced mature BMDCs with high CD11c and MHC-II expression in both groups. No significant changes were observed in the production of most cytokines examined (TNF-α, CXCL1, IL-6, IL-12), except for IL-23 which was consistently increased in the stimulated Zip8KO cells in comparison to WT control DCs. These results potentially reveal a vital axis that couples zinc homeostasis to IL-23 production in myeloid cells and ultimately host defense against invasive bacterial pathogens. To what extent this alters pathogen clearance and host recovery is the focus of future studies.