Neuropeptide Signaling Activates Dendritic Cell-Mediated Type 1 Immune Responses through Neurokinin-2 Receptor

Neurokinin A (NKA), a neurotransmitter distributed in the central and peripheral nervous system, strictly controls vital responses, such as airway contraction, by intracellular signaling through neurokinin-2 receptor (NK2R). However, the function of NKA NK2R signaling on involvement in immune responses is less-well defined. We demonstrate that NK2R-mediated neuropeptide signaling activates dendritic cell (DC)-mediated type 1 immune responses. IFN-gamma stimulation significantly induced NK2R mRNA and remarkably enhanced surface protein expression levels of bone marrow-derived DCs. In addition, the DC-mediated NKA production level was significantly elevated after IFN-gamma stimulation in vivo and in vitro. We found that NKA treatment induced type 1 IFN mRNA expressions in DCs. Transduction of NK2R into DCs augmented the expression level of surface MHC class II and promoted Ag-specific IL-2 production by CD4(+) T cells after NKA stimulation. Furthermore, blockade of NK2R by an antagonist significantly suppressed IFN-gamma production by both CD4(+) T and CD8(+) T cells stimulated with the Ag-loaded DCs. Finally, we confirmed that stimulation with IFN-gamma or TLR3 ligand (polyinosinic-polycytidylic acid) significantly induced both NK2R mRNA and surface protein expression of human PBMC-derived DCs, as well as enhanced human TACI mRNA, which encodes NKA and Substance P. Thus, these findings indicate that NK2R-dependent neuropeptide signaling regulates Ag-specific T cell responses via activation of DC function, suggesting that the NKA-NK2R cascade would be a promising target in chronic inflammation caused by excessive type 1-dominant immunity. The Journal of Immunology, 2012, 188: 4200-4208.