Migratory Dendritic Cells, Group 1 Innate Lymphoid Cells, and Inflammatory Monocytes Collaborate to Recruit NK Cells to the Virus-Infected Lymph Node

Abstract

Summary: Circulating natural killer (NK) cells help protect the host from lympho-hematogenous acute viral diseases by rapidly entering draining lymph nodes (dLNs) to curb virus dissemination. Here, we identify a highly choreographed mechanism underlying this process. Using footpad infection with ectromelia virus, a pathogenic DNA virus of mice, we show that TLR9/MyD88 sensing induces NKG2D ligands in virus-infected, skin-derived migratory dendritic cells (mDCs) to induce production of IFN-γ by classical NK cells and other types of group 1 innate lymphoid cells (ILCs) already in dLNs, via NKG2D. Uninfected inflammatory monocytes, also recruited to dLNs by mDCs in a TLR9/MyD88-dependent manner, respond to IFN-γ by secreting CXCL9 for optimal CXCR3-dependent recruitment of circulating NK cells. This work unveils a TLR9/MyD88-dependent mechanism whereby in dLNs, three cell types—mDCs, group 1 ILCs (mostly NK cells), and inflammatory monocytes—coordinate the recruitment of protective circulating NK cells to dLNs. : Wong et al. show that infected migratory dendritic cells (mDCs) in draining lymph nodes (dLNs) upregulate NKG2D ligands through TLR9/MyD88. This results in NKG2D-dependent IFN-γ production by group 1 innate lymphoid cells, mostly NK cells. IFN-γ induces CXCL9 in uninfected inflammatory monocytes, leading to the recruitment of protective NK cells to dLNs. Keywords: viral infection, mouse, poxvirus, ectromelia virus, NK cells, dendritic cells, monocytes, dendritic cells, innate lymphoid cells, interferon