Visualization of IFNβ production by plasmacytoid versus conventional dendritic cells under specific stimulation conditions in vivo

Type I interferons, a protein family of multiple IFN alpha s and a single IFN beta, initially identified on the basis of their antiviral activities have recently been attributed important roles in bacterial and parasitic infections. To assess the cellular sources of IFN beta, the IFN produced first in most situations, we created an IFN beta reporter-knockin mouse, in which yellow fluorescent protein (YFP) is expressed from a bicistronic mRNA linked by an internal ribosomal entry site to the endogenous IFN beta mRNA. This YFP expression allows spatiotemporal tracking of the initiation of the type I IFN response on a single-cell level. In vitro bone marrow-derived macrophages (BMM Phi s) and bone marrow-derived dendritic cells (BMDCs) show IFN beta production from distinct cell subpopulations in response to defined pathogen compounds. A subpopulation of GMCSF-derived BMDCs produced IFN beta after poly(I:C), 3'5'-cytidylylguanosine (CpG), or LPS treatment, whereas Flt3-L-cultured plasmacytoid DCs (pDCs) responded mainly to CpG. After poly(I: C) injection in vivo, IFN beta-producing cells localize to the splenic marginal zone and the lymph node subcapsular sinus. Infection with murine cytomegalovirus (MCMV) induces IFN beta/YFP expression exclusively in few activated pDCs at the T cell/B cell interface of the splenic white pulp. This IFN beta/YFP reporter mouse represents a reliable tool for the visualization and characterization of IFN beta-producing cells in vitro and in vivo.