Figure 6.

CD14 is dispensable for virus uptake but required for the induction of cytokines in ssRNA virus-infected macrophages. (A) Peritoneal macrophages from WT or CD14^−/− mice were infected with VSV that expresses a GFP-fused glycoprotein (VSV-GFP; MOI: 1) and analyzed by FACS. The histogram shows GFP positivity of uninfected cells (dashed lines) or cells that were infected for either 4 or 6 h (solid lines). Cells were gated on forward and sideward scatter. (B) Virus accumulation in supernatant of BMDMs that were infected with VSV (MOI: 1) for the indicated time periods. The graph shows the mean virus titer from three independent experiments. Data are mean ± SD. (C–E) Accumulation of IL-6 or type I IFN 14 h after infection of WT and CD14-deficient peritoneal macrophages (C and D) or BMDCs (E) with the indicated MOI of VSV and FluAV or stimulated with LPS. (F and G) BMDCs from WT or TLR7-deficient (F) or WT and CD14-deficient (G) mice were infected with the indicated amounts of VSV or VSV-M2, a mutant which is mainly recognized in the cytoplasm, or stimulated with imiquimod, LPS, or DMXAA. IL-6 accumulation was tested 14 h after stimulation. Data in C–G are presented as mean ± SD and are representative of at least two independent experiments. (H) The model shows that CD14 associates with DNA/ssRNA at the plasma membrane and promotes their endocytosis. ssRNA viruses enter the endosome in a CD14-independent way. Acidification destroys the viral envelope, releasing the viral ssRNA genome. In the endosome, CD14 functions as a coreceptor for TLR7 and TLR9 in the recognition of ssRNA and DNA.