Poly (I:C) induces co-stimulatory molecule expression on macrophages and DCs. Twenty-four hours after intraperitoneal injection with either poly (I:C) or control PBS, splenocytes were harvested, and macrophages and DCs were visualized with anti-F4/80 or anti-CD11c, respectively (not shown). After gating on macrophages (A) or DCs (B), staining with antibodies specific for the indicated costimulatory molecules was performed. Cells from mice treated with poly (I:C) (–) are compared with control mice injected with PBS (------). Staining from representative mice is shown, and y-axes of histograms represent percentage of maximum peak value. This experiment was performed 3 times with similar results.