Serum IL-10 levels in LCMV infected mice. a) Sera from naïve (dashed line) or mice infected with LCMVARM (squares) or LCMVClone13 (circles) were assayed for IL-10 by ELISA at the indicated time points. The limit of detection of IL-10 by ELISA was 4 pg/ml. Serum IL-10 levels in naïve mice were at or below the limit of detection. Each time point represents 3–10 mice. b) IL-10 receptor expression was measured on CD8+ T cells in naïve mice and days 8 and 30 post infection by LCMVARM and LCMVClone13. The light line is staining by the isotype control and the bold line is IL-10R expression on gated CD8+ T lymphocytes. c) IL-10R expression on virus-specific CD8 T cells is upregulated in the contexts of acute and viral infection. Mice were infected with LCMVARM (bold red line) or LCMVClone13 (dashed blue line) and IL-10R expression was assessed eight days post-infection. Lymphocytes were gated on CD8 and DbGP33 tetramers. The solid histogram is the expression of IL-10R on naïve P14 CD8+ lymphocytes.