Differences in peripheral blood cell populations in the aged and juvenile host following SARS-CoV infection. Peripheral blood was collected prior to and at 5 or 10 days post SARS-CoV infection while animals were under sedation. Complete white blood cell counts and cell differentials were assessed by the Lovelace Clinical Laboratory Staff. The number of cells × 10^3 per microliter (μl) blood are graphed for (A) white blood cells (WBC), (B) neutrophils, (C) monocytes, and (D) lymphocytes. (E-F) The number of CD8 T cells and B cells per microliter blood was calculated based on flow cytometric frequencies and total lymphocyte numbers. The gating strategy is depicted in Additional file 1: Figure S1. Graphs represent average values (+/−SE). *p < 0.05, ***p < 0.0005, ****p < 0.0001 in 2-way ANOVA comparing age and time post infection (d.p.i.) as indicated in the graphs.