Fig. 2

Programmed cell death protein 1 (PD-1) and signal-regulatory protein alpha (SIRPα) expression kinetics during Friend virus (FV) infection. Day 7 acute or chronically infected mice were adoptively transferred with 1 × 10⁶ bead-purified and CellTrace^TM (violet)–labeled CD8⁺ T cells from the spleens of naive Thy1.1⁺ CD8.TCR transgenic mice. The spleens of recipient mice were analyzed by flow cytometry at 72 h post-transfer. (a, e) Analysis of dual expression of PD-1 and SIRPα by Pearson correlation showed highly significant correlation (P < .0001 for both actue and chronic). Representative plots showing the expression of PD-1 (b, f) and SIRPα (c, g) during proliferation (analyzed by dilution of CellTrace^TM fluorescence) is shown on donor cells from acute and chronic recipients. Quantification of results from individual mice during acute (d) and chronic infection (h) are shown with each dot representing an individual mouse and the bar representing the mean. The 1–8 designation depicts the gating strategy for identifying individual cell divisions, but the numbers are only relative as the zero division expression of CellTrace was not evident. Data are from one of two independent experiments with similar results. Linear regression analyses were used to draw the lines in d (R² = 0.6148, P = 0.0369) and h (R² = 0.8837, P = 0.0053). The difference between the slopes of the lines for acute (m = 5.781) vs chronic (m = 1.836) was very significant, P = .0088. During transfer into chronically infected mice (h), there was a slight but significant increase in the proportion of cells expressing SIRPα between cell division 2 (mean = 23.5) and cell division 7 (mean = 32.83), P = 0.0241 by two-way Student’s t test. The flow cytometric gating strategy is shown in supplementary Fig. 6e–g