Expansion of Treg during infection with FV. Flow cytometry was used to quantify CD4⁺ Foxp3⁺ Treg in lymph nodes (A), spleen (B), and bone marrow (C) of naive mice and at different time points after infection with FV. Each column represents mean absolute numbers plus SEM of CD4⁺ Foxp3⁺ Treg per 1 million nucleated cells for a group of 5 to 10 mice. Data were pooled from 3 independent experiments with similar results. Differences between naive mice and mice infected for 10 days with FV were analyzed by the unpaired Student t test. Statistically significant differences between the groups are indicated in the figure.