CD28 and infection: In the early phase of the infection, 5 days post infection, ∼50% of activated CD4+ T cells had lost CD28 expression (Figure 2A), IL-2 production was intact (Figure 2B), and there were comparable proportions of proliferating cells in the medLN (Figure 2C) of Cd28flox/floxOx40cre/+ mice compared to controls, and between CD28+ and CD28− cells.