FIGURE 4.

Ag-experienced CD4⁺YFP⁺YFP⁻ T cell–derived memory cells, but not CD4⁺YFP⁺GFP⁺ T cell–derived memory cells, respond rapidly during the early phases of challenge infection. Splenic Ag-experienced CD4⁺YFP⁺GFP⁺ and CD4⁺YFP⁺GFP⁻ T cell subsets were sort purified from P.yoelii NL–infected (day 7: 1 × 10⁴ pRBCs [i.v.]) dual reporter mice (CD45.2⁺) and were adoptively transferred, separately, into infected (day 7 postinfection) CD45.1⁺ mice. Recipient mice were treated with pyrimethamine from day 9 of infection for 10 d. Recipient mice were reinfected (1 × 10⁴ pRBCs [i.v.]) on day 60 postinfection with homologous P. yoelii NL parasites. (A) Total numbers of Ag-experienced CD4⁺YFP⁺GFP⁺ and CD4⁺YFP⁺GFP⁻ T cell–derived memory cells in the spleen and liver of recipient mice on day 60 after primary infection and day 4 of secondary infection. (B) Representative histograms and (C) frequencies of Ag-experienced CD4⁺YFP⁺GFP⁺ and CD4⁺YFP⁺GFP⁻ T cell–derived memory cells expressing GFP in the spleen and liver of recipient mice on day 60 after primary infection and day 4 of secondary infection. (D) Numbers of CD4⁺YFP⁺GFP⁺ and CD4⁺YFP⁺GFP⁻ T cell–derived memory cells expressing YFP (left column) and/or GFP (right column) in the (top row) spleen and (bottom row) liver of recipient mice on day 60 after primary infection and day 4 of secondary infection. (E and F) Splenic CD4⁺CD11a⁺CD49d⁺ cells were sort purified from mice on day 60 postinfection and total CD4⁺ T cells were purified from uninfected mice (uninf). Cells were stimulated for (E) 24 or 72 h with anti-CD3 and anti-CD28 or (F) 4 h with PMA and ionomycin and supernatant was assayed for (E) IFN-γ production and IL-10 production or (F) IL-2 production. The results are the mean ± SEM of the group with three to five mice per group and are representative of three independent experiments. *p < 0.05. Significance was tested using an unpaired t test.