CD4 and infection: To directly investigate this, total splenic Ag-experienced CD4+ T cells (CD11a+CD49d+) and Ag-experienced YFP+GFP− and YFP+GFP+ subsets were purified from dual reporter mice on day 7 of infection (Fig. 3A), and equal numbers were adoptively transferred, separately, into infected CD45.1 congenic mice (day 7 of infection).