FIG. 4.

Purified peripheral blood CD4⁺ and CD8⁺ cells from volunteers vaccinated with serovar Typhi Ty21a were sorted by flow cytometry into CD45RA⁻ β₇^high and CD45RA⁻ β₇⁻-/CD45RA⁺β₇^intermediate subsets. The sorted cells were then stimulated with 10⁶ live Ty21a bacteria/ml in the presence of APC at different time points before and after vaccination. Two days after antigen stimulation, culture supernatants were removed, triplicate wells were pooled, and the IFN-γ levels were measured. The means ± standard errors of the means of values for IFN-γ production at the peak time points of the vaccinees tested (six CD4⁺ vaccinees and four CD8⁺ vaccinees) are shown. A paired t test was performed to compare levels between the sorted subsets. P = 0.0043 (A) and 0.046 (B).