FIG. 1.

Purified peripheral blood CD4⁺ (A) or CD8⁺ (B) cells from volunteers vaccinated with serovar Typhi Ty21a were stimulated with 10⁷ heat-killed Ty21a bacteria/ml in the presence of APC at different time points before and after vaccination. Five days after the antigen stimulation, the proliferative responses were measured and the results were normalized by division with the proliferation levels of PHA-stimulated cells. The data shown are fold increases of normalized rates of proliferation compared to the prevaccination levels. Prevaccination levels were as follows: for CD4⁺ cells, the median rate of proliferation was 13,900 cpm (range, 4,200 to 17,900 cpm); for CD8⁺ cells, the median rate of proliferation was 250 cpm (range, 80 to 640 cpm). Values from each of the six individual vaccinees are shown. A paired t test was performed to compare levels at the peak time point with the prevaccination levels. P = 0.0076 (A) and 0.055 (B).