TNF-α and IL-10 production in response to antigenic stimulation with purified S. Typhi flagella by PBMC obtained from subjects immunized with one (A, C) or two (B, D) doses of CVD 909. PBMC were obtained before immunization (Day 0), and at days 28 and 60 or 91 after the first immunization as indicated. Bars represent the mean ± SE of the net TNF-α (A, B) and net IL-10 (C, D) levels in 3-day culture supernatants calculated as described in Materials and Methods. *p<0.05 compared to pre-immunization levels.