TNF and infection: PBMC from Resistant volunteers produced significantly increased levels (above baseline) of net TNF-α (0.2–0.4%; p = 0.027 unpaired t test) and IL-2 (0.1–0.2%; p = 0.018 unpaired t test) on day 3 post infection in response to in vitro stimulation with CFA/I while Susceptible volunteers did not show increased cytokine production above baseline when stimulated with CFA/I (Fig 1).