TNFα-treated DC are more stimulatory than non–TNFα-cultured DC in a primary, 6-day allogeneic mixed leukocyte reaction. PBMC from two separate donors (B and C) were used to generate DC; a single PBMC donor (A) served as the source of responder T cells in the assay. Various responder: stimulator (R:S) ratios were included, as described in the Materials and Methods. DC cultured in the presence of TNFα stimulated greater T-cell proliferative responses at all R:S ratios tested. The SEM of triplicate wells was always less than 15% of the mean. Experiments were repeated five times with similar results.