IL-21 inhibits short-time, LPS-induced DC activation and proinflammatory cytokine production in vitro. Immature DCs (after 8 days of culture with GMCSF only) were activated with low-dose LPS (10 ng/mL) or with LPS plus IL-15, IL-21, or IL-10 for 24 hours. (A) Surface expression of costimulatory and MHC II molecules were analyzed by FACS. Given is the percentage of high positive cells defined by the marker M1. (B) Cytokines were analyzed in the DC culture supernatant. Significance was calculated using Student t test (^**P ≤ .01) and shown is the mean ± SD (note different scale for IL-6 concentration). One representative out of 4 experiments is shown.