Effect of IL-18 on pre-DC2 chemotaxis. IL-18 induces chemotaxis in pre-DC2s. (A) Direct chemotaxis of cells toward IL-18. Pre-DC2s were allowed to migrate into nitrocellulose toward various concentrations of IL-18 present in the lower wells of a Boyden microchemotaxis chamber. SDF (1μg/mL) served as positive control. (B) IL-18 receptor antibodies abrogate pre-DC2 migration toward IL-18. Pre-DC2s were preincubated with anti–IL-18Rα mAb at indicated concentrations and allowed to migrate toward a concentration gradient of IL-18 (10 ng/mL). (C) Anti–IL-18 antibodies abrogate pre-DC2 migration toward IL-18. Anti–IL-18 mAb was added to the lower wells of a microchemotaxis chamber containing IL-18 (10 ng/mL), and pre-DC2s were allowed to migrate into nitrocellulose. Migration time periods for all experiments were 180 minutes. Migration depth was quantified microscopically by the leading front assay. Data are expressed as the chemotaxis index: the ratio of the distance of stimulated and random migration of leukocytes into nitrocellulose filters (n = 6). *P < .05 in the Mann-Whitney U test after Kruskal-Wallis ANOVA. Error bars indicate SEM.