The effects of CD26 activity on chemotaxis of SS cells induced by SDF-1. (A) Chemotactic response of CD4⁺ SS cells following exposure of SDF-1 (300 ng/mL) in the absence or presence of soluble CD26 (sCD26), respectively, at a molecular ratio of SDF-1 and sCD26 of 200:1 and 20:1. Results (mean ± SEM from 3 separate experiments) are shown as migration indexes representing the ratio between the number of cells that migrated in the presence of SDF-1 alone or supplemented with sCD26 and the number of cells that migrated in response to medium alone. ^*Significant differences between SDF-1 supplemented with both sCD26 concentrations and SDF-1 alone calculated by the Student t test (SS, n = 3; P < .05). (B) Chemotaxis assay performed comparing Diprotin A-treated (▪) and untreated (□) Hut78 cell line. Treatment with 5 mM Diprotin A enhances up to 3.1-fold of SDF-1-directed chemotactic activity. ^*Significant differences between untreated and treated Hut78 cells by the Student t test (n = 6; P < .05).