Elastase expression by AML cells affects their SDF-1-induced transwell migration. (A) In vitro transwell migration assay of AML cells either untreated (▪) or treated for 30 minutes with EI (10 μg/mL; □). The results show the percentage of migrated cells toward 125 ng/mL SDF-1 after 4 hours. The percent of migrating cells in the absence of SDF-1 (spontaneous migration) was deduced from the percent of migrating cells in the presence of SDF-1. Statistical significance of the inhibition from all samples taken together was P = .039. (B-C) U937 and primary AML cells were assayed for SDF-1-induced migration after pretreatment with neutralizing antielastase Abs (30 and 70 μg/mL) for 30 minutes (B) or α1-antitrypsin (100 μg/mL, α1-AT) (C). Results represent mean ± SE of 3 experiments with U937 cells and 2 patient samples done in duplicate; ^*P ≤ .03. (D) Immunocytochemical analysis of membranal elastase and CXCR4 localization in primary PB AML cells either untreated or pretreated with EI in the presence or absence of 200 ng/mL SDF-1. Merged images are shown. Original magnification, × 40. Insert shows a cell that acquired highly polarized morphology in the presence of SDF-1.