NE regulates SLPI expression levels. (A) SLPI mRNA expression in BM CD33⁺ cells isolated from healthy individuals untreated (−) or treated with 1, 10, and 100 μg/mL of human purified neutrophils NE. SLPI mRNA expression, normalized to that of β-actin and expressed in arbitrary units (AUs), was measured by qRT-PCR; data are mean ± SD of triplicates (*P < .05). (B) Representative western blot images showing NE protein expression in total lysates from NB4 cells transduced with control (ctrl) cDNA, WT ELANE cDNA, or ELANE mutant cDNA. α-Tubulin staining was used as a loading control. (C) β-Actin–normalized SLPI mRNA expression, in arbitrary units (AU), in NB4 and HL-60 cell lines transduced with control, WT ELANE, or ELANE mutant cDNA, was measured by qRT-PCR; data represent mean ± SD of triplicates (*P < .05 vs control lv samples). (D) Western blot analysis of SLPI expression in NB4 cells transduced with control cDNA, WT ELANE cDNA, or ELANE mutant cDNA. β-Actin was used as a loading control. Representative images are depicted. (E) SLPI mRNA expression in CD34⁺ cells transduced with control, WT ELANE, or ELANE mutant cDNA and treated with G-CSF. mRNA expression, normalized to that of β-actin and presented in AUs, was measured by qRT-PCR; data represent means ± SDs of triplicates (*P < .05). (F) NB4 cells were untreated (ctrl) or treated with 2 mM of DDT for 4 hours. mRNA expression of indicated genes, normalized to that of β-actin and presented in AUs, was measured by qRT-PCR; data represent mean ± SD of triplicates (*P < .05). (G) Representative western blot images showing SLPI protein expression in total lysates from NB4 cells untreated (ctrl) or treated with DDT for 4 hours. β-Actin staining was used as a loading control.