SLPI mRNA expression in myeloid cells and PMNs and SLPI protein levels in plasma are severely downregulated in patients with CN. (A) SLPI mRNA expression in BM CD33⁺ cells of studied groups treated and untreated with G-CSF. CN, severe congenital neutropenia; IN, idiopathic neutropenia; ctrl, healthy control. SLPI mRNA expression, normalized to β-actin and presented as arbitrary units (AUs), was measured by qRT-PCR; data represent mean ± standard deviation (SD) of triplicates. (B) SLPI mRNA expression in PMNs from studied groups treated with G-CSF. SLPI mRNA expression is normalized to that of β-actin and presented in AUs; data represent mean ± SD measured in triplicate (*P < .05; **P < .01). (C) SLPI plasma levels were measured in healthy volunteers and the groups of patients indicated above using SLPI-specific ELISA. Data represent mean ± SD and are derived from 2 independent experiments, each in triplicate (*P < .05). (D) Representative micrograph of a BM section from a healthy individual showing immunostaining for SLPI (brown) and counterstaining with hematoxylin (blue). The image shows that myeloid cells express SLPI protein.