STEM-CELL FACTOR IN NASAL POLYPOSIS AND ALLERGIC RHINITIS - INCREASEDEXPRESSION BY STRUCTURAL CELLS IS SUPPRESSED BY IN-VIVO TOPICAL CORTICOSTEROIDS

Background: Mast cells are increased in nasal polyp (Np) and allergic rhinitis (AR) tissue and are suppressed by topical corticosteroid trea tment. Stem cell factor (SCF), a mast cell growth and survival factor, may explain these phenomena. Objective: We investigated structural ce ll gene expression and production of SCF in nasal tissues in patients who had received and who had not received in vivo intranasal corticost eroid therapy. Methods: Northern blot analyses for messenger RNA and E LISA for biologically active SCF protein from cultured Np epithelial c ells and fibroblasts mere performed. Immunostaining for SCF in culture d and tissue nasal structural cells in the presence or absence of ster oid treatment was also performed. Results: We detected significant exp ression of SCF mRNA and protein by cultured Np epithelial cells and Np fibroblasts; Np fibroblast SCF supported the differentiation of mast cells in vitro. There were more immunoreactive SCF-positive Np epithel ial cells in patients with AR than in control subjects (97.2 +/- 2.8 v s 45.6 +/- 22.0%; p < 0.0001). SCF that could be immunostained was sig nificantly diminished overall in Np structural cells in the group give n in vivo steroid treatment, with a modest (trend to significant) effe ct on any given cell type analyzed. In vitro treatment with budesonide of SCF-producing fibroblasts demonstrated inhibition of unstimulated, primary Np fibroblasts but not of IL-l-stimulated fibroblasts or tran sformed cell lines. Conclusions: Human Np and AR tissue structural cel ls express and produce increased SCF. Our in vitro studies suggest tha t intranasal steroids blunt SCP expression in Nps, an effect that may be responsible for a decrease in mast cells and symptoms.