Human bronchial smooth muscle cells in culture produce stem cell factor

A mast cell infiltration of the bronchial smooth muscle layer has been reported in patients sensitized to common allergens. Stem cell factor (SCF) is a chemotactic and survival factor for mast cells. SCF is expressed as a soluble (sSCF) and a membrane-bound (mSCF) form, after alternative splicing of the exon encoding the proteolytic cleavage site. SCF expression by human bronchial smooth muscle cells in culture was evaluated, comparing it to that of human lung fibroblasts in culture. sSCF released in the culture supernatant was assessed by an enzyme-linked immunosorbent assay. Total SCF messenger ribonucleic acid (mRNA) was measured by competitive polymerase chain reaction (PCR) after reverse transcription. Expression of the two forms of SCF mRNA was assessed by PCR, with primers spanning the alternatively spliced exon. Smooth muscle cells produced sSCF (21.9+/-2.6 pg x mL(-1)), although at lower levels than fibroblasts (35.9+/-3.5 pg x mL(-1)); the expression of total SCF mRNA was also at lower levels than in fibroblasts (8.6+/-0.2 and 19.0+/-2.0 amol x fmol glyceraldehyde 3-phosphate dehydrogenase complementary deoxyribonucleic acid(-1), respectively). However, smooth muscle cells expressed proportionally more (1.7-fold) mSCF mRNA than did fibroblasts. In conclusion, this study shows that bronchial smooth muscle cells express stem cell factor, with a relatively high expression of membrane-bound stem cell factor. This might be related to the presence of mast cells within the bronchial smooth muscle layer, i.e. at the site of bronchoconstriction, with possible implications in the pathophysiology of asthma.