Human bronchial smooth muscle cells in culture produce stem cell factor

A mast cell infiltration of the bronchial smooth muscle layer has been repo rted in patients sensitized to common allergens. Stem cell factor (SCF) is a chemotactic and survival factor for mast cells. SCF is expressed as a sol uble (sSCF) and a membrane-bound (mSCF) form, after alternative splicing of the exon encoding the proteolytic cleavage site. SCF expression by human b ronchial 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 i mmunosorbent assay. Total SCF messenger ribonucleic acid (mRNA) was measure d by competitive polymerase chain reaction (PCR) after reverse transcriptio n. Expression of the two forms of SCF mRNA was assessed by PCR, with primer s spanning the alternatively spliced exon. Smooth muscle cells produced sSCF (21.9+/-2.6 pg.mL(-1)), although at lower levels than fibroblasts (35.9+/-3.5 pg.mL(-1)); the expression of total SC F mRNA was also at lower levels than in fibroblasts (8.6+/-0.2 and 19.0+/-2 .0 amol.fmol glyceraldehyde 3-phosphate dehydrogenase complementary deoxyri bonucleic acid(-1), respectively). However, smooth muscle cells expressed p roportionally 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, ie. at the site of bronchoconstriction, wit h possible implications in the pathophysiology of asthma.