MYOFIBROBLAST ACCUMULATION INDUCED BY TRANSFORMING GROWTH-FACTOR-BETAIS INVOLVED IN THE PATHOGENESIS OF NASAL POLYPS

Myofibroblasts that express alpha-smooth muscle actin (alpha-SMA) are detected in many chronic inflammatory diseases. Transforming growth fa ctor-beta (TGF-beta) is a potent inducer of myofibroblast accumulation in tissues. In this study, scattered myofibroblasts and TGF-beta were quantified and localized in nasal polyps (NPs) and normal nasal mucos a (NM). NPs were sampled in 16 patients during ethmoidectomy and NM wa s obtained from 10 control subjects during rhinoplasty. alpha-SMA and TGF-beta were detected using immunohistochemistry and the numbers of l abeled cells were quantified (alpha-SMA and TGF-beta indices) and comp ared between NPs and NM. In eight NPs, in which the pedicle was preser ved, alpha-SMA and TGF-beta were evaluated and compared in the pedicle , central, and tip areas. Finally, TGF-beta expression was compared be tween low (zone 1), moderate (zone 2), and high (zone 3) zones of alph a-SMA positivity. alpha-SMA and TGF-beta indices were significantly hi gher in NPs than in NM. In the eight selected NPs, alpha-SMA-positive cells were significantly more abundant in the pedicle than in the cent ral and tip areas, whereas TGF-beta-positive cells were significantly more numerous in the pedicle than in the tip area. The number of TGF-b eta-positive cells was significantly higher in zone 3 than in zone 1 o f alpha-SMA positivity. Myofibroblasts, which are abundant in NPs but rare in NM, could be involved in the growth of NPs by inducing extrace llular matrix accumulation. The local development of myofibroblasts in NPs could be controlled by TGF-beta, locally produced by inflammatory cells.