Homologous serum increases fibronectin expression and cell adhesion in airway smooth muscle cells

This study describes altered patterns of growth and upregulation of fibronectin expression of cultured canine airway smooth muscle cells grown in homologous serum, which provides a model of the vascular leakage occurring in asthma, compared to fetal bovine serum (FBS). Cells were incubated in increasing concentrations of serum (2.5–40%) for 72 hours. Both homologous serum and FBS caused cellular proliferation which reached a maximum increase at 2.5–5% serum concentration. Differences in the cellular responses to the two types of sera were noted at higher concentrations of sera. At a concentration of 40% FBS, airway smooth muscle cells increased in number by 307±16% (n=5) compared to serum-free control cells, whereas in canine serum the increase in growth was significantly smaller, 239±25% (n=7) (P<0.05). Airway fibrocytes similarly treated increased in number by 256±43% (n=3) in 40% FBS, but exhibited a reduction in cell number to 80 ±10% (n=3) of controls in 40% homologous serum (P<0.05). Smooth muscle cells demonstrated a dose-dependent increase in fibronectin expression when grown in homologous serum, but not in FBS, suggesting phenotypic change occurred in these cells when exposed to homologous serum. These data suggest that the leakage of plasma in the asthmatic airway may trigger phenotypic change in both airway smooth muscle cells and airway fibrocytes leading to cellular proliferation and expression of extracellular matrix molecules. These in vitro changes are consistent with the histological findings in clinical asthma.