Integrin mediation of type II cell adherence to provisional matrix proteins

Lung injury causes alveolar type I epithelial cell death, basement membrane denudation, and alveolar flooding with serum fibronectin and fibrinogen. For successful restoration of normal architecture, the epithelium must be regenerated from progenitor type II alveolar cells. Using adhesion assays, we examined whether type II alveolar cells adhere to the provisional matrix proteins fibronectin, fibrinogen, and fibrin, and whether integrins mediate this adherence. Rat type II cells adhered to fibronectin, vitronectin, fibrinogen, and fibrin. Synthetic RGD (arginine-glycine-aspartic acid) peptide blocked this adhesion. Flow cytometry and Western analysis indicated that type II cells expressed β₁-and α(v)β₃-integrins. Anti- β₁- and anti-α(v)β₃-integrin antibodies blocked type II cell adhesion to fibronectin and to fibronectin and fibrinogen, respectively. In summary, type II cells adhered to fibronectin, fibrinogen, and fibrin, and adhesion was partially mediated by integrins. This study provides the first evidence of type II cell adhesion to fibrin gels and vitronectin, β₁- and α(v)β₃- integrin mediation of type II cell adhesion, and the presence of the α(v)β₃-integrin on type II epithelial cells.