Integrin αvβ8-Mediated Activation of Transforming Growth Factor-β Inhibits Human Airway Epithelial Proliferation in Intact Bronchial Tissue

Transforming growth factor (TGF)-β is a potent multifunctional cytokine that is an essential regulator of epithelial proliferation. Because TGF-β is expressed almost entirely in a latent state in vivo , a major source of regulation of TGF-β function is its activation. A subset of integrins, αvβ8 and αvβ6, which are expressed in the human airway, has recently been shown to activate latent TGF-β in vitro , suggesting a regulatory role for integrins in TGF-β function in vivo . Here we have developed a novel, biologically relevant experimental model of human airway epithelium using intact human bronchial tissue. We have used this model to determine the function of integrin-mediated activation of TGF-β in the airway. In human bronchial fragments cultured in vitro , authentic epithelial-stromal interactions were maintained and integrin and TGF-β expression profiles correlated with profiles found in normal lung. In addition, in this model, we found that either the integrin αvβ8 or TGF-β could inhibit airway epithelial cell proliferation. Furthermore, we found that one mechanism of integrin-αvβ8-dependent inhibition of cell proliferation was through activation of TGF-β because anti-β8 antibody blocked the majority (76%) of active TGF-β released from bronchial fragments. These data provide compelling evidence for a functional role for integrin-mediated activation of TGF-β in control of human airway epithelial proliferation in vivo .