Inflammation and tissue remodeling with pathologic
fibrosis are common consequences of Th2 responses in the lung and other organs.
Interleukin (IL)-13 and
transforming growth factor-beta1 (TGF-beta(1)) are frequently coexpressed in these responses and are believed to play important roles in the pathogenesis of Th2-induced pathologies. To shed light on the mechanisms of these responses, overexpression transgenic approaches were used to selectively target each of these
cytokines to the murine lung.
IL-13 proved to be a potent stimulator of eosinophilic
inflammation, mucus
metaplasia, tissue
fibrosis, and alveolar remodeling.
CC chemokines, specific
chemokine receptors (CCR2, CCR1),
adenosine metabolism,
vascular endothelial growth factor, and
IL-11 contributed to the genesis of these responses.
IL-13 also induced tissue
fibrosis, at least in part, via its ability to induce and activate TGF-beta(1). In the TGF-beta(1) transgenic mouse, epithelial apoptosis preceded the onset of tissue
fibrosis and alveolar remodeling. In addition, chemical (
Z-VAD-fmk) and genetic (null mutations of early growth response gene 1) interventions blocked apoptosis and ameliorated TGF-beta(1)-induced
fibrosis and alveolar restructuring. These studies define an IL-13-TGF-beta(1) pathway of tissue remodeling that regulates
inflammation, mucus
metaplasia, apoptosis, vascular responses, and
fibrosis in the lung. They also highlight the intimate relationship between apoptosis and
fibrosis induced by TGF-beta(1). By defining the complexities of this pathway, these studies highlight sites at which
therapies can be directed to control these important responses.