Cytokine-binding proteins in the lung.

Numerous cytokines and growth factors signal the normal processes of tissue maintenance and remodeling in the lung, yet the aberrant expression of these peptide mediators is involved in a variety of pulmonary diseases. Furthermore, several different binding proteins function in controlling the extracellular levels of many of these cytokines in the lung. For example, a variety of cytokines and growth factors bind to and are regulated by the ubiquitous proteinase inhibitor, alpha 2-macroglobulin. The insulin-like growth factors are controlled by a specific class of six different insulin-like growth factor binding proteins. The transforming growth factor-beta family and fibroblast growth factors interact with extracellular matrix proteins. Several growth factor receptors are shed into the extracellular milieu where they retain a functional binding domain and thereby act as specific binding proteins. Cytokine-binding proteins appear to have a diversity of functions and may serve as extracellular cytokine reservoirs, protective shields against proteolytic degradation of cytokines, modifiers of cytokine-induced biological activity, or as clearance avenues for cytokines. The wide spectrum of cytokine-regulating molecules is important in cell-cell communications under normal conditions, whereas cytokine-binding protein dysfunction could contribute to a number of pulmonary diseases.