Chemoattractants in fibrotic disorders

Fibrosis represents an excessive deposition of connective tissue which impedes the normal functions of an organ or tissue. The mechanisms leading to this increased deposition of connective tissue may be similar to those occurring in normal wound repair. We have previously shown that the repair process involves the migration of connective tissue cells to the site of injury and their subsequent proliferation. One of the principal factors controlling these events appears to be the platelet-derived growth factor (PDGF). PDGF acts as a potent chemoattractant and mitogen for connective tissue cells but not other cell types. In addition to PDGF, factors produced by monocytes and tissue macrophages also act as chemoattractants for connective tissue cells. These observations suggest that such activities may be abundant in areas of inflammation. In normal repair these factors would be present for a relatively short period of time, whereas in fibrosis the chronic inflammatory response could maintain a constant or repeated release of such factors. This would recruit additional connective tissue cells to the area of inflammation, changing the cellular composition of the affected organ or tissue, resulting in an expansive and permanent nodule of connective tissue.