Biologically active mediators: platelet-derived growth factor, monocyte chemoattractant protein-1, and transforming growth factor-beta.

The advent of tissue culture techniques provided efficient means to measure the activities of hormones that act at very low concentrations. By following a specific activity, biologically active mediators could then be efficiently purified from impure starting materials. Different assay systems allowed the purification of different types of factors. Growth-inducing factors, such as platelet-derived growth factor, were discovered because they could stimulate DNA synthesis in vitro. Chemotactic factors, such as monocyte chemoattractant protein-1, were discovered based on their capacity to stimulate migration of cells in vitro. Transforming growth factors were originally described because of their capacity to stimulate the growth of nontransformed cells in soft agar. This review describes the effects of biologically active mediators using platelet-derived growth factor, monocyte chemoattractant protein-1, and transforming growth factor-beta as examples.