Growth regulation by macrophages.

The evidence reviewed here indicates that macrophages, either acting alone or in concert with other cells, influence the proliferation of multiple types of cells. Most of the data indicate that these effects are mediated by soluble macrophage-elaborated products (probably proteins) although the role of direct cell-to-cell contacts cannot be ruled out in all cases. A degree of success has been achieved on the biochemical characterization of these factors, but such work has been hampered by the factors low specific activity in conditioned medium and the lack of rapid, specific assays. It is our belief that understanding the growth-regulating potential of macrophages is an important and needed area of research.