Lung cell population density determines the ratio of type III to type I collagens.

Cultured human lung fibroblasts produced 26 to 68% more type III collagen at confluency than at low cell density. This phenomenon occurred in cell lines from normal embryonic and adult lung tissue as well as in cultures established from fibrotic lung tissue. Modulation of the proportions of individual collagen types may be important in the genesis of pulmonary fibrosis.