Classification of “Fibroblasts” According to Their Physiological Properties.

Abstract

Years ago it was stated that epithelial cells cultivated in vitro dedifferentiated or returned to an indifferent cell type which could not be distinguished from fibroblasts. 1 However, the conclusions drawn at that time were mainly due to an inefficient technique which resulted in impure strains of tissue cells. Since we are now able to cultivate pure strains of tissue cells indefinitely, we know that the cells, under the conditions of the experiment, remain typical and retain their morphological characteristics throughout the entire period of cultivation. In the case of fibroblasts and epithelial cells, it has become a relatively simple matter to distinguish between the 2 cell types. One is aided not only by marked morphological differences in the cells themselves, but also by striking differences in the mode of growth of the cell colony. 2

Within recent years, we have been mainly interested in studying the maintenance of special properties of tissue cells under various experimental conditions in vitro. We now know that cell types which are morphologically similar may possess functions which are extremely diverse. Pigment epithelium, when cultivated in vitro, continues to produce pigment; 3 thyroid epithelium produces colloid; 4 cancerous epithelium, when inoculated in vivo, produces cancer. 5 These findings show clearly that cell properties are maintained under the conditions of cultivation in vitro.

The experiments, which are to be reported here, show that various mesenchyme cells, which would all be designated morphologically as “fibroblasts,” possess properties and characteristics which are decidedly unlike. Up to the present time, the fibroblasts which have been most intensely studied in vitro have been derived from the embryonic chick heart. The purpose of the present experiments was to study one of the more elementary properties of living tissues, namely, their inherent growth potencies.