Autocrine and/or paracrine mechanism operate during the growth of human bone marrow fibroblasts.

The growth of human marrow fibroblasts was studied at various plating cell densities. The growth rate of fibroblasts cultured with human plasma derived serum (PDS) increased depending on the cell density plated, whereas fibroblasts cultured with human serum proliferated almost independent of the cell density. Conditioned medium obtained from the culture with PDS at high cell density enhanced the growth of fibroblasts plated at low density, as well as that of fibroblast colony forming cells. Characterization of this conditioned medium showed heat unstable and acid stable peptide factor(s) with high molecular weight (approximately 10(6)) may be responsible for this activity. These results suggest that autocrine and/or paracrine mechanism can operate during the proliferation of marrow fibroblasts, a process thought to be involved in the progression of marrow fibrosis.