Differentiation of circulating monocytes into fibroblast-like cells

Abstract

Monocytes are produced in the bone marrow and enter the blood. They generally leave the blood and enter a tissue, and then become macrophages. In healing wounds, circulating monocytes also enter the tissue and instead of becoming macrophages, can differentiate into fibroblast-like cells called fibrocytes. Fibrocytes are also present in the lesions associated with fibrosing diseases such as congestive heart failure, end stage kidney disease, and pulmonary fibrosis. We have found that culturing blood monocytes, or white blood cell preparations containing monocytes, in serum-free media permits some of the monocytes to differentiate into fibrocytes within 5 days, and that this differentiation is inhibited by the blood plasma protein serum amyloid P.

Fig. 1

Appearance of human fibrocytes in serum-free conditions. (a) Viable human PBMC cultured in SFM for 5 days. (b) PBMC air-dried and stained with eosin and methylene blue. Solid arrow points to a fibrocyte, white arrow points to a dendritic cell, and asterisk is to the left of a macrophages. Bar is 50 μm.

Fig. 2

Example of purified SAP from murine serum. Purified mouse SAP was analyzed by PAGE, on a 4–15% reducing gel, and stained with Coomassie. Lane 1 Protein molecular weight markers (BenchMark protein standards, Invitrogen, Carlsbad, CA). Lanes 2–6 300, 100, 30, 10 and 3 μg/ml human SAP loading controls. Lane 7 Undiluted murine SAP preparation. Lanes 8–13 Murine SAP preparation diluted 1/10, 1/20, 1/40, 1/80, 1/100, and 1/160 with sodium phosphate buffer, respectively.