Fibrinogen and its fragment D stimulate proliferation of human hemopoietic cells in vitro.

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Abstract
Purified fibrinogen at concentrations of 3-30 nM stimulated continuous growth of human lymphoid and myeloid cell lines under serum-free conditions. A strong proliferative response resulted from the synergism elicited by the addition of fibrinogen to transferrin-supplemented medium. This effect was observed with the pre-B-cell line Raji, the T lymphoma-derived JM, and the monocytic cell line U-937, either at high or low cell densities. With the promyelocytic cell line HL-60, fibrinogen did not shorten the doubling time of cultures seeded at high cell densities (2 .times. 105 cells/ml). At cell densities lower by 2 orders of magnitude and in the same medium, it promoted growth with a doubling time similar to that obtained at high cell concentrations. Fibrinogen also increased the plating efficiency and colony size when human bone marrow cells were cultured in semisolid medium containing serum. In long-term bone marrow liquid cultures without fibrinogen, colony-forming cells were no longer detected after 6 wk. In those cultured with fibrinogen .apprx. 50 granulocyte-macrophage colonies/105 cells were obtained after 6, 10 and 12 wk. Purified fibrinogen fragment D possessed a stimulating activity similar to that of the intact fibrinogen molecule. This fragment cannot form fibrin, thus eliminating fibrin as a source of the mitogenic effect.