Comparison of the in vivo and in vitro proliferation of monoblasts, promonocytes, and the macrophage cell line J774.

Mononuclear phagocytes are localized in the bone marrow compartment (monoblasts, promonocytes and macrophages), the circulation (monocytes), and the tissues and serous cavities (macrophages). In vivo and in vitro studies done in murine bone marrow have shown that monoblasts and promonocytes are the most immature, dividing cells of the mononuclear phagocyte cell line; monocytes and resident macrophages do not divide. A very small percentage of the mononuclear phagocytes in the tissues, which are bone-marrow derived and have already the morphology of macrophages, divide once in vivo. The progeny of these dividing cells contribute to the maintenance of the tissue population of macrophages under steady-state conditions. In vitro an appreciable percentage of (young) macrophages divide, in all probability due to the influence of colony-stimulating factor. The cells of macrophage cell lines are transformed cells that proliferate continuously. The morphological, cytochemical and functional characteristics of all these kinds of cells, as well as their proliferative behavior in vivo and in vitro, show great similarity, although there are also distinct differences.