Human monocytes and macrophages: establishment and analysis of cloned populations and functional cell lines

Human monocytes and macrophages are heterogeneous cell populations, with numerous functions and activities. In the present work we review some new in vitro studies which made possible the development and research of cloned populations of macrophages and functional cell lines. Peripheral blood monocytes were cloned in semisolid media and the cloned monocyte/macrophage populations were analyzed for the expression of various markers. Based on the analysis of cloned populations of monocytes and on additional studies of macrophage functions and markers, we suggest the possibility that the human monocytes represent a unique multifunctional population, expressing reversible changes in functions and markers. The occurrence of stable subsets of cells could not be demonstrated by these methods. Cultures of human monocytes and mature macrophages could be maintained in vitro for long periods of time, but only a few studies reported the continuous proliferation of monocytes in culture. We describe here an approach for immortalization of monocytes by heterologous somatic cell hybridization. This method yielded monocyte hybrid cell lines which preserved some macrophage characteristics. The hybrid cell lines could be used for the isolation and study of monokines and for cytogenetic analysis of macrophage markers and functions.