[Macrophage precursors as cytotoxic effector cells (author's transl)].

We have shown previously that in liquid cultures of mouse bone marrow cultured in the presence of fibroblast-conditioned medium macrophage precursor cells are generated which show K- and NK-activity. We have now presented evidence that macrophage precursor cells are released from the bone marrow into the periphery under in vivo conditions. Both in the corynebacterium parvum-induced mouse peritoneal exsudate and in the spleen of nu/nu mice the existence of macrophages precursor cells can be demonstrated. If these cells are eliminated by the use of the alloantimacrophage serum Mph 1.2 + C' the NK-activity of both populations is greatly reduced. Also human peripheral blood leucocytes contain macrophage precursor cells in varying amounts. After complete depletion of mature macrophages from peripheral blood macrophage precursor cells mature to typical adherent macrophages within a culture period of 5 days. These macrophage precursor cells resemble morphologically medium-sized lymphocytes. They are nonadherent and nonphagocytic and stain negative for nonspecific esterase.