Organ-associated macrophage precursor activity: isolation of candidacidal and tumoricidal effectors from the spleens of cyclophosphamide-treated mice.

We recently reported the modulating effects of a single injection of the anti-neoplastic drug cyclophosphamide (Cy; 150 mg/kg i.p.) on in vivo resistance against the experimental Candida albicans infection. Increased resistance to microbial challenge occurred 12 to 18 days after treatment. We now show that the increased resistance is paralleled by the appearance of potent nonadherent nonphagocytic effectors in the spleen (day 12) that are capable both of candidacidal activity and natural killer (NK) activity against YAC-1 cells. The cells mediating the two reactivities have a low buoyant density, a strong proliferating activity in response to the macrophage colony stimulating factor (CSF-1), and are unable to kill the NK-insensitive lines EL-4 and P815. A clear cut isolation of macrophage precursor cells from this Percoll low density fraction has been performed in an indirect rosette assay on the basis of their positivity for the surface markers recognized by the highly specific rat-anti-mouse macrophages, monoclonal antibodies M143 and F4/80. We obtained an extremely homogeneous population of cells in the early stage of macrophage differentiation that is responsible for all the candidacidal activity and for a major part of the NK activity observed in the spleen of Cy-treated mice, and which is extremely sensitive to CSF-1 induction.