Functional heterogeneity of macrophage precursor cells from spleen of Leishmania donovani-infected and untreated mice

Cells belonging to the monocyte-macrophage lineage are known to be among the most important effectors of natural - as well as lymphokine - mediated cytotoxicity against tumor cells, microbial and fungal targets and protozoa. Recent observations (1) pressented evidence that macrophage precursor cells are not confined to the bone marrow compartment, but can also be found in a peripheral organ such as the spleen. Only a very small quantity of these cells is present in the spleens of normal, untreated mice. In contrast, large numbers of splenic macrophage precursors can be isolated from Leishmania donovani-infected C57BL/6 mice in the early stage of infection as well as three months post infectionem. We demonstrate the capability of these highly purified population of nonadherent, nonphagocytic macrophage precursors, derived from spleen parasitized with Leishmania donovani, to spontaneously kill the promastigote form of Leishmania donovani and Leishmania enriettii. These effector functions , however, are not found in healthy control C57BL/6 mice. The functional heterogeneity displayed by splenic macrophage precursors from Leishmania donovani-infected C57BL/6 mice and untreated animals is dicussed.