Tissue localization and fate in mice of injected multipotential colony-stimulating factor

The hemopoietic regulator multipotential colony-stimulating factor [Multi-CSF (interleukin 3)] has proliferative effects on a wide range of hemopoietic cells in vitro and in vivo. Native or recombinant Multi-CSF injected intravenously into adult mice had an initial half-life of 3-5 min and a second phase of 50 min. Clear labeling of hemopoietic cells was observed in the bone marrow and spleen of mice injected intravenously with recombinant 125I-labeled Multi-CSF showing that injected Multi-CSF can obtain access to such cells in situ. A high proportion of injected 125I-labeled Multi-CSF of both types became localized in the liver and in the kidney (in cells of the Bowman's capsule and proximal renal tubules). The kidney appeared to be an active site of degradation of Multi-CSF with the early appearance of low molecular weight labeled material in the urine.