IL-7 STIMULATES CSF-INDUCED PROLIFERATION OF MURINE BONE-MARROW MACROPHAGES AND MAC-1(-VITRO() MYELOID PROGENITORS IN)

The role of IL-7 as an important stimulator of the growth of B and T c ell precursors, as well as mature T cells, is well established. In con trast, the role of IL-7 in myelopoiesis has not been characterized tho roughly, and thus, IL-7 has been regarded as a lymphoid lineage-restri cted cytokine. However, we have recently reported that IL-7 enhanced C SF-induced myeloid proliferation of primitive murine hematopoietic (Li n(-)Sca-1(+)) progenitors, whereas IL-7 did not affect significantly t he proliferation of a population of more mature (Lin(-)) progenitors. The present study was initiated to investigate further whether IL-7 mi ght affect CSF-induced proliferation of subpopulations of committed my eloid progenitors as well as mature bone marrow macrophages. IL-7 enha nced macrophage colony-stimulating factor (CSF-1)-induced colony forma tion of single bone marrow macrophages 90%, whereas IL-7 alone had no effect. Furthermore, IL-7, in a concentration-dependent manner, increa sed the proliferation of mononuclear cells expressing the Mac-1 Ag (Ma c-1(+) mononuclear cells (MNC); CD11b) up to fivefold in response to C SF-1, granulocyte macrophage-CSF (GM-CSF), or IL-3. In contrast, no ef fect of IL-7 was observed on Mac-1(-) MNC. The synergistic effect of I L-7 on Mac-1+ MNC was caused by an increase in macrophage colonies (CF U-M) and mixed granulocyte-macrophage colonies (CFU-GM), whereas the t otal number of granulocyte colonies (CFU-G) was not affected. This sug gests that IL-7 can provide proliferative signals to Mac-1(+) progenit ors with a macrophage potential, but not to progenitors committed to p ure granulocyte differentiation.