Interleukin-13 selectively suppresses the growth of human macrophage progenitors at the late stage

Interleukin-13 (IL-13) is a pleiotropic cytokine that inhibits the production of inflammatory cytokines of monocytes. We investigated the effects of IL-13 on the clonal growth of human hematopoietic progenitors. IL-13 alone did not support any colony formation. IL-13 markedly suppressed macrophage colonies that were formed in the presence of IL-3 and erythropoietin, granulocyte-macrophage colony- stimulating factor, or macrophage colony-stimulating factor. Macrophage colony cells showed dendritic cell-line morphology and cellular aggregates. IL-13 did not affect granulocyte colony and erythroid burst formation. Delayed addition of IL-13 and replating onto the culture dishes with IL-13 showed that macrophage colony formation was suppressed during days 8 and 14 of culture. These results indicate that IL-13 affects the growth of the late stage of committed macrophage progenitors. Single-cell culture of isolated CD34+CD33+ cells with IL- 13 confirmed that macrophage colony formation was significantly suppressed. These results show that IL-13 directly suppresses the proliferation of differentiating macrophages. In addition, these suppressive effects of IL-13 were synergistic with IL-4. Furthermore, in the liquid culture of bone marrow cells in the presence of IL-13, the number of CD14 (monocyte-macrophage antigen)-positive cells decreased and CD18 (LFA-1 beta)-positive cells increased. It is concluded that IL-13 affects the growth of the late stage of macrophage precursors as well as mature monocytes. Induction of differentiation of human monocytes may be correlated with the suppression of their progenitors.