Suppressive Effect of LD78 on the Proliferation of Human Hemopoietic Progenitors

LD78 is a cDNA newly isolated front human stimulated tonsillar lymphocytes. The expression of LD78 is related to inflammatory responses and its structure has a homology with macrophage inflammatory protein 1‐α, which is known to have an inhibitory effect on murine CFU‐S. Using a colony assay technique, we examined the effects of LD78 on human hemopoietic progenitors. The addition of doses of 100 ng/ml or more of LD78 suppressed the colony formation of KMT‐2, a factor‐dependent myelomonocytic cell line established from cord blood cells; this suppressive activity was neutralized by the addition of antibody against LD78. The same doses of LD78 suppressed the formation of neutrophil, macrophage, and megakaryocytic colonies which were supported by human interleukin³ and erythropoietin; however, LD78 did not affect colony formation by either non‐phagocytic mono‐nuclear cells or sorted CD34⁺ cells. The conditioned medium of KMT‐2 cells or peripheral blood mononuclear cells cultured with LD78 suppressed colony formation by CD34⁺ cells. From these findings, it is suggested that LD78 affects phagocytic cells and induces factors that are inhibitory for hemopoiesis. We consider LD78 to be a new cytokine that plays an inhibitory role in hemopoiesis.