A new monocytic leukemia cell line (KP-1) was established from a 2-y-old Japanese girl with acute monocytic leukemia. The KP-1 cells were maintained in suspension culture with a doubling time of 96 h. The cells were positively stained with alpha-naphtyl butyrate esterase, but not with naphthol AS-D chloroacetate esterase, myeloperoxidase, and periodic acid-Schiff reagent. Cell surface marker analysis revealed that the cells were CD4, CD11a, CD11c, CD13, CD14, CD18, CD33, and HLA-DR positive. Karyotype analysis revealed near diploidy (47 XX) and a translocation t(11;19) was found. When treated with 12-o-tetradecanoylphorbol 13-acetate, KP-1 cells became tightly adherent, showed the enhanced reactivity for alpha-naphtyl butyrate esterase, and produced several monokines such as IL-1beta, tumor necrosis factor-alpha, and macrophage colony-stimulating factor. Immunoelectron microscopy demonstrated that the human macrophage scavenger receptor was expressed after 12-o-tetradecanoylphorbol-13-acetate treatment, and the cells accumulated a large amount of cholesterol esters in the presence of acetylated LDL. Compared with another human monocytic leukemia cell line, THP-1, KP-1 expressed scavenger receptor and accumulated cholesterol ester more rapidly in the presence of 12-o-tetradecanoyl phorbol-13-acetate and acetylated LDL. Scatchard analysis using I-125-labeled acetylated LDL revealed a typical saturation curve with an apparent k(d) of 1.7 x 10(-7) M and 3400 binding sites per cell. KP-1 retained the characteristics of monocyte-macrophage lineage cells and will facilitate the in vitro studies of the pathologic and physiologic roles of scavenger receptors.