Knocking down CD47 in CD34⁺CD38⁻ cells induces their engulfment by macrophages. (A) Knockdown of CD47 expression in normal CD34⁺CD38⁻ cells by siRNA for human CD47. Treatment of CD34⁺CD38⁻ cells with siRNA for 48 hours induced 60% reduction of CD47 expression in these cells. (B) CD34⁺CD38⁻ cells treated with the siRNA for human CD47 showed accelerated engulfment by normal macrophages. Vertical axis shows the phagocytosis index (phagocytosis index = phagocytic macrophages/number of macrophages) and the bars show mean value. *P < .01 by conventional t test. (C) Engulfment of CD34⁺CD38⁻ cells treated with siRNA by normal macrophages (Giemsa staining). Scale bars indicate 10 μm.