Ultrastructural and ultracytochemical observations on differentiation and fate of liver macrophages of the mouse embryo

胚胎肝巨噬细胞来源于血管内巨噬细胞。在肝脏开始造血之前，胚胎外周血在妊娠10天时就含有少量的游离吞噬细胞。根据精细结构标准，血管内巨噬细胞被认为是具有清血功能的专门性清道夫巨噬细胞，是肝造血起始时肝窦巨噬细胞的前体细胞。肝窦巨噬细胞移动并分化为红细胞岛的中央巨噬细胞。我们的超组织化学和超微结构研究表明，肝成红细胞岛的中心细胞不是来自肝细胞，而是来自肝窦巨噬细胞，SBA结合能力与肝巨噬细胞的成熟密切相关。肝巨噬细胞吞噬靶细胞的变化发生在肝造血的发育过程中。胎儿肝脏中老化的原始红细胞、原始红细胞的细胞碎片、特定红细胞排出的核和垂死的多形核白细胞在肝脏造血的不同阶段被巨噬细胞清除，早期新生儿肝脏红细胞岛消失，成人肝脏仍有窦状巨噬细胞。新生儿肝脏含有两种巨噬细胞：肝窦清道型巨噬细胞和红细胞岛中央巨噬细胞。5天后，红细胞逐渐离开岛内，失去周围红细胞的巨噬细胞由于许多长而扭曲的细胞质突起而变成海星状。胞核缩小、浓缩，胞浆碎裂、脱落。

Embryonic liver macrophages are derived from intravascular macrophages. Before the initiation of liver hemopoiesis, embryonic peripheral blood contained a few free phagocytes as early as 10 days of gestation. Based on fine structural criteria, lntravascular phagocytes were considered to be specialized scavenger macrophages with the function of clearing the blood, and they are the precursor cells of sinusoidal macrophages at the onset of liver hemopoiesis.Sinusoidal macrophages move and differentiate into central macrophages of erythroblastic islands. Our ultrahistochemical and ultrastructural studies showed that the central cells in liver erythroblastic islands do not originate from hepatocytes but from sinusoid macrophages and that SBA binding ability is closely concerned with liver macrophage maturation.Changes of phagocytotic targets of liver macrophage take place in developmental saquence of liver hemopoiesis. Aged primitive erythrocytes, cell fragments of primitive erythrocytes, nuclei expelled from definitive erythroblasts and dying polymorphonuclear leukocytes were removed from fetal liver by macrophages at the various stages of liver hemopoiesis.Erythroblastic islands disappear in early neonatal liver and sinusoidal macrophages remain in adult livers. Neonatal liver contained two kinds of macrophages ; sinusoidal scavenger macrophages and central macrophages of erythroblastic islands. After 5 days of age, erythroblasts gradually left the islands, and the macrophages which lost surrounding erythroblasts became starfish-shaped due to many long twisted cytoplasmic projections. Their nuclei became shrinked and condensed, and the cytoplasm was fragmental and removed.