Bodey B, Bodey B, Siegel S E, Kaiser H E
University of Southern California, Los Angeles, USA.
In Vivo. 1998 Nov-Dec;12(6):599-618.
Histogenetically, the thymus is the primary lymphopoietic organ and provides an optimal microenvironment for the differentiation of T lymphocytes, independently of the influence of foreign antigens. Lymphocytes with diverse potential are produced in a protective microenvironment optimal for their maturation, whose dual cellular network is provided by endodermally derived RE cells and numerous ectomesenchymal cells derived from the neural crest. The full development of intrathymic hematopoiesis depends upon the successful completion of a series of well coordinated cellular interactions between widely divergent (in terms of origin) cells [epithelium (primitive pharynx); ectomesenchyrne (neural crest); and PHSCs (yolk sac, fetal liver)]. The cells of the thymic epithelial primordium do not proliferate in the absence of "inductive" interactions with the ectomesenchyme. Moreover, the nature of the mesenchyme determines the behavior of the thymic epithelial anlagen. The ectomesenchymal origin of chemotactic stem cell factor secretion, responsible for hemopoietic stem cell immigration, is a distinct possibility. The human thymus is a generalized hematopoietic tissue with between 7 to 9 weeks of ontogenesis. In human and dog fetuses various elements of mammalian hematopoiesis were identified intrathymically: B lymphocytes, plasma cells, erythropoietic and granulocytopoietic (neutrophils and eosinophils) cells, antigen presenting dendritic cells, and mast cells. Our light and ultrastructural (transmission and scanning), as well as immunocytochemical observations have established that during the embryonal and fetal period, the thymus is seeded by pluripotent, yolk sac derived PHSCs characterized by the following immunophenotype CD34+CD43+CD38-Lin-HLA-DR+CD69+. Stem cell c-kit tyrosine kinase (also referred to as mast cell growth factor, stem cell factor, or steel factor) in combination with autocrine and paracrine growth factors and cytokines (IL-3, IL-4, IL-5, IL-6, IL-7, G-CSF, etc.) stimulates myelopoiesis, including erythropoiesis, as well as lymphopoiesis. These hematopoietic growth factors are produced by activated lymphoblastic cells and stromal RE cells under the influence of immunoneuroendocrine regulation, supported by the finding that experimental or spontaneous, in vivo neural crest ablation during early mammalian ontogenesis always results in an abnormal development of the thymus, as well as the heart and great vessels, thyroid, and parathyroid glands.
从组织发生学角度来看，胸腺是主要的淋巴细胞生成器官，能为T淋巴细胞的分化提供最佳微环境，不受外来抗原影响。具有多种潜能的淋巴细胞在有利于其成熟的保护性微环境中产生，该微环境的双重细胞网络由内胚层来源的网状上皮（RE）细胞和众多源自神经嵴的外间充质细胞构成。胸腺内造血的充分发育取决于一系列起源广泛不同（上皮（原始咽）、外间充质（神经嵴）和多能造血干细胞（卵黄囊、胎儿肝脏））的细胞之间成功完成一系列协调良好的细胞相互作用。胸腺上皮原基的细胞在缺乏与外间充质的“诱导”相互作用时不会增殖。此外，间充质的性质决定胸腺上皮原基的行为。趋化干细胞因子分泌的外间充质起源，负责造血干细胞迁移，这是一种明显的可能性。人胸腺在胚胎发育7至9周时是一种广义的造血组织。在人和狗的胎儿中，胸腺内可识别出哺乳动物造血的各种成分：B淋巴细胞、浆细胞、红细胞生成细胞和粒细胞生成细胞（中性粒细胞和嗜酸性粒细胞）、抗原呈递树突状细胞和肥大细胞。我们的光镜和超微结构（透射和扫描）以及免疫细胞化学观察表明，在胚胎期和胎儿期，胸腺由源自卵黄囊的多能多能造血干细胞播种，其免疫表型为CD34 + CD43 + CD38 - Lin - HLA - DR + CD69 +。干细胞c - kit酪氨酸激酶（也称为肥大细胞生长因子、干细胞因子或钢因子）与自分泌和旁分泌生长因子及细胞因子（IL - 3、IL - 4、IL - 5、IL - 6、IL - 7、G - CSF等）共同刺激骨髓生成，包括红细胞生成以及淋巴细胞生成。这些造血生长因子由活化的淋巴细胞和基质RE细胞在免疫神经内分泌调节的影响下产生，这一观点得到以下发现的支持：在哺乳动物早期胚胎发育过程中，实验性或自发性体内神经嵴切除总是导致胸腺以及心脏、大血管、甲状腺和甲状旁腺发育异常。
