The thymus has a key role in the development of an effective immune system as well as an endocrine function. The mature thymus epithelium has two main cell types: cortical thymic epithelial (cTECs) and medullary thymic epithelial cells (mTECs) or stromal cells. These thymic stromal cells provide signals for T cell differentiation. |
Newborn Thymus (modified from Gray's Anatomy) |
Page Links: Introduction | Some Recent Findings | Development Overview | References | Glossary
Rodewald HR. Thymus organogenesis. Annu Rev Immunol. 2008;26:355-88.
Boehm T, Bleul CC. The evolutionary history of lymphoid organs. Nat Immunol. 2007 Feb;8(2):131-5.
"During vertebrate evolution, primary lymphoid organs appeared earlier than secondary lymphoid organs. Among the sites of primary lymphopoiesis during evolution and ontogeny, those for B cell differentiation have differed considerably, although they often have had myelolymphatic characteristics. In contrast, only a single site for T cell differentiation has occurred, exclusively the thymus."
Assarsson E, Chambers BJ, Hogstrand K, Berntman E, Lundmark C, Fedorova L, Imreh S, Grandien A, Cardell S, Rozell B, Ljunggren HG. Severe defect in thymic development in an insertional mutant mouse model. J Immunol. 2007 Apr 15;178(8):5018-27.
The thymus and parathyroid are derived from 3rd pharyngeal pouches.
Development is a series of epithelial/mesenchymal inductive interactions between neural crest-derived arch mesenchyme and pouch endoderm. There is also the possibility that the surface ectoderm of 3rd pharyngeal clefts participates in thymus development.
Hassall's bodies form between 6 and 10 lunar months in humans. They appear after lymphopoiesis has been established and the cortex, medulla and the cortico-medullary junction are able to select of T lymphocytes undergoing progressive maturation. (Text modified from Bodey and Kaiser, 1997)
Experimental studies have shown that a neural crest contribution is also required during early thymic organogenesis.
Hollander G, Gill J, Zuklys S, Iwanami N, Liu C, Takahama Y. Cellular and molecular events during early thymus development. Immunol Rev. 2006 Feb;209:28-46.
"The thymic stromal compartment consists of several cell types that collectively enable the attraction, survival, expansion, migration, and differentiation of T-cell precursors. The thymic epithelial cells constitute the most abundant cell type of the thymic microenvironment and can be differentiated into morphologically, phenotypically, and functionally separate subpopulations of the postnatal thymus. All thymic epithelial cells are derived from the endodermal lining of the third pharyngeal pouch. Very soon after the formation of a thymus primordium and prior to its vascularization, thymic epithelial cells orchestrate the first steps of intrathymic T-cell development, including the attraction of lymphoid precursor cells to the thymic microenvironment. The correct segmentation of pharyngeal epithelial cells and their subsequent crosstalk with cells in the pharyngeal arches are critical prerequisites for the formation of a thymus anlage. Mutations in several transcription factors and their target genes have been informative to detail some of the complex mechanisms that control the development of the thymus anlage."
Hassall's bodies, also called Hassall's corpuscles, form between 6 and 10 lunar months in humans. They appear after lymphopoiesis has been established and the cortex, medulla and the cortico-medullary junction are able to select of T lymphocytes undergoing progressive maturation.Within the thymus their number increases until puberty, then decreases.
Named after Arthur Hill Hassall (1817-1894) a British physician and chemist.
Eya - human homolog of the Drosophila 'eyes absent' (Eya) gene.
Six - vertebrate genes which are homologs of the Drosophila 'sine oculis' (so) gene.
Links: OMIM - Eya | OMIM - Six1
References:Zou D, Silvius D, Davenport J, Grifone R, Maire P, Xu PX. Patterning of the third pharyngeal pouch into thymus/parathyroid by Six and Eya1. Dev Biol. 2006 May 15;293(2):499-512. | Xu PX, Zheng W, Laclef C, Maire P, Maas RL, Peters H, Xu X. Eya1 is required for the morphogenesis of mammalian thymus, parathyroid and thyroid. Development. 2002 Jul;129(13):3033-44.
Links: Journals | Online Textbooks | Search Textbooks | Reviews | Articles | Search PubMed | Glossary
Search NLM Online Textbooks "thymus" : Endocrinology | Molecular Biology of the Cell | The Cell- A molecular Approach
Reviews
Rodewald HR. Thymus organogenesis. Annu Rev Immunol. 2008;26:355-88.
Boehm T, Bleul CC. The evolutionary history of lymphoid organs. Nat Immunol. 2007 Feb;8(2):131-5.
Pearse G. Normal structure, function and histology of the thymus. Toxicol Pathol. 2006;34(5):504-14.
Hollander G, Gill J, Zuklys S, Iwanami N, Liu C, Takahama Y. Cellular and molecular events during early thymus development. Immunol Rev. 2006 Feb;209:28-46.
Gill J, Malin M, Sutherland J, Gray D, Hollander G, Boyd R. Thymic generation and regeneration. Immunol Rev. 2003 Oct;195:28-50.
Bodey B, Kaiser HE. Development of Hassall's bodies of the thymus in humans and other vertebrates (especially mammals) under physiological and pathological conditions: immunocytochemical, electronmicroscopic and in vitro observations. In Vivo. 1997 Jan-Feb;11(1):61-85.
"...our results indicate that the HBs are unique, antigenically distinct, functionally active, multicellular components of the nonlymphocytic, cellular microenvironment of the thymic medulla, and participate in the physiological activities of the prenatal and adult thymus."
Articles
Assarsson E, Chambers BJ, Hogstrand K, Berntman E, Lundmark C, Fedorova L, Imreh S, Grandien A, Cardell S, Rozell B, Ljunggren HG. Severe defect in thymic development in an insertional mutant mouse model. J Immunol. 2007 Apr 15;178(8):5018-27.
Zou D, Silvius D, Davenport J, Grifone R, Maire P, Xu PX. Patterning of the third pharyngeal pouch into thymus/parathyroid by Six and Eya1. Dev Biol. 2006 May 15;293(2):499-512.
Xu PX, Zheng W, Laclef C, Maire P, Maas RL, Peters H, Xu X. Eya1 is required for the morphogenesis of mammalian thymus, parathyroid and thyroid. Development. 2002 Jul;129(13):3033-44.
Search Mar 2007 "thymus development" 8,991 reference articles of which 1,019 were reviews.
Search PubMed: term = thymus development |
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This section of notes covers the thymus development and function as an endocrine organ.
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