Development of the thymus

Abstract

Proper development of the thymus is critical for an individual to acquire full immune capability. A full complement of the components that participate in thymic development, interacting with each other at the correct time, is required for maturation. In order to establish the microenvironment necessary for T‐cell differentiation, the epithelial primordium of the thymus must expand from pharyngeal endoderm with the aid of contributions from the ectoderm. Experimental studies have established the importance of mesenchymal derivatives from the neural crest in functional development of the epithelial primordium. Interfering with this process inhibits thymic development in a manner similar to that observed in congenital conditions such as the DiGeorge syndrome and the fetal alcohol syndrome. These observations provide clues to understanding the origin of defects in thymus‐dependent immunity, and point the way to studies that will expand our understanding of the controls that are involved in genetic and environmental factors impacting on this process. Microsc. Res. Tech. 38:209–215, 1997. © 1997 Wiley‐Liss, Inc.

SOME ASPECTS OF EARLY DEVELOPMENT OF THE THYMUS: EMBRYOLOGICAL BASIS FOR ECTOPIC THYMUS AND THYMOPHARYNGEAL DUCT CYST. Algunas observaciones acerca del temprano desarrollo del timo: bases embriológicas del timo ectópico y del quiste del conducto timofar

“…Mass of epithelial cells that constitutes the primordial thymus attracts lymphoid precursor cells to this region from the blood-stream. The lymphoid precursor cells leave the blood vessels and migrate through the neural crest-derived mesenchyme into a primitive epithelial organ (Bockman, 1997). The disruption of thymic descent can result in an ectopic thymus (ectopia thymi) or cervical extension of thymus (textus thymicus accessorius, lobuli thymici accessorii) localized anywhere from the mandibular angle to the upper mediastinum.…”

Neuro-immune modulation of the thymus microenvironment (Review)

“…This complex cellular architecture of the thymus parenchyma has its origin in the heterogeneous embryonal genesis of the organ. The long-held understanding that the thymus develops in the embryo from the endoderm of the third pharyngeal pouch, and from the ectoderm of the branchial clefts and related mesenchyma, which derive from pharyngeal arch (13,14), has been challenged. In their study, Gordon et al (15) showed through labelling experiments that ectoderm may not be involved in thymus genesis, and that endoderm cells alone seem to be sufficient to generate a complete thymic microenvironment.…”

Aspectos morfométricos do timo em gatos domésticos (Felis domesticus)

“…Mas sabe-se que o desenvolvimento da imunocompetência animal é depende da diferenciação dos linfócitos do timo, os quais são capazes de reativar células imunes mediadas, em adição à diferenciação em outros locais de células que sintetizam e secretam anticorpos (Bockman 1997). Além disso, o papel significativo do timo na imunidade é facilmente demonstrado, em algumas espécies, quando da realização da timectomia neonatal, o que ocasiona o enfraquecimento da reação de hipersensibilidade retardada e a diminuição na habilidade para produzir respostas mediadas por anticorpos (Banks 1992).…”