Morphogenesis of human fetal thymus during weeks 22-27 of development

摘要

Distinctive features of human fetal thymus morphogenesis in early ontogeny in the case ofuncomplicated pregnancy have been characterized. A steady increase of thymus dimensions and weightoccurred concomitantly to differentiation of morphofunctional zones within the organ. Cell differentiationin the subcapsular and inner cortical zones of the thymus lobes was manifested as changes in parameters ofexpression of T-lymphocyte antigens CD1, CD2, and CD3 and ultrastructural features of reticuloepithelialcells (REC) type I and II forming a microenvironment for lymphocytes. RECs of the medullar zone formeda glomerular syncytium with desmosomal interepithelial contacts by week 22 of fetal development. Smalllymphocytes predominated among thymocytes (66%). Hassall's corpuscles, the structural correlates of mor-phological and functional maturity, predominated in the fetal thymuses during developmental weeks 25-27.