T-Cell Development in Early Partially Decapitated Chicken Embryos

We have evaluated the immunohistological and cytofluorometric changes that occur in the thymus of chicken embryos partially decapitated at 33-38 hr of incubation (DCx embryos) in an attempt to analyze possible neuroendocrinological influences on T-cell differentiation and, indirectly, the ontogeny of the so-called neuroendocrine-immune network. The thymus of DCx embryos shows important variations that profoundly and selectively affect different T-cell subsets, but not the nonlymphoid cell components of thymic stroma. These modifications include the accumulation of cell precursors, mainly DN (CD4(-) CD8(-)) cells and immature CD8(high) CD4(-) cells, which expand but do not differentiate, resulting in an extreme decline of both DP (CD4(+) CD8(+)) cells and TcR c-expressing cells. Accordingly, both subcapsulary and outer cortex increase in size, whereas the deep cortex and principally the thymic medulla almost disappear in DCx embryos. In contrast, other T-cell subsets of DCx embryos, largely CDg(glow)CD4(-) cells and TcR γδ-expressing cells do not undergo significant variations throughout thymic ontogeny.