Structural changes of the wall of small blood vessels in thymoma versus normal human thymus.

It has been suggested that thè mesoderm-derived component of thymic strema (fibroblast and vessels) induces thymic epithelial-cell differentiation, although lìttle is known regarding specific mechanism of T-cell activation by thè thymic microenviroment. Moreover, thè blood-thymic barrier plays a criticai role in determining thè transit of T-cells. In order to get more insight into thè morpho-functional aspects of thè intra-thymic blood vessels, we examined samples of vessels of normal human thymus and thymoma. Samples wee processeti by transmission electron microscopy and immunohistochemistry. In thè normal human thymus, thè endothelium of small blood vessels doesn't show any discontinuities. The endothelial basai lamina, formed by lamina densa and lamina lucida, does not appear fenestrated but it appears very regular with regard to its shape and thickness. In thymoma, on thè contrary, thè endothelium of small blood vessels is altered: nuclei of endothelial celi show abnormalities of thè nuclear membrane and chromatin; cytoplasm is scattered and many vacuoles are present. Intercellular contacts are altered as well. The epithelial basai lamina presenta abnormalities as well as thè endothelial basai lamina which shows clear fenestrations of thè lamina densa. These findings support thè hypothesis that altered function of thè thymic tissue in thymoma has a morphologic substrate in thè vasai component and that it affects primarily T-cell transit.