A fine structure study of human thymus

The thymus in congenital heart disease

Some cases of thymus developmental defects (DiGeorge's syndrome) are associated with the development of defects of the heart and great vessels. To see if anomalies of the heart are also associated with anomalies of the thymus, a material of thymus tissue removed during operation for congenital heart disease was compared with thymus tissue from a forensic autopsy material representing the same age group, but without cardiac lesions. Among 27 cases of congenital heart disease, occurrence in the thymus of solid epithelial cords were seen in 6 and cyst- or duct-like structures were found in 7. Among 47 forensic cases, 1 showed cords and another showed duct-like structures. Of these, one had congenital anomalies in the form of hepatic hamartomas and nesidioblastosis, whereas the other had died from morbilli, raising the possibility of congenital immune deficiency. Anyhow, a striking occurrence of minor morphological deviations in the structure of the thymus was found in children with congenital heart disease. Such material therefore may be less suitable for studying the morphology and biology of the normal thymus gland.

The ultrastructure of the normal human thymus: a study of 36 cases

Electron microscopy of the normal human thymus demonstrates a supporting framework of epithelial-reticular cells with long branchticular cell processes lie lymphocytes, macrophages, and rare myoid cells. Both small and large lymphocytes are evident. No desmosomes are observed between the lymphocytes and the epithelial-reticular cells. Macrophages are most numerous in the cort(x were they often contain phagocytized nuclear debris. The possible functional significance of the above-described fine structural features is discussed.

Ultrastructure of the age-involuted adult human thymus

Age involuted thymus tissue from a middle aged (33 years) and an old (63 years) man have been examined by electron microscopy and compared with thymus tissue from children. Biopsies had been taken during surgical correction of congenital heart defects. The fine structural architecture of cortex, medulla and connective tissue in the remaining lymphatic islands in the adult thymus investigated was not different to the thymus of children. We were surprised to find vigorous lymphocytopoiesis in the cortical regions and to recognize extended areas of medulla with a cellular composition which obviously provides the same microenvironment for T-cell maturation as the medulla of the non involuted thymus. Our findings are discussed in relation to the increasing arguments that the human thymus serves an immunological function throughout life.