Immunohistochemical and histometrical studies of the human thymus with special emphasis on age-related changes in medullary epithelial and dendritic cells.

Age-related changes in medullary epithelial and dendritic cells in the human thymus were examined quantitatively using immunohistochemistry and histometry. The material used was thymic biopsy specimens obtained from 105 patients during cardiac surgery, none of whom had immunological abnormalities. By using keratin and tissue polypeptide antigen markers to identify epithelial cells and S-100 protein and LN-2 markers to identify dendritic cells, the numbers of these cells in the medulla were counted morphometrically. The relative proportions of the cortex, medulla, Hassall's bodies, perivascular space, connective tissue and fatty tissue were evaluated using a computer image-analysis system and the respective relative volumes were calculated. Our results indicate that the number of medullary dendritic cells/mm2 and the relative volume of cortical thymocytes decrease steadily up to the age of 40 years, whereas no major change was found in the number of medullary epithelial cells/mm2.