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Published on: October 2, 2018
Age-related changes in the human thymus studied with scanning electron microscopy
Carlo Cavallotti1, Vito D'Andrea, Gianfranco Tonnarini
1Section of Human Anatomy, Department of Cardiovascular Respiratory and Morphological Sciences, University La Sapienza, Rome, Italy. cavallotti@uniroma1.it
Insights
The aging human thymus retains thymocytes in all compartments. In elderly individuals, loose gaps in thymus microvessels may facilitate thymocyte movement.
Area of Science:
- Immunology
- Cell Biology
- Gerontology
Background:
- The human thymus undergoes significant age-related changes affecting its structure and function.
- Understanding thymic involution is crucial for comprehending immune system decline in aging.
Purpose of the Study:
- To investigate morphological and age-related alterations in human thymus compartments and cells.
- To quantitatively analyze age-associated changes in thymic microenvironment and cell populations.
Main Methods:
- Scanning electron microscopy of human thymus samples from young and elderly donors.
- Quantitative image analysis and statistical evaluation of morphological data.
Main Results:
- All thymus compartments maintain thymocyte presence, irrespective of age.
- Elderly thymic islets contain diverse cell types, similar to younger subjects.
- Thymus microvessel endothelial gaps tighten with age, potentially facilitating thymocyte transit.
Conclusions:
- The proportion of resident thymus cells, including thymocytes, is higher in younger individuals.
- Age-related changes in thymus microvessel permeability may influence thymocyte trafficking.
Abstract:
This investigation describes some morphological, age-related changes in different compartments and cells of the human thymus. Scanning electron microscopic observations were done on human thymus samples obtained from four young and eight elderly patients during thoracic surgery and/or diagnostic biopsy of the thymus, after receiving authorization from the Ethical Committee of our university. The morphological data were submitted to quantitative image analysis so as to obtain quantitative results. Subsequently, the related values were used for statistical analysis. Our findings demonstrate that (1) all thymus compartments (subcapsular spaces, cortical, medullar, thymus microenvironment) contain numerous thymocytes even after the thymus has aged. (2) In older humans, residual thymus lymphoid islets contain, in addition to fatty cells and/or fibrous cells, also the same types of resident and nonresident cells (permanent and moving cells) that are found in young and adult subjects. (3) Endothelial cells of thymus microvessels contain numerous gaps. These gaps are tight in young subjects and become loose with age. (4) Thymocytes, in older subjects, are always found near these loose endothelial gaps of thymus microvessels. (5) While thymus cortical microvessels are provided with pericytes and/or periarteriolar spaces, microvessels of the thymus medullar are free of such spaces. Our morphological and quantitative results lead us to consider the possibility that the thymus fraction of resident and permanent cells (including thymocytes and reticular epithelial cells) is larger in younger subjects compared with older ones. The endothelial loose gaps of thymus microvessels, in older subjects, can allow the bidirectional transit of thymocytes through the wall of the said microvessels.
