thesis
Ionizing radiation and the thymus : effects of whole-body irradiation with fast fission neutrons and X-rays on the murine thymus
- Publication date
- 1 October 1986
- Publisher
- As described in Chapter I of this thesis, the thymus is an extremely
complex lympho-epithelial organ in which bone marrow-derived
lymphoid precursor cells, i.e. prothymocytes, differentiate and mature
in a stromal matrix. During their differentiation in this specialized
microenvironment, thymocytes are selected on the basis of tolerance to
self-MHC gene products and they acquire the capacity to recognize
foreign antigens in the context of self-MHC antigens. Furthermore,
during this differentiation, the thymocytes acquire a number of cell
surface differentiation antigens. It is generally accepted that the
thymic stromal cells are involved in the process of differentiation and
maturation of T cells-
When animals are subjected to whole-body irradiation, severe effects
develop in the thymus. As shown by many authors, irradiation with
X-rays or gamma-rays, i.e. low LET radiation types, leads to a severe
depopulation of the thymus and, subsequently, thymus recovery has been
shown to follow a biphasic pattern (reviewed by Sharp & Crouse, 1980
and Watkins et al., 1980)- The initial phase in this biphasic thymic
recovery is brought about by radioresistant intrathymic precursor
cells which are not derived immediately from bone marrow stem cellsLimited
proliferative capacity and the resulting exhaustion of these
intrathymic precursor cells as well as an impaired production of
thymus precursor cells in the bone marrow are responsible for a second
thymus involution- The final recovery of the thymus is due to its
replenishment from extrathymic precursors in the regenerated bone
marrow.