The thymus. Finally getting some respect.
The thymus gland is no longer a structure in the anterior mediastinum of questionable use in the body economy. It is the sole source of cells that control the immune response and provide protection from life-threatening pathogens. Its primary function is to seed the periphery with mature T cells. Because these cells can maintain their numbers through self-replication, thymic function essentially is completed within the first few years of life. In response to a lack of need for its services, the thymus thereupon undergoes involution. A demand for renewed thymopoiesis has become necessary as the T-cell compartment of the immune system must be replenished following massive depletion of T cells by disease (e.g., AIDS) or the demands of cytoreduction necessary to achieve successful bone marrow transplantation. In older patients with AIDS (> 20-30 years), re-expansion of the post-thymic population may be adequate to restore the patient to reasonable or even normal T-cell immunity, but when the cytoablation is as massive as seen with bone marrow transplant conditioning regimens, the thymus must contribute to the repopulation. If involution has proceeded too far, thymic output must be augmented. This augmentation can be accomplished by thymus transplantation. The techniques for successful thymus transplantation in adults, however, have yet to be perfected. The thymus can play a major role in determining the response to MHC products of others (i.e., nonself). Novel manipulations of the thymus are being used to achieve transplant tolerance.
Hong
R
R
Department of Pediatrics, University of Vermont College of Medicine, Burlington, Vermont. rhong@salus.med.uvm.edu
D000328:Adult; D000368:Aged; D000375:Aging; D006801:Humans; D008206:Lymphatic Diseases / Q000628:therapy; D008875:Middle Aged; D013950:Thymus Gland / Q000473:pathology / Q000502:physiology / Q000637:transplantation