Mechanisms shaping the naïve T cell repertoire in the elderly - thymic involution or peripheral homeostatic proliferation?
The ability of the human immune system to repel infections is drastically diminished with age. Elderly individuals are more susceptible to new threats and are less able to control endogenous infections. The thymus, which is the sole source of new T cells, has been proposed as a target for regenerative efforts to improve immune competence, as thymic activity is dramatically reduced after puberty. In this review, we review the role of the thymus in the maintenance of T cell homeostasis throughout life and contrast the differences in mice and humans. We propose that in humans, lack of thymic T cell generation does not explain a decline in T cell receptor diversity nor would thymic rejuvenation restore diversity. Initial studies using next generation sequencing are beginning to establish lower boundaries of T cell receptor diversity. With increasing sequencing depth and the development of new statistical models, we are now in the position to test this model and to assess the impact of age on T cell diversity and clonality.
Department of Medicine, Palo Alto Veterans Administration Health Care System, Palo Alto, CA 94304, United States; Department of Medicine, Stanford University School of Medicine, Stanford, CA 94305, United States.
Qian
Q
Qi
Department of Medicine, Palo Alto Veterans Administration Health Care System, Palo Alto, CA 94304, United States; Department of Medicine, Stanford University School of Medicine, Stanford, CA 94305, United States.
David W
DW
Zhang
Department of Medicine, Palo Alto Veterans Administration Health Care System, Palo Alto, CA 94304, United States; Department of Medicine, Stanford University School of Medicine, Stanford, CA 94305, United States.
Cornelia M
CM
Weyand
Department of Medicine, Palo Alto Veterans Administration Health Care System, Palo Alto, CA 94304, United States; Department of Medicine, Stanford University School of Medicine, Stanford, CA 94305, United States. Electronic address: jgoronzy@stanford.edu.
Jörg J
JJ
Goronzy
D000328:Adult; D000368:Aged; D000818:Animals; D049109:Cell Proliferation / Q000502:physiology; D006706:Homeostasis / Q000502:physiology; D006801:Humans; D051379:Mice; D008875:Middle Aged; D011948:Receptors, Antigen, T-Cell / Q000502:physiology*; D016176:T-Lymphocyte Subsets / Q000502:physiology; D013601:T-Lymphocytes / Q000502:physiology*; D013950:Thymus Gland / Q000502:physiology*
D011948:Receptors, Antigen, T-Cell
Aging; Immunosenescence; T cell receptor repertoire; T cells; Thymus