Reduced thymus activity and infection prematurely age the immune system
Ronald E. Gress, Steven G. Deeks
Ronald E. Gress, Steven G. Deeks
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Commentary

Reduced thymus activity and infection prematurely age the immune system

Abstract

The aging process affects all aspects of the immune system, particularly the T cells. The immune system in older individuals is often characterized by lower T cell numbers, lower naive/memory T cell ratios, and lower T cell diversity. Most measures of inflammation increase with age. Why this happens, and why there is so much person-to-person variability in these changes, is not known. In this issue of the JCI, Sauce and colleagues show that removal of the thymus during infancy results in premature onset of many of these age-associated changes to the immune system (see the related article beginning on page 3070). The effect of thymectomy was particularly notable in those individuals who acquired CMV infection. Data from this study, as well as data from other observational settings, suggest that reduced thymic function and persistent viral infections combine to accelerate a decline in immunologic function.

Authors

Ronald E. Gress, Steven G. Deeks

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Figure 1

Mechanisms of naive T cell production.

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Mechanisms of naive T cell production. The naive T cell population can b...
The naive T cell population can be maintained by ongoing T cell production in the thymus. Hematopoietic stem cells in the bone marrow give rise to Lin–Sca-1+c-Kit+ (LSK) progenitors that settle in the thymus and give rise to naive T cells. With limited thymus function, proliferation of existing T cells in the periphery, which occurs via a thymus-independent pathway, can contribute to T cell numbers, but such T cell populations tend to be oligoclonal and have a memory phenotype. Complete surgical removal of the thymus early in life results in life-long reduction in naive T cell counts, as shown by Sauce and colleagues in their study in this issue of the JCI (1).