Editors' ChoiceImmunology

Maintaining the T Cell Status Quo

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Science Translational Medicine  02 Jan 2013:
Vol. 5, Issue 166, pp. 166ec1
DOI: 10.1126/scitranslmed.3005528

Keeping up with the Joneses can be even harder when times are tough. Indeed, to maintain appearances, people may choose to live beyond their means. T cells, too, fall on hard times: Thymic production of naïve T cells drastically decreases when we age or in patients who have been thymectomized at a young age. It's unclear how these individuals retain a sufficient naïve T cell compartment to fight microbial challenges. Sauce et al. studied maintenance of naïve T cells in human patients with decreased or absent thymic T cell input in order to investigate T cell maintenance in times of want. Confirming data from animal models, they found that increased naïve T cell expansion is responsible for the maintenance of peripheral T cell counts under these circumstances.

The HIV pandemic highlights the importance of maintenance of peripheral T cell counts. Work in mice and primates has shown that cytokines, major histocompatibility complex, commensal bacteria, and access to lymphoid tissues are critical for T cell maintenance. However, human data confirming the relevance of the model of peripheral T cell maintenance and the role of these factors has been lacking. Sauce et al. compared T cell parameters between healthy middle age controls, HIV-positive patients, older people, and people who had received surgical thymectomy as neonates. They found lower T cell counts with increased age—a known phenomenon—and that naïve T cells proliferated more in older people or in thymectomized patients. HIV infection had a similar effect regardless of viral load. There was an inverse association between peripheral T cell number and cell proliferation and the T cell cytokine interleukin-7.

Increasing numbers of patients are treated with T cell–depleting agents that also affect the thymus; therefore, it is important to understand the effects of these agents on T cell–mediated immunity. These data suggest that T cells are up to the task. When the going gets tough, T cells get going.

D. Sauce et al., Lymphopenia-driven homeostatic regulation of naive T cells in elderly and thymectomized young adults. J. Immunol. 189, 5541–5548 (2012). [PubMed]

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