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Reduced thymopoiesis and continuous mobilization of naive T cells into the effector-memory pool can lead to severe alterations of the naive T cell compartment. However, maintenance of the naive T cell population is essential to mount effective immune responses. Evidence of homeostatic regulation of naive T cells is currently debated in animal models. In humans, the situation remains unresolved, in particular with advanced age. In this study, we analyzed the CD4+ and CD8+ naive T cell compartments from elderly, young adults thymectomized during early childhood, and HIV-l-infected patients, which are characterized by T lymphocytopenia. We show a direct association between increased turnover and decreased frequency of naive T cells. Moreover, the IL-7-induced pathway was fully functional in naive T cells from elderly and young adults thymectomized during early childhood, who are characterized by elevated IL-7 plasma levels. Our findings support the establishment of homeostatic regulation of naive T cell proliferation in humans. This regulation is particularly active in lymphopenic hosts, such as elderly and thymec-tomized patients. [ABSTRACT FROM AUTHOR]

Epstein-Barr virus (EBV) provides a useful model to study cellular immunity to a genetically stable, persistent human virus. Different sets of proteins expressed during EBV's lyric and cell transforming infections induce qualitatively different cellular immune responses. The factors governing immunodominance hierarchies and the biological effectiveness of these different responses are now being revealed. Analysis of infectious mononucleosis (IN[), a clinical syndrome that can arise during primary EBV infection, has allowed the evolution of the responses to be tracked over time, giving an understanding of the immune response kinetics and of those determinants affecting selection into memory. Furthermore, following IM, expression of the receptor for the homeostatic cytokine IL- 15 on NK and T cells is lost within these individuals. This experiment of nature provides a system to advance understanding of immunological homeostasis in humans, illustrating how data obtained from the study of EBV have wider significance to the immunological community. [ABSTRACT FROM AUTHOR]

Compared with HTV-1, HIV-2 infection is characterized by a larger proportion of slow or nonprogressors. A better understanding of HIV-2 pathogenesis should open new therapeutic avenues to establish control of HIV-1 replication in infected patients. In this study, we studied the production of CD8+ T cells and their capacity for viral control in HIV-2 controllers from the French ANRS C05 HIV-2 cohort. HIV-2 controllers display a robust capacity to support long-term renewal of the CD8+ T cell compartment by preserving immune resources, including hematopoietic progenitors and thymic activity, which could contribute to the long-term maintenance of the CD8+ T cell response and the avoidance of premature immune aging. Our data support the presence of HTV-2 Gag-specific CD8+ T cells that display an early memory differentiation phenotype and robust effector potential in HTV-2 controllers. Accordingly, to our knowledge, we show for the first time that HIV-2 controllers possess CD8+ T cells that show an unusually strong capacity to suppress HIV-2 infection in autologous CD4+ T cells ex vivo, an ability that likely depends on the preservation of host immune resources. This effective and durable antiviral response probably participates in a virtuous circle, during which controlled viral replication permits the preservation of potent immune functions, thus preventing HIV-2 disease progression. [ABSTRACT FROM AUTHOR]

Aging is associated with impaired vaccine efficacy and increased susceptibility to infectious and malignant diseases. CD8+ T-cells are key players in the immune response against pathogens and tumors. In aged mice, the dwindling naïve CD8+ T-cell compartment is thought to compromise the induction of de novo immune responses, but no experimental evidence is yet available in humans. Here, we used an original in vitro assay based on an accelerated dendritic cell coculture system in unfractioned peripheral blood mononuclear cells to examine CD8+ T-cell priming efficacy in human volunteers. Using this approach, we report that old individuals consistently mount quantitatively and qualitatively impaired de novo CD8+ T-cell responses specific for a model antigen. Reduced CD8+ T-cell priming capacity in vitro was further associated with poor primary immune responsiveness in vivo. This immune deficit likely arises as a consequence of intrinsic cellular defects and a reduction in the size of the naïve CD8+ T-cell pool. Collectively, these findings provide new insights into the cellular immune insufficiencies that accompany human aging. [ABSTRACT FROM AUTHOR]