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Highly differentiated CD28 − effector T cells which accumulate in a variety of diseases and also with increasing age contribute to inflammatory processes, limit immunological space and diversity, and are associated with immunological dysfunction and reduced responses to vaccination. Elimination of CD28 − T cells has been suggested as a measure for immunological rejuvenation but may lead to the loss of important T cell specificities. Using T cells specific for the immunodominant CMV-derived epitope NLVPMVATV as a model, we show that the same clonotypes are present in CD8 + CD28 + naive/early memory and CD8 + CD28 − effector T cells. Therefore, CD28 − cells do not seem to contain clones which are not present in the residual population. The elimination of effector T cells would not lead to the loss of important specificities, as relevant clonotypes could be recruited and propagated from naive or early memory T cell subsets in the case of exposure to pathogen.

With aging the immune system undergoes significant age-related changes. These age-dependent changes are referred to as immunosenescence and are partially responsible for the poor immune response to infections and the low efficacy of vaccination in elderly persons. Immunosenescence is characterized by a decrease in innate and adaptive cell-mediated immune function in the peripheral blood and the bone marrow. The aging of bone marrow cells and in particular, of adaptive immune cells in the bone marrow has been addressed relatively rarely. It is therefore the goal of this review to summarize what is known about the effect of age on bone marrow immune cells and their precursors in mice and humans.

As individuals age their ability to respond and clear pathogens declines, leading to a greater incidence and severity of infectious diseases. Additionally, the efficacy of vaccines is frequently decreased in elderly persons. Increased susceptibility to infections and reduced protection after vaccination reflect the impact of age-related changes on the immune system. The immune system undergoes a wide range of changes with increasing age. The aim of this review is to summarize cellular and molecular aspects of aging CD4(+) T cells. CD4(+) T cells play an essential role in mediating both humoral and cellular immune responses. Therefore, age-associated dysfunctions within CD4(+) T cells have a strong clinical impact. Improving our understanding of the aged CD4(+) T cells, in particular but also of the aged immune system in general, is crucial for developing effective prevention and treatment programs which will facilitate healthy aging and improve the quality of life of the elderly population.