T cells and their cytokines in persistent stimulation of the immune system.

Age-dependent dysregulations of innate immunity impair effective priming of adaptive immunity. Alteration of helper functions of CD4 T cells during aging prevents them from sustaining cytotoxic responses of CD8 T cells against pathogens. The main characteristics of aged and/or differentiated T cells included telomere erosion, reduction of proliferation, decrease of IL-2 secretion and responsiveness, loss of CD28 and acquisition of cytotoxic properties. Phenotypic and functional modifications associated with aging affect development, differentiation, exhaustion/senescence status, migration, signalisation and metabolism of T lymphocytes. Magnitude and breadth of T cells responses are also regulated by the nature and extent of APCs activation. In our review, we focus on how the T cells age chronologically and within a persistent infection context. The T cell classification is not discussed in details here as it has been recently well documented [ 1 • ] however we focus on how cytokines may participate in immune senescence.