When aging reaches CD4CT-cells: phenotypic and functional changes.

Beyond midlife, the immune system shows aging features and its defensive capability becomes impaired, by a process known as immunosenescence that involves many changes in the innate and adaptive responses. Innate immunity seems to be better preserved globally, while the adaptive immune response exhibits profound age-dependent modifications. Elderly people display a decline in numbers of naïveT-cells in peripheral blood and lymphoid tissues, while, in contrast, their proportion of highly differentiated effector and memory T cells, such as the CD28null T-cells, increases markedly. Naïve and memory CD4C T-cells constitute a highly dynamic system with constant homeostatic and antigen-driven proliferation, influx, and loss of T-cells. Thymic activity dwindles with age and essentially ceases in the later decades of life, severely constraining the generation of new T-cells. Homeostatic control mechanisms are very effective at maintaining a large and diverse subset of naïve CD4C T-cells throughout life, but although later than in CD8CT-cell compartment, these mechanisms ultimately fail with age. [ABSTRACT FROM AUTHOR]