title: When Aging Reaches CD4+ T-Cells: Phenotypic and Functional Changes.
abstract: 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 naïve T-cells in peripheral blood and lymphoid tissues, while, in contrast, their proportion of highly differentiated effector and memory T-cells, such as the CD28(null) T-cells, increases markedly. Naïve and memory CD4+ 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 CD4+ T-cells throughout life, but although later than in CD8 + T-cell compartment, these mechanisms ultimately fail with age.
authors.affiliation: Immunology Department, Hospital Universitario Central de Asturias Oviedo, Spain.
authors.forename: Marco Antonio
authors.initials: MA
authors.lastname: Moro-García
authors.forename: Rebeca
authors.initials: R
authors.lastname: Alonso-Arias
authors.forename: Carlos
authors.initials: C
authors.lastname: López-Larrea
keywords: CMV; IL-15; NKRs; T-cells; immunosenescence; inflammation