Introduction to ageing of the adaptive immune system

Abstract

Like other somatic tissues and organs, the vertebrate immune system manifests age-associated alterations to its components and their functions. Unlike in invertebrates, in addition to the innate arm, vertebrates also possess adaptive immunity mediated by both cellular and humoral components. This chapter reviews data on age-associated alterations to adaptive immunity specifically in humans, mostly originating from cross-sectional studies (i.e., comparing young with old people). We summarise what is known about the effects of age on the different components of the adaptive immune system, particularly T cells, which appear most obviously different in the elderly. We consider the serious limitations inherent in cross-sectional studies, and discuss the crucial requirement to perform longitudinal studies (i.e., following the same individuals over time). Despite the logistical and financial constraints, longitudinal follow-up has provided the most biologically meaningful information about which of the many biomarkers apparently changing with age are actually relevant to medical parameters and for late-life health and longevity, and which, in contrast, may change with age but without clinical relevance. Given the lack of consistent data currently available, as a result of performing studies on heterogeneous populations using different analytical techniques, we emphasize the necessity for more numerous, more extensive and more detailed studies including assessments of the impact of psychosocial, nutritional and other thus-far rarely considered parameters on immunological and other biomarkers in longitudinal studies.