In later years the immune system falls into a malfunctioning state of overactivation and ineffectiveness, generating damaging chronic inflammation while at the same time failing to defend against pathogens and destroy damaged cells.
It is recognized that the immune system, comprising both innate (nonspecific) and acquired (specific) components, is an intricate defence system that is highly conserved across vertebrate species, and has, from an evolutionary perspective, undergone strong pressures to maximize survival to allow procreation. The significant improvements in human survival and lifespan to well beyond childbearing ages have been totally "unpredicted" by evolution. As a consequence, human immune systems are exposed to considerable additional antigenic exposure outside the forces of natural selection. It is in this situation that immunity begins to exert negative effects on human ageing (antagonistic pleiotropy), leading to gradual systemic failures.
Research into age-related changes of the immune system is gathering pace as its importance within the context of multiple pathologies in ageing populations is realized. As part of this advance, [researchers] described the phenomenon of "inflammaging" at the turn of the millennium as part of the spectrum of immunosenescence. Inflammaging denotes an upregulation of the inflammatory response that occurs with age, resulting in a low-grade chronic systemic proinflammatory state.
Inflammaging is believed to be a consequence of a cumulative lifetime exposure to antigenic load caused by both clinical and subclinical infections as well as exposure to noninfective antigens. The consequent inflammatory response, tissue damage and production of reactive oxygen species that cause oxidative damage also elicits the release of additional cytokines, principally from cells of the innate immune system but also from the acquired immune response. This results in a vicious cycle, driving immune system remodelling and favouring a chronic proinflammatory state where pathophysiological changes, tissue injury and healing proceed simultaneously. Irreversible cellular and molecular damage that is not clinically evident slowly accumulates over decades.