How greatly does the onset of dementia depend on the age-related decline of the immune system? The most evident contributions to neurodegeneration are vascular aging and the accumulation of protein aggregates such as amyloid-β, tau, and α-synuclein. These are only indirectly connected to the aging of the immune system, in the sense that immune function influences in some way near all aspects of tissue function, and its progressive failure tends to make everything at least a little less functional. Chronic inflammation appears to play a direct and important role in the progression of most neurodegenerative conditions, however, and there at least we can point to the immune system as a primary issue.
The immune system is responsible for defending against pathogens such as bacteria, viruses, and fungi to eliminate broken and harmful cells, like senescent cells and toxic or allergenic substances. Immunosenescence is a term that describes a different state of the immune system in aged people, in association with detrimental clinical outcome, due to reduced ability to respond to new antigens. Although immunosenescence is a phenomenon present in the majority of individuals, factors like genetic, environment, lifestyle, and nutrition are responsible for their heterogeneity
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