Abstract
Immunosenescence, an age-associated decline in immune function, is increasingly recognized as a central determinant of health and disease in older adults. Characterized by thymic involution, loss of naïve T cells, contraction of T cell receptor diversity, accumulation of senescent and exhausted lymphocytes, and a chronic inflammatory state known as inflammaging, immunosenescence compromises both innate and adaptive immune responses. Immunosenescence contributes to the pathogenesis of diverse age-related diseases. In autoimmune and metabolic diseases, premature accumulation of senescent T cells and impaired regulatory T cell function drive chronic inflammation and tissue damage, while in neurodegenerative diseases, microglial aging and sustained neuroinflammation exacerbate neuronal loss. These findings highlight immunosenescence as a unifying mechanism linking aging to systemic and organ-specific pathologies. Advances in biomarker discovery, including phenotypic markers, telomere attrition, and epigenetic signatures, have enabled the quantitative assessment of immune aging, while emerging therapeutic strategies, such as cytokine modulation, mTOR inhibition, senolytics, and epigenetic reprogramming, show promise in restoring immune competence. Here, we summarize recent research on immunosenescence in various diseases, particularly chronic inflammatory, metabolic, and neurodegenerative diseases, and suggest novel strategies for the development of senolytic drugs.