Immunosenescence

Immunosenescence is the age-related remodelling of the immune system characterised by a decline in naive lymphocyte output from the thymus and bone marrow, clonal expansion of antigen-experienced memory and effector cells, and a shift in cytokine balance toward a pro-inflammatory baseline. The result is a paradox of concurrent immunodeficiency — reduced capacity to respond to novel pathogens and vaccines — alongside chronic low-grade inflammation (inflammaging). Contributing factors include thymic involution, CMV-driven memory inflation, and accumulating senescent immune cells that secrete SASP components. These changes are associated with increased susceptibility to infections, reduced vaccine efficacy, and higher incidence of autoimmunity and malignancy in older adults.