International Journal of Clinical Case Reports, 2025, Vol.15, No.4, 190-199 http://medscipublisher.com/index.php/ijccr 191 2 Immune Characteristics of the Elderly 2.1 Immune aging Immune aging refers to the gradual weakening of the immune system with age, which can affect innate and acquired immunity. The main manifestations include thymus atrophy, reduction of new T cells and B cells, increase of memory T cells and aging T cells, and elevated inflammatory factors in the body. This state is called "inflammatory aging" (Oh et al., 2019). These changes make it more difficult for the elderly to cope with new viruses or bacteria, and at the same time, their bodies are more prone to long-term chronic inflammation, thereby making them more susceptible to infection, cancer or autoimmune diseases (Pera et al., 2015; Santoro et al., 2021; Liu et al., 2023). Immune aging can bring about many health problems. It not only increases the risk of infection but also reduces the efficacy of vaccines, such as the influenza vaccine. Reverse CD4/CD8 ratio and accumulation of terminally differentiated T cells often occur in the elderly, all of which are associated with a higher mortality rate (Pera et al., 2015). Understanding the mechanism of immune aging is helpful for developing specialized methods to enhance the immune function and vaccine response of the elderly (Figure 1) (Crooke et al., 2019; Oh et al., 2019). Figure 1 Immunological changes associated with aging and adaptive immunosenescence (Adopted from Crooke et al., 2019) Image caption: Specific changes in the T and B cell compartments are known to occur with aging and the onset of immunosenescence; Naïve lymphocyte production, lymphocyte repertoire diversity, and the proliferative and functional capacity of effector lymphocytes all decline with age; similarly, increases in differentiated memory cell populations, lymph node fibrosis, and altered cytokine production all occur; These phenomena have been collectively associated with diminished vaccine responses and an increased susceptibility to viral infectious diseases in older adults; The mechanisms by which immunosenescence operates are not fully understood, and systems biology approaches are currently focused on elucidating these mechanisms in order to inform the rational design of vaccines for older adults (Adopted from Crooke et al., 2019) 2.2 Changes in antibody reactivity With age, the ability of the elderly to produce antibodies will significantly decline, whether after infection or vaccination (Murdaca et al., 2023). The antibody response in the elderly is usually weaker, shorter in duration, poorer in memory lymphocyte production, and the effect of vaccine booster shots is often not obvious (Weinberger et al., 2008). This deterioration is partly due to the reduction in the types and functions of B cells, while the assistance of T cells is also weakened (Oh et al., 2019; Crooke et al., 2019). Therefore, it is more difficult for the elderly to establish or maintain effective immunity after vaccination, and better vaccine formulations and adjuvants need to be tailored for them (Oh et al., 2019; Hou et al., 2024). Regular monitoring of antibody levels and immune responses in this group of people can help identify those with poor vaccine responses and take measures to improve vaccination outcomes (Weinberger et al., 2008; Murdaca et al., 2023).
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