Immunosenescence

This overlaps with Question 7; the answer below is written as a focused, self-contained account of the entity itself — definition, mechanisms, measurement, consequences and interventions.

15–20 High-Yield Points (Textbook)

Summary of Changes with Ageing

Component Change with ageing Clinical consequence Thymus / marrow Involution; fall in thymosins; reduced marrow mass Reduced output of naive lymphocytes Naive T cells Decreased Poor response to new antigens and new vaccines Memory T cells Increased proportion; terminally differentiated Narrowed repertoire; reactivation of latent infection (zoster, TB)

IL-2 Reduced production and receptor expression Reduced clonal expansion; poor delayed hypersensitivity B cells Fewer precursors; impaired isotype switching Lower-affinity antibody; poorer vaccine response; MGUS, autoantibodies Neutrophils Reduced phagocytosis Bacterial infection risk Langerhans cells Reduced in skin Skin infection and cutaneous malignancy NK cells Function variable, often impaired Reduced tumour surveillance IL-6 / TNF-α / CRP Chronically raised (inflammaging) Frailty, sarcopenia, anaemia, atherosclerosis, delirium risk, mortality CD4/CD8 ratio Falls below 1 in a subset (IRP) Predicts mortality Latest Updates (2023–Present)

Chronic inflammation and dysbiosis were formally added to the hallmarks of ageing in the 2023 Cell update, placing inflammaging and the gut microbiome at the centre of immune ageing.

Cytomegalovirus is now viewed as a principal accelerant: persistent antigenic stimulation drives massive expansion of CMV-specific CD8 T cells expressing PD-1 and TIGIT with reduced cytotoxicity, raises intracellular TNF-α in B cells, reduces switched memory B cells, and correlates with poorer vaccine antibody responses in seropositive older adults.

The current mechanistic model adds loss of CD28 expression on T cells, impaired T-cell receptor signalling, reduced dendritic cell phagocytic activity, and accumulation of myeloid-derived suppressor cells, creating a self-amplifying immunosenescence–inflammaging feedback loop (2024–2025 reviews). Vaccine strategy has been redesigned around immunosenescence: adjuvanted and high-dose formulations, higher antigen content, recombinant platforms and mRNA platforms — exemplified by high-dose and MF59-adjuvanted influenza vaccines, the AS01B-adjuvanted recombinant zoster vaccine, and the adjuvanted and mRNA RSV vaccines licensed from 2023 for older adults.

Pharmacological reversal is being tested: mTOR inhibitors improved influenza vaccine responses in older adults (Mannick trials); senolytic therapy (dasatinib plus quercetin, fisetin, senolytic CAR-T cells), canagliflozin via AMPK activation, and anti-PD-1 antibodies clearing PD-L1-positive senescent cells all reduce senescent cell burden and, in principle, restore vaccine immunogenicity.

Practical, presently available measures that improve immune competence in older people remain correction of protein-energy undernutrition, correction of vitamin D and zinc deficiency, glycaemic control, regular physical activity, adequate sleep, smoking cessation and age-appropriate vaccination. Indian relevance: high background prevalence of latent tuberculosis, near-universal CMV seropositivity, high burden of diabetes and undernutrition, and very low adult vaccination coverage make immunosenescence clinically more consequential; the affordable, high-impact interventions are influenza and pneumococcal vaccination, nutrition and diabetes control rather than the newer costly vaccines.

Current Practice Update

Issue Textbook (Pathy 6e / Kane) Current Evidence (2023–present)

Terminology Immunosenescence as decline, with a note that Immune remodelling / immunobiography — remodelling is more accurate the individual's lifetime antigen exposure determines the phenotype Main external driver Not emphasised Chronic CMV infection is a principal driver of the immune risk phenotype Inflammaging Discussed as an association Formal hallmark of ageing; bidirectional loop with immunosenescence Microbiome Not covered Dysbiosis recognised as a hallmark and a modifier of vaccine response Clinical response No specific recommendations Enhanced vaccine platforms (high-dose, adjuvanted, recombinant, mRNA) are now standard for older adults Reversal Thymic hormones restore some function in vitro mTOR inhibitors and senolytics in early human trials; not yet clinical practice Exam One-Liners Immunosenescence = age-related remodelling of innate and adaptive immunity, not pure decline. Hallmark cellular change = ↓ naive T cells, ↑ memory T cells from thymic involution. Cytokine signature = IL-2 down, IL-6 up.

Immune risk phenotype = CD4/CD8 <1 — predicts mortality.

Immunosenescence + inflammaging = "two sides of the same coin".

B cells: impaired isotype switching → poor vaccine response, ↑ autoantibodies and MGUS. Commonest clinical manifestations = herpes zoster, pneumonia, TB reactivation, poor vaccine response, ↑ cancer.

Practical answer to immunosenescence today = enhanced vaccines + nutrition + vitamin D + exercise + glycaemic control.

Cross-Question Linking Points (useful for any of these eight answers)

One inflammatory axis runs through the whole set: TNF-α and IL-6 explain sarcopenia, frailty, anaemia, anorexia of ageing, delirium risk and immunosenescence. Naming this axis links five answers together. Sarcopenia is the biological substrate of physical frailty; deconditioning is acute sarcopenia; immunosenescence and inflammaging are the immunological expression of the same hallmarks of ageing.

The single intervention that appears in every answer is progressive resistance exercise with adequate protein — it improves frailty, sarcopenia, deconditioning and immune competence.

For any Indian answer, quote LASI for epidemiology, NPHCE and the Ayushman Vay Vandana Card for service delivery, and AWGS 2019 cut-offs rather than European cut-offs for muscle measurements.