Immune Aging & Inflammaging免疫衰老与慢性低度炎症 · Immune Aging & Inflammaging

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免疫不是变弱而是失调 + 失衡· 胸腺萎缩 → 对新抗原/疫苗应答迟钝 · 炎龄 (Franceschi): 衰老细胞 SASP + 内脏脂肪推高 IL-6/CRP · 拆穿免疫增强剂(更高 ≠ 更好) · 杠杆最大的是疫苗 + 运动 + 蛋白质, 不是补剂

Immunosenescence · not 'weaker', but 'dysregulated'

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免疫衰老 · 不是变弱, 是失调

'Immunity gets worse with age' gets it half-backwards. The age-related change in the immune system is, precisely, not a wholesale 'weakening' but a structural rewiring + regulatory failure — some functions genuinely slow down, while others become over-active. That combination is what the field calls immunosenescence.

The core hardware change: thymic involution (Thomas 2020)

The thymus is the 'recruit-training' organ — naïve T cells mature there and learn to recognize never-before-seen new antigens.The thymus degenerates year by year (thymic involution) from after puberty onward, is replaced by fat tissue, and from midlife outputs fewer and fewer new naïve T cells.The consequence: old antigens met across a lifetime (childhood measles, recurrent flu strains) are still guarded by memory cells; but facing a brand-new pathogen or vaccine antigen, there aren't enough 'recruits,' TCR diversity falls, and first recognition is slow and blunted.
This explains three things common in older adults

Slower clearance of new infections: the same virus runs a longer course with more complicationsBlunted vaccine response: the same vaccine dose generates fewer antibodies that last for less time (which is exactly why high-dose / adjuvanted vaccines exist for older adults — more below)Reduced immune surveillance: lower efficiency at clearing abnormal cells
But note the word 'dysregulated'

Immunosenescence is not simply 'firepower down.' It comes together with a rise in chronic low-grade inflammation (inflammaging, next scene) and an upward drift toward autoimmunity — meaning the aged immune system is blunt where it should respond, yet smolders chronically where it shouldn't.

This is the soul of the island: if the problem is 'dysregulation + imbalance,' then 'turn immunity up as high as possible' is the wrong direction from the start (the mechanistic basis for debunking 'immune boosters' later).

Atlas links: the general mechanism of chronic low-grade inflammation lives at (dive to chronic-inflammation); chronic stress accelerates this via immune dysregulation (dive to chronic-stress); it shares root causes with brain aging (dive to cognitive-aging).

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