Longevity, John Mill, and the Immune System

During my freshman year, I explored the ethics of longevity in my thesis project for Philosophy 104: Intro to Ethics, arguing, through a utilitarian lens, that extending life by reducing age-related disease increases what John Stuart Mill called “net happiness.”

A 2019 study by Alpert et al., published in Nature Medicine, brought me back to this idea.

Tracking 135 healthy individuals over 9 years, the researchers used high-dimensional cytometry (38 immune markers + a viability stain) to map how immune-cell populations shift with age and to build a quantitative measure of “immune age,” called IMM-AGE.

So what were their findings?

• They developed the IMM-Age score, a quantitative measurement of immune aging: IMM-AGE predicted mortality more accurately than chronological age and showed stronger associations with disease risk in some settings than DNA methylation age.
• Immune aging is individualized and dynamic, with some immune subsets stabilizing earlier in life whereas others continue to shift with age
• They correlated IMM-Age with mortality and disease risk, demonstrating that “immune age” could outperform chronological age when assessing these risks

While this study focused on aging, the immune system plays a central role in many diseases, from cancer to autoimmunity to neurodegeneration. By understanding how it evolves over time, we open the door to therapies that improve healthspan across populations.

Back to my paper, this isn’t just about living longer. It's about enabling more people to live healthier lives, therefore driving what Mill coined, a collective “net happiness.”

While this study focused on quantifying immune age, I see broader implications. The immune system underpins nearly every biological process. Harnessing tools like cytometry to track its dynamic changes could inform therapies that extend both healthspan and collective “net happiness,” as Mill envisioned.

Full paper here: https://pubmed.ncbi.nlm.nih.gov/30842675/

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