Sex shapes how the immune system ages

The immune system does more than fight infections. It also clears cells that have stopped dividing (senescence), signals tissue damage, and directs repair processes. As immune function deteriorates, all of these tasks suffer. That increases not just infection risk but also the risk of cancer and tissue deterioration.

Women generally have a more active immune response than men. That offers advantages early in life but works against them later. Women are more prone to autoimmune diseases, where the immune system attacks the body’s own tissue. Men show earlier and steeper decline in immune function on average, making them more vulnerable to infections in old age.

Hormones as a driving factor

Sex hormones play a central role. Estrogen amplifies immune responses in women; testosterone has a suppressive effect in men. After menopause, the estrogen boost disappears and immune decline accelerates in women. The researchers describe how that hormonal shift coincides with greater vulnerability to infectious disease and cardiovascular problems in women after the transition.

Immune cell composition also differs. Women retain larger pools of naive T-cells for longer. These are cells that have not previously encountered a specific pathogen and can therefore respond flexibly to new threats. In men, that reservoir shrinks faster, limiting the immune system’s ability to respond to novel challenges.

Implications for treatment and research

This overview has direct relevance for how longevity interventions are designed and tested. A drug that slows immune decline may work differently in men than in women, or may benefit one group while harming the other. Many clinical trials have historically not made that distinction.

The findings argue for sex-specific benchmarks in immune research and for treatment strategies that account for hormonal and cell-biological differences between men and women.

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