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Many thanks to Cynthia Beall for this commentary on Andrea Graham’s Plenary talk “Why do immune systems harm their bearers? The evolutionary biology of friendly fire”. 

Andrea Graham of Princeton University walked us through a tale of two species and two islands during her plenary talk “Why do immune systems harm their bearers? The evolutionary biology of friendly fire”.

The species were Soay sheep on Hirta Island, Scotland and humans on Taiwan. She reported that sheep with more antinuclear antibodies (ANAs, a measure of self-reactivity and thus risk for autoimmune disease) were more likely to survive severe winters and had longer lifetimes. The trade off, however, was lower reproduction for both male and female sheep. Elderly people on Taiwan manifest a fascinatingly similar profile of higher levels of ANA associated with lower risk of death.

Both studies highlight the crucial role of longitudinal studies for addressing major questions in evolutionary medicine. The Soay sheep study is 30 years old and the SEBAS study in Taiwan is 27 years old.
The apparent answer to the underlying question – is vulnerability to immune-mediated disease the price of a potent immune system – is yes. Self-reactivity aids somatic maintenance as well as parasite resistance.