From the article:
In the study, women had a generally stronger antibody response to the vaccine than men. But the average response mounted by men with relatively low testosterone levels was more or less equivalent to that of women.
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Women are known to have, on average, higher blood levels of signaling proteins that immune cells pass back and fort to jump-start inflammation, a key component of immune-system activation. Furthermore, previous research in animals and in cell-culture experiments has established that testosterone has anti-inflammatory properties, suggesting a possible interaction between the male sex hormone and immune response.
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However, the new study found no connection between circulating levels of pro-inflammatory proteins and responsiveness to the flu vaccine. Nor does testosterone appear to directly chill immune response; rather, it seems to interact with a set of genes in a way that damps that response, said the study’s senior author, Mark Davis, PhD, professor of microbiology and immunology and director of Stanford’s Institute for Immunity, Transplantation and Infection.
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Men are prone to suffer wounds from their competitive encounters, not to mention from their traditional roles in hunting, defending kin and hauling things around, increasing their infection risk.
While it’s good to have a decent immune response to pathogens, an overreaction to them – as occurs in highly virulent influenza strains, SARS, dengue and many other diseases – can be more damaging than the pathogen itself. Women, with their robust immune responses, are twice as susceptible as men to death from the systemic inflammatory overdrive called sepsis. So perhaps, Davis suggests, having a somewhat weakened (but not too weak) immune system can prove more lifesaving than life-threatening for a dominant male in the prime of life.