1,000+ genetic switches explain why women face higher autoimmune disease risk

A team of researchers has mapped more than a thousand genetic switches that operate differently in the immune cells of women compared to men, offering a biological explanation for why women develop autoimmune diseases at significantly higher rates. The work, published in The American Journal of Human Genetics, reveals that female immune systems are genetically configured to mount stronger inflammatory responses—a trait that provides excellent protection against infection but simultaneously increases the likelihood of the immune system attacking the body's own tissues.

For decades, scientists studying sex differences in immunity faced a fundamental limitation: the technology available could only measure average activity across millions of cells at once, obscuring the distinct behaviors of individual cell types. That changed with the arrival of single-cell sequencing, which allows researchers to examine each immune cell in granular detail. The team took advantage of this breakthrough by analyzing more than 1.25 million individual immune cells drawn from nearly 1,000 healthy people participating in the OneK1K cohort, a large Australian research initiative designed to understand how genetics shapes immune function across diverse populations.

The cellular profiles of men and women diverged in striking ways. Men carried higher proportions of monocytes, the immune system's first responders to threats, and their gene activity centered on basic cellular maintenance and protein production. Women, by contrast, had greater numbers of B cells and regulatory T cells, and their immune cells displayed substantially more genetic activity linked to inflammatory pathways. This heightened reactivity offers a genuine advantage: women's immune systems remain more primed to detect and fight viral infections. But the trade-off is severe. That same heightened state of alert appears to increase the risk of autoimmune misfires, where the immune system loses its ability to distinguish between genuine threats and the body's own healthy tissue.

Perhaps most surprising was where these sex-specific genetic switches were located. Researchers had long assumed that differences between male and female immunity stemmed primarily from the X and Y sex chromosomes. Instead, the team discovered that more than 1,000 of these genetic controls sat on autosomes—the chromosomes shared equally by both sexes. These switches function like volume controls, turning genes up or down with different intensity depending on whether the person is male or female. The finding challenges conventional thinking about the biological roots of sex differences in disease.

The implications for specific diseases became clear when the researchers examined lupus, a systemic autoimmune condition that strikes women roughly nine times more often than men. The team identified particular genetic variants that influenced how strongly two genes linked to lupus were expressed in female immune cells. While genetics alone does not determine disease risk—hormones and other factors also play crucial roles—these findings establish a distinct biological starting point that could shape a person's vulnerability to autoimmune attack.

Dr. Seyhan Yazar, the study's first author, emphasized that understanding these differences matters for how medicine is practiced. Many studies of immune function have historically relied on male participants, a bias that has obscured important biological realities. Current treatments for autoimmune diseases typically work by broadly suppressing immune activity throughout the body, an approach that does not work equally well for everyone. By identifying the specific genetic pathways that differ between male and female immunity, the research points toward a future in which treatments could be tailored to a patient's particular form of disease and their baseline genetic immune profile, rather than applying a single therapeutic approach to all patients regardless of sex.

The findings underscore a larger principle: that diseases do not develop or progress identically in men and women, and that precision medicine—the goal of matching treatments to individual biology—cannot be achieved without accounting for these fundamental differences. As researchers move forward, the challenge will be translating these genetic insights into clinical practice, developing therapies that work with the distinct immune architecture that men and women inherit.