Uncovering the Secrets of Female Immunity

Scientists have made a groundbreaking discovery that may help explain why women’s stronger immune defenses also leave them far more vulnerable to autoimmune disease.

According to a new study published in The American Journal of Human Genetics, researchers have identified over 1,000 genetic switches that behave differently in female and male immune cells. These differences appear to contribute to greater activity in inflammation-related pathways in females, offering a new biological explanation for why women may be more susceptible to autoimmune disease.

Women are diagnosed with autoimmune diseases far more often than men, and the genetic factors behind this striking difference have remained poorly understood. For example, lupus can affect as many as nine women for every one man, yet the genetic factors behind this difference have remained poorly understood.

The researchers, from the Garvan Institute of Medical Research and UNSW Sydney, have used new single-cell technologies to examine individual immune cells in much greater detail. They sequenced over 1.25 million peripheral blood mononuclear cells, which are immune cells circulating in the bloodstream, from nearly 1,000 healthy people.

Clear differences emerged when the researchers compared the cellular profiles of males and females. Males had larger proportions of monocytes, immune cells that serve as early responders to threats, and their gene activity was more strongly focused on fundamental cell maintenance and protein production.

Females, by comparison, had greater numbers of B cells and regulatory T cells, and their immune cells showed much more genetic activity associated with inflammatory pathways. While this highly reactive immune profile gives females an advantage in fighting viral infections, it comes with a biological trade-off: a greater predisposition to autoimmune diseases.

A more reactive immune system can provide valuable protection because it remains more prepared to respond to genuine threats. However, maintaining that heightened state of readiness may also increase the chance of immune ‘friendly fire,’ in which the body mistakenly attacks its own healthy tissues and triggers autoimmune disease.

The researchers identified over 1,000 genetic switches that function in one sex but not the other. These switches can be thought of as volume controls that influence how strongly particular genes are activated or suppressed. The team focused on genetic switches that are located on autosomes, the non-sex chromosomes shared by males and females, rather than the sex chromosomes.

Some of these genetic controls were directly associated with autoimmune disease. The researchers identified particular variants that influenced the female-biased expression of two genes linked to systemic lupus erythematosus. The finding could help explain why lupus occurs about nine times more often in women than in men.

The study’s findings have implications for people living with autoimmune conditions such as lupus. Current treatments do not work equally well for everyone, and many commonly used therapies broadly suppress immune activity throughout the body. By identifying distinct genetic pathways involved in male and female immunity, the research points toward a future in which treatments could be more precisely targeted to a patient’s particular form of disease rather than broadly weakening the entire immune system.

The researchers believe that their findings add strong evidence that female and male autoimmune diseases may not be the same, and the way we should treat them may not necessarily be the same. They also emphasize the importance of including both sexes in medical research, which has historically depended heavily on male study groups.