Study reveals why female immunity differs from men's–The science of the biological divide

Study reveals why female immunity differs from men's–The science of the biological divide The immune system is one of the body's most critical defense networks, constantly protecting you from viruses, bacteria, fungi and parasites. But scientists are finding that this complex system works differently in males and females, potentially influencing both disease resistance and the risk of autoimmune disorders. Researchers from the Garvan Institute of Medical Research and UNSW Sydney identified more than 1,000 genetic switches that may help explain why women generally mount stronger immune responses but are also more vulnerable to autoimmune diseases. Autoimmune diseases occur when the immune system mistakenly attacks the body's own healthy tissues. Conditions such as lupus disproportionately affect women, with some studies finding as many as nine women diagnosed for every one man. Yet the biological reasons behind this striking difference have remained difficult to explain. The study found that female immune systems appear genetically programmed for stronger inflammatory responses. Female participants also had higher numbers of B cells and regulatory T cells, while their immune cells showed greater genetic activity linked to inflammatory pathways. This heightened immune activity can give women an advantage when fighting viral infections, but it may also create a biological trade-off by increasing the likelihood of harmful immune reactions against healthy tissues. Male immune cells, by comparison, showed less inflammatory activity, potentially making men more vulnerable to certain infections and some non-reproductive cancers. The findings provide new insight into 'sexual immune dimorphism,' the biological differences between male and female immune systems. Importantly, the researchers found that these differences are not explained solely by the X and Y sex chromosomes. By examining individual immune cells, they identified sex-specific differences in genetic regulation that earlier studies using bulk blood samples may have missed. These differences appear to arise from a complex interaction of genetics, hormones and evolutionary trade-offs. Females, by comparison, had greater numbers of B cells and regulatory T cells. Their immune cells also 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. On the other hand, male immune cells are less primed for inflammation, making men generally more susceptible to infections and non-reproductive cancers," says co-senior author Dr. Sara Ballouz, Senior Lecturer at UNSW. Scientists believe examining individual cells allowed the researchers to detect sex specific genetic differences that earlier studies using bulk blood samples could not see. Researchers have often assumed that differences between male and female immune systems are largely driven by the X and Y sex chromosomes. The new findings challenged that expectation. "This is the first time we have shown that these differences occur at the genetic control level, providing a new layer of insight into human immunity," Dr. Ballouz says. "Having shown that female-biased genes are heavily enriched in inflammatory pathways, we now have another biological rationale for why the immune system can more easily mistakenly attack the body's own tissues in women." "Our 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." The study also reveals, approximately 80% of autoimmune disease cases are diagnosed in females, a direct result of their immune system's heightened reactivity. The researchers say the results could eventually help explain why autoimmune diseases can affect men and women differently and why sex-specific approaches to diagnosis and treatment may be necessary.