Your body’s immune system is a complex web of organs, cells, proteins, and chemicals that work to defend you against disease. It’s what lets you recover from colds and develop immunity – without it, you wouldn’t be able to survive.
However, this system depends upon one key thing – the ability to differentiate between self and non-self material (which involves the detection of antigens – proteins on the surface of non-self cells), and when this ability fails, autoimmune disorders can occur; healthy body cells are attacked and damaged, leading to a range of symptoms and conditions from rheumatoid arthritis (which affects the joints) to psoriasis (which affects the skin).
These disorders don’t occur indiscriminately – in fact, women are far more likely to have an autoimmune condition, and they make up around 80% of all patients diagnosed (with some variations depending on the condition). The causes of autoimmune disorders are unknown, but there are many theories as to how they arise, and most think that they are caused by a combination of genetic and environmental factors. The sex discrepancy is thought to mainly be linked to genetic differences – below are the two leading theories to explain it:
Sex Chromosomes
Typically, humans have two sex chromosomes, X and Y, and their combination determines the sex of the individual. Males have XY, and females have XX. This second X chromosome is thought to be linked to autoimmune diseases. Since the X chromosome is bigger than the Y chromosome, this ‘suggests that the X chromosome contains more genes than the Y chromosome’ and is linked to a ‘greater [quantity] of immune-related genes’, including those that help create the immune response in the body. So, by having two X chromosomes, women are at higher risk of autoimmune conditions than men. Additionally, having one more, or one less, X chromosome is linked to a ‘high prevalence of autoimmune disease’.
Since women have this extra X chromosome, they also undergo a process called X inactivation while still an embryo. This process happens so that the same genes present on the two X chromosomes aren’t both expressed. Usually this happens in a fairly even split, but some women may have more genes from their maternal or paternal chromosome. This variability means that women can be considered as ‘cellular mosaics’. If this balance is skewed too far in one direction, the body may not be able to recognise the opposite X chromosome, causing the body to view some of its cells as non-self, and attack them, prompting an unwanted immune response (this is the most popular theory to explain the autoimmune condition lupus).
Pregnancy and hormones
When someone becomes pregnant, the body must change a lot to accommodate the foetus growing inside. Hormonal levels change hugely, and the mother’s immune system is supressed since the foetus contains non-self cells; this change is believed to happen to prevent rejection of the foetus, but it can trigger the onset of autoimmune diseases. For example, rheumatoid arthritis is far more likely to occur in the ‘24 months after delivery’, than in the following years. Changes in hormones also happen during puberty, which can trigger these diseases.
Some hormones, such as oestrogen and progesterone, help prevent autoimmune diseases from impacting women. High levels of those two hormones have been linked to decrease in symptoms of rheumatoid arthritis.
While the exact causes of autoimmune conditions remain unknown, research around these diseases is evolving and, as scientists discover more about our genes and chromosomes, the exact links between them and autoimmunity will hopefully become clear.
