The Science Behind Autoimmune Disease

 As clever and effective as the immune system is at fending of infectious agents, mistakes are inevitably made and I was surprised to learn in Lewis Wolpert’s ‘How We Live and Why We Die’ that nearly 10% of the population is affected by autoimmune diseases. This got me thinking, what is an autoimmune disease and what causes it?

In a ‘normal’ healthy individual there is an education programme of sorts in which the immune system is schooled in how to distinguish between foreign and self, and how not to kill its own cells. This learning occurs during development; lymphocytes (a type of white blood cell) are attracted to the thymus which is a lymphoid organ located in the neck that produce T cells for the immune system. When at the thymus, any cells that recognise antigens in the body are eliminated through apoptosis – programmed cell death – and this prevents autoimmunity since the production of antibodies that will attack the body’s own cells is inhibited.

Unfortunately, this system sometimes goes wrong: autoimmune diseases occur when the immune system recognises normal body cells as foreign and mediates an attack. This includes the activation of T cells and antibodies to interact with normal cells and cause local inflammation and tissue damage. Cells themselves are aware of the autoimmune problem – there is one type of T cell dedicated to repressing immune responses that could prove harmful to the body.

Examples of autoimmune diseases include rheumatoid arthritis, Type 1 diabetes and multiples sclerosis.

• Rheumatoid arthritis: Mainly affects the joints in a very painful manner and can lead to the destruction of cartilage. The cause is not known but it is suspected that there is a genetic susceptibility.
• Type 1 diabetes: Results from the immune system destroying the cells in the pancreas that produce insulin, which enables glucose to enter our cells for respiration.
• Multiple sclerosis: The immune system destroys the cells that provide the electrical insulating cover (myelin sheaths) of nerve cells which prevents them from functioning properly. 

What causes such illnesses?

One idea involves the role of infection and disease. When the body identifies signs of infection, the immune system is activated to attack the pathogen and sometime healthy cells and tissues can get caught in the crossfire. Many scientists believe that this is what causes rheumatoid arthritis. Some scientists think injury may play a role in some types of diseases; in parts of the body subjected to repeated high stress, research has shown that this can expose tissue that shouldn’t normally be in contact with blood. Blood cells try to heal the exposure, but an abnormal immune response can cause inflammation. It’s possible that autoimmune disease occurs based on the ability of the immune system to handle stress. Genetics play a role in autoimmune disease – i.e. having a family member with multiple sclerosis means you have a 3-5% chance of developing it compared with a 0.25% risk in the rest of the population – but alone aren’t enough to cause it.

Sources:

>      ‘How We Live and Why We Die’ – Lewis Wolpert

>      https://www.hopkinsmedicine.org/health/wellness-and-prevention/autoimmune-disease-why-is-my-immune-system-attacking-itself#:~:text=On%20a%20basic%20level%2C%20autoimmune,into%20gear%20and%20attacks%20it.

>      https://my-ms.org/ce_cause.htm#:~:text=There%20is%20a%20higher%20rate,5%25%20chance%20of%20developing%20MS.