Scientists have identified a chain reaction that explains why our own bodies can turn against healthy cells, potentially transforming the way we look at autoimmune diseases and the way we treat them.

The reaction, discovered in 2017 after four years of research in mice, has been described as a "runaway train" where one error leads the body to develop a very efficient way of attacking itself.

The study focussed on B cells gone rogue. Ordinarily these cells produce antibodies and program the immune cells to attack unwanted antigens (or foreign substances), but scientists found an 'override switch' in mouse B cells that distorted this behaviour and caused autoimmune attacks.

"Once your body's tolerance for its own tissues is lost, the chain reaction is like a runaway train," said one of the team, Michael Carroll from Boston Children's Hospital and Harvard Medical School (HMS).

"The immune response against your own body's proteins, or antigens, looks exactly like it's responding to a foreign pathogen."

These B-cells-gone-awry could in turn explain the biological phenomenon known as epitope spreading, where our bodies start to hunt down different antigens that shouldn't be on the immune system's 'kill list'.

Epitope spreading has long been observed in the lab but scientists have been in the dark about how it happens, and why autoimmune diseases evolve over time to target an ever-expanding catalogue of healthy organs and tissues.

In this case the research looked at a mouse model of the lupus autoimmune disease, considered an archetypal or 'classic' type of autoimmune disease that many others are based on.

"Lupus is known as 'the great imitator' because the disease can have so many different clinical presentations resembling other common conditions," said one of the researchers, Søren Degn from Boston Children's Hospital and Aarhus University in Denmark, at the time.

"It's a multi-organ disease with a plethora of potential antigenic targets, tissues affected and 'immune players' involved."


Read more: https://www.sciencealert.com/we-may-have-found-how-autoimmune-diseases-start