A protein found in cow’s milk can trigger inflammation in the surrounding areas of neurons in mice, and may have implications for people with multiple sclerosis (MS). The corresponding study was published in PNAS.
"We hear again and again from sufferers that they feel worse when they consume milk, cottage cheese or yogurt," said Prof Stefanie Kürten, one of the authors of the study. "We are interested in the cause of this correlation."
MS is characterized by the body’s immune system destroying the protective, fatty coating around neurons known as ‘myelin sheaths’. Effects include paresthesia- a temporary burning or tickling sensation in the arms or feet, vision problems, and movement disorders. In more advanced cases of the condition, people may require wheelchairs.
In the present study, the researchers injected mice with different proteins from cow’s milk to see if any affected the nervous system. In doing so, they found that injection of a protein known as casein alongside an effect enhancer, led mice to develop neurological disorders. Electron microscopy revealed that these disorders were caused by damage to myelin sheaths.
"We suspected that the reason was a misdirected immune response, similar to that seen in MS patients," explained Rittika Chunder Ph.D., another author of the study. "The body's defenses actually attack the casein, but in the process they also destroy proteins involved in the formation of myelin."
To understand why this happens, the researchers compared casein to various molecules needed for myelin production. They found that casein closely resembles another protein known as ‘MAG’, to the extent that the same antibodies affect both molecules. This, concluded the researchers, means that the body’s own defenses both attacked casein and MAG. which leads to myelin destabilization.
To see how these effects may transfer to people with MS, the researchers added casein antibodies from mice to human brain tissue. These antibodies accumulated in cells responsible for myelin production in the brain. Further tests demonstrated that B cells in people with MS - immune cells responsible for antibody production- have a strong response to casein.
In people with MS who experience worsening symptoms upon drinking the milk, the researchers said that affected individuals likely developed an allergy to casein, and thus, after consuming fresh dairy products, their immune system produces casein antibodies which go on to damage MAG and nerve fibers.
The researchers are currently developing a self-test so individuals with MS may test if they are allergic to casein. People in this group should then avoid consuming dairy products to prevent worsening of their symptoms.
While further research is needed to confirm their findings and understand their implications, the researchers point out that MS rates are higher in populations that consume large quantities of cow’s milk. This link may indicate that drinking cow’s milk could increase the risk of developing MS in healthy individuals too; however, they emphasize that other factors likely work in tandem.
Sources: Science Daily, PNAS
