People with multiple sclerosis often complain of more severe disease symptoms after consuming dairy products. A protein in cow’s milk can trigger inflammation that targets the “insulating layer” around nerve cells. One study was able to demonstrate this link in mice, but also found evidence of a similar mechanism in humans. Certain groups of sufferers should therefore avoid dairy products, the scientists recommend.
(red) The study was triggered by reports from MS patients: “We hear time and again from people with MS that they feel worse when they eat milk, quark or yogurt,” explains Stefanie Kürten from the Institute of Anatomy at Bonn University Hospital (D). “We are interested in the cause of this connection.” The professor of neuroanatomy is considered a renowned MS expert. They began the study in 2018 at the University of Erlangen-Nuremberg (D). A year and a half ago, she moved to Bonn, where she continued the work together with her research group. “We injected mice with different proteins from cow’s milk,” she says. “So we wanted to find out if there was a component that they were responding to with symptoms of disease.”
In fact, the researchers found what they were looking for: When they gave the animals the cow’s milk ingredient casein together with an effect enhancer, the mice subsequently developed neurological disorders. Electron microscopy showed that the insulating layer around the nerve fibers, the myelin, was damaged. The fat-like substance prevents short circuits and additionally significantly accelerates stimulus conduction.
Perforated myelin layer
In multiple sclerosis, the body’s immune system destroys the myelin sheath. The consequences range from insensitivity to problems with vision and movement disorders. In extreme cases, those affected end up in a wheelchair. The insulating shell was also massively perforated in the mice – apparently triggered by casein administration. “We suspected the reason to be a misdirected immune response similar to the one in MS patients,” explains Rittika Chunder, who is a postdoctoral fellow in Prof. Kürten’s research group. “The body’s own defenses actually attack casein, but in the process they also destroy proteins that are involved in the formation of myelin.” Such cross-reactivity can occur when two molecules are very similar, at least in parts. The immune system then confuses them with each other, so to speak. “We compared casein to different molecules that are important for myelin production,” Chunder says. “In the process, we came across a protein called MAG. It looks very similar to casein in some respects – so much so that in the test animals, the antibodies against casein were also active against MAG.”
Thus, in the casein-treated mice, the body’s own defenses were also directed against MAG, destabilizing the myelin. But to what extent can the results be transferred to people with MS? To answer this question, the researchers added casein antibodies from mice to human brain tissue. In fact, they accumulated there on the cells responsible for myelin production in the brain.
Self-test for antibodies against casein
Certain white blood cells, the B cells, are responsible for antibody production. According to the study, the B cells in the blood of MS patients respond particularly strongly to casein. Presumably, the affected individuals developed an allergy to casein at some point through the consumption of milk. Therefore, as soon as they consume fresh dairy products, the immune system produces masses of casein antibodies. These also damage the myelin layer around nerve fibers due to cross-reactivity with MAG. However, this only affects MS patients who are allergic to cow’s milk casein. “We are currently developing a self-test with which affected individuals can check whether they carry corresponding antibodies,” says Kürten, who is also a member of the ImmunoSensation2 cluster of excellence. “At the very least, this subgroup should avoid consuming milk, yogurt, or cottage cheese.”
It is possible that cow’s milk also increases the risk of developing MS in healthy individuals. Because casein can also trigger allergies in them – which is probably not even that rare. Once such an immune response exists, cross-reactivity with myelin can theoretically occur. However, this does not mean that hypersensitivity to casein necessarily leads to the development of multiple sclerosis, the professor emphasizes. This would presumably require other risk factors. Still, Kürten says this connection is worrisome: “Studies show that MS rates are elevated in populations where a lot of cow’s milk is consumed.”
Source: Rittika Chunder, et al: Antibody cross-reactivity between casein and myelin-associated glycoprotein results in central nervous system demyelination with implications for the immunopathology of multiple sclerosis; PNAS; DOI: https://doi.org/10.1073/pnas.2117034119.
InFo NEUROLOGY & PSYCHIATRY 2022; 20(2): 20.
