On the trail of a critical link: A study shows why the consumption of dairy products can lead to a worsening of symptoms in multiple sclerosis (MS). In the neurological autoimmune disease, a “confusion” can therefore play a role: Aggressive overreactions to a milk protein are also directed against a component of the “insulating layer” around nerve cells. The researchers demonstrated this connection in an animal model, but also found evidence of a similar mechanism in humans. Certain groups of MS patients should therefore avoid dairy products.
According to estimates, more than 200,000 people are affected in Germany alone: MS is one of the most common neurological diseases in young adults. It manifests itself in the form of abnormal sensations, problems with vision and movement disorders, and in extreme cases pronounced paralysis can occur. However, there are very different forms and characteristics of the autoimmune disease. The symptoms are caused by the body’s own defense system attacking the fat-like substance that electrically insulates nerve fibers in the central nervous system. Damage to this so-called myelin sheath can then lead to short circuits and impairment of the stimulus transmission.
The causes of the emergence of MS and the factors in the development of the disease are complex and difficult to grasp to date. However, it seems clear that a mixture of genetic predispositions, environmental factors and behavior forms the basis of MS. Diet also plays an important role. The consumption of dairy products has long been considered important. This also formed the basis of the study by the researchers led by Stefanie Kürten from the University Hospital Bonn: “We keep hearing from those affected that they feel worse if they eat milk, quark or yoghurt. That’s why we decided to investigate the cause of this connection,” says the MS expert.
On the trail of a connection
In order to clarify which components of the milk could be responsible for the effect, Kürten and her colleagues first carried out experiments on animal models. As they explain, proteins were the main possible triggers. Therefore, the scientists injected mice with various proteins from cow’s milk in combination with certain booster substances. They then examined the extent to which the animals developed disease symptoms that can be associated with MS.
As the scientists report, they struck gold with a prominent milk protein: casein. When they gave the animals this ingredient along with an enhancer, some showed signs of neurological disorders. Electron microscopic examinations of the nerve tissue then revealed: In these animals, the myelin layer around the nerve fibers in the central nervous system showed signs of damage: Similar to MS patients, the insulating sheath was perforated – apparently caused by the administration of casein. “We suspected the reason to be a misguided immune reaction – similar to that in MS patients,” says lead author Rittika Chunder. According to her, this gave rise to a concrete suspicion: there could be cross-reactivity. “The body’s own defenses actually attack the casein, but also destroy proteins that are involved in the formation of the myelin,” says Chunder.
As the researchers explain, cross-reactivity can occur when two molecules are very similar, at least in certain parts. The immune system then confuses them with one another, so to speak. So the team investigated what could be the reason in the present case. “We compared the casein to different molecules that are important for the production of myelin,” explains Chunder. “In doing so, we came across a protein called MAG. It looks very similar to casein in some areas – so much so that the antibodies against casein in the test animals were also active against MAG,” says the researcher. In this way, the myelin was apparently destabilized in the treated animals.
Medical importance
But to what extent can the results in mice be extrapolated to humans with MS? In order to obtain information on this, the scientists added casein antibodies from mice to samples of human brain tissue in laboratory experiments. This confirmed that they accumulated there in the cells that are responsible for myelin production in the brain. In addition, another finding provided clues: According to the study results, the B cells responsible for antibody production in the blood of some MS patients often respond strongly to casein. It is now clear that those affected have probably developed an allergy to casein at some point through the consumption of milk. As soon as they eat dairy products, the immune system therefore forms antibodies against this protein. These then also damage the myelin layer around the nerve fibers due to cross-reactivity with MAG.
The scientists emphasize that milk does not play a role in MS in general – but the results show that it has a role in those MS sufferers who have a reaction to casein. Apparently, this is not always clearly recognizable for those affected. “We are currently developing a self-test that people can use to check whether they have the appropriate antibodies,” says Kürten. “At least this subgroup should refrain from consuming milk, yoghurt or quark.”
However, as the scientists conclude, the established mechanism also implies that milk consumption may be associated with a higher risk of developing MS. Because as soon as an immune response to casein has developed, cross-reactivity with the myelin can theoretically occur. The researchers emphasize that this does not mean, however, that hypersensitivity to casein will inevitably lead to multiple sclerosis. There are probably other risk factors involved. Nevertheless, a statistical connection makes you sit up and take notice, says Kürten: “According to studies, the MS numbers are increased in population groups in which a lot of cow’s milk is consumed.”
Source: Rheinische Friedrich-Wilhelms-Universität Bonn, specialist article: PNAS, doi: 10.1073/pnas.2117034119