For decades those with multiple sclerosis have suggested dairy products can exacerbate the symptoms of their disease. Now researchers from the Universities of Bonn and Erlangen-Nuremberg have demonstrated exactly how this could be occurring, by finding a specific protein in cow milk can trigger the immune cells known to damage neurons in MS.
"We hear again and again from sufferers that they feel worse when they consume milk, cottage cheese or yogurt," said Stefanie Kürten, a researcher working on this study since 2018. "We are interested in the cause of this correlation."
The first step was homing in on the particular constituent in milk that could be enhancing MS symptoms. Across a number of mouse experiments the researchers discovered casein was the main culprit. But that observation only affirmed the correlation. The researchers were most interested in how this particular milk protein could be triggering MS-related neuronal damage.
Rittika Chunder, another researcher working on the project, explained the hypothesis was that casein triggers a misdirected immune response. It meant casein must resemble the same antigens that lead immune cells to incorrectly target healthy brain cells.
"We compared casein to different molecules that are important for myelin production," said Chunder. "In the process, we came across a protein called MAG. It looks markedly similar to casein in some respects – so much so that antibodies to casein were also active against MAG in the lab animals."
The final step was establishing that this casein-triggered autoimmune response actually occurs in humans. To investigate this the researchers looked at how these casein antibodies behaved in human brain tissue.
The hypothesis was verified, the casein antibodies did aggregate in brain cells responsible for myelin production. Plus, the researchers found immune B cells taken from MS patients were particularly sensitive to casein.
The study ultimately concludes the relationship between dairy and MS symptoms is due to the casein protein in milk triggering an influx of immune antibodies. These immune cells mistakenly attack certain cells in the brain due to the MAG protein’s resemblance to casein.
The researchers are cautious to note this mechanism is only likely to occur in people with a pre-existing dairy allergy. Kürten said her team is already working on a test for MS patients that can identify their susceptibility to casein allergies.
"We are currently developing a self-test with which affected individuals can check whether they carry corresponding antibodies," said Kürten. "At least this subgroup should refrain from consuming milk, yogurt, or cottage cheese."
One question the new findings raise is what role sensitivity to casein could play in the development of MS in the first place?
Kürten does point out observational studies have detected higher rates of MS in populations known to consume large volumes of cow milk. So it is plausible that an allergic reaction to casein could lead to antibodies inadvertently damaging brain cells and beginning the cascade of reactions that lead to MS.
More research will be needed to investigate this hypothetical scenario, and Kürten does point out a casein allergy alone is not enough for someone to develop MS, as there are several other known risk factors that must coalesce for the disease to progress.
The new study was published in the journal PNAS.
Source: University of Bonn
