A real milk allergy occurs in about 3-5% of European children and more rarely in adults.
The disease is different from lactose intolerance, in which a lack of the enzyme lactase results in the inability to properly break down lactose, a sugar found in milk products.
In the case of a milk allergy, the immune system itself reacts with an immune response against milk proteins. Specialized immune cells are formed, which produce antibodies against the milk proteins and so trigger a potentially much more dangerous allergic reaction.
The milk protein beta-lactoglobulin, a relevant agent for allergic reactions, literally "pockets" a metabolite of vitamin A called retinoic acid.
This, however, would require cows to receive a sufficient supply of the vitamin, for example, through an abundance of green fodder.
Loading with retinoic acid
If infants become allergic to cow's milk, their bodies produce Th2 lymphocytes. These are specialized immune cells that produce antibodies to fight milk proteins as part of the immune system.
One of the most important of these so-called milk allergens is the protein Bos d 5. Also known as beta-lactoglobulin, it is part of a family of proteins known as the lipocalins.
"This special protein family is characterized by molecular pockets that can take in small molecules like retinoic acid, which is a metabolite of vitamin A," said study author Karin Hufnagl.
"Our study showed that an 'empty' milk protein supports the activation of Th2 lymphocytes and so initiates an allergic chain reaction.”
According to fellow researcher Erika Jensen-Jarolim, an adequate loading of the milk protein could prevent small children or even adults become sensitized and express a milk allergy.
No artificial supplements
Hufnagl said a sufficient supply of vitamin A to the milk producers, i.e. the cows, could counteract the effect in which a harmless food protein is converted into a milk allergen.
It is uncertain, however, whether the positive effect of natural vitamin A shown in the study can also be achieved through dietary supplements.
"Artificial supplementation of a diet with vitamins may not achieve the same effect as natural agents and will likely result in inadequate loading of the milk allergen,” Hufnagl said.
“It is therefore necessary to supply vitamin A to an appropriate extent during the keeping or feeding of the animals. This can be achieved, for example, by increasing the supply of green fodder.”
Hufnagl added that further studies on the subject need to be carried out.
Retinoic acid prevents immunogenicity of milk lipocalin Bos d 5 through binding to its immunodominant T-cell epitope
Authors: Hufnagl K., Ghosh D., Wagner S., Fiocchi A., Dada L., Bianchini R., Braun N., Steinborn R., Hofer M., Blaschitz M., Roth G., Hofstetter G., Roth-Walter F., Pacios LF. and Jensen-Jarolim E.
Source: Scientific Reports