Gut bacteria appear important for overcoming milk allergy

A research team led by the RIKEN Center for Integrative Medical Sciences has discovered a link between gut bacteria and the success of milk-allergy oral immunotherapy. Published in the journal Allergology International, their study may help in the development of more effective oral immunotherapies, perhaps by combining them with probiotic supplements.

Although most children with cow’s milk allergies eventually grow out of it, some are faced with a lifelong challenge to avoid all foods that include milk. Researchers have found that milk allergy is improved by oral immunotherapy, a treatment in which patients purposely drink small amounts of milk. Unfortunately, while allergic reactions are controlled during treatment, tolerance usually disappears soon after the treatment ends.

Gut bacteria are thought to help reduce allergic reactions to some foods, but little is known about the link between these bacteria and oral immunotherapy for milk allergy. The RIKEN team examined 32 children with cow’s milk allergy who received oral immunotherapy, with the first month being conducted in a hospital.

“Oral immunotherapy is not without risk,” said team leader Hiroshi Ohno. “We closely monitored the children in the hospital, and in fact four children had such severe reactions to the milk that we could not allow them to continue the treatment.”

The remaining 28 children completed an additional 12 months of treatment at home, after which point they avoided milk for two weeks; they were then tested on a double-blind, placebo-controlled food challenge to see if they could still tolerate milk without any allergic reactions. During the food challenge, children were initially given a tiny amount of placebo or milk — only 0.01 mL — which was gradually increased every 20 minutes until they had an allergic reaction or until they could drink the final 30 mL without a reaction.

The researchers found that, during treatment, immunological markers for cow’s milk allergy improved, and bacteria in the gut changed. Nevertheless, after two weeks of avoiding milk, only seven of the 28 children passed the food challenge, even though they had been able to drink milk safely at the end of the treatment.

To understand why the treatment worked for these seven children but not the others, the team looked for the clinical factors and types of gut bacteria that were related to successful treatment. Of the clinical factors, unsuccessful treatment was more likely in children who were being treated for eczema or asthma and in children who initially had higher levels of milk-protein antibodies. Among the gut bacteria, the presence of Bifidobacterium — a genus of beneficial bacteria in the Bifidobacteriaceae family — was related to a higher chance of successful treatment. In fact, only children who passed the final food challenge showed an increasing trend in these bacteria over the course of treatment. This is good news as, while the first two factors are difficult to change, the types of bacteria in one’s gut are not set in stone.

“With this study, we have identified gut environmental factors that help establish immune tolerance against cow’s milk allergy via oral immunotherapy,” Ohno said. “The next step is to examine the mechanisms underlying this phenomenon and to develop ways to improve the effectiveness of oral immunotherapy, such as the addition of probiotic supplements.”

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