Some babies are born with immune cells primed to cause food allergies, a new study suggests.
Umbilical cord blood of Australian infants who developed food allergies was loaded with overactive versions of immune cells called monocytes, researchers report in the Jan. 13 Science Translational Medicine. Those overexcited cells may push other immune cells to become allergy-causing cells, immunology researcher Yuxia Zhang of the Walter and Eliza Hall Institute of Medical Research in Parkville, Australia, and colleagues discovered. The findings may help researchers better understand how food allergies develop and to devise strategies to prevent these potentially life-threatening immune reactions.
As many as 15 million people in the United States — including an estimated 4 to 6 percent of children — have allergies to such foods as milk, eggs, peanuts and shellfish. In Australia, the rate is even higher: About 10 percent of children in a recent study in Melbourne had food allergies. Food allergies are on the rise and no one knows why, says Anne Marie Singh, a pediatric allergist and immunologist at Northwestern University’s Feinberg School of Medicine in Chicago. Research such as Zhang and colleagues’ may help uncover the mechanism behind that increase, she says.
The new results come from an ongoing study called the Barwon Infant Study, which is collecting data on more than 1,000 babies born from 2010 to 2013 in the Barwon region in southeastern Australia. The food allergy conclusions come from analyzing data from 697 babies who had fresh blood taken from their umbilical cords immediately after birth and who had been tested for food allergies at age 1.
Children who developed food allergies tended to have monocytes in their cord blood that reacted more strongly to components of bacterial cell walls than did monocytes from kids who didn’t end up with food allergies. How eagerly these white blood cells attack the cell wall component is a measure of immune system activity. Normally, a strong response is good; it means the immune cells are ready to fight bacteria and viruses. But for food-allergic kids, the pugnacious monocytes may be an early warning sign that children’s immune systems might go on to attack harmless food proteins.
Overactive monocytes make more inflammation-stimulating chemicals, called cytokines, than normal monocytes do, the researchers found. Those cytokines may push untrained immune cells called T cells into becoming allergy-provoking T helper 2 cells instead of T regulatory cells, which help quiet immune reactions, the researchers think. Another cytokine called IL2 made by the T cells may prevent the cells from morphing into allergy inducers, the researchers say.
Not all of the kids who had the hyperexcitable cells went on to have allergic reactions to foods at age 1, though. “I don’t think you could look at our data and cleanly predict a group of children who will go on to develop food allergies,” says coauthor Peter Vuillermin, a pediatrician at Deakin University in Geelong, Australia, who helps lead the Barwon Infant Study.
James R. Baker Jr. calls the new data “intriguing,” but says they “fly in the face of some dogma.” Usually, a strong inflammatory reaction in babies is associated with a healthy immune response to infections and vaccines, not with allergies, says Baker, an allergist and immunologist at the University of Michigan and chief executive officer of the nonprofit Food Allergy Research and Education. These results don’t indicate how the immune system gets primed, nor do they demonstrate exactly how or why the shift toward allergies happens in some children but not others.
Singh says she didn’t find the results counterintuitive. Good evidence suggests that things that occur during pregnancy could influence the development of allergic disease in kids, she says, but “there are so many complex factors we can’t tease out a direct cause and effect.” The study picks out “one small piece in a very, very big puzzle.” This same process may also happen with other types of allergic disease such as eczema and asthma, she says.
An editor’s note included with the study suggests that “anti-inflammatory strategies should be considered in preventing food allergy.” Baker sees no justification for giving babies anti-inflammatory drugs. “That just seems wholly crazy,” he says.
Vuillermin agrees that babies shouldn’t get anti-inflammatory drugs, but his research suggests some other early actions might head off food allergies. Some previous studies have indicated that friendly microbes may help protect against food allergies (SN: 10/4/14, p. 15). Vuillermin thinks that manipulating the types of bacteria mothers carry in pregnancy might alter the production of inflammatory cytokines and train babies’ immune systems not to develop allergies.
Editor’s note: This story was updated February 3, 2016, to clarify the location of the Barwon region and to correct details about the link between having hyperexcited monocytes and the development of a food allergy.