University of Virginia scientists seem to have uncovered the mystery of a strange allergy to red meat caused by certain tick bites. They report that they have found a way to trigger the allergy in laboratory mice – an important step in the study of the condition. And with the help of animal experiments, they should also have identified important changes in the immune system that could be caused by these bites.
An allergy to red meat occurs when people are hypersensitive to the alpha-gal sugar produced abundantly by most mammals, but not by primates (as we do). The symptoms are similar to those of a typical food allergy, with hives and swelling common. Like other food allergies, these reactions can be life-threatening and deserve immediate medical attention.
Allergic reactions to red meat are usually delayed for hours after a meal compared to the reactions that are almost instantaneous. And unlike other food allergies, the condition is predominantly, if not exclusively, caused by the bite of certain ticks. In the US, the main culprit was the Lone Star tick, which is common in the eastern, south-eastern and southern central states, but other ticks have been associated with allergy in other countries as well.
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At this time, there are even more questions than answers to the allergy to red meat. Although the disease is likely to be rare, we do not really know how often it occurs, and we also do not know how likely it is for a single bite to lead to an allergy. Above all, we do not know how these bites trigger the allergy. For example, everyone has antibodies to Alpha-Gal, but most of us do not have a specific immune response to meat that is triggered by an antibody called IgE and that characterizes the condition.
Animal models are often a crucial early step to studying diseases or disorders in humans. The authors of the new study, published in the Journal of Immunology, say they've succeeded in succeeding. However, according to senior author and UVA researcher Loren Erickson, it was not that easy as mice naturally produce Alpha-Gal. This means that they usually have no immune response to it at all.
"Our study used mice lacking the gene for the production of Alpha-Gal. This reflects people who also lack the gene for the production of Alpha-Gal. gal, "he said to Gizmodo.
In these alpha-gal-deficient mice, they were then able to elicit the same allergic IgE response to meat consumption seen in humans with this disease. And as with humans, they induced the allergy by exposing the skin of their mice to proteins found in Lone Star ticks.
Earlier researchers claimed to develop mouse models to study allergy to red meat. According to Erickson, his team's work is likely the first published study of a clinically relevant model that allows the team to study the immune responses of these allergic mice in "real time". This is something that would be much harder to do with people.
"One of the unanswered questions in this area is what's going on with the tick bite or the tick itself, which triggers an immune response to alpha gal," Erickson said. "This model could be used to find out which chemicals / compounds in the tick trigger an immune response."
The model could also help researchers understand the way in which these chemicals cause hypersensitivity of the immune system to alpha-gal.
In their early mouse experiments, for example, the team found evidence that a particular type of immune cell, a CD4 + T cell, plays a key role in the immune response to alpha-gal, both during initial tick exposure and when the mice then eat meat.
Other studies by the authors have shown that another type of immune cell, a B cell, is often found in high concentrations in humans with allergies to red meat. And when the team created mice whose B-cells could not produce a protein called MyD88, the mice did not produce IgE in response to the ticks. MyD88 is designed to help immune cells communicate with the outside world via certain signaling pathways.
Removing MyD88 in humans to prevent allergy to red meat is not exactly feasible or even practical (in people with genetic deficiencies, the greater the likelihood that they develop severe bacterial infections). But the findings provide researchers such as Erickson and his team with new clues to track down – clues that may someday reveal a possible treatment or a way to prevent it. While some sufferers report eating meat without incident after a certain period of time, others may have to live with the allergy forever.
The team plans to further investigate the types of immune cells responsible for the formation of the IgE antibodies that make us allergic to red meat and the beginning of the entire process.
"If we can figure out what these immune mechanisms are, there is the opportunity to develop therapeutic strategies to prevent the generation of IgE antibodies to alpha-gal," said Erickson.