Red meat allergy – who is ‘at steak’?
New test for a rare allergy
Those who have the allergy exhibit symptoms two to six hours after consuming red meat – which includes beef, pork, lamb or game. So far, it has been possible to detect the disposition to develop allergic symptoms using a method involving special antibodies against alpha-gal and skin testing. However, the only way to determine whether someone is at risk of a severe, clinically relevant allergic reaction has been to perform a so-called oral provocation test, or in other words, a gradually increased intake of the very foods suspected of triggering the allergy. This elaborate and risky method must be performed under medical observation. Now, the German-Luxembourgish research team has been able to replace it to a great extend with a blood test.
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In this blood test, certain white blood cells called basophils are activated by adding artificial allergens. The stronger the basophils react, the stronger they give off a fluorescent signal, which the researchers can measure. If the basophils react strongly to only trace amounts of allergens, then this is a clear indicator of alpha-gal syndrome. The team, comprising Dr. Christiane Hilger and Prof. Markus Ollert of LIH, Dr. Martine Morisset and Dr. Françoise Codreanu-Morel of the Centre Hospitalier de Luxembourg (CHL), Dr. Jörg Fischer of the University of Tübingen, as well as the leading participants Jana Mehlich, Prof. Bernadette Eberlein and Prof. Tilo Biedermann of the Technical University of Munich, published its results in the prestigious Journal of Allergy and Clinical Immunology (https://doi.org/10.1016/j.jaci.2018.06.049). The first author of the article, Jana Mehlich, was granted a junior scientist award in the frame of the annual meeting of the German Society of Allergy and Clinical Immunology (DGAKI).
The thought of biting down into a juicy barbeque steak fills some with horror – and no, not only vegetarians: in 2009, American scientists confirmed that people can develop an allergy to mammalian meat. In particular, for those who have once suffered a severe inflammatory response to a tick bite, this food intolerance becomes a serious risk. Possible consequences of eating red meat then include symptoms like skin rashes, shortness of breath, or even anaphylactic shock.
The direct trigger for this rare condition, known as alpha-gal syndrome, is a highly specific sugar named galactose-alpha-1,3-galactose, or alpha-gal for short. Alpha-gal resides on the surface of cells in mammals like cattle, pigs, lambs, or game animals. Human cells, in contrast, do not have this sugar. If alpha-gal gets into the bloodstream after meat consumption, it can provoke an allergic reaction. Although, this does not happen as soon as the food is chewed – as is the case with apple allergy for example – but in most cases only after a delay of two to six hours. It is therefore not easy to attribute the allergic symptoms to the consumption of meat.
The team of scientists and clinicians from Luxembourg and Germany has now developed further a far more efficient test for diagnosing alpha-gal syndrome. It has already been possible to identify a so-called sensitisation to alpha-gal, by detecting the presence of antibodies specific to alpha-gal. However, this method has never helped to estimate the actual severity of an allergic reaction. “So far, the only way to do that has been to perform a provocation test, where sufferers would eat increasingly large amounts – under medical supervision – until an allergic reaction occurred,” says the lead scientist of the project at LIH, Dr. Christiane Hilger, Principal Investigator of the team of Molecular and Translational Allergology. “Because of the time delay, this test has always been very elaborate and not without risks.”
For their work, the researchers analysed the behaviour of a certain class of human immune cells called basophils. A number of studies had namely revealed these cells to be of interest for advanced allergy diagnostics. They react strongly to various allergens, including the sugar alpha-gal, if an allergy exists. The scientists therefore further developed a test that contains, among other things, the allergen alpha-gal and certain fluorescent biomarkers. Upon allergen stimulation the detection of these markers on white blood cells is enforced (basophil activation test), as Dr. Hilger explains: “Blood is drawn from the patient and brought into contact with the substances of the test kit. Next, the basophils are studied by so-called flow cytometry. If the basophils have reacted strongly to the alpha-gal, they light up clearly in the test device due to the fluorescent markers. In subjects who do not present any allergic reaction, on the other hand, we find a much weaker or no fluorescent signal at all.”
In order to confirm their new approach, the research team studied blood samples from more than 50 patients. The results were clear, as Prof. Eberlein relates: “From the fluorescence signal, we were able to identify very clearly those persons who have developed a meat allergy and are at high risk of an allergic reaction when eating meat. The test should help significantly reduce the number of provocation tests that need to be performed.”
For the scientists of LIH, CHL, the University of Tübingen and the Technical University of Munich, however, the work is not over – not by a long way: “We still know very little about the causes and immunological bases of alpha-gal syndrome,” declares Dr. Hilger. “It has been observed that people tend to develop a meat allergy especially if they have had a particularly strong inflammatory response to a tick bite. We now want to find out, through our research, what substances in the ticks’ saliva trigger this reaction, and exactly what goes on in the immune system.” This continuing project of the collaboration partners is being supported with a bilateral funding by both the CORE funding scheme of the Luxembourg National Research Fund (FNR) and the Deutsche Forschungsgemeinschaft (DFG).
Original publication
Jana Mehlich, Jörg Fischer, MD, Christiane Hilger, PhD, Kyra Swiontek, MSc, Martine Morisset, MD, PhD, Françoise Codreanu-Morel, MD, Maximilian Schiener, Simon Blank, PhD, Markus Ollert, MD, Ulf Darsow, MD, Tilo Biedermann, MD, Bernadette Eberlein, MD, "The basophil activation test differentiates between patients with alpha-gal syndrome and asymptomatic alpha-gal sensitization"; Journal of Allergy and Clinical Immunology; 2018
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