Increasing prevalence of galactose-α-1,3-galactose sensitization in the Danish general adult population.

BACKGROUND: Alpha-gal syndrome is a novel food allergy to the oligosaccharide galactose-α-1,3-galactose (alpha-gal) present in mammalian meat. Tick bites are considered an important route of sensitization to alpha-gal. Data on alpha-gal sensitization in the general population is scant. We utilized a unique data source of repeated population-based health examination studies to assess prevalence, time trends, risk factors, and characteristics of alpha-gal sensitization. METHODS: Alpha-gal sensitization was assessed in >11.000 adults from four health examination studies of randomly invited residents in the Copenhagen region conducted in 1990-1991, 2011-2012, 2012-2015, and 2016-2017. Alpha-gal sensitization was defined as serum specific IgE (sIgE) to alpha-gal ≥0.1 kUA/L; ≥0.35 kUA/L; ≥0.7 kUA/L; ≥3.5 kUA/L. The population was characterized according to genetically determined ABO blood group, aeroallergen sensitization, and pets at home. RESULTS: The prevalence of sIgE to alpha-gal ≥0.1 kUA/L was 1.3% in 1990-1991, 3.7% in 2012-2015 and 3.2% in 2016-2017. Of those sensitized to alpha-gal >97% reported to consume red meat at least once a week, even for sIgE to alpha-gal ≥3.5 kUA/L. Male sex, older age, aeroallergen sensitization, cat at home, and blood group A were associated with increased odds of alpha-gal sensitization. The known protective effect of blood group B was confirmed. CONCLUSION: In this general adult population, the prevalence of alpha-gal sensitization had doubled from 1990-1991 to 2016-2017. This could potentially be due to increased tick exposure and an increased atopic predisposition.

[TWO CASES OF α-GAL SYNDROME CAUSED BY INGESTION OF WILD BOAR MEAT].

α-Gal syndrome (AGS) is an allergic reaction to galactose-α-1,3-galactose (α-gal) found in the salivary glands of ticks, mammalian meat excluding primates, and some antibody preparations, such as cetuximab. We report two cases of AGS diagnosed after ingestion of wild boar meat. Patient 1, a male in his 70s, developed anaphylactic shock about 3 h after eating wild boar meat. He was transported to our acute and critical care center in Nagasaki University Hospital because he had difficulty in moving. Patient 2, a female in her 60s, developed a skin rash about 2.5 h after ingesting wild boar meat. After visiting our department to investigate the cause of the disease, the sera of both patients were found to be positive for α-gal specific IgE antibody and were diagnosed with AGS caused by ingestion of wild boar meat. Reports of AGS diagnosed after ingestion of wild boar meat are rare in Japan. Compared with other prefectures, the consumption of wild boar meat in Nagasaki is relatively high in Japan. In the past 10 years, four cases of AGS were diagnosed at our department, half of which were caused by the ingestion of wild boar meat, the ratio is possibly higher than that in other prefectures in Japan.

Unraveling Alpha-Gal Syndrome: A Case Study of a Rare Meat Allergy.

Allergies are a very common pathology and their manifestations consist of a spectrum of presentations, ranging from minimal discomfort like a runny nose to lethal reactions like anaphylaxis and death. Meat allergy is not a very common form of allergy, even though there is a relatively high level of meat consumption. One of the rare forms of non-primate mammalian meat allergy is alpha-gal syndrome (AGS). It is related to IgE antibodies specific for galactose-α-1,3-galactose (α-Gal). It is triggered in sensitized individuals due to multiple bites of lone star tick bites (Amblyomma americanum). Here we present a 63-year-old male with a complaint of recurrent hives and tongue swelling, developed recently after traveling to Twinsburg, OH. There is no significant history of any allergic conditions. Vital signs were stable with a normal physical examination. The patient had normal routine labs including eosinophil count, thyroid-stimulating hormone (TSH), iron panel, and negative HIV. Allergy testing showed normal total IgE but increased levels of IgE for allergens like beef, lamb, and pork (18.4, 6.71, and 7.62 respectively) and greatly increased levels of IgE for alpha-gal (42.7). Sensitization to alpha-gal can cause delayed allergic symptoms upon consuming various non-primate mammalian types of meat, particularly beef, pork, and lamb. Conditions like AGS are rare and can be missed as an initial diagnosis in many patients. A high degree of vigilance is required to diagnose such conditions.

Alpha-Gal Syndrome: An Underrated Serious Disease and a Potential Future Challenge.

Over the past decades, red meat allergy, also known as mammalian meat allergy, which manifests differently from classic food allergies, has been reported in different countries and regions, including China. The allergen of this disease is not a protein but an oligosaccharide: galactose-α-1,3-galactose, i.e., alpha-gal or α-gal. Therefore, this clinical syndrome is also called α-gal syndrome (AGS). It clinically manifests as delayed anaphylaxis, i.e., patients generally develop allergic symptoms 2-6 h after ingesting red meat. This clinical manifestation is believed to be related to sensitization to α-gal after tick bites. Sensitized individuals may also develop anaphylaxis after ingesting food and medicine or being exposed to medical equipment containing α-gal, such as cetuximab and gelatin. Here, the literature on AGS is reviewed for a better understanding of its pathogenesis, clinical diagnosis, and treatment.

Thyroglobulin specific IgE and a possible link to suspected penicillin induced allergic skin manifestations - cross sectional study.

Porcine thyroglobulin was important in the discovery of alpha-Gal allergy. Here, the linkage of porcine thyroglobulin-specific IgE with IgE positivity to routinely assessed allergens and to the incoming diagnosis within a population of suspected atopic individuals is explored. IgE, IgA, total IgG and IgG subclasses to porcine thyroglobulin, IgE to bovine, human thyroglobulin and meat extract were measured with ELISA. The following correlations were observed in IgE binding to porcine and bovine thyroglobulin (r = 0.910, p = 1x10-17), porcine and human thyroglobulin (r = 0.635, p = 4x10-6), human and bovine thyroglobulin (r = 0.746, p = 6x10-9) and porcine thyroglobulin and meat extract (r = 0.482, p = 0.0009). Only one out of ten samples which showed binding to porcine thyroglobulin in ELISA tested positive with ImmunoCAP alpha-Gal, implying different epitope/s. Increased IgE binding was detected towards a more electronegative fraction of porcine thyroglobulin separated according to charge and the binding could be partially inhibited by galactose. Anti-thyroglobulin IgE was found in 29.7% of the population, in subjects who were significantly younger, p < 0.0001 and it occurred more frequently in patients referred for testing penicillin specific IgE (OR 2.48, p = 0.0059) and were negative. IgE specific to porcine, bovine and possibly human thyroglobulin may be implicated in post-infectious skin manifestation misinterpreted as penicillin allergy.

A case of alpha-gal syndrome: Recall urticaria and 10 years of measurements of IgE to galactose-α-1,3-galactose.

Alpha-gal IgE level can change rapidly. Reassessment of a patient's alpha-gal IgE level may be helpful in the patient's clinical follow-up. Pruritus related to the site of a previous tick bite strengthens the diagnosis of alpha-gal syndrome.

Mammalian Meat Allergy and IgE to Alpha-Gal in Central Virginia: Findings From a COVID-19 Vaccine and Patient Cohort.

BACKGROUND: IgE to galactose-alpha-1,3-galactose (alpha-gal) is linked to tick bites and an important cause of anaphylaxis and urticarial reactions to mammalian meat. The alpha-gal syndrome (AGS) is recognized as being common in the southeastern United States. However, prevalence studies are lacking and open questions remain about risk factors and clinical presentation of alpha-gal sensitization. OBJECTIVE: Here we characterized the prevalence as well as the presentation and risk factors of AGS and alpha-gal IgE sensitization in adults in central Virginia recruited without regard to the history of allergic disease. METHODS: Adults in central Virginia, primarily University of Virginia Health employees, were recruited as part of a COVID-19 vaccine study. Subjects provided at least one blood sample and answered questionnaires about medical and dietary history. We used ImmunoCAP for IgE assays and assessed the ABO blood group by reverse typing using stored serum. We also investigated biobanked serum from COVID-19 patients. RESULTS: Median age of the 267 enrollees was 42 years, 76% were female, and 43 (16%) were sensitized to alpha-gal (cutoff of 0.1 IU/mL), of which mammalian meat allergy was reported by seven (2.6%). Sensitized subjects (1) were older, (2) had higher total IgE levels but a similar frequency of IgE to common respiratory allergens, and (3) were more likely to report tick bites than were nonsensitized subjects. Among those who were sensitized, alpha-gal IgE levels were higher among meat-allergic than nonallergic subjects (geometric mean, 9.0 vs 0.5 IU/mL; P < .001). Mammalian meat and dairy consumption was common in individuals with low-level sensitization. CONCLUSION: In central Virginia, AGS is a dominant cause of adult food allergy with a prevalence approaching or exceeding 2%.

Alpha-Gal, epitope responsible for allergy to red meat, in the Mediterranean tick Hyalomma lusitanicum.

Alpha-Gal/α-Gal is an oligosaccharide produced by non-primate mammals. Humans have developed an immune response mediated by anti-α-Gal antibodies that can trigger an allergic reaction and cause anaphylaxis. In recent years, cases of patients with delayed allergic reaction to mammalian meat have been reported worldwide. In Spain, these cases have been related to the species Ixodes ricinus L. (Ixodida: Ixodidae), whose distribution is located in the north of the country. In this work, the presence of α-Gal in water-soluble extracts from samples of salivary glands and digestive tracts of Hyalomma lusitanicum Koch (Ixodida: Ixodidae) both engorged and collected from vegetation were studied. The presence of that epitope was confirmed by the presence of reactive proteins of >250 kDa in both samples. The highest concentrations of α-Gal were detected in salivary glands. Neither sex nor diet influenced the concentration of α-Gal, which seems to indicate its endogenous production and its possible inoculation to the host during tick feeding.

Alpha-gal syndrome: when treatment of hypovolemic shock can lead to anaphylaxis.

Delayed anaphylaxis after ingestion of red meat because of galactose-alpha-1,3-galactose (alpha-gal) syndrome has increased in recent years. The mechanism involves an immunoglobulin E reaction to alpha-gal, a molecule found in mammalian meat, dairy products, medications and excipients containing mammalian-derived components, and tick salivary glycans. Sensitization occurs due to the bite of a lone star tick and the transmission of alpha-gal molecules into person's bloodstream. We describe a case of alpha-gal syndrome with severe food, drug, and perioperative allergy in which anaphylaxis with hypovolemic shock occurred immediately after an emergency surgical procedure, when a gelatin-containing drug was injected. This case study confirms that the clinical manifestations of alpha-gal syndrome could be different depending on the route of administration, with immediate reactions if an alpha-gal-containing drug is injected and delayed type allergic manifestations occurring several hours after oral intake. The purpose of this report is to highlight the importance of risk communication in case of exposure to medical products and surgical procedures of patients with alpha-gal syndrome and to encourage drug manufacturers to indicate clearly the origin of excipients in product literature.

Red Meat Hypersensitivity and Probable Alpha-Gal Syndrome: Prevalence Among Adolescents.

INTRODUCTION: It is unknown whether late adolescents represent a particular risk group for the development of red meat hypersensitivity (RMH) and alpha-gal syndrome (AGS). This age group's physiological changes and eating habits could play a determining role. This study aimed to estimate the self-reported prevalence of RMH and probable AGS among late adolescents. METHODS: A cross-sectional study analyzed a sample of 1992 Mexican adolescents between 15 and 18 years of age. The data were obtained with a previously validated questionnaire that asked about the clinical manifestations related to red meat intake. Confidence intervals at 95% (95% CI) were estimated for proportions. RESULTS: In total, there were 19 adolescents with RMH, a prevalence of 1.0% (95% CI: 0.6-1.5%). The main red meats related to symptoms were pork (89.5%), beef (21.1%), lamb (10.5%), and mutton (5.1%). The most frequent manifestations of RMH were gastrointestinal (73.7%), respiratory (63.2%), and cutaneous (63.2%). Once the symptoms were grouped, there were two cases of urticaria (2/19, 10.5%) and six cases with probable anaphylaxis (6/19, 31.6%). Finally, three adolescents were considered probable cases of AGS, which represents a prevalence of 0.15% (95% CI: 0.1-0.4%). CONCLUSION: Although the prevalence of RMH in late adolescents is low, early detection is justified because approximately one-third present with severe symptoms.

Gene-edited pigs: a translational model for human food allergy against alpha-Gal and anaphylaxis.

The prevalence of food allergy is rising and is estimated to approach 10%. Red meat allergy is the first known food allergy elicited by immunoglobulin E (IgE) antibodies recognizing a carbohydrate. Due to the loss of function of the alpha-1,3-galactosyltransferase (GGTA1) gene in humans, the disaccharide galactose-α-1,3-galactose (α-Gal) cannot be synthesized and therefore became immunogenic. IgE sensitization is elicited through the skin by repetitive tick bites transmitting α-Gal. The underlying mechanisms regarding innate and adaptive immune cell activation, including the B-cell isotype switch to IgE, are poorly understood, requiring further research and physiologically relevant animal models. Here, we describe a new animal model of red meat allergy using percutaneous α-Gal sensitization of gene-edited GGTA1-deficient pigs. Total and α-Gal-specific IgG, IgG1, IgG2, IgG4, and IgE levels were tracked. Further key factors associated with allergic skin inflammation, type 2 immunity, and allergy development were measured in PBMCs and skin samples. Significant increases in α-Gal-specific IgG1 and IgE levels indicated successful sensitization to the allergen α-Gal. Intracutaneous sensitizations with α-Gal recruited lymphocytes to the skin, including elevated numbers of T helper 2 (Th2) cells. Finally, α-Gal-sensitized pigs not only recognized α-Gal as non-self-antigen following α-Gal exposure through the skin but also developed anaphylaxis upon antigen challenge. Based on the similarities between the porcine and human skin, this new large animal model for α-Gal allergy should help to unveil the consecutive steps of cutaneous sensitization and aid the development of prophylactic and treatment interventions.

Electrochemical bioplatform to manage alpha-gal syndrome by tracking the carbohydrate allergen in meat.

This work presents the first bioplatform described to date for the determination of galactose-α-1,3-galactose (α-Gal), a non-primate mammalian oligosaccharide responsible for almost all cases of red meat allergy. The bioplatform is based on the implementation of an indirect competitive immunoassay and enzymatic labeling with the enzyme horseradish peroxidase (HRP) built on the surface of magnetic microparticles (MBs) and amperometric transduction on screen-printed carbon electrodes (SPCEs) using the H2O2/hydroquinone (HQ) system. The target α-Gal competed with biotinylated α-Gal immobilized on the surface of neutravidin-modified MBs for the limited immunorecognition sites of a detection antibody enzymatically labeled with an HRP-conjugated secondary antibody. The resulting magnetic immunoconjugates were trapped on the surface of the SPCE working electrode and amperometric transduction was performed, providing a cathodic current variation inversely proportional to the concentration of α-Gal in the analyzed sample. The developed biotool was optimized, characterized and applied with satisfactory results to the determination of the target allergen in different samples of raw and processed meats.

Tick bites, IgE to galactose-alpha-1,3-galactose and urticarial or anaphylactic reactions to mammalian meat: The alpha-gal syndrome.

The recent recognition of a syndrome of tick-acquired mammalian meat allergy has transformed the previously held view that mammalian meat is an uncommon allergen. The syndrome, mediated by IgE antibodies against the oligosaccharide galactose-alpha-1,3-galactose (alpha-gal), can also involve reactions to visceral organs, dairy, gelatin and other products, including medications sourced from non-primate mammals. Thus, fittingly, this allergic disorder is now called the alpha-gal syndrome (AGS). The syndrome is strikingly regional, reflecting the important role of tick bites in sensitization, and is more common in demographic groups at risk of tick exposure. Reactions in AGS are delayed, often by 2-6 h after ingestion of mammalian meat. In addition to classic allergic symptomatology such as urticaria and anaphylaxis, AGS is increasingly recognized as a cause of isolated gastrointestinal morbidity and alpha-gal sensitization has also been linked with cardiovascular disease. The unusual link with tick bites may be explained by the fact that allergic cells and mediators are mobilized to the site of tick bites and play a role in resistance against ticks and tick-borne infections. IgE directed to alpha-gal is likely an incidental consequence of what is otherwise an adaptive immune strategy for host defense against endo- and ectoparasites, including ticks.

Alpha-Gal IgE Prevalence Patterns in the United States: An Investigation of 3,000 Military Recruits.

BACKGROUND: IgE to the oligosaccharide galactose-alpha-1,3-galactose (alpha-gal) is an important cause of allergic reactions to mammalian meat. The "alpha-gal syndrome" is strongly associated with a preceding history of tick bites and in the United States is most commonly reported in parts of the southeast, but there has been limited investigation into national alpha-gal sensitization patterns and the relevance of other risk factors. OBJECTIVE: To systematically investigate alpha-gal IgE prevalence, regional patterns, and risk factors. METHODS: Alpha-gal IgE was measured by ImmunoCAP in biobanked serum samples collected from 3000 service members who presented for intake to 1 of 10 military bases in the central/eastern United States. Alpha-gal IgE sensitization (cutoff 0.1 international units/mL) was related to home of record at enlistment. RESULTS: Of the cohort, 2456 (81.9%) subjects were male, median age was 19 years (interquartile range: 18-22 years), and alpha-gal IgE was detected in 179 (6.0%). Home of record spanned all 50 states, with a median of 36 recruits per state (range: 3-261). The highest prevalence rates were in Arkansas (39%), Oklahoma (35%), and Missouri (29%), with several other southeastern states >10%. Granular mapping revealed sensitization patterns that closely mimicked county-level Amblyomma americanum reports and Ehrlichia chaffeensis infections. Sensitization was associated with male sex, rural residence, and White race in univariate and multivariable models. CONCLUSIONS: In this systematic survey, the prevalence of alpha-gal IgE among incoming military personnel was 6.0%. There were significant regional differences, with an overall pattern consistent with the known range of the lone star tick (A. americanum) and highest frequency in an area including Arkansas, Oklahoma, and Missouri.

IgE and anaphylaxis specific to the carbohydrate alpha-gal depend on IL-4.

BACKGROUND: Alpha-gal (Galα1-3Galß1-4GlcNAc) is a carbohydrate with the potential to elicit fatal allergic reactions to mammalian meat and drugs of mammalian origin. This type of allergy is induced by tick bites, and therapeutic options for this skin-driven food allergy are limited to the avoidance of the allergen and treatment of symptoms. Thus, a better understanding of the immune mechanisms resulting in sensitization through the skin is crucial, especially in the case of a carbohydrate allergen for which underlying immune responses are poorly understood. OBJECTIVE: We aimed to establish a mouse model of alpha-gal allergy for in-depth immunologic analyses. METHODS: Alpha-galactosyltransferase 1-deficient mice devoid of alpha-gal glycosylations were sensitized with the alpha-gal-carrying self-protein mouse serum albumin by repetitive intracutaneous injections in combination with the adjuvant aluminum hydroxide. The role of basophils and IL-4 in sensitization was investigated by antibody-mediated depletion. RESULTS: Alpha-gal-sensitized mice displayed increased levels of alpha-gal-specific IgE and IgG1 and developed systemic anaphylaxis on challenge with both alpha-gal-containing glycoproteins and glycolipids. In accordance with alpha-gal-allergic patients, we detected elevated numbers of basophils at the site of sensitization as well as increased numbers of alpha-gal-specific B cells, germinal center B cells, and B cells of IgE and IgG1 isotypes in skin-draining lymph nodes. By depleting IL-4 during sensitization, we demonstrated for the first time that sensitization and elicitation of allergy to alpha-gal and correspondingly to a carbohydrate allergen is dependent on IL-4. CONCLUSION: These findings establish IL-4 as a potential target to interfere with alpha-gal allergy elicited by tick bites.

Tick bite-induced Alpha-Gal Syndrome and Immunologic Responses in an Alpha-Gal Deficient Murine Model.

Introduction: Alpha-Gal Syndrome (AGS) is a delayed allergic reaction due to specific IgE antibodies targeting galactose-α-1,3-galactose (α-gal), a carbohydrate found in red meat. This condition has gained significant attention globally due to its increasing prevalence, with more than 450,000 cases estimated in the United States alone. Previous research has established a connection between AGS and tick bites, which sensitize individuals to α-gal antigens and elevate the levels of α-gal specific IgE. However, the precise mechanism by which tick bites influence the hosts immune system and contribute to the development of AGS remains poorly understood. This study investigates various factors related to ticks and the host associated with the development of AGS following a tick bite, using mice with a targeted disruption of alpha-1,3-galactosyltransferase (AGKO) as a model organism. Methods: Lone-star tick (Amblyomma americanum) and gulf-coast tick (Amblyomma maculatum) nymphs were used to sensitize AGKO mice, followed by pork meat challenge. Tick bite site biopsies from sensitized and non-sensitized mice were subjected to mRNA gene expression analysis to assess the host immune response. Antibody responses in sensitized mice were also determined. Results: Our results showed a significant increase in the titer of total IgE, IgG1, and α-gal IgG1 antibodies in the lone-star tick-sensitized AGKO mice compared to the gulf-coast tick-sensitized mice. Pork challenge in Am. americanum -sensitized mice led to a decline in body temperature after the meat challenge. Gene expression analysis revealed that Am. americanum bites direct mouse immunity toward Th2 and facilitate host sensitization to the α-gal antigen, while Am. maculatum did not. Conclusion: This study supports the hypothesis that specific tick species may increase the risk of developing α-gal-specific IgE and hypersensitivity reactions or AGS, thereby providing opportunities for future research on the mechanistic role of tick and host-related factors in AGS development.

The Feline and the Swine: A Peculiar Case in an Allergy Clinic.

Cross-reactivity between mammalian proteins, such as that in Pork Cat Syndrome, remains a topic of great interest. This syndrome, characterized by an immunoglobulin E (IgE)-mediated response to porcine albumin triggered by sensitization through cat epithelium, has been sparsely documented. We discuss a 41-year-old female who developed a pruritic rash within 30 minutes of consuming pork. Notably, she exhibited elevated serum IgE levels with specific reactions to cat dander, dog dander, and pork. A skin prick test for pork was positive. The patient was treated conservatively with allergen avoidance, vitamin D supplementation, fexofenadine, and doxycycline for systemic reactions, and topical corticosteroids for localized skin reactions, yielding a resolution of symptoms. This case underscores the significance of recognizing rare cross-reactivities in allergy and immunology and the manifestations of Pork Cat Syndrome, necessitating a comprehensive patient history and awareness for improved diagnosis and management.

Delayed Hypersensitivity Reaction to Infliximab Due to Mammalian Meat Allergy.

Mammalian meat allergy is a delayed immunoglobulin E (IgE) mediated hypersensitivity reaction to galactose-alpha-1,3-galactose (alpha-gal). Alpha-gal is an oligosaccharide present on glycoproteins and glycolipids of nonprimate mammals as well as biologic agents prepared using mammalian cells including infliximab. We describe a pediatric patient with Crohn's disease who developed urticaria and pruritus roughly 6 hours after her very first infliximab infusion that progressed to chronic urticaria following subsequent infliximab infusions. She was diagnosed with mammalian meat allergy based on an elevated serum IgE level directed against alpha-gal. Her symptoms resolved once infliximab infusions were discontinued and did not recur after commencing therapy with adalimumab.

Alpha-gal Syndrome - A Case Report of Tick-Borne Anaphylactic Shock.

The most common cause of vasoplegic shock in critical care is sepsis. However, although rarely and only in specifically sensitised individuals previously bitten by a tick, red meat may provoke a delayed allergic reaction called an alpha-gal syndrome. We present a case of a protracted life-threatening manifestation of alpha-gal syndrome, which, due to an unusual absence of typical features of anaphylaxis can masquerade as septic shock and calls attention to the premature diagnostic closure as a contributor to diagnostic error. Alpha-gal syndrome is a relatively new, but increasingly recognised health issue. We propose that alpha-gal syndrome should be considered in the differential diagnosis of vasoplegic shock of unclear aetiology even in the absence of typical allergic symptomatology and typical allergen exposure since alpha-gal is present in a wide variety of carriers. LEARNING POINTS: Alpha-gal syndrome, otherwise known as "red meat allergy", is a potentially life-threatening allergic syndrome induced by the immunological properties of tick saliva.A typical case of alpha-gal syndrome is a patient bitten by a tick who develops an allergic reaction, anaphylaxis or anaphylactic shock even after an ingestion of a significant amount of alpha-gal, typically present in red mammalian meat or organs.As global warming continues, we may expect tick-borne diseases to spread wider around the globe and due to the possibility of complete absence of typical allergic symptomatology and the delayed onset of symptoms, this syndrome needs to be considered when encountering vasoplegic shock of uncertain origin.

Bos d 13, A Novel Heat-Stable Beef Allergen.

SCOPE: Red meat, a staple food of Western diets, can also induce IgE-mediated allergic reactions. Yet, apart from the heat-labile protein serum albumin and the carbohydrate α-Gal, the molecules causing allergic reactions to red meat remain unknown. METHODS AND RESULTS: IgE reactivity profiles of beef-sensitized individuals are analyzed by IgE-immunoblotting with protein extracts from raw and cooked beef. Two IgE-reactive proteins are identified by peptide mass fingerprinting as myosinlight chain 1 (MYL1) and myosin light chain 3 (MYL3) in cooked beef extract and are designated Bos d 13 isoallergens. MYL1 and MYL3 are produced recombinantly in Escherichia coli. ELISAs proved their IgE reactivity and circular dichroism analysis showed that they represent folded molecules with remarkable thermal stability. In vitro gastrointestinal digestion experiments showed the higher stability of rMYL1 as compared to rMYL3. Exposure of a monolayer of Caco-2 cells to rMYL1 indicated that the molecule is able to cross intestinal epithelial cells without disturbing the integrity of the tight junctions, suggesting the sensitizing capacity of MYL1. CONCLUSION: MYLs are identified as novel heat-stable bovine meat allergens.