Distribution of Gal alpha 1----3Gal beta 1----4GlcNAc residues on secreted mammalian glycoproteins (thyroglobulin, fibrinogen, and immunoglobulin G) as measured by a sensitive solid-phase radioimmunoassay

The α-Gal epitope - the cause of a global allergic disease

The galactose-α-1,3-galactose (α-Gal) epitope is the cause of a global allergic disease, the α-Gal syndrome (AGS). It is a severe form of allergy to food and products of mammalian origin where IgE against the mammalian carbohydrate, α-Gal, is the cause of the allergic reactions. Allergic reactions triggered by parenterally administered α-Gal sources appear immediately, but those triggered via the oral route appear with a latency of several hours. The α-Gal epitope is highly immunogenic to humans, apes and old-world monkeys, all of which produce anti-α-Gal antibodies of the IgM, IgA and IgG subclasses. Strong evidence suggests that in susceptible individuals, class switch to IgE occurs after several tick bites. In this review, we discuss the strong immunogenic role of the α-Gal epitope and its structural resemblance to the blood type B antigen. We emphasize the broad abundance of α-Gal in different foods and pharmaceuticals and the allergenicity of various α-Gal containing molecules. We give an overview of the association of tick bites with the development of AGS and describe innate and adaptive immune response to tick saliva that possibly leads to sensitization to α-Gal. We further discuss a currently favored hypothesis explaining the mechanisms of the delayed effector phase of the allergic reaction to α-Gal. We highlight AGS from a clinical point of view. We review the different clinical manifestations of the disease and the prevalence of sensitization to α-Gal and AGS. The usefulness of various diagnostic tests is discussed. Finally, we provide different aspects of the management of AGS. With climate change and global warming, the tick density is increasing, and their geographic range is expanding. Thus, more people will be affected by AGS which requires more knowledge of the disease.

Accelerated Burn Healing in a Mouse Experimental Model Using α-Gal Nanoparticles

Macrophages play a pivotal role in the process of healing burns. One of the major risks in the course of burn healing, in the absence of regenerating epidermis, is infections, which greatly contribute to morbidity and mortality in such patients. Therefore, it is widely agreed that accelerating the recruitment of macrophages into burns may contribute to faster regeneration of the epidermis, thus decreasing the risk of infections. This review describes a unique method for the rapid recruitment of macrophages into burns and the activation of these macrophages to mediate accelerated regrowth of the epidermis and healing of burns. The method is based on the application of bio-degradable "α-gal" nanoparticles to burns. These nanoparticles present multiple α-gal epitopes (Galα1-3Galβ1-4GlcNAc-R), which bind the abundant natural anti-Gal antibody that constitutes ~1% of immunoglobulins in humans. Anti-Gal/α-gal nanoparticle interaction activates the complement system, resulting in localized production of the complement cleavage peptides C5a and C3a, which are highly effective chemotactic factors for monocyte-derived macrophages. The macrophages recruited into the α-gal nanoparticle-treated burns are activated following interaction between the Fc portion of anti-Gal coating the nanoparticles and the multiple Fc receptors on macrophage cell membranes. The activated macrophages secrete a variety of cytokines/growth factors that accelerate the regrowth of the epidermis and regeneration of the injured skin, thereby cutting the healing time by half. Studies on the healing of thermal injuries in the skin of anti-Gal-producing mice demonstrated a much faster recruitment of macrophages into burns treated with α-gal nanoparticles than in control burns treated with saline and healing of the burns within 6 days, whereas healing of control burns took ~12 days. α-Gal nanoparticles are non-toxic and do not cause chronic granulomas. These findings suggest that α-gal nanoparticles treatment may harness anti-Gal for inducing similar accelerated burn healing effects also in humans.

Bovine γ-globulin, lactoferrin, and lactoperoxidase are relevant bovine milk allergens in patients with α-Gal syndrome

BACKGROUND

Mammalian meat is the most common trigger of the allergic reactions in patients with α-Gal syndrome (AGS). Milk and dairy, although less often, also cause a significant number of allergic manifestations. The aim of this study was to identify α-Gal-containing bovine milk proteins with allergenic properties among AGS patients.

METHODS

Thirty-eight AGS patients with IgE to milk were included in the study. Milk proteins were analyzed for the presence of α-Gal and for binding by patients' IgE using immunoblot, ImmunoCAP, and inhibition ELISA. Allergenicity of milk and milk proteins was assessed by basophil activation test.

RESULTS

More than half of the AGS patients reported allergic reactions to milk or dairy products. Bovine γ-globulin (BGG), lactoferrin (LF), and lactoperoxidase (LPO) were identified as α-Gal carrying proteins which were recognized by AGS patients' IgE. Whey mirrored the anti-α-Gal and IgE reactivity of BGG, LF, and LPO. Eighty-nine percent of the patients displayed IgE to BGG, 91% to LF, and 57% to LPO. Inhibition of α-Gal-specific IgE binding was achieved by BGG, LF, LPO, and whey. These proteins also activated AGS patients' basophils. Interestingly, at lower concentrations, LF was the most potent inhibitor of IgE binding, and the most potent activator of basophils.

CONCLUSION

BGG, LF, and LPO were all found to be relevant milk α-Gal-containing glycoproteins that bound AGS patients' IgE antibodies and activated their basophils. These proteins are probably involved in the allergic reactions to milk in AGS patients. LPO was for the first time shown to be an allergen.

Searching for glycomic biomarkers for predicting resilience and vulnerability in a rat model of posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) is triggered by traumatic events in 10-20% of exposed subjects. N-linked glycosylation, by modifying protein functions, may provide an important environmental link predicting vulnerability. Our goals were (1) to find alterations in plasma N-glycome predicting stress-vulnerability; (2) to investigate how trauma affects N-glycome in the plasma (PGP) and in three PTSD-related brain regions (prefrontal cortex, hippocampus and amygdala; BGP), hence, uncover specific targets for PTSD treatment. We examined male (1) controls, (2) traumatized vulnerable and (3) traumatized resilient rats both before and several weeks after electric footshock. Vulnerable and resilient groups were separated by z-score analysis of behavior. Higher freezing behavior and decreased social interest were detected in vulnerable groups compared to control and resilient rats. Innate anxiety did not predict vulnerability, but pretrauma levels of PGP10(FA1G1Ga1), PGP11(FA2G2), and PGP15(FA3G2) correlated positively with it, the last one being the most sensitive. Traumatic stress induced a shift from large, elaborate N-glycans toward simpler neutral structures in the plasma of all traumatized animals and specifically in the prefrontal cortex of vulnerable rats. In plasma trauma increased PGP17(A2G2S) level in vulnerable animals. In all three brain regions, BGP11(F(6)A2B) was more abundant in vulnerable rats, while most behavioral correlations occurred in the prefrontal cortex. In conclusion, we found N-glycans (especially PGP15(FA3G2)) in plasma as possible biomarkers of vulnerability to trauma that warrants further investigation. Posttrauma PGP17(A2G2S1) increase showed overlap with human results highlighting the utility and relevance of this animal model. Prefrontal cortex is a key site of trauma-induced glycosylation changes that could modulate the behavioral outcome.

Amplifying immunogenicity of prospective Covid-19 vaccines by glycoengineering the coronavirus glycan-shield to present α-gal epitopes

The many carbohydrate chains on Covid-19 coronavirus SARS-CoV-2 and its S-protein form a glycan-shield that masks antigenic peptides and decreases uptake of inactivated virus or S-protein vaccines by APC. Studies on inactivated influenza virus and recombinant gp120 of HIV vaccines indicate that glycoengineering of glycan-shields to present α-gal epitopes (Galα1-3Galβ1-4GlcNAc-R) enables harnessing of the natural anti-Gal antibody for amplifying vaccine efficacy, as evaluated in mice producing anti-Gal. The α-gal epitope is the ligand for the natural anti-Gal antibody which constitutes ~1% of immunoglobulins in humans. Upon administration of vaccines presenting α-gal epitopes, anti-Gal binds to these epitopes at the vaccination site and forms immune complexes with the vaccines. These immune complexes are targeted for extensive uptake by APC as a result of binding of the Fc portion of immunocomplexed anti-Gal to Fc receptors on APC. This anti-Gal mediated effective uptake of vaccines by APC results in 10-200-fold higher anti-viral immune response and in 8-fold higher survival rate following challenge with a lethal dose of live influenza virus, than same vaccines lacking α-gal epitopes. It is suggested that glycoengineering of carbohydrate chains on the glycan-shield of inactivated SARS-CoV-2 or on S-protein vaccines, for presenting α-gal epitopes, will have similar amplifying effects on vaccine efficacy. α-Gal epitope synthesis on coronavirus vaccines can be achieved with recombinant α1,3galactosyltransferase, replication of the virus in cells with high α1,3galactosyltransferase activity as a result of stable transfection of cells with several copies of the α1,3galactosyltransferase gene (GGTA1), or by transduction of host cells with replication defective adenovirus containing this gene. In addition, recombinant S-protein presenting multiple α-gal epitopes on the glycan-shield may be produced in glycoengineered yeast or bacteria expression systems containing the corresponding glycosyltransferases. Prospective Covid-19 vaccines presenting α-gal epitopes may provide better protection than vaccines lacking this epitope because of increased uptake by APC.

Diagnosis & management of alpha-gal syndrome: lessons from 2,500 patients

INTRODUCTION

Alpha-gal Syndrome (AGS) is a unique allergy to non-primate mammalian meat (and derived-products) that is associated with tick bites and is due to a specific IgE antibody to the oligosaccharide galactose-α-1,3-galactose (alpha-gal). AGS has many novel features that broaden the paradigm of food allergy, including that reactions are delayed 3-6 hours after exposure and patients have frequently tolerated red meat for many years prior to the development of allergic reactions. Due to the ubiquitous inclusion of mammal-derived materials in foods, medications, personal products and stabilizing compounds, full avoidance is difficult to achieve.

AREAS COVERED

This review describes the author's experience with diagnosis, management, and design of appropriate avoidance for patients with AGS and provides clinicians with practical advice for care of these patients.

EXPERT OPINION

The number of patients with AGS is rising and may have exceeded awareness of the diagnosis amongst healthcare providers. In summarizing experience gained to thus far, we hope to create a resource for identifying and managing this unique allergic syndrome.

Dynamic Temporal Variations in Bovine Lactoferrin Glycan Structures

It has been reported previously that glycosylation of bovine lactoferrin changes over time. A detailed structural overview of these changes over the whole course of lactation, including predry period milk, is lacking. In this study, a high-throughput analysis method was applied to the glycoprofile of lactoferrin isolated from colostrum, mature, and predry period mature milk, which was analyzed over two subsequent lactation cycles for 8 cows from diverse genetic backgrounds. In addition, comparisons are made with commercial bovine lactoferrin samples. During the first 72 h, dynamic changes in lactoferrin glycosylation occurred. Shifts in the oligomannose distribution and the number of sialylated and fucosylated glycans were observed. In some cows, we observed (α2,3)-linked sialic acid in the earliest colostrum samples. The glycoprofiles appeared stable from 1 month after delivery, as well as between cows. In addition, the glycosylation profiles of commercial lactoferrins isolated from pooled mature milk were stable over the year. Lactoferrin glycosylation in the predry period resembles colostrum lactoferrin. The variations in lactoferrin glycosylation profiles, lactoferrin concentrations, and other milk parameters provide detailed information that potentially assists in unraveling the functions and biosynthesis regulation of lactoferrin glycosylation.

[Diagnostics of alpha-gal syndrome : Current standards, pitfalls and perspectives]

α-Gal syndrome results from sensitization to the carbohydrate epitope galactose-α-1,3-galactose (α‑gal). The allergen occurs in mammalian meat and innards, but also in other foods and medical products of animal origin. Allergic reactions generally occur delayed after allergen intake with a latency period, depending on the individual tolerance threshold and the influence of cofactors. Details in the patient's medical history can help to establish the suspected diagnosis of α‑gal syndrome. Confirmation of the diagnosis requires the expertise of specialists, experienced with the implementation and interpretation of in vitro and in vivo diagnostic tests. Whereas skin prick testing with commercial whole-meat extracts often does not provide reliable results, allergen-specific IgE (α-gal) is generally detectable in affected patients. Cell-based tests such as the basophil activation test are currently only employed in an experimental setting. To evaluate, whether a sensitization is clinically relevant, an in-patient oral food challenge should be performed, using for example cooked pork or porcine kidney in addition to suspected cofactors.

A bite so sweet: the glycobiology interface of tick-host-pathogen interactions

Vector-borne diseases constitute 17% of all infectious diseases in the world; among the blood-feeding arthropods, ticks transmit the highest number of pathogens. Understanding the interactions between the tick vector, the mammalian host and the pathogens circulating between them is the basis for the successful development of vaccines against ticks or the tick-transmitted pathogens as well as for the development of specific treatments against tick-borne infections. A lot of effort has been put into transcriptomic and proteomic analyses; however, the protein-carbohydrate interactions and the overall glycobiology of ticks and tick-borne pathogens has not been given the importance or priority deserved. Novel (bio)analytical techniques and their availability have immensely increased the possibilities in glycobiology research and thus novel information in the glycobiology of ticks and tick-borne pathogens is being generated at a faster pace each year. This review brings a comprehensive summary of the knowledge on both the glycosylated proteins and the glycan-binding proteins of the ticks as well as the tick-transmitted pathogens, with emphasis on the interactions allowing the infection of both the ticks and the hosts by various bacteria and tick-borne encephalitis virus.

A standardized quantitative method for detecting remnant alpha-Gal antigen in animal tissues or animal tissue-derived biomaterials and its application

Alpha-Gal (Gal) epitopes present in animal tissues are known to be the key xenoantigens that elicit xenorejection. However, a standardized method to determine Gal epitope in animal tissue-derived biomaterials does not exist. Herein, a standardized method for quantitative detection of Gal antigen was established based on an ELISA inhibition assay with Gal antibody. In this method, the key optimized experimental conditions were: (1) Gal-antigen positive and negative reference materials were developed, and used as positive and negative control in the test system, respectively; (2) A mixture of artificial Gal-BSA antigen plus Gal-negative matrix was used as the calibration standard sample, making it has similar composition with test sample; and (3) The lysis buffer was combined with the homogenate to expose the Gal antigen as much as possible. The results from validation and application experiments showed that the standardized method had good reproducibility (RSD = 12.48%), and the lower detection limit (LDL) is ~7.1 × 10¹¹ Gal epitopes/reaction. This method has been further developed into a detection Kit (Meitan 70101, China), and it has been developed as a standard method for detecting remnant immunogen of animal tissue derived medical devices, and as the industry standard has been released in China. (YY/T 1561–2017).

Meat allergy and allergens

IgE-mediated hypersensitivity to ingested animal products, including both mammalian and avian sources, is increasingly appreciated as an important form of food allergy. Traditionally described largely in children, it is now clear that allergy to meat (and animal viscera) impacts both children and adults and represents a heterogeneous group of allergic disorders with multiple distinct syndromes. The recognition of entities such as pork-cat syndrome and delayed anaphylaxis to red meat, i.e- the α-Gal syndrome, have shed light on fundamental, and in some cases newly appreciated, features of allergic disease. These include insights into routes of exposure and mechanisms of sensitization, as well as the realization that IgE-mediated reactions can be delayed by several hours. Here we review mammalian and avian meat allergy with an emphasis on the molecular allergens and pathways that contribute to disease, as well as the role of in vitro IgE testing in diagnosis and management.

Peptidomics of an in vitro digested α-Gal carrying protein revealed IgE-reactive peptides

The mammalian carbohydrate galactose-α1,3-galactose (α-Gal) causes a novel form of food allergy, red meat allergy, where patients experience severe allergic reactions several hours after red meat consumption. Here we explored gastric digestion of α-Gal glycoproteins using an in vitro model. Bovine thyroglobulin (BTG), a typical α-Gal carrying glycoprotein, was digested with pepsin. The resulting peptides were characterised by SDS PAGE, immunoblot and ImmunoCAP using sera from 20 red meat allergic patients. During pepsinolysis of BTG, a wide range of peptide bands was observed of which 14 to 17 kDa peptides remained stable throughout the gastric phase. The presence of the α-Gal epitope on the obtained peptides was demonstrated by an anti-α-Gal antibody and IgE from red meat allergic patients. The α-Gal digests were able to inhibit up to 86% of IgE reactivity to BTG. Importantly, basophil activation test demonstrated that the allergenic activity of BTG was retained after digestion in all four tested patients. Mass spectrometry-based peptidomics revealed that these peptides represent mostly internal and C-terminal parts of the protein, where the most potent IgE-binding α-Gal residues were identified at Asn₁₇₅₆, Asn₁₈₅₀ and Asn₂₂₃₁. Thus allergenic α-Gal epitopes are stable to pepsinolysis, reinforcing their role as clinically relevant food allergens.

Accurate assessment of alpha-gal syndrome using cetuximab and bovine thyroglobulin-specific IgE

SCOPE

IgE against galactose-α-1,3-galactose (α-Gal) causes alpha-gal syndrome. Bovine thyroglobulin (BTG) and cetuximab share this epitope. We aimed to determine the utility of specific IgE (sIgE) against cetuximab as compared to BTG for diagnosing alpha-gal syndrome.

METHODS AND RESULTS

Twelve patients with alpha-gal syndrome, 11 patients with immediate beef or pork allergy, 18 asymptomatic individuals with meat sensitization, and 10 non-atopic subjects were enrolled. We checked the levels of sIgE against BTG and cetuximab using the streptavidin CAP assay. Additionally, IgE reactivity to BTG and cetuximab was assessed by immunoblotting. All alpha-gal syndrome patients had a high concentration of sIgE against BTG, and cetuximab. In contrast to alpha-gal syndrome, patients with immediate allergic reactions to meat consumption and those with asymptomatic sensitization had significantly lower concentration of BTG and cetuximab sIgE, and a high prevalence of sIgE against bovine or porcine serum albumin. Although the concentration of sIgE against alpha-gal was lower in individuals with asymptomatic sensitization, IgE immunoblotting showed the presence of sIgE against α-Gal in this group.

CONCLUSION

Differentiation of alpha-gal syndrome from patients with immediate allergy to meat consumption or asymptomatic sensitization requires quantification of cetuximab- or BTG-induced sIgE via detection of IgE for α-gal.

Alpha-gal is a possible target of IgE-mediated reactivity to antivenom

BACKGROUND

Antivenoms are mammalian immunoglobulins with the ability to neutralize snake venom components and to mitigate the progression of toxic effects. Immediate hypersensitivity to antivenoms often occurs during the first administration of these heterologous antibodies. A comparable clinical situation occurred after introduction of cetuximab, a chimeric mouse-human antibody, for cancer treatment. The carbohydrate epitope galactose-alpha-1,3-galactose, located on the Fab region of cetuximab, was identified as the target responsible for IgE reactivity.

OBJECTIVE

To investigate whether serum IgE antibodies directed to the α-gal epitope are associated with hypersensitivity to equine antivenoms.

METHODS

Antivenoms were screened for α-gal epitopes via immunoblot and in comparison with cetuximab and pork kidney by IgE reactivity assays. Basophil activation tests were used to investigate reactivity to antivenoms in samples from 20 patients with specific IgE antibodies to α-gal and 10 controls. Additional IgE detection, IgE inhibition, ImmunoCAP inhibition, and skin prick tests were performed using samples from selected patients.

RESULTS

Both antivenoms and cetuximab induced positive skin prick test results in patients with sIgE to α-gal. Alpha-gal epitopes were detected by immunoblotting on antivenoms. Measurements of IgE reactivity and ImmunoCAP inhibition indicated that the antivenoms contained lower α-gal contents than cetuximab. Deglycosylation assays and IgE inhibition tests confirmed that IgE-mediated reactivity to antivenom is associated with α-gal. Antivenoms, pork kidney, and cetuximab activated basophils from patients with IgE to α-gal.

CONCLUSION

Alpha-gal is a potential target of IgE-mediated reactivity to equine antivenom and a possible cause of the high incidence of hypersensitivity reactions during the first application of equine antivenom.

The red meat allergy syndrome in Sweden

In the last decade, a novel type of food allergy presenting with severe allergic reactions several hours after consumption of red meat has been recognized. The allergic responses are due to IgE antibodies directed against the carbohydrate epitope galactose-α-1,3-galactose (α-Gal) found in mammalian meat. This review presents the red meat allergy syndrome in Sweden, discusses the features of the immune response to carbohydrates, and highlights the presence of heat stable α-Gal-containing proteins in meat.

The number of diagnosed red meat allergy cases in Sweden has increased significantly over the past few years. All patients have been tick bitten. Our recent work has shown that α-Gal is present in the European tick Ixodes ricinus (I. ricinus), thus potentially explaining the strong association between anti-α-Gal IgE and tick bites, with development of red meat allergy as a secondary phenomenon. Further studies using immunoproteomics have identified novel α-Gal-containing meat proteins that bound IgE from red meat allergic patients. Four of these proteins were stable to thermal processing pointing to the fact that the allergenicity of red meat proteins is preserved in cooked meat. In keeping with the fact that the α-Gal epitope is structurally related to the blood group B antigen, a positive association with the B-negative blood groups among our red meat allergic patients was noted. A selective IgE reactivity to the pure carbohydrate moiety was observed when investigating the specificity of the α-Gal immune response. IgE from red meat allergic patients does not recognize the other major mammalian carbohydrate, N-glycolylneuraminic acid (Neu5Gc), also present in high amounts in red meat. Furthermore, neither common cross-reactive carbohydrate determinants (CCDs) from plants nor venoms are targets of the IgE response in these patients.

Taken together, the α-Gal carbohydrate has shown to be a potentially clinically relevant allergen that should be taken into account in the diagnosis of food allergy. Many new findings in the field of red meat allergy have been obtained during the past years, but further efforts to understand the process of digestion, absorption, and delivery of α-Gal-containing molecules to the circulation are needed.

Delayed anaphylaxis to alpha-gal, an oligosaccharide in mammalian meat

IgE-mediated hypersensitivity refers to immune reactions that can be rapidly progressing and, in the case of anaphylaxis, are occasionally fatal. To that end, identification of the associated allergen is important for facilitating both education and allergen avoidance that are essential to long-term risk reduction. As the number of known exposures associated with anaphylaxis is limited, discovery of novel causative agents is crucial to evaluation and management of patients with idiopathic anaphylaxis. Within the last 10 years several apparently separate observations were recognized to be related, all of which resulted from the development of antibodies to a carbohydrate moiety on proteins. Interestingly, the exposure differed from airborne allergens but was nevertheless capable of producing anaphylactic and hypersensitivity reactions. Our recent work has identified these responses as being due to a novel IgE antibody directed against a mammalian oligosaccharide epitope, galactose-alpha-1,3-galactose (“alpha-gal”). This review will present the historical summary of the identification of cetuximab hypersensitivity due to alpha-gal IgE and discuss the non-primate mammalian meat food allergy as well as current goals and directions of our research programs.

Red meat allergic patients have a selective IgE response to the α-Gal glycan

Galactose-α-1,3-galactose (α-Gal) is a mammalian carbohydrate with significance in a novel type of food allergy. Patients with IgE against α-Gal report severe allergic symptoms 3-6 h after consumption of red meat. We investigated whether IgE from red meat allergic patients recognizes other mammalian glycans than α-Gal or glycans from the plant kingdom and insects of importance in allergy. We found that none of the 24 red meat allergic patients investigated had an IgE antibody response against the other abundant mammalian glycan N-glycolylneuraminic acid or against cross-reactive carbohydrate determinants from plant or venom sources (nCup a 1, nArt v 1, and MUXF3). Deglycosylation of an α-Gal-containing protein, bovine thyroglobulin, significantly reduced the IgE response. In conclusion, we show that red meat allergic patients have a selective IgE response to the α-Gal glycan found in red meat. Other common glycans reactive in allergic disease are not targets of red meat allergic patients' IgE.

Delayed Anaphylaxis Involving IgE to Galactose-alpha-1,3-galactose

Hypersensitivity in the allergic setting refers to immune reactions, stimulated by soluble antigens that can be rapidly progressing and, in the case of anaphylaxis, are occasionally fatal. As the number of known exposures associated with anaphylaxis is limited, identification of novel causative agents is important in facilitating both education and other allergen-specific approaches that are crucial to long-term risk management. Within the last 10 years, several seemingly separate observations were recognized to be related, all of which resulted from the development of antibodies to a carbohydrate moiety on proteins where exposure differed from airborne allergens but which were nevertheless capable of producing anaphylactic and hypersensitivity reactions. Our recent work has identified these responses as being due to a novel IgE antibody directed against a mammalian oligosaccharide epitope, galactose-alpha-1,3-galactose (alpha-gal). This review will present the history and biology of alpha-gal and discuss our current approach to management of the mammalian meat allergy and delayed anaphylaxis.

The alpha-gal story: lessons learned from connecting the dots

Anaphylaxis is a severe allergic reaction that can be rapidly progressing and fatal, and therefore establishing its cause is pivotal to long-term risk management. Our recent work has identified a novel IgE antibody response to a mammalian oligosaccharide epitope, galactose-alpha-1,3-galactose (alpha-gal). IgE to alpha-gal has been associated with 2 distinct forms of anaphylaxis: (1) immediate-onset anaphylaxis during first exposure to intravenous cetuximab and (2) delayed-onset anaphylaxis 3 to 6 hours after ingestion of mammalian food products (eg, beef and pork). Results of our studies and those of others strongly suggest that tick bites are a cause, if not the only significant cause, of IgE antibody responses to alpha-gal in the southern, eastern, and central United States; Europe; Australia; and parts of Asia. Typical immune responses to carbohydrates are considered to be T-cell independent, whereas IgE antibody production is thought to involve sequential class-switching that requires input from T cells. Therefore, establishing the mechanism of the specific IgE antibody response to alpha-gal will be an important aspect to address as this area of research continues.

Immunoproteomics of processed beef proteins reveal novel galactose-α-1,3-galactose-containing allergens

BACKGROUND

Red meat allergy presents a novel form of food allergy with severe delayed allergic reactions where IgE antibodies are directed against the carbohydrate α-Gal epitope. Food preparation and processing can influence the allergenicity of proteins. The aim of this study was to characterize the proteomic profile of different beef preparations and to investigate their α-Gal reactivity and potential allergenicity.

METHODS

Extracts from raw, boiled, fried, and medium rare prepared beef were assessed by 2D PAGE for the comparison of protein profiles. IgE-binding proteins were identified using immunoblot-coupled proteomic analysis using sera from red meat-allergic patients. Presence of the α-Gal epitope was verified using anti-α-Gal antibody and IgE inhibition immunoblot with α-Gal.

RESULTS

Multiple IgE-binding proteins were detected in the different beef preparations, many of which were also recognized by the anti-α-Gal antibody. Protein spots reacting with IgE in patient sera were analyzed by MS/MS, resulting in identification of 18 proteins with high identification scores. Seven of the 18 beef allergens identified using meat-allergic patient sera were also recognized by the anti-α-Gal monoclonal antibody, and four of them were stabile to thermal treatment. Furthermore, a dose-dependent inhibition of red meat-allergic patients' IgE to beef by α-Gal was demonstrated.

CONCLUSIONS

We show that the α-Gal epitope is commonly present in IgE-reactive beef proteins recognized by meat-allergic patients. Seven novel α-Gal-containing IgE-binding proteins were identified, of which four were stable to heat treatment. Thus, the allergenicity of red meat proteins is preserved even upon different thermal cooking.

Laminin γ-1 and collagen α-1 (VI) chain are galactose-α-1,3-galactose-bound allergens in beef

BACKGROUND

Sensitization to the carbohydrate galactose-α-1,3-galactose (α-Gal) has been reported in patients with beef allergy. However, the proteins responsible for this allergy have not yet been identified. This study aimed to identify beef proteins that predominantly react with serum IgE in Japanese patients with beef allergy.

METHODS

Sera were collected from 29 patients with beef allergy who had allergic reaction(s) such as urticaria, abdominal pain, vomiting, and anaphylactic shock after ingestion of beef and pork; the sera tested positive for IgE against beef and pork. IgE-binding proteins were detected by immunoblotting sera from the patients and identified using a combination of two-dimensional gel electrophoresis and peptide mass fingerprinting techniques. The involvement of carbohydrate in the binding of IgE to allergens was examined by periodate treatment and an inhibition assay with cetuximab by immunoblotting. Specific IgE binding to cetuximab was measured using the CAP-fluorescent enzyme immunoassay.

RESULTS

Two IgE-binding proteins (240 kDa and 140 kDa) were detected in beef extract and identified as laminin γ-1 and the collagen α-1 (VI) chain from Bos taurus, respectively. Periodate treatment or the inhibition assay resulted in the loss of IgE binding to these proteins. Immunoblotting with anti-α-Gal antibody revealed the presence of α-Gal on the 240- and 140-kDa beef proteins. The amount of IgE bound to cetuximab was significantly correlated with that to beef in the patients with beef allergy.

CONCLUSION

The carbohydrate moiety (α-Gal) on laminin γ-1 and collagen α-1 (VI) chain are possibly common IgE-reactive proteins in the Japanese patients with beef allergy.

Possible role of a cell surface carbohydrate in evolution of resistance to viral infections in old world primates

Due to inactivation of the α1,3-galactosyltransferase gene (GGTA1, or the α1,3GT gene) approximately 28 million years ago, the carbohydrate αGal (Galα1,3Galβ1,4GlcNAc) is not expressed on the cells of Old World monkeys and apes (including humans) but is expressed in all other mammals. The proposed selective advantage of this mutation for these primates is the ability to produce anti-Gal antibodies, which may be an effective immune component in neutralizing αGal-expressing pathogens. However, loss of α1,3GT expression may have been advantageous by providing natural resistance against viral pathogens that exploited the α1,3GT pathway or cell surface αGal for infection. Infections of paired cell lines with differential expression of α1,3GT showed that Sindbis viruses (SINV) preferentially replicate in α1,3GT-positive cells, whereas herpes simplex viruses type 1 and type 2 (HSV-1 and HSV-2) preferentially grow in cells lacking α1,3GT. Viral growth and spread correlated with the ability of the different viruses to successfully initiate infection in the presence or absence of α1,3GT expression. GT knockout (KO) suckling mice infected with SINV strains (AR339 and S.A.AR86) experienced significant delay in onset of disease symptoms and mortality compared to wild-type (WT) B6 suckling mice. In contrast, HSV-2-infected GT KO mice had higher viral titers in spleen and liver and exhibited significantly more focal hepatic necrosis than WT B6 mice. This study demonstrates that α1,3GT activity plays a role in the course of infections for certain viruses. Furthermore, this study has implications for the evolution of resistance to viral infections in primates.

[Update on meat allergy. α-Gal: a new epitope, a new entity?]

The association between the carbohydrate galactose-[alpha]-1,3-galactose (α-Gal) and anaphylaxis was first documented after severe hypersensitivity reactions to cetuximab, a chimeric mouse-human IgG1 monoclonal antibody approved for targeted therapy of carcinomas of colon, as well as of the head and neck region. α-Gal is a ubiquitous glycan moiety expressed on cells and tissue of non-primate mammals. Since this epitope is not expressed in humans, it is very immunogenic for them. α-Gal is located on the Fab portion of cetuximab and thus on the murine part of the chimera. The anaphylactic reactions to the antibody were mediated by IgE specific for α-Gal. Anti-α-Gal-IgE were first detected in sera of patients from the southeastern U.S. and reacted with a wide range of mammalian allergens. The geographic distribution prompted investigations of sensitization routes apart from the ingestion of red meat, such as tick bites und parasitic infections. Anti-α-Gal-IgE seems to be of clinical relevance for allergy to red meat and for the pork-cat syndrome. It is also associated with a novel form of delayed anaphylaxis, which appears more than 3 hours following the ingestion of red meat (beef, pork and lamb), a phenomenon which is still to be elucidated. For most of these patients conventional skin prick tests with commercial reagents proved insufficient for diagnosis.

Alpha1,3-galactosyltransferase knockout does not alter the properties of porcine extracellular matrix bioscaffolds

Extracellular matrix (ECM) bioscaffolds, such as porcine small intestine submucosa (SIS) and urinary bladder matrix (UBM), have been successfully used to improve soft tissue healing. Yet they contain plenty of galactose α1,3 galactose (αGal) epitopes, which cause rejection responses in pig organ transplantation to human. Recently, ECM bioscaffolds derived from genetically modified pigs that are αGal-deficient (αGal(-)) have become available. To ensure that the ECM bioscaffolds from these pigs can be used as alternatives, we examined their morphological, bioactive and biomechanical properties and compared them with those from the wild-type pigs (n=5 per group). Morphologically, the αGal(-) ECMs were found to be similar to the wild-type ECMs in gross observation and matrix appearance with hematoxylin and eosin staining. Growth factors commonly known to be present in ECM bioscaffolds, including FGF-2, TGF-β1, VEGF, IGF-1 and PDGF-BB, also showed no significant differences in terms of quantity (p>0.05) and distribution in tissue from the results of enzyme-linked immunosorbent assay, Western blot analysis and immunohistochemistry. Furthermore, a bromodeoxyuridine cell proliferation assay confirmed the bioactivity of the extracts from the αGal(-) bioscaffolds to be similar to the wild-type bioscaffolds. Under uniaxial tensile testing, no significant differences were found between the αGal(-) and wild-type bioscaffolds in terms of their viscoelastic and mechanical properties (p>0.05). These multidisciplinary results suggest that genetic modification to eliminate the αGal epitopes in the ECM bioscaffolds had not altered the properties of these ECM bioscaffolds and, as such, they should retain their performance in tissue engineering in humans.

Reverse genetics technology for Rift Valley fever virus: current and future applications for the development of therapeutics and vaccines

The advent of reverse genetics technology has revolutionized the study of RNA viruses, making it possible to manipulate their genomes and evaluate the effects of these changes on their biology and pathogenesis. The fundamental insights gleaned from reverse genetics-based studies over the last several years provide a new momentum for the development of designed therapies for the control and prevention of these viral pathogens. This review summarizes the successes and stumbling blocks in the development of reverse genetics technologies for Rift Valley fever virus and their application to the further dissection of its pathogenesis and the design of new therapeutics and safe and effective vaccines.

Gas-phase oligosaccharide nonreducing end (GONE) sequencing and structural analysis by reversed phase HPLC/mass spectrometry with polarity switching

Here we describe a technique to obtain all the N-linked oligosaccharide structures from a single reversed-phase (RP) HPLC run using on-line tandem MS in both positive and negative ion modes with polarity switching. Oligosaccharides labeled with 2-aminobenzamide (2AB) were used because they generated good ionization efficiency in both ion polarities. In the positive ion mode, protonated oligosaccharide ions lose sugar residues sequentially from the nonreducing end with each round of MS fragmentation, revealing the oligosaccharide sequence from greatly simplified tandem MS spectra. In the negative ion mode, diagnostic ions, including those from cross-ring cleavages, are readily observed in the MS2 spectra of deprotonated oligosaccharide ions, providing detailed structural information, such as branch composition and linkage positions. Both positive and negative ion modes can be programmed into the same LC/MS experiment through polarity switching of the MS instrument. The gas-phase oligosaccharide nonreducing end (GONE) sequencing data, in combination with the diagnostic ions generated in negative ion tandem MS, allow both sequence and structural information to be obtained for all eluting species during a single RP-HPLC chromatographic run. This technique generates oligosaccharide analyses at high speed and sensitivity, and reveals structural features that can be difficult to obtain by traditional methods.

Delayed anaphylaxis, angioedema, or urticaria after consumption of red meat in patients with IgE antibodies specific for galactose-alpha-1,3-galactose

BACKGROUND

Carbohydrate moieties are frequently encountered in food and can elicit IgE responses, the clinical significance of which has been unclear. Recent work, however, has shown that IgE antibodies to galactose-alpha-1,3-galactose (alpha-gal), a carbohydrate commonly expressed on nonprimate mammalian proteins, are capable of eliciting serious, even fatal, reactions.

OBJECTIVE

We sought to determine whether IgE antibodies to alpha-gal are present in sera from patients who report anaphylaxis or urticaria after eating beef, pork, or lamb.

METHODS

Detailed histories were taken from patients presenting to the University of Virginia Allergy Clinic. Skin prick tests (SPTs), intradermal skin tests, and serum IgE antibody analysis were performed for common indoor, outdoor, and food allergens.

RESULTS

Twenty-four patients with IgE antibodies to alpha-gal were identified. These patients described a similar history of anaphylaxis or urticaria 3 to 6 hours after the ingestion of meat and reported fewer or no episodes when following an avoidance diet. SPTs to mammalian meat produced wheals of usually less than 4 mm, whereas intradermal or fresh-food SPTs provided larger and more consistent wheal responses. CAP-RAST testing revealed specific IgE antibodies to beef, pork, lamb, cow's milk, cat, and dog but not turkey, chicken, or fish. Absorption experiments indicated that this pattern of sensitivity was explained by an IgE antibody specific for alpha-gal.

CONCLUSION

We report a novel and severe food allergy related to IgE antibodies to the carbohydrate epitope alpha-gal. These patients experience delayed symptoms of anaphylaxis, angioedema, or urticaria associated with eating beef, pork, or lamb.

Immune response to biologic scaffold materials

Biologic scaffold materials composed of mammalian extracellular matrix are commonly used in regenerative medicine and in surgical procedures for the reconstruction of numerous tissue and organs. These biologic materials are typically allogeneic or xenogeneic in origin and are derived from tissues such as small intestine, urinary bladder, dermis, and pericardium. The innate and acquired host immune response to these biologic materials and the effect of the immune response upon downstream remodeling events has been largely unexplored. Variables that affect the host response include manufacturing processes, the rate of scaffold degradation, and the presence of cross species antigens. This manuscript provides an overview of studies that have evaluated the immune response to biologic scaffold materials and variables that affect this response.

The Galalpha1,3Galbeta1,4GlcNAc-R (alpha-Gal) epitope: a carbohydrate of unique evolution and clinical relevance

In 1985, we reported that a naturally occurring human antibody (anti-Gal), produced as the most abundant antibody (1% of immunoglobulins) throughout the life of all individuals, recognizes a carbohydrate epitope Galalpha1-3Galbeta1-4GlcNAc-R (the alpha-gal epitope). Since that time, an extensive literature has developed on discoveries related to the alpha-gal epitope and the anti-Gal antibody, including the barrier they form in xenotransplantation and their reciprocity in mammalian evolution. This review covers these topics and new avenues of clinical importance related to this unique antigen/antibody system (alpha-gal epitope/anti-Gal) in improving the efficacy of viral vaccines and in immunotherapy against cancer.

Isolation of the feline alpha1,3-galactosyltransferase gene, expression in transfected human cells and its phylogenetic analysis

The enzyme alpha 1,3-galactosyltransferase (alpha1,3-GT), which catalyzes synthesis of terminal alpha-galactosyl epitopes (Gal alpha1,3Gal beta1-4GlcNAc-R), is produced in non-primate mammals, prosimians and new-world monkeys, but not in old-world monkeys, apes and humans. We cloned and sequenced a cDNA that contains the coding sequence of the feline alpha1,3-GT gene. Flow cytometric analysis demonstrated that the alpha-galactosyl epitope was expressed on the surface of a human cell line transduced with an expression vector containing this cDNA, and this alpha-galactosyl epitope expression subsided by alpha-galactosidase treatment. The open reading frame of the feline alpha1,3-GT cDNA is 1,113 base pairs in length and encodes 371 amino acids. The nucleotide sequence and its deduced amino acid sequence of the feline alpha1,3-GT gene are 88-90% and 85-87%, respectively, similar to the reported sequences of the bovine, porcine, marmoset and cebus monkey alpha1,3-GT genes, while they are 88% and 82-83%, respectively, similar to those of the orangutan and human alpha1,3-GT pseudogenes, and 81% and 77%, respectively, similar to the murine alpha1,3-GT gene. Thus, the alpha1,3-GT genes and pseudogenes of mammals are highly similar. Ratios of non-synonymous nucleotide changes among the primate pseudogenes as well as the primate genes are still higher than the ratios of non-primates, suggesting that the primate alpha1,3-GT genes tend to be divergent.

Novel Carbohydrate-binding Activity of Pancreatic Trypsins to N-Linked Glycans of Glycoproteins

How glycosylation affects the reactivity of proteins to trypsin is not well understood. Bovine and porcine pancreatic trypsins were discovered to bind to alpha-Man, Neu5Acalpha2,6Galbeta1,4Glc, and alpha-galactose sequences by binding studies with biotinylated sugar-polymers. Quantitative kinetic studies supported that phenylmethylsulfonyl fluoride (PMSF)-treated trypsin binds to glycolipid analogues possessing alpha-Man or alpha-NeuAc but not to those possessing beta-galactose or beta-GlcNAc residue. Enzyme-linked immunosorbent assay (ELISA) showed that trypsin binds to six kinds of biotinylated glycoproteins possessing high mannose-type and complex-type N-glycans but not to bovine submaxillary mucin, which possesses only O-glycans. Further, the binding of trypsin to glycoproteins was differentially changed by treatments with sequential exoglycosidases, endoglycosidase H, or N-glycosidase F. Quantitative kinetic studies indicated that PMSF-treated trypsin binds with bovine thyroglobulin with the affinity constant of 10(10) m(-1), which was the highest among the glycoproteins examined, and that alpha-galactosidase treatment decreased it to 10(5) m(-1). PMSF-treated trypsin bound to other glycoproteins, including ovomucoid, a trypsin inhibitor, with the affinity constants of 10(8)-10(5) mol(-1) and were markedly changed by glycosidase treatments in manners consistent with the sugar-binding specificities suggested by ELISA. Thus, the binding site for glycans was shown to be distinct from the catalytic site, allowing trypsin to function as an uncompetitive activator in the hydrolysis of a synthetic peptide substrate. Correspondingly the carbohydrate-binding activities of trypsin were unaffected by treatment with PMSF or soybean trypsin inhibitor. The results indicate the presence of an allosteric regulatory site on trypsin that sugar-specifically interacts with glycoproteins in addition to the proteolytic catalytic site.

The alpha-gal epitope and the anti-Gal antibody in xenotransplantation and in cancer immunotherapy

The alpha-gal epitope (Galalpha1-3Galbeta1-(3)4GlcNAc-R) is abundantly synthesized on glycolipids and glycoproteins of non-primate mammals and New World monkeys by the glycosylation enzyme alpha1,3galactosyltransferase (alpha1,3GT). In humans, apes and Old World monkeys, this epitope is absent because the alpha1,3GT gene was inactivated in ancestral Old World primates. Instead, humans, apes and Old World monkeys produce the anti-Gal antibody, which specifically interacts with alpha-gal epitopes and which constitutes approximately 1% of circulating immunoglobulins. Anti-Gal has functioned as an immunological barrier, preventing the transplantation of pig organs into humans, because anti-Gal binds to the alpha-gal epitopes expressed on pig cells. The recent generation of alpha1,3GT knockout pigs that lack alpha-gal epitopes has resulted in the elimination of this immunological barrier. Anti-Gal can be exploited for clinical use in cancer immunotherapy by targeting autologous tumour vaccines to APC, thereby increasing their immunogenicity. Autologous intact tumour cells from haematological malignancies, or autologous tumour cell membranes from solid tumours are processed to express alpha-gal epitopes by incubation with neuraminidase, recombinant alpha1,3GT and with uridine diphosphate galactose. Subsequent immunization with such autologous tumour vaccines results in in vivo opsonization by anti-Gal IgG binding to these alpha-gal epitopes. The interaction of the Fc portion of the vaccine-bound anti-Gal with Fcgamma receptors of APC induces effective uptake of the vaccinating tumour cell membranes by the APC, followed by effective transport of the vaccinating tumour membranes to the regional lymph nodes, and processing and presentation of the tumour-associated antigen (TAA) peptides. Activation of tumour-specific T cells within the lymph nodes by autologous TAA peptides may elicit an immune response that in some patients will be potent enough to eradicate the residual tumour cells that remain after completion of standard therapy. A similar expression of alpha-gal epitopes can be achieved by transduction of tumour cells with an adenovirus vector (or other vectors) containing the alpha1,3GT gene, thus enabling anti-Gal-mediated targeting of the vaccinating transduced cells to APC. Intratumoral delivery of the alpha1,3GT gene by various vectors results in the expression of alpha-gal epitopes. Such expression of the xenograft carbohydrate phenotype is likely to induce anti-Gal-mediated destruction of the tumour lesion, similar to rejection of xenografts by this antibody. Opsonization of the destroyed tumour cell membranes by anti-Gal IgG further targets them to APC, thus converting the tumour lesion, treated by the alpha1,3GT gene, into an in situ autologous tumour vaccine.

Tracing the history of Galalpha1-4Gal on glycoproteins in modern birds

Galalpha1-4Gal is typically found in mammalian glycolipids in small quantities, and recognized by some pathogens, such as uropathogenic Escherichia coli. In contrast, glycoproteins containing Galalpha1-4Gal were rarely found in vertebrates except in a few species of birds and amphibians until recently. However, we had previously reported that pigeon (Columba livia) egg white and serum glycoproteins are rich in N-glycans with Galalpha1-4Gal at non-reducing termini. Our investigation with egg white glycoproteins from 181 avian species also revealed that the distribution of (Galalpha1-4Gal)-containing glycoproteins was not rare among avians, and is correlated with the phylogeny of birds. The differentiated expression was most likely emerged at earlier stage of diversification of modern birds, but some birds might have lost the facility for the expression relatively recently.

N-glycan structures of pigeon IgG: a major serum glycoprotein containing Galalpha1-4 Gal termini

We had shown previously that all major glycoproteins of pigeon egg white contain Galalpha1-4Gal epitopes (Suzuki, N., Khoo, K. H., Chen, H. C., Johnson, J. R., and Lee, Y. C. (2001) J. Biol. Chem. 276, 23221-23229). We now report that Galalpha1-4Gal-bearing glycoproteins are also present in pigeon serum, lymphocytes, and liver, as probed by Western blot with Griffonia simplicifolia-I lectin (specific for terminal alpha-Gal) and anti-P1 (specific for Galalpha1-4Galbeta1-4GlcNAcbeta1-) monoclonal antibody. One of the major glycoproteins from pigeon plasma was identified as IgG (also known as IgY), which has Galalpha1-4Gal in its heavy chains. High pressure liquid chromatography, mass spectrometric (MS), and MS/MS analyses revealed that N-glycans of pigeon serum IgG included (i) high mannose-type (33.3%), (ii) disialylated biantennary complex-type (19.2%), and (iii) alpha-galactosylated complex-type N-glycans (47.5%). Bi- and tri-antennary oligosaccharides with bisecting GlcNAc and alpha1-6 Fuc on the Asn-linked GlcNAc were abundant among N-glycans possessing terminal Galalpha1-4Gal sequences. Moreover, MS/MS analysis identified Galalpha1-4Galbeta1-4Galbeta1-4GlcNAc branch terminals, which are not found in pigeon egg white glycoproteins. An additional interesting aspect is that about two-thirds of high mannose-type N-glycans from pigeon IgG were monoglucosylated. Comparison of the N-glycan structures with chicken and quail IgG indicated that the presence of high mannose-type oligosaccharides may be a characteristic of these avian IgG.

Relative purity of thrombin-based hemostatic agents used in surgery

BACKGROUND

Hemostatic agents used in surgery contain thrombin isolated from either a bovine or human source. The use of thrombin derived from a bovine source has been associated with the development of an abnormal immune response, but a study of the immunoreactivity of the various commercially available thrombin preparations has not been conducted. This study determined the relative purity of commercially available thrombin preparations, if humans have natural antibodies that recognize these preparations, and if elicited antibodies against bovine thrombin cross-react with other bovine or human hemostatic agents.

STUDY DESIGN

The purity of hemostatic agents was determined by protein and substrate assays, electrophoresis, and immunoblotting. The natural antigenicity and cross-reactivity of elicited antibodies were measured by ELISA using serum samples from 82 donors from the Red Cross and serum collected from patients exposed to bovine thrombin, respectively.

RESULTS

All of the bovine thrombin preparations were found to contain the xenogeneic carbohydrate galactosealpha1-3galactose. The natural antigenicity of the bovine thrombin preparations was greater than that of a human thrombin preparation and similar to that of porcine aortic endothelial cells. Antibodies elicited against bovine thrombin were found to cross-react with other bovine preparations and other xenoantigens but not with human hemostatic preparations.

CONCLUSIONS

All patients have antibovine thrombin antibodies, even before exposure to bovine thrombin-containing hemostatic agents. The cross-reactivity of elicited antibovine thrombin antibodies indicates that if a patient has been sensitized to a bovine product, it is likely safer to use a human-derived product in lieu of a bovine product.

Multivalent Galalpha1,3Gal-substitution makes recombinant mucin-immunoglobulins efficient absorbers of anti-pig antibodies

Hyperacute organ xenograft rejection can be prevented by removing anti-pig antibodies by extracorporeal absorption prior to transplantation. A novel recombinant absorber of anti-pig antibodies was developed by fusing the cDNA encoding the extracellular part of a mucin-type protein, P-selectin glycoprotein ligand-1, with an antibody Fc fragment cDNA, which upon coexpression with the porcine alpha1,3 galactosyltransferase carried the xenogeneic epitope, Galalpha1,3Gal (Liu J., Qian Y., Holgersson J., Transplantation 1997, 63, 1673-1682). The biochemical characterization of the mucin/Ig and its absorption efficacy compared with that of porcine thyroglobulin and Galalpha1,3Gal-conjugated beads are reported. The carbohydrate portion of the mucin/Ig constituted 43% of its molecular weight and the majority of the Galalpha1,3Gal epitopes were O-linked as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blotting following N-glycosidase F digestion. Gas chromatography-mass spectrometry of reduced and acetylated saccharides released by alpha-galactosidase treatment revealed that the fusion protein carried approximately 140 mol of terminal, alpha-linked galactose per mole protein. Based on the reduction in pig aortic endothelial cell cytotoxicity, Galalpha1,3Gal-substituted mucin/Igs on agarose beads were, on a carbohydrate molar basis, shown to be approximately 20 times more efficient than agarose-conjugated pig thyroglobulin, and approximately 5000 and 30,000 times more efficient than Galalpha1,3Gal-substituted agarose and macroporous glass beads, respectively. Structural features of the mucin backbone and its carbohydrate core saccharide chains determine the structural context, spatial orientation and spacing of Galalpha1,3Gal epitopes and are likely to explain the superior absorption efficacy of the recombinant mucin-type chimera.

Elimination of anti-Gal B cells by alpha-Gal ricin1

BACKGROUND

A major barrier in pig to human organ transplantation is the binding of human anti-Gal to alpha-gal epitopes (Gal alpha 1-3Gal beta 1-4GlcNAc-R) on pig cells, resulting in hyperacute and acute vascular rejection of pig xenografts. Moreover, the immune system in xenograft recipients is activated by these epitopes to produce high affinity anti-Gal, which is also detrimental to xenografts. Production of anti-Gal can be prevented by specific elimination of anti-Gal B cells. This was achieved with the toxin ricin A, coupled to human alpha1-acid glycoprotein modified to carry alpha-gal epitopes. This complex, designated alpha-gal ricin, is targeted in vivo to anti-Gal B cells by interaction with the immunoglobulin molecules (i.e., B cell receptors) on these cells.

METHODS

Carbohydrate chains on alpha 1-acid glycoprotein were converted to carry alpha-gal epitopes by enzymatic treatment with recombinant alpha 1,3 galactosyltransferase (alpha 1,3GT). This molecule and ricin A were biotinylated and coupled by avidin to generate alpha-gal ricin. The efficacy of alpha-gal ricin in eliminating anti-Gal B cells was studied in the experimental model of alpha 1,3GT knockout (KO) mice. These mice produce large amounts of anti-Gal immunoglobulin G when immunized with pig kidney membranes, as measured by ELISA with alpha-gal epitopes linked to bovine serum albumin (BSA). In the absence of anti-Gal B cells, these mice lack the ability to produce anti-Gal.

RESULTS

Repeated administration of alpha-gal ricin into alpha1,3GT KO mice resulted in elimination of anti-Gal B cells, thereby preventing production of anti-Gal immunoglobulin G after immunization with pig kidney membranes. This prevention of anti-Gal production occurred with doses of alpha-gal ricin that were not toxic to the mice and did not affect production of antibodies with other specificities.

CONCLUSIONS

Administration of alpha-gal ricin results in specific elimination of anti-Gal B cells in alpha 1,3GT KO mice. The elimination of these B cells may prove to be helpful in attempts to achieve immune tolerance to alpha-gal epitopes in primates.

Expression of alpha-gal epitopes on HeLa cells transduced with adenovirus containing alpha1,3galactosyltransferase cDNA

Alpha1,3galactosyltransferase (alpha1,3GT) synthesizes alpha-gal epitopes (Gal(alpha)1-3Galbeta1-4GlcNAc-R) on glycoconjugates in nonprimate mammals but not in humans. Transduction of alpha1,3GT gene into human HeLa cells by an adenovirus vector allowed for accurate kinetics studies on the appearance of alpha1,3GT and of its product, the alpha-gal epitope, in the transduced cells. Mouse alpha1,3GT cDNA was inserted into a replication-defective adenovirus vector. This viral vector, designated Ad(alpha)GT, could be propagated in human 293 cells that have the viral E1 complementing gene. Transduction of HeLa cells resulted in immediate penetration of approximately 20 Ad(alpha)GT copies into each cell and the appearance of alpha1,3GT mRNA after 4h. Catalytic activity of alpha1,3GT was first detected in the cells after 6 h. The initial appearance of alpha-gal epitopes (approximately 6 x 10(4)/cell) on cell surface glycoconjugates was detected 10 h posttransduction, whereas 24 h posttransduction each cell expressed 2 x 10(6) epitopes. The activity of alpha1,3GT in cells transduced with approximately two copies of Ad(alpha)GT was eightfold lower than that in cells transduced with approximately 20 Ad(alpha)GT copies; however, the number of alpha-gal epitopes/cell remained closely similar. This implies that increased alpha1,3GT activity above a certain saturation level does not result in a corresponding increase in the carbohydrate product, possibly because of competing glycosyltransferases.

The structure of anti-Gal immunoglobulin genes in naïve and stimulated Gal knockout mice

BACKGROUND

Naturally occurring antibodies (Nabs) that bind to terminal galactose alpha1,3-galactose carbohydrate structures (Gal) are present in humans and Old World monkeys but are negatively regulated in other mammalian species because they express Gal epitopes on their cell surfaces. A Gal knockout mouse (Gal-/-) model, generated by homologous disruption of alpha1,3-galactosyltransferase gene, is capable of producing natural anti-Gal Abs.

METHODS

To study the genetic control of the anti-Gal response, we have generated anti-Gal hybridomas from Gal-/- mice and analyzed VH genes of anti-Gal Abs from naïve animals and from mice stimulated by rat heterotopic heart transplantation.

RESULTS

Six immunoglobulin (Ig)M anti-Gal hybridomas derived from naïve Gal-/- mice exhibited anti-Gal binding activity with some cross-reactivity to related carbohydrate structures. These naïve anti-Gal Abs used five different VH genes in a germline configuration. Anti-Gal IgM hybridomas isolated after a rat heterotopic heart xenograft (4 days) utilized germline VH gene segments from the VH7183 family and exhibited less cross-reactivity. In contrast to mice 4 days after xenograft, we have predominantly isolated IgG anti-Gal hybridomas from mice 21 days after rat heterotopic heart xenografts, indicating an isotype switch. Nine of the IgG anti-Gal hybridomas secreted IgG3 subclass and one produced IgG1. Sequence analysis of the VH gene usage from the induced anti-Gal IgG antibodies demonstrated a restricted gene utilization (VHJ606-V14A).

CONCLUSION

Our results demonstrate that the anti-Gal response in naïve Gal-/- mice is encoded by multiple germline progenitors. In response to a xenograft, the induced anti-Gal Abs exhibited a restricted gene usage and somatic mutations, indicating a positive selection.

Synthesis of alpha-gal epitopes (Galalpha1-3Galbeta1-4GlcNAc-R) on human tumor cells by recombinant alpha1,3galactosyltransferase produced in Pichia pastoris

This study describes the processing of human tumor cells or cell membranes to express alpha-gal epitopes (Galalpha1-3Gal-beta1-4GlcNAc-R) by the use of New World monkey (marmoset) recombinant alpha1,3galactosyltransferase (ralpha1,3GT), produced in the yeast Pichia pastoris. Such tumor cells and membranes may serve, in cancer patients, as autologous tumor vaccines that are targeted in vivo to antigen-presenting cells by the anti-Gal antibody. This ralpha1,3GT lacks transmembrane and cytoplasmic domains, ensuring its solubility without detergent. It is effectively produced in P. pastoris under constitutive expression of the P(GAP) promoter and is secreted into the culture medium in a soluble, truncated form fused to a (His)(6) tag. This tag enables the simple affinity purification of ralpha1,3GT on a nickel-Sepharose column and elution with imidazole. The purified enzyme appears in SDS-PAGE as two bands with the size of 40 and 41 kDa and displays the same acceptor specificity as the mammalian native enzyme. ralpha1,3GT is very effective in synthesizing alpha-gal epitopes on membrane-bound carbohydrate chains and displays a specific activity of 1.2 nM membrane bound alpha-gal epitopes/min/mg. Incubation of very large amounts of human acute myeloid leukemia cells (1 x 10(9 )cells) with neuraminidase, ralpha1,3GT, and UDP-Gal resulted in the synthesis of approximately 6 x 10(6 )alpha-gal epitopes per cell. Effective synthesis of alpha-gal epitopes could be achieved also with as much as 2 g cell membranes prepared from the tumor of a patient with ovarian carcinoma. These data imply that ralpha1,3GT produced in P. pastoris is suitable for the synthesis of alpha-gal epitopes on bulk amounts of tumor cells or cell membranes required for the preparation of autologous tumor vaccines.

Binding of Griffonia simplicifolia 1 isolectin B4 (GS1 B4) to alpha-galactose antigens

Glycoconjugates with terminal Galalpha1-3Galbeta1-4GlcNAc sequences (alpha-galactosyl epitopes, natural xenoreactive antigens) are present on various tissues in pigs and are recognized by human anti-alphagalactosyl (alphaGal) antibodies1. Hence xenotransplantation (pig-to-human) would trigger immune reactions involving complement activation and lead to the hyperactute rejection of the graft. Xenoreactive antigens are often studied by using the lectin Griffonia simplicifolia 1 isolectin B4 (GS1 B4), which shows high affinity to galactose. We here estimate the specificity of GS1 B4 for detecting various galactosyl epitopes by measuring lectin binding to neoglycoproteins, thyroglobulin and pig skeletal muscle. Enzyme linked lectin assays confirmed that GS1 B4 was highly specific to alpha-galactosylated neoglycoproteins while the lectin did not detect a beta-galactosylated ligand. The length of the sugar chains influenced the lectin-carbohydrate interaction. A monosaccharide linked to serum albumin showed higher lectin affinity than did neoglycoproteins with di- and tri-alpha-galactosyl epitopes. When the carbohydrate was extended, as in the xenoreactive pentasaccharide (Galalpha1-3Galbeta1-4GlcNAcbeta1-3Galbeta1-4Glc), the carbohydrate- lectin interaction was meagre. Not only the terminal, but also the subterminal sugar affected the lectin binding because the GS1 B4 affinity to Galalpha1-3Gal was much stronger than to Galalpha1-3GalNAc. In bovine and porcine thyroglobulin most alphaGal epitopes appear to be cryptic, but are unmasked by a heat denaturation. In pig skeletal muscle there was lectin reaction not only in the muscle capillaries, but also in the connective tissue and intracellularly in muscle fibres. In Western blots of isolated proteins from pig muscle at least three bands were strongly stained after incubation with lectin.