Only α‐Gal bound to lipids, but not to proteins, is transported across enterocytes as an IgE‐reactive molecule that can induce effector cell activation

Abstract

BackgroundThe oligosaccharide galactose‐α‐1,3‐galactose (α‐Gal), present in mammalian proteins and lipids, causes an unusual delayed allergic reaction 3 to 6 hours after ingestion of mammalian meat in individuals with IgE antibodies against α‐Gal. To better understand the delayed onset of allergic symptoms and investigate whether protein‐bound or lipid‐bound α‐Gal causes these symptoms, we analyzed the capacity of α‐Gal conjugated proteins and lipids to cross a monolayer of intestinal cells.MethodsExtracts of proteins and lipids from beef were prepared, subjected to in vitro digestions, and added to Caco‐2 cells grown on permeable supports. The presence of α‐Gal in the basolateral medium was investigated by immunoblotting, thin‐layer chromatography with immunostaining and ELISA, and its allergenic activity was analyzed in a basophil activation test.ResultsAfter addition of beef proteins to the apical side of Caco‐2 cells, α‐Gal containing peptides were not detected in the basolateral medium. Those peptides that crossed the Caco‐2 monolayer did not activate basophils from an α‐Gal allergic patient. Instead, when Caco‐2 cells were incubated with lipids extracted from beef, α‐Gal was detected in the basolateral medium. Furthermore, these α‐Gal lipids were able to activate the basophils of an α‐Gal allergic patient in a dose‐dependent manner.ConclusionOnly α‐Gal bound to lipids, but not to proteins, is able to cross the intestinal monolayer and trigger an allergic reaction. This suggests that the slower digestion and absorption of lipids might be responsible for the unusual delayed allergic reactions in α‐Gal allergic patients and identifies glycolipids as potential allergenic molecules.

Allergic Reactions and Immunity in Response to Tick Salivary Biogenic Substances and Red Meat Consumption in the Zebrafish Model

“…Humans evolved with the inactivation of the α1,3-GalT gene, which resulted in the recognition of the carbohydrate α-Gal as a non-self-antigen, thus inducing the production of high antibody titers against this molecule (Galili, 2018). This evolutionary trait benefits humans by providing immunity to pathogens containing α-Gal in the surface while increasing the risks of developing the AGS triggered by the IgE antibody response against α-Gal present in glycoproteins and glycolipids from tick saliva and tissues of non-catarrhine mammals (Commins et al, 2009;Van Nunen et al, 2009;Platts-Mills et al, 2015;Steinke et al, 2015;Galili, 2018;Cabezas-Cruz et al, 2019;de la Fuente et al, 2019;Hilger et al, 2019;Román-Carrasco et al, 2019;Park et al, 2020). The AGS is characterized by delayed anaphylaxis to red meat consumption and immediate anaphylaxis to tick bites, xenotransplantation, and certain drugs such as cetuximab (Mateos-Hernández et al, 2017;Hilger et al, 2019).…”

Alpha-Gal and Cross-Reactive Carbohydrate Determinants in the N-Glycans of Salivary Glands in the Lone Star Tick, Amblyomma americanum

“…In all mammals except old world monkeys and humans, aGal is produced by an alpha-1,3-galactosyltransferase, which is mutated in humans [20,60]. A recent study proposed that RMA is elicited by glycolipids containing aGal but not by glycoproteins due to the difference in transport across the gut cell layer [61]. However, the nature of RMA sensitizers, likely originating from tick salivary secretion, needs to be further investigated.…”

The History of Carbohydrates in Type I Allergy

“…While most ingested proteins are transported to the bloodstream within 1–2 h after ingestion, the majority of lipids enters the blood as part of chylomicrons around 4 h postmeal ( 64 ). Indeed, using proteins and lipids extracted from grilled beef, Roman-Carrasco et al demonstrated that alpha-gal containing glycolipids but not -proteins were able to cross a monolayer of intestinal cells as part of chylomicrons ( 65 ). As relevant alpha-gal carrying allergens in pork kidney, angiotensin-I-converting enzyme (ACE I) and aminopeptidase N (AP-N) have been identified ( 66 ).…”