Current and Future Strategies for the Diagnosis and Treatment of the Alpha-Gal Syndrome (AGS)

Abstract

The α-Gal syndrome (AGS) is a pathognomonic immunoglobulin E (IgE)-mediated delayed anaphylaxis in foods containing the oligosaccharide galactose-α-1,3-galactose (α-Gal) such as mammalian meat or dairy products. Clinical presentation of AGS can also comprise immediate hypersensitivity due to anticancer therapy, gelatin-containing vaccines or mammalian serum-based antivenom. The IgE initial sensitization is caused by hard-bodied tick bites and symptomatic individuals typically develop delayed pruritus, urticaria, angioedema, anaphylaxis, malaise or gut-related symptoms. Due to inapparent presentation, delayed reactions and a wide variety of patients´ clinical history, the AGS diagnosis and treatment remain challenging. This review covers not only current diagnostic methods used for AGS such as the skin prick test (SPT), the oral food challenge (OFC), anti-α-Gal IgE levels measurement and the basophil activation test (BAT), but also potentially relevant next-generation diagnostic tools like the mast cell activation test (MAT), the histamine-release (HR) assay, omics technologies and model-based reasoning (MBR). Moreover, it focuses on the therapeutical medical and non-medical methods available and current research methods that are being applied in order to elucidate the molecular, physiological and immune mechanisms underlying this allergic disorder. Lastly, future treatment and preventive tools are also discussed, being of utmost importance for the identification of tick salivary molecules, with or without α-Gal modifications, that trigger IgE sensitivity as they could be the key for further vaccine development. Bearing in mind climate change, the tick-host paradigm will shift towards an increasing number of AGS cases in new regions worldwide, which will pose new challenges for clinicians in the future.

Keywords: AGS; IgE; alpha-Gal; alpha-Gal syndrome; food allergy; glycan; tick.

Figure 1

Alpha-Gal syndrome (AGS). (A) Sensitization after several tick bites. Tick saliva contains glycoproteins, glycolipids with α-Gal epitopes and other unknown salivary biomolecules that could be involved in the pathology of AGS. The glycan α-Gal is presented to T helper 2 (Th2) cells through antigen-presenting cells (APCs) as dendritic cells, macrophages or even B cells. Once T cells are activated, B cells are leading to produce IgE against α-Gal (anti α-Gal-IgE) in an enriched interleukin environment and potentiate IgE production in plasma cells. Free IgE are now available to interact and bind to IgE receptors present in basophils and mast cells. (B) Allergic Reaction. When AGS patients ingest mammalian meat containing α-Gal bound to proteins or lipids, these molecules expressing the allergen epitope are absorbed and incorporated to lipid/protein macromolecules during digestion (chylomicrons, lipoproteins), which will be processed and transport through protein or lipid metabolism to systemic circulation and peripheral tissues. About 3–6 hours post-consumption, IgE-mediated and coated effectors will recognize the allergen, leading to degranulation of basophils and mast cells and promoting a systemic delayed allergic reaction. AGS can also comprise an immediate anaphylactic reaction, triggered using α-Gal containing drugs, administered via parenteral due to therapeutic reasons.

Figure 2

Conventional and next generation methods for the diagnosis of the alpha-Gal syndrome (AGS).

Figure 3

Anti-IgE therapy. IgE-mediated reaction with release of histamine and other co-factors occurs due to interaction of allergen-specific IgE available with IgE receptor in mediator cells (basophils, eosinophils or mast cells), which are degranulated and increase the risk of life-threatening anaphylactic adverse reactions. The pharmacological and clinical aims of the use of anti-IgEs monoclonal antibodies (mAbs) as drugs is to downregulate and/or decrease IgE production by B cells. Anti-IgE antibodies bind to both IgE-expressing B cells and free serum IgE, markedly decreasing IgE levels available for binding to IgE receptor in allergic reaction-mediator cells and, consequently, gradually compromising mast cells and basophils sensitivity to allergens.