Glycans and glycan-specific IgE in clinical and molecular allergology: Sensitization, diagnostics, and clinical symptoms  Arne Homann, PhD, Gabriele Schramm, PhD, Uta Jappe, MD, MSc  Journal of Allergy and Clinical Immunology  Volume 140, Issue 2, Pages 356-368 (August 2017) DOI: 10.1016/j.jaci.2017.04.019 Copyright © 2017 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 1 Groups of subjects with different sensitization patterns after contact with glycosylated allergens. Many subjects do not have IgE, whereas others form significant allergen-specific IgE. This IgE is directed against glycans (group A) and/or peptides (group B). Although allergy diagnoses for subjects of group B are more frequently covered by molecular allergy diagnostics for several important allergen sources, the interpretation of anti-glycan IgE in patient serum is not clear for the allergologist. After the discovery of the allergen α-Gal, patients with IgE against α-Gal (group A1) can receive correct diagnoses, whereas in the past, the delayed-type anaphylaxis to meat and innards was missed by using allergy in vitro diagnostic tests. However, the allergy diagnosis for patients with IgE to classical CCDs of a different specificity (group A2) remains challenging. Journal of Allergy and Clinical Immunology 2017 140, 356-368DOI: (10.1016/j.jaci.2017.04.019) Copyright © 2017 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 2 Structure of N-glycans on allergens. A, Chemical structure (left) and symbol simplification according to Consortium for Functional Glycomics conventions are shown for the N-glycan core glycan. Note that the substitutions of the N-glycan core on allergens are either nonhuman carbohydrates (xylose) or nonhuman carbohydrate linkages and positions (α-1,3 fucosylation on the first GlcNAc of the chitobiose core). B, IgE against classical CCDs are known to cause no or minor allergy symptoms. C, IgE against α-Gal can cause severe allergy symptoms. Nonhuman carbohydrate substitutions of the N-glycan core are indicated by red brackets. The monosaccharide residues in brackets are present or not in different species. PLA2, Phospholipase A2. Journal of Allergy and Clinical Immunology 2017 140, 356-368DOI: (10.1016/j.jaci.2017.04.019) Copyright © 2017 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 3 Selection of nonhuman IgE-binding glycan structures from insects, plants, parasites, and nonhuman mammals. Glycans from different species show a high degree of similarity that results in the often observed human anti-CCD IgE cross-reactivity. Small differences in the carbohydrate structure have pronounced immunologic effects, either foreign monosaccharides, such as xylose and Neu5Gc, or nonhuman carbohydrate linkages, as in the case of α-Gal. Journal of Allergy and Clinical Immunology 2017 140, 356-368DOI: (10.1016/j.jaci.2017.04.019) Copyright © 2017 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 4 Immunologic scenarios for clinical significance or nonsignificance of IgE. A, Model for the development of high- versus low-affinity IgE through differential B-cell class-switching.4 B, Activation of FcεR+ cells through receptor cross-linking is dependent on multivalent antigens (allergens). C, The therapeutic mAb CTX is particularly effective in IgE binding and FcεR cross-linking.1 D, IgE binding to allergens might be blocked by allergen-specific IgG.2,3 Consequences of IgG binding to allergens depend on the IgG subclass. Journal of Allergy and Clinical Immunology 2017 140, 356-368DOI: (10.1016/j.jaci.2017.04.019) Copyright © 2017 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 5 Association of structure and function of foreign and human-like glycans from allergens and parasites. Top, Representative structures of the predominant N-glycans from S mansoni egg antigens (SEA). Although IPSE/alpha-1 and omega-1 direct the immune system toward TH2, the N-glycan core of kappa-5 is a target of glycan-specific IgE. No IgE is formed against IPSE/alpha-1 or omega-1.7-10 Bottom, Glycans mirroring or mimicking human glycan structures and have an effect on the human immune system are indicated in the table. h, Human; i, insect p, plant; s, schistosome. LeX,5,6,11-13 di-N-acetyl-lactosamine (LDN),5,14-21 LDNF,5,6,17,20,22-24 FLDN,5,25-28 and LDNdF.26-29 “F” indicates conjugated fucose as shown in the respective oligosaccharide structure. Journal of Allergy and Clinical Immunology 2017 140, 356-368DOI: (10.1016/j.jaci.2017.04.019) Copyright © 2017 American Academy of Allergy, Asthma & Immunology Terms and Conditions

Fig 6 Immunologic effects of selected carbohydrate receptors on human immune cells. Known carbohydrate ligands and resulting immunologic effects are indicated. Top scheme, Simplified examples of cellular cross-talk on receptor interaction with glycans. Attachment and uptake of glycoproteins with specific N-glycans is mediated, for example, by MR or the DC-SIGN receptor. Cross-linking of IgE, such as by allergens containing α-Gal, and Toll-like receptor (TLR) stimulation by glycan-containing LPS induces proinflammatory cellular responses. MR,33 DC-SIGN,27 sialic acid–binding immunoglobulin-like lectin (SIGLEC),32 selectin,34 macrophage galactose lectin 1 (MGL1),20 epidermal growth factor–like module-containing mucin-like hormone receptor-like 2 (EMR2),35 Toll-like receptor (TLR),30,36 and FcγR.31,37 Journal of Allergy and Clinical Immunology 2017 140, 356-368DOI: (10.1016/j.jaci.2017.04.019) Copyright © 2017 American Academy of Allergy, Asthma & Immunology Terms and Conditions