Sugar sequences of allergenically active oligosaccharide alcohols isolated from a large-molecular-size sea squirt antigen termed H-antigen

Carbohydrate epitopes currently recognized as targets for IgE antibodies

Until recently, glycan epitopes have not been documented by the WHO/IUIS Allergen Nomenclature Sub-Committee. This was in part due to scarce or incomplete information on these oligosaccharides, but also due to the widely held opinion that IgE to these epitopes had little or no relevance to allergic symptoms. Most IgE-binding glycans recognized up to 2008 were considered to be "classical" cross-reactive carbohydrate determinants (CCD) that occur in insects, some helminths and throughout the plant kingdom. Since 2008, the prevailing opinion on lack of clinical relevance of IgE-binding glycans has been subject to a reevaluation. This was because IgE specific for the mammalian disaccharide galactose-alpha-1,3-galactose (alpha-gal) was identified as a cause of delayed anaphylaxis to mammalian meat in the United States, an observation that has been confirmed by allergists in many parts of the world. Several experimental studies have shown that oligosaccharides with one or more terminal alpha-gal epitopes can be attached as a hapten to many different mammalian proteins or lipids. The classical CCDs also behave like haptens since they can be expressed on proteins from multiple species. This is the explanation for extensive in vitro cross-reactivity related to CCDs. Because of these developments, the Allergen Nomenclature Sub-Committee recently decided to include glycans as potentially allergenic epitopes in an adjunct section of its website (www.allergen.org). In this article, the features of the main glycan groups known to be involved in IgE recognition are revisited, and their characteristic structural, functional, and clinical features are discussed.

The History of Carbohydrates in Type I Allergy

Although first described decades ago, the relevance of carbohydrate specific antibodies as mediators of type I allergy had not been recognized until recently. Previously, allergen specific IgE antibodies binding to carbohydrate epitopes were considered to demonstrate a clinically irrelevant cross-reactivity. However, this changed following the discovery of type I allergies specifically mediated by oligosaccharide structures. Especially the emerging understanding of red meat allergy characterized by IgE directed to the oligosaccharide alpha-gal showed that carbohydrate-mediated reactions can result in life threatening systemic anaphylaxis which in contrast to former assumptions proves a high clinical relevance of some carbohydrate allergens. Within the scope of this review article, we illustrate the historical development of carbohydrate-allergen-research, reaching from only diagnostically relevant crossreactive-carbohydrate-determinants to clinically important antigens mediating type I allergy. Focusing on clinical and immunological features of the alpha-gal syndrome, we highlight the discovery of oligosaccharides as potentially highly immunogenic antigens and mediators of type I allergy, report what is known about the route of sensitization and the immunological mechanisms involved in sensitization and elicitation phase of allergic responses as well as currently available diagnostic and therapeutic tools. Finally, we briefly report on carbohydrates being involved in type I allergies different from alpha-gal.

Role and Mechanism of Galactose-Alpha-1,3-Galactose in the Elicitation of Delayed Anaphylactic Reactions to Red Meat

Purpose of Review

The alpha-Gal (α-Gal) syndrome is characterized by the presence of IgE antibodies directed at the carbohydrate galactose-alpha-1,3-galactose (α-Gal). In this article, we review the presence of α-Gal in food and non-food sources; we discuss the evolutionary context of the antibody response to α-Gal and highlight immune responses to α-Gal and other carbohydrates.

Recent findings

IgE antibodies have been associated with delayed allergy to red meat. In addition to food, drugs, and other products of animal origin are increasingly perceived as a risk for patients sensitized to α-Gal. The link between tick bites and anti-α-Gal IgE-antibody production that has been established first by epidemiological studies has now been confirmed in mouse models.

Summary

The anti-α-Gal immune response is complex and characterized by a unique feature. IgM and IgG antibodies have been found to confer protection against pathogens whereas the IgE-response to α-Gal is detrimental and causes severe reactions upon exposure to mammalian meat and other products.

Characterization of a novel allergenic protein from the octocoral Scleronephthya gracillima (Kuekenthal) that corresponds to a new GFP-like family named Akane

Certain marine organisms have been known to cause allergic reactions among occupational fishermen. We have previously reported that bronchial asthma among the workers engaged in spiny lobster fishing in Japan was caused by octocorals such as Dendronephthya sp. and Scleronephthya gracillima (previously named Alcyonium gracillimum). Now we have found another octocoral, Scleronephthya gracillima (Kuekenthal), which causes the allergic disease in fishermen. The octocoral was characterized as a new green fluorescent protein (GFP)-like family. The new allergen has a molecular mass of 27 kDa in 1D and 2D SDS-PAGE under reduced conditions. The 27 kDa component was determined to be an allergen by western blotting, ECL immune staining method and absorption of patient sera with the antigen. Furthermore, the combination of analysis with LC-ESI-MS/MS and MASCOT search in the NCBInr database concluded the 27 kDa component had the sequence YPADI/LPDYFK, and that the 22 kDa component had the sequence QSFPEGFSWER, which both matched a GFP-like protein in Acropora aculeus and in Montastraea annularis. Further analysis by MALDI-TOF/MS/MS and MASCOT search in the NCBInr database of all 27 kDa eight spot components from 2D SDS-PAGE indicated that the sequence QSFPEGFSWER also matched as GFP-like protein in Lobophyllia hemprichii and Scleractinia sp. To our knowledge, this is the first report of the new allergenic protein that corresponds to a new GFP-like protein named Akane, and which has fluorescent emissions in the red and green part of the spectra at 628 nm and 508 nm, respectively.

Carbohydrates as food allergens

The literature supports the notion that carbohydrate epitopes, on their own, do not contribute significantly to the induction of allergic reactions. They bind weakly to IgE antibodies and have been termed as cross reactive carbohydrate determinants. These epitopes cause confusion in in vitro IgE testing through nonspecific cross-reactivity. Coincident with the rising trends in food allergy prevalence, there has recently been reports of anaphylaxis induced by carbohydrate epitopes. There are two distinct groups, each with unique characteristics and geographical distribution. Anaphylaxis and acute allergic reactions related to the carbohydrate galactose-α-1,3-galactose (α-Gal) epitope that are present in the monoclonal antibody, cetuximab and red meat have been described in the United States and Europe populations where tick bites have been found to be the primary sensitizer. Another carbohydrate inducing anaphylaxis is galacto-oligosaccharides in commercial milk formula which has been described in the several Asian populations including Singapore. The latter is unique in that the allergen is a pure carbohydrate. We summarize the current literature on carbohydrate-induced food allergy, and evaluate the two new groups of carbohydrate allergy that have defied previous findings on carbohydrates and their role.

Cross-reactivity of IgE antibodies to allergens

The cross-reactivity of IgE antibodies is of interest for various reasons, three of which are discussed. Firstly, from the clinical view, it is important to know the patterns of cross-reactivity, because they often (but not always) reflect the pattern of clinical sensitivities. We discuss the cross-reactivities associated with sensitization to pollen and vegetable foods: PR-10 (Bet v 1-related), profilin, the cross-reactive carbohydrate determinant (CCD), the recently described isoflavone reductase, and the (still elusive) mugwort allergen that is associated with celery anaphylaxis; cross-reactivities between allergens from invertebrates, particularly tropomyosin, paramyosin, and glutathione S-transferase (GST); and latex-associated cross-reactivities. Clustering cross-reactive allergens may simplify diagnostic procedures and therapeutic regimens. Secondly, IgE cross-reactivity is of interest for its immunologic basis, particularly in relation to the regulation of allergic sensitization: are IgE antibodies to allergens more often cross-reactive than IgG antibodies to "normal" antigens? If so, why? For this discussion, it is relevant to compare not only the structural relation between the two allergens in question, but also the relatedness to the human equivalent (if any) and how the latter influences the immune repertoire. Thirdly, prediction of IgE cross-reactivity is of interest in relation to allergic reactivity to novel foods. Cross-reactivity is a property defined by individual antibodies to individual allergens. Quantitative information (including relative affinity) is required on cross-reactivity in the allergic population and with specific allergens (rather than with whole extracts). Such information is still scarce, but with the increasing availability of purified (usually recombinant) allergens, such quantitative information will soon start to accumulate. It is expected that similarity in short stretches of the linear amino-acid sequence is unlikely to result in relevant cross-reactivity between two proteins unless there is similarity in the protein fold.

N- and O-linked oligosaccharides of allergenic glycoproteins

Cross-linking of cell-bound IgE on mast cells or basophils by polyvalent antigens causes the release of histamine and other mediators of the allergic response which then lead to the development of allergic symptoms. In this event not only peptide epitopes, but also carbohydrates can act as cross-linking elements. Since peptide epitopes of allergens are subject of most published studies, this review is focused on glycosidic epitopes. The current knowledge of the structures and possible epitopes of oligosaccharides linked to allergenic glycoproteins is briefly reviewed, showing that complex plant N-glycans containing alpha1,3 fucose and beta1,2 xylose are most frequently involved in the structures of IgE epitopes. In own studies a prevalence of up to 29% anti-glycan IgE was determined among pollen-allergic patients. The clinical relevance of these carbohydrate specific IgE antibodies is still a matter of controversial discussions.

Beta(1,2)-xylose and alpha(1,3)-fucose residues have a strong contribution in IgE binding to plant glycoallergens

Primary structures of the N-glycans of two major pollen allergens (Lol p 11 and Ole e 1) and a major peanut allergen (Ara h 1) were determined. Ole e 1 and Ara h 1 carried high mannose and complex N-glycans, whereas Lol p 11 carried only the complex. The complex structures all had a beta(1,2)-xylose linked to the core mannose. Substitution of the proximal N-acetylglucosamine with an alpha(1, 3)-fucose was observed on Lol p 11 and a minor fraction of Ole e 1 but not on Ara h 1. To elucidate the structural basis for IgE recognition of plant N-glycans, radioallergosorbent test analysis with protease digests of the three allergens and a panel of glycoproteins with known N-glycan structures was performed. It was demonstrated that both alpha(1,3)-fucose and beta(1,2)-xylose are involved in IgE binding. Surprisingly, xylose-specific IgE antibodies that bound to Lol p 11 and bromelain did not recognize closely related xylose-containing structures on horseradish peroxidase, phytohemeagglutinin, Ole e 1, and Ara h 1. On Lol p 11 and bromelain, the core beta-mannose is substituted with just an alpha(1,6)-mannose. On the other xylose-containing N-glycans, an additional alpha(1,3)-mannose is present. These observations indicate that IgE binding to xylose is sterically hampered by the presence of an alpha(1,3)-antenna.

Purification and characterization of sea squirt α-N-acetylgalactosaminidase

Sea squirt alpha-N-acetylgalactosaminidase was purified to homogeneity. Its molecular weight was estimated to be approximately 160,000 by gel filtration and 40,000 by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing condition. The chromatographic and electrophoretic behaviors indicated that the enzyme was composed of four subunits. The optimum pH of the enzyme reaction was about 4.0 at 37 degrees C, while the enzyme was stable in the range of pH 5.0 to 6.0 during 4 h preincubation at 37 degrees C. Although the enzyme (0.1 unit) was stable at 0 degrees C for 30 min in the presence of 7.5 mM metal ions (Al3+, Ba2+, Ca2+, K+, Mn2+, Pb2+, Sr2+, and Zn2+), almost 40% of the enzyme activity was lost in the presence of Cu2+, Hg2+, monoiodoacetic acid, and EDTA. The enzyme hydrolyzed aryl N-acetyl-alpha-D-galactosaminide as well as GalNAcalpha1(-->4GalNAcalpha1-->)n 4GalNAc-p-aminobenzoic acid ethyl ester (ABEE) (n = 1-4), but GalNAcalpha1-->4GalNAc-ABEE only scarcely. Furthermore, an allergenic pentasaccharitol ABEE derivative, GalNAcalpha1-->2Fucalpha1-->3(GalNAcbeta1-->4) GlcNAcbeta1-->2(3-acetoamido-3-deoxy)L-threose-ABEE, the minimum structural unit for the sea squirt allergenicity was hydrolyzed to 95 mol% for 72 h incubation with the enzyme. The enzyme could be utilized as a powerful tool for the structural analyses of the carbohydrate epitopes of the sea squirt allergen molecules.

IgE-binding and histamine-release capabilities of the main carbohydrate component isolated from the major allergen of olive tree pollen, Ole e 1

BACKGROUND

Pollen from olive trees (Olea europaea ) is a cause of pollinosis and an aggravating of asthma in Mediterranean regions. Recently, Ole e 1, the major allergen from olive tree pollen, has been isolated and its amino acid sequence has been elucidated. It is a glycoprotein whose carbohydrate moiety is involved in an IgE-binding epitope responsible for cross-reactivity among plant glycoproteins. However, the allergenicity of the free carbohydrate side chains remains to be clarified.

OBJECTIVE

The purpose of this study was to isolate the main carbohydrate component of Ole e 1 allergen and analyze its IgE-binding and histamine-release capabilities.

METHODS

Deglycosylation treatment of Ole e 1 with PNGase F and gel exclusion chromatography were used to isolate the main sugar component of the allergen. Sera of patients who are allergic to olive pollen and sera sensitive to Ole e 1 have been used in dot blotting assays of IgE binding to the isolated carbohydrate. Heparinized whole blood obtained from patients sensitive to Ole e 1 were stimulated by the free carbohydrate; the resulting histamine release was measured.

RESULTS

The main sugar component of Ole e 1 has been isolated. Free carbohydrate was able to bind IgE from sera of patients allergic to olive pollen; the sera of 65% of these patients contained anticarbohydrate reacting IgE, and 100% of those patients were sensitive to Ole e 1. The free carbohydrate promoted in vitro histamine release from basophils of sensitized patients.

CONCLUSION

The carbohydrate moieties of allergenic glycoproteins can constitute significant determinants on the binding to IgE of the sera from patients who are hypersensitive and can be responsible for inducing histamine release from blood cells.

Identification of a novel hydroxyproline-rich glycoprotein as the major allergen in Parthenium pollen

BACKGROUND

The airborne pollen of the Compositae weed, Parthenium hysterophorus, is a major cause of allergic rhinitis in the Indian subcontinent and in certain parts of the southern United States and western Australia. Earlier studies have identified a 31 kd protein as the major allergen in Parthenium pollen.

OBJECTIVE

This study was undertaken to carry out the purification, immunochemical characterization, sequencing, and epitope analysis of this major allergen, designated as Par h I.

METHODS

The IgE-binding activity of the allergen was evaluated by immunoblot and inhibition ELISAs. Pronase digestion, periodate oxidation, and chemical deglycosylation were performed to determine the role of peptide and carbohydrate components of the allergen in IgE binding.

RESULTS

The data provide evidence for the involvement of carbohydrate moieties on Par h 1 in its IgE-binding ability. The N-terminal 91 amino acid sequence of Par h 1 shows 81% identity with a protein from sunflower anther, and the hydroxyproline-rich region of Par h 1 is 30% to 40% identical to similar stretches in extensins, a class of hydroxyproline-rich cell wall glycoproteins from different plant species. IgE antibodies in the sera of individuals allergic to Parthenium cross-reacted with a 50 kd hydroxyproline-arabinose-rich extensin precursor from potato tuber, and this binding was periodate-sensitive.

CONCLUSIONS

It appears that a group of soluble plant glycoproteins, which are related to the ubiquitous extensins, have certain carbohydrate-containing IgE-binding epitopes that may contribute to allergenic cross-reactivity among specific pollens and foods.

UVB radiation affects the mobility of epidermal growth factor receptors in human keratinocytes and fibroblasts

Growth factor receptors transmit biological signals for the stimulation of cell growth in vitro and in vivo and their autocrine stimulation may be involved in tumorigenesis. It is therefore, of great value to understand receptor reactions in response to ultraviolet (UV) light which certain normal human cells are invaribly exposed to during their growth cycle. UV irradiation has recently been shown to deplete antioxidant enzymes in human skin. The aims of the present study were a) to compare the lateral mobility of epidermal growth factor receptors (EGF-R) in cultured human keratinocytes and human foreskin fibroblasts, b) to investigate effects of ultraviolet B radiation on the mobility of EGF-R in these cells, and c) study the response of EGF-R on addition of antioxidant enzymes. The epidermal growth factor receptors were labeled with rhodaminated EGF, the lateral diffusion was determined and the fraction of mobile EGF-R assessed with the fluorescence recovery after photobleaching (FRAP). We found that human keratinocytes display a higher basal level of EGF-R mobility than human skin fibroblasts, viz. with diffusion coefficients (D +/- standard error of the mean, SEM) of 4.2 +/- 0.2 x 10(-10) cm2/s, and 1.8 +/- 0.2 x 10(-10) cm2/s, respectively. UVB-irradiated fibroblasts showed an almost four-fold increase in the diffusion coefficient; D was 6.3 +/- 0.3 x 10(-10) cm2/s. The keratinocytes, however, displayed no significant increase in receptor diffusion after irradiation; D was 5.1 +/- 0.8 x 10(-10) cm2/s. In both cell types the percentage of EGF-R fluorescence recovery after photobleaching, i.e. the fraction of mobile receptors, was significantly increased after irradiation. In keratinocytes it increased from 69% before irradiation to 78% after irradiation. Analogous figures for fibroblasts were 61% and 73%. The effect of UVB on fibroblast receptors was abolished by prior addition of superoxide dismutase (SOD) and catalase (CAT). It is concluded that UVB radiation of fibroblasts and keratinocytes can affect their biophysical properties of EGF-R. The finding that addition of antioxidant enzymes prevented the UVB effect in fibroblasts may indicate the involvement of reactive oxygen metabolites.

Conversion of GalNAc beta(1-4)GlcNAc beta-OMe into GalNAc beta (1-4)-[Fuc alpha(1-3)]GlcNAc beta-OMe using human milk alpha 3/4-fucosyltransferase. Synthesis of a novel terminal element in glycoprotein glycans

Incubation of GalNAc beta(1-4)GlcNAc beta-OMe with GDP-Fuc in the presence of human milk alpha 3/4-fucosyltransferase resulted in the formation of GalNAc beta(1-4)[Fuc alpha(1-3)]GlcNAc beta-OMe. Under conditions that led to complete alpha 3-fucosylation of Gal beta(1-4)GlcNAc beta-OEt, GalNAc beta(1-4)GlcNAc beta-OMe was fucosylated for more than 85%. For the identification of the isolated fucosylated products one- and two-dimensional 1H-NMR spectroscopy was applied. In vacuo molecular dynamics simulations of Gal beta(1-4)[Fuc alpha(1-3)]GlcNAc beta-OEt and GalNAc beta(1-4)[Fuc alpha(1-3)]GlcNAc beta-OMe using the CHARMm based force field CHEAT, demonstrated only small differences between the conformations of these compounds. This illustrates the minor conformational influence of the substituent at C-2', i.e. a hydroxyl function versus a N-acetyl group.

Human urokinase contains GalNAc beta (1-4)[Fuc alpha (1-3)]GlcNAc beta (1-2) as a novel terminal element in N-linked carbohydrate chains

Structural analysis of enzymically released N-linked carbohydrate chains of human urokinase (urinary-type plasminogen activator) by 1H NMR spectroscopy and FAB-MS demonstrated that the N-linked oligosaccharides on the only N-glycosylation site contain diantennary structures with the novel GalNAc beta (1-4) [Fuc alpha (1-3)]GlcNAc beta (1-2) element in the upper or the lower branch.

Further characterization of allergenically active oligosaccharitols isolated from a sea squirt H-antigen

Complete primary structures of five allergenically active oligosaccharitols (HPG-beta 2-N5a, -N6, -N7a, -N7b, and -N9) derived from a sea squirt H-antigen were studied. Structural characterization was carried out by a new method in which products of limited periodate oxidation, followed by derivatization with p-aminobenzoic acid ethyl ester, were analyzed by a combination of HPLC, fast atom-bombardment mass spectrometry, sequential glycosidase digestion, methylation analysis, and 500-MHz 1H NMR. Established structures of GalNAc beta 1-4 (GalNAc alpha 1-2Fuc alpha 1-3) GlcNAc beta 1-3GalNAc-ol, GalNAc beta 1-4GlcNAc beta 1-3 (GalNAc beta 1-4GlcNAc beta 1-6) GalNAc-ol, GalNAc beta 1-4GlcNAc beta 1-3[GalNAc beta 1-4 (Fuc alpha 1-3) GlcNAc beta 1-6] GalNAc-ol, GalNAc beta 1-4 (Fuc alpha 1-3) GlcNAc beta 1-3[GalNAc beta 1-4 (Fuc alpha 1-3) GlcNAc beta 1-6] GalNAc-ol, and GalNAc beta 1-4 (GalNAc alpha 1-2Fuc alpha 1-3)GlcNAc beta 1-3 [GalNAc beta 1-4 (GalNAc alpha 1-2Fuc alpha 1-3)GlcNAc beta 1-6]GalNAc-ol are represented by HPG-beta 2-N5a, -N6, -N7a, -N7b, and -N9, respectively. These structures have not been encountered previously. Oligosaccharide units GalNAc alpha 1-2Fuc alpha 1-, GalNAc beta 1-4GlcNAc beta 1-, and Fuc alpha 1-3GlcNAc beta 1- are considered to be the allergenically specific epitopes. Partial assignments of 500-MHz 1H NMR spectra of these novel O-linked oligosaccharitols were attempted.