Structural and functional analyses of antibodies specific for modified core N-glycans suggest a role in TH 2 responses

IgE to cross-reactive carbohydrate determinants (CCD) in childhood: Prevalence, risk factors, putative origins

BACKGROUND

IgE antibodies to cross-reactive carbohydrate determinants (CCD) are usually clinically irrelevant but they can be a cause of false positive outcomes of allergen-specific IgE tests in vitro. Their prevalence and levels have been so far cross-sectionally examined among adult allergic patients and much less is known about their origins and relevance in childhood.

METHODS

We examined CCD with a cross-sectional approach in 1263 Italian pollen allergic children (Panallergen in Paediatrics, PAN-PED), as well as with a longitudinal approach in 612 German children (Multicenter Allergy Study, MAS), whose cutaneous and IgE sensitization profile to a broad panel of allergen extracts and molecules was already known. The presence and levels of IgE to CCD were examined in the sera of both cohorts using bromelain (MUXF3) as reagent and a novel chemiluminescence detection system, operating in a solid phase of fluorescently labelled and streptavidin-coated paramagnetic microparticles (NOVEOS, HYCOR, USA).

RESULTS

IgE to CCD was found in 22% of the Italian pollen allergic children, mainly in association with an IgE response to grass pollen. Children with IgE to CCD had higher total IgE levels and were sensitized to more allergenic molecules of Phleum pratense than those with no IgE to CCD. Among participants of the German MAS birth cohort study, IgE to CCD emerged early in life (even at pre-school age), with IgE sensitization to group 1 and 4 allergen molecules of grasses, and almost invariably persisted over the full observation period.

CONCLUSIONS

Our results contribute to dissect the immunological origins, onset, evolution and risk factors of CCD-sIgE response in childhood, and raise the hypothesis that group 1 and/or 4 allergen molecules of grass pollen are major inducers of these antibodies through an antigen-specific, T-B cell cognate interaction.

High-throughput N-glycoproteomics with fast liquid chromatographic separation

N-glycosylation is a common protein post translation modification, which has tremendous structure diversity and wide yet delicate regulation of protein structures and functions. Mass spectrometry-based N-glycoproteomics has become a state-of-the-art pipeline for both qualitative and quantitative characterization of N-glycosylation at the intact N-glycopeptide level, providing comprehensive information of peptide backbones, N-glycosites, monosaccharide compositions, sequence and linkage structures. For high-throughput analysis of large-cohort clinic samples, fast and high-performance separation is indispensable. Here we report our development of 1-h liquid chromatography gradient N-glycoproteomics method and accordingly optimized MS parameters. In the benchmark analysis of cancer and paracancerous tissue of hepatocellular carcinoma, 5,218 intact N-glycopeptides were identified, where 422 site- and structure-specific differential N-glycosylation on 145 N-glycoproteins was observed. The method, representing substantial increase of throughput, can be adopted for fast and efficient analysis of N-glycoproteomes at large scale.

The role of glycosylation in clinical allergy and immunology

While glycans are among the most abundant macromolecules on the cell with widespread functions, their role in immunity has historically been challenging to study. This is in part due to difficulties assimilating glycan analysis into routine approaches used to interrogate immune cell function. Despite this, recent developments have illuminated fundamental roles for glycans in host immunity. The growing field of glycoimmunology continues to leverage new tools and approaches to uncover the function of glycans and glycan-binding proteins in immunity. Here we utilize clinical vignettes to examine key roles of glycosylation in allergy, inborn errors of immunity, and autoimmunity. We will discuss the diverse functions of glycans as epitopes, as modulators of antibody function, and as regulators of immune cell function. Finally, we will highlight immune modulatory therapies that harness the critical role of glycans in the immune system.

Potential and limitations of epitope mapping and molecular targeting in Hymenoptera venom allergy

Hymenoptera venom (HV) allergy can lead to life threatening conditions by specific IgE (sIgE)-mediated anaphylactic reactions. The knowledge about major allergens from venom of different clinically relevant species increased in the last decades, allowing the development of component-resolved diagnostics in which sIgE to single allergens is analysed. Despite these advances, the precise regions of the allergens that bind to IgE are only known for few HV allergens. The detailed characterization of IgE epitopes may provide valuable information to improve immunodiagnostic tests and to develop new therapeutic strategies using allergen-derived peptides or other targeted approaches. Epitope-resolved analysis is challenging, since the identification of conformational epitopes present in many allergens demands complex technologies for molecular analyses. Furthermore, functional analysis of the epitopeś interaction with their respective ligands is needed to distinguish epitopes that can activate the allergic immune response, from those that are recognized by irrelevant antibodies or T cell receptors from non-effector cells. In this review, we focus on the use of mapping and molecular targeting approaches for characterization of the epitopes of the major venom allergens of clinically relevant Hymenoptera species. The screening of the most relevant allergen peptides by epitope mapping could be helpful for the development of molecules that target major and immunodominant epitopes blocking the allergen induced cellular reactions as novel approach for the treatment of HV allergy.

Extract-Shaped Immune Repertoires as Source for Nanobody-Based Human IgE in Grass Pollen Allergy

The presence of allergen-specific IgE in serum is a biomarker for allergic disease. Specific IgE antibodies for research and diagnostics, however, remain scarce. In contrast to prototypic antibodies, camelid species have evolved single domains as moiety for antigen recognition. These so-called nanobodies represent a versatile platform for the development of diagnostic and therapeutic approaches. In this study, we aimed for generating nanobodies and derived IgE formats from an extract-shaped immune repertoire. Timothy grass pollen represents a complex, but well-defined mixture of individual allergens. Therefore, a repertoire library from a timothy grass pollen extract immunised llama was established. The selection by phage display yielded 3 nanobodies with immunoreactivity to the extract. IgE-like nanobody-based human IgE (nb-hIgE) antibodies were produced in mammalian cells and assessed in different immunoassays and commercial platforms. Immunoblotting and diagnostic ImmunoCap analysis of single timothy grass pollen allergens identified the major allergens Phl p 6 and Phl p 4 as targets. Assessment of immunoreactivity further documented significant molecular cross-reactivity with pollen extract of different grass species and variant presence of allergens within extracts of Pooideae grasses. In summary, our study shows that extract-based immunisation enables the generation of allergen-specific nanobodies and derived nb-hIgE formats linking nanobody technologies with allergological applications.

Identification and characterization of an α-1,3 mannosidase from Elizabethkingia meningoseptica and its potential attenuation impact on allergy associated with cross-reactive carbohydratedeterminant

Core α-1,3 mannose is structurally near the core xylose and core fucose on core pentasaccharide from plant and insect glycoproteins. Mannosidase is a useful tool for characterization the role of core α-1,3 mannose in the composition of glycan related epitope, especially for those epitopes in which core xylose and core fucose are involved. Through functional genomic analysis, we identified a glycoprotein α-1,3 mannosidase and named it MA3. We used MA3 to treat allergen horseradish peroxidase (HRP) and phospholipase A2 (PLA2) separately. The results showed that after MA3 removed α-1,3 mannose on HRP, the reactivity of HRP with anti-core xylose polyclonal antibody almost disappeared. And the reactivity of MA3-treated PLA2 with anti-core fucose polyclonal antibody decreased partially. In addition, when PLA2 was conducted enzyme digestion by MA3, the reactivity between PLA2 and allergic patients' sera diminished. These results demonstrated that α-1,3 mannose was an critical component of glycan related epitope.