Natural human Bet v 1-specific IgG antibodies recognize non-conformational epitopes whereas IgE reacts with conformational epitopes

BACKGROUND

The nature of epitopes on Bet v 1 recognized by natural IgG antibodies of birch pollen allergic patients and birch pollen-exposed but non-sensitized subjects has not been studied in detail.

OBJECTIVE

To investigate IgE and IgG recognition of Bet v 1 and to study the effects of natural Bet v 1-specific IgG antibodies on IgE recognition of Bet v 1 and Bet v 1-induced basophil activation.

METHODS

Sera from birch pollen allergic patients (BPA, n = 76), allergic patients without birch pollen allergy (NBPA, n = 40) and non-allergic individuals (NA, n = 48) were tested for IgE, IgG as well as IgG1 and IgG4 reactivity to folded recombinant Bet v 1, two unfolded recombinant Bet v 1 fragments comprising the N-terminal (F1) and C-terminal half of Bet v 1 (F2) and unfolded peptides spanning the corresponding sequences of Bet v 1 and the apple allergen Mal d 1 by ELISA or micro-array analysis. The ability of Bet v 1-specific serum antibodies from non-allergic subjects to inhibit allergic patients IgE or IgG binding to rBet v 1 or to unfolded Bet v 1-derivatives was assessed by competition ELISAs. Furthermore, the ability of serum antibodies from allergic and non-allergic subjects to modulate Bet v 1-induced basophil activation was investigated using rat basophilic leukaemia cells expressing the human FcεRI which had been loaded with IgE from BPA patients.

RESULTS

IgE antibodies from BPA patients react almost exclusively with conformational epitopes whereas IgG, IgG1 and IgG4 antibodies from BPA, NBPA and NA subjects recognize mainly unfolded and sequential epitopes. IgG competition studies show that IgG specific for unfolded/sequential Bet v 1 epitopes is not inhibited by folded Bet v 1 and hence the latter seem to represent cryptic epitopes. IgG reactivity to Bet v 1 peptides did not correlate with IgG reactivity to the corresponding Mal d 1 peptides and therefore does not seem to be a result of primary sensitization to PR10 allergen-containing food. Natural Bet v 1-specific IgG antibodies inhibited IgE binding to Bet v 1 only poorly and could even enhance Bet v 1-specific basophil activation.

CONCLUSION

IgE and IgG antibodies from BPA patients and birch pollen-exposed non-sensitized subjects recognize different epitopes. These findings explain why natural allergen-specific IgG do not protect against allergic symptoms and suggest that allergen-specific IgE and IgG have different clonal origin.

Monomeric agonist peptide/MHCII complexes activate T-cells in an autonomous fashion

Molecular crowding of agonist peptide/MHC class II complexes (pMHCIIs) with structurally similar, yet per se non-stimulatory endogenous pMHCIIs is postulated to sensitize T-cells for the recognition of single antigens on the surface of dendritic cells and B-cells. When testing this premise with the use of advanced live cell microscopy, we observe pMHCIIs as monomeric, randomly distributed entities diffusing rapidly after entering the APC surface. Synaptic TCR engagement of highly abundant endogenous pMHCIIs is low or non-existent and affects neither TCR engagement of rare agonist pMHCII in early and advanced synapses nor agonist-induced TCR-proximal signaling. Our findings highlight the capacity of single freely diffusing agonist pMHCIIs to elicit the full T-cell response in an autonomous and peptide-specific fashion with consequences for adaptive immunity and immunotherapeutic approaches.

Bos d 13, A Novel Heat-Stable Beef Allergen

SCOPE

Red meat, a staple food of Western diets, can also induce IgE-mediated allergic reactions. Yet, apart from the heat-labile protein serum albumin and the carbohydrate α-Gal, the molecules causing allergic reactions to red meat remain unknown.

METHODS AND RESULTS

IgE reactivity profiles of beef-sensitized individuals are analyzed by IgE-immunoblotting with protein extracts from raw and cooked beef. Two IgE-reactive proteins are identified by peptide mass fingerprinting as myosinlight chain 1 (MYL1) and myosin light chain 3 (MYL3) in cooked beef extract and are designated Bos d 13 isoallergens. MYL1 and MYL3 are produced recombinantly in Escherichia coli. ELISAs proved their IgE reactivity and circular dichroism analysis showed that they represent folded molecules with remarkable thermal stability. In vitro gastrointestinal digestion experiments showed the higher stability of rMYL1 as compared to rMYL3. Exposure of a monolayer of Caco-2 cells to rMYL1 indicated that the molecule is able to cross intestinal epithelial cells without disturbing the integrity of the tight junctions, suggesting the sensitizing capacity of MYL1.

CONCLUSION

MYLs are identified as novel heat-stable bovine meat allergens.

Isolation of nanobodies with potential to reduce patients' IgE binding to Bet v 1

BACKGROUND

Recent studies showed that a single injection of human monoclonal allergen-specific IgG antibodies significantly reduced allergic symptoms in birch pollen-allergic patients. Since the production of full monoclonal antibodies in sufficient amounts is laborious and expensive, we sought to investigate if smaller recombinant allergen-specific antibody fragments, that is, nanobodies, have similar protective potential. For this purpose, nanobodies specific for Bet v 1, the major birch pollen allergen, were generated to evaluate their efficacy to inhibit IgE-mediated responses.

METHODS

A cDNA-VHH library was constructed from a camel immunized with Bet v 1 and screened for Bet v 1 binders encoding sequences by phage display. Selected nanobodies were expressed, purified, and analyzed in regards of epitope-specificity and affinity to Bet v 1. Furthermore, cross-reactivity to Bet v 1-homologues from alder, hazel and apple, and their usefulness to inhibit IgE binding and allergen-induced basophil activation were investigated.

RESULTS

We isolated three nanobodies that recognize Bet v 1 with high affinity and cross-react with Aln g 1 (alder) and Cor a 1 (hazel). Their epitopes were mapped to the alpha-helix at the C-terminus of Bet v 1. All nanobodies inhibited allergic patients' polyclonal IgE binding to Bet v 1, Aln g 1, and Cor a 1 and partially suppressed Bet v 1-induced basophil activation.

CONCLUSION

We identified high-affinity Bet v 1-specific nanobodies that recognize an important IgE epitope and reduce allergen-induced basophil activation revealing the first proof that allergen-specific nanobodies are useful tools for future treatment of pollen allergy.

Neutralization of SARS-CoV-2 requires antibodies against conformational receptor-binding domain epitopes

Background

The determinants of successful humoral immune response to the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) are of critical importance for the design of effective vaccines and the evaluation of the degree of protective immunity conferred by exposure to the virus. As novel variants emerge, understanding their likelihood of suppression by population antibody repertoires has become increasingly important.

Methods

In this study, we analyzed the SARS‐CoV‐2 polyclonal antibody response in a large population of clinically well‐characterized patients after mild and severe COVID‐19 using a panel of microarrayed structurally folded and unfolded SARS‐CoV‐2 proteins, as well as sequential peptides, spanning the surface spike protein (S) and the receptor‐binding domain (RBD) of the virus.

Results

S‐ and RBD‐specific antibody responses were dominated by immunoglobulin G (IgG), mainly IgG₁, and directed against structurally folded S and RBD and three distinct peptide epitopes in S2. The virus neutralization activity of patients´ sera was highly correlated with IgG antibodies specific for conformational but not sequential RBD epitopes and their ability to prevent RBD binding to its human receptor angiotensin‐converting enzyme 2 (ACE2). Twenty percent of patients selectively lacked RBD‐specific IgG. Only immunization with folded, but not with unfolded RBD, induced antibodies against conformational epitopes with high virus‐neutralizing activity. Conformational RBD epitopes required for protection do not seem to be altered in the currently emerging virus variants.

Conclusion

These results are fundamental for estimating the protective activity of antibody responses after natural infection or vaccination and for the design of vaccines, which can induce high levels of SARS‐CoV‐2–neutralizing antibodies conferring sterilizing immunity.

Past, present, and future of allergen immunotherapy vaccines

Allergen-specific immunotherapy (AIT) is an allergen-specific form of treatment for patients suffering from immunoglobulin E (IgE)-associated allergy; the most common and important immunologically mediated hypersensitivity disease. AIT is based on the administration of the disease-causing allergen with the goal to induce a protective immunity consisting of allergen-specific blocking IgG antibodies and alterations of the cellular immune response so that the patient can tolerate allergen contact. Major advantages of AIT over all other existing treatments for allergy are that AIT induces a long-lasting protection and prevents the progression of disease to severe manifestations. AIT is cost effective because it uses the patient´s own immune system for protection and potentially can be used as a preventive treatment. However, broad application of AIT is limited by mainly technical issues such as the quality of allergen preparations and the risk of inducing side effects which results in extremely cumbersome treatment schedules reducing patient´s compliance. In this article we review progress in AIT made from its beginning and provide an overview of the state of the art, the needs for further development, and possible technical solutions available through molecular allergology. Finally, we consider visions for AIT development towards prophylactic application.

Resistance of parvalbumin to gastrointestinal digestion is required for profound and long-lasting prophylactic oral tolerance

Background

Early introduction of food allergens into children's diet is considered as a strategy for the prevention of food allergy. The major fish allergen parvalbumin exhibits high stability against gastrointestinal digestion. We investigated whether resistance of carp parvalbumin to digestion affects oral tolerance induction.

Methods

Natural Cyp c 1, nCyp c 1, and a gastrointestinal digestion‐sensitive recombinant Cyp c 1 mutant, mCyp c 1, were analyzed for their ability to induce oral tolerance in a murine model. Both antigens were compared by gel filtration, circular dichroism measurement, in vitro digestion, and splenocyte proliferation assays using synthetic Cyp c 1‐derived peptides. BALB/c mice were fed once with high doses of nCyp c 1 or mCyp c 1, before sensitization to nCyp c 1. Immunological tolerance was studied by measuring Cyp c 1‐specific antibodies and cellular responses by ELISA, basophil activation, splenocyte proliferations, and intragastric allergen challenge.

Results

Wild‐type and mCyp c 1 showed the same physicochemical properties and shared the same major T‐cell epitope. However, mCyp c 1 was more sensitive to enzymatic digestion in vitro than nCyp c 1. A single high‐dose oral administration of nCyp c 1 but not of mCyp c 1 induced long‐term oral tolerance, characterized by lack of parvalbumin‐specific antibody and cellular responses. Moreover, mCyp c 1‐fed mice, but not nCyp c 1‐fed mice developed allergic symptoms upon challenge with nCyp c 1.

Conclusion

Sensitivity to digestion in the gastrointestinal tract influences the capacity of an allergen to induce prophylactic oral tolerance.

A hypoallergenic peptide mix containing T cell epitopes of the clinically relevant house dust mite allergens

Background

In the house dust mite (HDM) Dermatophagoides pteronyssinus, Der p 1, 2, 5, 7, 21, and 23 have been identified as the most important allergens. The aim of this study was to define hypoallergenic peptides derived from the sequences of the six allergens and to use the peptides and the complete allergens to study antibody, T cell, and cytokine responses in sensitized and nonsensitized subjects.

Methods

IgE reactivity of HDM‐allergic and non‐HDM‐sensitized individuals to 15 HDM allergens was established using ImmunoCAP ISAC technology. Thirty‐three peptides covering the sequences of the six HDM allergens were synthesized. Allergens and peptides were tested for IgE and IgG reactivity by ELISA and ImmunoCAP, respectively. Allergenic activity was determined by basophil activation. CD4+ T cell and cytokine responses were determined in PBMC cultures by CFSE dilution and Luminex technology, respectively.

Results

House dust mite allergics showed IgE reactivity only to complete allergens, whereas 31 of the 33 peptides lacked relevant IgE reactivity and allergenic activity. IgG antibodies of HDM‐allergic and nonsensitized subjects were directed against peptide epitopes and higher allergen‐specific IgG levels were found in HDM allergics. PBMC from HDM‐allergics produced higher levels of IL‐5 whereas non‐HDM‐sensitized individuals mounted higher levels of IFN‐gamma, IL‐17, pro‐inflammatory cytokines, and IL‐10.

Conclusion

IgG antibodies in HDM‐allergic patients recognize peptide epitopes which are different from the epitopes recognized by IgE. This may explain why naturally occurring allergen‐specific IgG antibodies do not protect against IgE‐mediated allergic inflammation. A mix of hypoallergenic peptides containing T cell epitopes of the most important HDM allergens was identified.

BTK inhibition is a potent approach to block IgE-mediated histamine release in human basophils

Background

Recent data suggest that Bruton's tyrosine kinase (BTK) is an emerging therapeutic target in IgE receptor (IgER)‐cross‐linked basophils.

Methods

We examined the effects of four BTK inhibitors (ibrutinib, dasatinib, AVL‐292, and CNX‐774) on IgE‐dependent activation and histamine release in blood basophils obtained from allergic patients (n=11) and nonallergic donors (n=5). In addition, we examined the effects of these drugs on the growth of the human basophil cell line KU812 and the human mast cell line HMC‐1.

Results

All four BTK blockers were found to inhibit anti‐IgE‐induced histamine release from basophils in nonallergic subjects and allergen‐induced histamine liberation from basophils in allergic donors. Drug effects on allergen‐induced histamine release were dose dependent, with IC₅₀ values ranging between 0.001 and 0.5 μmol/L, and the following rank order of potency: ibrutinib>AVL‐292>dasatinib>CNX‐774. The basophil‐targeting effect of ibrutinib was confirmed by demonstrating that IgE‐dependent histamine release in ex vivo blood basophils is largely suppressed in a leukemia patient treated with ibrutinib. Dasatinib and ibrutinib were also found to counteract anti‐IgE‐induced and allergen‐induced upregulation of CD13, CD63, CD164, and CD203c on basophils, whereas AVL‐292 and CNX‐774 showed no significant effects. Whereas dasatinib and CNX‐774 were found to inhibit the growth of HMC‐1 cells and KU812 cells, no substantial effects were seen with ibrutinib or AVL‐292.

Conclusions

BTK‐targeting drugs are potent inhibitors of IgE‐dependent histamine release in human basophils. The clinical value of BTK inhibition in the context of allergic diseases remains to be determined.

Epitope specificity determines cross-protection of a SIT-induced IgG4 antibody

Background

The calcium‐binding 2EF‐hand protein Phl p 7 from timothy grass pollen is a highly cross‐reactive pollen pan‐allergen that can induce severe clinical symptoms in allergic patients. Recently, a human monoclonal Phl p 7‐specific IgG₄ antibody (mAb102.1F10) was isolated from a patient who had received grass pollen‐specific immunotherapy (SIT).

Methods

We studied epitope specificity, cross‐reactivity, affinity and cross‐protection of mAb102.1F10 towards homologous calcium‐binding pollen allergens. Sequence comparisons and molecular modelling studies were performed with ClustalW and SPADE, respectively. Surface plasmon resonance measurements were made with purified recombinant allergens. Binding and cross‐reactivity of patients' IgE and mAb102.1F10 to calcium‐binding allergens and peptides thereof were studied with quantitative RAST‐based methods, in ELISA, basophil activation and IgE‐facilitated allergen presentation experiments.

Results

Allergens from timothy grass (Phl p 7), alder (Aln g 4), birch (Bet v 4), turnip rape (Bra r 1), lamb's quarter (Che a 3) and olive (Ole e 3, Ole e 8) showed high sequence similarity and cross‐reacted with allergic patients' IgE. mAb102.1F10 bound the C‐terminal portion of Phl p 7 in a calcium‐dependent manner. It cross‐reacted with high affinity with Ole e 3, whereas binding and affinity to the other allergens were low. mAb102.1F10 showed limited cross‐inhibition of patients' IgE binding and basophil activation. Sequence comparison and surface exposure calculations identified three amino acids likely to be responsible for limited cross‐reactivity.

Conclusions

Our results demonstrate that a small number of amino acid differences among cross‐reactive allergens can reduce the affinity of binding by a SIT‐induced IgG and thus limit cross‐protection.