Developing an Optical Interferometric Detection Method based biosensor for detecting specific SARS-CoV-2 immunoglobulins in Serum and Saliva, and their corresponding ELISA correlation

The standard rapid approach for the diagnosis of coronavirus disease 2019 (COVID-19) is the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA. The detection of specific anti-SARS-CoV-2 immunoglobulins is crucial for screening people who have been exposed to the virus, whether or not they presented symptoms. Recent publications report different methods for the detection of specific IgGs, IgMs, and IgAs against SARS-CoV-2; these methods mainly detect immunoglobulins in the serum using conventional techniques such as rapid lateral flow tests or enzyme-linked immunosorbent assay (ELISA). In this article, we report the production of recombinant SARS-CoV-2 spike protein and the development of a rapid, reliable, cost-effective test, capable of detecting immunoglobulins in serum and saliva samples. This method is based on interferometric optical detection. The results obtained using this method and those obtained using ELISA were compared. Owing to its low cost and simplicity, this test can be used periodically for the early detection, surveillance, detection of immunity, and control of the spread of COVID-19.

Unraveling Kiwifruit Allergy Diagnosis: Usefulness of the Current Diagnostic Tests

OBJECTIVES

To determine the usefulness of the in vitro and in vivo methods used in the diagnosis of kiwifruit allergy, focusing on the impact of the seed proteins on their sensitivity.

MATERIAL AND METHODS

Skin prick tests (SPTs) using different commercial extracts, homemade pulp and seed extracts, and prick-prick test with kiwifruit were performed on 36 allergic patients. The presence of specific IgE (sIgE) was assessed using ImmunoCAP (kiwifruit extract), ELISA (Act d 1, Act d 2), ISAC and FABER assays. Immunoblotting of seed extract was carried out, and a single blinded oral food challenge with whole seeds was performed in seed-sensitized subjects.

RESULTS

The prick prick test with kiwifruit demonstrated the highest diagnostic capacity (81.8% sensitivity and 94.1% specificity) among the in vivo tests. The sIgE levels measured by ImmunoCAP-kiwifruit extract showed a similar sensitivity to that of global ISAC and FABER (63.9%, 59.5% and 58.3%, respectively). Act d 1 was the major allergen, and sensitization to it was associated with positive sIgE to whole kiwifruit extract detected by ImmunoCAP (p <0.000). A positive SPT with kiwifruit seeds was associated with severe symptoms with kiwifruit (p = 0.019) as a marker of an advanced disease, but not with clinically relevant sensitization. The challenge to kiwifruit seeds performed on eight seed-sensitized patients resulted negative.

CONCLUSION

Sensitization to Act d 1 is related to a positive result in conventional diagnostic techniques, whereas kiwifruit seed sensitization does not increase the sensitivity of the evaluated diagnostic techniques.

Allergen Profile of London Plane Tree Pollen: Clinical and Molecular Pattern in Central Spain

BACKGROUND AND OBJECTIVE

Platanus acerifolia is a deciduous tree of the Platanaceae family. Sensitisation to this plant varies with geography. Madrid, located in central Spain, has one of the highest pollen concentration levels of this tree of the Iberian Peninsula. Objectives: We evaluated both the clinical characteristics and molecular sensitisation pattern of patients with allergy to the London Plane tree in the region of Madrid.

PATIENTS AND METHODS

Thirty-eight patients allergic to London Plane tree pollen were selected according to clinical symptoms, positive skin prick test, and/or specific IgE. Serum was collected and allergen components were evaluated by immunodetection techniques as well as ImmunoCAP. IgE-binding proteins detected were identified and characterised by mass spectrometry.

RESULTS

Analysis of serum samples from allergic patients revealed 9 IgE-binding bands in London Plane tree-pollen extract. Among these, the 45-kDa protein, corresponding to Pla a 2, was detected in 76.3% of patients. However, the 18-kDa (Pla a 1) and 9-kDa (Pla a 3) bands were detected in 44.7% and 23.7% of sera, respectively. These results were confirmed using purified proteins. Allergen characterisation identified the 27-kDa protein to be glutathione-S-transferase.

CONCLUSIONS

The molecular profile of patients sensitised to London Plane tree pollen differs from that reported in studies from other locations. Our population showed a higher prevalence of Pla a 2 compared to Pla a 1 and Pla a 3. In addition, the minor allergen previously referred to as Pla a 4 was characterised as glutathione-S-transferase.

Mechanisms underlying induction of allergic sensitization by Pru p 3

BACKGROUND

Recently, the nature of the lipid-ligand of Pru p 3, one of the most common plant food allergens in southern Europe, has been identified as a derivative of the alkaloid camptothecin bound to phytosphingosine. However, the origin of its immunological activity is still unknown.

OBJECTIVE

We sought to evaluate the role of the Pru p 3 lipid-ligand in the immunogenic activity of Pru p 3.

METHODS

In vitro cultures of different cell types (monocyte-derived dendritic cells [moDCs], PBMCs [peripheral blood mononuclear cells] and epithelial and iNKT-hybridoma cell lines) have been used to determine the immunological capacity of the ligand, by measuring cell proliferation, maturation markers and cytokine production. To study the capacity of the lipid-ligand to promote sensitization to Pru p 3 in vivo, a mouse model of anaphylaxis to peach has been produced and changes in the humoral and basophil responses have been analysed.

RESULTS

The lipid-ligand of Pru p 3 induced maturation of moDCsc and proliferation of PBMCs. Its immunological activity resided in the phytosphingosine tail of the ligand. The adjuvant activity of the ligand was also confirmed in vivo, where the complex of Pru p 3-ligand induced higher levels of IgE than Pru p 3 alone. The immunological capacity of the Pru p 3 ligand was mediated by CD1d, as maturation of moDCs was inhibited by anti-CD1d antibodies and Pru p 3-ligand co-localized with CD1d on epithelial cells. Finally, Pru p 3-ligand presented by CD1d was able to interact with iNKTs.

CONCLUSIONS AND CLINICAL RELEVANCE

The Pru p 3 lipid-ligand could act as an adjuvant to promote sensitization to Pru p 3, through its recognition by CD1d receptors. This intrinsic adjuvant activity of the accompanying lipid cargo could be a general essential feature of the mechanism underlying the phenomenon of allergenicity.

Bronchial Challenge With Tri a 14 as an Alternative Diagnostic Test for Baker's Asthma

BACKGROUND

Baker's asthma (BA) is the most prevalent occupational respiratory disease in developed countries. It is caused by inhalation of wheat dust in the working environment and affects 1%-10% of workers in the baking industry. Diagnosis of BA is based on bronchial challenge with wheat, a technique that carries a high risk for patients. The wheat lipid transfer protein Tri a 14 is a major allergen in BA.

OBJECTIVE

The aim of our study was to characterize Tri a 14 as a marker of BA in order to prevent patients from having to undergo bronchial challenge with wheat.

METHODS

The study population comprised 55 patients selected at the Rio Hortega Hospital, Valladolid, Spain. Patients with BA were diagnosed using a skin prick test (SPT) with wheat and Tri a 14 and bronchial challenge test (BCT) with wheat. Patients with food allergy had a clear clinical history of allergy to peach confirmed by positive SPT to peach extract and Pru p 3.

RESULTS

All patients in the BA group had a positive SPT result with wheat (100%), and most had positive results with Tri a 14 (95%). A positive BCT result with Tri a 14 was also observed in 22 of 27 of the patients with BA (82%). The response to Tri a 14 was specifically associated with BA.

CONCLUSION

Tri a 14 is a good marker of BA and can be used in SPT and BCT as an alternative diagnostic method, thus avoiding bronchial challenge with wheat and reducing the risk associated with this technique.

Transport of Pru p 3 across gastrointestinal epithelium - an essential step towards the induction of food allergy?

BACKGROUND

Since intestinal absorption of food protein can trigger an allergic reaction, the effect of plant food allergen on intestinal epithelial cell permeability and its ability to cross the epithelial monolayer was evaluated.

OBJECTIVE

To study the interaction of Pru p 3 with intestinal epithelium, its natural entrance, analyzing transport kinetics and cellular responses that trigger.

METHODS

This was achieved using Pru p 3, the peach LTP, as a model. Enterocytic monolayers were established by culturing Caco 2 cells, as a model of enterocytes, on permeable supports that separate the apical and basal compartments. Pru p 3 was added to the apical compartment, the transepithelial resistance (TEER) was measured, and the transport was quantified.

RESULTS

The peach allergen that crossed the cell monolayer was detected in the cell fraction and in the basal medium by immunodetection with specific antibodies and the quantity was measured by ELISA assay. Pru p 3 was able to cross the monolayer without disturbing the integrity of the tight junctions. This transport was significantly higher than that of a non-allergenic peach LTP, LTP1, and occurred via lipid raft pathway. The incubation of Caco 2 cells with Pru p 3 and LTP1 produced the expression of epithelial-specific cytokines TSLP, IL33 and IL25.

CONCLUSION

These results suggest that Pru p 3 was able to cross the cell monolayer by the transcellular route and then induce the production of Th2 cytokines. The results of the present study represent a step towards clarifying the importance of Pru p 3 as a sensitizer.

CLINICAL RELEVANCE

The capacity of food allergens to cross the intestinal monolayer could explain their high allergenic capacity and its fast diffusion through the body associating to severe symptoms.

Characterization of profilin and polcalcin panallergens from ash pollen

BACKGROUND

Ash (Fraxinus excelsior) is an important source of allergenic pollen in temperate areas of Europe. Profilin and polcalcin are 2 important panallergens involved in cross-reactivity between different sources.

OBJECTIVE

To clone and produce Fra e 2 (profilin) and Fra e 3 (polcalcin) as recombinant proteins and evaluate their immunological properties using the natural forms obtained from ash pollen.

METHODS

Total RNA from ash pollen was used as a template to obtain the specific complementary DNA (cDNA) sequences of the 2 panallergens. The cDNA-encoding sequences were cloned into the pET11b expression vector and used to transform BL21 (DE3) Escherichia coli cells. Proteins were expressed, purified by chromatography, and characterized structurally by circular dichroism, mass spectrometry, and immunologically by western blot and ELISA using profilin and polcalcin polyclonal antibodies and human sera from ash pollen-sensitized patients.

RESULTS

Profilin and polcalcin amino acid sequences from ash pollen showed a high degree of identity with homologous allergens from different sources. The cDNA-encoding allergen sequences were expressed as nonfusion recombinant proteins and purified to homogeneity. Secondary structure values were similar to those obtained from other members of these families. Allergenic properties of the recombinant allergens were observed to be equivalent to those of the natural counterparts of F excelsior pollen.

CONCLUSIONS

Fra e 2 and Fra e 3 recombinant allergens might be used in clinical diagnosis to determine profilin- and polcalcin-specific IgE levels present in the sera of ash pollen-sensitized patients, thus facilitating the finding of the sensitizing source in areas with complex sensitization profiles.

Allergenic characterization of new mutant forms of Pru p 3 as new immunotherapy vaccines

Nowadays, treatment of food allergy only considered the avoidance of the specific food. However, the possibility of cross-reactivity makes this practice not very effective. Immunotherapy may exhibit as a good alternative to food allergy treatment. The use of hypoallergenic molecules with reduced IgE binding capacity but with ability to stimulate the immune system is a promising tool which could be developed for immunotherapy. In this study, three mutants of Pru p 3, the principal allergen of peach, were produced based on the described mimotope and T cell epitopes, by changing the specific residues to alanine, named as Pru p 3.01, Pru p 3.02, and Pru p 3.03. Pru p 3.01 showed very similar allergenic activity as the wild type by in vitro assays. However, Pru p 3.02 and Pru p 3.03 presented reduced IgE binding with respect to the native form, by in vitro, ex vivo, and in vivo assays. In addition, Pru p 3.03 had affected the IgG4 binding capacity and presented a random circular dichroism, which was reflected in the nonrecognition by specific antibodies anti-Pru p 3. Nevertheless, both Pru p 3.02 and Pru p 3.03 maintained the binding to IgG1 and their ability to activate T lymphocytes. Thus, Pru p 3.02 and Pru p 3.03 could be good candidates for potential immunotherapy in peach-allergic patients.