The Western blot is a highly sensitive and efficient technique in diagnosing allergy to wasp venom

Medical and molecular biophysical techniques as substantial tools in the era of mRNA-based vaccine technology

The COVID-19 pandemic prompted the advancement of vaccine technology using mRNA delivery into the host cells. Consequently, mRNA-based vaccines have emerged as a practical approach against SARS-CoV-2 owing to their inherent properties, such as cost-effectiveness, rapid manufacturing, and preservation. These features are vital, especially in resource-constrained regions. Nevertheless, the design of mRNA-based vaccines is intricately intertwined with the refinement of biophysical technologies, thereby establishing their high potential. The preparation of mRNA-based vaccines involves a sequence of phases combining medical and molecular biophysical technologies. Furthermore, their efficiency depends on the capability to optimize their positive attributes, thus paving the way for their subsequent preclinical and clinical evaluations. Using biophysical techniques, the characterization of nucleic acids extends from their initial formulation to their cellular internalization abilities and encapsulation in biomolecule complexes, such as lipid nanoparticles (LNPs), for designing mRNA-based LNPs. Furthermore, nanoparticles are subjected to a series of careful screening steps to assess their physical and chemical characteristics before achieving an optimum formulation suitable for preclinical and clinical studies. This review provides a comprehensive understanding of the fundamental role of biophysical techniques in the complex development of mRNA-based vaccines and their role in the recent success during the COVID-19 pandemic.

Quantitative computerized western blotting in detail

The analysis of antibody reactivity against multiple antigens separated according to their molecular weights is facilitated by western blotting. The distinction between immune dominant and recessive antigens is often difficult and carried out by qualitative or empirical means. Quantitative computerized western blotting (QCWB) analyzes reactivity to specific antigens by providing a statistically measurable value for each band allowing differentiation between immunodominant and immunorecessive determinants. QCWB is useful for both single time point analysis and longitudinal studies where multiple time points are evaluated and the relativities against individual bands compared. This technique can be employed to study humoral responses to complex antigenic mixtures such as allergens and infectious agents, or identify serologic markers for early diagnosis of cancer, autoimmune or infectious diseases, or to monitor patient's clinical status.

Detection of Allergen-Specific IgE Antibody Responses

Allergen-specific IgE production is the central event in the pathogenesis of atopic disorders and increases in specific IgE serum antibodies are an indicator of immediate hypersensitivity responses in humans and in animal models of allergy. Consequently, accurate and user-friendly methods are needed to measure serum levels of allergen-specific IgE. This review examines historical and recent developments in in vivo and in vitro methods for the detection of allergen-specific IgE in humans and in animal models. Routinely, in vitro methods such as enzyme-linked immunosorbant assays or radioallergosorbant tests and in vivo methods such as the skin prick test (SPT) for humans and the passive cutaneous anaphylaxis assay (PCA) used in animals are utilized to detect allergen-specific IgE. While in vivo assays are usually more accurate than in vitro assays since they provide a functional readout of IgE activity, they are relatively costly and require considerable expertise. On the other hand in vitro assays are limited by the fact that the amount of allergen-specific serum IgG exceeds IgE antibody by several orders of magnitude, resulting in competition for allergen binding. Consequently, methods that use allergen as a direct capture step are limited by the availability of free allergen binding sites for IgE. In order to circumvent this problem, in vitro methods usually require prior depletion of IgG or use high amounts of allergen in order to facilitate availability of free binding sites for IgE detection. Clearly, these approaches are limited for small sample volumes and allergens that are in short supply. New methods such as protein microarray could potentially overcome this problem by providing high allergen concentrations in a relatively small reaction volume. Currently, in vitro methods are rarely used in isolation for prognosis but are used primarily to complement the information obtained from in vivo assays. With the emergence of new technologies it is conceivable that in vitro assays may in the future replace in vivo assays, however until then in vivo assays remain the gold standard of allergen-specific IgE detection.

The prevalence and identity of Chlamydia-specific IgE in children with asthma and other chronic respiratory symptoms

Background

Recent studies have confirmed the presence of viable Chlamydia in the bronchoalveolar lavage (BAL) fluid of pediatric patients with airway hyperresponsiveness. While specific IgG and IgM responses to C. pneumoniae are well described, the response and potential contribution of Ag-specific IgE are not known. The current study sought to determine if infection with Chlamydia triggers the production of pathogen-specific IgE in children with chronic respiratory diseases which might contribute to inflammation and pathology.

Methods

We obtained BAL fluid and serum from pediatric respiratory disease patients who were generally unresponsive to corticosteroid treatment as well as sera from age-matched control patients who saw their doctor for wellness checkups. Chlamydia-specific IgE was isolated from BAL and serum samples and their specificity determined by Western blot techniques. The presence of Chlamydia was confirmed by species-specific PCR and BAL culture assays.

Results

Chlamydial DNA was detected in the BAL fluid of 134/197 (68%) patients. Total IgE increased with age until 15 years old and then decreased. Chlamydia-specific IgE was detected in the serum and/or BAL of 107/197 (54%) patients suffering from chronic respiratory disease, but in none of the 35 healthy control sera (p < 0.0001). Of the 74 BAL culture-positive patients, 68 (91.9%, p = 0.0001) tested positive for Chlamydia-specific IgE. Asthmatic patients had significantly higher IgE levels compared to non-asthmatics (p = 0.0001). Patients who were positive for Chlamydia DNA or culture had significantly higher levels of serum IgE compared to negative patients (p = 0.0071 and p = 0.0001 respectively). Only 6 chlamydial antigens induced Chlamydia-specific IgE and patients with C. pneumoniae-specific IgE had significantly greater levels of total IgE compared to C. pneumoniae-specific IgE negative ones (p = 0.0001).

Conclusions

IgE antibodies play a central role in allergic inflammation; therefore production of Chlamydia-specific IgE may prove significant in the exacerbation of chronic, allergic airway diseases, thus highlighting a direct role for Chlamydia in asthma pathogenesis.

[Standards and pitfalls of in-vitro diagnostics of Hymenoptera venom allergy]

In patients with a history of anaphylactic sting reactions, in-vitro tests are performed in order to demonstrate venom sensitization to the causative venom. Measurement of specific IgE-antibodies (sIgE) to the natural composite venom represents the standard in-vitro method to demonstrate venom sensitization. If sensitization to the composite venom cannot be demonstrated, one may determine sIgE to recombinant allergen compounds, in order to demonstrate sensitization to molecular venom allergens. Moreover, several cellular tests are available to confirm venom sensitization. Herein basophils, which carry cell-bound sIgE, can be used to produce a confirmatory response upon incubation with venom allergens. Reactions to both honey bee and vespid venom may either indicate true double sensitization or cross sensitization. The identification of antibodies cross-reacting to venoms and to other allergen sources does not exclude clinical relevance. Elevated baseline serum tryptase is a risk factor for severe systemic reactions after a field sting and during venom immunotherapy (VIT), the latter in particular for VIT with vespid venom. Serum tryptase measurement should, therefore, be included into routine diagnostics of venom allergy. The measurement of IgG-antibodies specific to venom is not recommended for routine work-up. None of the mentioned in-vitro tests, which may be used before, during or after VIT, allow, however, a precise prognosis with respect to future sting reactions, or to side effects and to the efficacy of VIT, respectively. To validate the reason for a VIT, one should also consider patient history and results of other tests.

Quantitative computerized western blotting

Western blotting allows analysis of antibody reactivity against multiple antigens separated according to their molecular weights. The distinction between immune dominant and recessive antigens is often difficult and carried out by qualitative or empirical means. Quantitative computerized western blotting (QCWB) addresses this difficulty by analyzing reactivity to specific antigens and providing a statistically measurable value for each band. This allows differentiation between immunodominant and immunorecessive determinants. QCWB is appropriate for either single time point analysis or longitudinal studies where multiple time points are evaluated and the reactivities against individual bands compared. This technique can be used to study humoral responses to complex antigenic mixtures such as allergens and infectious agents, or to identify serologic markers for early diagnosis of cancer, autoimmune, or infectious diseases, or to monitor patient's clinical status.

[In vitro allergy testing]

Along with the history, skin tests and provocation tests, in vitro test procedures are essential for the adequate care for patients with allergies. While serological investigations of immediate-type allergic reactions primarily detect allergen-specific IgE antibodies, basophil activation tests with different read-out parameters are available for cellular diagnosis of immediate-type reaction patterns. If clinically necessary, further immunological methods (i. e. immunoblots, lymphocyte transformation tests) can be employed. New options are provided by allergen microarray technology, which makes it possible to determine not only the specific antigenic protein but also to analyze different epitopes.

Bacterial fermentation of recombinant major wasp allergen Antigen 5 using oxygen limiting growth conditions improves yield and quality of inclusion bodies

A process for bacterial expression and purification of the recombinant major wasp allergen Antigen 5 (Ves v 5) was developed to produce protein for diagnostic and therapeutic applications for type 1 allergic diseases. Special attention was focused on medium selection, fermentation conditions, and efficient refolding procedures. A soy based medium was used for fermentation to avoid peptone from animal origin. Animal-derived peptone required the use of isopropyl-beta-D-thiogalactopyranoside (IPTG) for the induction of expression. In the case of soy peptone, a constitutive expression was observed, suggesting the presence of a component that mimics IPTG. Batch cultivation at reduced stirrer speed caused a reduced biomass due to oxygen limitation. However, subsequent purification and processing of inclusion bodies yielded significantly higher amount of product. Furthermore, the protein composition of the inclusion bodies differed. Inclusion bodies were denatured and subjected to diafiltration. Detailed monitoring of diafiltration enabled the determination of the transition point. Final purification was conducted using cation-exchange and size-exclusion chromatography. Purified recombinant Ves v 5 was analyzed by RP-HPLC, CD-spectroscopy, SDS-PAGE, and quantification ELISA. Up to 15 mg highly purified Ves v 5 per litre bioreactor volume were obtained, with endotoxin concentrations less than 20 EU mg(-1) protein and high comparability to the natural counterpart. Analytical results confirm the suitability of the recombinant protein for diagnostic and clinical applications. The results clearly demonstrate that not only biomass, but especially growth conditions play a key role in the production of recombinant Ves v 5. This has an influence on inclusion body formation, which in turn influences the renaturation rate and absolute product yield. This might also be true for other recombinant proteins that accumulate as inclusion bodies in Escherichia coli.

Diagnosis of Hymenoptera venom allergy

The purpose of diagnostic procedure is to classify a sting reaction by history, identify the underlying pathogenetic mechanism, and identify the offending insect. Diagnosis of Hymenoptera venom allergy thus forms the basis for the treatment. In the central and northern Europe vespid (mainly Vespula spp.) and honeybee stings are the most prevalent, whereas in the Mediterranean area stings from Polistes and Vespula are more frequent than honeybee stings; bumblebee stings are rare throughout Europe and more of an occupational hazard. Several major allergens, usually glycoproteins with a molecular weight of 10-50 kDa, have been identified in venoms of bees, vespids. and ants. The sequences and structures of the majority of venom allergens have been determined and several have been expressed in recombinant form. A particular problem in the field of cross-reactivity are specific immunoglobulin E (IgE) antibodies directed against carbohydrate epitopes, which may induce multiple positive test results (skin test, in vitro tests) of still unknown clinical significance. Venom hypersensitivity may be mediated by immunologic mechanisms (IgE-mediated or non-IgE-mediated venom allergy) but also by nonimmunologic mechanisms. Reactions to Hymenoptera stings are classified into normal local reactions, large local reactions, systemic toxic reactions, systemic anaphylactic reactions, and unusual reactions. For most venom-allergic patients an anaphylactic reaction after a sting is very traumatic event, resulting in an altered health-related quality of life. Risk factors influencing the outcome of an anaphylactic reaction include the time interval between stings, the number of stings, the severity of the preceding reaction, age, cardiovascular diseases and drug intake, insect type, elevated serum tryptase, and mastocytosis. Diagnostic tests should be carried out in all patients with a history of a systemic sting reaction to detect sensitization. They are not recommended in subjects with a history of large local reaction or no history of a systemic reaction. Testing comprises skin tests with Hymenoptera venoms and analysis of the serum for Hymenoptera venom-specific IgE. Stepwise skin testing with incremental venom concentrations is recommended. If diagnostic tests are negative they should be repeated several weeks later. Serum tryptase should be analyzed in patients with a history of a severe sting reaction.

Patients with negative skin tests

PURPOSE OF REVIEW

The aim of this article is to present and discuss the clinical problem of systemic anaphylaxis to Hymenoptera venoms in patients without detectable immunoglobulin E, as it appears in recent literature. Reported at variable frequency in large series of patients undergoing evaluation, systemic anaphylaxis was previously considered to reflect lost sensitization or to involve non-immunoglobulin E mediated mechanisms. Sporadic case-reports drew attention to the fact that severe or even fatal reactions may occur in patients with negative skin tests.

RECENT FINDINGS

A breakthrough article by Golden et al., who performed deliberate stings on skin test negative venom anaphylaxis patients, demonstrated that clinical sensitivity was still present in a subset of these subjects and pointed out to the limitations of present diagnostic methods or reagents. New immunobiochemical methods and highly specific recombinant allergens--when all clinically relevant Hymenoptera venom allergens have been identified, cloned, sequenced and expressed in the proper system--are anticipated to increase the diagnostic yield. Non-specific mechanisms causing anaphylactoid reactions will probably explain some enigmatic, skin test negative radioallergosorbent test negative cases in the future. Occult mastocytosis, predisposing patients to anaphylactoid reactions, has been reported with increasing frequency among skin test negative patients. Lastly, other causes mimicking venom anaphylaxis may on rare occasions contribute to the problem.

SUMMARY

With the present understanding of venom allergy, the practising clinician is not infrequently faced with the dilemma of the skin test negative patient. Once other identifiable causes have been carefully ruled out, referral to a specialized center for deliberate sting-challenges appears in selected cases to be a medically appropriate and ethically justified management approach.

Diagnosis of Hymenoptera venom sensitivity

PURPOSE OF REVIEW

The objective of this review is to highlight recent advances in the preparation, documentation and performance of reagents and methods used in the diagnosis of Hymenoptera-venom-induced immediate-type hypersensitivity.

RECENT FINDINGS

The following potent allergens have been reported: (1) a low-molecular-weight honey-bee allergen (Api m 6) has been described; (2) venom allergens in the North American species of bumble-bee (Bombus pennsylvanicus) have been more fully characterized, with the focus on phospholipase A2; (3) the vespid venom Ves v 5 allergen has been structurally mapped to identify immunoglobulin-E-binding epitopes; (4) the possible role of carbohydrate antigen epitopes as a cause of cross-reactivity among honey-bee and vespid venom proteins has been reported; and (5) the venom of Pachycondyla chinensis, an ant found commonly in the Far East, has been described. The most significant reports during this period have focused on the less-than-ideal performance of the intradermal venom skin-test reagents. The issue of the patient that is positive for venom allergy history but negative for an intradermal venom skin test is raised, and it is suggested that there is a need for caution and the use of serology as a supplementary diagnostic test.

SUMMARY

The important issue this year is the reminder that intradermal skin tests may be negative in venom-allergic patients, possibly because of changes in the potency of the extracts. The clinical history should drive the diagnosis of insect-sting allergy. When negative confirmatory venom skin-test or serology results are considered to be inconsistent with a positive history, they should be repeated.