Characterization of latex allergens and correlation of serum IgE/IgG antibody ratio with clinical symptoms

Novel Bead-Based Epitope Assay is a sensitive and reliable tool for profiling epitope-specific antibody repertoire in food allergy

Identification of allergenic IgE epitopes is instrumental for the development of novel diagnostic and prognostic methods in food allergy. In this work, we present the quantification and validation of a Bead-Based Epitope Assay (BBEA) that through multiplexing of epitopes and multiple sample processing enables completion of large experiments in a short period of time, using minimal quantities of patients’ blood. Peptides that are uniquely coupled to beads are incubated with serum or plasma samples, and after a secondary fluorophore-labeled antibody is added, the level of fluorescence is quantified with a Luminex reader. The signal is then normalized and converted to epitope-specific antibody binding values. We show that the effect of technical artifacts, i.e. well position or reading order, is minimal; and batch effects - different individual microplate runs - can be easily estimated and eliminated from the data. Epitope-specific antibody binding quantified with BBEA is highly reliable, reproducible and has greater sensitivity of epitope detection compared to peptide microarrays. IgE directed at allergenic epitopes is a sensitive biomarker of food allergy and can be used to predict allergy severity and phenotypes; and quantification of the relationship between epitope-specific IgE and IgG4 can further improve our understanding of the immune mechanisms behind allergic sensitization.

Potential, pitfalls, and prospects of food allergy diagnostics with recombinant allergens or synthetic sequential epitopes

This article aims to critically review developments in food allergy diagnostics with regard to the verification of specific IgE antibodies and the identification of the responsible allergens. Results of IgE-binding tests with food extracts are hampered by cross-reactive proteins, low-quality test agents, or both. Specificity can be increased by defining adequate cutoff values, whereas sensitivity can be improved by using high-quality test agents. IgE-binding tests with purified allergens enabled reliable quantification of allergen-specific IgE titers, with higher levels found in individuals with food allergy compared with individuals without food allergy. However, the overlap in individual test reactivity between allergic and nonallergic subjects complicates interpretation. Recombinant allergens and synthetic sequential epitopes enabled detection of sensitization profiles, with IgE specific to several allergens and substructures now being suggested as markers of severity, persistence, or both. However, high-power quantitative studies with larger numbers of patients are required to confirm these markers. IgE-binding tests merely indicate sensitization, whereas the final proof of clinical relevance still relies on family/case history, physical examinations, and provocation tests. Novel technologies promise superior diagnostics. Microarray technology permits simultaneous measurement of multiple IgE reactivities regarding specificity, abundance, reactivity, or interaction. Improved functional tests might enable reliable estimation of the clinical relevance of IgE sensitizations at justifiable expenses.

Differential stimulation of IgE production, STAT activation and cytokine and CD86 expression by 2,4-dinitrochlorobenzene and trimellitic anhydride

It has been reported that dermal exposure to trimellitic anhydride (TMA, 50%), a respiratory allergen, induced greater production of serum IgE and expression of Th2 cytokines than 2,4-dinitrochlorobenzene (DNCB, 1%), a potent contact sensitizer, in female BALB/C mice. To determine if there is any strain difference, four strains (B6C3F1, C57BL/6, BDF1 and BALB/C) of female mice were employed in this study to compare the differential effects of these chemicals on the hypersensitivity responses. Serum IgE levels were increased in TMA-treated B6C3F1, C57BL/6 and BDF1 mice when compared with the DNCB treatment and vehicle controls; in contrast, no difference was observed between TMA- and DNCB-treated BALB/C mice, although both chemicals induced greater IgE production than vehicle controls. In vitro expression of interleukin 4 (IL-4) and IL-13 mRNA by overnight concanavalin A (ConA)-stimulated draining lymph node cells was enhanced following in vivo treatment with TMA but not with DNCB in the B6C3F1, C57BL/6 and BDF1 mice. In contrast, TMA and DNCB induced similar levels of IL-4 and IL-13 mRNA in the BALB/C mice. The IL-4 protein levels in the supernatants of overnight ConA-treated draining lymph node cells were also increased in TMA-treated B6C3F1 and C57BL/6 mice when compared with the DNCB treatment and vehicle controls. Further mechanistic evaluation in the B6C3F1 mice indicated that the activation of STAT6 but not STAT4 by ConA plus IL-2-treated draining lymph node cells was increased in TMA- but not DNCB-treated mice when compared with the vehicle controls. Furthermore, surface expression of B7.2 (CD86) by B cells was increased in both TMA- and DNCB-treated B6C3F1 mice when compared with the vehicles; however, greater B7.2 expression was observed in TMA-treated compared with DNCB-treated. Overall, these results demonstrate that a similar pattern of IgE and cytokine production was observed in these strains of mice except for BALB/C. Furthermore, differential activation of STAT6 and expression of CD86 following exposure to TMA and DNCB may contribute to the differential production of IgE and cytokines.

The pharmacological basis of anti-IgE therapy

The treatment of asthma and allergic rhinitis using unique, humanized anti-IgE monoclonal antibodies with very particular binding specificities is now supported by the results of multiple phase II and III human clinical studies. The therapeutic efficacy of this approach is attributable to several pharmacological mechanisms. In addition to the expected effects of these monoclonal antibodies in neutralizing free IgE and inhibiting IgE production by B cells, several indirect biochemical and cellular effects have been uncovered during the course of the clinical trials. These include the accumulation of potentially beneficial IgE-anti-IgE immune complexes and the downregulation of the high-affinity IgE Fc receptors (FcvarepsilonRI) on basophils and mast cells. This article analyzes the structural basis of the specificity of the anti-IgE antibodies and pertinent results from in vitro experiments, animal model studies, and human clinical trials in an attempt to provide a cogent pharmacological interpretation of the therapeutic effects of anti-IgE therapy in both the near- and long term. The development of anti-IgE therapy over the past 10 years provides an interesting example of the emergence of a conceptually new, biotechnology-produced pharmaceutical.

Characterization of latex allergenic components by capillary zone electrophoresis and N-terminal sequence analysis

In a previous study, protein components purified from latex gloves that elicited allergenic reactions were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and yielded apparent molecular weights of 14, 22, 30, 34, 46, and 58 kD. These allergenic components were isolated for further characterization by capillary zone electrophoresis and N-terminal amino acid sequence analysis. These components all migrated at approximately 25 and 35 min on capillary zone electrophoresis. Diode array spectral analysis detected indistinguishable characteristics between these two protein peaks. In addition, complex formation of these components with patients' immunoglobulin was demonstrated by capillary zone electrophoresis. Analysis of components separated by SDS-PAGE on a polyvinylidene difluoride membrane showed that the first 13 residues were identical to the sequence of hevein. Based on the criteria of charge-to-mass ratio and N-terminal amino acid sequence, our results suggest that these components of latex proteins are similar in the primary structure.