Peanut allergy is a hypersensitivity reaction with symptoms varying from mild to severe anaphylaxis, tends to be lifelong and very few are able to outgrow this allergy. The prevalence of peanut allergy is highest among the Western countries and over the past decade, a 3.5 fold increase in prevalence of peanut allergy was reported among children in the United States. Increasing prevalence has also been observed among the Asian countries. As with other food allergies, peanut allergy reduces quality of life for the affected individuals and the social and economy burden of healthcare for peanut allergy is substantial. To date, there is no effective treatment for peanut allergy and disease management is by avoidance or relieve of symptoms via administration of epinephrine. Peanut allergy is a type-1 hypersensitivity reaction due to specific IgE production by activated T-helper type 2 (TH2) cells. Studies on various immunotherapy routes such as oral immunotherapy (OIT), sublingual immunotherapy and epicutaneous immunotherapy trials using peanut have shown the ability to induce desensitisation, shifting the allergen-specific cytokine production away from a TH2 respond. In the recent years, lactic acid bacteria probiotics have been reported to down-regulate allergy due to its inherent immunomodulatory properties. Wild-type probiotic in combination with peanut proteins or recombinant probiotics harbouring peanut allergens have been explored for OIT due to its ability to down-regulate allergen-specific-IgE production and the TH2 responses, while increasing the beneficiary population of TH1 regulatory T cells (Treg). This review discusses the current strategies in immunotherapy for peanut allergy.
Current diagnostic tools for peanut allergy using crude peanut extract showed low predictive value and reduced specificity for detection of peanut allergen-specific immunoglobulin E (IgE). The Ara h 2.02, an isoform of the major peanut allergen Ara h 2, contains three IgE epitope recognition sequence of 'DPYSPS' and may be a better reagent for component resolve diagnosis. This research aimed to generate a codon-optimised Ara h 2.02 gene for heterologous expression in Escherichia coli and allergenicity study of this recombinant protein. The codon-optimised gene was generated by PCR using overlapping primers and cloned into the pET-28a (+) expression vector. Moderate expression of a 22.5 kDa 6xhistidine-tagged recombinant Ara h 2.02 protein (6xHis-rAra h 2.02) in BL21 (DE3) host cells was observed upon induction with 1 mM isopropyl β-D-1-thiogalactopyranoside (IPTG). The insoluble recombinant protein was purified under denaturing condition using nickel-nitrilotriacetic acid (Ni-NTA) affinity chromatography and refolded by dialysis in decreasing urea concentration, amounting to a yield of 74 mg/l of expression culture. Matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) and immunoblot analysis confirmed the production of the recombinant 6xHis-rAra h 2.02. The refolded recombinant 6xHis-rAra h 2.02, with or without adjuvant, was able to elicit comparable level of allergen-specific IgE and IgG1 in sensitised Balb/c mice. In addition, the specific IgE antibodies raised against the recombinant protein were able to recognise the native Ara h 2 protein, demonstrating its allergenicity and potential as a reagent for diagnosis and therapeutic study.