Identification of a vicilin-like major allergen from Prosopis juliflora exhibiting cross- reactivity with legume food allergens.

BACKGROUND: Prosopis juliflora is a clinically relevant allergic sensitizer worldwide and shares cross-reactivity with allergens from several tree pollen and food. The present study aims to purify and immunobiochemically characterize a major allergen from Prosopis pollen. The allergen was further investigated for its cross-reactivity with legume allergens. METHODS: Prosopis extract was fractionated by Q Sepharose and Superdex 75 gel filtration column to purify the allergen. Specific IgE against purified protein was estimated via ELISA and immunoblot. The protein was subjected to mass spectrometric analysis. Glycan characterization was performed by Schiff staining and lectin binding assay followed by deglycosylation studies. The functional activity of the purified protein was evaluated by the basophil activation test. Cross-reactivity was assessed by inhibition studies with legume extracts. RESULTS: A 35 kDa protein was purified and showed 75% IgE reactivity with the patients' sera by ELISA and immunoblot. Glycan characterization of protein demonstrated the presence of terminal glucose and mannose residues. A reduction of 40% and 27% in IgE binding was observed upon chemical and enzymatic deglycosylation of the protein, respectively. The glycoprotein allergen upregulates the expression of CD203c on basophils which was significantly reduced upon deglycosylation, signifying its biological ability to activate the effector cells. The identified protein shared significant homology with Lup an 1 from the lupine bean. Immunoblot inhibition studies of the purified allergen with legume extracts underlined high cross-reactive potential. Complete inhibition was observed with peanut and common bean, while up to 70% inhibition was demonstrated with soy, black gram, chickpea, and lima bean. CONCLUSION: A 35 kDa vicilin-like major allergen was isolated from P. juliflora. The protein possesses glycan moieties crucial for IgE binding and basophil activation. Furthermore, the purified protein shows homology with Lup an 1 and exhibits cross-reactivity with common edible legume proteins.

Effect of thermal processing and γ-irradiation on allergenicity of legume proteins.

Legumes are implicated in IgE mediated food allergy in different countries. The present study aimed to investigate the effect of different processing methods on allergenicity of legume proteins. The extracts were processed by boiling, γ-irradiation or by combination of both. The changes in soluble protein content, specific IgE binding and allergenic potential of legume proteins were assessed. Thermal processing resulted in a 3- to 4-fold reduction in soluble protein. Specific IgE binding was reduced 74±6.5%, 83±11.6% and 62±7.2% in the soluble protein of kidney bean, black gram and peanut, respectively, after boiling (p<0.01) whereas there was 34±5.2%, 74±15.6% and 44±11.1% IgE binding reduction in the insoluble protein fraction of respective legumes. Boiling followed by γ-irradiation reduced IgE binding significantly (p<0.05). Biopotency of soluble protein of kidney bean, black gram and peanut was reduced 7-, 3- and 26-folds (p<0.001), respectively, and that of insoluble protein decreased 6-, 4- and 8-folds (p<0.001), respectively, after boiling. Combination treatment was effective in reducing the potency of both soluble and insoluble protein significantly as compared to boiling alone (p<0.001). However, γ-irradiation alone did not bring any change in allergenicity. In conclusion, boiling followed by γ-irradiation is effective in attenuating allergenicity of legume proteins.