Phaseolin: a 47.5kDa protein of red kidney bean (Phaseolus vulgaris L.) plays a pivotal role in hypersensitivity induction.

Red kidney bean (Phaseolus vulgaris L.), a protein rich legume, is consumed globally due to its delicacy. This study was aimed to purify, characterize and assess allergenicity of one of its clinically relevant allergens, later identified as phaseolin. This study was carried out using clinical, in vivo and ex vivo approaches. Phaseolin, an abundant protein of red kidney bean, was purified by column chromatography and reverse-phase-HPLC techniques and characterized by peptide mass fingerprinting. The IgE immunoblotting using red kidney bean allergic patients sera showed phaseolin as a major IgE binding protein of red kidney bean. Phaseolin treated mice demonstrated enhanced levels of specific IgE and IgG1, mouse mast cell protease-1, mRNA expressions of IL-4, IL-5, IL-13 and GATA-3 in the lungs, spleen and intestine along with anaphylactic symptoms indicative of allergic responses. Further, flow cytometry analysis and immunohistochemical studies indicated increased levels of IL-4, IL-5, IL-13 and GATA-3, respectively as compared to controls. The level of Foxp3 was found suppressed in the intestine of phaseolin treated mice when compared to the control. Further, phaseolin treated mice showed positive results in type 1 skin test. Bone marrow derived mast cells (BMMCs) and rat basophilic leukemia (RBL-2H3) cells showed enhanced release of allergic mediators like β-hexosaminidase, histamine, cysteinyl leukotrienes and prostaglandin D2. Taken together, phaseolin was found to possess characteristics of a potential allergen that may lead to hypersensitivity responses in the susceptible individuals and this may be one of the major proteins responsible for allergenicity of red kidney bean.