Immunoglobulin E (IgE)-mediated cross-reactivity between mesquite pollen proteins and lima bean, an edible legume

Abstract

Immunoglobulin E (IgE)-mediated food allergy often develops as a consequence of allergic sensitization to pollen proteins. Mesquite (Prosopis juliflora) tree pollen is reported to be cross-reactive with other pollen species, but little has been reported on its cross-reactivity with plant-derived foods belonging to the same/different families. The present study investigates the in vitro cross-reactivity of mesquite pollen and lima bean (Phaseolus lunatus), an edible seed belonging to the Leguminosae family. Of 110 patients (asthma, rhinitis or both) tested intradermally, 20 showed marked positive reactions with Prosopis pollen extract. Of these, 12 patients showed elevated specific IgE to Prosopis pollen extract alone and four to both Phaseolus and pollen extract. In vitro cross-reactivity was investigated using inhibition assays [enzyme-linked immunosorbent assay (ELISA) inhibition, immunoblot inhibition], histamine release and lymphoproliferation. P. lunatus extract could inhibit IgE binding to P. juliflora in a dose-dependent manner, requiring 400 ng of protein for 50% inhibition in ELISA assay. Immunoblot and immunoblot inhibition demonstrated the presence of 20, 26, 35, 66 and 72 kDa as shared IgE binding components between the two extracts. Histamine release, peripheral blood mononuclear cells proliferation and interleukin (IL)-4 levels also suggested allergenic cross-reactivity. In conclusion, there is humoral and cellular cross-reactivity between Prosopis pollen and Phaseolus seed allergens.

Fig. 1

Immunoglobulin E (IgE) enzyme-linked immunosorbent assay (ELISA) inhibition with Prosopis juliflora pollen and P. lunatus seeds extract. Prosopis extract, 1 µg/well, was coated and incubated with a mixture containing Prosopis pooled sera (1:10) and 1, 10, 100, 1000 and 10 000 ng of extract as inhibitors (▪ PJ; P. juliflora, □ PL; P. lunatus). The bound IgE was determined using anti-human IgE-horseradish peroxidase (HRP). The values represent the mean of three independent experiments.

Fig. 2

(a) Sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS-PAGE) profile of Prosopis juliflora (PJ) pollen and P. lunatus (PL) seed extract. (b) Immunoblot of P. juliflora pollen (PJ) and P. lunatus (PL) seeds extract showing immunoglobulin E (IgE)-reactive bands. Extracts were probed with serum pool from P. juliflora-sensitive patients. NHS: probed with pooled normal human serum; CL: strip containing Curvularia lunata as an irrelevant control. (c) IgE immunoblot inhibition with P. juliflora pollen and P. lunatus seed extracts. P. juliflora protein strips were incubated with serum pool containing 200 µg (PJ 200) of pollen extract and 200 µg (PL 200) and 600 µg (PL 600) of seed extract as inhibitors. PJ: P. juliflora strip probed with serum pool without inhibitor NHS: probed with pooled normal human sera; Mw: molecular weight markers.

Fig. 3

(a) Stripped basophil histamine release assay. Leucocytes obtained from non-atopic individuals were stripped of their immunoglobulin E (IgE) and sensitized with Prosopis juliflora hypersensitive individual patients' serum (n = 10: patients 1, 3, 4, 5, 7, 10, 11, 18, 19 and 20). Passively sensitized basophils were then stimulated with three concentrations (0.001, 1.0 and 1000 ng/ml) of P. juliflora pollen extract. (b) Stripped basophil histamine release assay. Leucocytes obtained from non-atopic individuals were stripped of their IgE and sensitized with P. juliflora hypersensitive individual patients' sera (n = 4: patients 3, 5, 10 and 20). Sensitized basophils were then stimulated with three concentrations (0.001, 1.0 and 1000 ng/ml) of P. lunatus seed extract. P: Pooled patients' sera. (c) Histamine release on stimulation of passively sensitized (sensitized with individual patient serum from patients 1, 3, 4, 5, 7, 10, 11, 18, 19 and 20, separately) basophils with P. juliflora (PJ) and P. lunatus (PL) extracts at 1 µg/ml (1000 ng/ml) concentration.

Fig. 4

Lymphoproliferation (SI) of peripheral blood mononuclear cells (PBMC) derived from 10 Prosopis-sensitized patients (patients 1, 3, 4, 5, 7, 10, 11, 18, 19 and 20) in response to stimulation with 5 µg of P. lunatus (PL) and P. juliflora (PJ) extract. Horizontal lines indicate the median value. Proliferative responses induced by PL were significantly lower than PJ (Wilcoxon signed ranks test, P = 0.001).