Potato lectin activates basophils and mast cells of atopic subjects by its interaction with core chitobiose of cell-bound non-specific immunoglobulin E

Abstract

A major factor in non-allergic food hypersensitivity could be the interaction of dietary lectins with mast cells and basophils. Because immunoglobulin E (IgE) contains 10-12% carbohydrates, lectins can activate and degranulate these cells by cross-linking the glycans of cell-bound IgE. The present objective focuses on the effect of potato lectin (Solanum tuberosum agglutinin; STA) for its ability to release histamine from basophils in vitro and mast cells in vivo from non-atopic and atopic subjects. In this study, subjects were selected randomly based on case history and skin prick test responses with food, pollen and house dust mite extracts. Skin prick test (SPT) was performed with STA at 100 microg/ml concentration. Histamine release was performed using leucocytes from non-atopic and atopic subjects and rat peritoneal exudate cells. SPT on 110 atopic subjects using STA showed 39 subjects positive (35%); however, none showed STA-specific IgE; among 20 non-atopic subjects, none were positive by SPT. Maximal histamine release was found to be 65% in atopic subjects (n = 7) compared to 28% in non-atopic subjects (n = 5); the release was inhibited specifically by oligomers of N-acetylglucosamine and correlates well with serum total IgE levels (R(2) = 0.923). Binding of STA to N-linked glycoproteins (horseradish peroxidase, avidin and IgG) was positive by dot blot and binding assay. As potato lectin activates and degranulates both mast cells and basophils by interacting with the chitobiose core of IgE glycans, higher intake of potato may increase the clinical symptoms as a result of non-allergic food hypersensitivity in atopic subjects.

Fig. 1

Histamine release from leucocytes. (a) Histamine release (HR) (from atopic subjects) as a function of protein concentration. Inset: sodium dodecyl sulphate-polyacrylamide gel electrophoresis (12%, reducing) analyses of Solanum tuberosum agglutinin (STA) (lane 1), Lycopersicon esculentum agglutinin (lane 2) and concanavalin A (Con A) (lane 3). Lane 4: mol. wt. markers [bovine serum albumin (BSA), ovalbumin (OVA), lysozyme]. (b) HR from non-atopic (N; n = 5) and atopic (A; n = 7) subjects as a function of STA concentration. OVA: negative control; Con A: positive control.

Fig. 2

(a) Correlation of leucocyte histamine release to serum total IgE (enzyme-linked immunosorbent assay units at A₄₉₂), n = 30. (◊), non-atopic subjects (n = 10); (♦), atopic subjects (n = 20). (b) Histamine release (HR) from leucocytes of non-atopic and atopic subjects at 2 µg/ml Solanum tuberosum agglutinin or Lycopersicon esculentum agglutinin and its inhibition by chitosan (C), chitosan oligomers (CO) or GlcNAc at 50 µg/ml.

Fig. 3

(a) Binding of Solanum tuberosum agglutinin (STA) and Lycopersicon esculentum agglutinin (5 µg/spot on NC) to N-linked glycoproteins by dot blot [rows a–c: horseradish peroxidase (HRP); rows d–f: avidin-alkaline phosphatase (AP); bovine serum albumin (BSA): non-lectin control; concanavalin A (Con A): lectin control]. (a) HRP alone; (b) HRP + 50 µg/ml chitosan oligomers; (c) HRP + 50 µg/ml GlcNAc; (d) avidin-AP alone; (e) avidin-AP + 50 µg/ml chitosan oligomers; (f) avidin-AP + 50 µg/ml GlcNAc. (b) Histamine release (HR) from rat peritoneal exudates cells by Solanum tuberosum agglutinin and other proteins, at 4 µg/ml. Compound 48/80 (10 µg/ml) was used as a positive control for HR from mast cells present in peritoneal exudate cells.

Fig. 4

Structure of complex bi-antennary type N-glycan of IgE [42,43] showing the binding site for concanavalin A (Con A) [specificity for mannose shown as Man (shown in a smaller box), and for trimannosidic core (shown in a larger box)], and Solanum tuberosum agglutinin (specificity for GlcNAc oligomers shown as circled chitobiose). Fucose (Fuc) is absent in avidin. Horseradish peroxidase has high-mannose type, IgE and IgG have complex bi-antennary type, and avidin has hybrid type N-glycans [12,42,43]. One of the two branches of the IgE glycans may or may not contain sialic acid (SA).