Effects of glycinin on IgE-mediated increase of mast cell numbers and histamine release in the small intestine

Soybean allergy represents a significant health threat to individuals with food allergies. Glycinin, the main storage protein in soybean, has been identified as a major food allergen. The present study was conducted to investigate the mechanism of glycinin-induced hypersensitivity in a swine model. The relationship between glycinin dose and the severity of hypersensitive reactions was also explored. Twenty-four piglets weaned at 18 days were gastric sensitized and subjected to repeated oral challenges with diets containing 0%, 2%, 4% and 8% glycinin. The results showed that dietary supplementation of glycinin reduced piglet performance (P<.01) while increasing occurrence of diarrhea (P<.05) and erythema area (P=.01) in response to an intradermal injection of glycinin. Intestinal mast cell numbers (P<.05) and immunoglobulin E (IgE) levels (P<.05) were increased linearly, whereas the histamine content in intestinal specimens (except in the duodenum) was decreased (P<.01), indicating that more histamine had been released in glycinin-fed piglets than in control. Serum concentrations of total IgE, glycinin-specific IgG1 and interleukin (IL)-4 and IL-10 were also greater (P<.05) in the pigs treated with glycinin. In this study, we found that glycinin-induced hypersensitivity is a predominantly Th2-type immune response, mediated by IgE and associated with increases in intestinal mast cell numbers and histamine release as well as IL-4 and IL-10 concentrations in the serum of sensitized piglets, resulting in diarrhea and reduced performance. The severity of the hypersensitive reactions depends on the dose of glycinin. Higher dose may cause more severe anaphylactic symptoms.