Paracellular transport of soybean beta-congylcinin subunits using an in vitro model of the intestinal epithelium

Soybeans are one of the eight most prevalent food allergens worldwide largely in part to the 7S globulin, β-conglycinin. β-conglycinin is comprised of homo- or hetero-trimers of evolutionarily related a, a' and B subunits. The allergenic response to seed storage proteins is thought to be due in part to the passage of undigested proteins through gaps in intercellular tight junctions and mucosal layer in the gut epithelium, where they become accessible to gut associated lymphoid tissue. The goal of this study is to compare the passage of homo- and hetero-trimers of β-conglycinin through a gastrointestinal epithelium model under both normal conditions and those conditions associated with an allergenic response. β-conglycinin purified from soybean seeds as well as further separated into trimers of only the α and α' subunits, as well as the b subunit were used in this study. A Transwell plate was constructed using Caco-2 and HT29-MTX cells in a ratio of 3:1. The integrity of the tight junctions of the cell monolayer was gauged by measuring transepithelial resistance (TER) and occludin expression. To measure protein passage through the cell monolayer, the proteins were applied to the apical chamber and the medium collected from both the apical and basolateral chambers after a period of 2 hours. The amounts of protein in both chambers were quantified using rabbit polyclonal antisera specific to the soybean β-conglycinins. The passage of β-conglycinin of different subunit compositions through the cell co-culture model were compared as a function of TER. When the cell monolayer showed a TER of 150-200 Ω*cm2, which is indicative of healthy conditions, there was no detectable β-conglycinin transport. In contrast, when the TER was 50-100 Ω*cm2, which is indicative of sensitized conditions, the β-conglycinin did pass through the cell monolayer.