An intestinal galactose‐specific lectin mediates the binding of murine IgE to mouse intestinal epithelial cells

Abstract

A number of lactose-binding lectins have recently been identified in the rat and mouse intestine, one of which corresponds to the C-terminal domain of IgE-binding proteins, originally identified in rat basophilic leukemia (RBL) cells and mouse 3T3 fibroblasts. In the present report, we describe the affinity purification of a rat intestinal lactose-specific lectin which binds murine IgE antibodies. This binding most likely occurs via the immunoglobulin carbohydrate chains, as it is inhibited by lactose. This intestinal lectin molecule is also immunologically related to the previously described IgE-binding protein (EBP) isolated from RBL cells, since it is recognized by antibodies raised against recombinant EBP. This intestinal form of EBP has a molecular mass of 17.5 kDa, which is much lower than that of its RBL cell analogue (31 kDa). The attachment of IgE to the mouse intestinal epithelium was demonstrated by immunohistochemistry, along with the presence of a corresponding mouse intestinal EBP. The carbohydrate-dependent nature of this attachment was established by demonstrating that IgE binding to mouse epithelium was specifically abolished by lactose (4 mM) and by a blood-group-A-active tetrasaccharide (0.2 mM), but not by mannose (10 mM). Finally, the association of IgE with the mouse intestinal epithelium was prevented by competition with the purified IgE-binding lectin isolated from rat intestine. Although the physiological function of this intestinal protein is still unknown, the finding that IgE binds to a lectin in the intestinal epithelium pinpoints a possible novel mechanism for the regulation of IgE-mediated disorders, such as food allergy.IgE, through its interaction with cell-surface receptors, plays a key role in triggering allergic disorders [l]. Many IgEbinding molecules have been described, including the highaffinity and the low-affinity receptors for the E chain, the IgEbinding factors and the newly discovered IgE-binding protein (EBP) [2]. This latter protein was first evidenced by translation of mRNA from rat basophilic leukemia (RBL) cells in Xenopus oocytes 131. This molecule was shown to exhibit an intrinsic IgE-binding activity and therefore was referred as cBP [4, 51. Interestingly, evidence has emerged that EBP has a carbohydrate-binding activity, because its binding to IgE can be reversed by lactose [6]. Furthermore, it was found to exhibit a high sequence similarity with the carbohydrate-binding protein 35 (CBP 35) [6], which is a galactose-binding lectin originally identified in mouse 3T3 fibroblasts [7] and also found in mouse lung [8]. Similarly, recent data indicate that the EBP is identical to a rat lung lectin (RL) of 29 kDa 19, 101, also known to be a [j-galactoside-binding protein. Moreover, recent work showed that Mac-2 antigen (a murine macrophage cell-surface marker) is a j-galactoside lectin of 32 kDa, which binds IgE and whose sequence is almost identical to those of CBP 35 and cBP [ll]. Finally, a human EBP has recently been described, whose sequence exhibits extensive ...

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Activation of Human Basophils by A549 Lung Epithelial Cells Reveals a Novel IgE-Dependent Response Independent of Allergen

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Immunoelectron microscopic localization of galectin‐3, an IgE binding protein, in human mast cells and basophils

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