The influence of pH on the adhesion of twoLactobacillus strains to Caco-2 human intestinal cells was investigated. One strain, Lactobacillus johnsonii La1, was adherent at any pH between 4 and 7. The other one, L. acidophilus La10, did not attach to this cell line under the same experimental conditions. On the basis of these results, we used the monoclonal antibody technique as a tool to determine differences on the surface of these bacteria and to identify a factor for adhesion. Mice were immunized with live La1, and the hybridomas produced by fusion of spleen cells with ONS1 cells were screened for the production of antibodies specific for L. johnsonii La1. A set of these monoclonal antibodies was directed against a nonproteinaceous component of the L. johnsonii La1 surface. It was identified as lipoteichoic acid (LTA). This molecule was isolated, chemically characterized, and tested in adhesion experiments in the same system. The adhesion of L. johnsonii La1 to Caco-2 cells was inhibited in a concentration-dependent way by purified LTA as well as by L. johnsonii La1 culture supernatant that contained LTA. These results showed that the mechanism of adhesion of L. johnsonii La1 to human Caco-2 cells involves LTA.

No 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 ...