Is the sugar always sweet in intestinal inflammation?

Immune responses are mediated mainly by protein/protein interactions. In addition, protein/carbohydrate (sugar) interactions through specific protein families termed lectin and chi-lectin are also involved in several immune and biological responses under not only the state of health but also inflammatory conditions. Interestingly, recent studies have identified unexpected roles of animal lectins (galectin-1 and galectin-4) and chi-lectin (chitinase 3-like-1) in intestinal inflammation. Galectin-1 contributes to the suppression of intestinal inflammation by the induction of effector T cell apoptosis. In contrast, galectin-4 is involved in the exacerbation of this inflammation by specifically stimulating intestinal CD4+ T cells to produce IL-6. CHI3L1 enhances the host/microbial interaction that leads to the exacerbation of intestinal inflammation. In this review, we discuss a novel aspect of lectin/carbohydrate interactions in intestinal inflammation.