Galectin-2 Agglutinates Helicobacter pylori via Lipopolysaccharide Containing H Type I Under Weakly Acidic Conditions

Galectins are β-galactoside-binding animal lectins involved in various biological functions, such as host defense. Galectin-2 and -3 are members of the galectin family that are expressed in the stomach, including the gastric mucosa and surface mucous cells. Galectin-3 exhibits aggregation and bactericidal activity against <i>Helicobacter pylori</i> in a β-galactoside-dependent manner. We previously reported that galectin-2 has the same activity under neutral pH conditions. In this study, the <i>H. pylori</i> aggregation activity of galectin-2 was examined under weakly acidic conditions, in which <i>H. pylori</i> survived. Galectin-2 agglutinated <i>H. pylori</i> even at pH 6.0, but not at pH 5.0, correlating with its structural stability, as determined using circular dichroism. Additionally, galectin-2 binding to the lipopolysaccharide (LPS) of <i>H. pylori</i> cultured under weakly acidic conditions was investigated using affinity chromatography and Western blotting. Galectin-2 could bind to <i>H. pylori</i> LPS containing H type I, a Lewis antigen, in a β-galactoside-dependent manner. In contrast, galectin-3 was structurally more stable than galectin-2 under acidic conditions and bound to <i>H. pylori</i> LPS containing H type I and Lewis X. In conclusion, galectin-2 and -3 might function cooperatively in the defense against <i>H. pylori</i> in the stomach under different pH conditions.