Binds galactosides. Has high affinity for the Forssman pentasaccharide. Ligand for HAVCR2/TIM3. Binding to HAVCR2 induces T-helper type 1 lymphocyte (Th1) death. Also stimulates bactericidal activity in infected macrophages by causing macrophage activation and IL1B secretion which restricts intracellular bacterial growth. Ligand for P4HB; the interaction retains P4HB at the cell surface of Th2 T-helper cells, increasing disulfide reductase activity at the plasma membrane, altering the plasma membrane redox state and enhancing cell migration. Ligand for CD44; the interaction enhances binding of SMAD3 to the FOXP3 promoter, leading to up-regulation of FOXP3 expression and increased induced regulatory T (iTreg) cell stability and suppressive function. Promotes ability of mesenchymal stromal cells to suppress T-cell proliferation. Expands regulatory T-cells and induces cytotoxic T-cell apoptosis following virus infection. Activates ERK1/2 phosphorylation inducing cytokine (IL-6, IL-8, IL-12) and chemokine (CCL2) production in mast and dendritic cells. Inhibits degranulation and induces apoptosis of mast cells. Induces maturation and migration of dendritic cells. Inhibits natural killer (NK) cell function. Can transform NK cell phenotype from peripheral to decidual during pregnancy. Astrocyte derived galectin-9 enhances microglial TNF production. May play a role in thymocyte-epithelial interactions relevant to the biology of the thymus. May provide the molecular basis for urate flux across cell membranes, allowing urate that is formed during purine metabolism to efflux from cells and serving as an electrogenic transporter that plays an important role in renal and gastrointestinal urate excretion. Highly selective to the anion urate. Isoform 2: Acts as an eosinophil chemoattractant. It also inhibits angiogenesis. Suppresses IFNG production by natural killer cells. Peripheral blood leukocytes and lymphatic tissues. Expressed in lung, liver, breast and kidney with higher levels in tumor endothelial cells than normal endothelium (at protein level) (PubMed:24333696). Expressed in trophoblast cells in decidua and placenta in pregnancy (at protein level) (PubMed:23242525, PubMed:25578313). Isoform 2 is the most abundant isoform expressed in endothelial cells (PubMed:24333696). Upon endothelial cell activation isoform 2 expression decreases while expression of isoform 3 and isoform 5 increases (PubMed:24333696). Isoform 4 decreases in pathological pregnancy (PubMed:23242525). 6 alternatively spliced human isoforms have been reported. Note: This description may include information from UniProtKB.
Molecular Function: carbohydrate binding; enzyme binding; galactoside binding; protein binding; protein serine/threonine kinase activator activity; signaling receptor binding
Biological Process: cellular response to virus; chemotaxis; female pregnancy; heterophilic cell-cell adhesion via plasma membrane cell adhesion molecules; immune system process; maintenance of protein location; negative regulation of CD4-positive, alpha-beta T cell proliferation; negative regulation of gene expression; negative regulation of inflammatory response; negative regulation of interferon-gamma production; negative regulation of interferon-gamma secretion; negative regulation of natural killer cell activation; negative regulation of natural killer cell degranulation; positive regulation of chemokine production; positive regulation of cytokine production; positive regulation of defense response to bacterium; positive regulation of gene expression; positive regulation of innate immune response; positive regulation of interleukin-1 production; positive regulation of interleukin-10 secretion; positive regulation of interleukin-6 secretion; positive regulation of macrophage activation; positive regulation of oxidoreductase activity; positive regulation of pathway-restricted SMAD protein phosphorylation; positive regulation of regulatory T cell differentiation; positive regulation of T cell migration; positive regulation of transcription regulatory region DNA binding; positive regulation of tumor necrosis factor production; regulation of natural killer cell differentiation; response to lipopolysaccharide; toll-like receptor 3 signaling pathway