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.
Biological Process: cellular response to interferon-gamma; cellular response to virus; chemotaxis; ERK1 and ERK2 cascade; female pregnancy; inflammatory response; maternal process involved in female pregnancy; natural killer cell tolerance induction; negative regulation of activated T cell proliferation; negative regulation of CD4-positive, alpha-beta T cell proliferation; negative regulation of chemokine production; negative regulation of gene expression; negative regulation of interferon-gamma production; negative regulation of mast cell degranulation; negative regulation of natural killer cell mediated cytotoxicity; negative regulation of tumor necrosis factor production; p38MAPK cascade; positive regulation of activated T cell autonomous cell death; positive regulation of CD4-positive, alpha-beta T cell proliferation; positive regulation of CD4-positive, CD25-positive, alpha-beta regulatory T cell differentiation involved in immune response; positive regulation of cysteine-type endopeptidase activity involved in apoptotic signaling pathway; positive regulation of dendritic cell apoptotic process; positive regulation of dendritic cell chemotaxis; positive regulation of dendritic cell differentiation; positive regulation of ERK1 and ERK2 cascade; positive regulation of gene expression; positive regulation of interferon-gamma secretion; positive regulation of interleukin-1 beta secretion; positive regulation of interleukin-10 secretion; positive regulation of interleukin-12 secretion; positive regulation of interleukin-13 secretion; positive regulation of interleukin-4 production; positive regulation of interleukin-6 secretion; positive regulation of interleukin-8 secretion; positive regulation of monocyte chemotactic protein-1 production; positive regulation of NF-kappaB transcription factor activity; positive regulation of NIK/NF-kappaB signaling; positive regulation of T cell activation via T cell receptor contact with antigen bound to MHC molecule on antigen presenting cell; positive regulation of transforming growth factor beta production; positive regulation of tumor necrosis factor secretion; positive regulation of viral entry into host cell; response to interleukin-1; response to lipopolysaccharide