Lectin that binds beta-galactoside and a wide array of complex carbohydrates (PubMed:21210196). Plays a role in regulating apoptosis, cell proliferation and cell differentiation. Inhibits CD45 protein phosphatase activity and therefore the dephosphorylation of Lyn kinase. Strong inducer of T-cell apoptosis. Has hemaglutinating activity towards human erythrocytes (PubMed:21210196). Optimum pH for hemagglutinating activity is 7.4. Retains hemagglutinating activity up to 42 degrees Celsius. The activity then drops and is completely lost at 65 degrees Celsius. Homodimer. Binds LGALS3BP. Interacts with CD2, CD3, CD4, CD6, CD7, CD43, ALCAM and CD45. Interacts with laminin (via poly-N-acetyllactosamine). Interacts with SUSD2. Interacts with cargo receptor TMED10; the interaction mediates the translocation from the cytoplasm into the ERGIC (endoplasmic reticulum-Golgi intermediate compartment) and thereby secretion. Can be secreted; the secretion is dependent on protein unfolding and facilitated by the cargo receptor TMED10; it results in protein translocation from the cytoplasm into the ERGIC (endoplasmic reticulum-Golgi intermediate compartment) followed by vesicle entry and secretion.