EXPRESSION AND FUNCTION OF GALECTIN-3, A BETA-GALACTOSIDE-BINDING LECTIN, IN HUMAN MONOCYTES AND MACROPHAGES

A family of beta-galactoside-binding animal lectins has recently been designated as galectins. One member of this family, galectin-3, has be en known as epsilon BP for its IgE-binding activity and as Mac-2, a ma crophage surface antigen, CBP35, CBP30, L-29, and L-34. Although much information has accumulated on the expression of this lectin irt murin e macrophages and human monocytic cell lines, little is known about th e expression and function of this protein in normal human monocytes/ma crophages. We now report that galectin-3 is expressed in normal human peripheral blood monocytes and its level increases dramatically as hum an monocytes differentiate into macrophages upon culturing in vitro. I mmunoblot analysis showed that there was a 5-fold increase in the leve l of galectin-3 after 1 day of culture and greater than a 12-fold incr ease after 5 days. Immunocytochemical analysis confirmed this progress ive increase of galectin-3 expression in cultured monocytes. Immunogol d cytochemistry/electron microscopy analysis revealed that galectin-3 was expressed on the surface of human monocytes and that the level of cell surface galectin-3 increased progressively as these cells differe ntiated into macrophages. The level of galectin-3 in human monocytes/m acrophages was modulated by stimuli such as lipopolysaccharide and int erferon-gamma, and galectin-3 was secreted when monocytes were stimula ted by calcium ionophore A23187. Soluble galectin-3 caused superoxide release from human monocytes; this activity was dependent on the lecti n property of galectin-3, as it was inhibitable by lactose. Thus, gale ctin-3 may modulate the function of this cell type in an autocrine or paracrine fashion through binding to cell surface glycoconjugates.