CR3 (CD11b, CD18): a phagocyte and NK cell membrane receptor with multiple ligand specificities and functions

Abstract

SUMMARY The C3 receptor CR3 is expressed on phagocytie cells, minor subsets of B and T eells, and natural killer (NK) cells. It has important functions both as an adhesion molecule and a membrane receptor mediating recognition of diverse ligands such as intercellular adhesion molecule-1 (ICAM-1) and fixed iC3b. The receptor is capable of undergoing an activation event that regulates both its specificity for various ligands and its ability to mediate phagocytosis or extracellular eytotoxieily. Certain bacteria express earbohydrates or lipopolysaccharidcs (LPS) that can bind to and activate CR3, allowing the receptor to assume its activated state. Soluble β-glucan derived frotn the yeast Saccharomyces cerevisiae is a particularly potent stimulator of CR3, and produces an activated state of the receptor that permits neutrophil phagocytosis of iC3b-coated erytbrocytes or NK cell eytotoxicity of iC3b-coated tumour cells, tbat are normally resistant to NK cells.