Stimulation of Cells to Generate Superoxide by Heat-Aggregated IgG

When human polymorphonuclear leukocytes encounter particles coated with immunoglobulins of the IgG class, the cells undergo a burst of oxidative metabolism, i.e., they consume increased amounts of oxygen (by a mechanism that is insensitive to cyanide) to produce superoxide anion radicals and hydrogen peroxide. ^{1 , 2} Simultaneously, the cells degranulate; lysosomes fuse with invaginated portions of the plasma membrane and discharge their contents either into phagocytic vacuoles or extracellularly. ¹ Polymorphonuclear leukocytes respond similarly when they encounter either immune complexes (formed when IgG antibodies react with soluble antigens) or aggregates of IgG (prepared by heating and by chemical treatment). ^{1 , 3 - 5} There is ample evidence that these responses occur independently of phagocytosis and are mediated by interactions between the Fc regions of IgG immunoglobulins and specific receptors on the plasma membranes of polymorphonuclear leukocytes. ^{1 , 4 , 6 - 8}