Parallelism between regulatory effects of erythrocyte glycoproteins on phagocytosis and on the alternative complement pathway.

Major membrane glycoprotein fractions from erythrocytes of humans, rats, sheep and rabbits were isolated and reconstituted into dinitrophenyl (DNP)-haptenated liposomes, in an attempt to compare their effects on the phagocytic response of human polymorphonuclear leucocytes (PMN) and on the alternative pathway of human complement. These glycoproteins on liposomes, by themselves, barely induced the nitroblue tetrazolium blue (NBT)-reducing reaction in PMN cells, but exhibited a suppressive effect to a variable extent on the Fc receptor-mediated uptake of haptenated liposomes opsonized with IgG, as judged by NBT reaction. The rank order in the suppressive activity was human greater than rat, sheep greater than rabbit. In parallel to their effect on phagocytosis, these glycoproteins were also found to suppress the alternative pathway of human complement which was initiated by IgG molecules attached to the same liposome surface. The results are taken to suggest that a molecular mechanism analogous to that in the complement cascade might also be involved in the phagocytic recognition system.