Studies on the In Vivo Effects of Antibody INTERACTION OF IgM ANTIBODY AND COMPLEMENT IN THE IMMUNE CLEARANCE AND DESTRUCTION OF ERYTHROCYTES IN MAN

Abstract

A B S T R A C T Purified human IgM isoagglutinins wereutilized to sensitize 'Cr-labeled erythrocytes so as to produce a known number of complement-fixing sites.These cells were then reinfused into the erythrocyte donor. A minimum of 20 Cl-fixing sites/erythrocyte were required for decreased survival. As the amount of antibody coating the erythrocytes was increased, a larger percentage was sequestered. With 80 Cl-fixing sites, more than 75% of the injected erythrocytes were removed from the circulation within 10 min. In each case, the clearance pattern consisted of rapid hepatic sequestration followed by a gradual return of a portion of the erythrocytes into the circulation where they survived normally.Clearance was shown to be dependent upon activation of the classical complement pathway, since sensitized cells survived normally in hereditary angioedema patients with low levels of C4 and no detectable C2. Exposure of sensitized cells to fresh serum for 15 min led to the deposition of 550-800 C3 molecules/Cl-fixing site. Such cells were immune adherence positive, were agglutinated by anti-C3b, formed rosettes with human alveolar macrophages, and were sequestered in vivo, presumably because of the interaction of cell-bound C3b with the C3b receptor on hepatic macrophages. After exposure to heated serum as a source of the C3b inactivator, the cells were immune adherence negative, were agglutinated only by anti-C3d, did not form rosettes with macrophages, and survived normally in vivo despite, being Coombs positive. Cleavage of cell-bound C3b to C3d may explain the release phase of the IgM clearance pattern. Whereas erythrocytes coated with IgM antibody and complement were previously thought to be sequestered in the liver because of extensive membrane damage, these experiments

Eculizumab prevents intravascular hemolysis in patients with paroxysmal nocturnal hemoglobinuria and unmasks low-level extravascular hemolysis occurring through C3 opsonization

“…Approximately 550-800 C3b molecules per red cell are required to activate the hepatic clearance mechanism through Kupffer cells. 20,21 CD55 or DAF is a GPI-anchored protein that is also absent from the surface of the PNH red cell. CD55 is a complement regulatory protein that plays a key role in inhibiting the generation of C3b by regulating the formation of the C3 convertases and accelerating their dissociation.…”

Reticulocytes bearing C4d as biomarkers of disease activity for systemic lupus erythematosus

“…Schreiber and Frank (44,45) originally demonstrated that erythrocytes coated with cold agglutinin IgG/IgM and complement C3b are cleared/sequestrated rapidly by phagocytes in the spleen and liver. Other investigators have subsequently shown that erythrocytes bound by immune complexes opsonized with complement C3b are quickly stripped off by phagocytic cells, leaving behind C3dg fragments that are covalently bound on cells (43,46,47). Nevertheless, it is possible, and perhaps likely, that some erythrocytes coated with C3-derived ligands may be cleared from the circulation during these processes before completing a 120-day life cycle.…”

Demonstration of defective C3-receptor-mediated clearance by the reticuloendothelial system in patients with acquired immunodeficiency syndrome.

“…Infusion of G3-sensitized erythrocytes is followed by a triphasic clearance curve (23,24). There is an initial rapid clearance of cells from the circulation due to attachment to C3 receptors of RES cells, primarily hepatic macrophages (Kupffer cells).…”

“…In the normal animal virtually all the cleared cells were returned to the circulation as the membrane-bound C3 was cleaved. When these studies were repeated in man (23,24) it was found that human macrophages behaved as if they were partially activated. A portion of the C3-coated erythrocytes were cleared from the circulation, but many were phagocytosed.…”