Regulation by membrane sialic acid of β1H-dependent decay-dissociation of amplification C3 convertase of the alternative complement pathway

Abstract

Sheep erythrocytes in their native state did not activate the alternative complement pathway, as measured by Iysis in dilutions of normal human serum containing [ethyl-enebis(oxyethylenenitrilo)J tetraacetic acid but acquired this capacity after membrane sialic acid residues had been removed (by sialidase) or modified (by NaIO4). Activation of the alternative pathway by sheep erythrocytes required removal or modification of at least 40% of the membrane sialic acid to reach threshold, and it increased proportionately when larger amounts of sialic acid had been affected. Studies with isolated proteins of the alternative pathway demonstrated that the altered erythrocyte membranes resembled natural activators in protecting bound C3b from inactivation by C3b inactivator and j#1H and protecting bound amplification C3 convertase (C3bBb) from decay-dissociation by fl1H. A 1% decrease in intact sialic acid was associated with a 1% decrease in fl1H activity in decay-dissociation of membrane bound C3bBb. Because removal of the C8 and C9 carbon atoms from the polyhydroxylated side chain of sialic acid by oxidation with NaIQ4 was functionally equivalent to removal of the entire sialic acid moiety, secondary effects of the latter reaction, such as diminution of the negative charge of the membrane or exposure of penultimate galactose residues, were not considered to be responsible for the altered activity of j#1H. These studies suggest that facilitation, by membrane sialic acid residues, of the interaction between bound C3b and ,B1H is essential to prevent the particle from effectively activating the alternative pathway.Activation of the classical complement pathway is dependent on primary recognition of foreign substances by IgG or IgM (1, 2), whereas activation-of the alternative complement pathway is not necessarily dependent on antibody for formation of its C3 convertase. In the human, this latter pathway can serve a primary recognition function for various particulate microbial polysaccharides-such as zymosan (3), a derivative of yeast cell walls, and Gram-negative bacterial lipopolysaccharide (4)-and certain mammalian cells such as rabbit erythrocytes (5) and some human lymphoblastoid cell lines (6). Cleavage of C3, a fl-globulin of Mr 185,000, by the alternative pathway occurs in two distinct phases: (i) continuous low-grade fluid phase generation of C3b, the 180,000 Mr cleavage fragment of C3 by interaction of native C3, B, D, and properdin (7, 8) that is independent of an activating particle and (ii) subsequent C3b-dependent amplified cleavage of C3 by a particle-associated C3 convertase (9, 10). Significant C3b deposition occurs only in the latter phase in which C3b (11) reversibly binds B, a 90,000 Mr fl-globulin that is then cleaved by D (11, 12) (9), rabbit erythrocytes (10), and Escherichia coli (25) is relatively resistant to decay-dissociation by #1H. Similarly, C3b is rapidly inactivated by C3bINA in a proteolytic reaction that is accelerated by flH (24, 26); however, if C3b is bound to an activator,...

Critical Role of the C-Terminal Domains of Factor H in Regulating Complement Activation at Cell Surfaces

“…Early studies showed that regulation of alternative pathway activation on targets was quantitatively different from that on host cells (61). This was later shown to be due to the presence of sialic acids or other polyanions on nonactivating cells (47,48) and this was subsequently shown to be due to polyanion recognition by factor H (37). Clinical evidence has appeared in recent years indicating that alleles and mutations that affect polyanion recognition domains in factor H result in pathology involving complement activation.…”

“…The C-terminal site has also been shown to bind sialic acids (25,34). Interactions with polyanions are important because the 10-fold higher affinity of factor H for C3b on host cells and other nonactivators (47,48) requires the presence of sialic acid clusters or other polyanions on the surface. The polyanion binding site in domain 7 has been strongly associated with a disease of the retina, age-related macular degeneration, suggesting the possibility of tissue specific polyanion recognition by individual sites of factor H (49 -52).…”

Presence and Characterization of Complement-like Activity in the Amphioxus Branchiostoma belcheri tsingtauense

“…It is known that the terminal sugars on the glycoproteins on the surface of RBC in addition to some associated serum proteins are important factors to activate the AP. RaRBC are missing sialic acid and therefore make them excellent test cells to assay AP complement activity (Fearon, 1978;Dijk et al, 1985;Sunyer and Tort, 1995). Sheep RBC, on the other hand, have a lot of sialic acid, and this is one aspect of their inability to activate the AP and be lyzed by the terminal pathway.…”

Exceptional Resistance of Human H2 Glioblastoma Cells to Complement-Mediated Killing by Expression and Utilization of Factor H and Factor H-Like Protein 1

“…Isopropyl alcohol-precipitated RNA was dissolved in diethylpyrocarbonate-treated water, and 1 g of RNA was denaturated at 70°C for 10 min and then immediately chilled on ice. Reverse-transcriptase reactions were conducted using RNA in a total volume of 20 l containing 10 mM DTT (Life Technologies), 500 M dNTP mix (Pharmacia), 25 g/ml oligo(dT) [12][13][14][15][16][17][18] (Pharmacia), and 200 U Moloney murine leukemia virus reverse transcriptase (Life Technologies) in a reverse-transcriptase buffer (Life Technologies). The reaction was allowed to occur for 1 h at 37°C.…”