Failure of oligosaccharide MOPC-104E IgM complexes to bind C1q and to activate C1

The capacity of anti-dextran MOPC-104E IgM to bind and activate the first complement component (C1) in the presence of various specific monovalent oligosaccharides was investigated. Enzyme-linked immunosorbent assay revealed that IgM-oligosaccharide complexes saturated up to 97% with ligands were not capable of binding C1q under physiological conditions. Nor was any activation of reconstituted C1 observed. These results indicate that occupation of the single IgM binding sites by a monovalent ligand is not sufficient to induce a signal for complement activation.