Cell surface sialic acid affects immunoglobulin binding to macrophages.

We demonstrate that guinea pig peritoneal macrophages pretreated with neuraminidase from Vibrio cholerae bind more 125I-IgG than non-treated cells. Estimation of binding constants (Ka and Bmax) shows that the elevation of binding is the result of an increase in affinity and not in the number of receptors for IgG. The change of affinity is proportional to amounts of sialic acid liberated from the cells by increasing doses of neuraminidase. It is also shown that affinity of interactions of IgG with the macrophage receptor is pH dependent. These results indicate that electrostatic forces are important for IgG binding to the macrophage Fc gamma R. The IgG-Fc gamma R interaction can be modulated by changing the degree of sialylation of the macrophage surface glycoconjugates.