The Fc gamma receptor on human placental plasma membrane. I. Studies on the binding of homologous and heterologous immunoglobulin G1
van der Meulen, J.A.; McNabb, T.C.; Haeffner-Cavaillon, N.; Klein, M.; Dorrington, K.J.
Journal of Immunology 124(2): 500-507
1980
ISSN/ISBN: 0022-1767 PMID: 6766159 Document Number: 163500
Plasma membrane vesicles prepared from human placental syncitiotrophoblast agglutinate IgG-sensitized red blood cells in an Fc specific manner. This agglutination could be inhibited by monomeric IgG and Fc in a dose-dependent fashion, whereas neither IgA nor IgM were inhibitory. This phenomenon formed the basis of an assay that was used to investigate the binding specificity of the Fc receptor. Experiments with human subclass proteins indicated that IgG1 and 3 (and their corresponding Fc fragments) were more effective inhibitors than IgG2 and 4. The ability of IgG from several species to inhibit agglutination was also determined, and the order observed was human IgG1 > rabbit IgG; mouse IgG2a or guinea pig IgG2 > guinea pig IgG1, mouse IgG1, mouse IgG2b or dog IgG. IgG from sheep, goat and cow did not inhibit agglutination over the concentration range tested. A role for the hinge region disulfides in maintaining the binding site on IgG is implied by the fact that IgG or Fc that has been mildly reduced and alkylated and a mutant IgG1 (DOB) that has a hinge region deletion showed a markedly reduced ability to inhibit agglutination compared to the native molecules. A fragment corresponding to the C.gamma.3 domain of Fc was not able to inhibit agglutination. The site on IgG with which the Fc receptor interacts apparently involves C.gamma.2 and C.gamma.3.