Localization of the binding site on IgG for solubilized placental Fc gamma receptor

Placental Fc gamma R (FcR) inhibited the rosette formation between monocytes and rabbit IgG-sensitized erythrocytes (EA), whereas the rosette formation with granulocytes was not impaired. Staphylococcal protein A (SpA) inhibited the rosette formation with both cell types. Results obtained in absorption and agglutination experiments showed that SpA blocked the binding of FcR to IgG, and Cl did not. Furthermore, FcR did not interfere with the binding of SpA to IgG, whereas C1 affected this binding. FcR apparently bind to the C gamma 3 region. Since FcR inhibited the binding of EA to monocytes, the monocyte FcR binding site is probably also located within the C gamma 3 region.