Further investigation of nonspecific biological substance in anti-Rh(D) preparations.

Fc receptor-blocking activity, based on the EA rosetting inhibition of anti-Rh(D) gamma-globulin preparations, was determined during biological analyses. After sample purification by means of precipitation with a low concentration of ammonium sulphate, fractions were obtained containing anti-D activity and Fc receptor-blocking activity separately. Fc receptor-blocking antibodies inhibited both the formation of EA rosettes and the antibody-dependent cellular cytotoxicity activity. It is suggested that Fc receptor-blocking antibodies obtained during hyperimmunization probably result in the immunosuppressive effect of Rh immune globulin (via the blocking of Fc receptors of activated lymphocytes) that decreases in turn the progress of Rh immunization.