Effect of Human Immunoglobulin Preparations on Fc Rosette Formation between Anti-D-Coated Erythrocytes and Lymphocytes

Human immunoglobulin (Ig) preparations were tested for their inhibitory effect on Fc rosette formation between anti-D-coated human erythrocytes and lymphocytes, as compared to their complement activating capacity. Both of the two biological activities ascribed to the sites in the Fc portion of the IgG molecules were found to be reduced in the pepsin-treated, as well as in the S-sulfonated Ig preparations, as compared to the activities of the normal human Ig preparation. In the plasmin-treated Ig preparation, which was found to be composed of three major components: plasmin-Fab, plasmin-Fc and plasminresistant IgG, the activity of inhibiting the Fc rosette formation was well retained, in contrast to its low complement activating capacity.