Ia antigens and Fc receptors.

The function of Fc receptors (FcR) on mouse spleen cells as detected by a sensitive rosetting system using antibody-labeled bovine erythrocytes as indicator cells was shown to be inhibited by anti-Ia antiserum. Furthermore, the Ia specificities of each I-region sublocus (I-1A, I-1B, I-C) seem to be associated with FrR, since FcR function was also inhibited when the blocking anti-Ia antiserum recognized only restricted Ia specificities. Antiserum directed against antigens coded for by the K-end of the major histocompatibility complex did not inhibit FcR function. The function of C3 receptors and Fc receptors on macrophages and Fc-receptor-positive cells in the fetal liver was not inhibited by anti-Ia antiserum. These findings are discussed in view of a possible arrangement of Fc receptors and Ia antigens on the cell membrane.