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Specific Inhibition of Receptors for Cytophilic Antibody on Macrophages by Isoantibody

Departments of Medicine and Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06510

Hyperimmune isoantibody (Ab) to leukemia L1210 inhibited the development of macrophage-mediated immunity to the tumor in allogeneic (C57BL/6) hosts. Administration of 0.4 ml of Ab i.p. 1 day before challenge i.p. with L1210 prevented formation of the enlarged, vacuolated "activated" macrophages usually observed 10 days after the challenge. Instead, the peritoneal cells of the host were small and monocytic, lacking stainable acid phosphatase granules and showing no attached or engulfed tumor cells. Addition of proved cytophilic antibody to L1210 failed to restore the capacity of the monocytes to attach L1210 cells in vivo or in vitro. However, Ab-suppressed peritoneal monocytes were able to form "rosettes" with sheep erythrocytes after the addition of cytophilic antibody to the erythrocytes. The suppressive activity of Ab was found entirely in the IgG fraction. These experiments suggest that Ab to L1210 blocked or damaged receptors on the surface of peritoneal monocytic cells, receptors that appear to be specific for cytophilic antibodies to L1210.

¹ Scholar of the Leukemia Society of America. Study supported by a grant from the Upjohn Company and by American Cancer Society Grant In-31-J-2.

Received 11/ 8/71. Accepted 1/14/72.