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Catabolism Physical, and Immunologic Properties of Endocytosed Isologous and Heterologous -Globulins by Mouse Macrophages¹

Division of Immunology and Allergy, Wilsdorf Laboratory, Department of Medicine, and Policlinique Universitaire de Médecine, Hôpital Cantonal, Geneva, Switzerland

Abstract

The catabolism of completely endocytosed isologous and heterologous -globulins by mouse macrophages was studied in vitro. Mouse, human, and rabbit ¹²⁵I-IgG were coupled to mouse, human, or sheep erythrocytes either as antibodies or by covalent binding. They were exposed to macrophages for 1 hr and the non-endocytosed erythrocytes were then removed with a Ficoll gradient centrifugation. Catabolism was evaluated after 2, 5, and 18 hr in culture by measuring the radioactivity released into the culture medium as well as the radioactivity that remained associated with cells. It was found that all -globulins were catabolized in a similar fashion, and that the type of carrier erythrocytes (isologous or heterologous) had no influence on catabolism. Some of the material that remained associated with macrophages was on the cell membrane and could be removed by trypsin. Some of the material that was released by macrophages was completely degraded but some was either not degraded or only partially degraded. Sucrose density gradient analysis and SDS-polyacrylamide gel electrophoresis showed that this material had kept some physical properties of native -globulins. It was also found with the antigen-binding inhibition test and incubation with erythrocytes that the released material contained molecules carrying Fab determinants and was able to bind specifically to erythrocytic antigens. Taken together, these observations show that -globulins phagocytosed in the form of antigen-antibody complexes are only incompletely degraded and that the material associated with the plasma membrane of macrophages or found in the culture medium is a product of cell catabolism.

Footnotes

¹ This work was supported by Grant 3.768.72 from the Swiss National Foundation for Scientific Research.