J. Biochem, 1984, Vol. 95, No. 6 1593-1602
© 1984 Japanese Biochemical Society
research-article |
Structural Studies of Fc Receptors. V. Effect of Phospholipase C Treatment on the Binding Activities of the Fc Receptor of Macrophage or Its Isolated Plasma Membrane1
*Department of Biochemistry, Institute for Medical Immunology, Kumamoto University Medical School Honjo, Kumamoto, Kumamoto 860
**Department of Medical Technology, College of Medical Science, Kumamoto University Honjo, Kumamoto, Kumamoto 860
The effect of phospholipase C treatment on the binding activity of the Fc receptor of guinea pig macrophage was studied to analyze the interaction of the Fc receptor with membrane phospholipids necessary for the activity. It was confirmed by subcellular fractionation that the receptor is localized on the plasma membrane. Treatment of the whole cell or isolated plasma membrane with phospholipase C of Clostridium perfringens diminished the binding of soluble IgG2-immune complex to Fc receptors on the cell or membrane. On the other hand, phospholipase C of Bacillus cereus did not affect the activity when it acted on the whole cell but it did diminish the activity when it acted on the isolated plasma membrane. Analysis of the phospholipids of untreated and treated macrophages or plasma membrane showed that phosphatidylcholine molecules, particularly those located in the membrane (not accessible to attack from the cell surface by phospholipase C of B. cereus), appear to be crucial for efficient interaction of macrophage Fc receptors with immune complex. Ligand-binding experiments with macrophages showed that the diminished binding activity was due to a decrease of the avidity for immune complex, but did not seem to be due to a decrease in the number or affinity of Fc receptors for monomeric IgG2. Taken together with the previous results which demonstrated that Fc receptors which had apparently lost the activity due to delipidation could be reconstituted with phosphatidyicholine but not with most other phospholipids, the results seem to indicate that the diminution of the binding activity to the immune complex of macrophage or its plasma membrane caused by phospholipase C treatment is due to the impairment of multivalent interaction between Fc receptor molecules on the membrane and IgG2 molecules in the immune complex, probably as a result of the loss of interaction of the groups of phospholipids with Fc receptor molecules and the change in membrane properties resulting from the increase of diglycerides.
1This work was supported in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture and a Grant for Research on Intractable Diseases from the Ministry of Health and Welfare, Japan.
2Department of Endodontics and Periodontics, Faculty of Dentistry, Kyushu University, Maidashi 3-1-1, Higashi-ku, Fukuoka, Fukuoka 812