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Depletion of Specific Cell Populations by Complement Depletion
Published on: February 5, 2010
Effects of anti-C4 antibody on complement production by splenic and peritoneal macrophages
J N Goldman1, K S O'Rourke, J D McMannis
1Department of Medicine, Michael Reese Hospital and Medical Center, Chicago, Ill.
Insights
Anti-C4 antibody suppresses complement component 4 (C4) synthesis in macrophages. Intact antibodies, not fragments, induce long-term suppression by accelerating C4 processing, reducing intracellular C4 levels.
Area of Science:
- Immunology
- Molecular Biology
- Cell Biology
Background:
- The complement system, particularly complement component 4 (C4), plays a crucial role in immune responses.
- Previous studies indicated that anti-C4 antibody can suppress C4 synthesis and secretion, requiring lymphoid cells for maximal effect.
- Macrophages are key C4-secreting cells involved in immune regulation.
Purpose of the Study:
- To investigate the effects of anti-C4 antibody on C4 synthesis and secretion in peritoneal macrophages.
- To compare the suppression dynamics between peritoneal macrophages and splenic fragments.
- To elucidate the mechanism behind long-term C4 suppression and the role of antibody integrity.
Main Methods:
- Treatment of peritoneal macrophages with intact anti-C4 antibody.
- Pulse-chase experiments to track C4 processing.
- Analysis of intracellular and secreted C4 levels.
- Comparison of intact antibody versus F(ab')2 fragments.
Main Results:
- Intact anti-C4 antibody reduced intracellular and secreted C4 in peritoneal macrophages.
- Intracellular pro-C4 levels normalized rapidly in peritoneal macrophages post-treatment.
- Splenic macrophages showed sustained low intracellular pro-C4 after suppression due to accelerated processing.
- Only intact anti-C4 antibody induced full magnitude and duration of suppression; F(ab')2 fragments were ineffective.
Conclusions:
- Intact anti-C4 antibody effectively suppresses C4 production in macrophages.
- The mechanism of long-term suppression involves accelerated intracellular processing of nascent C4.
- Antibody integrity is essential for achieving sustained suppression of C4 synthesis and secretion.
Abstract:
We have previously shown that administration of anti-C4 antibody to cells in culture can suppress the synthesis and secretion of C4. Lymphoid cells must be present along with the C4 secreting macrophages to achieve suppression of full magnitude and long duration. In this publication we have demonstrated that treatment of peritoneal macrophages with intact anti-C4 antibody results in reduction of intracellular and secreted C4. Intracellular levels of pro-C4 rapidly returned to normal after removal of the suppressing antibody and extracellular levels of C4 secreted into the media returned to normal within 24-48 h. This is in marked contrast to our previously published results with splenic fragments where intracellular pro-C4 remained markedly reduced long after removal of anti-C4. Using pulse-chase experiments we now demonstrate that, after recovery from suppression, intracellular pro-C4 levels remain low in splenic macrophages because nascent C4 is processed through the cell more rapidly. This results in a smaller intracellular pool of C4, even in the face of normal or high levels of C4 synthesis in the postsuppression phase. Finally, we demonstrate that suppression of full magnitude and duration could only be achieved with intact anti-C4 antibody. F(ab')2 fragments were not capable of inducing complete suppression.
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