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Effect of EDTA and citrate on the functional activity of the first component of complement, C1, and the C1q
Insights
Ethylenediaminetetraacetic acid (EDTA) significantly inactivates the complement system
Area of Science:
- Immunology
- Biochemistry
Background:
- The first component of complement (C1) is crucial for immune responses.
- C1 is a calcium-dependent complex composed of C1q, C1r, and C1s subcomponents.
- Previous studies indicated EDTA treatment reduces C1 hemolytic activity.
Purpose of the Study:
- To investigate EDTA's effects on C1 and its subcomponents beyond simple chelation.
- To compare EDTA's chelating effect with citrate.
- To determine if EDTA has an inhibitory effect on C1q.
Main Methods:
- Treatment of purified C1 and serum with EDTA and citrate.
- Assessing hemolytic activity after calcium re-addition.
- Evaluating C1q activity in EDTA-treated serum.
- Testing the ability of EDTA-treated C1q to form active C1 complexes.
Main Results:
- EDTA treatment caused up to 90% loss of hemolytic C1 activity, even after recalcification.
- Citrate dissociation allowed full recovery of C1q activity.
- EDTA-treated serum showed concentration-dependent loss of C1q hemolytic activity.
- EDTA-treated C1q could not form a functional C1 complex with C1r and C1s.
Conclusions:
- EDTA exhibits a direct inhibitory effect on C1q, independent of its chelating function.
- EDTA significantly impairs the classical complement pathway.
- EDTA's inactivation of C1q has implications for complement-mediated immune functions.
Abstract:
The first component of complement, C1, is a calcium-dependent complex of the three distinct subcomponents, C1q, C1r, and C1s. Earlier observations revealed that treatment of C1 with EDTA led to a loss of hemolytic C1 activity even after recalcification. Therefore, it was of interest to study whether EDTA has an additional effect on C1 and its subcomponents, beside its chelating capacity. The chelating effect of EDTA was compared to that of citrate. It was found that treatment of C1 or C1 with EDTA followed by addition of Ca++ led to a loss of hemolytic activity up to 90%, depending on EDTA concentration. Even pretreatment of EDTA with varying amounts of Ca++ did not prevent the inactivation of C1 or C1. In contrast, after dissociation of C1 or C1 by citrate, 100% of the original C1q activity is recoverable on addition of C1q deficient serum as source of C1r and C1s. EDTA-treated serum, however, showed a concentration-dependent loss of hemolytic C1q activity, indicating an inhibitory effect of EDTA on C1q. EDTA-treated C1q, fluid phase or bound to EA, was no longer able to form an hemolytically active C1 complex by interaction with C1r and C1s.