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Protective and inactivating effects of neutrophil myeloperoxidase on C1q activity
G Zabucchi1, R Menegazzi, L Roncelli
1Istituto di Patologia Generale, Università di Trieste, Italy.
Abstract:
This study investigated the interaction between neutrophil myeloperoxidase (MPO) and the C1q component of the complement system. Using a dot-spot assay, MPO was found to bind to C1q in a dose-dependent manner. The specificity of this reaction was proved by the inhibitory effect of F(ab')2 antibodies to C1q and by the inability of MPO to bind to C1r, C1s and IgG. The interaction between MPO and C1q did not influence the enzymatic activity of the peroxidase but resulted in a more stable C1q as assessed by hemolytic assay for C1q. The protective effect of MPO on C1q did not require the presence of H2O2 in the reaction mixture nor was it inhibited by sodium azide, whereas it was abolished by heating the peroxidase. Lactoferrin and lysozyme, unlike MPO, were ineffective in protecting C1q from functional decay. Addition of H2O2 and chloride to MPO and C1q led to a complete inactivation of C1q, which could not be induced by H2O2 alone. The hypochlorite, which is known to be generated during the reaction of MPO with H2O2 and chloride, exhibited a similar inactivating effect on C1q, which was prevented by an external source of methionine.
Insights
Neutrophil myeloperoxidase (MPO) binds to C1q, stabilizing it against decay. However, MPO-generated hypochlorite inactivates C1q, a process inhibited by methionine.
Area of Science:
- Immunology
- Biochemistry
- Complement System
Background:
- Neutrophil myeloperoxidase (MPO) is crucial in innate immunity.
- The C1q component initiates the classical complement pathway.
- Interactions between MPO and complement components are not fully understood.
Purpose of the Study:
- To investigate the interaction between MPO and C1q.
- To determine the functional consequences of this interaction on MPO and C1q activity.
- To elucidate the role of MPO-derived reactive species in C1q stability.
Main Methods:
- Dot-spot assay to assess MPO-C1q binding.
- Hemolytic assays to evaluate C1q functional activity.
- Enzymatic activity assays for MPO.
- Inhibition studies using antibodies and chemical agents.
Main Results:
- MPO binds to C1q in a dose-dependent and specific manner.
- MPO binding stabilizes C1q without affecting MPO enzymatic activity.
- MPO-derived hypochlorite inactivates C1q, but this is preventable with methionine.
- Lactoferrin and lysozyme did not protect C1q.
Conclusions:
- MPO interacts with C1q, modulating its stability.
- The balance between MPO's protective and MPO-derived reactive species' damaging effects on C1q is critical.
- This interaction may have implications for inflammatory and autoimmune processes.