Related Experiment Videos
CRP-mediated activation of complement in vivo: assessment by measuring circulating complement-C-reactive protein
G J Wolbink1, M C Brouwer, S Buysmann
1Central Laboratory of the Netherlands Red Cross Blood Transfusion Service, Amsterdam.
Insights
The study developed a new method to detect C-reactive protein (CRP) activating complement in vivo. Elevated levels of complement-CRP complexes were found in kidney transplant patients, suggesting CRP
Area of Science:
- Immunology
- Biochemistry
Background:
- The in vivo role of C-reactive protein (CRP) remains unclear.
- CRP is known to activate complement in vitro, but in vivo evidence is lacking.
Purpose of the Study:
- To develop a novel method for assessing CRP-mediated complement activation in vivo.
- To investigate the presence and significance of complement-CRP complexes in clinical settings.
Main Methods:
- Developed specific ELISAs to detect complexes of CRP with complement factors C4b, C4d, C3b, and C3d.
- Assessed complement-CRP complexes in normal donors and kidney allograft recipients.
- Utilized mAb OKT3 infusion to differentiate CRP-dependent and independent complement activation.
Main Results:
- Complement-CRP complexes formed specifically during CRP-dependent activation in vitro.
- Circulating complement-CRP complexes were undetectable in healthy individuals.
- Significantly increased levels of complement-CRP complexes were observed in kidney transplant patients.
- Levels of complement-CRP complexes did not increase after mAb OKT3 infusion, confirming CRP independence.
Conclusions:
- Measurement of complement-CRP complexes is a viable tool for studying CRP-mediated complement activation in vivo.
- Increased complement-CRP complexes in clinical samples suggest CRP's role in activating complement in vivo.
Abstract:
The in vivo function of C-reactive protein (CRP) is unknown. Among the in vitro functions assigned to CRP is the ability to activate complement via the classical pathway. To date, there is no evidence supporting that CRP exerts this function in vivo. We here show a novel approach to assess CRP-mediated complement activation in vivo, which is based on the property that activated complement factors C3 and C4 fix to CRP during complement activation induced by this acute phase protein. We developed specific ELISAs for complexes between CRP and C4b, C4d, C3b, or C3d. We established that in vitro complement-CRP complexes were formed only during CRP-dependent activation, and not during activation by other activators, even in the presence of high CRP levels. Circulating levels of complement-CRP complexes were undetectable in normal donors, but significantly increased in nine patients following implantation of a renal allograft. Importantly, levels of complement-CRP complexes did not change in these patients upon a bolus infusion of mAb OKT3, which induces activation of the classical complement pathway, demonstrating in vivo that complement-CRP complexes are not formed during CRP-independent activation of complement, even when CRP is elevated. We conclude that measurement of complement-CRP complexes provides a suitable tool to study CRP-mediated activation of complement in vivo. Furthermore, increased levels of these complexes occur in clinical samples, indicating that CRP may induce activation of complement in vivo.