Unraveling the C-reactive Protein Complement-Cascade in Destruction of Red Blood Cells: Potential Pathological Implications in Plasmodium Falciparum Malaria

BACKGROUND: Deficiencies of the complement-regulatory proteins on RBC (RBC(Mal)) of patients with Plasmodium falciparum were reported. Here, we sought to determine the role of affinity-purified C-reactive protein from patients (CRP(Mal)), in modulating the complement-regulatory proteins and downstream effect on complement-cascade. METHODS: CRP(Mal) was characterized by analytical ultracentrifuge and electrophoretic analysis. Surface plasmon resonance, Western blotting, co-immuno-precipitation, flow-cytometry and ELISA determined the binding of CRP(Mal) with RBC(Mal). Modifications of membranes for RBC(Mal)-CRP(Mal) binding were explored by scanning electron microscopy, osmotic and turbulence fragility, hydrophobicity and oxyhemoglobin release. Flow-cytometry, ELISA, Western blotting and Scatchard analysis monitored the status of complement-regulatory proteins on RBC(Mal). Complement-activation via CRP(Mal) was quantified by C3-deposition and hemolysis. RESULTS: CRP(Mal) binds specifically to RBC(Mal) through distinct molecules. Such binding altered the normal discoid-shape of RBC(Mal) with increased membrane fluidity and hydrophobicity. In the presence of CRP, RBC(Mal) showed reduced complement-regulatory proteins (CR1 or CD35, CD55 and CD59) with decreased affinity. These changes caused enhanced C3-deposition and complement-mediated hemolysis. CONCLUSION: Taken together, we have established the contributory effect of CRP(Mal) causing decreased complement-regulatory proteins, possibly providing a new mechanism of complement-fueled RBC(Mal) destruction refractory to erythrophagocytosis and may account for pathogenesis of anemia.