SLE serum deposits C4d on red blood cells, decreases red blood cell membrane deformability, and promotes nitric oxide production

Objective Systemic lupus erythematosus (SLE) is characterized by intravascular activation of the complement system and deposition of complement fragments (C3 and C4) on plasma membranes of circulating cells, including red blood cells (RBC). The aim of this study was to address whether this process affects the biophysical properties of RBC.

Methods Serum and red blood cells were isolated from patients with SLE, and healthy controls. RBC from healthy O Rh negative individuals were incubated with SLE or control serum. We used flow cytometry to assess complement fragment deposition on RBC. RBC membrane deformability was measured using 2D microchannel arrays. Protein phosphorylation levels were quantified by western blot.

Results Incubation of healthy donor RBC with sera from patients with SLE but not control sera led to deposition of C4 fragments on the RBC. Complement decorated RBC exhibited significant decrease in both membrane deformability and flickering. Sera from SLE patients triggered a transitory Ca++ influx in RBC that was associated with decreased phosphorylation of ?-spectrin, and increased phosphorylation of band 3, two key proteins of RBC cytoskeleton. Finally, SLE but not control sera led to the production of nitric oxide (NO) by RBC.

Conclusion Our data suggest that complement activation in patients with SLE leads to calcium dependent cytosketeletal changes in RBC that render them less deformable, likely impairing their flow through capillaries. This phenomenon may negatively impact the delivery of oxygen to the tissues.