Elevation of the terminal complement activation products C5a and C5b-9 in ALS patient blood

• Plasma C5a and C5b-9 levels are elevated in amyotrophic lateral sclerosis (ALS) patients.
• Plasma C3a and C4a are not significantly altered in ALS patients.
• Leukocyte associated C5a is also significantly elevated in ALS blood.
• Results suggest heightened terminal pathway activation in ALS.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease, characterized by the progressive loss of motor neurons within the central nervous system. Neural degeneration and inflammatory processes, including activation of the complement system are hallmarks of this pathology. Our past work in ALS animal models (hSOD1G93A rodents) has revealed that blockade of the receptor for complement activation fragment C5a (C5aR), improves ALS-like symptoms and extends survival. We now show that the levels of C5a and C5b-9, but not C3a nor C4a, are significantly elevated in plasma from ALS patients compared to healthy controls. C5a was also elevated within leukocytes from ALS patients suggesting heightened C5a receptor interaction. Overall, these findings indicate that there is enhanced peripheral immune complement terminal pathway activation in ALS, which may have relevance in the disease process.