Complement C5a receptor 1 (C5aR1/CD88)

Class

Selective oral C5a receptor antagonist

Pathway

Complement (alternative pathway) C5a/C5aR1 signaling — neutrophil activation in ANCA-associated vasculitis

The complement system is part of the body's innate immune defenses, a network of blood proteins that detect and destroy microbes and help clear damaged tissue. When this system is activated, it generates a small signaling fragment called C5a. C5a binds to a receptor named C5a receptor 1 (C5aR1, also called CD88), found mainly on neutrophils and related white blood cells. This binding activates the cells, drawing them toward sites of inflammation and triggering release of enzymes and reactive molecules that damage tissue. In antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis, autoantibodies prime neutrophils to attack small blood vessels, and excess complement activation with ongoing C5a signaling amplifies this attack, injuring vessel walls in the kidneys and other organs. A small-molecule antagonist that blocks C5aR1 interrupts this recruitment and activation signal, aiming to dampen vascular inflammation while leaving other complement functions, such as pathogen tagging and the membrane attack complex, largely intact. Because this approach targets a specific inflammatory signal rather than suppressing immunity broadly, it is designed to reduce dependence on high-dose corticosteroids, which carry their own significant toxicity. The underlying mechanism is relevant wherever C5a-driven neutrophil activation contributes to tissue injury, though it is best established in ANCA-associated vasculitis.