Complement in ANCA-associated vasculitis.

Area of Science:

• Immunology
• Nephrology
• Rheumatology

Background:

• Antineutrophil cytoplasmic autoantibodies (ANCA) are linked to necrotizing small-vessel vasculitis and crescentic glomerulonephritis.
• ANCA-associated glomerulonephritis shows less immunoglobulin and complement in vessel walls compared to other crescentic glomerulonephritis types.

Purpose of the Study:

• To investigate the role of the alternative complement pathway in ANCA-associated disease pathogenesis.
• To elucidate the mechanism of ANCA-induced neutrophil activation and its inflammatory consequences.

Main Methods:

• Review of experimental data from animal models and in vitro studies.
• Analysis of clinical observations in patients with ANCA disease, comparing active disease and remission states.
• Measurement of complement components (C3a, C5a, C4d, Bb, soluble C5b-9) in patient plasma.

Main Results:

• Experimental data indicate ANCA activates neutrophils, generating C5a, which recruits and primes more neutrophils.
• Clinical data show elevated levels of C3a, C5a, C5b-9, and Bb in active ANCA disease compared to remission.
• No significant difference in C4d levels was observed between active and remission states.

Conclusions:

• ANCA-induced neutrophil activation triggers the alternative complement pathway, generating C5a.
• C5a perpetuates inflammation by recruiting and priming neutrophils, forming a self-fueling loop.
• This amplification loop leads to destructive necrotizing vascular injury in ANCA-associated diseases.