Autoantibodies Against C3b-Functional Consequences and Disease Relevance

Area of Science:

• Immunology
• Complement System Biology

Background:

• Complement component C3 is central to the immune system's complement cascade.
• Activated C3 fragments are targets for autoantibodies, including anti-C3b antibodies (immunoconglutinins).
• These antibodies have been historically observed post-infection and more recently linked to autoimmune diseases.

Purpose of the Study:

• To review the discovery, disease relevance, and functional impact of anti-C3b autoantibodies.
• To explore the role of anti-C3b antibodies in systemic lupus erythematosus, lupus nephritis, C3 glomerulopathy, and immune complex glomerulonephritis.
• To understand the functional consequences and potential therapeutic implications of anti-C3b autoantibodies.

Main Methods:

• Review of existing literature on anti-C3b autoantibodies.
• Analysis of antibody epitope recognition.
• In vitro studies assessing effects on complement pathway activity and regulator binding.

Main Results:

• Anti-C3b autoantibodies recognize epitopes shared across C3 fragments (C3(H2O)/C3b/iC3b/C3c).
• These antibodies correlate with low plasma C3 levels and increased alternative pathway C3 convertase activity in patients.
• They interfere with the binding of negative regulators Factor H and Complement Receptor 1.

Conclusions:

• Anti-C3b autoantibodies have functional consequences and are associated with disease severity.
• Further research is needed to establish their direct role in tissue injury.
• Targeting C3 may benefit patients with complement overactivation driven by anti-C3b antibodies.