It plays a central role in the complement system of vertebrate animals and contributes to innate immunity.

Once C3 is activated to C3b, it exposes a reactive thioester that allows the peptide to covalently attach to any surface that can provide a nucleophile such as a primary amine or a hydroxyl group.

First, the proteolytic component of the convertase, Bb, is removed by complement regulatory proteins having decay-accelerating factor (DAF) activity.

The C3 precursor protein is first processed by the removal of 4 Arginine residues, forming two chains, beta and alpha, linked by a disulfide bond.

[19] Some data shows that acquired C3 deficiency, including when this is intentionally done for medical immunosuppression purposes, may not significantly impact a person's immune function long-term.

[19] Additionally, several forms of C3 deficiency contribute to the development of systemic lupus erythematosus and other autoimmune diseases.

[19] This article incorporates text from the United States National Library of Medicine, which is in the public domain.