Complement C2 is a protein that in humans is encoded by the C2gene. The protein encoded by this gene is part of the classical pathway of complement system.
In the "classical" pathway of complement activation, activated C1 cleaves C4a and C4b, and cleaves C2 into C2a and C2b. The complex of the large fragments of C2 and C4, called C4b2a, is the classical C3 convertase and can activate C3. Deficiency of C2 has been associated with certain autoimmune diseases.
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