C3

prostatic tumor with seminal vesical involvement [Jewett staging system]; third cervical nerve; third cervical vertebra; third component of complement

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a component of both the classical and alternative complement pathways; it can be cleaved spontaneously at low level (tickover) or by one of the C3 convertases (C4b,2a or C3b,Bb) to form C3a and C3b. Deficiency of C3 may be associated with repeated severe pyogenic bacterial infection.