Complement component 4



Complement component 4 is a protein involved in the complement system.

It is cleaved into proteins 4a and 4b.
 * C4a is an anaphylatoxin.
 * C4b forms part of C3-convertase, in conjunction with 2a:
 * C4b can bind CR1.

Clinical significance
It is responsible for the Chido Rodgers blood group system.

C4d has been identified as a biomarker for systemic lupus erythematosus.