C4d

**Semantic type:** Amino Acid, Peptide, or Protein

**Definition:** C4d (380 aa, ~41 kDa) is a fragment of complement component-4. This protein plays a role in the regulation of the classical and lectin complement pathways. It may be a biomarker for complement activation during antibody-mediated rejection of transplants and in other pathological conditions.

**Synonyms:** - C4D - Complement C4d - Complement Component 4d - Complement Component-4d