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Complement component 4

complement component 4A (Rodgers blood group)
Identifiers
Symbol	C4A
Entrez	720
HUGO	1323
OMIM	120810
RefSeq	NM_007293
UniProt	P0C0L4
Other data
Locus	Chr. 6 p21.3

complement component 4B (Childo blood group)
Identifiers
Symbol	C4B
Entrez	721
HUGO	1324
OMIM	120820
RefSeq	NM_000592
UniProt	P0C0L5
Other data
Locus	Chr. 6 p21.3

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

It is cleaved into proteins 4a and 4b.

Clinical significance

It is responsible for the Chido Rodgers blood group system.^[1]

C4d has been identified as a biomarker for systemic lupus erythematosus.^[2]

^ Chido Rodgers blood group system at BGMUT Blood Group Antigen Gene Mutation Database at NCBI, NIH
^ Liu CC, Manzi S, Kao AH, Navratil JS, Ruffing MJ, Ahearn JM (2005). "Reticulocytes bearing C4d as biomarkers of disease activity for systemic lupus erythematosus". Arthritis Rheum. 52 (10): 3087–99. doi:10.1002/art.21305. PMID 16200588.

v • d • e Proteins: complement system (C, L, A)
Activators	CLA: C3-convertase - MAC (C6, C7, C8, C9) - L: Mannan-binding lectin - A: Factor P/Properdin
Enzymes	C: C1Q/C1R/C1S - C4 (A) - C2 - CLA: C3 - C5 (C5a) - L: MASP1 - MASP2 - A: Factor B - Factor D
Inhibitors	CLA: C1-inhibitor - Decay accelerating factor - Factor I - CL: C4BP - A: Factor H
Complement receptors	CR1 - CR2 - CR3 - CR4 - CD11b/CD11c/CD18 - Anaphylatoxin (C3a, C5a)