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Protein C4A PDB 1hzf.png
Available structures
PDB Ortholog search: PDBe RCSB
Aliases C4A, C4, C4A2, C4A3, C4A4, C4A6, C4AD, C4S, CO4, CPAMD2, RG, complement component 4A (Rodgers blood group)
External IDs MGI: 98320 HomoloGene: 36030 GeneCards: C4A
RNA expression pattern
PBB GE C4A 214428 x at fs.png

PBB GE C4A 208451 s at fs.png
More reference expression data
Species Human Mouse
RefSeq (mRNA)



RefSeq (protein)



Location (UCSC) Chr 6: 31.98 – 32 Mb n/a
PubMed search [1] [2]
View/Edit Human View/Edit Mouse

Complement C4-A is a protein that in humans is encoded by the C4A gene.[3]


This gene encodes the acidic form of complement factor 4, part of the classical activation pathway. The protein is expressed as a single chain precursor which is proteolytically cleaved into a trimer of alpha, beta, and gamma chains prior to secretion. The trimer provides a surface for interaction between the antigen-antibody complex and other complement components. The alpha chain may be cleaved to release C4 anaphylatoxin, a mediator of local inflammation. Deficiency of this protein is associated with systemic lupus erythematosus and type I diabetes mellitus.[4][5][6][7][8][9] This gene localizes to the major histocompatibility complex (MHC) class III region on chromosome 6. Varying haplotypes of this gene cluster exist, such that individuals may have 1, 2, or 3 copies of this gene.[3]

See also[edit]


  1. ^ "Human PubMed Reference:". 
  2. ^ "Mouse PubMed Reference:". 
  3. ^ a b "Entrez Gene: C4A complement component 4A (Rodgers blood group)". 
  4. ^ Dawkins RL, Uko G, Christiansen FT, Kay PH (Sep 1983). "Low C4 concentrations in insulin dependent diabetes mellitus". British Medical Journal. 287 (6395): 839. doi:10.1136/bmj.287.6395.839-b. PMC 1549128Freely accessible. PMID 6412852. 
  5. ^ Vergani D, Johnston C, B-Abdullah N, Barnett AH (Mar 1983). "Low serum C4 concentrations: an inherited predisposition to insulin dependent diabetes?". British Medical Journal. 286 (6369): 926–8. doi:10.1136/bmj.286.6369.926. PMC 1547358Freely accessible. PMID 6403137. 
  6. ^ Mijovic CH, Fletcher JA, Bradwell AR, Barnett AH (Oct 1987). "Low C4 levels in type 1 (insulin-dependent) diabetes". Diabetologia. 30 (10): 824. doi:10.1007/bf00275752. PMID 3428499. 
  7. ^ Thomsen M, Mølvig J, Zerbib A, de Preval C, Abbal M, Dugoujon JM, Ohayon E, Svejgaard A, Cambon-Thomsen A, Nerup J (1988). "The susceptibility to insulin-dependent diabetes mellitus is associated with C4 allotypes independently of the association with HLA-DQ alleles in HLA-DR3,4 heterozygotes". Immunogenetics. 28 (5): 320–7. doi:10.1007/BF00364230. PMID 3139557. 
  8. ^ Jenhani F, Bardi R, Gorgi Y, Ayed K, Jeddi M (Apr 1992). "C4 polymorphism in multiplex families with insulin dependent diabetes in the Tunisian population: standard C4 typing methods and RFLP analysis". Journal of Autoimmunity. 5 (2): 149–60. doi:10.1016/0896-8411(92)90196-w. PMID 1352685. 
  9. ^ Lhotta K, Auinger M, Kronenberg F, Irsigler K, König P (1996). "Polymorphism of complement C4 and susceptibility to IDDM and microvascular complications". Diabetes Care. 19 (1): 53–55. doi:10.2337/diacare.19.1.53. 

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