Gene SymbolC8A
Full NameComplement Component 8 Alpha Chain
Chromosomal Location1p31.3
Ensembl IDENSG00000157216
Associated DiseasesComplement Deficiency, Neiserria Infections
The C8A gene encodes the alpha chain of complement component 8 (C8α), a terminal complement protein essential for membrane attack complex (MAC) formation. C8 is composed of three chains (alpha, beta, and gamma) that form a heterotrimeric complex. The gene is located on chromosome 1p31.3 and encodes a protein of 579 amino acids [1].
C8 is a critical component of the complement terminal pathway. The alpha chain contains a hydrophobic region that inserts into the target cell membrane, while the gamma chain is a lipocalin-like protein. Together with C5b, C6, C7, and C9, C8 participates in forming the cytolytic MAC [2].
The C8 alpha chain functions as:
- Membrane Stabilization: Stabilizes the C5b-7 complex on the target cell membrane
- Scaffold for C9: Provides a platform for C9 polymerization and pore formation
- Pore Formation: Contributes to efficient membrane pore formation by the MAC
- Lipid Binding: The alpha chain contains a lipophilic region that inserts into lipid bilayers
The complete C8 complex (αβγ) binds to C5b-7 to form C5b-8, which then allows C9 polymerization to form the mature MAC (C5b-9).
- C8 Deficiency: Individuals with C8 deficiency have increased susceptibility to Neisseria infections, particularly Neisseria meningitidis
- Recurrent Infections: Lack of functional MAC leads to impaired bacterial killing
- MAC-mediated Injury: Sublytic MAC formation can contribute to neuronal injury in various neurodegenerative conditions
- Glial Activation: MAC deposition may activate glial cells and contribute to neuroinflammation
- Liver: Primary site of synthesis (hepatocytes)
- Brain: Low baseline expression in astrocytes and microglia
- Various tissues: Widely expressed at low levels
- C8 expression is upregulated during acute phase response
- Inflammatory cytokines can modulate C8 synthesis
- C8A polymorphisms may affect complement activity levels
- Rare variants cause hereditary C8 deficiency
- Diagnostic Markers: C8 levels can be measured for complement deficiency workup
- Therapeutic Potential: Modulating C8 activity may have applications in treating complement-mediated diseases
- Haddad et al., Molecular characterization of C8 alpha chain deficiency (2006)
- Miller et al., C8 deficiency and meningococcal infection (1988)
- Nishikawa et al., Structure of complement component C8 (1992)
- Würzner et al., Membrane attack complex deficiency (1995)
- Riley et al., Evolution of the complement system (2002)
- Baran et al., C8B deficiency with recurrent infections (2010)
- Skerka et al., Complement deficiencies (1993)
- Frank et al., Complement in disease (1995)