The C1S gene encodes a component of the complement system, part of the innate immune system involved in inflammation and immune response.
Gene SymbolC1S
Full NameComplement Component 1, S Subcomponent (C1s)
Chromosomal Location12p13.31
Ensembl IDENSG00000159189
Associated DiseasesSystemic Lupus Erythematosus, Age-Related Macular Degeneration
The C1S gene encodes complement component 1, s subcomponent (C1s), a serine protease that is part of the C1 complex. C1s is the effector protease of the C1 complex, responsible for cleaving C4 and C2 to initiate the classical complement cascade.
The C1 complex assembly:
- One C1q molecule (recognition)
- Two C1r molecules (protease)
- Two C1s molecules (protease)
Upon activation, C1s cleaves:
- C4 → C4a (anaphylatoxin) + C4b (opsonin)
- C2 → C2a (vasoactive) + C2b (protease fragment)
The C4b2a complex forms the C3 convertase of the classical pathway.
- Alzheimer's Disease: C1s is part of the complement cascade activated in AD brain, contributing to synaptic loss and neuroinflammation.
- Parkinson's Disease: Complement activation is involved in neuroinflammation in PD.
- Age-Related Macular Degeneration: Genetic variants in complement genes, including C1S pathway genes, are associated with AMD risk.
- Brain: Microglia, astrocytes, and neurons can express C1s, especially under inflammatory conditions
- Liver: Primary site of complement protein synthesis
- Immune cells: Macrophages, monocytes
- Stephan et al., Complement and microglia in brain development and function (2013)
- Woodruff et al., Complement in the brain (2010)
- Janeway et al., Immunobiology (9th ed., 2016)
- Ricklin et al., Complement in disease (2013)
- Merle et al., Complement system (2015)