Complement C1q subcomponent subunit C

C1QC encodes the complement C1q subcomponent subunit C, a core component of the C1 complex that initiates the classical complement cascade. The protein works with C1QA and C1QB to recognize and bind immunoglobulin Fc regions on antigen-antibody complexes, activating downstream proteolytic signaling that promotes pathogen phagocytosis and clearance (UniProt: P02747). This complement recognition function also extends to phosphatidylserine on apoptotic cells, potentially triggering complement activation during programmed cell death.

C1QC is broadly expressed and participates in innate immune responses. UniProt disease records associate the C1QC gene with C1q deficiency 3 (C1QD3, MIM 620322), an autosomal recessive disorder marked by impaired classical pathway activation, chronic infections, and increased risk of systemic lupus erythematosus and glomerulonephritis (UniProt: P02747).

In Alzheimer's disease, C1QC is significantly upregulated in post-mortem AD brain tissue compared to age-matched controls, with a mean log2 fold-change of 0.86 (Chaparral AD proteomics). This elevation is consistent with emerging evidence that complement activation, particularly classical pathway components, may play a role in neuroinflammatory processes associated with neurodegeneration in AD.