This gene encodes a serine protease, which is a major constituent of the human complement subcomponent C1. C1s associates with two other complement components C1r and C1q in order to yield the first component of the serum complement system. Defects in this gene are the cause of selective C1s deficiency. [provided by RefSeq, Mar 2009]
Forensic Context
A study in human blood plasma demonstrated that the C1S (Complement C1s subcomponent) was significantly upregulated with age and contributed to a proteomic aging clock model achieving an R² of 0.59 ± 0.02, with the combined protein and miRNA model improving predictions to R² = 0.70 ± 0.01 [Salignon et al. DOI:10.18632/aging.204787]. In a mouse model of traumatic brain injury, microglial expression of C1s was significantly upregulated at 14 days post-injury, indicating its role in the complement system's activation during the subacute neuroinflammatory phase [Izzy et al. DOI:10.3389/fncel.2019.00307].