Complement C1q subcomponent (C1q)

The Complement C1q subcomponent is the initiator of the classical complement pathway, a critical arm of the innate immune system. It is a large, multimeric protein composed of 18 polypeptide chains (six A, six B, and six C chains) that form a structure resembling a bouquet of tulips, which allows it to recognize and bind to the Fc regions of IgM and IgG antibodies, as well as various non-immune ligands like C-reactive protein and apoptotic cells (UniProt P02745, P02746, P02747). Beyond its role in systemic immunity, C1q is expressed in the central nervous system where it mediates synaptic pruning during development and is pathologically upregulated in neurodegenerative diseases, leading to aberrant synapse loss (PubMed: 23125244). In autoimmune conditions like systemic lupus erythematosus, C1q deficiency or the presence of anti-C1q antibodies is strongly linked to disease pathogenesis due to defective clearance of apoptotic debris (PubMed: 25100335). Therapeutic targeting of C1q, such as with the monoclonal antibody ANX005, aims to inhibit classical pathway-mediated tissue damage in neurodegenerative and autoimmune disorders (Annexon Biosciences, 2023).

Other names

Complement component 1qC1q complexComplement C1qC1q subcomponent

Inhibition of the classical complement pathway by blocking C1q binding to its ligands (such as the Fc region of antibodies or apoptotic debris), thereby preventing the formation of the C3 convertase and subsequent inflammatory cascades.