The C1QB antibody targets the C1q B-chain, a critical component of the C1 complex in the complement system's classical pathway. C1q, a hexameric protein composed of three subunits (C1QA, C1QB, C1QC), initiates immune responses by binding to pathogens or antibody-antigen complexes, triggering complement activation. C1QB antibodies are essential tools in research and diagnostics, enabling detection of C1q expression or dysfunction. In autoimmune diseases like systemic lupus erythematosus (SLE), anti-C1q antibodies are biomarkers linked to severe manifestations, such as lupus nephritis, as they correlate with complement consumption and disease activity. These antibodies also aid in studying C1q's role in non-immune processes, including tissue homeostasis, apoptosis, and neuroinflammation. Additionally, genetic deficiencies in C1QB are associated with susceptibility to infections and autoimmune disorders. By employing techniques like ELISA, Western blot, or immunohistochemistry, C1QB antibodies help elucidate complement-driven pathologies and therapeutic targets, bridging insights into immune regulation and disease mechanisms.