C1QB encodes the B chain of complement component C1q, a core component of the C1 complement complex that initiates the classical complement pathway 1. C1QB, along with C1QA and C1QC, forms the C1q subcomplex that specifically recognizes and binds to the Fc regions of IgG or IgM immunoglobulins complexed with antigens on pathogen surfaces, leading to complement activation and subsequent pathogen elimination 1. The protein functions in immune surveillance by recognizing phosphatidylserine on apoptotic cells and facilitating their clearance 1. C1QB expression is significantly associated with macrophage populations, particularly in tumor microenvironments where C1QB+ macrophages contribute to immune regulation 23. In disease contexts, C1QB serves as a biomarker for various conditions: it distinguishes mature macrophages in inflammatory bowel disease 1, identifies immunosuppressive tumor-associated macrophages in cancers 23, and functions as a diagnostic marker for tuberculosis infection 4. The gene shows differential expression patterns across multiple diseases including lung cancer, Alzheimer's disease, atherosclerosis, and thyroid conditions, highlighting its broad role in immune-mediated pathological processes 567. C1QB deficiency is associated with complement deficiency disorders affecting immune function.