{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Complement component 4 (C4), in humans, is a protein involved in the intricate complement system, originating from the human leukocyte antigen (HLA) system. It serves several critical functions in immunity, tolerance, and autoimmunity with the other numerous components.Low serum complement activity or low protein concentrations of complement C4 are found on systemic lupus erythematosus and it is often associated with congenital C4 deficiency. According to research, complete deficiencies of complement components are among the strongest genetic risk factors for SLE or lupus-like disease, across HLA haplotypes and racial backgrounds."}]}]}