<unk>  <unk> , in humans, is a protein involved in the intricate<unk>  system, originating from the human leukocyte antigen (HLA) system. It serves a number of critical functions in immunity, tolerance, and autoimmunity with the other numerous<unk> s. Furthermore, it is a crucial factor in connecting the recognition pathways of the overall system instigated by antibody-antigen (Ab-Ag) complexes to the other effector proteins of the innate immune response. For example, the severity of a dysfunctional<unk>  system can lead to fatal diseases and infections. Complex variations of it can also lead to schizophrenia. Yet, the<unk>  protein derives from a simple two-locus allelic model, the<unk> A-C4B genes, that allows for an abundant variation in the levels of their respective proteins within a population. Originally defined in the context of the Chido/Rodgers blood group system, the<unk> A-C4B genetic model is under investigation for its possible role in schizophrenia risk and development.
Complement component 4
Complement component 3
Complement component 5a
Complement receptor 1
Major basic protein
Neutrophil elastase
Macrophage-activating factor
Immunophilins