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C4: C4 deficiency is highly associated with systemic lupus erythematosus. [3] Aβ42, a protein involved in Alzheimer's disease, can cause activation of C4 (even in plasma deficient of C1q). [18] At least one study indicates that the genetic variation of C4 plays a role in schizophrenia. [19]
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 a number of critical functions in immunity, tolerance, and autoimmunity with the other numerous components.
Complement 4 deficiency; Specialty: Immunology: Complement tests C4 ... Complement 4 deficiency is a genetic condition affecting complement component 4. [1]
Complement component 5 is a protein that in humans is encoded by the C5 gene. [5] Complement component 5 is involved in the complement system. It is cleaved into C5a and C5b: C5a plays an important role in chemotaxis. [6] C5b forms the first part of the complement membrane attack complex. Deficiency is thought to cause Leiner's disease.
Deficiency in the C1q protein of the classical complement pathway can lead to development of systemic lupus erythematosus. [2] [16] Among the many functions of C1q, C1q triggers clearance of immune complexes and apoptotic cells by activating the classical pathway and binding directly onto phagocytes.
The trimer provides a surface for interaction between the antigen-antibody complex and other complement components. The alpha chain may be cleaved to release C4 anaphylatoxin, a mediator of local inflammation. Deficiency of this protein is associated with systemic lupus erythematosus and type I diabetes mellitus.
Terminal complement pathway deficiency is a genetic condition affecting the complement membrane attack complex (MAC). It involves deficiencies of C5, C6, C7, and C8. (While C9 is part of the MAC, and deficiencies have been identified, [1] it is not required for cell lysis. [2]) People with this condition are prone to meningococcal infection. [3]
B cells low but present or normal, but with reduction in 2 or more isotypes (usually IgG & IgA, sometimes IgM): common variable immunodeficiency (CVID), CD19 deficiency, TACI (TNFRSF13B) deficiency, BAFF receptor deficiency. Normal numbers of B cells with decreased IgG and IgA and increased IgM: Hyper-IgM syndromes