Complement component 2

Complement component 2 (C2) is a protein that plays a significant role in the immune system and is a part of the complement system, which is a complex innate immune mechanism responsible for enhancing the ability of antibodies and phagocytic cells to clear pathogens from an organism. C2 is involved in the classical and lectin pathways of complement activation.

Structure and Function

C2 is synthesized in the liver and is present in the blood serum as a single polypeptide chain. Upon activation by the C1 complex in the classical pathway or by mannose-binding lectin (MBL) in the lectin pathway, C2 interacts with activated C4 to form the C4b2a complex, also known as the C3 convertase of the classical and lectin pathways. This enzyme complex cleaves C3, leading to the generation of the opsonin C3b, and the initiation of a series of reactions that culminate in the formation of the membrane attack complex (MAC), which can lyse pathogen cell membranes.

Genetics

The gene encoding C2 is located on chromosome 6 in humans, within the major histocompatibility complex (MHC) class III region. Genetic variations in the C2 gene can lead to deficiencies in the C2 protein, which are associated with an increased susceptibility to certain infections and autoimmune diseases.

Clinical Significance

C2 deficiency is one of the most common complement deficiencies and is associated with a variety of autoimmune and infectious diseases, including systemic lupus erythematosus (SLE), recurrent bacterial infections, and increased susceptibility to type III hypersensitivity reactions. Diagnosis of C2 deficiency typically involves serum assays to measure the levels of complement proteins, and genetic testing can be used to identify mutations in the C2 gene.

Treatment and Management

Management of conditions associated with C2 deficiency focuses on treating the underlying infections and autoimmune conditions. In some cases, replacement therapy with fresh frozen plasma, which contains functional complement proteins, may be used to temporarily restore complement activity.

Research Directions

Ongoing research is aimed at better understanding the molecular mechanisms underlying C2 function and its role in disease. This includes studies on the genetic basis of C2 deficiency and the development of novel therapeutic approaches to modulate complement activity in diseases associated with complement dysregulation.