Complement receptor 1

A receptor involved in the immune system

Complement receptor 1 (CR1), also known as CD35, is a protein found on the surface of various immune cells, including erythrocytes, leukocytes, and follicular dendritic cells. It plays a crucial role in the immune system by mediating the clearance of immune complexes and enhancing phagocytosis.

Structure

Complement receptor 1 is a large glycoprotein that belongs to the regulators of complement activation (RCA) family. It is composed of multiple short consensus repeats (SCRs), also known as complement control protein (CCP) domains. These domains are responsible for binding to complement components such as C3b and C4b. The structure of CR1 allows it to interact with various ligands and participate in different immune functions.

Function

CR1 serves several important functions in the immune system:

• Clearance of Immune Complexes: CR1 on erythrocytes binds to C3b- and C4b-coated immune complexes, facilitating their transport to the liver and spleen for removal by phagocytes.

• Regulation of Complement Activation: CR1 acts as a cofactor for the cleavage of C3b and C4b by factor I, thereby regulating the complement cascade and preventing excessive inflammation.

• Enhancement of Phagocytosis: CR1 on phagocytic cells such as macrophages and neutrophils enhances the uptake and destruction of opsonized pathogens.

Clinical Significance

Alterations in CR1 expression or function can have significant clinical implications. Reduced levels of CR1 on erythrocytes have been associated with systemic lupus erythematosus (SLE) and other autoimmune diseases. Additionally, CR1 polymorphisms have been linked to susceptibility to malaria, as the receptor is involved in the clearance of Plasmodium falciparum-infected erythrocytes.

Genetics

The CR1 gene is located on chromosome 1 and exhibits significant polymorphism. Variations in the number of SCRs can lead to different isoforms of the protein, which may affect its function and expression levels. These genetic variations can influence an individual's susceptibility to certain diseases and their response to infections.

Related pages

• Complement system
• Immune system
• Phagocytosis
• Autoimmune disease

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