complement receptor activity

Definition

Target type: molecularfunction

Combining with any component or product of the complement cascade and transmitting the signal from one side of the membrane to the other to initiate a change in cell activity. [GOC:add, GOC:ai, GOC:pg, GOC:signaling, ISBN:0781735149, PMID:11884446]

Complement receptor activity is a molecular function that describes the ability of a protein to bind to and interact with complement proteins. These proteins play a crucial role in the innate immune system, mediating a cascade of events leading to the elimination of pathogens and the removal of cellular debris. Complement receptors are transmembrane proteins expressed on various immune cells, such as macrophages, neutrophils, B lymphocytes, and erythrocytes. They recognize and bind to specific complement components, primarily C3b and its breakdown products, which are deposited on the surface of target cells, such as bacteria, viruses, or apoptotic cells. This binding initiates a series of downstream signaling events within the immune cell, triggering a variety of effector functions:
* **Phagocytosis:** Complement receptors facilitate the engulfment and destruction of pathogens by phagocytic cells like macrophages and neutrophils. By recognizing C3b fragments on the surface of microbes, these receptors trigger the internalization of the pathogens into the phagocytic cell, where they are destroyed by lysosomal enzymes.
* **Opsonization:** The binding of complement receptors to C3b fragments on a target cell enhances the efficiency of phagocytosis. This process, known as opsonization, effectively tags the target cell for destruction by phagocytes.
* **Immune complex clearance:** Complement receptors are crucial for the removal of immune complexes, aggregates of antigens bound to antibodies. These complexes can deposit in tissues, causing inflammation and tissue damage. Complement receptors on erythrocytes bind to immune complexes and transport them to the liver and spleen for clearance.
* **Inflammation:** Complement receptors can also activate inflammatory signaling pathways within immune cells. The binding of C3b to complement receptors can trigger the release of pro-inflammatory cytokines and chemokines, which recruit and activate other immune cells to the site of infection or injury.
* **Complement regulation:** Complement receptors are also involved in the regulation of the complement cascade, preventing uncontrolled activation and tissue damage. Some complement receptors, such as CR1, can bind to C3b and C4b, inhibiting the formation of the C3 convertase and preventing further activation of the cascade.

Overall, complement receptor activity is a critical component of the innate immune response, contributing to pathogen clearance, immune complex removal, and inflammatory signaling. These receptors play a vital role in maintaining immune homeostasis and protecting the host from infection and disease.'
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Proteins (2)

Compounds (8)