complement receptor mediated signaling pathway

Definition

Target type: biologicalprocess

The series of molecular signals generated as a consequence of a component of the complement pathway binding to a complement receptor. Such components include both whole complement proteins and fragments of complement proteins generated through the activity of the complement pathway. [GO_REF:0000022, GOC:add, ISBN:0781735149]

The complement receptor (CR)-mediated signaling pathway is a crucial component of the innate immune response, primarily involved in the recognition and clearance of pathogens. It is initiated when complement proteins, part of the humoral immune system, bind to the surface of target cells, such as bacteria, viruses, or damaged cells. This binding activates a cascade of events, ultimately leading to the recruitment of immune cells and the elimination of the target.

**Key steps in the CR-mediated signaling pathway:**

1. **Complement Protein Binding:** Complement proteins, such as C3b and C4b, are deposited on the surface of the target cell. These proteins act as opsonins, enhancing the recognition and phagocytosis of the target by immune cells.

2. **CR Binding:** Complement receptors (CRs), expressed on the surface of immune cells like macrophages and neutrophils, bind to these complement proteins. The most important CRs involved are:
* **CR1 (CD35):** Binds to C3b and C4b, facilitating phagocytosis and promoting the release of soluble complement inhibitors.
* **CR2 (CD21):** Binds to C3dg, a breakdown product of C3b, and plays a role in B cell activation.
* **CR3 (CD11b/CD18) and CR4 (CD11c/CD18):** Bind to iC3b, a further breakdown product of C3b, and participate in phagocytosis and immune cell adhesion.

3. **Signal Transduction:** Binding of CRs to complement proteins triggers a signaling cascade within the immune cell. This cascade involves the activation of intracellular signaling molecules, such as kinases and adaptor proteins. These molecules initiate a series of events, including:
* **Phagocytosis:** The immune cell engulfs the target cell, effectively removing it from circulation.
* **Immune Cell Activation:** CR signaling activates immune cells, such as macrophages and neutrophils, leading to the release of cytokines, chemokines, and other inflammatory mediators. These molecules further recruit additional immune cells to the site of infection and enhance the inflammatory response.
* **Complement Regulation:** CR signaling also promotes the release of soluble complement inhibitors, which can modulate the complement cascade and prevent excessive inflammation.

4. **Immune Cell Recruitment and Effector Functions:** Activated immune cells, guided by chemokines and other signaling molecules, migrate to the site of infection and initiate a range of effector functions. These functions include:
* **Phagocytosis and Killing:** Immune cells engulf and destroy pathogens and damaged cells.
* **Antibody Production:** B cells can be activated by complement-mediated signals, leading to the production of antibodies against the target.
* **Cytokine Release:** Immune cells release cytokines, which can further activate other immune cells and initiate inflammation.

**Overall, the CR-mediated signaling pathway is a critical component of the innate immune response. It ensures the rapid recognition and clearance of pathogens, contributing to the overall immune defense against infections.**'
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Proteins (5)

Compounds (12)