What Are Complement Receptors?
The complement system, functioning as an assist or enhancement of antibodies and immunocytes, plays a significant role in pathogen resistance and host homeostasis. As an integral part of the immune system, the complement system eliminates pathogens mainly by phagocytosis, promote inflammation, and membrane attack, all of which are inseparable from the normal functions of complement members, enzymes and complement receptors (CRs).
The complement system consists of more than 30 functional proteins, including 8 CRs. CR is a group of membrane proteins expressed on the surface of immune cells, which is an important connection between complement components and cellular functions, as well as the innate immune system and the adaptive immune system. By binding to corresponding complement ligands, CRs mediate activations of canonical, alternative, and lectin complement pathways to eliminate antigens. Not only microorganisms but also autoantigens, allergens, and tumor cells, CRs are potential targets for the treatment of immune-related diseases and cancers. Based on state-of-the-art technical platform, Creative Biolabs has developed a series of high-quality products and customized services for these potential CR targets.
Fig. 1 Schematic diagram of major complement receptors.1
How Many Complement Receptors Are There?
CRs are important components on the surface of the cell, which involve in the regulation of multiple bio-activities, such as phagocytosis, immunoregulation, adhesion, inflammation, immune complex (IC) clearance, etc. Currently, about 9 types of CRs have been identified, each of which has different distribution and function.
Table.1 A List of Current Complement Receptors of Complement System.
|
Complement Receptor
|
Aliases
|
Ligand(s)
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Expressed cells
|
Functions
|
Related Diseases
|
|
CR1
|
CD35
|
C3b; C4b; MBL
|
Red blood cell; granulocyte; phagocyte; lymphocyte; dendritic cell
|
IC clearance; opsonization; assist Factor I cleave C3b and C4b; FcRn-mediated phagocytosis enhancement.
|
Malaria; Plasmodium Falciparum Malaria
|
|
CR2
|
CD21
|
iC3b; C3dg; C3d; EBV
|
B lymphocyte; nasopharyngeal epithelial cell
|
B cell proliferation, differentiation, and activation; alternative pathway activation.
|
Immunodeficiency, Common Variable, 7; Systemic Lupus Erythematosus 9
|
|
CR3
|
CD18/CD11b; ITGAM; Mac-1
|
iC3b
|
Granulocyte; macrophage; NK cell
|
Participation in adhesion, chemotaxis, and opsonization.
|
Systemic Lupus Erythematosus 6; Systemic Lupus Erythematosus
|
|
CR4
|
CD18/CD11c; ITGAX; P150/95
|
iC3b
|
Eosinophils
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FcRn-mediated phagocytosis enhancement; inducement non-FcRn dependent phagocytosis.
|
Hairy Cell Leukemia; Benign Cephalic Histiocytosis
|
|
Anaphylatoxin Receptors
|
C3aR
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C3aR1
|
C3a; C4a
|
Lymphocyte; neutrophil; eosinophil; basophils; mast cells
|
Stimulation chemotaxis, granule enzyme release, and superoxide anion production.
|
Complement Component 3 Deficiency; Complement Component 5 Deficiency
|
|
C5aR1
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CD88; C5aR1
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C5a
|
Granulocyte; Monocytes; Dendritic cells; Astrocytes; Microglia
|
Stimulation of chemotaxis, granule enzyme release, intracellular calcium release, and superoxide anion production.
|
Hypersensitivity Reaction Type Iii Disease; Mast-Cell Sarcoma
|
|
C5aR2
|
GPR77; C5L2
|
C3a, C4a, and C5a anaphylatoxins and their dearginated forms
|
Granulocyte; Monocytes; Dendritic cells; Astrocytes; Microglia
|
Participation in degranulation and leucocyte chemoattraction.
|
Complement Component 5 Deficiency; Myasthenic Syndrome, Congenital, 8
|
|
C1qR
|
CD93
|
C1q; MBL2; SPA
|
B lymphocyte; monocyte/macrophage; neutrophil; endothelial cell
|
Promotion of phagocytosis and ADCC effect; regulation of B-cell activity and platelet function.
|
C1 Inhibitor Deficiency; Familial Hypercholesterolemia
|
|
CRIg
|
_
|
C3b; iC3b
|
Kupffer cell
|
C3-opsonized particles clearance; inhibition of T cell activation.
|
Infections
|
Abbreviations: CRIg-Complement receptor of the immunoglobulin family; MBL mannose-binding lectin; SPA-pulmonary surfactant protein A; ADCC- Antibody-dependent cellular cytotoxicity
Recently, molecular biology research on the complement system has made dramatic progress. Further investigations on the complement system are needed to reveal the relationship between CRs and diseases and their therapeutic value. Committed to human health improvement for years, Creative Biolabs lend every effort in our power to offer a spectrum of high-quality CR products and related services to global clients.
Just directly contact us without hesitation. We are more than happy to share our experience and expertise with you.
Reference
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Vandendriessche, Sofie, et al. "Complement receptors and their role in leukocyte recruitment and phagocytosis." Frontiers in Cell and Developmental Biology 9 (2021): 624025.
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