Complement receptor, CR concept:
A glycoprotein present on the cell membrane that binds to the complement active molecule.
(1) CR1 (CD35)
Distribution: expressed on many types of cell surface (erythrocytes, granulocytes, macrophages, lymphocytes, etc.)
Ligand: C3b, C4b (C3bR/C4bR)
Main biological functions:
1. Binding C3b and C4b inhibits complement activation, assisting factor I to cleave C3b and C4b;
2. Conditioning: granulocytes, macrophages
3. Promote immune complex clearance: red blood cells à liver
4. Immunoregulation: occurs in the early stages of B cell development, promoting differentiation of B cells
(2) CR2 (CD21)
Distribution: mainly expressed in B cells, nasopharyngeal epithelial cells
Ligand: iC3b, C3dg, C3d
Main biological functions:
1. Immunomodulatory effects:
Regulates B cell proliferation, differentiation, memory and antibody production
2. As an Epstein-Barr virus receptor: associated with certain diseases
Infectious mononucleosis
African childhood lymphoma (ie Burkitt lymphoma)
Nasopharyngeal carcinoma
Epstein-Barr virus: Epstein-Barr virus (EBV), human herpesvirus
Discover: Epstein and Barr (1964)
Found in Burkitt African Children's Lymphoma Cells
3. Pathogenicity: widespread infection in the population,
(1) The positive rate of EB virus IgG antibody in children aged 3 to 5 years in China is over 90%. Most children have no obvious symptoms after infection, or cause mild pharyngitis and upper respiratory tract infection.
(2) Primary infection occurs in adolescence, and about 50% of infectious mononucleosis occurs. It is mainly transmitted through saliva and can also be transmitted through blood transfusion. Epstein-Barr virus proliferates in oropharyngeal epithelial cells and then infects B lymphocytes, which enter the bloodstream in large numbers and cause systemic infections. It can be lurking in human lymphoid tissue for a long time. When the immune function of the body is low, the latent Epstein-Barr virus activation forms a recurrent infection.
(3) Middle-aged and elderly people over 40 years old, high incidence of nasopharyngeal carcinoma
(iii) CR3 (Mac-1, CD11b/CD18)
Distribution: expressed on the surface of various bone marrow-derived cells (granulocytes, monocytes, macrophages, mast cells, NK cells, etc.)
Ligand: iC3b
Main biological functions:
1. Mediate adhesion: granule/mononuclear à endothelial cells à inflammatory cell accumulation (CR3)
2. Enhance phagocytic function: mediate adhesion to phagocytic cells (CR3+ iC3b)
3. Lectin activity: combined with specific carbohydrates to promote phagocytosis (CR3)
(4) CR4 (P150/95, CD11c/CD18)
Distribution: similar to CR3
Ligand: iC3b and C3dg
Main biological functions:
Also similar to CR3 enhances Fc receptor-mediated phagocytosis
(5) C3a/C4a receptors and C5a receptors
Ligand: C3a/C4a and C5a
Main biological functions:
Inflammatory effects that mediate complement activation
(6) C1q receptor
Ligand: C1q
Main biological functions:
Immunomodulatory effects and regulation of platelet function.
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