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Deficiencies of human C3 complement receptors type 1 (CR1, CD35) and type 2 (CR2, CD21)
1Unité d'Immunopathologie and INSERM U28, Hôpital Broussais, Paris, France.
Insights
Complement receptors 1 (CR1) and 2 (CR2) are key proteins involved in immune responses. This review details their molecular biology, functions, and altered expression in diseases like systemic lupus erythematosus.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- Complement receptors 1 (CR1/CD35) and 2 (CR2/CD21) are transmembrane glycoproteins crucial for the complement system.
- CR1 binds C3b, while CR2 binds C3dg, playing roles in immune complex clearance and B-cell function.
- These receptors are encoded by genes located in the RCA locus on chromosome 1.
Purpose of the Study:
- To review the molecular biology and functional characteristics of CR1 and CR2.
- To focus on the alterations in CR1 and CR2 expression in various diseases.
- To emphasize genetic and acquired factors causing defective CR1 expression in systemic lupus erythematosus.
Main Methods:
- Literature review of existing studies on CR1 and CR2.
- Analysis of molecular structures and ligand-binding properties.
- Examination of gene localization and expression patterns.
Main Results:
- CR1 has broad cellular distribution, mediating immune complex transport, phagocytosis, IL-1 secretion, and B-cell differentiation.
- CR2 is restricted to B lymphocytes and follicular dendritic cells, modulating B-cell growth and serving as the Epstein-Barr virus (EBV) receptor.
- Defective CR1 expression in systemic lupus erythematosus is linked to genetic and acquired factors.
Conclusions:
- CR1 and CR2 are vital for distinct immunological functions.
- Altered expression of these receptors is implicated in disease pathogenesis.
- Understanding these alterations, particularly for CR1 in SLE, is crucial for therapeutic strategies.
Abstract:
CR1 (CD35) and CR2 (CD21) are structurally related integral transmembrane glycoproteins that function as cellular receptors for human C3b and C3dg, respectively. The primary sequence of the most common structural allotype of CR1 and that of CR2 have been established, and ligand binding on the molecules has been mapped. CR1 and CR2 genes are located in close vicinity in the RCA locus of chromosome 1. CR1 has a wide cellular/tissular distribution and mediates a variety of biologic functions, including the transport of C3-bearing immune complexes on erythrocytes, enhancement of phagocytosis, induction of IL-1 secretion and enhancement of B-cell differentiation. Expression of CR2 is restricted to B lymphocytes and follicular dendritic cells. The receptor modulates B-cell growth. CR2 also serves as the receptor for EBV and determines the cellular tropism of the virus. This review discusses the molecular biology and functional characteristics of CR1 and CR2. It focuses on alterations of expression of the receptors in disease, with particular emphasis on the genetic and acquired factors that contribute to the defective expression of CR1 in patients with systemic lupus erythematosus.