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Expression of the MHC class III genes
Summary
Complement component C4 gene expression varies due to post-transcriptional processing defects in guinea pigs and mRNA levels in mice. Macrophage maturation influences biosynthesis of complement components C2, C4, and factor B.
Area of Science:
- Immunogenetics
- Molecular Biology
- Cell Biology
Background:
- Genes for complement components C2, C4, and factor B are located within the major histocompatibility complex (MHC).
- These proteins are synthesized in the liver and by mononuclear phagocytes.
- Complementary DNA probes enable the study of molecular mechanisms controlling class III MHC gene expression.
Purpose of the Study:
- To investigate the genetic control of complement component C4 gene expression in two model systems.
- To analyze molecular mechanisms regulating biosynthesis of MHC class III products during monocyte-macrophage maturation.
- To understand the regulation of complement protein synthesis in macrophages.
Main Methods:
- Analysis of C4-specific RNA processing in a C4-deficient guinea pig strain.
- Quantification of mature C4 liver mRNA levels in different mouse strains.
- Monitoring of C2 and factor B secretion rates and mRNA levels in cultured human monocytes and macrophages.
- Investigating C4 gene regulation in guinea pig and mouse macrophages using extracellular C4 feedback mechanisms.
Main Results:
- A defect in post-transcriptional processing of C4 RNA causes a deficiency in mature C4 mRNA in guinea pigs.
- Quantitative differences in mature C4 liver mRNA levels explain genetic variations in C4 levels among mouse strains.
- Monocyte-to-macrophage maturation increases secretion rates of C2 and factor B, with higher proportions of C2-producing cells in macrophages.
- Guinea pig macrophages exhibit C4 gene regulation via a feedback mechanism involving extracellular C4 binding to the cell surface.
- Mouse macrophages display feedback-independent mechanisms for regulating C4 and factor B mRNA levels, differing from guinea pig macrophages.
Conclusions:
- Genetic regulation of C4 expression involves post-transcriptional processing and mRNA levels, varying between species.
- Monocyte-macrophage differentiation significantly alters the expression of MHC class III products.
- Macrophages possess distinct regulatory mechanisms for complement component gene expression, influenced by cell type and external factors.
- These findings provide a basis for understanding inflammation, mononuclear phagocyte maturation, and complement protein deficiencies.