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Functional Complementation Analysis FCA: A Laboratory Exercise Designed and Implemented to Supplement the Teaching of Biochemical Pathways
Published on: June 24, 2016
Classical pathway deficiencies - A short analytical review
1Department of Laboratory Medicine, Section of Microbiology, Immunology and Glycobiology, Lund University, University Hospital of Skåne, 22185 Lund, Sweden.
Insights
Deficiencies in complement pathways increase bacterial infection risk and lupus erythematosus development. C1q, C4, and C2 deficiencies impact classical and lectin pathways differently, with varying genetic causes and treatment implications.
Area of Science:
- Immunology
- Genetics
Background:
- Deficiencies in the classical complement pathway present diverse clinical features.
- These deficiencies are linked to increased bacterial infections and systemic lupus erythematosus (SLE).
Purpose of the Study:
- To explore the distinct characteristics and implications of deficiencies in complement components C1q, C4, and C2.
- To understand the genetic basis, pathway involvement, and therapeutic possibilities for these deficiencies.
Main Methods:
- Comparative analysis of clinical and genetic features of C1q, C4, and C2 deficiencies.
- Review of complement pathway activation mechanisms, including classical and lectin pathways.
- Examination of genetic loci and cellular origins of complement components.
Main Results:
- C1q, C4, and C2 deficiencies increase susceptibility to bacterial infections.
- C1q deficiency strongly associates with SLE; C4 and C2 deficiencies show lesser association.
- C1q deficiency impacts only the classical pathway, while C4 and C2 deficiencies affect both classical and lectin pathways.
- Genetic heterogeneity exists for C1q and C4 deficiencies, whereas C2 deficiency often results from a specific deletion.
- Hematopoietic stem cell transplantation has been explored for C1q deficiency.
Conclusions:
- Complement component deficiencies have varied clinical and genetic profiles.
- Understanding these differences is crucial for diagnosis, risk assessment, and potential therapeutic strategies like stem cell transplantation.
Abstract:
Deficiencies in the classical pathway of complement activation have some common features but show also great differences. Deficiencies of each of the components (C1q, C1s, C1r, C4 and C2) imply increased susceptibility to bacterial infections. They are also associated with increased risk to develop systemic lupus erythematosus where deficiency of C1q is strongly associated to the disease while C4 less and C2 much less. Deficiency of C1q affects only activation of the classical pathway while deficiency of C4 and C2 also prevent activation of the lectin pathway. Bypass mechanisms may result in complement activation also in absence of C2 but not in absence of C1q or C4. The genes for C2 and C4 isotypes are closely located within the MHC class III region on chromosome 6p and the genes for the 3 C1q chains are on chromosome 1p. Deficiencies of C1q and of C4 show genetic heterogeneity while deficiency of C2 in the great majority of cases is caused by a specific deletion. The production of C4 and C2 is mainly by the hepatocytes in the liver while C1q is produced by monocytic bone marrow derived cells. This has implications for the possibility to treat the deficiency and hematopoietic stem cell transplantation has been tried in C1q deficiency.
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