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Hypomorphic C4B* 15 variant of the fourth component of complement
M J Christenson1, T LaRosa, M Jung
1Department of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
FEBS Letters
|January 29, 1990
Summary
A rare hypomorphic C4 allotype, C4B*15, was identified. This variant shows weak staining and hemolytic activity but is detectable with specific monoclonal antibodies, potentially missed by standard methods.
Area of Science:
- Immunogenetics
- Complement System Biology
Background:
- The complement system plays a crucial role in innate immunity.
- Complement component 4 (C4) is a key protein in the classical and lectin pathways.
- Rare C4 allotypes can impact immune function and disease susceptibility.
Purpose of the Study:
- To characterize a rare hypomorphic C4 allotype, C4B*15.
- To investigate its detection using different immunological and genetic methods.
- To understand its implications for standard C4 phenotyping.
Main Methods:
- Agarose immunoelectrophoresis with polyclonal and monoclonal antibodies.
- Hemolytic activity assays.
- TaqI restriction fragment length polymorphism (RFLP) analysis.
- Haplotype analysis.
Main Results:
- C4B*15 exhibited faint staining with polyclonal anti-C4 and weak hemolytic activity.
- It showed strong reactivity with a monoclonal antibody to the Rodgers 1 epitope.
- RFLP analysis indicated segregation with specific C4 gene fragments (7 kb and 5.4 kb) and a particular HLA haplotype.
- The 5.4-kb fragment appeared more intense, suggesting duplication.
Conclusions:
- C4B*15 is a hypomorphic C4 allotype with diminished expression of common C4 epitopes.
- This allotype may be overlooked by conventional C4 phenotyping techniques.
- Its genetic basis involves specific C4 gene fragments and linkage to a known HLA haplotype.