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Molecular genetics of the fourth component of human complement
Biochemical Society Symposium
|January 1, 1986
Summary
The human complement component 4 (C4) genes, C4A and C4B, are polymorphic within the HLA complex. Gene deletions, not protein variations, cause most C4 null alleles, impacting immune response.
Area of Science:
- Immunogenetics
- Molecular Biology
- Human Genetics
Background:
- The fourth component of human complement (C4) is crucial for immune responses.
- C4A and C4B are closely linked loci within the HLA class III region, differing slightly in amino acid sequence but significantly in hemolytic activity.
- Both C4 loci exhibit considerable polymorphism, potentially enabling interaction with diverse pathogens.
Purpose of the Study:
- To investigate the genetic basis of C4 null alleles.
- To determine if C4 null alleles are due to gene deletions or other structural variations.
- To analyze the deleted region in specific haplotypes.
Main Methods:
- Southern blot analysis of 24 haplotypes using C4 probes.
- Identification of null alleles associated with deleted C4 genes.
- Cosmid library preparation from a deleted haplotype DNA.
- Restriction mapping of the deleted region.
Main Results:
- Protein studies indicated polymorphic gene expression, including null alleles and duplications.
- Southern analysis revealed that only three out of 24 C4 null alleles studied were due to gene deletions.
- The majority of null alleles appeared structurally normal, suggesting other mechanisms.
- Restriction mapping characterized the deleted region in one specific haplotype.
Conclusions:
- C4 gene deletion is not the primary cause of most observed C4 null alleles.
- The genetic basis for C4 polymorphism and null alleles is complex and warrants further investigation.
- Understanding C4 gene structure and variation is vital for comprehending immune system function and disease susceptibility.