Genetic variability at the human tumor necrosis factor loci

Area of Science:

• Immunogenetics
• Molecular Biology
• Human Genetics

Background:

• Human tumor necrosis factor (TNF-alpha) and lymphotoxin (TNF-beta) gene structural variations may influence HLA gene complex functional polymorphism.
• Understanding TNF-beta gene variability is crucial for comprehending immune system regulation and disease susceptibility.

Purpose of the Study:

• To characterize an allelic restriction fragment length polymorphism (RFLP) in the human TNF-beta gene using the NcoI restriction enzyme.
• To investigate the nature of restriction fragment variability observed with AccI digestion and its relationship with DNA methylation.
• To explore the potential role of DNA methylation in regulating TNF-beta gene expression.

Main Methods:

• Genomic DNA digestion with restriction endonucleases NcoI and AccI.
• Southern blotting using TNF-alpha gene probes to detect hybridizing fragments.
• Analysis of DNA methylation patterns in peripheral blood leukocytes (neutrophils and T lymphocytes).

Main Results:

• An allelic RFLP of the TNF-beta gene was identified using NcoI, with a 10.5-kb fragment present in 64-72% of Caucasian haplotypes.
• The polymorphic NcoI site is located within the first intron of the TNF-beta gene.
• Variability in restriction fragments with AccI was attributed to differential DNA methylation, with higher methylation in TNF-beta nonproducing neutrophils and lower methylation in TNF-beta producing T lymphocytes.

Conclusions:

• A specific allelic polymorphism within the TNF-beta gene has been characterized.
• DNA methylation patterns exhibit cell-type-specific variation and are inversely correlated with TNF-beta gene expression.
• These findings strongly suggest that epigenetic modifications, specifically DNA methylation, play a significant role in the regulation of TNF-beta gene expression.