The rs12971860 C/T SNP in the interferon lambda3 (IL28B) gene influences the expression of thymidine phosphoryase and cytidine deaminase, two enzymatic markers of inflammation — ASN Events
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  3. The rs12971860 C/T SNP in the interferon lambda3 (IL28B) gene influences the expression of thymidine phosphoryase and cytidine deaminase, two enzymatic markers of inflammation

The rs12971860 C/T SNP in the interferon lambda3 (IL28B) gene influences the expression of thymidine phosphoryase and cytidine deaminase, two enzymatic markers of inflammation (#224)

Sara Bonanzinga 1 2 3 , Tim Shaw 2 4
  1. Molecular Microbiology, Victorian Infectious Diseases Reference Laboratory, Melbourne, VIC, Australia
  2. Peter Doherty Institute, Melbourne, VIC, Australia
  3. Department of Microbiology, Monash University, Clayton, VIC, Australia
  4. Molecular Pharmacology, Victorian Infectious Diseases Reference Laboratory, Melbourne, VIC, Australia

Background
Some chronic viral infections are responsive to treatment with interferon alpha (IFN-a), but outcomes are variable and unpredictable. In the case of chronic hepatitis C virus (HCV) infection, single nucleotide polymorphisms (SNPs) affecting the gene for interferon IFN-L3, (alias interleukin-28B (IL28B), affect response to IFN-a-based treatments. The most studied SNP is C/T at rs12971860 in the IFN-L3 gene’s CpG rich promoter region, with the ranked probability of favourable response (viral clearance) being CC>CT>TT. The biological mechanisms responsible for this phenomenon are not known. One hypothesis to explain the observed ranking proposes that the T allele lowers the threshold for immune activation, consequently inducing a refractory state by raising the threshold and reducing the dynamic range available for response to additional immunogenic stimuli from exogenous cytokines. Thymidine phosphorylase (TP) and cytidine deaminase (CDA) are evolutionarily conserved enzymes of pyrimidine metabolism that are inducible directly and indirectly (respectively) by pro-inflammatory cytokines. Increases in TP and CDA activity are therefore indicative of immune activation.
Hypothesis and Aim
If the IFN-L3 rs12971860 T allele is associated with increased immune activation, it may increase the activities of TP and CDA, which are easily measurable in peripheral blood.
Methods
A simple HPLC-based assay for whole blood TP and CDA activity was devised and used to measure enzyme activities in >200 blood samples obtained from individuals whose IFNL3 genotype was determined by a PCR-based method.
Results and Conclusions
Remarkably, concentrations of thymidine and cytidine close to a million-fold greater than their normal (submicromolar) plasma concentrations were required to saturate blood TP and CDA. A very large (~10-fold) range of both activities was found. Correlation with IFNL3 genotyping results revealed a ranked difference in enzyme activities in the order TT>CT>CC, supporting the hypothesis that the rs1291860 T allele is associated with increased pro-inflammatory activity.