Gene-gene interaction and functional impact of polymorphisms on innate immune genes in controlling Plasmodium falciparum blood infection level

PLoS One. 2012;7(10):e46441. doi: 10.1371/journal.pone.0046441. Epub 2012 Oct 12.

Abstract

Genetic variations in toll-like receptors and cytokine genes of the innate immune pathways have been implicated in controlling parasite growth and the pathogenesis of Plasmodium falciparum mediated malaria. We previously published genetic association of TLR4 non-synonymous and TNF-α promoter polymorphisms with P.falciparum blood infection level and here we extend the study considerably by (i) investigating genetic dependence of parasite-load on interleukin-12B polymorphisms, (ii) reconstructing gene-gene interactions among candidate TLRs and cytokine loci, (iii) exploring genetic and functional impact of epistatic models and (iv) providing mechanistic insights into functionality of disease-associated regulatory polymorphisms. Our data revealed that carriage of AA (P = 0.0001) and AC (P = 0.01) genotypes of IL12B 3'UTR polymorphism was associated with a significant increase of mean log-parasitemia relative to rare homozygous genotype CC. Presence of IL12B+1188 polymorphism in five of six multifactor models reinforced its strong genetic impact on malaria phenotype. Elevation of genetic risk in two-component models compared to the corresponding single locus and reduction of IL12B (2.2 fold) and lymphotoxin-α (1.7 fold) expressions in patients'peripheral-blood-mononuclear-cells under TLR4Thr399Ile risk genotype background substantiated the role of Multifactor Dimensionality Reduction derived models. Marked reduction of promoter activity of TNF-α risk haplotype (C-C-G-G) compared to wild-type haplotype (T-C-G-G) with (84%) and without (78%) LPS stimulation and the loss of binding of transcription factors detected in-silico supported a causal role of TNF-1031. Significantly lower expression of IL12B+1188 AA (5 fold) and AC (9 fold) genotypes compared to CC and under-representation (P = 0.0048) of allele A in transcripts of patients' PBMCs suggested an Allele-Expression-Imbalance. Allele (A+1188C) dependent differential stability (2 fold) of IL12B-transcripts upon actinomycin-D treatment and observed structural modulation (P = 0.013) of RNA-ensemble were the plausible explanations for AEI. In conclusion, our data provides functional support to the hypothesis that de-regulated receptor-cytokine axis of innate immune pathway influences blood infection level in P. falciparum malaria.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3' Untranslated Regions
  • Alleles
  • Cell Line
  • Epistasis, Genetic*
  • Haplotypes
  • Humans
  • Immunity, Innate / genetics*
  • Interleukin-12 Subunit p40 / genetics
  • Malaria, Falciparum / blood
  • Malaria, Falciparum / genetics*
  • Malaria, Falciparum / immunology
  • Polymorphism, Genetic*
  • Real-Time Polymerase Chain Reaction
  • Toll-Like Receptor 4 / genetics

Substances

  • 3' Untranslated Regions
  • Interleukin-12 Subunit p40
  • Toll-Like Receptor 4

Grants and funding

This work was supported by the Department of Science and Technology, New Delhi (SERC Fast Track Scheme - SR/FTP/L-56/2005 dated 25.04.2006) and University Grants Commission (Major Research Project - F. No 33-232/2007(SR) dated 13.03.2008). MB is supported by a pre-doctoral fellowship from University Grants Commission-Special Assistance Programme-The Research Fellowship in Sciences for meritorious students (UGC-SAP-RFSMS) scheme, and Council of Scientific and Industrial Research (CSIR)-Senior Research Fellowship (Sanction no. 09/(0829)/2010-EMR-I dated 29.3.11). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.