A common polymorphism of tumor necrosis factor receptor-associated factor 6 (TRAF6) is associated with an increased risk for spontaneous bacterial peritonitis

Background: Spontaneous bacterial infection (SBP) is a frequent complication of decompensated cirrhosis contributing to high mortality rates exceeding 60% per year. Monocytes and peritoneal macrophages are potential cellular immune regulators in SBP exhibiting pattern-recognition-receptors (PRR) to detect bacterial infections. In this context, tumor necrosis factor receptor-associated factor 6 (TRAF6) is a critical mediator in PRR signaling.

Aims: We hypothesized that genetic polymorphisms of TRAF6 are associated with an increased risk of SBP by modulating monocytic immune responses in patients with decompensated cirrhosis.

Methods: TRAF6 haplotype-tagging single nucleotide polymorphisms (SNPs) rs331457 (G/A) and rs5030419 (C/G) were determined by Fluorescence Resonance Energy Transfer/Melting Curve analysis in 404 prospectively characterized hospitalized patients with decompensated cirrhosis who underwent diagnostic paracentesis at the Jena University Hospital. Episodes of SBP were identified from electronic records. We investigated the expression of TRAF6 mRNA by real-time reverse transcription polymerase chain reaction (qRT-PCR) in immunomagnetically isolated monocytes and peritoneal macrophages. IL-6 secretion of these cells was quantified by Enzyme Linked Immunosorbent Assay (ELISA) 24 hours after stimulation with 10 ng/ml lipopolysaccharide (LPS).

Results: The minor allele frequency for rs331457 was 16.5% and 14.4% for rs5030419. 193 (48%) patients presented the TRAF6 wild-type (GGCC), 113 (28%) were carriers of the rs5030419 mutation (AGCG; GGCG; GGGG) and 98 (24%) were carriers of a haplotype indicated by the rs5030419 wild-type and the rs331457 mutation (AGCC; AACC). 117 (29%) patients had at least one episode of SBP. Patients carrying the AGCC/AACC genotype had an increased risk of SBP (OR 1.93; 95% CI 1.20 – 3.12; p = 0.007) compared to patients not carrying this variant, which remained significant after adjustment for sex, age and MELD score. However, TRAF6 mRNA expression in monocytes and peritoneal macrophages and secretion of IL-6 after TLR4 stimulation in vitro did not differ significantly between the investigated haplotypes.

Conclusion: A common variant in TLR signaling is associated with an increased risk of SBP in patients with decompensated cirrhosis, which may be employed for genotype-based primary prophylaxis. The biological mechanism underlying the clinical association is subject of our current studies.

Corresponding author: Bruns, Tony

E-Mail: [e-mail]