Common TNF-α, IL-1β, PAI-1, uPA, CD14 and TLR4 polymorphisms are not associated with disease severity or outcome from Gram negative sepsis
© Jessen et al; licensee BioMed Central Ltd. 2007
Received: 27 March 2007
Accepted: 18 September 2007
Published: 18 September 2007
Several studies have investigated single nucleotide polymorphisms (SNPs) in candidate genes associated with sepsis and septic shock with conflicting results. Only few studies have combined the analysis of multiple SNPs in the same population.
Clinical data and DNA from consecutive adult patients with culture proven Gram negative bacteremia admitted to a Danish hospital between 2000 and 2002. Analysis for commonly described SNPs of tumor necrosis-α, (TNF-α), interleukin-1β (IL-1β), plasminogen activator-1 (PAI-1), urokinase plasminogen activator (uPA), CD14 and toll-like receptor 4 (TLR4) was done.
Of 319 adults, 74% had sepsis, 19% had severe sepsis and 7% were in septic shock. No correlation between severity or outcome of sepsis was observed for the analyzed SNPs of TNF-α, IL-1β, PAI-1, uPA, CD14 or TLR-4. In multivariate Cox proportional hazard regression analysis, increasing age, polymicrobial infection and haemoglobin levels were associated with in-hospital mortality.
We did not find any association between TNF-α, IL-1β, PAI-1, uPA, CD14 and TLR4 polymorphisms and outcome of Gram negative sepsis. Other host factors appear to be more important than the genotypes studied here in determining the severity and outcome of Gram negative sepsis.
The syndromes of severe sepsis and septic shock are frequent and associated with high mortality . Their pathophysiology is complex and results from the interaction between infecting pathogens and inflammatory and coagulation pathways [2, 3]. Among the numerous microorganisms that cause sepsis, Gram negative bacteria, predominantly Enterobacteriacea, account for one third of all cases .
Innate host defence is integrally linked to inflammation and coagulation [3, 4]. Gram negative bacterial lipopolysaccharide (LPS, endotoxin) is sensed by LPS-binding protein (LBP) by the human host. The LPS-LBP complex binds to the cellular surface receptor CD14 and interacts with the toll-like receptor 4 (TLR4) to induce nuclear factor κ-B signalling and transcription of cytokines, chemokines, adhesion and coagulation factors . Among these, tumor necrosis factor α (TNF-α) and interleukin-1β (Il-1β) are decisive proinflammatory mediators. Blood clotting can be initiated by TNF-α and endotoxin and is counteracted by fibrinolysis. Fibrinolysis is initiated by two types of plasminogen activators, the urokinase-type (uPA) and the tissue-type (tPA) and may be inhibited by the plasminogen activator inhibitors, PAI-1 and PAI-2.
Genetic epidemiologic studies suggest a strong genetic influence on the outcome from sepsis . Since dysregulation of innate immunity is believed to be central for the manifestations of sepsis, studies of genetic susceptibility to and outcome of septic shock have focused on genes involved in inflammatory and coagulation pathways. Synonymous and non-synonymous single nucleotide polymorphisms (SNPs) may alter the expression or function of transcribed gene products. We included SNPs that had been shown in other studies to have either clinical or experimental relevance with sepsis outcome through the inflammatory and coagulation pathways. Data indicate that SNPs of TNF-α [7, 8], Il-1β [9, 10], PAI-1 [11, 12], and CD14  may be associated with a poor prognosis from sepsis. Polymorphisms in TLR4  and CD14  are further associated with an increased susceptibility to infection. The uPA polymorphism has not previously been studied in sepsis.
Here we present a genetic association study of Gram negative sepsis with focus on six SNPs previously linked to sepsis pathogenesis and survival.
All patients older than 17 years admitted to Hvidovre Hospital between June 2000 and May 2002 with a positive blood culture yielding a Gram negative organism were included in the study. Demographic, clinical and laboratory data were extracted on a standardized form. Sepsis, severe sepsis and septic shock were classified according to international guidelines . The study was approved by the Ethics Committee for Copenhagen and Frederiksberg Counties (01-085/2000). None of the patients were lost to follow-up.
Deoxyribonucleic Acid Extraction
1.5 mL of positive blood culture media was lysed with 1.5 mL of 5 M guanidinium-HCl-100 mM Tris (pH 8.0) . DNA was then extracted with QIAamp mini Spin columns (Qiagen, Hilden, Germany) as described by the manufacturer and stored at -20°C.
Primers, probes and restriction enzymes
G- 308 A
5'- TCTCGGTTTCTTCTCCATCG -3'
5G allele; 5 ' -GTCTGGACACGTGGGGG-3 ' 4G allele; 5 ' -GTCTGGACACGTGGGGA-3 '
5 ' -TGCAGCCAGCCACGTGATTGTCTAG-3 '
C 422 T
Hardy-Weinberg equilibrium (HWE)
HWE analysis was performed for each SNP by comparing the detected genotype distribution with the theoretical distribution estimated on the basis of the SNP allelic frequencies. P > 0.05 (χ2 statistics) was considered to indicate equilibrium.
Genotype distributions were compared using χ2 statistics. Relative risk (RR) with 95% confidence interval (CI) of in-hospital mortality associated with genotypes and other variables was estimated using Cox proportional hazards regression analysis by forced entry. Each covariate was entered separately and covariates that were associated with disease at the P < 0.1 level were included in the multivariate model. Survival curves were constructed by the method of Kaplan-Meier. The date of diagnosis (baseline) was defined as the date of blood culture. Analysis was performed with SPSS 11.5 (Statistical Package for Social Sciences, Chicago, IL.). Power And Precision 2.00 (Biostat, Englewood, NJ) was used to calculate statistical power to detect changes in survival.
From June 2000 through May 2002, 452 consecutive episodes of Gram negative bacteremia were diagnosed among 427 individuals at Hvidovre Hospital. Of these, 319 were a first episode and had DNA collected. There were no statistical significant differences between individuals included and excluded from the present study. The median age was 76 (interquartile range: 61–84), 172 (54%) of subjects were women, and 255 (80%) had at least one chronic underlying illness. In most patients the infectious focus was the urinary tract (83%) and the most common Gram negative bacteria were Escherichia coli (69%) and Klebsiella pneumoniae (11%). Nineteen other Gram negative bacteria accounted for the remaining 20%.
Association between genotype and disease severity
Severe sepsis (%)
Septic shock (%)
TLR4 (A 896G)
Genotypes and baseline characteristics
No associations were found between genotypes and demographics (age, sex, and comorbidity), temperature, mean arterial blood pressure, white blood cell count, C-reactive protein or causative organism at the time of blood culture.
Disease severity and genotype
The majority of patients met the criteria for sepsis at the time of blood culture (74%). 19% met the criteria for severe sepsis and 7% were in septic shock.
Neither TNF-α, Il-1β, PAI-1, uPA, TLR4, nor CD14 SNPs were associated with disease severity.
Mortality and genotype
In-hospital mortality according to genotype
In-hospital mortality (%)
TLR4 (A 896G)
Multivariate analysis of factors associated with outcome
Multivariate analysis of factors associated with in-hospital mortality
RR (95% CI)
RR (95% CI)
RR (95% CI)
Age, per year increment
Intensive care admission
Hemoglobin, per μmol/L increase
Leukocyte count, per 10 9 /mL increase
C-reactive protein, per milligram/L increase
Urea, per μmol/L increase
Alanine transferase, per unit/L increase
We did not find any association between disease severity and putative SNPs involved in inflammatory and coagulation pathways during the course of sepsis nor were any of the SNPs associated with outcome. The homozygous TNF-α AA and heterozygous TLR4 AG SNPs were associated with an increased but statistically non-significant risk of death.
Genetic association studies notoriously contradict one another . Conflicting results have been reported for TNF-α (G-308A), which was associated to disease severity and outcome in some [7, 8, 23] but not other studies [24–26]. Controversy also exists regarding the role of for PAI-1 [11, 12, 27], CD14 (C-159T) [13, 28], TLR4 (A896G) [20, 29], although IL-1β (C3953T) have consistently been reported to be without association to disease severity or outcome . Methological problems may explain many of the discrepancies. In particular, many studies have insufficient sample size to make firm statistical conclusions. The present study provided > 80% power to detect a 1.5-fold increase in relative risk of death for the heterozygous forms of TNF-α, Il-1β, PAI-1, uPA, and CD14, while a 2.5-fold was necessary to provide 80% power to detect differences associated with the lesser frequent allele frequencies of TLR4. Although, the level of association may be debated, we find 1.5–2.5-fold changes reasonable. The study was, however, underpowered to detect associations with the lesser frequent homozygous TNF-α, IL-1β, uPA and heterozygous TLR4 genotypes. Publication bias may also influence the true genetic association between disease severity and outcome because negative association studies are less likely to be published than studies that find an association. Our negative findings may be due to the fact that our population differs from the previous reported studies showing a positive correlation, e.g. studies of meningococcal disease alone (PAI-1, TLR4 and TNF-α) and of patients with severe sepsis in intensive care settings (TNF-α and TLR4).
Strengths of the present study include the fact that the cohort represents unselected and consecutive patients with Gram negative sepsis. Limitations relate to the sample size because larger samples would detect smaller associations than studied here. Meta-analysis of multiple cohorts could add power to discriminate between potential genetic associations and statistical uncertainties of polymorphisms of genes in the inflammatory and coagulative pathways. Use of novel technologies that permit genome-wide genetic analysis of SNPs and haplotypes will likely be useful in future genetic association studies.
Funding: Danish Medical Association Research Fund; Danish Hospital Foundation for Medical Research; Region of Copenhagen, the Faroe Islands and Greenland; Copenhagen Hospital Corporation Research Fund; and the A.P. Møller Foundation for the Advancement of Medical Science.
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