Genetic Control of the Variable Innate Immune Response to Asymptomatic Bacteriuria

The severity of urinary tract infection (UTI) reflects the quality and magnitude of the host response. While strong local and systemic innate immune activation occurs in patients with acute pyelonephritis, the response to asymptomatic bacteriuria (ABU) is low. The immune response repertoire in ABU has not been characterized, due to the inherent problem to distinguish bacterial differences from host-determined variation. In this study, we investigated the host response to ABU and genetic variants affecting innate immune signaling and UTI susceptibility. Patients were subjected to therapeutic urinary tract inoculation with E. coli 83972 to ensure that they were exposed to the same E. coli strain. The innate immune response repertoire was characterized in urine samples, collected from each patient before and after inoculation with bacteria or PBS, if during the placebo arm of the study. Long-term E. coli 83972 ABU was established in 23 participants, who were followed for up to twelve months and the innate immune response was quantified in 233 urine samples. Neutrophil numbers increased in all but two patients and in an extended urine cytokine/chemokine analysis (31 proteins), the chemoattractants IL-8 and GRO-α, RANTES, Eotaxin-1 and MCP-1, the T cell chemoattractant and antibacterial peptide IP-10, inflammatory regulators IL-1-α and sIL-1RA and the T lymphocyte/dendritic cell product sIL-2Rα were detected and variably increased, compared to sterile samples. IL-6, which is associated with symptomatic UTI, remained low and numerous specific immune mediators were not detected. The patients were also genotyped for UTI-associated IRF3 and TLR4 promoter polymorphisms. Patients with ABU associated TLR4 polymorphisms had low neutrophil numbers, IL-6, IP-10, MCP-1 and sIL-2Rα concentrations. Patients with the ABU-associated IRF3 genotype had lower neutrophils, IL-6 and MCP-1 responses than the remaining group. The results suggest that the host-specific, low immune response to ABU mainly includes innate immune mediators and that host genetics directly influence the magnitude of this response

Consistency of the individual host response to <i>E. coli</i> 83972 inoculation.

<p>A. The host response in urine samples from the first (blue) and second inoculations (grey) were compared (Geometric means + SEs) in six patients that had received repeated inoculations. B. Kinetics of the host response during the first and second ABU episode in one high and one low responder.</p

Host response to <i>E. coli</i> 83972 bacteriuria.

<p><i>E. coli</i> 83972 ABU triggered an increase in PMN numbers and IL-8 concentrations (p<0.0001) but IL-6 levels were unchanged (n.s., Mann-Whitney test). Group-wise comparison of monthly urine samples collected during <i>E. coli</i> 83927 ABU or after PBS inoculations. Coded patient IDs are noted on the x-axis. A. Means + SEs of neutrophil numbers, IL-8 and IL-6 concentrations during <i>E. coli</i> 83972 bacteriuria (pink) or sterile conditions (blue). B. Intra-individual comparison of samples obtained during <i>E. coli</i> 83972 bacteriuria (pink) and sterile intervals (blue). C. Box-plot of intra-individual host response variation during <i>E. coli</i> 83972 ABU.</p

Patients and samples.

<p>Samples from patients participating in a clinical trial of induced <i>E. coli</i> 83972 ABU were analyzed. All collected urine samples were subjected to PMN, IL-6 and IL-8 quantification, and blood samples from eleven patients were collected for genotyping of promoter polymorphisms in TLR4 and IRF3. Blood and urine samples from these eleven patients were also selected for an extended urine protein analysis.</p

Promoter polymorphisms and the host response to ABU.

<p>A. Three of five <i>TLR4</i> genotypes associated with primary ABU were detected (blue hexagons) in five of the eleven patients. These patients had significantly lower neutrophil numbers (p<0.002) and IL-6 (p<0.0001), MCP-1 (p<0.01), IP-10 (p<0.0001), and sIL-2Rα (p<0.0001) concentrations than the patients with non-ABU associated <i>TLR4</i> genotypes XIX, IV, XX and IX (red squares). Each column represents one patient and each hexagon or square one monthly urine sample. B. The heterozygous <i>IRF3</i> promoter genotype associated with ABU (A/G-C/T, blue hexagon) was detected in four of the eleven patients, who had significantly lower neutrophil numbers (p = 0.01) and IL-6 (p<0.001) and MCP-1 (p = 0.0001) concentrations than patients with the homozygous, pyelonephritis-associated genotype (A/A-C/C, red square). Each column represents one patient and each hexagon or square one monthly urine sample.</p

Patient Characteristics.

<p>The table displays data from trials performed between 1993 and June, 2005. All patients had incomplete bladder emptying (residual urine ≥100 ml) and UTI susceptibility with a history ≥3 UTI/ year with urinary cultures showing uropathogenic growth, two years prior to the study.</p><p>1) M =  Male, F =  Female.</p><p>2) Clean Intermittent Catheterization. All patients had been instructed to use CIC regularly. Of the 8 patients who did not use CIC during the study 2 patients refused because of practical reasons and the remaining 6 patients had residual urine <300 ml, and had not experienced any improvement from previously performed regular CIC.</p