Spencer Hedges

Interleukin-8 and the neutrophil response to mucosal gram-negative infection.

Urinary tract infections activate a mucosal inflammatory response, which includes cytokine secretion and neutrophil influx. The mechanisms involved in the neutrophil influx have not been identified. Interleukin-8, a potent chemoattractant for neutrophils, is produced by urinary tract epithelial cell lines in vitro. This study analyzed the human IL-8 response to deliberate Escherichia coli infection of the urinary tract. Urine and serum samples were obtained before and after intravesical instillation of E. coli. Neutrophil numbers were determined on uncentrifuged urine, and IL-8 levels were measured by ELISA. A urinary IL-8 response was found in all patients after bacterial instillation, but no serum IL-8 was detected. There was a strong correlation between urinary IL-8 levels and urinary neutrophil numbers. The same E. coli strains used to colonize the patients stimulated IL-8 production in urinary tract epithelial cells. The level of IL-8 secreted by epithelial cell lines was influenced by the fimbrial properties of the E. coli. These results demonstrated that E. coli elicit a mucosal IL-8 response in humans, and suggested that IL-8 is involved in the onset of pyuria. Epithelial cells may be an important source of IL-8 during urinary tract infection.

Epithelial cytokine responses and mucosal cytokine networks

Localized at the border between the external environment and the internal tissue, epithelial cells are exposed to stimulants from two directions. Microorganisms in the lumen can activate the transcription of cytokine mRNA and cytokine secretion, and cytokines in the mucosal environment can modify endogenous and microbially induced epithelial cytokine responses. Epithelial cells thus actively participate in mucosal immunity and inflammation.

Bacterial Adherence and Mucosal Cytokine Production

1. Uropathogenic E. coli adhere to mucosal sites. 2. In the urinary tract, adherence is followed by inflammation, including a mucosal cytokine response. 3. Bacteria activate epithelial cells to secrete IL-6 and IL-8. IL-6 may cause the fever and acute phase response that accompany systemic urinary tract infections. IL-8 may function as a neutrophil chemoattractant. 4. E. coli up-regulate adhesion molecule expression on epithelial cell lines and neutrophil migration through epithelial cell monolayers. This process is inhibited by antibodies to CD18 and ICAM-1. 5. Cytokines released by nonepithelial cells (T cells and monocytes) modify the epithelial cell cytokine response to bacteria.

Cytokines Induce an Epithelial Cell Cytokine Response

Intravesical inoculation of gram negative bacteria or isolated bacterial products into mice induces an IL-6 response which can be measured within miutes of the infection.1,2 In such infections, IL-6 is initially detected in the urine and subsequently in the serum. Similar IL-6 responses were found in human patients deliberately colonized in the urinary tract with E. coli Hu7343. IL-6 was secreted intermittantly into the urine in response to continuous bacterial infection in humans, but was not detected in serum. The rapid secretion of IL-6 into urine after bacterial stimulation, and the separation of local from systemic secretion in both humans and mice suggested that IL-6 was produced at the site of infection. Since epithelial cells dominate the naive urinary tract mucosal surface, we suggested that epithelial cells are one source of mucosally produced cytokines.4 Epithelial cell lines of urinary tract origin secrete IL-6 and IL-8, and can produce other cytokines after bacterial stimulation.5–7 In this paper we demonstrate that epithelial cell lines of urinary tract origin can respond to exogenous cytokines. This response includes the up-regulation of a variety of cytokine mRNA species as well as secretion of IL-6 and IL-8. Furthermore, this response is specific to the stimulus used, with different cytokine mRNA species induced by different cytokine stimuli.

Bacterial Adherence and Epithelial Cell Cytokine Production

Epithelial cell lines produce the cytokines IL-1 alpha, IL-6 and IL-8 when stimulated with Escherichia coli. The cytokine response is enhanced by P fimbriae. The epithelial cell lines also respond to stimulation with other cytokines. These in vitro findings were confirmed in vivo in patients with E. coli infection who secreted IL-6 and IL-8 into the urine. The observations suggest that epithelial cells play a more active role in the mucosal immune response than previously recognized.

Cyclosporin A does not Inhibit IL‐lα‐Induced Epithelial Cell IL‐6 Secretion

Trauma and infection activated a murine mucosal IL‐6 response in different ways: the IL‐6 response to bacteria was sensitive to Cyclosporin A (CsA); the IL‐6 response to trauma was not. The aim of the present study was to identify possible activators of the CsA‐insensitive IL‐6 secretion at the epithelial cell level. Two human epithelial cell lines from the kidney (A498) and bladder (J82) were exposed to Escherichia coli Hu734, interleukin‐lα (IL‐lα) and tumour necrosis factor a (TNF‐α). The E. coli strain had been used for the in vivo experiments which led to this study, and IL‐lα and TNF‐α were likely to be released during infections and trauma. The secretion of IL‐6 into the supernatants was compared between cells stimulated in the presence or absence of CsA. E. coli Hu734, IL‐lα and TNF‐α stimulated an IL‐6 response in the two epithelial cell lines. The IL‐lα‐induced IL‐6 response was rapid, and the secreted IL‐6 levels were significantly higher than those induced by E. coli Hu734 or TNF‐α. The IL‐6 response to IL‐ lα was insensitive to CsA. By contrast, the IL‐6 response to E. coli Hu734 and TNF‐α was inhibited by CsA. These results demonstrated that the inhibitory effect of CsA depends on the stimulus triggering the IL‐6 response. IL‐lα may play a role in the induction of trauma‐associated CsA‐insensitive IL‐6 secretion.

The mucosal cytokine response to urinary tract infections

This review focussed on the cytokine responses to urinary tract infections. Colonization of the human urinary tract with E. coli activates the intermittant secretion of IL-6 and IL-8 into urine. In contrast, local bacterial challenge did not give rise to detectable serum IL-6 or IL-8 levels. IL-6 is detected in the urine at the time of diagnosis in most patients with natural urinary tract infections; however, IL-6 was only detected in the serum of symptomatic patients. These observations suggested that the cytokine response during UTI can have local and systemic components. Epithelial cells have been examined as a likely source of the local cytokines produced in response to UTI. The profile of cytokines produced by uroepithelial cells in response to E. coli is similar to that secreted during UTI (IL-6 and IL-8, but no IL-1 or TNF). Adhering bacteria and isolated P fimbriae stimulate higher levels of IL-6 production in cells that express the globoseries of glycolipids such as kidney epithelial cells. Uroepithelial cells also respond to stimulation by cytokines; IL-1alpha and TNFalpha induce the secretion of IL-6 and IL-8 and the upregulation of mRNAs for IL-1alpha, IL-1beta, IL-6 and IL-8. This cytokine profile is similar to that detected after bacterial stimulation; however, the magnitude and kinetics of the epithelial cell cytokine responses differed between the stimulants. Interleukin-4 induced epithelial cell IL-6 and IL-8 production; gamma-interferon only induced IL-6 production. This suggests that epithelial cells produce primary and secondary cytokine responses, and can function in mucosal cytokine networks with a variety of cells. Cytokines are mediators of immune functions and inflammation and it is likely that the local cytokine production influences both the induction of symptoms as well as the eventual outcome of the infection. Examination of local cytokine levels during UTI may prove to be a useful diagnostic tool; however, this possibility requires further evaluation.

Bacterial Activation of Mucosal Cytokine Production

Publisher Summary Epithelial cells are the target of attaching microorganisms in the lumen and of mediators from cells in the mucosal environment, and as such are essential for the outcome of the cross-talk between bacteria and their hosts. Pathogens express virulence factors that enable them to overcome mucosal defenses and tilt the balance in the cross-talk in their favor. The pathogens use specific adherence factors to localize to the site of infection; they secrete toxins that trigger changes in the mucosal barrier and cross the mucosa with the help of invasion factors. Inflammation is a key to the very early steps in the pathogenesis of mucosal infections, and the virulence factors can act by directly triggering inflammatory processes in the mucosa. The symptoms and signs of acute UTI are attributable to the inflammatory response that the bacteria induce when they enter the urinary tract. There is elevated temperature, an acute-phase response in serum (C-reactive protein, CRP; erythrocyte sedimentation rate, ESR), a local inflammatory response in the urine, and a mucosal immune response dominated by s-IgA antibodies. These host response parameters suggested that the mucosa produced cytokines in response to infection, and that these cytokines were involved as mediators of disease. This chapter reviews and summarizes some aspects of the studies on mucosal cytokine responses to bacterial infection.

[18] Strategies for studying bacterial adhesion in Vivo

Publisher Summary The ultimate goal of studies on microbial adhesion is to understand what molecular interactions between the host and microbe occur in vivo and the impact of these interactions on disease processes. With this goal in mind, the problem can be approached at four levels. At the biochemical level, the host receptors at the relevant colonization site are identified; at the cell biology level, consequences of bacterial binding to host epithelial cells are studied in cell culture; at the physiological level, the consequences of bacterial binding are studied in experimental animals or humans; and at the population level, the consequences of receptor binding for colonization are studied by epidemiological methods. This chapter provides an example of studies at each level and discusses the implications for what might occur in vivo .

IL-8 Production During Urinary Tract Infection

Infection of the urinary tract leads to a local inflammatory response mediated at the mucosa. In patients with natural urinary tract infection (UTI) and in patients deliberately colonized with Escherichia coli in the urinary tract there is a rapid recruitment of neutrophils into the urine. We have shown previously that urinary tract epithelial cell lines produce a range of cytokines including IL-8 following stimulation with E. coli (1). In this study we analyzed the urine of patients following deliberate colonization of the urinary tract with three E. coli strains, for the influx of PMNs and presence of IL-8. IL-8 was found in the urine of all patients following UTI. There was a strong correlation of 0.7 between levels of IL-8 and numbers of PMNs in the urine. IL-8 was not found in the serum of patients during the period of colonization. The J82 bladder and A498 kidney epithelial cell lines and neutrophils collected from fresh human blood produced large amounts of IL-8 in response to the same E. coli strains. These results suggest that IL-8 may play an important role in neutrophil influx during UTI and that local epithelial cells as well as activated neutrophils may be involved in the production of this protein at the site of infection.