Direct activation of human peritoneal mesothelial cells by heat-killed microorganisms

Analysis of early mesothelial cell responses to Staphylococcus epidermidis isolated from patients with peritoneal dialysis-associated peritonitis

The major complication of peritoneal dialysis (PD) is the development of peritonitis, an infection within the abdominal cavity, primarily caused by bacteria. PD peritonitis is associated with significant morbidity, mortality and health care costs. Staphylococcus epidermidis is the most frequently isolated cause of PD-associated peritonitis. Mesothelial cells are integral to the host response to peritonitis, and subsequent clinical outcomes, yet the effects of infection on mesothelial cells are not well characterised. We systematically investigated the early mesothelial cell response to clinical and reference isolates of S. epidermidis using primary mesothelial cells and the mesothelial cell line Met-5A. Using an unbiased whole genome microarray, followed by a targeted panel of genes known to be involved in the human antibacterial response, we identified 38 differentially regulated genes (adj. p-value < 0.05) representing 35 canonical pathways after 1 hour exposure to S. epidermidis. The top 3 canonical pathways were TNFR2 signaling, IL-17A signaling, and TNFR1 signaling (adj. p-values of 0.0012, 0.0012 and 0.0019, respectively). Subsequent qPCR validation confirmed significant differences in gene expression in a number of genes not previously described in mesothelial cell responses to infection, with heterogeneity observed between clinical isolates of S. epidermidis, and between Met-5A and primary mesothelial cells. Heterogeneity between different S. epidermidis isolates suggests that specific virulence factors may play critical roles in influencing outcomes from peritonitis. This study provides new insights into early mesothelial cell responses to infection with S. epidermidis, and confirms the importance of validating findings in primary mesothelial cells.

Cutting edge: Divergent cell-specific functions of MyD88 for inflammatory responses and organ injury in septic peritonitis

Although global MyD88 deficiency attenuates lethal inflammation in sepsis, cell-specific functions of MyD88 remain largely unknown. Using mice with selective expression of MyD88 in myeloid cells (Myd88(MYEL)), we show that, during polymicrobial septic peritonitis, both myeloid and nonmyeloid cells contribute to systemic inflammation, whereas myeloid cell MyD88 was sufficient to fully establish the peritoneal cytokine response. Importantly, Myd88(MYEL) mice developed markedly aggravated liver injury that was linked to impaired upregulation of cellular inhibitor of apoptosis protein 2 and an excessive production of TNF-α. Upregulation of inducible cAMP early repressor (ICER), a known transcriptional repressor of the Tnfa gene, was impaired in Myd88(MYEL) mice. Moreover, Myd88(MYEL) mice showed enhanced transcription of the Tnfa gene and an excessive production of CCL3, which is also negatively regulated by ICER, but they had normal levels of CXCL1, which is expressed in an ICER-independent manner. Together, these findings suggest a novel protective role for nonmyeloid cell MyD88 in attenuating liver injury during septic peritonitis.

Early detection of anastomotic leakage after elective low anterior resection

BACKGROUND

Colorectal anastomotic leakage is a serious complication leading to major postoperative morbidity and mortality. In the present study, we investigated the early detection of anastomotic leakage before its clinical presentation.

METHOD

Fifty-six patients with rectal cancer were included prospectively in this study. All patients underwent elective low anterior resection. Peritoneal samples were collected from the abdominal drains at the first, third, and fifth days postoperatively for bacteriological study (quantitative cultures for both aerobes and anaerobes) and cytokines (IL-6, IL-10, TNF) measurement. Patients were divided into two groups: those without symptomatic or clinical evidence of anastomotic leakage (AL; group 1) and those with clinical evidence of AL (group 2). Study variables included hospital stay, wound infection, operative time, blood loss, height of anastomosis, intraperitoneal cytokines, and microbiological study of peritoneal fluid.

RESULT

Clinically evident AL occurred in eight patients (14.3%) and diagnosed postoperatively on median day 6. Intraperitoneal bacterial colonization and cytokine levels were significantly higher in patients with clinical evidence of AL. Wound infection was significantly higher in anastomotic leakage group. The hospital stay for the patients with anastomotic leakage was significantly longer than those without AL (14 ± 1.41 vs. 5.43 ± 0.89 days). A significant difference among two groups was observed regarding operative time, blood loss, blood transfusion, and height of the anastomosis.

CONCLUSION

The peritoneal cytokines levels and intraperitoneal bacterial colonization might be an additional diagnostic tool that can support the decision making of surgeons for early detection of anastomotic leak in colorectal surgery.

Preferential attachment of peritoneal tumor metastases to omental immune aggregates and possible role of a unique vascular microenvironment in metastatic survival and growth

Controlling metastases remains a critical problem in cancer biology. Within the peritoneal cavity, omental tissue is a common site for metastatic disease arising from intraperitoneal tumors; however, it is unknown why this tissue is so favorable for metastatic tumor growth. Using five different tumor cell lines in three different strains of mice, we found that the omentum was a major site of metastases growth for intraperitoneal tumors. Furthermore, initial attachment and subsequent growth were limited to specific sites within the omentum, consisting of organized aggregates of immune cells. These immune aggregates contained a complex network of capillaries exhibiting a high vascular density, which appear to contribute to the survival of metastatic cells. We found that the vasculature within these aggregates contained CD105+ vessels and vascular sprouts, both indicators of active angiogenesis. A subset of mesothelial cells situated atop the immune aggregates was found to be hypoxic, and a similar proportion was observed to secrete vascular endothelial growth factor-A. These data provide a physiological mechanism by which metastatic tumor cells preferentially grow at sites rich in proangiogenic vessels, apparently stimulated by angiogenic factors produced by mesothelial cells. These sites provide metastatic cells with a microenvironment highly conducive to survival and subsequent growth.

Peritoneal mesothelial cells produce inflammatory related cytokines

BACKGROUND

Peritonitis involves cascading interactions between cytokines that initiate robust signalling processes via the interferon-g and nuclear factor kappa B pathways. The present study evaluates the interplay between various putative inducers of peritonitis and a battery of inflammation-related cytokines.

METHODS

Cultures of peritoneal mesothelial cells were isolated from omenta harvested from male Wistar rats. These cultures were exposed to tumour necrosis factor (TNF)-alpha, lipopolysaccharide, zymosan, myeloperoxidase, peritoneal fluid from rats with zymosan-induced peritonitis, and peritoneal fluid from control animals. The production of TNF-alpha, interleukin (IL)-1beta, IL-6, and IL-10 was assessed after 4, 12 and 24 h.

RESULTS

Lipopolysaccharide and zymosan stimulated TNF-alpha, IL-1beta, and IL-10 production; and peritoneal fluids from both control animals and animals with zymosan-induced peritonitis stimulated the production of TNF-alpha, IL-1RII, and IL-6. Expression and secretion of TNF-alpha occurred in a constitutive manner and was regulation at the protein level. The decoy molecule IL-1 receptor type II (IL-1RII) was produced at the same time as IL-1beta and production of the anti-inflammatory cytokine IL-10 was evident within 4 h. IL-6 was constitutively expressed and regulated at the transcriptional level as indicated by a marked discontinuity between the amount of IL-6 produced and the extent IL-6 messenger ribonucleic acid (mRNA) expression.

CONCLUSIONS

Tumour necrosis factor-alpha might not be the sole primary mediator of peritonitis. The anti-inflammatory molecules IL-1RII and IL-10 are induced at the same time as the pro-inflammatory cytokines TNF-alpha, IL-1beta, and IL-6. This suggests that complex control systems are set in place by the factors that stimulate peritoneal mesothelial cells and might have the potential to cause peritonitis.

CD40 is expressed on human peritoneal mesothelial cells and upregulates the production of interleukin-15 and RANTES

Limited data are available concerning the interaction between lymphocytes and human peritoneal mesothelial cells (HPMC) during peritonitis. CD40 is a member of the tumor necrosis factor (TNF) family of receptors whose ligand (CD154) is mainly expressed on the membrane of activated CD4-positive lymphocytes. CD154-CD40 cross-linking is a central event in antigen presentation, B-cell activation by T cells, and regulation of cytokine secretion from various types of cells. The goal of this study was to demonstrate in vitro the presence of CD40 on HPMC and to test its functionality in inducing interleukin-15 (IL-15) and RANTES. We assayed the levels of CD40 by reverse transcription-PCR and flow cytometry and IL-15 and RANTES by enzyme-linked immunosorbent assay. Genetically modified L cells that express elevated levels of CD154 (CD40L cells) were used to stimulate CD40. HPMC express CD40 mRNA and protein. After stimulation with interferon-gamma (IFNgamma, 5U/ml) or TNFalpha (1 ng/ml), there was a small increase in CD40 mRNA and protein levels; when both cytokines were applied, the increase in CD40 levels was more than threefold. CD40 ligation induced IL-15 production by HPMC and was additive to IFNgamma stimulation. CD40 ligation was strongly synergistic with IFNgamma in induction of RANTES (20-fold as compared with unstimulated HPMC), whereas neither ligation nor IFNgamma alone could induce RANTES. Pretreatment of HPMC with TNFalpha and IFNgamma increased the response to CD40 ligation in magnitudes that correlated with the elevation of CD40 levels induced by the pretreatment. To conclude, the presence of a functional CD40 on HPMC whose ligation induced IL-15 and RANTES production was detected. It is possible that this receptor acts as a major mediator of T-cell-regulated immune and inflammatory response during peritonitis.

Heat-killed microorganisms induce PAI-1 expression in human peritoneal mesothelial cells: role of interleukin-1alpha

Human peritoneal mesothelial cells (HMCs) have a critical role in maintaining the intraperitoneal balance between fibrinolysis and coagulation by expressing the fibrinolytic enzyme, tissue-type plasminogen activator (tPA), as well as a specific plasminogen activator inhibitor (type 1; PAI-1). During bacterial peritonitis, the balance between intraperitoneal generation and degradation of fibrin is disturbed. As a consequence, severe peritoneal damage occurs, which is one of the leading causes of patient dropout from continuous ambulatory peritoneal dialysis (CAPD) therapy. Cultured HMCs isolated from omental biopsy specimens were used to study the effect of heat-killed strains (2 x 10(8)/mL) of Staphylococcus aureus, Staphylococcus epidermidis, and Escherichia coli on the synthesis of tPA and PAI-1. Conditioned media were obtained by incubating cells with the different bacterial strains. tPA and PAI-1 antigen concentrations were measured in the cell supernatants by enzyme-linked immunosorbent assay. Each of the three heat-killed microorganisms induced a time-dependent increase in PAI-1 synthesis. After a 48-hour incubation period, the strongest effect was seen in the presence of S aureus (3.5-fold versus control), followed by S epidermidis (2.5-fold versus control) and E coli (1.5-fold versus control). Under the same conditions, tPA antigen levels did not change after exposure to S aureus or E coli, whereas the addition of S epidermidis resulted in enhanced tPA antigen production (2-fold versus control). The increase in PAI-1 synthesis in the presence of the heat-killed microorganisms was preceded by similar changes in interleukin-1alpha (IL-1alpha) levels. Inhibiting the activity of IL-1alpha with a neutralizing antibody significantly reduced bacterial-induced PAI-1 production. Our results indicate that the fibrinolytic imbalance during bacterial peritonitis depends on the bacterial species. The increase in PAI-1 synthesis, not the decrease in the production of tPA, alters mesothelial fibrinolytic activity. Because the increase in PAI-1 expression is significantly quenched by blocking the activity of IL-1alpha, the mesothelial release of this cytokine is involved in bacterial-induced changes in the fibrinolytic system.

Activated mesothelial cells produce heparin-binding growth factors: implications for tumour metastases

Curative surgery for gastrointestinal malignancy is commonly thwarted by local tumour recurrence. The heparin-binding growth factors, basic fibroblast growth factor (bFGF), heparin-binding epidermal growth factor-like growth factor (HB-EGF) and vascular epidermal growth factor (VEGF) are all implicated in the metastatic process, but whether or not these essential growth factors are produced by the activated peritoneum is unknown. This study reveals that peritoneal mesothelial cells constitutively express mRNA for bFGF, HB-EGF and two VEGF spliced variants, VEGF121 and VEGF165. Mesothelial activation with interleukin (IL)-1b or tumour necrosis factor (TNF)-a produced an up-regulation of mRNA for HB-EGF and VEGF, but not bFGF expression. IL-6 failed to stimulate growth factor expression, whereas IL-2 produced a marked suppression in HB-EGF and bFGF, but not VEGF expression. Mesothelial cells were shown to predominantly express mRNA for the intermediate affinity (bg(c)) IL-2 receptor. Cytokine-induced growth factor up-regulation was confirmed at the protein level using Western blotting of mesothelial cell lysates for HB-EGF and culture supernatant enzyme-linked immunosorbent assay for VEGF. The production of these growth factors by human mesothelial cells may play a significant role in post-operative peritoneal tumour recurrence. Their common heparin-binding property offers a potential therapeutic target for manipulating the growth factor environment of the human peritoneum.

Secretion of IL-6, monocyte chemoattractant protein-1, macrophage inflammatory protein-1alpha, and TNFalpha by cultured intact human peritoneum

The peritoneum is an important site of host defence. The mesothelial cells, lining the peritoneum, and the fibroblasts found in the layers below are potent sources of a variety of mediators. Furthermore, granulocytes, mast cells, and macrophages, either resident or attracted by inflammatory processes, are interspersed within the tissue. We investigated the production of mediators by samples of fresh human peritoneum. The method described here has the advantage that the cellular composition of the human peritoneum remains intact. Samples of peritoneum were excised at the beginning of elective abdominal operations in infection-free patients. The tissue was placed across the wells of a microtitre plate, fixed in place by the plate cover and incubated with culture medium with or without lipopolysaccharide (LPS) for up to 5 h. The accumulation of IL-6, monocyte chemoattractant protein-1 (MCP-1), macrophage inflammatory protein-1alpha (MIP-1alpha) and TNFalpha in culture supernatants was measured by ELISA. Production of MCP-1 and IL-6 occurred spontaneously during incubation and was enhanced by as much as 4-fold in the presence of different concentrations of LPS (0. 5-500 ng/ml) in a dose-dependent manner. MIP-1alpha and TNFalpha were detected in culture supernatants of LPS-stimulated samples with concentrations about 8 times as high as those of samples cultured with no such stimulus. The addition of IL-1beta resulted in an increase in the release of IL-6 and MCP-1, similar to that observed with LPS stimulation, but failed to increase the production of TNFalpha. MIP-1alpha production was only marginally enhanced by IL-1beta. In conclusion, our experimental system is suitable for the investigation of chemokine and cytokine production by the human peritoneum, with the aim of assessing aspects of local immunocompetence.

Culture of human peritoneum--a new method to measure the local cytokine response and the effect of immunomodulators

The production of cytokines and chemokines, which are involved in cell activation and cell migration in native pieces of peritoneum, was measured to investigate immune regulatory reactions in the human peritoneum. The samples were obtained during abdominal surgery and cultured immediately afterwards. In order to test therapeutic options in vitro, the effect of IL-10 and IFN-gamma on the cytokine and chemokine production was also studied. The chemokine monocyte chemotactic protein-1 (MCP-1) was produced and released spontaneously. When lipopolysaccharide (LPS) was added, MCP-1 production increased. In addition, TNF-alpha production was induced by LPS. When IL-10 was added, LPS-stimulated TNF-alpha production was reduced towards baseline levels, LPS-induced MCP-1 production was reduced by 37%. IFN-gamma did not affect LPS-induced TNF-alpha and MCP-1 production, but increased baseline MCP-1 production. It can be concluded that short-time culture of native human peritoneum is a method to investigate peritoneal chemokine and cytokine production in patients undergoing abdominal surgery. Further studies are intended to detect cytokine patterns which identify patients at risk of developing peritonitis. In addition, the effects of medications may be tested in vitro in order to investigate options for preventive modulation of the peritoneal immune response in such patients.

Peritoneal cytokine release after elective gastrointestinal surgery and postoperative complications

BACKGROUND

Laparotomy is known to give rise to systemic and local cytokine release. In the present study we investigated the course of the peritoneal response of tumor necrosis factor alpha (TNFalpha), interleukin (IL)-6, and IL-10 after elective gastrointestinal surgery and studied the differences in local cytokine response in patients developing postoperative complications.

METHODS

Twelve consecutive patients underwent pancreatoduodenectomy (n = 9) or biliary and gastric bypass (n = 3) for pancreatic carcinoma. Sampling (TNFalpha, IL-6, IL-10) of fluid from abdominal drains was performed at return to the recovery unit (T=0), and at 3, 6, 18, 30, 42, 54, 66, 78 hours. Systemic sampling was performed at T=0, 3, 6, 18, 42, 66 hours. Postoperative cytokine response in patients with and without postoperative complications was compared.

RESULTS

In patients without postoperative complications, peritoneal TNFalpha and IL-10 levels decreased in time (P = 0.07 and P = 0.01, respectively), whereas IL-6 did not change significantly during sampling (P = 0.28). Systemic IL-6 and IL-10 levels decreased 10-fold within 66 hours (IL-6, P = 0.04; IL-10, P = 0.06). Four patients experienced postoperative complications. All 4 patients with complications showed a second rise in peritoneal TNFalpha levels preceding the complication. All 4 patients had positive bacterial drain cultures from the abdominal drain, following the TNFalpha rise.

CONCLUSIONS

After elective abdominal surgery, cytokines are released into the abdominal cavity. Intra-abdominal complications are accompanied or preceded by a peritoneal TNFalpha rise. In patients after elective gastrointestinal surgery, monitoring of peritoneal TNFalpha might be helpful in the early detection of severe intra-abdominal complications.

Bacterial products primarily mediate fibroblast inhibition in biomaterial infection

PURPOSE

The stimulation of fibroblast growth is essential for the normal healing and tissue integration of biomaterials. The local elevation of proinflammatory mediators in infected perigraft fluid (PGF) may inhibit this growth. We sought to determine whether infected PGF inhibited fibroblast growth, and, if so, whether this was primarily dependent on the biomaterial, bacteria, or host.

METHODS

In vivo Dacron or expandable polytetra-fluoroethylene (ePTFE) grafts, sterile or colonized with slime-producing (RP-62A, viable or formalin-killed) or nonslime-producing (RP-62NA) Staphylococcus epidermidis (1 x 10(7) CFU/cm2), were implanted in Swiss Webster mice, and the PGF was harvested at 7 and 28 days. Antibodies to tumor necrosis factor alpha, interleukin 1 alpha, interferon gamma (7 micrograms/day), and indomethacin (50 micrograms/day) were administered by microinfusion pumps for 7 days and the PGF was harvested. Inhibition of the proinflammatory mediators was confirmed by enzyme-linked immunosorbant assay. The nontreated, heat-treated, or trypsin-digested in vivo PGF was incubated with an in vitro [3H]thymidine murine fibroblast (ATCC CCL-12) proliferation assay.

RESULTS

Fibroblast inhibition was significant at 7 and 28 days with infected PGF incubation compared with sterile and was not dependent on bacterial slime production or viability. Dacron sterile PGF did not significantly inhibit fibroblasts compared with control, whereas sterile ePTFE stimulated (P < 0.05) fibroblasts. Treatment of the PGF with proinflammatory cytokines, heat, and trypsin failed to reverse fibroblast inhibition in the infected state.

CONCLUSION

Biomaterial infection is associated with fibroblast inhibition that is dependent primarily on bacterial products and not the host or biomaterial. Conservative intervention strategies for graft infection need to address the problem of poor healing as well as bacterial clearance.

Early responses to infection: chemokines as mediators of inflammation

Chemokines are a superfamily of small related protein molecules that are secreted by a variety of cells and that have, among their diverse biological properties, the ability to recruit a wide range of immune cells to the sites of infection and disease. Chemokines are secreted in response to bacterial, viral, parasitic, and mycobacterial pathogens. Our recent progress in understanding the patterns of chemokine secretion in response to various pathogens and their impact on disease manifestations is likely to lead to the development of novel therapeutic approaches for a variety of serious infections.