Cytokine response by human monocytes to Clostridium difficile toxin A and toxin B

Toxins-useful biochemical tools for leukocyte research

Leukocytes are a heterogeneous group of cells that display differences in anatomic localization, cell surface phenotype, and function. The different subtypes include e.g., granulocytes, monocytes, dendritic cells, T cells, B cells and NK cells. These different cell types represent the cellular component of innate and adaptive immunity. Using certain toxins such as pertussis toxin, cholera toxin or clostridium difficile toxin, the regulatory functions of Gα_i, Gαs and small GTPases of the Rho family in leukocytes have been reported. A summary of these reports is discussed in this review.

Clostridium difficile toxin B differentially affects GPCR-stimulated Ca2+ responses in macrophages: independent roles for Rho and PLA2

Clostridium difficile toxins cause acute colitis by disrupting the enterocyte barrier and promoting inflammation. ToxB from C. difficile inactivates Rho family GTPases and causes release of cytokines and eicosanoids by macrophages. We studied the effects of ToxB on GPCR signaling in murine RAW264.7 macrophages and found that ToxB elevated Ca(2+) responses to Galphai-linked receptors, including the C5aR, but reduced responses to Galphaq-linked receptors, including the UDP receptors. Other Rho inhibitors also reduced UDP Ca(2+) responses, but they did not affect C5a responses, suggesting that ToxB inhibited UDP responses by inhibiting Rho but enhanced C5a responses by other mechanisms. By using PLCbeta isoform-deficient BMDM, we found that ToxB inhibited Ca(2+) signaling through PLCbeta4 but enhanced signaling through PLCbeta3. Effects of ToxB on GPCR Ca(2+) responses correlated with GPCR use of PLCbeta3 versus PLCbeta4. ToxB inhibited UDP Ca(2+) signaling without reducing InsP3 production or the sensitivity of cellular Ca(2+) stores to exogenous InsP3, suggesting that ToxB impairs UDP signaling at the level of InsP3/Ca(2+)coupling. In contrast, ToxB elevated InsP3 production by C5a, and the enhancement of Ca(2+) signaling by C5a was prevented by inhibition of PLA(2) or 5-LOX but not COX, implicating LTs but not prostanoids in the mechanism. In sum, ToxB has opposing, independently regulated effects on Ca(2+) signaling by different GPCR-linked PLCbeta isoforms in macrophages.

Infectious diarrhea: Cellular and molecular mechanisms

Diarrhea caused by enteric infections is a major factor in morbidity and mortality worldwide. An estimated 2-4 billion episodes of infectious diarrhea occur each year and are especially prevalent in infants. This review highlights the cellular and molecular mechanisms underlying diarrhea associated with the three classes of infectious agents, i.e., bacteria, viruses and parasites. Several bacterial pathogens have been chosen as model organisms, including Vibrio cholerae as a classical example of secretory diarrhea, Clostridium difficile and Shigella species as agents of inflammatory diarrhea and selected strains of pathogenic Escherichia coli (E. coli) to discuss the recent advances in alteration of epithelial ion absorption. Many of the recent studies addressing epithelial ion transport and barrier function have been carried out using viruses and parasites. Here, we focus on the rapidly developing field of viral diarrhea including rotavirus, norovirus and astrovirus infections. Finally we discuss Giardia lamblia and Entamoeba histolytica as examples of parasitic diarrhea. Parasites have a greater complexity than the other pathogens and are capable of creating molecules similar to those produced by the host, such as serotonin and PGE(2). The underlying mechanisms of infectious diarrhea discussed include alterations in ion transport and tight junctions as well as the virulence factors, which alter these processes either through direct effects or indirectly through inflammation and neurotransmitters.

Intravenous immunoglobulin for the treatment of severe Clostridium difficile colitis: an observational study and review of the literature

BACKGROUND

Clostridium difficile colitis (CDC) is the most common cause of hospital-acquired diarrhea. The increase in the incidence and fatality rate of CDC over the past decade has stimulated a search for new therapies, including intravenous immunoglobulin (IVIG). We report our experience with IVIG for the treatment of 21 patients with severe CDC.

METHOD

Retrospective review of patients with severe CDC who received IVIG between July 2002 and April 2006 at a teaching hospital. The existing literature on IVIG infusion for severe CDC was also reviewed.

RESULTS

Twenty-one of 1230 patients with CDC were treated with IVIG. The mean age was 68 (range, 35-98) years, with mean hospital stay of 23 (range, 9-64) days. Conventional treatment was used for an average of 8 (range, 1-25) days before IVIG infusion. All patients had evidence of pancolitis (radiologically) or ileus (clinically). The mean Acute Physiological Assessment and Chronic Health Evaluation (APACHE II) score was 25 (range, 6-39) at day 1 of IVIG infusion. Nine patients (43%) survived their hospitalization with colitis resolution while 12 (57%) died. One patient developed pulmonary edema after IVIG infusion. Symptoms resolved after an average of 10 (range, 2-20) days for survivors. Two patients underwent urgent colectomy.

CONCLUSIONS

This is the largest case series describing IVIG use for patients with severe CDC and the one with the highest mortality rate to date. The use of IVIG in this setting does not seem to benefit all patients. Benefit appears to depend on the extent of systemic involvement. Further studies are needed before adopting IVIG as routine treatment for severe CDC.

Clostridium difficile infection in the intensive care unit

Clostridium difficile infection (CDI) is an increasing nosocomial problem in North America and Western Europe, where outbreaks caused by a more virulent, toxin-hyperproducing strain have been recently reported. Clostridium difficile infection is now characterized by a higher incidence, more frequent relapses, and a higher case-fatality ratio. As a consequence, fulminant cases requiring admission to the intensive care unit (ICU) are much more common than previously. In recent years, metronidazole has appeared to lose some of its effectiveness in CDI management and vancomycin is now recognized as the first-line treatment of severe cases. Rapid diagnosis and institution of infection control measures are critical components of CDI management. The current review focuses on recent changes in the epidemiology, diagnostic methods, and treatment of CDI, with special emphasis on complicated cases managed in the ICU.

Essential role of the glucosyltransferase activity in Clostridium difficile toxin-induced secretion of TNF-alpha by macrophages

Clostridium difficile causes serious and potentially fatal inflammatory diseases of the colon. Two large protein toxins, TcdA and TcdB, have been clearly implicated in pathogenesis. The goal of this study was to determine whether the glucosyltransferase activity of the toxins is critical for the induction of tumor necrosis factor-alpha (TNF-alpha), an important cytokine mediating both local and systematic inflammatory response. A dose-dependent TNF-alpha secretion was demonstrated in murine macrophage cell line RAW 264.7 after exposure to TcdA or TcdB. TNF-alpha production was blocked by anti-toxin antibodies, indicating that the cytokine-driven response is mediated by the toxins. Both toxins disrupted the cytoskeleton of host cells, while cytoskeleton disruptions using Cytochalasin-D and latrunculin B did not affect TNF-alpha production. The TNF-alpha synthesis was inhibited by reagents that target clathrin-dependent endocytosis or prevent endosomal acidification, suggesting that the endocytosis pathway is necessary for the induction of TNF-alpha. Furthermore, knockout of the enzymatic activity by mutating two key amino acids in the catalytic domain of TcdA abolished its cytokine-inducing activity. Our studies demonstrated a crucial role of the glucosyltransferase activity of C. difficile toxins in the induction of TNF-alpha in macrophages.

Antibody-enhanced, Fc gamma receptor-mediated endocytosis of Clostridium difficile toxin A

Toxin A (TcdA) and toxin B (TcdB) are major virulence factors of Clostridium difficile. These two toxins intoxicate cultured cells by similar mechanisms, and TcdB generally is more potent than TcdA in cultured cells. The exact reason for this difference is unclear. Here, we report that the cellular effects of TcdA can be substantially enhanced via an opsonizing antibody through Fc gamma receptor I (FcgammaRI)-mediated endocytosis. A TcdA-specific monoclonal antibody, A1H3, was found to significantly enhance the cytotoxicity of TcdA to macrophages and monocytes. The A1H3-dependent enhancement of glucosyltransferase activity, cytoskeleton disruption, and tumor necrosis factor alpha production induced by TcdA was further demonstrated using RAW 264.7 cells. Subsequent experiments indicated that the interaction of FcgammaRI with A1H3 underlays the antibody-dependent enhancement of the cellular effects of TcdA. While blocking FcgammaRII and FcgammaRIII with anti-CD16/32 antibodies did not affect the TcdA-mediated glucosylation of Rac1 in RAW 264.7 cells, presaturation of FcgammaRI with anti-CD64 antibodies in THP1 cells significantly reduced this activity. Incubation of a TcdA-A1H3 immune complex with recombinant mouse CD64 completely abrogated the A1H3-mediated enhancement of the glucosyltransferase activity of TcdA in RAW 264.7 cells. Moreover, expression of FcgammaRI in CHO cells strikingly enhanced the sensitivity of these cells to TcdA complexed with A1H3. We showed that the presence of A1H3 facilitated cell surface recruitment of TcdA, contributing to the antibody-dependent, FcgammaRI-mediated enhancement of TcdA activity. Finally, studies using chlorpromazine and endosomal acidification inhibitors revealed an important role of the endocytic pathway in the A1H3-dependent enhancement of TcdA activity.

Bacterial toxins as immunomodulators

Bacterial toxins are the causative agent at pathology in a variety of diseases. Although not always the primary target of these toxins, many have been shown to have potent immunomodulatory effects, for example, inducing immune responses to co-administered antigens and suppressing activation of immune cells. These abilities of bacterial toxins can be harnessed and used in a therapeutic manner, such as in vaccination or the treatment of autoimmune diseases. Furthermore, the ability of toxins to gain entry to cells can be used in novel bacterial toxin based immuno-therapies in order to deliver antigens into MHC Class I processing pathways. Whether the immunomodulatory properties of these toxins arose in order to enhance bacterial survival within hosts, to aid spread within the population or is pure serendipity, it is interesting to think that these same toxins potentially hold the key to preventing or treating human disease.

Clinical review of the management of fulminant clostridium difficile infection

BACKGROUND

Clostridium difficile infection (CDI) is a frequent cause of morbidity and mortality among elderly hospitalized patients. A small but increasing number of patients have developed fulminant CDI, and a significant number of these patients require emergency colectomy. In this review, we discuss the risk factors, pathophysiology, diagnosis, and management of fulminant CDI.

DATA SOURCES

A literature search (Medline, Embase, Cochrane Library, Biosis, Science Citation Index, Ovid Journals) was performed from the period between January 1980 and June 2008 using the key words "Clostridium difficile,""pseudomembranous enterocolitis,""colectomy,""acute abdomen,""antibiotic-associated diarrhea," or "fulminant Clostridium difficile colitis." Articles not in English or not related to human subjects were excluded. For this review, we analyzed the articles identified in our original search and those articles cited in the original review articles. No randomized trials were found on the surgical management of fulminant CDI and only retrospective studies with a minimum of five patients were used in the review. With respect to medical treatment, we based our review on guideline articles, systematic reviews, and available randomized trials.

CONCLUSION

Both the incidence and severity of CDI are increasing. Fulminant CDI is underappreciated as a life-threatening disease because of a lack of awareness of its severity and its nonspecific clinical syndrome. Early diagnosis and treatment are essential for a good outcome, and early surgical intervention should be used in patients who are unresponsive to medical therapy. The surgical procedure of choice is a total abdominal colectomy with end ileostomy, although the mortality rate remains high.

Clostridium difficile TxAC314 and SLP-36kDa enhance the immune response toward a co-administered antigen

This study evaluated the in vivo adjuvant activity of two peptides derived from Clostridium difficile: a fragment of the receptor-binding domain of toxin A (TxAC314) and a fragment of the 36 kDa surface-layer protein (SLP-36kDa) from strain C253. Their ability to affect the magnitude, distribution and polarization of the immune response against fibronectin-binding protein A (FnbpA), a protective vaccine antigen against Staphylococcus aureus, was evaluated using two different routes of immunization: intranasal and subcutaneous. It was shown that (i) the route of immunization affected the magnitude of the immune response; (ii) both peptides enhanced the production of circulating anti-FnbpA IgG and IgA; (iii) following mucosal immunization TxAC314 was more effective than SLP-36kDa at inducing antibody in the gastrointestinal tract; (iv) the adjuvant influenced the Th1/Th2 balance; and (v) TxAC314 was more effective than SLP-36kDa in inducing a cell-mediated response. These studies provide insight into the ability of different C. difficile-derived peptides to differentially affect and polarize the activity of the immune system and on their potential use as adjuvants in newly developed vaccines.

C-terminal repeats of Clostridium difficile toxin A induce production of chemokine and adhesion molecules in endothelial cells and promote migration of leukocytes

The C-terminal repeating sequences of Clostridium difficile toxin A (designated ARU) are homologous to the carbohydrate-binding domain of streptococcal glucosyltransferases (GTFs) that were recently identified as potent modulins. To test the hypothesis that ARU might exert a similar biological activity on endothelial cells, recombinant ARU (rARU), which was noncytotoxic to cell cultures, was analyzed using human umbilical vein endothelial cells. The rARU could bind directly to endothelial cells in a serum- and calcium-dependent manner and induce the production of interleukin-6 (IL-6), IL-8, and monocyte chemoattractant protein 1 in a dose-dependent manner. An oligosaccharide binding assay indicated that rARU, but not GTFC, binds preferentially to Lewis antigens and 3'HSO3-containing oligosaccharides. Binding of rARU to human endothelial or intestinal cells correlated directly with the expression of Lewis Y antigen. Bound rARU directly activated mitogen-activated protein kinases and the NF-kappaB signaling pathway in endothelial cells to release biologically active chemokines and adhesion molecules that promoted migration in a transwell assay and the adherence of polymorphonuclear and mononuclear cells to the endothelial cells. These results suggest that ARU may bind to multiple carbohydrate motifs to exert its biological activity on human endothelial cells.

Inflammation and apoptosis in Clostridium difficile enteritis is mediated by PGE2 up-regulation of Fas ligand

BACKGROUND & AIMS

Clostridium difficile toxin A causes acute inflammation and fluid secretion in experimental animals and patients with C difficile infection. We previously reported that toxin A increased cyclooxygenase-2/prostaglandin E(2) (PGE(2)) expression and apoptosis in human colonocytes. Here, we assessed the role of secreted PGE(2) in inflammation and enterocyte apoptosis in toxin A enteritis.

METHODS

Effects of PGE(2) and PGE(2) blockade on toxin A-induced apoptosis of human colonocytes (NCM460) and of PGE(2) or toxin A on the Fas ligand (FasL) induction were analyzed by flow cytometry and Western blot. Functional activity of elevated FasL on colonocytes was assessed by coculture of colonocytes with Fas bearing Jurkat T cells. The involvement of PGE(2)-dependent Fas/FasL activation in toxin A enteritis was further assessed in either scid or FasL and Fas deficient mice.

RESULTS

Inhibition of cyclooxygenase-2 by NS-398 and of PGE(2) using a blocking antibody markedly attenuated apoptosis in colonocytes exposed to toxin A. Enhanced expression and release of FasL followed PGE(2) or toxin A exposure in vivo and in vitro and also was significantly attenuated by treatment with NS-398 and PGE(2) blocking antibody. PGE(2) acting through an EP1 receptor activated nuclear factor-kappaB, which induced transcription of FasL. Toxin A enteritis was accompanied by increased cellular infiltration, fluid secretion, and mucosal damage in control mice, but this response was markedly reduced in both Fas(-/-) and FasL(-/-) mice.

CONCLUSIONS

Toxin A enteritis involves release of PGE(2), which activates the Fas/FasL system, causing enterocyte apoptosis and inflammation.

Clostridium difficile: association with thrombocytosis and leukocytosis

BACKGROUND

Apart from leukocytosis, few laboratory markers suggestive of Clostridium difficile infections have been described.

METHODS

We retrospectively analyzed the association between thrombocytosis, leukocytosis and C. difficile infections at the Atlanta Veterans Affairs Medical Center.

RESULTS

Of 162 patients with C. difficile infection, 36 (22%) had thrombocytosis, and 97 (60%) had leukocytosis. C difficile toxin A ELISA was performed in 46/695 (6.6%) patients with thrombocytosis and was positive in 18 (39.1%). Leukocytosis was present in 16/18 (89%) of patients with positive C. difficile toxin A ELISA and thrombocytosis, but also in 21/28 (75%) of patients with negative C. difficile toxin A ELISA and thrombocytosis. Among patients with marked leukocytosis, C. difficile toxin A was more frequently detected in those with concomitant thrombocytosis (P = 0.07).

CONCLUSIONS

The presence of thrombocytosis may be helpful to improve the pretest probability for C difficile infections.

Epithelial cell I kappa B-kinase beta has an important protective role in Clostridium difficile toxin A-induced mucosal injury

Toxin A released by Clostridium difficile interacts with the single layer of intestinal epithelial cells that lines the host's intestinal tract and leads to mucosal damage and inflammation that manifests clinically as antibiotic-associated diarrhea and pseudomembranous colitis. Activation of the transcription factor NF-kappaB in intestinal epithelial cells is important for regulating the expression of epithelial cell proinflammatory genes and cell survival. However, the role of NF-kappaB activation in the pathogenesis of C. difficile toxin A-induced colitis is unknown. To determine the functional importance in vivo of NF-kappaB activation in intestinal epithelium in the pathogenesis of C. difficile-induced colitis, we used mutant mice that do not activate the classical NF-kappaB signaling pathway in intestinal epithelial cells due to a conditional deficiency in those cells of the IkappaB-kinase beta (IKKbeta) subunit of IKK. C. difficile toxin A challenge of intestinal loops in intestinal epithelial cell IKKbeta-deficient mice induced a rapid and significant increase in intestinal epithelial apoptosis compared with littermate controls. This was accompanied by a significant increase in acute mucosal inflammation, mucosal injury, luminal fluid secretion, and bacterial translocation. We conclude that activation of intestinal epithelial cell NF-kappaB by toxin A plays an important host mucosal protective role after C. difficile toxin A exposure that is mediated, at least in part, through promoting epithelial cell survival by abrogating epithelial cell apoptosis.

Effect of novel A2A adenosine receptor agonist ATL 313 on Clostridium difficile toxin A-induced murine ileal enteritis

Clostridium difficile is a spore-forming, anaerobic, gram-positive bacillus that releases two main virulence factors: toxins A and B. Toxin A plays an important pathogenic role in antibiotic-induced diarrhea and pseudomembranous colitis, a condition characterized by intense mucosal inflammation and secretion. Agonist activity at A2A adenosine receptors attenuates inflammation and damage in many tissues. This study evaluated the effects of a new selective A2A adenosine receptor agonist (ATL 313) on toxin A-induced injury in murine ileal loops. ATL 313 (0.5 to 5 nM) and/or the A2A adenosine receptor antagonist (ZM241385; 5 nM) or phosphate-buffered saline (PBS) were injected into ileal loops immediately prior to challenge with toxin A (1 to 10 microg/loop) or PBS. Intestinal fluid volume/length and weight/length ratios were calculated 3 h later. Ileal tissues were collected for the measurement of myeloperoxidase, adenosine deaminase activity, tumor necrosis factor alpha (TNF-alpha) production, histopathology, and detection of cell death by the TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) method. Toxin A significantly increased volume/length and weight/length ratios in a dose-dependent fashion. ATL 313 treatment significantly (P < 0.05) reduced toxin A-induced secretion and edema, prevented mucosal disruption, and neutrophil infiltration as measured by myeloperoxidase activity. ATL 313 also reduced the toxin A-induced TNF-alpha production and adenosine deaminase activity and prevented toxin A-induced cell death. These protective effects of ATL 313 were reversed by ZM241385. In conclusion, the A2A adenosine receptor agonist, ATL 313, reduces tissue injury and inflammation in mice with toxin A-induced enteritis. The finding of increased ileal adenosine deaminase activity following the administration of toxin A is new and might contribute to the pathogenesis of the toxin A-induced enteritis by deaminating endogenous adenosine.

The outcome of surgery in fulminant Clostridium difficile colitis

BACKGROUND

The clinical presentation of Clostridium difficile infection ranges from asymptomatic carriage, colitis with or without pseudomembranes, to fulminant colitis. Although not common, fulminant C. difficile colitis can result in bowel perforation and peritonitis with a high mortality rate. Colectomy is often indicated in these cases.

METHODS

We retrospectively analysed the outcome of 14 patients who underwent surgery for fulminant C. difficile colitis in the period 1996-2003 in our Unit.

RESULTS

The indications for surgery were systemic toxicity and peritonitis (n = 10), radiological and clinical evidence of progressive toxic colonic dilatation (n = 3) and progressive colonic dilatation with bowel perforation (n = 1). C. difficile infection as the cause of colitis was diagnosed pre-operatively in seven (50%) patients, six of whom underwent a total colectomy and one a right hemicolectomy. Overall mortality in our series was 35.7%. Total colectomy was associated with a lower mortality rate of 11.1% (1/9) when compared with left hemicolectomy was 100% (4/4) (P = 0.01). One patient who underwent a right hemicolectomy (on the basis of deceptively normal external appearance of the rest of the colon intra-operatively) survived after a prolonged hospital stay.

CONCLUSIONS

Early or pre-operative microbiological diagnosis of C. difficile infection can be difficult in patients with a fulminant presentation. Those patients with C. difficile colitis, who develop signs of toxicity, peritonitis or perforation, should undergo a total colectomy as the operation of choice.

Human mucosa/submucosa interactions during intestinal inflammation: involvement of the enteric nervous system in interleukin-8 secretion

Interleukin-8 (IL-8) is a key chemokine upregulated in various forms of intestinal inflammation, especially those induced by bacteria such as Clostridium difficile (C. difficile). Although interactions between different mucosal and submucosal cellular components have been reported, whether such interactions are involved in the regulation of IL-8 secretion during C. difficile infection is unknown. Moreover, whether the enteric nervous system, a major component of the submucosa, is involved in IL-8 secretion during an inflammatory challenge remains to be determined. In order to investigate mucosa/submucosa interactions that regulate IL-8 secretion, we co-cultured human intestinal mucosa and submucosa. In control condition, IL-8 secretion in co-culture was lower than the sum of the IL-8 secretion of both tissue layers cultured alone. Contrastingly, IL-8 secretion increased in co-culture after mucosal challenge with toxin B of C. difficile through an IL-1 beta-dependent pathway. Moreover, we observed that toxin B of C. difficile increased IL-8 immunoreactivity in submucosal enteric neurones in co-culture and in intact preparations of mucosa/submucosa, through an IL-1 beta-dependent pathway. IL-1 beta also increased IL-8 secretion and IL-8 mRNA expression in human neuronal cell lines (NT2-N and SH-SY5Y), through p38 and ERK1/2 MAP kinase-dependent pathways. Our results demonstrate that mucosa/submucosa interactions regulate IL-8 secretion during inflammatory processes in human through IL-1 beta-dependent pathways. Finally we observed that human submucosal neurones synthesize IL-8, whose production in neurones is induced by IL-1 beta via MAPK-dependent pathways.

Pathophysiology and impact of enteric bacterial and protozoal infections: new approaches to therapy

Despite numerous scientific advances in the past few years regarding the pathogenesis, diagnostic tools and treatment of infectious enteritis, enteric infections remain a serious threat to health worldwide. With globalization of the food supply, the increase in travel, mass food processing and antibiotic resistance, infectious diarrhea has become a critical concern for both developing and developed countries. Oral rehydration therapy has been cited as the most important medical discovery of the century due to the millions of lives that have been saved. However, statistics concerning diarrhea-induced mortality and the highly underestimated morbidity continue to demonstrate the severity of the problem. A more complete understanding of the pathogenesis of infectious diarrhea and potential new vaccines and effective treatments are badly needed. In addition, public health preventive actions, such as early detection of outbreaks, care with food, water and sanitation and, where relevant, immunization, should be considered a priority. This article provides an overview of the epidemiological impact, pathogenesis and new approaches to the management of enteric infections.

Monocytes are highly sensitive to clostridium difficile toxin A-induced apoptotic and nonapoptotic cell death

In this study we investigated the in vitro responses of peripheral blood mononuclear preparations and purified monocytes to Clostridium difficile toxin A. In contrast to the responses of T and B cells, exposure to toxin A led to a rapid loss of monocytes in a time- and dose-dependent fashion (the majority of cells were lost within 24 h of exposure to >100 ng of toxin per ml). Transmission electron microscopy, flow cytometry, and fluorescence microscopy after propidium iodide and Hoechst staining showed that cell death in purified preparations of monocytes following exposure to 100 and 1,000 ng of toxin A per ml occurred by apoptosis. Further studies showed that 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazole-carbocyanine iodide aggregates were retained within toxin A-exposed monocyte mitochondria, but cytochrome c was released, suggesting that the apoptotic cascade was triggered in the absence of mitochondrial permeability transition. There was also an increase in caspase-3 activity in toxin A-stimulated monocytes. Following exposure to very high concentrations of toxin A (30 microg/ml), monocyte cell death was predominantly of the necrotic type, with rapid extracellular release of lactate dehydrogenase. These studies demonstrated that C. difficile toxin A has a cell-specific effect, in which monocytes exhibit greater susceptibility than lymphocytes and their death is induced in a concentration-dependent manner.

Clostridium difficile toxin A carboxyl-terminus peptide lacking ADP-ribosyltransferase activity acts as a mucosal adjuvant

The receptor binding domains of the most potent mucosal adjuvants, bacterial toxins and plant lectins, are organized in repeat units to recognize specific sugar residues. The lectin-like structure of the C-terminal region of Clostridium difficile toxin A prompted us to investigate the mucosal adjuvant properties of a nontoxigenic peptide corresponding to amino acids 2394 to 2706 (TxA(C314)). We compared TxA(C314) adjuvant activity to those of cholera toxin (CT) and Escherichia coli heat-labile enterotoxin subunit B (EtxB) coadministered orally or nasotracheally with poor peptide antigens (keyhole limpet hemocyanin [KLH] and hen egg lysozyme [HEL]). Levels of anti-KLH-specific serum immunoglobulin G (IgG) and IgA as well as that of mucosal IgA were significantly higher in animals immunized orally with TxA(C314) plus KLH than with KLH alone, CT plus KLH, or EtxB plus KLH. Following intranasal immunization with TxA(C314) plus HEL, levels of serum- and mucosa-specific antibodies were comparable to those induced by coadministering HEL with CT or EtxB. The TxA(C314) adjuvant effect following oral, but not intranasal, immunization was dose dependent. The analysis of the subclasses of anti-KLH-specific IgG isotypes and the cytokines released from splenocytes of immunized mice challenged in vitro with KLH indicates the induction of a mixed Th1/Th2-type immune response, with prevalence of the Th1 branch. We conclude that TxA(C314) enhances immune responses against mucosa-coadministered foreign antigens and represents a promising mucosal adjuvant, especially because its ability to stimulate mixed Th1/Th2 responses with a strong a Th1 component is extremely worthwhile against intracellular pathogens.

Toxin B of Clostridium difficile activates human VIP submucosal neurons, in part via an IL-1beta-dependent pathway

This study investigated whether toxin B of Clostridium difficile can activate human submucosal neurons and the involved pathways. Isolated segments of human colon were placed in organ culture for 3 h in the presence of toxin B or IL-1beta. Whole mounts of internal submucosal plexus were stained with antibodies against c-Fos, neuron-specific enolase (NSE), vasoactive intestinal polypeptide (VIP), and substance P (SP). The membrane potential (Vm) response of submucosal neurons to local application of toxin B and IL-1beta was determined by a multisite optical recording technique. Toxin B (0.1 to 10 ng/ml) increased the proportion of c-Fos-positive neurons dose dependently compared with the control. In the presence of toxin B (10 ng/ml), most c-Fos-positive neurons were immunoreactive for VIP (79.8 +/- 22.5%) but only 19.4 +/- 14.0% for SP. Toxin B induced a rapid rise in IL-1beta mRNA level and a sixfold increase in IL-1beta protein in supernatant after 3 h of incubation. c-Fos expression induced by toxin B was reduced dose dependently by IL-1 receptor antagonist (0.1-10 ng/ml). IL-1beta significantly increased c-Fos expression in submucosal neurons compared with the control (34.2 +/- 10.1 vs. 5.1 +/- 1.3% of NSE neurons). Microejection of toxin B had no effect on the Vm of enteric neurons. Evidence of a direct excitatory effect of IL-1beta on Vm was detected in a minority of enteric neurons. Therefore, toxin B of C. difficile activates VIP-positive submucosal neurons, at least in part, via an indirect IL-1beta-dependent pathway.

Clostridium difficile colitis associated with hemolytic-uremic syndrome

The authors report the case of a 46-year-old woman who presented with vomiting and profuse bloody diarrhea. Laboratory studies were significant for a hematocrit of 27% and lactate dehydrogenase of 5,394 U/L (5,394 U/L). Her renal function deteriorated rapidly with a peak creatinine of 12.4 mg/dL (1,096.4 micromol/L), and platelet count dropped simultaneously to a nadir of 123,000/microL (123 x 10(9)/L]. Schistocytes were observed in peripheral blood smear. Stool was positive for Clostridium difficile toxin A by enzyme immunoassay (EIA). Stool assay for Shiga-like toxin was negative by EIA, and stool cultures returned negative for Escherichia coli O157:H7 and other enteric pathogens. A diagnosis of C difficile colitis associated with hemolytic-uremic syndrome was made; the patient received plasmapheresis and recovered with no relapse after 10 months of follow-up. This is the second reported case of C difficile colitis associated with hemolytic-uremic syndrome in an adult.

Regulation of the NK-1 receptor gene expression in human macrophage cells via an NF-kappa B site on its promoter

We report here that human monocytic/macrophage THP-1 cells express the neurokinin 1 receptor (NK-1R), and that exposure of these cells to the proinflammatory cytokine IL-1 beta increased the expression of the NK-1R gene at the mRNA and protein levels. Because IL-1 beta function involves nuclear factor kappa B (NF-kappa B) activation, these data suggest that this increase in the expression of the NK-1R gene is mediated by the NF-kappa B transcription factor. An earlier report noted that the promoter region of the human NK-1R gene contains a putative binding site for NF-kappa B [Takahashi, K., Tanaka, A., Hara, M. & Nakanishi, S. (1992) Eur. J. Biochem. 204, 1025-1033]. Here we demonstrate that this is indeed a functional NF-kappa B-binding site, and that NF-kappa B is responsible for regulating the expression of the NK-1R gene by binding to the promoter region of the NK-1R gene. To further substantiate that the observed NF-kappa B-dependent IL-1 beta induction of the human NK-1R gene is regulated via a transcriptional event through this NF-kappa B site on the NK-1R gene promoter, we transfected THP-1 cells with a luciferase promoter-reporter construct containing the 5' promoter region of the human NK-1R gene. Exposure of these cells to IL-1 beta or overexpression of NF-kappa B cDNAs resulted in a significant increase in the amount of luciferase activity that was diminished greatly in cells transfected with I kappa B alpha, the NF-kappa B inhibitor. These results directly implicate NF-kappa B in the regulation of the NK-1R gene and provide a molecular mechanism for the increase in expression of the NK-1R gene in responsive cells.

Differential expression and polarized secretion of CXC and CC chemokines by human intestinal epithelial cancer cell lines in response to Clostridium difficile toxin A

Intestinal epithelial cells are the initial sites of host response to Clostridium difficile infection and can play a role in signaling the influx of inflammatory cells. To further explore this role, the regulated expression and polarized secretion of CXC and CC chemokines by human intestinal epithelial cells were investigated. An expression of the CXC chemokines, including IL-8 and growth-related oncogene (GRO)-alpha, and the CC chemokine monocyte chemoattractant protein (MCP)-1 from HT-29 cells increased in the 1-6 hr following C. difficile toxin A stimulation, assessed by quantitative RT-PCR. In contrast, the expression of neutrophil activating protein-78 (ENA-78) was delayed for 18 hr. The up-regulated mRNA expression of chemokines was paralleled by the increase of protein levels. However, the expression of macrophage inflammatory protein (MIP)-1alpha, RANTES (regulated on activation normal T cells expressed and secreted), and interferon-gamma-inducible protein-10 (IP-10) was not changed in HT-29 or Caco-2 cells stimulated with toxin A. Upon stimulation of the polarized Caco-2 epithelial cells in a transwell chamber with toxin A, CXC and CC chemokines were released predominantly into the basolateral compartment. Moreover, the addition of IFN-gamma and TNF-alpha to toxin A stimulated Caco-2 cells increased the basolateral release of CC chemokine MCP-1. In contrast, IFN-gamma and TNF-alpha had no effect on the expression of the CXC chemokines IL-8 and GRO-alpha. These results suggest that a CXC and CC chemokine expression from epithelial cells infected with C. difficile may be an important factor in the mucosal inflammatory response.

Corticotropin-releasing hormone antagonists possess anti-inflammatory effects in the mouse ileum

BACKGROUND & AIMS

Corticotropin-releasing hormone (CRH) released at local sites of inflammation promotes inflammation in the periphery. We investigated its effects in the intestinal responses caused by toxin A from Clostridium difficile, the causative agent of antibiotic-associated colitis.

METHODS

Ileal loops were injected with 10 microg of toxin A, and enterotoxic responses were measured at various time points.

RESULTS

Pretreatment of mice with 2.5 microg/kg of the CRH receptor antagonist alpha-helical CRH((9-41)) that blocks both CRH receptor subtypes reduced toxin A-mediated ileal secretion, epithelial cell damage, mucosal edema, neutrophil infiltration, and mucosal content of interleukin 1 beta and tumor necrosis factor alpha. Pretreatment with the specific CRH(1) receptor antagonist antalarmin (20 mg/kg, IP) also inhibited toxin A-induced fluid secretion and toxin A-associated histologic changes. CRH messenger RNA and protein were increased in mouse ileum 30 minutes after intraluminal toxin A administration. In situ hybridization and immunohistochemistry demonstrated that toxin A at 1 hour caused a substantial increase in the expression of both CRH receptor subtypes in the ileal mucosa.

CONCLUSIONS

Peripheral CRH may play a proinflammatory role in toxin A-induced intestinal secretion and inflammation and that CRH(1) receptor, at least in part, is important in the mediation of these responses.

Fulminant Clostridium difficile: an underappreciated and increasing cause of death and complications

OBJECTIVE

To review the epidemiology and characteristics of patients who died or underwent colectomy secondary to fulminant Clostridium difficile colitis.

SUMMARY BACKGROUND DATA

In patients with C. difficile colitis, a progressive, systemic inflammatory state may develop that is unresponsive to medical therapy; it may progress to colectomy or death.

METHODS

The authors reviewed 2,334 hospitalized patients with C. difficile colitis from January 1989 to December 2000. Sixty-four patients died or underwent colectomy for pathologically proven C. difficile colitis.

RESULTS

In 2000, the incidence of C. difficile colitis in hospitalized patients increased from a baseline of 0.68% to 1.2%, and the incidence of patients with C. difficile colitis in whom life-threatening symptoms developed increased from 1.6% to 3.2%. Forty-four patients required a colectomy and 20 others died directly from C. difficile colitis. Twenty-two percent had a prior history of C. difficile colitis. A recent surgical procedure and immunosuppression were common predisposing conditions. Lung transplant patients were 46 times more likely to have C. difficile colitis and eight times more likely to have severe disease. Abdominal computed tomography scan correctly diagnosed all patients, whereas 12.5% of toxin assays and 10% of endoscopies were falsely negative. Patients undergoing colectomy for C. difficile colitis had an overall death rate of 57%. Significant predictors of death after colectomy were preoperative vasopressor requirements and age.

CONCLUSIONS

C. difficile colitis is a significant and increasing cause of death. Surgical treatment of C. difficile colitis has a high death rate once the fulminant expression of the disease is present.

Effects of Clostridium difficile toxins on epithelial cell barrier

Clostridium difficile is the primary agent responsible for many patients with antibiotic-associated diarrhea and almost all patients with pseudomembranous colitis following antibiotic therapy. C. difficile infection is the most frequent form of colitis in hospitals and nursing homes and affects millions of patients in the United States and abroad. The first event in the pathogenesis of C. difficile infection involves alterations of the indigenous colonic microflora by antibiotics, followed by colonization with C. difficile. C. difficile causes diarrhea and colitis by releasing two high molecular weight protein exotoxins, toxin A and toxin B, with potent cytotoxic and enterotoxic properties. Evidence presented here indicates that C. difficile toxins compromise the epithelial cell barrier by at least two pathophysiologic pathways, one involving disaggregation of actin microfilaments in colonocytes via glucosylation of the Rho family of proteins leading to epithelial cell destruction and opening of the tight junctions, whereas the other appears to involve early release of proinflammatory cytokines from intestinal epithelial cells probably via activation of MAP kinases. We speculate that cytokines released from intestinal epithelial cells in response to toxin A exposure will diffuse into the lamina propria and activate macrophages, enteric nerves, and sensory neurons to release SP, CGRP, and NT, which, in turn, interact with immune and inflammatory cells and amplify the inflammatory response. Dissection of this inflammatory cascade may help us understand the pathophysiology of inflammatory diarrhea caused by this important pathogen.

Microbes and microbial toxins: paradigms for microbial-mucosal interactions II. The integrated response of the intestine to Clostridium difficile toxins

Clostridium difficile, the major etiologic factor of antibiotic-associated diarrhea and colitis, mediates its effects by releasing two large protein exotoxins, toxins A and B. A major toxin effect is related to the disassembly of actin microfilaments, leading to impairment of tight junctions in human colonocytes. The mechanism of actin disaggregation involves monoglucosylation of the signaling proteins Rho A, Rac, and Cdc 42, which control stress fiber formation directly by toxins A and B. An important aspect of C. difficile infection is the acute necroinflammatory changes seen in patients with pseudomembranous colitis. The early mechanism of toxin-mediated inflammation involves toxin effects on cellular mitochondria, release of reactive oxygen species, and activation of mitogen-activated protein kinases and the transcription factor nuclear factor-kappaB. Injection of toxin A into animal intestine triggers secretion of fluid and intestinal inflammation characterized by epithelial cell destruction and neutrophil activation. A critical feature of C. difficile enterotoxicity is communication between enterocytes and lamina propria nerves, macrophages, and mast cells mediated via release of neuropeptides and proinflammatory cytokines.

Absence of intestinal secretion on supernatants from macrophages stimulated with Clostridium difficile toxin B on rabbit ileum

Several studies have documented the involvement of both Clostridium difficile, toxins, A and B in the pathogenesis of antibiotic-associated diarrhea. Recently, we demonstrated that IL-1 beta is the intestinal secretory factor released by macrophages stimulated with toxin A. The aim of this study was to evaluate the importance of macrophages stimulated with toxin B on rabbit ileal ion transport. The changes in ion transport were analyzed by studying the short-circuit current of the rabbit ileal mucosa mounted in Ussing chambers. The supernatants of macrophages treated with toxin B (3.6 x 10(-7) M) had no effect on the ion transport (change in short-circuit current =28.0+/-9.2 vs. control=26.8+/-3.6 microA cm(-2)). Supernatants of macrophages stimulated with toxin A (3.2 x 10(-7) M), our positive control, induced a significant change in ileal ion transport (delta I(sc)=55.2+/-5.7 mA cm(-2)). It was also observed that, like toxin A, toxin B stimulated macrophages to produce TNF-alpha (555.0+/-37.9 pg/ml vs. control=182.0+/-39.8 pg/ml; p<0.05). Nevertheless, in contrast to toxin A, toxin B did not stimulate IL-1 beta synthesis (28.0+/-7.5 pg/ml vs. control=40. 0+/-14.4 pg/ml; p>0.05). We conclude that the supernatants of macrophages stimulated with toxin B are not able to stimulate ion transport and that both toxins stimulate the genesis of TNF-alpha, but only toxin A induces the synthesis of IL-1 beta, which, we have earlier reported, causes an electrogenic intestinal response in rabbit ileum.

Update on Clostridium difficile infection

Clostridium difficile is a major cause of antibiotic-associated diarrhea in hospital and community settings, spreading endemic and epidemic disease in developed and developing areas throughout the world. Its toxins A and B cause epithelial disruption, inflammation, and secretion. Diagnosis of infection with C. difficile is based on appropriate clinical presentation and demonstration of the presence of either toxin A or B, or both. Established treatment is still predominantly metronidazole and vancomycin. The association of antibiotic therapy with recurrent disease and antimicrobial resistance, especially vancomycin-resistant enterococci, highlights the need for new approaches to managing C. difficile infection.

p38 MAP kinase activation by Clostridium difficile toxin A mediates monocyte necrosis, IL-8 production, and enteritis

Clostridium difficile toxin A causes acute neutrophil infiltration and intestinal mucosal injury. In cultured cells, toxin A inactivates Rho proteins by monoglucosylation. In monocytes, toxin A induces IL-8 production and necrosis by unknown mechanisms. We investigated the role of mitogen-activated protein (MAP) kinases in these events. In THP-1 monocytic cells, toxin A activated the 3 main MAP kinase cascades within 1 to 2 minutes. Activation of p38 was sustained, whereas stimulation of extracellular signal-regulated kinases and c-Jun NH(2)-terminal kinase was transient. Rho glucosylation became evident after 15 minutes. IL-8 gene expression was reduced by 70% by the MEK inhibitor PD98059 and abrogated by the p38 inhibitor SB203580 or by overexpression of dominant-negative mutants of the p38-activating kinases MKK3 and MKK6. SB203580 also blocked monocyte necrosis and IL-1beta release caused by toxin A but not by other toxins. Finally, in mouse ileum, SB203580 prevented toxin A-induced neutrophil recruitment by 92% and villous destruction by 90%. Thus, in monocytes exposed to toxin A, MAP kinase activation appears to precede Rho glucosylation and is required for IL-8 transcription and cell necrosis. p38 MAP kinase also mediates intestinal inflammation and mucosal damage induced by toxin A.

Roles of Intracellular Calcium and NF-κB in the Clostridium difficile Toxin A-Induced Up-Regulation and Secretion of IL-8 from Human Monocytes

Clostridium difficile causes an intense inflammatory colitis through the actions of two large exotoxins, toxin A and toxin B. IL-8 is believed to play an important role in the pathophysiology of C. difficile-mediated colitis, although the mechanism whereby the toxins up-regulate the release of IL-8 from target cells is not well understood. In this study, we investigated the mechanisms through which toxin A induces IL-8 secretion in human monocytes. We found that cellular uptake of toxin A is required for the up-regulation of IL-8, an effect that is not duplicated by a recombinant toxin fragment comprising the cell-binding domain alone. Toxin A induced IL-8 expression at the level of gene transcription and this effect occurred through a mechanism requiring intracellular calcium and calmodulin activation. Additionally, the effects of toxin A were inhibited by the protein tyrosine kinase inhibitor genistein, but were unaffected by inhibitors of protein kinase C and phosphatidylinositol-3 kinase. We determined that toxin A activates nuclear translocation of the transcription factors NF-κB and AP-1, but not NF-IL-6. NF-κB inhibitors blocked the ability of toxin A to induce IL-8 secretion, and supershift analysis indicated that the major isoform of NF-κB activated by the toxin is a p50-p65 heterodimer. This study is the first to identify intracellular signaling pathways and transcription factors involved in the C. difficile toxin-mediated up-regulation of IL-8 synthesis and release by target cells. This information should increase our understanding of the pathogenesis of C. difficile colitis and the nature of IL-8 gene regulation as well.

Immunoglobulin A1 protease, an exoenzyme of pathogenic Neisseriae, is a potent inducer of proinflammatory cytokines

A characteristic of human pathogenic Neisseriae is the production and secretion of an immunoglobulin (Ig)A1-specific serine protease (IgA1 protease) that cleaves preferentially human IgA1 and other target proteins. Here we show a novel function for native IgA1 protease, i.e., the induction of proinflammatory cytokines such as tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6, and IL-8 from peripheral blood mononuclear cells. The capacity of IgA1 protease to elicit such cytokine responses in monocytes was enhanced in the presence of T lymphocytes. IgA1 protease did not induce the regulatory cytokine IL-10, which was, however, found in response to lipopolysaccharide and phytohemagglutinin. The immunomodulatory effects caused by IgA1 protease require a native form of the enzyme, and denaturation abolished cytokine induction. However, the proteolytic activity is not required for the cytokine induction by IgA1 protease. Our results indicate that IgA1 protease exhibits important immunostimulatory properties and may contribute substantially to the pathogenesis of neisserial infections by inducing large amounts of TNF-alpha and other proinflammatory cytokines. In particular, IgA1 protease may represent a key virulence determinant of bacterial meningitis.

Serum antitoxin antibodies mediate systemic and mucosal protection from Clostridium difficile disease in hamsters

Clostridium difficile is the bacterial pathogen identified as the cause of pseudomembranous colitis and is principally responsible for nosocomial antibiotic-associated diarrhea and colitis. The pathologic findings associated with this infection are believed to be caused by two large (approximately 300-kDa) exotoxins, toxins A and B. Because of the mucosal nature of this infection, vaccination strategies aimed at providing prophylactic or therapeutic immune protection have included immunization by mucosal routes. Using the hamster model of C. difficile infection, we examined the protective efficacy of inactivated toxin (toxoid) vaccine formulations prepared as either culture filtrate or partially purified toxoid. We compared combination parenteral and mucosal vaccination regimens involving intranasal, intragastric, or rectal routes of immunization and found that rectal immunization in conjunction with intramuscular (i.m.) vaccination provided full protection of hamsters from death and diarrhea while the other mucosal routes did not. Protection was associated with high levels of toxin-neutralizing antibodies in serum. The requirement for adjuvants for protection was assessed by using sequential i.m. and rectal or i.m. vaccination regimens. Unexpectedly, i.m. immunization without adjuvant conferred the highest protection from death and diarrhea; this regimen elicited the highest serum anti-toxin B titers as well as toxin B neutralizing titers. Passive transfer of mouse antitoxin antibodies protected hamsters in a dose-dependent manner, demonstrating the principal role of circulating antitoxin antibodies in immunity from this toxin-mediated mucosal disease. These results suggest that prophylactic parenteral vaccination or intravenous immunotherapy could provide protection from C. difficile disease in humans.

[Clostridium difficile as an inducer of inflammatory diarrhea]

Clostridium difficile has been pointed out as an important agent of diarrheal diseases associated with antibiotic use. However, due to its complexity, the physiopathology of these diseases is only partially elucidated, although a series of scientific works has demonstrated the importance of toxins A and B in the pathogenesis of the inflammatory diarrhea induced by this microorganism. The inflammatory mechanisms involved in the biological activities of these toxins are complex. There are some studies demonstrating that toxin B has no enterotoxic activity in vivo. However, this toxin causes dose-dependent eletrophysiologic and morphologic modifications of human colonic mucosa in vitro. In addition, toxin B stimulates the synthesis of potent inflammatory mediators by monocytes and macrophages. The effects provoked by toxin A on the intestinal mucosa are quite evident and are characterized by intense fluid secretion and by inflammatory cell accumulation, such as macrophages, mast cells, lymphocytes and neutrophils, with the consequent release of mediators such as prostaglandins, leukotrienes, platelet activating factor, nitric oxide and cytokines.

Intestinal secretory factor released by macrophages stimulated with Clostridium difficile toxin A: role of interleukin 1beta

Clostridium difficile toxin A is associated with enterocolitis in animals and humans. However, the mechanisms of its secretory and damaging effects are not totally understood. In this work, we examined the intestinal secretion of electrolytes and water caused by supernatants from macrophages stimulated with toxin A in rabbit ileal mucosa mounted in Ussing chambers. We also investigated the mechanism by which the intestinal secretory factor (ISF) is released from stimulated macrophages. Supernatants from macrophages stimulated with toxin A caused potent intestinal secretion (change in short-circuit current [DeltaIsc], 76 microA x cm-2; P < 0.01). The release of the ISF was pertussis toxin sensitive (reduction, 61%; P < 0.01) and was also reduced (P < 0.05) by a protein synthesis inhibitor (67%), protease inhibitors (57%), a phospholipase A2 inhibitor (54%), a cyclo-oxygenase inhibitor (62%), a dual cyclo- and lipoxygenase inhibitor (48%), a platelet-activating factor (PAF) receptor antagonist (55%), and tumor necrosis factor alpha (TNF-alpha) synthesis inhibitors (48%). However, this release was not inhibited by a lipo-oxygenase inhibitor. Monoclonal anti-interleukin 1beta (IL-1beta) but not anti-IL-1alpha antibody blocked (72%; P < 0.01) the secretory action of the ISF, as did recombinant human IL-1 receptor antagonist (80%; P < 0.01). High levels of IL-1beta (3,476 pg/ml) were detected by an enzyme-linked immunosorbent assay in the above supernatants. Furthermore, the addition of IL-1beta to the serosal side caused a potent secretory effect (DeltaIsc, 80 microA x cm-2; P < 0.01). These results show that macrophages stimulated with toxin A release an ISF capable of provoking intestinal secretion. The regulation of this factor is dependent upon the activation of the G protein. In addition, prostaglandins, PAF, and TNF-alpha are involved in the release of the ISF. We conclude that IL-1beta is probably the ISF released by macrophages in response to toxin A.

In vitro effects of Clostridium difficile toxins on hepatocytes

BACKGROUND

Clostridium difficile infections are associated with development of the systemic inflammatory response, including the production of hepatic acute phase proteins. Lipopolysaccharide (LPS) directly stimulates the production of at least one of these proteins, a 23-kDa acute phase protein (the LPS-induced protein, or LIP) by murine hepatocytes in vitro. The aim of the present study was to determine if C. difficile toxins also stimulated the synthesis of this protein in vitro.

METHODS

Cultured murine hepatocytes were treated for 24 h with various concentrations of C. difficile culture extract or purified toxins A and B in the presence or absence of dexamethasone or interleukin-1 (IL-1) receptor antagonist (IL-1 RA). The cells were then metabolically radiolabeled with [35S]methionine. Secretory proteins were identified using electrophoresis and autoradiography, and their synthesis was quantitated by image analysis of the autoradiograms.

RESULTS

The C. difficile culture extract, at dilutions as low as 1:200,000, significantly stimulated LIP synthesis in vitro. Toxins A and B, at concentrations as low as 1.6 and 0.02 pg/ml, respectively, also induced production of this protein. Dexamethasone further augmented C. difficile toxin-stimulated synthesis of LIP, but IL-1 RA inhibited the effects of these toxins on the synthesis of this protein. Only minimal quantities of IL-1 were found in culture supernatants following treatment with the toxins.

CONCLUSIONS

C. difficile toxins A and B, at very low concentrations, stimulate hepatocyte acute phase protein synthesis. Even though IL-1 RA inhibits this process, it does not appear that local production of IL-1 mediates the action of these toxins.

Effects of toxin A from Clostridium difficile on mast cell activation and survival

Toxins A and B from Clostridium difficile are the main cause of antibiotic-associated diarrhea and pseudomembranous colitis. They cause fluid accumulation, necrosis, and a strong inflammatory response when inoculated in intestinal loops. Since mast cells are a rich source of inflammatory mediators, abundant in the gut, and known to be involved in C. difficile-induced enteritis, we studied the in vitro effect of toxin A on isolated mast cells. Normal rats sensitized by infection with Nippostrongilus brasiliensis were used to isolate peritoneal mast cells (PMC). PMC from naive rats were stimulated with calcium ionophore A23187 as a model of antigen-independent activation, and PMC from sensitized rats were stimulated with N. brasiliensis antigens to study immunoglobulin E-dependent mast cell activation. After 4 h, toxin A did not induce release of nitric oxide or histamine in naive PMC. However, 10 ng of toxin per ml caused a significant release of tumor necrosis factor alpha (TNF-alpha). In contrast, 1 microg of toxin per ml inhibited antigen or A23187-induced histamine release by PMC. Toxin A at 1 microg/ml for 4 h caused disruption of actin which aggregated in the cytoplasm and around the nucleus. After 24 h, chromatin condensation, cytoplasmic blebbing, and apoptotic-like vesicles were observed; DNA fragmentation was documented also. These results suggest that mast cells may participate in the initial inflammatory response to C. difficile infection by releasing TNF-alpha upon interaction with toxin A. However, longer exposure to toxin A affects the release of inflammatory mediators, perhaps because of the alteration of the cytoskeleton and induction of apoptosis. The impaired functions and survival of mast cells by C. difficile toxin A could hamper the capacity of these cells to counteract the infection, thus prolonging the pathogenic effects of C. difficile toxins.

Interactions between bacterial toxins and intestinal cells

Bacterial toxins which act on intestinal cells display a great diversity of size, structure and mode of action. Some toxins interact with the cell by transducing a signal across the membrane leading to stimulation of intracellular second messenger (E. coli heat stable enterotoxin), others form pores (C. perfringens enterotoxin, ...) permitting the leakage of cellular components and cell lysis. The most sophisticated toxins comprise at least two functional domains or components, one being a binding domain permitting the internalization into the cell of an enzymatic domain which modifies an intracellular target. The enzymatic modification (ADP-ribosylation, UDP-glucosylation, glycohydrolysis, proteolysis, ...) of a specific target (heterotrimeric G-protein, small G-protein, monomeric actin, ribosomal RNA, ...) alters the cell physiology (increase of ions and water secretion, cytoskeleton rearrangement, protein synthesis inhibition, apoptosis, ...) and tissue organization (modification of barrier permeability, necrosis, ...). The study of bacterial toxins leads to the understanding of the interactions between pathogenic bacteria and their hosts and constitutes also a new approach in cell biology, by facilitating the exploration of certain regulatory pathways such as that controlling actin polymerization.

IL-8 release and neutrophil activation by Clostridium difficile toxin-exposed human monocytes

Neutrophil infiltration is central to the pathogenesis of Clostridium difficile toxin A-induced enterocolitis. This study examines whether monocyte activation by C. difficile toxins is instrumental in initiating neutrophil activation and recruitment. Human monocytes were exposed to low concentrations of highly purified C. difficile toxins, and the conditioned media were harvested for cytokine and functional assays. Monocytes exposed to C. difficile toxin A (10(-10) M) or toxin B (10(-12) M) released 100 and 20 times basal levels, respectively, of the neutrophil chemoattractant interleukin-8 (IL-8). Reverse transcriptase-polymerase chain reaction demonstrated a marked increase in IL-8 mRNA expression by monocytes 3 h after toxin exposure. Conditioned media from toxin A- and toxin B-treated monocytes stimulated neutrophil migration (324 and 245% of control, respectively). This effect was completely blocked by IL-8 antiserum. These media also upregulated neutrophil CD11b/CD18 and endothelial cell intercellular adhesion molecule-1 expression. C. difficile toxins, at low concentrations, potently activate monocytes to release factors, including IL-8, that facilitate neutrophil extravasation and tissue infiltration. Our findings indicate a major role for toxin-mediated monocyte and macrophage activation in C. difficile colitis.

Are bacterial exotoxins cytokine network regulators?

Bacterial exotoxins are generally thought to act by damaging cells or altering cell metabolism. However, recent work has established that many exotoxins modulate eukaryotic cell cytokine synthesis. Cytokine induction may play a significant role in exotoxin action, and therapeutic targeting of cytokines could be beneficial in infectious diseases involving bacterial exotoxins.

Epidermal growth factor attenuates Clostridium difficile toxin A- and B-induced damage of human colonic mucosa

Epidermal growth factor (EGF) exhibits a cytoprotective effect on gastrointestinal epithelia via a receptor-mediated mechanism. We investigated the effect of EGF on Clostridium difficile toxin A (TxA)- and toxin B (TxB)-induced damage of human colon. Ussing-chambered colonic mucosa was exposed serosally to EGF before and during luminal exposure to TxA and TxB. Resistance was calculated from potential difference and short-circuit current. Epithelial damage was assessed by light microscopy and alteration of F-actin by fluoresceinated phalloidin. Luminal exposure of colonic strips to TxA and TxB caused a time- and dose-dependent decrease in electrical resistance, necrosis and dehiscence of colonocytes, and disruption and condensation of enterocyte F-actin. These effects were inhibited by prior, but not simultaneous, serosal application of EGF (20 nM). Administration of the tyrosine kinase inhibitor genistein (10(-6) M) inhibited the protective effects of EGF. We conclude that EGF protects against TxA and TxB probably by stabilizing the cytoskeleton, the main target of these toxins.

Clostridium difficile toxin A induces the release of neutrophil chemotactic factors from rat peritoneal macrophages: role of interleukin-1beta, tumor necrosis factor alpha, and leukotrienes

Clostridium difficile produces a potent enterotoxin and cytotoxin, toxins A and B, respectively, which appear to be responsible for pseudomenbranous colitis and antibiotic-associated diarrhea. In the present study we explored the neutrophil migration evoked by toxin A in the peritoneal cavities and subcutaneous air pouches of rats and examined the role of macrophages and their inflammatory mediators in this process. Toxin A causes a significant dose-dependent neutrophil influx into the peritoneal cavity, with a maximal response at 0.1 microg/ml and at 4 h. The depletion of macrophages by peritoneal washing prevents the toxin A-induced neutrophil migration into the peritoneal cavity. In contrast, an increase in macrophages induced by peritoneal injection of thioglycolate amplifies this toxin effect on neutrophil migration. Furthermore, the injection of supernatants from toxin A-stimulated macrophages into the rat peritoneal cavity causes significant neutrophil migration. Pretreatment of rats with BWA4C, nordihydroguaiaretic acid, mepacrine, or dexamethasone inhibits the neutrophil migration evoked by toxin A in the peritoneal cavities. However, pretreatment with the cyclooxygenase inhibitor indomethacin or the platelet-activating factor antagonist BN52021 fails to alter toxin A-induced neutrophil migration. Toxin A was also injected into air pouches of normal rats or rats pretreated with anti-interleukin-1beta (anti-IL-1beta) or anti-tumor necrosis factor alpha (anti-TNF-alpha) antibodies. Anti-TNF-alpha or anti-IL-1beta antibodies significantly reduce the neutrophil migration induced by toxin A. These data suggest that neutrophil migration evoked by toxin A is in part dependent on macrophage-derived cytokines, such as TNF-alpha and IL-1beta, and leukotrienes. These mediators may help to explain the intense inflammatory colitis caused by C. dificile toxin A in an experimental animal model of this disease.

The involvement of macrophage-derived tumour necrosis factor and lipoxygenase products on the neutrophil recruitment induced by Clostridium difficile toxin B

Clostridium difficile (Cd) toxins appear to mediate the inflammatory response in pseudomembranous colitis and/or colitis associated with the use of antibiotics. In contrast to Cd Toxin A (TxA), Cd Toxin B (TxB) has been reported not to promote fluid secretion or morphological damage in rabbits and hamsters and also does not induce neutrophil chemotaxis in vitro. However, TxB is about 1000 times more potent than TxA in stimulating the release of tumour necrosis factor-alpha (TNF-alpha) by cultured monocytes. In the present study, we investigated the ability of TxB to promote neutrophil migration into peritoneal cavities and subcutaneous air-pouches of rats. We also examined the role of resident peritoneal cells in this process as well as the inflammatory mediators involved. TxB caused a significant and dose-dependent neutrophil influx with a maximal response at 0.1 microgram/cavity after 4 hr. Depleting the peritoneal resident cell population by washing the peritoneal cavity or increasing this population by pretreating the animals with thioglycollate blocked and amplified the TxB-induced neutrophil migration, respectively. Pretreating the animals with MK886 (a lipoxygenase inhibitor), NDGA (a dual cyclo- and lipoxygenase inhibitor) or the glucocorticoid, dexamethasone, but not with indomethacin (a cyclo-oxygenase inhibitor), or BN52021 (a platelet-activating factor antagonist), inhibited the neutrophil migration evoked by TxB. Pretreatment with dexamethasone or the administration of anti-TNF-alpha serum into the air-pouches also significantly reduced the TxB-induced neutrophil migration. Supernatants from TxB-stimulated macrophages induced neutrophil migration when injected into the rat peritoneal cavity. This effect was attenuated by the addition of either MK886 or dexamethasone to the macrophage monolayer and by preincubating the supernatants with anti-TNF-alpha serum. TxB also stimulated the release of TNF-alpha by macrophages. Overall, these results suggest that TxB induces an intense neutrophil migration which is mediated by macrophage-derived TNF-alpha and lipoxygenase products.

Role of tumor necrosis factor and nitric oxide in the cytotoxic effects of Clostridium difficile toxin A and toxin B on macrophages

Clostridium difficile, the bacterium involved in antibiotic-associated colitis, produces two exotoxins, toxin A (TxA) and toxin B (TxB). Although these toxins are well recognized as being cytotoxic to several mammalian cell types, the mechanisms involved are not fully understood. The aim of the present investigation was to examine the cytotoxicity of TxA and TxB to peritoneal macrophages in culture and to investigate whether tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) are involved in the process. As a control, the effect of E. coli LPS was also investigated. TxA, TxB and LPS were dose-dependently cytotoxic to macrophage monolayers, with TxB being the most potent. All of the toxins stimulated the release of TNF-alpha from macrophages. TxB was again the most active in inducing this response. The TNF-alpha released appears to be involved in the action of LPS and TxA, but not of TxB, since a mAb against TNF-alpha inhibited the cytotoxicity of the former two but had no effect on the latter. NO is not involved in the effects of TxA and TxB since these toxins did not induce the production of this mediator in macrophages, even in the presence of IFN-gamma. In addition, L-imino-ethyl-L-ornithine (L-NIO), a NO synthase inhibitor, did not modify the macrophage death caused by TxA or TxB. Although LPS was able to induce the production of high amounts of NO, NO did not mediate the LPS cytotoxicity since L-NIO did not influence the degree of macrophage death caused by LPS. TxA and TxB therefore appear to exert cytotoxic effects on cultured macrophages by different mechanisms. TNF-alpha is involved in TxA and LPS-mediated cytotoxicity but not in the toxicity caused by TxB. NO is not involved in the killing action of any of these toxins.

Microbial/host interactions in health and disease: who controls the cytokine network?

The interacting cellular and molecular systems which we classify as immunity and inflammation evolved to protect the organism from exogenous parasites including viruses and bacteria. Cytokines play a pivotal, but paradoxical, role both in immunity and inflammation. These local peptide hormone-like molecules form a major arm of the organisms, defenses against infectious microorganisms but they are also implicated as potent mediators of the pathology of infectious diseases. The apparently lethal effects of interleukin-1 and tumor necrosis factor in experimental septic shock testify to the latter. In the current paradigm, cytokine induction, as a protective or pathological mechanism, is a direct response to the presence of infectious microorganisms. Evidence is now accumulating that cytokines play a much more complex role in the interplay between exogenous microorganisms and the host. For example, it has been established that viruses have evolved pro-active methods of subverting the cytokine network by producing: (i) soluble cytokine receptors which bind and inactivate cytokines, (ii) immunomodulatory cytokine homologues, and (iii) ICE inhibitors. The possibility exists that the major role of these 'viral cytokines' is to neutralize certain host responses. Recent cytokine transgenic knockouts demonstrate that the normal benign response to commensal gut microflora becomes a lethal inflammatory state in the absence of the cytokines interleukin 2 or interleukin 10. The human body contains an enormous number of microorganisms which constitute the normal microflora. It is estimated that the average human contains 10(13) eukaryotic cells but 10(14) bacteria. We propose that the ability of the multicellular organism to live harmoniously with its commensal microflora must depend on mutual signalling involving eukaryotic cytokines and prokaryotic cytokine-like molecules. Such interactive signalling sets up non-inflammatory cytokine networks in tissues which form the background on which responses to infectious microorganisms must be built and related. The capacity of bacteria to induce cytokine synthesis was believed to be due to a small number of components, such as lipopolysaccharide (LPS), which is only active as a complex with host factors (lipopolysaccharide binding protein and CD14). However, it is now clear that bacteria contain and produce a large number of diverse molecules which can selectively induce the synthesis of both pro-inflammatory and immunomodulatory/anti-inflammatory cytokines. Many toxins are potent inducers of cytokine release or synthesis and some can inhibit LPS-induced cell activation. We have introduced the term bacteriokine to describe these bacterial cytokine inducers. The question that has to be addressed therefore is - who controls the cytokine network (eukaryotic or prokaryotic cells) and how is it controlled? It is proposed that an understanding of this question will bring with it an understanding of how to control the pathological inflammatory response and may allow the development of truly effective anti-inflammatory agents.

Effect of Clostridium difficile toxin A on CD11/CD18 expression in vitro

Clostridium difficile toxin A is chemotactic for neutrophils and induces their emigration into the colonic mucosae of rodents. We found that toxin A did not upregulate neutrophil beta 2 integrins on isolated human neutrophils. These data support the hypothesis that in C. difficile colitis, these adhesion molecules are upregulated by endogenous mediators.