Division of Gastroenterology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
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-B. 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.
intestinal inflammation; neuropeptides; Rho proteins; mast cells; neutrophils
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
SINCE ITS IDENTIFICATION 20 years ago as the major cause of antibiotic-associated pseudomembranous colitis, Clostridium difficile has now emerged as the leading cause of nosocomial enteric infections, with an estimated annual incidence of more than 3 million cases in the United States. C. difficile produces colitis entirely by the action of two potent exotoxins, toxin A (308 kDa) and toxin B (270 kDa). C. difficile toxins can trigger profound intestinal inflammation (colitis), in contrast to cholera toxin and Escherichia coli enterotoxin, which elicit secretion (diarrhea) without an acute inflammatory component. The bacterium itself is not invasive, and all of the pathological manifestations are related to an integrated hierarchy of proinflammatory signals triggered by binding of toxins to their receptors located on the apical (luminal) surface of enterocytes. The mechanisms of C. difficile toxins can be divided into two broad categories: direct actions on enterocytes and indirect actions on lamina propria cells triggered by cytokines, neuropeptides, and other neuroimmune mediators. Our review focuses on how these two mechanisms produce a complex pathophysiological response involving specific neuroimmune and inflammatory pathways.
![]() |
STRUCTURE OF C. DIFFICILE TOXINS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Toxins A and B are encoded by two very large genes (Fig.
1) present in all toxigenic strains of
C. difficile (17). The toxin A gene (8,130 nucleotides) encodes one of the largest bacterial toxins known (2,710 amino acids, mol. mass 308 kDa). Toxin A, often referred to as the
"enterotoxin," produces fluid secretion and a necroinflammatory
response in intestinal loops of experimental animals. The toxin B gene
(7,098 bp) encodes a 2,366-amino acid protein (mol. mass 270 kDa) that
possesses potent cytotoxic activity against cells in culture but no
enterotoxic effects in rodent or rabbit models. Recent experiments in
human intestinal explants exposed in vitro to pure toxins
indicate that both toxins possess enterotoxic activity in human colon,
thus making the designations "enterotoxin" and "cytotoxin"
rather nonspecific.
|
The two toxins are closely related to each other, with 49% amino acid
identity and similar overall structure. They are members of a family of
related toxins from C. sordelli and C. novyi,
which share considerable sequence homology (23). The
enzymatic (catalytic) domain containing the critical
glucosyltransferase activity is expressed in the first 550 NH2-terminal amino acids of both toxins, and the receptor
binding domain resides in the COOH-terminal one-third of toxin A and
probably also in toxin B, although this has not yet been proven
(11, 12). Deletion mutants of toxin B lacking the
COOH-terminal repeats have a 10-fold reduction in cytotoxicity compared
with holotoxin, whereas removal of the repeat region plus the conserved
cysteine at position 1625 causes complete loss of activity. The
receptor binding domain in toxin A consists of repeating units of
20-30 amino acids that function as a multivalent lectin with high
binding specificity for the trisaccharide
Gal1-3Gal
1-4GlcNAc (15). This structure is
thought to bind toxin A to its intestinal receptor in rodents and other
animals but not in humans, who lack the
-galactosyltransferase
required for assembly of this trisaccharide. This implies that binding
of toxin A to human enterocytes involves a different oligosaccharide or
possibly a protein-protein interaction.
The NH2-terminal glucosyltransferase domain is also critical for toxin action. As discussed below, the molecular targets of this enzyme activity are low-molecular-weight GTPases of the Rho family (Rho ABC, Rac, and CDC 42), key regulators of cellular actin (9). A 63-kDa fragment comprising the first 546 amino acids of toxin B contains the glucosyltransferase activity and causes cell rounding when microinjected into target cells. By itself, this fragment is nontoxic because it is unable to bind the receptor and enter the cell. The middle portion of these toxins, between the NH2-terminal one-third carrying the catalytic function and the COOH-terminal repeats, may be involved with cellular uptake and processing. Mutant toxins deleted of the middle third but containing intact catalytic and binding domains have sharply reduced cytotoxicity. Site-directed mutagenesis and deletion mutations should allow more precise assignment of structure-function relationships of C. difficile toxins.
![]() |
RECEPTOR BINDING AND INTERNALIZATION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The specific cell surface receptors for toxins A and B have
not yet been identified, although some information on receptor structure and function is available. The observations that nearly all
cultured cells as well as freshly isolated neutrophils, lymphocytes, and macrophages are sensitive to these toxins suggests that their receptors are ubiquitous on mammalian cells. As noted above, the trisaccharide Gal1-3Gal
1-4GlcNAc, expressed in all
mammals and some nonhuman primates, is required in some cells for toxin
A binding. It is likely that the mammalian cell receptor is a
glycoprotein, whereas on rabbit erythrocytes toxin A binds to a cell
surface glycolipid. Rabbit intestinal sucrase-isomaltase binds toxin
even when expressed in nonintestinal cells, and antibody to this
digestive enzyme blocks toxin A fluid secretion in rabbit ileal loops
(19). However, this enzyme is not expressed in adult colon
and therefore is not likely to be a colonocyte receptor. The
carbohydrate antigens I, X, and Y, all of which are expressed on human
colonocytes, bind toxin A, but the functional role of such binding is unknown.
Once toxin A binds to its plasma membrane receptor, internalization begins within minutes. Toxin-receptor binding is irreversible within a few minutes, after which time rescue of cells with antitoxins or by washing is ineffective. After 5-10 min toxin is localized to mitochondria, and this binding is accompanied by a precipitous fall in intracellular ATP concentrations, release of mitochondrial cytochrome c, and generation of reactive oxygen species (10). Mitochondrial dysfunction has been observed in toxin A-exposed Chinese hamster ovary cells and human colonic cell lines and occurs well before the onset of Rho glucosylation at 15-30 min. Toxin A also appears to localize to a lysosomal compartment, because prior treatment of cells with ammonium chloride or chloroquine partially prevents cell rounding. It is not yet known whether internalized toxins require processing in acid compartments or by activating proteases or if they preferentially modify Rho proteins segregated in a specific organelle or in the cytoplasm.
![]() |
RHO GLUCOSYLATION AND CYTOSKELETAL DAMAGE |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
C. difficile toxins catalyze the transfer of glucose from UDP-glucose to threonine-37 in Rho A and threonine-35 in Rac and Cdc 42, rendering these signaling proteins nonfunctional (1). Rho proteins are critical regulators of a large and growing number of cell functions including the formation of actin-containing stress fibers, cell-cell contacts, regulation of tight junctions, and membrane trafficking. Impairment of Rho function by C. difficile toxins leads to disaggregation of actin-containing stress fibers, loss of adhesion, and cell rounding of tissue culture cells. In human colonic epithelial cell lines and human colonic explants, both toxins dose-dependently impair tight junction function with increased paracellular permeability, loss of the perijunctional actinomyosin ring, and diminished electrical resistance (21). Increased blood-to-lumen permeability is also observed in vivo in rat and rabbit intestine exposed to toxin A. Subsequent events in intoxicated cells include diminished protein synthesis, reduced cell division, and apoptosis or necrosis.
As discussed in detail below, toxin A produces a severe acute necroinflammatory reaction in the mammalian small and large intestine that involves activation of mast cells, nerves, vascular endothelium, and immune cells. Because the toxins bind to apical receptors facing the lumen and are too large to be transported intact into the plasma, it is presumed that this integrated inflammatory response results from cytokines or other mediators released by enterocytes, but the details of this linkage are still not complete. It is likewise not clear whether Rho inactivation is essential for cytokine release or whether other Rho-independent effects of toxins (for example, mitochondrial dysfunction) may activate epithelial and other cell types.
An important early event in C. difficile pathogenesis is
activation of nuclear factor-B (NF-
B) with subsequent release of neutrophil chemoattractants. Macrophage inflammatory protein 2 (MIP-2),
a potent neutrophil chemoattractant in rodents, is secreted by rat
macrophages and epithelial cells after exposure to inflammatory stimuli. MIP-2 mRNA and protein are elevated in rat ileal epithelial cells 30 min after intraluminal exposure to toxin A (4).
Pretreatment of rats with an antibody to MIP-2 significantly blocked
the enterotoxicity of toxin A (4), suggesting that
enterocyte release of MIP-2 is a major early signal in the enterotoxic
cascade. However, these results would not explain the observation that
rat intestinal mast cells and substance P (SP)-containing neurons are
activated before MIP-2 release.
Several observations support the evolving hypothesis that some important cellular responses to C. difficile toxins may occur before (and independently of) Rho glucosylation. For example, mitochondrial damage from toxins A and B occurs before Rho glucosylation and may be an important mechanism of interleukin (IL)-8 release in enterocytes. We recently reported that p38 mitogen-activated protein (MAP) kinase activation after toxin A exposure is independent of Rho and is the major signal transduction pathway for IL-8 release (24). Thus the classic teaching that the enzymatic effect of C. difficile toxins is required for toxicity may not be entirely correct, but further exploration of these potentially important non-Rho pathways is required to allow a more definitive statement.
![]() |
TOXIN A IS A PROINFLAMMATORY ENTEROTOXIN |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
One of the primary features of C. difficile colitis in
humans is the presence of an inflammatory infiltrate in the colonic mucosa characterized by epithelial cell necrosis and presence of
neutrophils in the colonic lumen. Experiments in intact animals demonstrated that injection of toxin A into ileal or colonic loops stimulates secretion of fluid accompanied by increased mucosal permeability, epithelial cell destruction, and neutrophil infiltration (4, 5, 18). This is in contrast to cholera toxin and
E. coli enterotoxins, which trigger intestinal secretion
without intestinal inflammation. The mechanism of toxin A-mediated
intestinal secretion and inflammation involves activation of neurons
and immune and inflammatory cells in the intestinal mucosa, leading to
release of proinflammatory mediators and recruitment of neutrophils (Fig. 2). Several mediators are released
in the intestinal mucosa in response to toxin A, including leukotriene
(LT)B4, PGE2, and tumor necrosis factor
(TNF)- in animal intestine (3, 6, 22) and IL-8 in human
colon (2). Furthermore, administration of drugs that
reduce cytokine synthesis results in a reduction of the intestinal
effects of toxin A (22), indicating that proinflammatory cytokines mediate part of the in vivo responses to this toxin. However,
toxin A is also able to directly activate monocytes to release IL-1
and IL-6 (8) and increase neutrophil migration in vitro
(14). These responses may be important in the pathogenesis of toxin A-induced enterocolitis after the inflammation is established, allowing toxin A to cross the epithelial cell barrier and activate cells of the lamina propria.
|
Role of neutrophils and mast cells. Several studies indicate that neutrophil activation and transmigration are important determinants in the pathophysiology of toxin A enterocolitis. Neutrophil-derived proinflammatory mediators act on epithelial cells, causing destruction and necrosis of enterocytes and colonocytes (22). The pathophysiological importance of neutrophils in the in vivo mechanism of toxin A is underscored by the significant inhibition of fluid secretion and inflammation when neutrophil infiltration is inhibited by administration of antibodies directed against the leukocyte adhesion molecule CD18 or against the potent chemoattractant MIP-2 (4, 14). Induction of neutropenia in rats resulted in a significant inhibition of toxin A-mediated ileal secretory and inflammatory changes (20).
Intestinal mast cells are critically involved in neutrophil activation in toxin A-mediated inflammation. Mucosal mast cells are activated after administration of toxin A into the intestinal lumen, as evidenced by the increased mucosal and circulating levels of the specific mucosal mast cell enzyme rat mast cell protease II (RMCP II) and by electron microscopy studies demonstrating significant degranulation of mucosal mast cells 15-30 min after toxin A exposure (5). Administration of mast cell inhibitors not only reduced the intestinal levels of mast cell-derived mediators but also attenuated toxin A-induced neutrophil activation and fluid secretion. Using intravital microscopy in toxin A-exposed rat mesenteric venules, Kurose et al. (16) showed substantially increased leukocyte adherence and emigration at 15-30 min of toxin A exposure that were associated with mast cell degranulation and albumin leakage. In addition, toxin A-induced increased albumin leakage was significantly reduced by pretreatment with the mast cell blocker lodoxamide, the histaminase diamine oxidase, or the histamine receptor subtype 1 (H1) antagonist hydroxyzine (16). Thus histamine is responsible, at least in part, for the leukocyte-endothelial cell adhesion in response to toxin A by interacting with H1 receptors on endothelial cells. Experiments using mice genetically deficient in mast cells provide evidence for the critical involvement of mast cells in the secretory and inflammatory effects of toxin A. Previous studies demonstrated that these animals do not contain mast cells in the periphery, including the gastrointestinal tract. Compared with normal mice, mast cell-deficient mice had significantly attenuated fluid secretion and neutrophil infiltration after toxin A administration (25). Reconstitution of mast cell-deficient mice with mast cells obtained from normal mice restored toxin A-associated responses (25). These results strongly suggest that mast cell activation represents a major step in the expression of toxin A-mediated enteritis and that neutrophil recruitment in response to this enterotoxin is strongly mast cell dependent.Nitric oxide as a mediator of the toxin A inflammatory response. Nitric oxide (NO) is an important modulator of intestinal injury and inflammation. Because NO is involved in mast cell degranulation, leukocyte adherence, and mucosal permeability, it seemed likely that NO may be involved in toxin A-associated changes in rat ileum. We found that the toxin A-induced increases in mannitol permeability and secretion of fluid were enhanced in animals treated with either the NO synthase inhibitor nitro-L-arginine methyl ester (L-NAME) or the neuronal NO synthase inhibitor 7-nitroindazole, whereas pretreatment of rats with the NO donor S-nitroso-N-acetyl-L-cysteine (SNAC) substantially inhibited these toxin A responses (20). Mast cell degranulation and neutrophil infiltration occurring after ileal injection of toxin A were also blocked by the NO donor SNAC (20). These results suggest that NO, probably of neuronal origin, protects the intestinal mucosa from the effects of toxin A by reducing mast cell degranulation and neutrophil infiltration activated by this toxin.
Role of neuropeptides and nerve-immune cell interactions.
One of the highlights of C. difficile toxin A
pathophysiology is the dependence of the toxin A-associated intestinal
responses on activation of intestinal nerves and neuropeptides. Early
experiments using anesthetized animals demonstrated that either local
application of the anesthetic lidocaine or systemic administration of
the ganglionic blocker hexamethonium dramatically inhibited toxin A-induced ileal fluid secretion and mucosal permeability and
inflammation (5). Interestingly, chronic administration of
capsaicin, a neurotoxin that desensitizes primary sensory neurons,
almost completely normalized the intestinal effects of toxin A,
including degranulation of mucosal mast cells (5). These
results suggested a major role for primary sensory neurons in the
induction of toxin A-mediated enteritis. Because SP and calcitonin
gene-related peptide (CGRP) are the major constituents of primary
sensory neurons, we tested the possibility that these peptides are
involved in the intestinal effects of toxin A. Administration of either
nonpeptide SP receptor antagonists or a peptide CGRP antagonist to rats
dramatically reduced intestinal secretion, mucosal permeability, and
release of proinflammatory cytokines from the intestinal mucosa in
response to toxin A (13, 18), suggesting a proinflammatory
role for these peptides during toxin A enteritis. Consistent with these observations, administration of toxin A into ileal segments led to an
early (30 min) increase of SP and CGRP mRNA and increased content of
these peptides in the cell bodies of spinal dorsal root ganglia
followed by increased SP and CGRP expression in the intestinal mucosa
(3, 13). In addition, lamina propria macrophages, activated during the inflammatory response to toxin A, express high-affinity (neurokinin-1; NK-1) receptors for SP and binding of SP
to these receptors leads to release of the potent chemokine TNF-
(3). A major role for SP and its NK-1 receptor in
the mediation of the enterotoxic effects of toxin A is further
supported by recent results showing that mice lacking NK-1 receptors
have significantly attenuated intestinal responses to toxin A
(6). Thus activation of primary sensory afferent nerves
and binding of the sensory peptides SP and CGRP to receptors on mucosal
immune cells represent a major amplification system that controls the in vivo effects of toxin A.
![]() |
SUMMARY |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
The mechanism of enterotoxin action has been expanded considerably in the past several decades after the pioneering experiments of Lundgren and colleagues, who showed the critical role of the neuroimmune system in the physiological responses to toxins and other secretagogues. Cholera toxin, the prototypical enterotoxin, produces a fluid secretory response that is dependent on the activation of enteric neural pathways mediated by cholinergic and vasoactive intestinal polypeptide (VIP)-dependent nerves. C. difficile toxin A exerts its potent secretory and necroinflammatory responses in mammalian intestine by a separate neural pathway involving the activation of mucosal mast cells and release of SP and CGRP from sensory neurons. The cholera toxin and toxin A neural pathways are distinct and specific with no molecular or junctional overlap. Their function appears to be amplification of initiating signals in enterocytes after binding of small amounts of toxins to enterocyte receptors facing the lumen. It seems likely that parallel but separate neuroimmune pathways exist for other toxins and luminal secretagogues (e.g., bile salts). Elucidation of the elements of these amplification pathways should lead to better control of diarrheal diseases arising from a wide variety of causes.
![]() |
ACKNOWLEDGEMENTS |
---|
This work was supported by National Institute of Diabetes and Digestive and Kidney Diseases Grants DK-47343 to C. Pothoulakis and DK-34583 to J. T. LaMont and by funding from the Crohn's and Colitis Foundation of America Inc.
![]() |
FOOTNOTES |
---|
Address for reprint requests and other correspondence: C. Pothoulakis, Beth Israel Deaconess Medical Center, Harvard Medical School, Div. of Gastroenterology, Dana 601, 330 Brookline Ave., Boston, MA 02115 (E-mail: cpothoul{at}caregroup.harvard.edu).
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
1.
Aktories, K,
and
Just I.
Monoglucosylation of low-molecular-mass GTP-binding Rho proteins by clostridial cytotoxin.
Trends Cell Biol
5:
441-443,
1995[ISI].
2.
Branka, JE,
Vallette G,
Jarry A,
Bou-Hanna C,
Lemarre P,
Van PN,
and
Laboisse CL.
Early functional effects of Clostridium difficile toxin A on human colonocytes.
Gastroenterology
112:
1887-1894,
1997[ISI][Medline].
3.
Castagliuolo, I,
Keates AC,
Qiu BS,
Kelly CP,
Nikulasson ST,
Leeman SE,
and
Pothoulakis C.
Increased substance P responses in dorsal root ganglia and intestinal macrophages during Clostridium difficile toxin A enteritis in rats.
Proc Natl Acad Sci USA
94:
4788-4793,
1997
4.
Castagliuolo, I,
Keates AC,
Wang CC,
Pasha A,
Valenick L,
Kelly CP,
Nikulasson ST,
LaMont JT,
and
Pothoulakis C.
Clostridium difficile toxin A stimulates macrophage inflammatory protein-2 production in rat intestinal epithelial cells.
J Immunol
160:
6039-6045,
1998
5.
Castagliuolo, I,
LaMont JT,
Letourneau R,
Kelly CP,
O'Keane JC,
Jaffer A,
Theoharides TC,
and
Pothoulakis C.
Neuronal involvement in the intestinal effects of Clostridium difficile toxin A and Vibrio cholerae enterotoxin.
Gastroenterology
107:
657-665,
1994[ISI][Medline].
6.
Castagliuolo, I,
Riegler M,
Nikulasson S,
Lu B,
Gerard C,
Gerard NP,
and
Pothoulakis C.
NK-1 receptor is required in Clostridium difficile-induced enteritis.
J Clin Invest
101:
1547-1550,
1998
7.
Castagliuolo, I,
Wang CC,
Valenick L,
Pasha A,
Nikulasson S,
Carraway RE,
and
Pothoulakis C.
Neurotensin is a proinflammatory peptide in colonic inflammation.
J Clin Invest
103:
843-849,
1999
8.
Flegel, WA,
Muller F,
Daubener W,
Fischer HG,
Hadding U,
and
Northoff H.
Cytokine response by human monocytes to Clostridium difficile toxin A and B.
Infect Immun
59:
3659-3666,
1991[ISI][Medline].
9.
Hall, A.
Rho GTPases and the actin cytoskeleton.
Science
279:
509-514,
1998
10.
He, D,
Hagen SJ,
Pothoulakis C,
Chen M,
Medina ND,
Warny M,
and
LaMont JT.
Clostridium difficile toxin A causes early damage to mitochondria in cultured cells.
Gastroenterology
119:
139-150,
2000[ISI][Medline].
11.
Hofmann, F,
Busch C,
and
Aktories K.
Chimeric clostridial cytotoxins: identification of the N-terminal region involved in protein substrate recognition.
Infect Immun
66:
1076-1081,
1998
12.
Hofmann, F,
Busch C,
Prepens U,
Just I,
and
Aktories K.
Localization of the glucosyltransferase activity of Clostridium difficile toxin B to the N-terminal part of the holotoxin.
J Biol Chem
272:
11074-11078,
1997
13.
Keates, AC,
Castagliuolo I,
Qiu B,
Nikulasson S,
Sengupta A,
and
Pothoulakis C.
CGRP upregulation in dorsal root ganglia and ileal mucosa during Clostridium difficile toxin A-induced enteritis.
Am J Physiol Gastrointest Liver Physiol
274:
G196-G202,
1998
14.
Kelly, CP,
Becker SD,
Linevsky JK,
Joshi MA,
O'Keane JK,
Dickey BF,
LaMont JT,
and
Pothoulakis C.
Neutrophil recruitment in Clostridium difficile toxin A enteritis.
J Clin Invest
93:
1257-1265,
1994[ISI][Medline].
15.
Krivan, HC,
Clark GF,
Smith DF,
and
Wilkins TD.
Cell surface binding site for Clostridium difficile enterotoxin: evidence for a glycoconjugate containing the sequence Gal1-3Gal
1-4 GlcNAc.
Infect Immun
53:
573-581,
1986[ISI][Medline].
16.
Kurose, I,
Pothoulakis C,
LaMont JT,
Anderson DC,
Paulson JC,
Miyasaka M,
Wolf R,
and
Granger DN.
Clostridium difficile toxin A-induced microvascular dysfunction. Role of histamine.
J Clin Invest
94:
1919-1926,
1994[ISI][Medline].
17.
Moncrief, JS,
and
Wilkins TD.
Genetics of Clostridium difficile toxin.
In: Clostridium difficile, edited by Aktories K,
and Wilkins TC.. Berlin: Springer, 2000, p. 35-54.
18.
Pothoulakis, C,
Castagliuolo I,
LaMont JT,
Jaffer A,
O'Keane JC,
Snider M,
and
Leeman SE.
CP-96,345, a specific substance P receptor antagonist inhibits rat intestinal responses to Clostridium difficile toxin A, but not cholera toxin.
Proc Natl Acad Sci USA
91:
947-951,
1994[Abstract].
19.
Pothoulakis, C,
Gilbert J,
Cladaras C,
Castagliuolo I,
Semenza G,
Hitti Y,
Moncrief JS,
Linevsky J,
Kelly CP,
Nikulasson S,
Desai HP,
Wilkins TD,
and
LaMont JT.
Rabbit sucrase-isomaltase contains a functional intestinal receptor for Clostridium difficile toxin A.
J Clin Invest
98:
641-649,
1996
20.
Qiu, B,
Pothoulakis C,
Castagliuolo I,
Nikulasson S,
and
LaMont JT.
Participation of reactive oxygen metabolites in Clostridium difficile toxin A-induced enteritis in rats.
Am J Physiol Gastrointest Liver Physiol
276:
G485-G490,
1999
21.
Riegler, M,
Sedivy R,
Pothoulakis C,
Hamilton G,
Zacherl J,
Bischof G,
Consentini E,
Feil W,
Schiessel R,
LaMont JT,
and
Wenzl E.
Clostridium difficile toxin B is more potent than toxin A in damaging human colonic epithelium in vitro.
J Clin Invest
95:
2004-2011,
1995[ISI][Medline].
22.
Triadafilopoulos, G,
Pothoulakis C,
Weiss R,
Giampaolo C,
and
LaMont JT.
Comparative study of Clostridium difficile toxin A and cholera toxin in rabbit ileum. Role of prostaglandins and leukotrienes.
Gastroenterology
97:
1186-1192,
1989[ISI][Medline].
23.
Von Eichel-Streiber, CV,
Boquet P,
and
Sauerborn M.
Large clostridial cytotoxinsa family of glucosyltransferases modifying small GTP-binding proteins.
Trends Microbiol
4:
375-382,
1996[ISI][Medline].
24.
Warny, M,
Keates AC,
Keates S,
Castagliuolo I,
Zacks JK,
Aboudola S,
Qamar A,
Pothoulakis C,
LaMont JT,
and
Kelly CP.
p38 MAP kinase activation by C. difficile toxin A mediates monocyte necrosis, IL-8 production and enteritis.
J Clin Invest
105:
1147-1156,
2000
25.
Wershil, B,
Castagliuolo I,
and
Pothoulakis C.
Mast cell involvement in Clostridium difficile toxin A-induced intestinal fluid secretion and neutrophil recruitment in mice.
Gastroenterology
114:
956-964,
1998[ISI][Medline].