Mucosal injury and disruption of intestinal barrier function in HIV-infected individuals with and without diarrhea and cryptosporidiosis in northeast Brazil

OBJECTIVES

To determine the relative effects of AIDS-related diarrhea with or without cryptosporidiosis and microsporidiosis on intestinal function and injury.

METHODS

We studied 40 HIV-infected patients (20 with and 20 without diarrhea) and 13 healthy volunteers, using the differential urinary excretion of ingested lactulose and mannitol as respective markers of barrier disruption and overall villous surface area. We also examined them for fecal leukocytes, lactoferrin, and alpha 1-antitrypsin. Fasting subjects drank test solution containing lactulose (5 g) and mannitol (1 g). Urine was collected for 5 h and tested for sugars by high-performance liquid chromatography with pulsed amperometric detection.

RESULTS

HIV-positive patients with diarrhea had a 2.8-fold higher lactulose:mannitol excretion ratio (L:M) than HIV-positive patients without diarrhea (p = 0.01) and 10.4-fold higher than healthy volunteers (p = 0.004). This was accounted for by a 1.5- to 3.1-fold higher rate of lactulose excretion by HIV patients with diarrhea than by those without diarrhea or by healthy volunteers. Mannitol excretion was 32-55% less in patients with diarrhea than in those without diarrhea or in healthy volunteers. Patients with cryptosporidial diarrhea had a nearly 6-fold higher L:M ratio than those without diarrhea (p < 0.001) and nearly 3-fold higher than those with non-cryptosporidial diarrhea (p = 0.02). One patient with microsporidial infection had a nearly 3-fold higher L:M ratio than controls without diarrhea. Alpha 1-Antitrypsin was positive in 40% of HIV-positive patients with cryptosporidial infections and none of 12 HIV-positive patients with non-cryptosporidial diarrhea. Fecal lactoferrin or leukocytes were increased in all HIV patients with diarrhea.

CONCLUSION

HIV infection is associated with intestinal dysfunction and injury, even in patients who do not have diarrhea. However, those with diarrhea, especially with cryptosporidiosis or microsporidiosis, have even greater disruption of intestinal barrier function with potentially important nutritional consequences.

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.

Fecal lactoferrin, fecal leukocytes and occult blood in the diagnostic approach to childhood invasive diarrhea

OBJECTIVE

To compare fecal screening tests in the diagnostic approach to childhood invasive diarrhea.

SETTING AND PATIENTS

We assessed 125 consecutive children with acute diarrhea for fecal lactoferrin, fecal leukocytes and occult blood from November, 1995, to June, 1996.

RESULTS

Lactoferrin showed a greater overall sensitivity than fecal leukocytes or occult blood for detecting invasive pathogens. Combinations of lactoferrin or fecal leukocytes and of lactoferrin or occult blood or both yielded sensitivities and negative predictive values close to 100%, being superior to all other combinations. All patients with full breast-feeding and mixed feeding had a positive lactoferrin test with a 1:50 dilution used as the cutoff. In controls without diarrhea being exclusively bottle-fed, 3 of 15 (20%) still showed a positive lactoferrin result at the dilution of 1:50. This compared with 15 of 15 (100%) positive results among controls fully breast-fed, 14 of 15 (93%) among controls predominantly breast-fed and 11 of 15 (73%) among control children predominantly bottle-fed.

CONCLUSIONS

This study confirms the usefulness of lactoferrin testing as a negative predictor. Breast-feeding lowers the specificity of the test but does not alter the sensitivity. Fecal lactoferrin may be viewed as the screening test of choice to avoid expensive stool cultures in the diagnostic approach to invasive diarrhea.

Association of torovirus with acute and persistent diarrhea in children

OBJECTIVE

To study the etiologic role of toroviruses as a cause of gastroenteritis in humans.

METHODS

The design was a case-control study. We compared the rate of torovirus detection in fecal specimens from a selection of children with acute or persistent diarrhea and controls without diarrhea from a study of childhood diarrhea in an urban Brazilian slum. Stool samples were coded and tested in a blinded fashion for the presence of torovirus antigen by enzyme-linked immunosorbent assay, other enteropathogens, toxins and fecal leukocytes.

RESULTS

Thirty-three children with acute diarrhea, 41 children with persistent diarrhea and 17 controls were enlisted in the study. Torovirus antigen was detected in 9 (27%) samples from children with acute diarrhea, 11 (27%) samples from children with persistent diarrhea and none of the samples from controls (P < 0.05). In addition the presence of enteroaggregative E. coli was associated with persistent diarrhea and the presence of Cryptosporidium oocysts was common although not significant (P = 0.08); torovirus and Cryptosporidium occurred in different subsets of samples, whereas torovirus and enteroaggregative Escherichia coli were commonly found in combination.

CONCLUSIONS

These data indicate that toroviruses, alone or in combination with enteroaggregative E. coli, may play a pathogenic role in acute and possibly persistent diarrhea. Further studies are warranted to determine the etiologic role of toroviruses in gastroenteritis.

Role of platelet-activating factor in Chinese hamster ovary cell responses to cholera toxin

Cholera toxin (CT)-induced intestinal secretion and Chinese hamster ovary cell (CHO) elongation involves cyclic adenosine monophosphate and protein synthesis-dependent prostaglandin formation. We previously reported inhibition of CT-induced intestinal secretion and CHO elongation by platelet-activating factor (PAF) receptor antagonists and secretion of PAF by human intestinal epithelial cells exposed to CT. Herein, we show that PAF is involved after cAMP and that PAF, like CT, mediates prostaglandin E2 synthesis in CHO cells. CT-induced CHO elongation was blocked by specific PAF receptor antagonists, BN52021 and SR27417. SR27417 blocked dibutyryl cAMP-induced CHO elongation, but did not alter CHO elongation caused by PGE2. Neither CT-stimulated cAMP accumulation nor PGE2 production was inhibited by SR27417. Both PGE2 and PAF caused significant CHO elongation, but the latter did not stimulate significant cAMP production. In addition, PAF, like CT and dibutyryl cAMP, stimulated significant PGE2 production. Finally, the protein synthesis inhibitor cycloheximide, which completely blocks the effect of CT on prostaglandin synthesis, also blocked that of PAF, suggesting that PAF also mediates protein synthesis-dependent prostaglandin formation. We conclude that PAF is involved in CHO cytoskeletal responses to CT after the accumulation of cAMP and, like CT, PAF stimulates protein synthesis-dependent prostaglandin accumulation.

Cryptosporidiosis: an emerging, highly infectious threat

Cryptosporidium parvum, a leading cause of persistent diarrhea in developing countries, is a major threat to the U.S. water supply. Able to infect with as few as 30 microscopic oocysts, Cryptosporidium is found in untreated surface water, as well as in swimming and wade pools, day-care centers, and hospitals. The organism can cause illnesses lasting longer than 1 to 2 weeks in previously healthy persons or indefinitely in immunocompromised patients; furthermore, in young children in developing countries, cryptosporidiosis predisposes to substantially increased diarrheal illnesses. Recent increased awareness of the threat of cryptosporidiosis should improve detection in patients with diarrhea. New methods such as those using polymerase chain reaction may help with detection of Cryptosporidium in water supplies or in asymptomatic carriers. Although treatment is very limited, new approaches that may reduce secretion or enhance repair of the damaged intestinal mucosa are under study.

Protozoal agents: what are the dangers for the public water supply?

Safe and efficient treatment of drinking water has been one of the major public health advances of the twentieth century. People in developed countries generally take for granted that their water is safe to drink, a luxury the majority of the world's population does not have. The leading cause of infant mortality in the developing world is infectious diarrhea, and the prevalence of diarrheal pathogens is largely influenced by the quality and quantity of clean water available for drinking and washing. Until recently, modern water treatment had all but eliminated these concerns in developed nations. Over the past two decades, however, the safety of our water supply has been threatened by the emergence of Cryptosporidium parvum, a protozoal pathogen. The hearty oocysts of this organism survive chlorination and filtration to cause a diarrheal illness that, while unpleasant enough in healthy people, is devastating in immunocompromised individuals. The 1993 Milwaukee outbreak, in which 403,000 people developed diarrhea from drinking water that met all the updated federal safety standards, demonstrated the tremendous public health importance of this organism. While earlier attention had focused on Giardia and amebic infections, the other "emerging" protozoan besides Cryptosporidium is Cyclospora. This review discusses the protozoal pathogens, including Cryptosporidium parvum, Giardia lamblia, Entamoeba histolytica, and Cyclospora cayetanensis, that cause waterborne diarrheal outbreaks and the threats they pose to the public.

Seroepidemiology of Entamoeba histolytica in a slum in northeastern Brazil

Infection with the human pathogenic parasite Entamoeba histolytica has not been well-characterized in northeastern Brazil. In this study, the prevalence of E. histolytica infection in a slum in northeastern Brazil was assayed using an enzyme-linked immunosorbent assay (ELISA) for antibodies against the galactose/N-acetyl-D-galactosamine (Gal/GalNAc)-inhibitable adherence lectin of E. histolytica. Sera from a total of 335 individuals were examined for anti-Gal/GalNAc lectin antibodies. The overall seropositivity was 24.7%; 29.4% of females and 19.4% of males were positive. Among different age groups there was a peak of 40% positivity in the 6-14-year-old age group. There was also familial clustering of seropositivity. To examine colonization, stool samples from 155 people were examined microscopically for the presence of the parasite. Fourteen of 155 stools (9.0%) were identified as containing E. histolytica or nonpathogenic E. dispar. These 14 positive stools were analyzed with an ELISA that detects Gal/GalNAc lectin antigen and can distinguish between E. histolytica and E. dispar. Four stools (29%) were positive for E. histolytica and the remaining 10 were identified as E. dispar-positive. Although the overall colonization rate by microscopy was only 9%, with a third identified as E. histolytica, up to 40% of older children develop serologic evidence of having experienced pathogenic E. histolytica infection. The results of this study demonstrate that this community in northeastern Brazil is highly endemic for E. histolytica with infection rates similar to other developing nations.

Use of a lactoferrin assay in the differential diagnosis of female genital tract infections and implications for the pathophysiology of bacterial vaginosis

BACKGROUND AND OBJECTIVES

Lactoferrin has served as a marker for leukocytes (polymorphonuclear neutrophils [PMN]) in clinical specimens.

GOAL

To investigate the potential of a lactoferrin latex agglutination test in the differential diagnosis of female genital infection.

STUDY DESIGN

Lactoferrin was quantified in the vaginal discharge of women with genital infections. Polymorphonuclear neutrophils were added to vaginal discharge and observed over 8 hours.

RESULTS

Vaginal lactoferrin titers were significantly elevated in women with trichomoniasis, candidiasis, and bacterial vaginosis (BV). Using a lactoferrin titer of > or = 1:40, the assay has a sensitivity of 79.3% and a specificity of 83.3% for the presence of trichomoniasis or bacterial vaginosis. Vaginal discharge from women with BV significantly destroyed added PMN.

CONCLUSIONS

Vaginal lactoferrin determinations may provide a useful screen for inflammatory genital infections and identify individuals who require additional diagnostic evaluation. The observed absence of PMN in bacterial vaginosis may result from the destruction of PMN in vaginal discharge rather than the absence of a primary inflammatory response.

Direct analysis of mannitol, lactulose and glucose in urine samples by high-performance anion-exchange chromatography with pulse amperometric detection. Clinical evaluation of intestinal permeability in human immunodeficiency virus infection

Clinically, the ratio of lactulose/mannitol excretion in urine after administration of these non-metabolized sugars has been used to evaluate the extent of malabsorption and intestinal permeability disruption in several infections and nutritional diseases, including human immunodeficiency virus (HIV) infection. A range of methodologies have been reported to determine the lactulose/mannitol ratio, including enzymatic assay, gas-liquid chromatography (GC), thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). Most published methods involve tedious sample preparations, rendering them unsuitable for routine or automated clinical laboratory testing. We describe in this paper a method in which weak anion-exchange high-performance liquid chromatography in conjunction with a pulsed amperometric detector was used. It requires very simple sample preparation and avoids interference by other components present in the urine. The linear range of determination for mannitol, lactulose and glucose are up to 10 nmol, in a single injection. The limits of detection are 8, 12, 47 and 52 pmol, respectively, for mannitol, glucose, lactose and lactulose. The separation and quantification using this method are highly reproducible, yielding standard errors of less than 2.5% for retention times and less than 3.5% for quantitation. The ratios of lactulose/mannitol recovery in controls and in HIV-infected subjects with and without diarrhea showed striking differences, which are in close agreement with the published results derived with similar HPLC methods.

Summary of the thirty-first United States-Japan Joint Conference on Cholera and Related Diarrheal Diseases

The 31st United States-Japan Cholera and Related Diarrheal Diseases Conference was held in conjunction with the United States-Japan Malnutrition Conference at Kiawah Island, South Carolina, 30 November to 3 December 1995. In addition to the overall conference theme of the role of cytokines in the pathogenesis of enteric infections and malnutrition, researchers described substantial advances in cholera epidemiology, detection, molecular mechanisms, and pathophysiology plus new mechanisms for enterotoxigenic, enteroadherent, enterohemorrhagic, and enteroinvasive Escherichia coli. There was also emphasis on new work with and vaccine development with Bacteroides fragilis and Yersinia, Shigella, and Salmonella species.

Fecal screening tests in the approach to acute infectious diarrhea: a scientific overview

OBJECTIVE

To evaluate the value of fecal leukocytes, fecal occult blood, fecal lactoferrin and combination of fecal leukocytes with clinical data in the workup of patients with inflammatory diarrhea.

DATA IDENTIFICATION

A systematic literature search in all languages using MEDLINE (1970 to 1994), reference lists of articles primarily retrieved and of review articles and correspondence with experts in the field.

STUDY SELECTION

The search identified 2603 references, 81 of which were deemed relevant on the basis of prespecified selection criteria. Of these 25 contained sufficient data for further analysis and thus were finally included.

DATA EXTRACTION

All data from the selected articles were extracted by one observer whereas the second reviewer checked these data for accuracy. True positive rates and false positive rates were calculated from each 2 x 2 table.

RESULTS OF DATA ANALYSIS

The study summarizes the diagnostic accuracy of the signaled tests as predictors of inflammatory diarrhea as defined by stool culture (the reference test). Plots of true positive rates against false positive rates demonstrated widely scattered points, indicating heterogeneity. A summary receiver operating characteristic curve was fitted to the data with the use of logistic transforms and weighted least squares linear regression. Of the 25 studies analyzed 38 data points were used to construct summary receiver operating characteristic curves for index tests.

CONCLUSIONS

Fecal lactoferrin was the most accurate index test. Fecal leukocytes showed the lowest performance as assessed by the area under the curve. Occult blood and combination of fecal leukocytes with clinical data yielded intermediate curves. A limited number of studies (fecal lactoferrin, and fecal leukocytes with clinical data) and methodologic flaws identified in the assessed studies must be solved in future primary studies to improve the usefulness of the metaanalytic approach used here.

Effects of high-dose oral vitamin A on diarrheal episodes among children with persistent diarrhea in a northeast Brazilian community

The mean +/- SEM duration of diarrheal episodes decreased from 7.1 +/- 2.2 days to 4.3 +/- 0.9 days (P < 0.05) while the incidence of diarrheal episodes remained steady (2.2 +/- 0.3 versus 2.4 +/- 0.5 episodes; P = not significant) between two three-month periods before and after the oral administration of a single large age-adjusted dose of vitamin A among children at historical risk for persistent diarrhea in an impoverished Brazilian community.

To culture or not to culture: fecal lactoferrin screening for inflammatory bacterial diarrhea

Because of its low yield in unselected specimens, stool culture is often cost ineffective. We tested 55 fecal samples from Fairfax Hospital (46 patients with diarrhea and 9 from controls without diarrhea) for lactoferrin by latex agglutination (LFLA) with the Leukotest (Techlab, Blacksburg, Va.) as a marker for inflammatory diarrhea. Of the 28 samples with Salmonella, Shigella, or Campylobacter infection, 93% had detectable fecal lactoferrin at > or = 1:50 (61% had LFLA titers of > or = 1:400), while 83% of 18 samples with rotavirus or no detectable pathogen were LFLA negative at a titer of 1:50 (100% were negative at 1:400). All 9 controls without diarrhea were LFLA negative at 1:50. The use of fecal lactoferrin to screen for inflammatory diarrhea selects specimens for which stool culture is fivefold more likely to yield an invasive bacterial pathogen (reducing the cost per positive result by over $800) and thus may greatly enhance a cost-effective approach to evaluating diarrheal illness.

Correlation of lactoferrin with neutrophilic inflammation in body fluids

We have reported that lactoferrin, a 77-kDa iron-binding glycoprotein found in secondary neutrophil granules, provides a useful marker of fecal leukocytes in fecal specimens from patients with inflammatory diarrhea (R. L. Guerrant, V. Araujo, E. Soares, K. Kotloff, A. A. M. Lima, W. H. Cooper, and A. G. Lee, J. Clin. Microbiol. 30:1238-1242, 1992). In order to determine the usefulness of this marker of neutrophilic inflammation in different body fluids, we examined blood, gingival swabs, sputum, and saliva using antilactoferrin antibodies (lactoferrin latex agglutination [LFLA]). LFLA titers in whole blood samples were < or = 1:4 in all eight samples from patients with neutropenia (absolute neutrophil count [ANC] = < 150 polymorphonuclear cells [PMNs] per microliter), < or = 1:8 in samples from 13 individuals with moderate leukocyte counts (ANC = 150 to 8,000), and 1:8 to 1:32 in samples from six patients with neutrophilia (ANC > 8,000). While the overlap precludes a useful role in the identification of neutropenia, these data confirm that lactoferrin titers of > 1:100 indeed indicate inflammation in fluid specimens. On quantitative elution of lactoferrin from gingival swabs, all 7 patients with dental plaque had titers of 1:200 to 1:400; 9 of 12 patients with clinical gingivitis had LFLA titers of 1:200 to 1:1,600, while all 7 individuals with healthy gums and teeth and 4 edentulous patients had LFLA titers of < or = 1:100. Eight purulent sputum samples had titers of > or = 1:400 (7 were 1:1,600) while 11 normal saliva samples showed titers of < or = 1:100. Lactoferrin titers in sputum, gingival swabs, and whole blood correlate with the presence of neutrophils or inflammation in these specimens and may offer a convenient rapid test for inflammatory processes.

Cryptosporidium and cryptosporidiosis

The tiny, iodine- and chlorine-resistant protozoan oocysts of Cryptosporidium parvum, long recognized by veterinarians, have become increasingly noted as a cause of watery diarrhea in developed and developing countries throughout the world. For immunocompromised patients, particularly those with AIDS, this diarrhea can be severe and life-threatening. Clovis Martins and Richard Guerrant here discuss the increasing recognition of this important pathogen in immunocompetent patients as well, and outline new challenges to improved water treatment, immunologic and antiparasite chemotherapy.

Etiology and epidemiology of persistent diarrhea in northeastern Brazil: a hospital-based, prospective, case-control study

With the improved therapy for acute diarrhea, persistent diarrhea (> 14 days) is emerging as a major problem in developing countries. However, the etiologies and pathogenesis of persistent diarrhea remain poorly understood. We conducted a prospective case-control study in children < 3 years old presenting to the hospital with persistent diarrhea in Fortaleza, Brazil. Over the study period (August 1988 to March 1991), 56 children seen with persistent diarrhea, 52 children seen with acute diarrhea, and 42 controls attending the same hospital/clinic for illnesses other than diarrhea were enrolled. A potential pathogen was found in 91% of children with persistent diarrhea and 90% of those with acute diarrhea versus 45% of controls (both p's < 0.01). Thirty-four percent of persistent (19/56) and 38% of acute (20/52) diarrhea cases versus 2% (1/42) of controls (both p's < 0.01) had multiple pathogens. Enteroaggregative Escherichia coli (EAggEC) were found in 68% (38/56) of children with persistent diarrhea versus 31% (13/42) of controls (p < 0.01) and in 46% (24/52) of those with acute diarrhea. Furthermore, when the EAggEC were subdivided into aggregative adherence (AA) gene probe positive (18/56; 32%) and negative (20/56; 36%), both subgroups were still significantly different from controls [6/42 (14%) and 7/42 (17%), respectively; both p's < 0.05].(ABSTRACT TRUNCATED AT 250 WORDS)

Concurrence of Clostridium difficile toxin A enzyme-linked immunosorbent assay, fecal lactoferrin assay, and clinical criteria with C. difficile cytotoxin titer in two patient cohorts

The accurate and sensitive diagnosis of Clostridium difficile-related diarrhea, normally treated with vancomycin, has become increasingly important in light of the emergence of dangerous new strains of vancomycin-resistant enterococci. In order to improve the threshold for C. difficile diagnosis and treatment, a number of commonly used assays for the diagnosis of C. difficile diarrhea were examined. These included an enzyme-linked immunosorbent assay for C. difficile toxin A (ToxA), a CHO cell culture assay for fecal C. difficile (cyto)toxin B, and a lactoferrin latex agglutination assay for fecal lactoferrin (LFLA). We studied 722 fecal specimens submitted by physicians for C. difficile toxin testing at the Salem, Va., Veterans' Affairs Hospital and at the University of Virginia Medical Center in Charlottesville. Charts were reviewed from 123 Veterans' Hospital patients and 114 University of Virginia patients for clinical criteria indicative of C. difficile diarrhea. An increasing titer of CHO cell cytotoxicity was correlated with an increasing likelihood of ToxA positivity (5 to 90%), LFLA positivity (39 to 77%), and clinical agreement (28 to 85%). However, some data indicate that the CHO cell cytotoxicity assay may be nonspecific when positive only at low titers. When the CHO assay result is positive at high titers, it remains the best diagnostic tool. Yet, when it is positive at a low titer, careful interpretation of the results in conjunction with other assays and the clinical setting is warranted, especially in light of new drug-resistant strains of microorganisms.

Role of platelet activating factor in the inflammatory and secretory effects of Clostridium difficile toxin A

Clostridium difficile is a major recognized cause of antibiotic-associated diarrhea, an effect mediated through its toxin A. Toxin A has been reported to disrupt epithelial tight junctions, attract neutrophils, and cause striking intestinal inflammation and secretion. Having demonstrated that phospholipase A2 inhibitors block the secretory effects of toxin A, we next wished to examine whether platelet activating factor (PAF) was involved in either the direct epithelial or secretory effects of toxin A. The effects of toxin A on net secretion in ligated rabbit ileal segments were significantly inhibited by the PAF antagonists 10(-4)-10(-5) M BN 52021, 10(-5) M WEB 2170, or 10(-5) M SR 27417 by 59-102%. SR 27417 also inhibited secretion induced by toxin A in loops adjacent to the drug (by 58%). Furthermore, the striking inflammation and epithelial disruption seen at 6 h and ligated ileal segments with toxin A was largely prevented by simultaneous treatment with the PAF antagonist SR 27417. In addition, we noted a significant synergistic effect of 10(-8) M PAF with 10 micrograms/ml toxin A in the ligated rabbit ileal segments. To examine direct effects of PAF antagonists on toxin A in T-84 epithelial cell monolayers, rhodamine-labeled phalloidin stained F-actin demonstrated significant disruption of F-actin by toxin A that was reduced by the PAF antagonist BN 52021 or WEB 2170. However, the PAF antagonists (10(-4) M WEB, 10(-5) M BN or 10(-4) M SR) failed to alter the disruption of T-84 cell tissue resistance by C. difficile toxin A (0.03 micrograms/ml). We conclude that PAF may be involved in the secretory effects of C. difficile toxin A, and that PAF antagonists deserve further study in C. difficile diarrhea.