Cholera toxin and O-specific polysaccharide immune responses after oral cholera vaccination with Dukoral in different age groups of Bangladeshi participants.

Vaccination is important to prevent cholera. There are limited data comparing anti-O-specific polysaccharide (OSP) and anti-cholera toxin-specific immune responses following oral whole-cell with cholera toxin B-subunit (WC-rBS) vaccine (Dukoral, Valneva) administration in different age groups. An understanding of the differences is relevant because young children are less well protected by oral cholera vaccines than older children and adults. We compared responses in 50 adults and 49 children (ages 2 to <18) who were administered two doses of WC-rBS at a standard 14-day interval. All age groups had significant IgA and IgG plasma-blast responses to the OSP and cholera toxin B-subunit (CtxB) antigens that peaked 7 days after vaccination. However, in adults and older children (ages 5 to <18), antibody responses directed at the OSP antigen were largely IgA and IgG, with a minimal IgM response, while younger children (ages 2 to <5) mounted significant increases in IgM with minimal increases in IgA and IgG antibody responses 30 days after vaccination. In adults, anti-OSP and CtxB memory B-cell responses were detected after completion of the vaccination series, while children only mounted CtxB-specific IgG memory B-cell responses and no OSP-memory B-cell responses. In summary, children and adults living in a cholera endemic area mounted different responses to the WC-rBS vaccine, which may be a result of more prior exposure to Vibrio cholerae in older participants. The absence of class-switched antibody responses and memory B-cell responses to OSP may explain why protection wanes more rapidly after vaccination in young children compared to older vaccinees.IMPORTANCEVaccination is an important strategy to prevent cholera. Though immune responses targeting the OSP of V. cholerae are believed to mediate protection against cholera, there are limited data on anti-OSP responses after vaccination in different age groups, which is important as young children are not well protected by current oral cholera vaccines. In this study, we found that adults mounted memory B-cell responses to OSP, which were not seen in children. Adults and older children mounted class-switched (IgG and IgA) serum antibody responses to OSP, which were not seen in young children who had only IgM responses to OSP. The lack of class-switched antibody responses and memory B-cell responses to OSP in younger participants may be due to lack of prior exposure to V. cholerae and could explain why protection wanes more rapidly after vaccination in young children.

Equity, Diversity and Inclusion (EDI) in Organ Transplantation: An ESOT Survey About EDI Within ESOT as an Organization and its Educational Activities, and Transplantation Research and Science.

The European Society of Organ Transplantation (ESOT) strives to promote equity, diversity, and inclusion (EDI) across all its activities. We surveyed the transplant community's experiences and perspectives regarding EDI within ESOT as an organization and its educational activities, and research in general. A total of 299 respondents completed the questionnaire. About half agreed that ESOT's Executive Committee, Council, and Sections/Committees are diverse and inclusive (51%) and that ESOT promotes EDI in its live and digital educational activities (54%). Forty percent of respondents agreed that scientific and clinical trials in the field of transplantation are diverse and inclusive. Despite the wide distribution of the survey, most of the respondents self-identified as White and were either physician or surgeon. However, the results contribute a unique insight into the experiences and perspectives of the transplantation community regarding EDI. Whilst ESOT is committed to the principles of EDI, perceptions and the high number of proposals show the apparent need to prioritize efforts to embed EDI across ESOT and transplantation science. These data should constitute a starting point for change and provide guidance for future efforts to promote EDI within the transplantation community.

Comparison of O-specific polysaccharide responses in patients following infection with Vibrio cholerae O139 versus vaccination with a bivalent (O1/O139) oral killed cholera vaccine in Bangladesh.

Cholera caused by Vibrio cholerae O139 emerged in the early 1990s and spread rapidly to 11 Asian countries before receding for unclear reasons. Protection against cholera is serogroup-specific, which is defined by the O-specific polysaccharide (OSP) component of lipopolysaccharide (LPS). V. cholerae O139 also expresses the OSP-capsule. We, therefore, assessed antibody responses targeting V. cholerae O139 OSP, LPS, capsule, and vibriocidal responses in patients in Bangladesh with cholera caused by V. cholerae O139. We compared these responses to those of age-gender-blood group-matched recipients of the bivalent oral cholera vaccine (OCV O1/O139). We found prominent OSP, LPS, and vibriocidal responses in patients, with a high correlation between these responses. OSP responses primarily targeted the terminal tetrasaccharide of OSP. Vaccinees developed OSP, LPS, and vibriocidal antibody responses, but of significantly lower magnitude and responder frequency (RF) than matched patients. We separately analyzed responses in pediatric vaccinees born after V. cholerae O139 had receded in Bangladesh. We found that OSP responses were boosted in children who had previously received a single dose of bivalent OCV 3 yr previously but not in vaccinated immunologically naïve children. Our results suggest that OSP-specific responses occur during cholera caused by V. cholerae O139 despite the presence of capsules, that vaccination with bivalent OCV is poorly immunogenic in the short term in immunologically naïve individuals, but that OSP-specific immune responses can be primed by previous exposure, although whether such responses can protect against O139 cholera is uncertain. IMPORTANCE Cholera is a severe dehydrating illness in humans caused by Vibrio cholerae serogroups O1 or O139. Protection against cholera is serogroup-specific, which is defined by the O-specific polysaccharide (OSP) of V. cholerae LPS. Yet, little is known about immunity to O139 OSP. In this study, we assessed immune responses targeting OSP in patients from an endemic region with cholera caused by V. cholerae O139. We compared these responses to those of the age-gender-blood group-matched recipients of the bivalent oral cholera vaccine. Our results suggest that OSP-specific responses occur during cholera caused by V. cholerae O139 and that the OSP responses primarily target the terminal tetrasaccharide of OSP. Our results further suggest that vaccination with the bivalent vaccine is poorly immunogenic in the short term for inducing O139-specific OSP responses in immunologically naïve individuals, but OSP-specific immune responses can be primed by previous exposure or vaccination.

Longevity of memory B cells and antibodies, as well as the polarization of effector memory helper T cells, are associated with disease severity in patients with COVID-19 in Bangladesh.

The longevity of immune responses induced by different degrees of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection provides information important to understanding protection against coronavirus disease 2019 (COVID-19). Here, we report the persistence of SARS-CoV-2 spike receptor-binding domain (RBD) specific antibodies and memory B cells recognizing this antigen in sequential samples from patients in Bangladesh with asymptomatic, mild, moderate and severe COVID-19 out to six months following infection. Since the development of long-lived memory B cells, as well as antibody production, is likely to be dependent on T helper (Th) cells, we also investigated the phenotypic changes of Th cells in COVID-19 patients over time following infection. Our results show that patients with moderate to severe COVID-19 mounted significant levels of IgG antibodies out to six months following infection, while patients with asymptomatic or mild disease had significant levels of IgG antibodies out to 3 months following infection, but these then fell more rapidly at 6 months than in patients with higher disease severity. Patients from all severity groups developed circulating memory B cells (MBCs) specific to SARS-CoV-2 spike RBD by 3 months following infection, and these persisted until the last timepoint measured at 6 months. A T helper cell response with an effector memory phenotype was observed following infection in all symptomatic patients, while patients with asymptomatic infection had no significant increases in effector Th1, Th2 and Th17 effector memory cell responses. Our results suggest that the strength and magnitude of antibody and memory B cells induced following SARS-CoV-2 infection depend on the severity of the disease. Polarization of the Th cell response, with an increase in Th effector memory cells, occurs in symptomatic patients by day 7 following infection, with increases seen in Th1, Th2, Th17 and follicular helper T cell subsets.

Correlation of antigen-specific immune response with disease severity among COVID-19 patients in Bangladesh.

Coronavirus disease 2019 (COVID-19) is a protean disease causing different degrees of clinical severity including fatality. In addition to humoral immunity, antigen-specific T cells may play a critical role in defining the protective immune response against SARS-CoV-2, the virus that causes this disease. As a part of a longitudinal cohort study in Bangladesh to investigate B and T cell-specific immune responses, we sought to evaluate the activation-induced marker (AIM) and the status of different immune cell subsets during a COVID-19 infection. We analyzed a total of 115 participants, which included participants with asymptomatic, mild, moderate, and severe clinical symptoms. We observed decreased mucosal-associated invariant T (MAIT) cell frequency on the initial days of the COVID-19 infection in symptomatic patients compared to asymptomatic patients. However, natural killer (NK) cells were found to be elevated in symptomatic patients just after the onset of the disease compared to both asymptomatic patients and healthy individuals. Moreover, we found a significant increase of AIM+ (both OX40+CD137+ and OX40+CD40L+) CD4+ T cells in moderate and severe COVID-19 patients in response to SARS-CoV-2 peptides (especially spike peptides) compared to pre-pandemic controls who are unexposed to SARS-CoV-2. Notably, we did not observe any significant difference in the CD8+ AIMs (CD137+CD69+), which indicates the exhaustion of CD8+ T cells during a COVID-19 infection. These findings suggest that patients who recovered from moderate and severe COVID-19 were able to mount a strong CD4+ T-cell response against shared viral determinants that ultimately induced T cells to mount further immune responses to SARS-CoV-2.

Proportion of Risk Factors among Women Attending Antenatal Checkup Unit of A Tertiary Level Hospital of Bangladesh.

Women constitute a large population group in any country and they are the vulnerable or special risk group. The risk is associated with child-bearing. The purpose of antenatal care is to detect early the high risk cases from a large group of antenatal women and to arrange special skilled care for them. Aim of this cross sectional descriptive type of observational study was to find out the proportion of risk factors among women attending antenatal checkup unit of a tertiary level hospital and carried out in the antenatal checkup unit of Model Family Planning Clinic of Mymensingh Medical College Hospital, Bangladesh from January 2022 to June 2022. Data were collected from purposively selected 403 women seeking antenatal care by face to face interview, clinical examination and necessary laboratory investigations. Data were analyzed by using SPSS version 26.0. More than three forth (320, 79.4%) of the respondents were in the age group of less than 30 years and the remaining (83, 20.6%) were in the age group of 30 years and over. Mean age of the pregnant women was 24.7 years with a standard deviation of 4.7 years. Most of the pregnant women were housewives (350, 86.8%); 41(10.2%) were students and 12(3.0%) were service holders. Among the respondents rural women (254, 63.0%) were more than urban women (149, 37.0%). Seventy seven (19.1%) respondents were interviewed during 1st trimester; 140(34.7%) during 2nd semester and 186(46.2%) during 3rd semester. It was found that 12 (3.0%) women were elderly primi and 6(1.5%) were short statured primi. Eighteen (4.5%) pregnant women had malpresentations- 17(94.4%) had breech presentation and 1(5.6%) had transverse lie. Each 18(4.5%) had threatened abortion and antepartum haemorrhage. Pre-eclampsia was found in 4(1.0%) and anaemia in 14 (3.5%); twin pregnancy was found in 4 (1.0%) and hydramnios in 9(2.2%) pregnant women. Thirty one (7.7%) women had previous history of either still birth or intrauterine death or manual removal of placenta. One (0.2%) pregnant women was categorized as elderly grand multiparas. Prolonged pregnancy was found in 4(1.0%) women and 76(18.9%) women had the history of previous caesarean or instrumental delivery. Nine (2.2%) pregnant women had general diseases along with pregnancy- 5(55.6%) had asthma, 3(33.3%) had diabetes mellitus and 1(11.1%) had cardiovascular disease. Four (1.0%) women got pregnant after treatment for infertility and 2 (0.5%) women had history of three or more spontaneous consecutive abortions. Finally all the pregnant women under study were categorized on the basis of criteria of "high risk cases" and 97(24.1%) women had high risk pregnancy and the remaining 306 (75.9%) had normal pregnancy. Proportion of women with high risk pregnancy in this study is 24.1% who needs special attention and skilled care in addition to continuing better Maternal and Child Health (MCH) services for all pregnant women.

Defining Polysaccharide-Specific Antibody Targets against Vibrio cholerae O139 in Humans following O139 Cholera and following Vaccination with a Commercial Bivalent Oral Cholera Vaccine, and Evaluation of Conjugate Vaccines Targeting O139.

Cholera caused by Vibrio cholerae O139 could reemerge, and proactive development of an effective O139 vaccine would be prudent. To define immunoreactive and potentially immunogenic carbohydrate targets of Vibrio cholerae O139, we assessed immunoreactivities of various O-specific polysaccharide (OSP)-related saccharides with plasma from humans hospitalized with cholera caused by O139, comparing responses to those induced in recipients of a commercial oral whole-cell killed bivalent (O1 and O139) cholera vaccine (WC-O1/O139). We also assessed conjugate vaccines containing selected subsets of these saccharides for their ability to induce protective immunity using a mouse model of cholera. We found that patients with wild-type O139 cholera develop IgM, IgA, and IgG immune responses against O139 OSP and many of its fragments, but we were able to detect only a moderate IgM response to purified O139 OSP-core, and none to its fragments, in immunologically naive recipients of WC-O1/O139. We found that immunoreactivity of O139-specific polysaccharides with antibodies elicited by wild-type infection markedly increase when saccharides contain colitose and phosphate residues, that a synthetic terminal tetrasaccharide fragment of OSP is more immunoreactive and protectively immunogenic than complete OSP, that native OSP-core is a better protective immunogen than the synthetic OSP lacking core, and that functional vibriocidal activity of antibodies predicts in vivo protection in our model but depends on capsule thickness. Our results suggest that O139 OSP-specific responses are not prominent following vaccination with a currently available oral cholera vaccine in immunologically naive humans and that vaccines targeting V. cholerae O139 should be based on native OSP-core or terminal tetrasaccharide. IMPORTANCE Cholera is a severe dehydrating illness of humans caused by Vibrio cholerae serogroup O1 or O139. Protection against cholera is serogroup specific, and serogroup specificity is defined by O-specific polysaccharide (OSP). Little is known about immunity to O139 OSP. In this study, we used synthetic fragments of the O139 OSP to define immune responses to OSP in humans recovering from cholera caused by V. cholerae O139, compared these responses to those induced by the available O139 vaccine, and evaluated O139 fragments in next-generation conjugate vaccines. We found that the terminal tetrasaccharide of O139 is a primary immune target but that the currently available bivalent cholera vaccine poorly induces an anti-O139 OSP response in immunologically naive individuals.

Vibrio cholerae Sialidase-Specific Immune Responses Are Associated with Protection against Cholera.

Cholera remains a major public health problem in resource-limited countries. Vaccination is an important strategy to prevent cholera, but currently available vaccines provide only 3 to 5 years of protection. Understanding immune responses to cholera antigens in naturally infected individuals may elucidate which of these are key to longer-term protection seen following infection. We recently identified Vibrio cholerae O1 sialidase, a neuraminidase that facilitates binding of cholera toxin to intestinal epithelial cells, as immunogenic following infection in two recent high-throughput screens. Here, we present systemic, mucosal, and memory immune responses to sialidase in cholera index cases and evaluated whether systemic responses to sialidase correlated with protection using a cohort of household contacts. Overall, we found age-related differences in antisialidase immune response following cholera. Adults developed significant plasma anti-sialidase IgA, IgG, and IgM responses following infection, whereas older children (≥5 years) developed both IgG and IgM responses, and younger children only developed IgM responses. Neither older children nor younger children had a rise in IgA responses over the convalescent phase of infection (day 7/day 30). On evaluation of mucosal responses and memory B-cell responses to sialidase, we found adults developed IgA antibody-secreting cell (ASC) and memory B-cell responses. Finally, in household contacts, the presence of serum anti-sialidase IgA, IgG, and IgM antibodies at enrollment was associated with a decrease in the risk of subsequent infection. These data show cholera patients develop age-related immune responses against sialidase and suggest that immune responses that target sialidase may contribute to protective immunity against cholera.IMPORTANCE Cholera infection can result in severe dehydration that may lead to death within a short period of time if not treated immediately. Vaccination is an important strategy to prevent the disease. Oral cholera vaccines provide 3 to 5 years of protection, with 60% protective efficacy, while natural infection provides longer-term protection than vaccination. Understanding the immune responses after natural infection is important to better understand immune responses to antigens that mediate longer-term protection. Sialidase is a neuraminidase that facilitates binding of cholera toxin to intestinal epithelial cells. We show here that patients with cholera develop systemic, mucosal, and memory B-cell immune responses to the sialidase antigen of Vibrio cholerae O1 and that plasma responses targeting this antigen correlate with protection.

Past, Present, and Future of Dynamic Kidney and Liver Preservation and Resuscitation.

The increased demand for organs has led to the increased usage of "higher risk" kidney and liver grafts. These grafts from donation after circulatory death or expanded criteria donors are more susceptible to preservation injury and have a higher risk of unfavorable outcomes. Dynamic, instead of static, preservation could allow for organ optimization, offering a platform for viability assessment, active organ repair and resuscitation. Ex situ machine perfusion and in situ regional perfusion in the donor are emerging as potential tools to preserve and resuscitate vulnerable grafts. Preclinical findings have ignited clinical organ preservation research that investigates dynamic preservation, its various modes (continuous, preimplantation) and temperatures (hypo-, sub, or normothermic). This review outlines the current status of dynamic preservation of kidney and liver grafts and describes ongoing research and emerging clinical trials.

Using an Integrated -Omics Approach to Identify Key Cellular Processes That Are Disturbed in the Kidney After Brain Death.

In an era where we are becoming more reliant on vulnerable kidneys for transplantation from older donors, there is an urgent need to understand how brain death leads to kidney dysfunction and, hence, how this can be prevented. Using a rodent model of hemorrhagic stroke and next-generation proteomic and metabolomic technologies, we aimed to delineate which key cellular processes are perturbed in the kidney after brain death. Pathway analysis of the proteomic signature of kidneys from brain-dead donors revealed large-scale changes in mitochondrial proteins that were associated with altered mitochondrial activity and morphological evidence of mitochondrial injury. We identified an increase in a number of glycolytic proteins and lactate production, suggesting a shift toward anaerobic metabolism. Higher amounts of succinate were found in the brain death group, in conjunction with increased markers of oxidative stress. We characterized the responsiveness of hypoxia inducible factors and found this correlated with post-brain death mean arterial pressures. Brain death leads to metabolic disturbances in the kidney and alterations in mitochondrial function and reactive oxygen species generation. This metabolic disturbance and alteration in mitochondrial function may lead to further cellular injury. Conditioning the brain-dead organ donor by altering metabolism could be a novel approach to ameliorate this brain death-induced kidney injury.

In vitro cerebrovascular modeling in the 21st century: current and prospective technologies.

The blood-brain barrier (BBB) maintains the brain homeostasis and dynamically responds to events associated with systemic and/or rheological impairments (e.g., inflammation, ischemia) including the exposure to harmful xenobiotics. Thus, understanding the BBB physiology is crucial for the resolution of major central nervous system CNS) disorders challenging both health care providers and the pharmaceutical industry. These challenges include drug delivery to the brain, neurological disorders, toxicological studies, and biodefense. Studies aimed at advancing our understanding of CNS diseases and promoting the development of more effective therapeutics are primarily performed in laboratory animals. However, there are major hindering factors inherent to in vivo studies such as cost, limited throughput and translational significance to humans. These factors promoted the development of alternative in vitro strategies for studying the physiology and pathophysiology of the BBB in relation to brain disorders as well as screening tools to aid in the development of novel CNS drugs. Herein, we provide a detailed review including pros and cons of current and prospective technologies for modelling the BBB in vitro including ex situ, cell based and computational (in silico) models. A special section is dedicated to microfluidic systems including micro-BBB, BBB-on-a-chip, Neurovascular Unit-on-a-Chip and Synthetic Microvasculature Blood-brain Barrier.

Recent clinical trials of pharmacologic cardiovascular interventions in patients with chronic kidney disease.

End stage kidney disease (ESKD) is associated with a 10- to 20-fold increased risk of cardiovascular mortality compared with age- and sex-matched controls without CKD. In spite of this marked increase in risk, the vast majority of cardiovascular intervention clinical trials to date have specifically excluded subjects with CKD. The aim of this paper is to critically review the recently published clinical trial evidence that cardiac outcomes in CKD patients are modified by cardiovascular risk factor interventions, including erythropoiesis stimulating agent therapy (US Normal Hematocrit, CHOIR and CREATE trials), statins (PPP, 4D and ALERT), fibrates (VA-HIT), folic acid (ASFAST, US folic acid trial, HOST), anti-oxidative stress therapy (SPACE, HOPE and ATIC), N-acetylcysteine, sevelamer (D-COR), cinacalcet (Cunningham meta-analysis), carvedilol, angiotensin converting enzyme inhibitor (FOSIDIAL), telmisartan, aspirin (HOT study re-analysis) and multidisciplinary multiple cardiovascular risk factor intervention clinics (LANDMARK). Although none of these studies could be considered conclusive, the negative trials to date should raise significant concerns about the heavy reliance of current clinical practice guidelines on extrapolation of findings from cardiovascular intervention trials in the general population. It may be that cardiovascular disease in dialysis populations is less amenable to intervention, either because of the advanced stage of CKD or because the pathogenesis of cardiovascular disease in CKD patients is different to that in the general population. Further large, well-conducted, multi-centre randomised controlled trials in this area are urgently required.

Cutaneous manifestations of cytomegalovirus disease in renal transplant recipients: a case series.

Cytomegalovirus (CMV) is an important and well-described opportunistic virus in the immunocompromised host, with infection occurring mainly after the first month in the new renal transplant recipient. CMV can present as primary infection, reinfection, or reactivation of latent disease. It is capable of protean manifestations. Cutaneous manifestations are variable, rare, and diagnosis often delayed. We present 3 cases of cutaneous CMV disease in renal transplant recipients. Manifestations in our patients included ulceration of the tongue and perianal areas, facial petechiae, and nodular lesion involving the ear. This case series serves to highlight the importance of early skin biopsy in the diagnosis and management of cutaneous CMV disease.

Cardiovascular disease in patients with chronic kidney disease. A clinical review.

Cardiovascular disease (CVD) remains the most common cause of premature death in the chronic kidney disease (CKD) population. Individuals with CKD are at 10-20 times greater risk of cardiac death than controls without CKD, despite stratification for age, race, sex and diabetes. Heightened CVD mortality begins with mild kidney disease and rises further with more advanced kidney disease. Traditional risk factors account for up to 50% of cardiovascular disease in CKD, whilst renal specific markers, including anemia, disordered bone mineral metabolism and oxidative stress, also likely contribute to the total cardiovascular burden in CKD. Despite the increased mortality, there has been a dearth of interventional cardiovascular randomized controlled trials (RCTs) in the CKD population. Furthermore, many patients with kidney disease have been excluded from the majority of mainstream cardiovascular interventional trials. While recently published RCTs on traditional and non-traditional risk factors including dyslipidemia (PPP, 4D and ALERT, VA-HIT), cardiomyopathy (FOSIDIAL, telmisartan, carvedilol), anemia (US Normal Hematocrit, CHOIR and CREATE trials), hyperhomocystenemia (ASFAST, US folic acid trial, HOST), disordered bone mineral metabolism (Cunningham meta-analysis, DCOR), oxidative stress therapy (SPACE, HOPE and ATIC, N-acetylcysteine) and multidisciplinary multiple cardiovascular risk factor intervention clinics (LANDMARK) have added to the available pool of clinical data, level 1 clinical evidence remains significantly lacking. The negative findings in many of these trials highlight the potential dangers of extrapolating findings from non kidney disease patients to those with CKD. Further large, well-designed trials are urgently required to address this issue.

Identification of protective epitopes by sequencing of the major outer membrane protein gene of a variant strain of Chlamydia psittaci serotype 1 (Chlamydophila abortus).

Protective monoclonal antibodies (MAbs) to the major outer membrane protein (MOMP) of species of the family Chlamydiaceae, which is the primary vaccine candidate antigen, recognize nonlinear epitopes conferred by the oligomeric conformation of the molecule. Protective MAbs failed to recognize oligomeric MOMP of the variant strain LLG, which bears amino acid substitutions in variable segments (VSs) 1, 2, and 4, and competed with monomer-specific MAbs mapping to these VSs in reference strain 577. The results suggest that multiple sites located in the three VSs contribute to the epitope of protective MAbs.

Evidence for a 5-HT3 receptor involvement in the facilitation of peristalsis on mucosal application of 5-HT in the guinea pig isolated ileum.

1. The 5-HT receptor involved in the effect of mucosal application of 5-HT to facilitate peristalsis was investigated in the isolated guinea pig ileum. 2. An application of 5-HT (3-100 microM) to the mucosal surface (by inclusion of 5-HT in the Krebs-Henseleit solution passing through the lumen of the ileum) caused a concentration related facilitation of peristalsis characterized by a reduction in the peristaltic threshold. 3. Peristalsis was not modified by methiothepine (0.1 microM), ritanserin (0.1 microM), ondansetron (5 microM), granisetron (1 microM) or SB 204070 (0.1 microM) administered alone to the mucosal surface. 4. The concentration-response curve to mucosally applied 5-HT was not altered by the mucosally applied 5-HT1/2 receptor antagonist methiothepine (0.1 microM), the 5-HT2 receptor antagonist ritanserin (0.1 microM) or the 5-HT4 receptor antagonist SB 204070 (0.1 microM). However, the mucosally applied 5-HT3 receptor antagonists ondansetron (5 microM) and granisetron (1 microM) shifted the response curves to mucosally applied 5-HT to the right in a parallel and surmountable manner. The pD2 values in the absence and presence of ondansetron were 5.42 +/- 0.07 and 4.12 +/- 0.10, respectively, (n = 6) and that of granisetron were 5.45 +/- 0.12 and 4.50 +/- 0.10 respectively, (n = 5). 5. Serosally applied ondansetron (5 microM) or granisetron (1 microM) had no effect on the concentration-response curve to mucosally applied 5-HT. However, the serosally applied ondansetron and granisetron antagonised the facilitatory effect of serosally applied 5-HT (10 microM) when administered in the presence of serosally applied SB 204070 (0.1 microM). 6. It is concluded that the facilitatory effect of mucosally applied 5-HT to reduce the peristaltic threshold in the guinea pig ileum is mediated via a 5-HT3 receptor located on the mucosal and not the serosal side of the ileum.