Heme binding to the SARS-CoV-2 spike glycoprotein

The target for humoral immunity, SARS-CoV-2 spike glycoprotein, has become the focus of vaccine research and development. Previous work demonstrated that the N-terminal domain (NTD) of SARS-CoV-2 spike binds biliverdin-a product of heme catabolism-causing a strong allosteric effect on the activity of a subset of neutralizing antibodies. Herein, we show that the spike glycoprotein is also able to bind heme (KD = 0.5 ± 0.2 μM). Molecular modeling indicated that the heme group fits well within the same pocket on the SARS-CoV-2 spike NTD. Lined by aromatic and hydrophobic residues (W104, V126, I129, F192, F194, I203, and L226), the pocket provides a suitable environment to stabilize the hydrophobic heme. Mutagenesis of N121 has a substantive effect on heme binding (KD = 3000 ± 220 μM), confirming the pocket as a major heme binding location of the viral glycoprotein. Coupled oxidation experiments in the presence of ascorbate indicated that the SARS-CoV-2 glycoprotein can catalyze the slow conversion of heme to biliverdin. The heme trapping and oxidation activities of the spike may allow the virus to reduce levels of free heme during infection to facilitate evasion of the adaptive and innate immunity.

Crystal structure of Trypanosoma cruzi heme peroxidase and characterization of its substrate specificity and compound I intermediate

The protozoan parasite Trypanosoma cruzi is the causative agent of American trypanosomiasis, otherwise known as Chagas disease. To survive in the host, the T. cruzi parasite needs antioxidant defense systems. One of these is a hybrid heme peroxidase, the T. cruzi ascorbate peroxidase-cytochrome c peroxidase enzyme (TcAPx-CcP). TcAPx-CcP has high sequence identity to members of the class I peroxidase family, notably ascorbate peroxidase (APX) and cytochrome c peroxidase (CcP), as well as a mitochondrial peroxidase from Leishmania major (LmP). The aim of this work was to solve the structure and examine the reactivity of the TcAPx-CcP enzyme. Low temperature electron paramagnetic resonance spectra support the formation of an exchange-coupled [Fe(IV)=O Trp233•+] compound I radical species, analogous to that used in CcP and LmP. We demonstrate that TcAPx-CcP is similar in overall structure to APX and CcP, but there are differences in the substrate-binding regions. Furthermore, the electron transfer pathway from cytochrome c to the heme in CcP and LmP is preserved in the TcAPx-CcP structure. Integration of steady state kinetic experiments, molecular dynamic simulations, and bioinformatic analyses indicates that TcAPx-CcP preferentially oxidizes cytochrome c but is still competent for oxidization of ascorbate. The results reveal that TcAPx-CcP is a credible cytochrome c peroxidase, which can also bind and use ascorbate in host cells, where concentrations are in the millimolar range. Thus, kinetically and functionally TcAPx-CcP can be considered a hybrid peroxidase.

XFEL Crystal Structures of Peroxidase Compound II

Oxygen activation in all heme enzymes requires the formation of high oxidation states of iron, usually referred to as ferryl heme. There are two known intermediates: Compound I and Compound II. The nature of the ferryl heme-and whether it is an FeIV =O or FeIV -OH species-is important for controlling reactivity across groups of heme enzymes. The most recent evidence for Compound I indicates that the ferryl heme is an unprotonated FeIV =O species. For Compound II, the nature of the ferryl heme is not unambiguously established. Here, we report 1.06 Å and 1.50 Å crystal structures for Compound II intermediates in cytochrome c peroxidase (CcP) and ascorbate peroxidase (APX), collected using the X-ray free electron laser at SACLA. The structures reveal differences between the two peroxidases. The iron-oxygen bond length in CcP (1.76 Å) is notably shorter than in APX (1.87 Å). The results indicate that the ferryl species is finely tuned across Compound I and Compound II species in closely related peroxidase enzymes. We propose that this fine-tuning is linked to the functional need for proton delivery to the heme.

XFEL Crystal Structures of Peroxidase Compound II

Oxygen activation in all heme enzymes requires the formation of high oxidation states of iron, usually referred to as ferryl heme. There are two known intermediates: Compound I and Compound II. The nature of the ferryl heme-and whether it is an FeIV=O or FeIV-OH species-is important for controlling reactivity across groups of heme enzymes. The most recent evidence for Compound I indicates that the ferryl heme is an unprotonated FeIV=O species. For Compound II, the nature of the ferryl heme is not unambiguously established. Here, we report 1.06 Å and 1.50 Å crystal structures for Compound II intermediates in cytochrome c peroxidase (CcP) and ascorbate peroxidase (APX), collected using the X-ray free electron laser at SACLA. The structures reveal differences between the two peroxidases. The iron-oxygen bond length in CcP (1.76 Å) is notably shorter than in APX (1.87 Å). The results indicate that the ferryl species is finely tuned across Compound I and Compound II species in closely related peroxidase enzymes. We propose that this fine-tuning is linked to the functional need for proton delivery to the heme.

Normal and abnormal response to sperm deposition in female dogs: A review and new hypotheses for endometritis

In mammalian species there are significant physiological responses of the female reproductive tract to the deposition of sperm. These are particularly notable in species where sperm are deposited directly into the uterus, and function both to facilitate sperm transport to the sperm reservoir, and to eliminate introduced contaminants. In the bitch, sperm are deposited into the vagina and are rapidly transported through the open cervix. Sperm are then distributed around the uterus by uterine contractions such that transportation to the tip of the uterine horns occurs within 1 min of the start of mating. The main sperm reservoir appears to be the distal part of the utero-tubal junction which forms a pre-uterine tube reservoir. Sperm remain attached here by their heads to uterine epithelium and remain viable. In non-capacitating conditions sperm slowly detach from this site and this seems important to replenish the uterine tube reservoir, where sperm may re-attach to the epithelium. Post-ovulatory signals trigger capacitation changes and subsequent hyperactivated motility that is associated with detachment of sperm from both reservoirs; thus facilitating fertilization. After mating, a physiological post-mating uterine inflammatory response occurs, evidenced by an influx of polymorphonuclear neutrophils, increased uterine contractions, an increased uterine artery blood flow and a decrease of the resistance index indicating a short-duration vasodilation. Disturbance of this tightly regulated system has the potential to impact fertility by a failure of elimination of the introduced contaminants (such that a clinically-significant post-breeding endometritis ensues) but also by impairing sperm transport.

Discovery of a heme-binding domain in a neuronal voltage-gated potassium channel

The EAG (ether-à-go-go) family of voltage-gated K⁺ channels are important regulators of neuronal and cardiac action potential firing (excitability) and have major roles in human diseases such as epilepsy, schizophrenia, cancer, and sudden cardiac death. A defining feature of EAG (Kv10-12) channels is a highly conserved domain on the N terminus, known as the eag domain, consisting of a Per-ARNT-Sim (PAS) domain capped by a short sequence containing an amphipathic helix (Cap domain). The PAS and Cap domains are both vital for the normal function of EAG channels. Using heme-affinity pulldown assays and proteomics of lysates from primary cortical neurons, we identified that an EAG channel, hERG3 (Kv11.3), binds to heme. In whole-cell electrophysiology experiments, we identified that heme inhibits hERG3 channel activity. In addition, we expressed the Cap and PAS domain of hERG3 in Escherichia coli and, using spectroscopy and kinetics, identified the PAS domain as the location for heme binding. The results identify heme as a regulator of hERG3 channel activity. These observations are discussed in the context of the emerging role for heme as a regulator of ion channel activity in cells.

Heme binding to human CLOCK affects interactions with the E-box

The circadian clock is an endogenous time-keeping system that is ubiquitous in animals and plants as well as some bacteria. In mammals, the clock regulates the sleep-wake cycle via 2 basic helix-loop-helix PER-ARNT-SIM (bHLH-PAS) domain proteins-CLOCK and BMAL1. There is emerging evidence to suggest that heme affects circadian control, through binding of heme to various circadian proteins, but the mechanisms of regulation are largely unknown. In this work we examine the interaction of heme with human CLOCK (hCLOCK). We present a crystal structure for the PAS-A domain of hCLOCK, and we examine heme binding to the PAS-A and PAS-B domains. UV-visible and electron paramagnetic resonance spectroscopies are consistent with a bis-histidine ligated heme species in solution in the oxidized (ferric) PAS-A protein, and by mutagenesis we identify His144 as a ligand to the heme. There is evidence for flexibility in the heme pocket, which may give rise to an additional Cys axial ligand at 20K (His/Cys coordination). Using DNA binding assays, we demonstrate that heme disrupts binding of CLOCK to its E-box DNA target. Evidence is presented for a conformationally mobile protein framework, which is linked to changes in heme ligation and which has the capacity to affect binding to the E-box. Within the hCLOCK structural framework, this would provide a mechanism for heme-dependent transcriptional regulation.

Solution structure of the cytochrome P450 reductase-cytochrome c complex determined by neutron scattering

Electron transfer in all living organisms critically relies on formation of complexes between the proteins involved. The function of these complexes requires specificity of the interaction to allow for selective electron transfer but also a fast turnover of the complex, and they are therefore often transient in nature, making them challenging to study. Here, using small-angle neutron scattering with contrast matching with deuterated protein, we report the solution structure of the electron transfer complex between cytochrome P450 reductase (CPR) and its electron transfer partner cytochrome c This is the first reported solution structure of a complex between CPR and an electron transfer partner. The structure shows that the interprotein interface includes residues from both the FMN- and FAD-binding domains of CPR. In addition, the FMN is close to the heme of cytochrome c but distant from the FAD, indicating that domain movement is required between the electron transfer steps in the catalytic cycle of CPR. In summary, our results reveal key details of the CPR catalytic mechanism, including interactions of two domains of the reductase with cytochrome c and motions of these domains relative to one another. These findings shed light on interprotein electron transfer in this system and illustrate a powerful approach for studying solution structures of protein-protein complexes.

Veterinary practitioners' selection of diagnostic tests for the primary evaluation of colic in the horse

The aim of this study was to survey veterinary practitioners’ selection of diagnostic tests for horses with clinical signs of abdominal pain. A questionnaire was distributed to veterinary surgeons involved in the primary evaluation of horses with abdominal pain, including the respondent's demographics, selection of diagnostic tests and factors affecting decision-making. Data analysis included descriptive analysis, categorisation of free text and simple univariable correlations to explore the relationships between independent variables and the relative self-estimated frequency that diagnostic tests were performed. A total of 228 responses were analysed. Participants worked in mixed practice (55.7 per cent), first opinion equine (22.8 per cent), first and second opinion equine (17.9 per cent) and referral practice (3.1 per cent). The majority (48.2 per cent, 105/218) were very confident managing a colic case (confidence level 4/5). The most frequently used diagnostic tests were ‘response to analgesia’ (87.2±24.0 per cent cases), rectal examination (75.9±21.2 per cent) and nasogastric intubation (43.8±27.6 per cent). Approach varied between practitioners, and for all diagnostic tests with frequency of use ranging from 0 to 100 per cent of cases. ‘Risk to personal safety’ was the most common reason for not using rectal examination. Practitioner's opinion of their confidence level in managing a colic case was associated with how frequently they used different diagnostic tests. There was marked variation in practitioners’ approaches, highlighting the need for further evidence to support decision-making.

Clinical Research Abstracts of the British Equine Veterinary Association Congress 2015

REASONS FOR PERFORMING STUDY

Colic is a common reason for owners to seek veterinary treatment for their working equids in Morocco. There is no information available regarding cultural, religious or educational barriers to obtaining treatment or about the typical workload of these animals which may predispose them to colic.

OBJECTIVES

To characterise the typical workload and feeding regimens of working equids in Morocco; to characterise the ability of owners to recognise the clinical signs and causes of colic; and to identify specific barriers to the veterinary treatment of colic.

STUDY DESIGN

Questionnaire-based survey.

METHODS

A standardised, structured questionnaire was administered, with the assistance of an Arabic speaking interpreter, to the owners of working equids presenting their animals to 2 centres run by SPANA (The Society for the Protection of Animals Abroad). Participation was voluntary and informed consent was obtained prior to the interview.

RESULTS

All of the 102 participants that completed questionnaire were male. Ninety-eight owners used their animals for pulling carts, with 12% of animals working 7 days per week. 14% of animals were offered water by their owner once per day and 2% every other day. 25% of animals were loose and allowed free to feed unsupervised when not working. 29% of owners were not able to name any cause of colic and 25% did not recognise any clinical signs; only 12% associated colic with gastrointestinal pain. 83% of owners would not seek veterinary treatment due to financial constraints if free treatment at SPANA centres were not available.

CONCLUSIONS

Colic remains a common problem amongst working equids in Morocco. Improved knowledge of management factors associated with colic and how to recognise abdominal pain may reduce the incidence of colic and improve prognosis. The findings presented can be used to inform and develop owner education programmes. Ethical animal research: The study was reviewed and approved by the Ethics Committee, School of Veterinary Medicine and Science, University of Nottingham. Informed consent for participation in the study was obtained from all owners and was delivered in the native language. No details identifying the owner were recorded.

SOURCE OF FUNDING

None. Competing interests: None declared.

Clinical Research Abstracts of the British Equine Veterinary Association Congress 2015

REASONS FOR PERFORMING STUDY

Colic is the most common equine emergency problem, and one of the main causes of equid deaths. The horse owners' ability to recognise colic is a critical first step in determining case outcome.

OBJECTIVES

To assess equine owners' knowledge and recognition of colic.

STUDY DESIGN

Online questionnaire of horse owners.

METHODS

An online survey was designed to evaluate owners' approach to colic in the horse. The survey included questions on owner demographics, their recognition of colic (including owner's opinions of their ability to recognise colic, their approach, and their recognition of colic using case vignettes), and their knowledge of normal ranges for clinical parameters. Descriptive and chi squared statistical analysis was performed.

RESULTS

The survey was completed by 1061 UK respondents. Six per cent of owners thought they could recognise all types of colic, 61% said they could recognise most cases and 30% said they could recognise some but not all cases. Owners said they would assess faecal output (73% of respondents), gastrointestinal sounds (69%), respiratory rate (62%) and heart rate (50%) in horses with suspected colic. One fifth (22%) of owners would call a vet immediately without assessing any parameters. Many respondents either did not know, or provided incorrect estimates of normal values for clinical parameters: 30.4% were 'unsure' of the normal heart rate and 35.5% gave heart rate values which were outside reference ranges; only 24.5% gave appropriate values for normal respiratory rates and only 31% gave normal temperature values. There was no statistical significance between participants' age, educational qualifications, or their experience with horses and their knowledge of normal clinical parameters.

CONCLUSIONS

Owners varied in their approach and ability to recognise colic, and many had significant gaps in their knowledge of normal parameters. Educational materials and/or training to assist owners could help address these issues. Ethical animal research: The study did not involve animal research. The study was reviewed and approved by the Ethics Committee, School of Veterinary Medicine and Science, University of Nottingham. The questionnaire was conducted in accordance with the 1998 Data Protection Act, and the British Educational Research Association's Revised Ethical Guidelines for Educational Research (2004).

SOURCE OF FUNDING

Adelle Bowden's studentship is funded by the School of Veterinary Medicine and Science, University of Nottingham. Competing interests: None declared.

Water intake, faecal output and intestinal motility in horses moved from pasture to a stabled management regime with controlled exercise

Reasons for performing study

A change in management from pasture to stabling is a risk factor for equine colic.

Objectives

To investigate the effect of a management change from pasture with no controlled exercise to stabling with light exercise on aspects of gastrointestinal function related to large colon impaction. The hypothesis was that drinking water intake, faecal output, faecal water content and large intestinal motility would be altered by a transition from a pastured to a stabled regime.

Study design

Within-subject management intervention trial involving changes in feeding and exercise using noninvasive techniques.

Methods

Seven normal horses were evaluated in a within-subjects study design. Horses were monitored while at pasture 24 h/day, and for 14 days following a transition to a stabling regime with light controlled exercise. Drinking water intake, faecal output and faecal dry matter were measured. Motility of the caecum, sternal flexure and left colon (contractions/min) were measured twice daily by transcutaneous ultrasound. Mean values were pooled for the pastured regime and used as a reference for comparison with stabled data (Days 1–14 post stabling) for multilevel statistical analysis.

Results

Drinking water intake was significantly increased (mean ± s.d. pasture 2.4 ± 1.8 vs. stabled 6.4 ± 0.6 l/100 kg bwt/day), total faecal output was significantly decreased (pasture 4.62 ± 1.69 vs. stabled 1.81 ± 0.5 kg/100 kg bwt/day) and faecal dry matter content was significantly increased (pasture 18.7 ± 2.28 vs. stabled 27.2 ± 1.93% DM/day) on all days post stabling compared with measurements taken at pasture (P<0.05). Motility was significantly decreased in all regions of the large colon collectively on Day 2 post stabling (-0.76 contractions/min), and in the left colon only on Day 4 (-0.62 contractions/min; P<0.05).

Conclusions

There were significant changes in large intestinal motility patterns and parameters relating to gastrointestinal water balance during a transition from pasture to stabled management, particularly during the first 5 days.

Prevalence and effect of uterine luminal free fluid on pregnancy and litter size in bitches

Free fluid within the uterine lumen has been identified ultrasonographically as a transient finding in normal bitches in the period immediately after mating, and delayed clearance of the fluid has been documented in bitches with endometrial hyperplasia. This study used B-mode ultrasonography to investigate the prevalence of free fluid in the uterine lumen in normal bitches (n = 53) and bitches with endometrial hyperplasia (n = 10) on Days -7, 0, +5, and +14 in relation to estimated ovulation. For normal bitches without endometrial hyperplasia, 47 (86.6%) bitches become pregnant, whereas for bitches with endometrial hyperplasia, 3 (30%) become pregnant. In both the groups, the presence of uterine fluid on Days -7 and 0 was not associated with the probability of a bitch becoming pregnant, whereas the presence of uterine fluid on either Day +5 or +14 was significantly associated with a reduced likelihood of pregnancy. In pregnant bitches, uterine luminal fluid present on Day 0 was associated with a smaller litter size. This is the first study to establish the prevalence and effect of uterine luminal free fluid in bitches. We postulate that as the uterine luminal free fluid may be detected in normal bitches before mating and has no effect on the pregnancy rate or litter size in either group, this fluid is "physiological." However, it seems that the later in estrus the uterine fluid is present, the more likely it is to have an adverse effect on fertility. In some cases, this is manifest as a reduced litter size, while, importantly, the presence of fluid 5 to 14 days after ovulation is strongly associated with an absence of pregnancy, both in bitches with and without endometrial hyperplasia. We propose that ultrasonographic detection of uterine luminal free fluid after mating may be a useful prognostic indicator for pregnancy outcome, which may allow the targeting of treatments specifically to a population of animals that presumably develop mating-induced endometritis.

Enhancing clinical learning in the workplace: a qualitative study

Workplace learning (WPL) is seen as an essential component of clinical veterinary education by the veterinary profession. This study sought to understand this type of learning experience more deeply. This was done utilising observations of students on intramural rotations (IMR) and interviews with students and clinical staff. WPL was seen as an opportunity for students to apply knowledge and develop clinical and professional skills in what is generally regarded as a safe, authentic environment. Clinical staff had clear ideas of what they expected from students in terms of interest, engagement, professionalism, and active participation, where this was appropriate. In contrast, students often did not know what to expect and sometimes felt under-prepared when entering the workplace, particularly in a new species area. With the support of staff acting as mentors, students learned to identify gaps in their knowledge and skills, which could then be addressed during specific IMR work placements. Findings such as these illustrate both the complexities of WPL and the diversity of different workplace settings encountered by the students.

Follicular dynamics, ovulation and conception rates in bitches

Real-time ultrasound imaging was used in a clinical study to estimate the number of follicles of different sizes, ovulation and conception rates, and to study follicle dynamics following oestrus-induction of bitches. Follicles were identified during late anoestrus (between 100 and 60 days prior to the pre-ovulatory LH surge) and there appeared to be a shift in the population from small follicles (1-3 mm in diameter) to large follicles (>4 mm diameter) approximately 2 days prior to the LH surge. Corpora lutea could be reliably identified although the majority were cavitated. High ovulation rates (97-100%) and pregnant rates (86-100%) were detected, and although the conception rate was approximately 70% it varied between 8 and 92%. Within the narrow range of the clinical population studied there were trends relating age to reproduction performance. Oestrus induction with a gonadotrophin regime appeared to result in large numbers of small follicles that did not ovulate, whilst when using cabergoline the number of small and large follicels and the number of copora lutea were similar to those of control cycles.

Cardiopulmonary effects and pharmacokinetics of i.v. dexmedetomidine in ponies

REASONS FOR PERFORMING STUDY

Currently available sedatives depress cardiopulmonary function considerably; therefore, it is important to search for new, less depressive sedatives. The study was performed to assess duration and intensity of cardiopulmonary side effects of a new sedative, dexmedetomidine (DEX), in horses.

OBJECTIVES

To study pharmacokinetics and cardiopulmonary effects of i.v. DEX.

METHODS

Pharmacokinetics of 3.5 microg/kg bwt i.v. DEX were studied in a group of 8 mature (mean age 4.4 years) and 6 old ponies (mean age 20 years). Cardiopulmonary data were recorded in mature ponies before and 5, 10, 20, 30, 45 and 60 mins after administration of DEX 3.5 microg/kg bwt i.v. Data were analysed using ANOVA for repeated measures, and where appropriate Dunnett's t test was used to detect differences from resting values (P < 0.05).

RESULTS

Within 2 h after DEX administration, plasma levels were beyond limits of quantification (0.05 ng/ml). Mean values for kinetic parameters for mature and old ponies were: Cmax (ng/ml) 4.6 and 3.8, t 1/2 (min) 19.8 and 28.9 and AUC (ng.min/ml) 34.5 and 44.3, respectively. Heart rate, central venous pressure, pulmonary artery pressure and pulmonary capillary wedge pressure did not change significantly compared to presedation values throughout the 60 min observation period. Compared to presedation values, stroke volume and mixed venous PO2 were reduced for the first 5 mins, paralleled by an increase in systemic and pulmonary vascular resistance. Cardiac index was reduced for the first 10 mins, arterial blood pressures at 20, 30 and 45 mins and respiratory rate throughout the 60 min observation period, but no change in arterial PO2 or PCO2 occurred.

CONCLUSIONS

DEX administration i.v. causes similar cardiopulmonary changes to those caused by other alpha-2 adrenoceptor agonists, but of very short duration. DEX is redistributed particularly rapidly.

POTENTIAL RELEVANCE

DEX might be safer for sedation of horses because of its very short-lasting cardiopulmonary side effects. For long duration sedation, its kinetics favour its use as a continuous infusion.

Treatment of spontaneous pyometra in 22 bitches with a combination of cabergoline and cloprostenol

Twenty-two bitches with ultrasonographically diagnosed spontaneous pyometra were treated with a combination of 5 microg/kg cabergoline per day and 5 mug/kg cloprostenol every third day, and potentiated sulphonamide twice a day. Bitches with either open-cervix or closed-cervix pyometra showed a rapid clinical improvement, associated with a reduction in plasma progesterone concentration, increased vulval discharge and a reduction in the diameter of the uterus. The haematological profiles of 21 of the bitches returned to normal within six days of treatment, and their biochemical profiles returned to normal within nine days; 19 of the bitches were managed successfully by a 10-day period of treatment. Two bitches required a further three days of treatment, and in one bitch with a partial uterine torsion the treatment was not successful. Adverse effects of the treatment were limited to the 60 minutes immediately after the administration of prostaglandin, and included retching, vomiting, mild abdominal straining, diarrhoea and panting. The incidence of adverse effects was reduced after each successive dose of prostaglandin. Eleven of the 21 successfully treated bitches were mated at the next oestrus, and seven became pregnant; their litters were smaller than the published breed averages. In four of the bitches the pyometra recurred after the next oestrus.

Relationship between the fertile period and sperm transport in the bitch

Following ejaculation into the vagina, dog sperm remain functionally competent for many days, acquire the ability to fertilize, and are delivered to an appropriate site within the uterine tube synchronously with the appearance of fertile oocytes. The mechanisms involved in regulating this system are complex, and allow for sperm storage within the female reproductive tract. The aim of this paper is to review current knowledge of the transportation of sperm and their biology within the reproductive tract of the bitch.

Luminal glucose sensing in the rat intestine has characteristics of a sodium-glucose cotransporter

The presence of glucose in the intestinal lumen elicits a number of changes in gastrointestinal function, including inhibition of gastric emptying and food intake and stimulation of pancreatic and intestinal secretion. The present study tested the hypothesis that Na(+)-glucose cotransporter (SGLT)-3, a member of the SGLT family of transport proteins, is involved in detection of luminal glucose in the intestine. Gastric emptying, measured in awake rats, was significantly inhibited by perfusion of the intestine with glucose (60 and 90 mg); this effect was mimicked by alpha-methyl glucose (nonmetabolizable substrate of SGLT-1 and -3) but not 2-deoxy-d-glucose (substrate for GLUT-2) or isoosmotic mannitol. Gastric motility and intestinal fluid secretion, measured in anesthetised rats, were significantly inhibited and stimulated, respectively, by duodenal glucose but not galactose, which has a much lower affinity for SGLT-3 than glucose. Duodenal glucose but not galactose stimulated the release of 5-HT into mesenteric lymph and stimulated the discharge of duodenal vagal afferent fibers. mRNA for SGLT-3 was identified in the duodenal mucosa. Together these data suggest that detection of glucose in the intestine may involve SGLT-3, possibly expressed by enterochromaffin cells in the intestinal mucosa, and release of 5-HT.

Nitric oxide inhibitable isoforms of adenylate cyclase mediate epithelial secretory dysfunction following exposure to ionising radiation

BACKGROUND

Hyporesponsiveness of the intestinal epithelium to secretagogues occurs in different models of intestinal injury, including radiation enteropathy, and in human disease. While this impairment of barrier function has been linked to increased inducible nitric oxide synthase (iNOS) activity, the cellular target of NO in this phenomenon is not known, although recent studies suggest that some isoforms of adenylate cyclase are inhibited by NO.

AIMS

To determine adenylate cyclase isoform distribution in colonic epithelial cells and, in particular, the physiological significance of NO inhibitable adenylate cyclase isoforms 5 and 6 in radiation induced epithelial secretory dysfunction.

METHODS

Reverse transcription-polymerase chain reaction (RT-PCR), immunocytochemistry, and immunohistochemistry were used to examine adenylate cyclase expression. The responsiveness of mouse colon to secretagogues 72 hours post-15 Gy gamma radiation or following in vitro exposure to NO donors was measured in Ussing chambers. Also, cAMP, cGMP, and ATP levels were measured.

RESULTS

RT-PCR, immunocytochemistry, and immunohistochemistry showed that adenylate cyclase 5 was expressed in mouse colon, and isoforms 5 and 6 were expressed in human biopsies and intestinal epithelium. Pharmacological studies showed that these isoforms are functionally important in chloride secretion. NO mediated hyporesponsiveness to secretagogues is primarily a result of decreased adenylate cyclase activity, and not G(i) activation or decreased cellular ATP levels.

CONCLUSIONS

NO inhibitable isoforms of adenylate cyclase are expressed in mouse and human secretory colonic epithelia, and appear to be the target of radiation induced NO to reduce the responsiveness to cAMP dependent secretagogues.

Medetomidine-ketamine anaesthesia induction followed by medetomidine-propofol in ponies: infusion rates and cardiopulmonary side effects

REASONS FOR PERFORMING STUDY

To search for long-term total i.v. anaesthesia techniques as a potential alternative to inhalation anaesthesia.

OBJECTIVES

To determine cardiopulmonary effects and anaesthesia quality of medetomidine-ketamine anaesthesia induction followed by 4 h of medetomidine-propofol anaesthesia in 6 ponies.

METHODS

Sedation consisted of 7 microg/kg bwt medetomidine i.v. followed after 10 min by 2 mg/kg bwt i.v. ketamine. Anaesthesia was maintained for 4 h with 3.5 microg/kg bwt/h medetomidine and propofol at minimum infusion dose rates determined by application of supramaximal electrical pain stimuli. Ventilation was spontaneous (F(I)O2 > 0.9). Cardiopulmonary measurements were always taken before electrical stimulation, 15 mins after anaesthesia induction and at 25 min intervals.

RESULTS

Anaesthesia induction was excellent and movements after pain stimuli were subsequently gentle. Mean propofol infusion rates were 0.89-0.1 mg/kg bwt/min. No changes in cardiopulmonary variables occured over time. Range of mean values recorded was: respiratory rate 13.0-15.8 breaths/min; PaO2 29.1-37.9 kPa; PaCO2 6.2-6.9 kPa; heart rate 31.2-40.8 beats/min; mean arterial pressure 90.0-120.8 mmHg; cardiac index 44.1-59.8 ml/kg bwt/min; mean pulmonary arterial pressure 11.8-16.4 mmHg. Recovery to standing was an average of 31.1 mins and ponies stood within one or 2 attempts.

CONCLUSIONS

In this paper, ketamine anaesthesia induction avoided the problems encountered previously with propofol. Cardiovascular function was remarkably stable. Hypoxaemia did not occur but, despite F(I)O2 of > 0.9, minimal PaO2 in one pony after 4 h anaesthesia was 8.5 kPa.

POTENTIAL RELEVANCE

The described regime might offer a good, practicable alternative to inhalation anaesthesia and has potential for reducing the fatality rate in horses.

Cardiovascular effects of romifidine in the standing horse

The cardiovascular effects of romifidine, an alpha-2 adrenoreceptor agonist, were investigated in six horses using two doses (80 and 120 microg kg(-1)) in a cross-over study design. Cardiac index and mixed venous oxygenation were significantly decreased at 15 and 30 minutes after both doses of romifidine. Systemic vascular resistance was significantly increased with romifidine (120 microg kg(-1)). Arterial blood pressure increased initially and then gradually decreased; the doses of decrease was significant at 90 and 120 minutes with romifidine 80 and 120 microg kg(-1). There were minimal differences between the two doses of romifidine, and both should be used with care especially in horses with cardiovascular compromise, or when used in combination with other cardiovascular depressant drugs.

Effect of romifidine on gastrointestinal motility, assessed by transrectal ultrasonography

A technique of transrectal ultrasonography was developed to investigate the effects of romifidine 80 and 120 microg/kg bwt on intestinal motility in the horse. Motility of the small intestine, caecum and left ventral colon were assessed following injection of romifidine and a saline control, using a blinded, cross-over study design in 6 horses. Measurements were taken at 15, 30, 60, 120, 180 and 240 min after drug administration. There was a slight nonsignificant decrease in motility in the control group over the 4 h study period. Both doses of romifidine produced a marked decrease in gastrointestinal motility and were associated with the presence of reduced (nonpropulsive) contractions. Transrectal ultrasonography proved suitable for monitoring changes in the type and frequency of intestinal motility in the horse.

Cardiopulmonary effects of prolonged anesthesia via propofol-medetomidine infusion in ponies

OBJECTIVE

To determine cardiopulmonary effects of total IV anesthesia with propofol and medetomidine in ponies and effect of atipamezole on recovery.

ANIMALS

10 ponies.

PROCEDURE

After sedation was induced by IV administration of medetomidine (7 microg/kg of body weight), anesthesia was induced by IV administration of propofol 12 mg/kg) and maintained for 4 hours with infusions of medetomidine (3.5 microg/kg per hour) and propofol 10.07 to 0.11 mg/kg per minute). Spontaneous respiration was supplemented with oxygen. Cardiopulmonary measurements and blood concentrations of propofol were determined during anesthesia. Five ponies received atipamezole (60 microg/kg) during recovery.

RESULTS

During anesthesia, mean cardiac index and heart rate increased significantly until 150 minutes, then decreased until cessation of anesthesia. Mean arterial pressure and systemic vascular resistance index increased significantly between 150 minutes and 4 hours. In 4 ponies, PaO2 decreased to < 60 mm Hg. Mean blood propofol concentrations from 20 minutes after induction onwards ranged from 2.3 to 3.5 microg/ml. Recoveries were without complications and were complete within 28 minutes with atipamezole administration and 39 minutes without atipamezole administration.

CONCLUSIONS AND CLINICAL RELEVANCE

During total IV anesthesia of long duration with medetomidine-propofol, cardiovascular function is comparable to or better than under inhalation anesthesia. This technique may prove suitable in equids in which prompt recovery is essential; however, in some animals severe hypoxia may develop and oxygen supplementation may be necessary.

Infusion of a combination of propofol and medetomidine for long-term anesthesia in ponies

OBJECTIVE

To determine the minimal infusion rate of propofol in combination with medetomidine for long-term anesthesia in ponies and the effects of atipamezole on recovery.

ANIMALS

12 ponies.

PROCEDURE

Ponies were sedated with medetomidine (7 microg/kg of body weight, IV). Ten minutes later, anesthesia was induced with propofol (2 mg/kg, IV). Anesthesia was maintained for 4 hours, using an infusion of medetomidine (3.5 microg/kg per hour, IV) and propofol at a rate sufficient to prevent ponies from moving after electrical stimulation. Arterial blood pressures and blood gas analysis, heart rates, and respiratory rates were monitored. For recovery, 6 ponies were given atipamezole (60 microg/kg, IV). Induction and recovery were scored.

RESULTS

Minimal propofol infusion rates ranged from 0.06 to 0.1 mg/kg per min. Mean arterial blood pressure was stable (range, 74 to 86 mm Hg), and heart rate (34 to 51 beats/min) had minimal variations. Variable breathing patterns were observed. Mean PaO2 (range, 116 to 146 mm Hg) and mean PaCO2 (range, 48 to 51 mm Hg) did not change significantly with time, but hypoxemia was evident in some ponies (minimal PaO2, 47 mm Hg). Recovery was fast and uneventful with and without atipamezole (completed in 20.2 and 20.9 minutes, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

Infusion of a combination of medetomidine and propofol was suitable for prolonged anesthesia in ponies. Recovery was rapid and uneventful. A combination of propofol and medetomidine may prove suitable for long-term anesthesia in horses. Monitoring of blood gases is essential because of potential hypoxemia.

Radiation-induced acute intestinal inflammation differs following total-body versus abdominopelvic irradiation in the ferret

PURPOSE

The studies were designed to investigate the differences in the intestinal inflammatory response following abdominopelvic or total-body irradiation in a ferret model.

MATERIALS AND METHODS

Ferrets were exposed either to total-body or to abdominopelvic gamma-radiation (5 Gy) and various parameters of inflammation studied in the jejunum, ileum and colon 2 and 7 days later.

RESULTS

Abdominopelvic and, to a greater extent, total-body irradiation caused weight loss by 7 days. White blood cell counts were reduced in both groups, but more so following total-body irradiation. Myeloperoxidase activity was significantly increased in the ileum 2 days after abdominopelvic irradiation, but it was reduced after total-body irradiation. Total-body irradiation increased tissue prostaglandin E2 levels in all regions at 2 days and decreased jejunal leukotriene B4 levels in the jejunum at both time points. Ileal prostaglandin E2 levels were increased 2 days after abdominopelvic irradiation. Expression of inducible nitric oxide synthase was not altered by either irradiation protocol.

CONCLUSIONS

The data show that there are regional differences in the intestinal response to irradiation, depending on whether it was delivered to the whole body or locally to the abdominopelvic region. In particular, the ileum exhibited an acute increase in myeloperoxidase activity following abdominopelvic but not total-body irradiation.

Cardiopulmonary effects of romifidine and detomidine used as premedicants for ketamine/halothane anaesthesia in ponies

The cardiopulmonary effects of romifidine at 80 microg/kg (R80) or 120 pg/kg (R120), and detomidine at 20 pg/kg (D20) when used as premedicants for ketamine/halothane anaesthesia were investigated in six ponies. Using a blinded crossover design, acepromazine (0-04 mg/kg) was administered followed by the alpha-2 agonist. Anaesthesia was induced with ketamine at 2.2 mg/kg and maintained with halothane (expired concentration 1.0 per cent) in oxygen for three hours. During anaesthesia, arterial blood pressure, cardiac index, PaO2 and PmvO2 decreased, and systemic vascular resistance and PaCO2 increased. The cardiac indices for R80, R120 and D20 were, respectively, 39, 39 and 32 ml/kg/minute at 30 minutes and 29, 29 and 26 ml/kg/minute at 180 minutes. The alpha-2 agonists had similar cardiovascular effects, but PaO2 was significantly lower with R120. The quality of anaesthesia was similar in all three groups.

Investigation of romifidine and detomidine for the clinical sedation of horses

The effects of two intravenous doses of romifidine (80 and 120 microg/kg) and one dose of detomidine (20 microg/kg) were compared in a blinded study in 30 horses requiring to be sedated for routine dental treatment. Several physiological parameters were assessed before and for two hours after the administration of the drugs, and the horses' teeth were rasped 30 minutes after they were administered. Romifidine produced a dose-dependent effect on most parameters. Detomidine at 20 microg/kg was similar to romifidine at 120 microg/kg in the magnitude of its sedative effects, but was similar to romifidine at 80 pg/kg in its duration. There were no significant differences between the three treatments in terms of the clinical procedure score.

Interleukin-12 differentially regulates expression of IFN-gamma and interleukin-2 in human T lymphoblasts

Interleukin-12 (IL-12) is known to upregulate expression of interferon-gamma (IFN-gamma) by activated T cells. However, the effects of IL-12 on production of other Th1-type cytokines are less well defined. In this study, we examined the effects of IL-12 on expression of several cytokines, including IFN-gamma, IL-2, tumor necrosis factor-alpha (TNF-alpha), and IL-10, by primary human CD3(+) T cells. Although purified resting T cells were largely nonresponsive to IL-12 stimulation, anti-CD3-activated T cell blasts were strongly responsive, as demonstrated by the ability of IL-12 to induce Stat4 DNA-binding activity. Restimulation of T lymphoblasts on immobilized anti-CD3 monoclonal antibodies (mAb) induced rapid expression of TNF-alpha mRNA and more gradual increases in mRNA levels for IL-2, IFN-gamma, and IL-10. IL-12 markedly upregulated expression of IFN-gamma and IL-10 but downregulated expression of IL-2 in a dose-dependent and time-dependent manner. The levels of IL-2 produced by IL-12-treated T cells correlated inversely with the levels of IL-10. Moreover, neutralization of IL-10 activity with anti-IL-10 antibodies normalized IL-2 production by IL-12-treated T cells, confirming that the inhibition of IL-2 production by IL-12 was IL-10 mediated. Thus, IL-12 amplified expression of IFN-gamma and IL-10 and, via its ability to upregulate production of IL-10, inhibited expression of IL-2. These findings demonstrate that IL-12 differentially regulates expression of the Th1-type lymphokines, IFN-gamma and IL-2, in T lymphoblasts.

Modulation of hyperoxia-induced TNF-alpha expression in the newborn rat lung by thalidomide and dexamethasone

The effect of high oxygen concentrations on lungs of neonatal rats was studied. In addition, some oxygen-exposed animals were treated with either dexamethasone or thalidomide. No gross histologic changes were noted in the lungs following exposure to 95% oxygen nor were there changes in the total number or the phenotypic distribution of BAL cells obtained from these lungs compared to lungs from air exposed (control) neonatal rats. The majority of the BAL cells were CD45+ leukocytes (macrophages). However, when BAL cells were exposed to LPS in vitro, TNF-alpha production was higher in cells from rats exposed to 95% oxygen compared to cells from rats exposed to ambient air. In addition, lung TNF-alpha and IL-6 mRNA levels were increased after exposure to 95% oxygen. In the lungs of animals treated with either dexamethasone or thalidomide, TNF-alpha mRNA levels were reduced, while only dexamethasone treatment also reduced IL-6 mRNA levels.

Contact of dog spermatozoa with homologous uterine tube epithelium prolongs flagellar activity in relation to the stage of the estrous cycle

There is scant information about the storage of spermatozoa within the reproductive tract of the bitch. In several species the uterine tube plays a significant role in sperm storage. The present study was performed to investigate the interaction between spermatozoa and the epithelium of the uterine tube, in particular how this interaction might influence the flagellar activity of spermatozoa in relation to the stage of the estrous cycle. Epithelium was harvested from uterine tubes of 24 bitches at various stages of the estrous cycle (estrus, luteal phase or anestrus), and cultured with pooled spermatozoa collected from 6 dogs. Spermatozoa rapidly bound to the epithelial surface by their heads and the majority of attached spermatozoa were motile. The intimate association between spermatozoa and the uterine tube epithelium maintained motility in a manner that was related to the stage of the estrous cycle. Flagellar activity was significantly greater for spermatozoa bound to estrous epithelium than epithelium from the luteal phase or anestrus. On average, approximately 10% of spermatozoa that were attached to the uterine tube epithelium of estrous bitches retained their flagellar activity for 48 h after innoculation. There was no apparent influence of the region of the uterine tube on this effect. These findings suggest that the uterine tube may form a functional spermatozoal reservoir in the bitch.

Introducing residents to a career in management: the Physician Management Pathway

To prepare their students and residents for the practice of medicine in a rapidly changing environment, medical educators must teach the business of medicine as well as the science and art of medicine. Recognizing the value of and demand for physician leaders, the authors sought to introduce residents to diverse aspects of medical administration within the context of an academically rigorous internal medicine residency program. The Physician Management Pathway (PMP) was developed in 1997 to expose interested residents to the management concepts employed by physician managers; to help physician trainees begin to develop the leadership and technical skills they will use as physician managers; to provide career mentoring; to provide experiences that enrich the resident's training in clinical medicine; to enhance resident-directed educational activities; and to produce physicians who can successfully work in any health care environment. The PMP curriculum consists of a monthly seminar series, a preceptorship experience in the second year of residency, and a supervised project in the third year. The program was not designed to provide competency in management, but rather is intended to provide an opportunity for new physicians to explore options in this exciting and changing profession.

Ionizing radiation induces iNOS-mediated epithelial dysfunction in the absence of an inflammatory response

Ionizing radiation induces intestinal epithelial hyporesponsiveness to secretagogues through an unknown mechanism. We investigated the role of the inducible isoform of nitric oxide (NO) synthase (iNOS)-derived NO in radiation-induced hyporesponsiveness. C57BL/6 mice were sham treated or exposed to 10-Gy gamma-radiation and were studied 3 days later. Tissues were mounted in Ussing-type diffusion chambers to assess chloride secretion in response to electrical field stimulation (EFS) and forskolin (10 microM). Transport studies were also repeated in iNOS-deficient mice. White blood cell counts were significantly lower in irradiated mice, and there was no inflammatory response as shown by myeloperoxidase activity and histological assessment. iNOS mRNA levels and nitrate/nitrite concentrations were significantly elevated in irradiated colons. iNOS immunoreactivity localized to the epithelium. Colons from irradiated wild-type, but not iNOS-deficient, mice exhibited a significant reduction in the responsiveness of the tissue to EFS and forskolin. The hyporesponsiveness was reversed by L-N(6)-(1-iminoethyl)lysine, 1400W, and dexamethasone treatments. iNOS-derived NO mediates colonic hyporesponsiveness 3 days after irradiation in the mouse in the absence of an inflammatory response.

Thalidomide analogue CC1069 inhibits development of rat adjuvant arthritis

The cytokine tumour necrosis factor-alpha (TNF-alpha) has been implicated in the aetiology of rheumatoid arthritis in humans as well as of experimental arthritis in rodents. Thalidomide, and to a greater extent the new thalidomide analogue CC1069, inhibit monocyte TNF-alpha production both in vitro and in vivo. The aim of the present study is to establish whether these drugs block production of TNF-alpha as well as IL-2 by rat leucocytes and whether this inhibition affects the development of rat adjuvant arthritis (AA). Cultured splenocytes were stimulated with either lipopolysaccharide (LPS) or concanavalin A (Con A) in the presence of thalidomide, CC1069, or solvent, and the production of TNF-alpha and IL-2 were compared. Next, adjuvant was injected into the base of the tail of rats without or with daily intraperitoneal injections with 100-200 mg/kg per day thalidomide or 50-200 mg/kg per day CC1069. Disease activity, including ankle swelling, hind limb radiographic and histological changes, weight gain, and ankle joint cytokine mRNA levels, were monitored. CC1069, but not the parent drug thalidomide, inhibited in vitro production of TNF-alpha and IL-2 by stimulated splenocytes in a dose-dependent manner. In vivo, a dose-dependent suppression of AA disease activity occurred in the CC1069-treated animals. In contrast, thalidomide-treated rats experienced comparable arthritis severity to placebo-treated animals. There was also a reduction in TNF-alpha and IL-2 mRNA levels in the ankle joints of CC1069-treated rats compared with thalidomide- and placebo-treated arthritic rats. Early initiation of CC1069 treatment suppressed AA inflammation more efficiently than delayed treatment. We conclude that thalidomide, which did not suppress TNF-alpha or IL-2 production in vitro by Lewis rat cells, did not suppress development of rat AA. However, the development of rat AA can be blocked by the thalidomide analogue CC1069, which is an efficient inhibitor of TNF-alpha production and IL-2 in vitro.

Comparison of sedative effects of romifidine following intravenous, intramuscular, and sublingual administration to horses

OBJECTIVE

To compare sedative effects of romifidine following IV, IM, or sublingual (SL) administration in horses.

ANIMALS

30 horses that required sedation for routine tooth rasping.

PROCEDURE

Horses (n = 10/group) were given romifidine (120 microg/kg) IV, IM, or SL. Heart rate, respiratory rate, head height, distance between the ear tips, thickness of the upper lip, response to auditory stimulation, response to tactile stimulation, and degree of ataxia were recorded every 15 minutes for 180 minutes. Tooth rasping was performed 60 minutes after administration of romifidine, and overall adequacy of sedation was assessed.

RESULTS

IV and IM administration of romifidine induced significant sedation, but SL administration did not induce significant sedative effects. Scores for overall adequacy of sedation after IV and IM sedation were not significantly different from each other but were significantly different from scores for horses given romifidine SL. Sedative and other effects varied among groups during the first 60 minutes after drug administration; thereafter, effects of IV and IM administration were similar.

CONCLUSIONS AND CLINICAL RELEVANCE

Onset of action was fastest and degree of sedation was greater after IV, compared with IM, administration of romifidine, but duration of action was longer after IM administration. Sublingual administration did not result in clinically important sedative effects.

Interleukin-10 upregulates tumor necrosis factor receptor type-II (p75) gene expression in endotoxin-stimulated human monocytes

Interferon-gamma (IFN-gamma) upregulates expression of certain genes in monocytes, including cell-surface molecules such as HLA class II, B7, and ICAM-1. IFN-gamma also potentiates production of cytokines such as tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta) and IL-12. Conversely, IL-10 downregulates expression of many of these same genes and often antagonizes the effects of IFN-gamma. IL-10 is known to inhibit TNF-alpha production in lipopolysaccharide (LPS)-stimulated monocytes; however, the effects of IL-10 on TNF receptor (TNF-R) expression are not well defined. We examined the effects of IL-10 on production of both membrane-associated (m) and soluble (s) TNF-R type II (sTNF-RII) by purified human CD14(+) monocytes. We also compared the effects of IFN-gamma and IL-10 on production of TNF-alpha and sTNF-RII by these cells. Monocytes constitutively expressed low levels of TNF-RII mRNA and mTNF-RII protein. LPS stimulation induced rapid, but transient loss (shedding) of mTNF-RII molecules and a delayed, but marked increase in TNF-RII mRNA levels. IL-10 increased expression of both mTNF-RII and sTNF-RII by LPS-stimulated monocytes, whereas IFN-gamma decreased their expression. The increased levels of sTNF-RII in cultures of IL-10-treated monocytes correlated directly with increased levels of TNF-RII mRNA and inversely with the levels of TNF-alpha mRNA. The ability of IL-10 to upregulate TNF-RII gene expression was transcriptionally mediated because actinomycin D blocked this effect. Furthermore, IL-10 treatment did not alter the half-life of TNF-RII mRNA transcripts in LPS-stimulated monocytes. To further examine the mechanism by which IL-10 potentiates TNF-RII gene expression, a 1.8-kb fragment of the human TNF-RII promoter cloned into a luciferase expression vector (pGL2-basic) was transfected into the IL-10-responsive macrophage cell line, RAW264.7. Although IL-10 alone induced only minimal promoter activity in these cells, it markedly increased the LPS-induced response, providing further evidence that the ability of IL-10 to amplify TNF-RII gene expression is transcriptionally controlled. Together, these findings demonstrate that IL-10 coordinately downregulates expression of TNF-alpha and upregulates expression of TNF-RII, particularly the soluble form of this receptor, in monocytes.

TCR vbeta usage of TSH receptor-specific CD4+ T cells in Graves' disease patients and healthy humans

Healthy humans have CD4+ T cells specific for self-components. Since autoreactive T cells in autoimmune patients may use a limited number of TCR V-region genes, we investigated here whether this also occurs for the potentially autoreactive CD4+ cells present in healthy persons. We studied CD4+ cells specific for human TSH receptor (TSHr) sequences, that are present with high frequency in healthy subjects and, as expected, in Graves' disease (GD) patients. We used short-term CD4+ cell lines propagated from four GD patients and five healthy subjects by cycles of stimulation with a pool of overlapping synthetic peptides corresponding to the putative extracellular parts of the TSHr sequence. The lines recognized the pool of TSHr peptides specifically and vigorously. Their epitope repertoire had been characterized previously: each line recognized one or a few TSHr peptides, different for each subject. We determined their TCR Vbeta usage by a semi-quantitative reverse transcriptase PCR assay, using primers specific for each known human Vbeta region family, in conjunction with a constant region primer. Six lines preferentially used one Vbeta family (42-94%), different for each line. In all lines, three or less Vbeta families accounted for approximately 60% or more of the Vbeta usage. Different Vbeta regions were used by each subject. There was no obvious difference between the Vbeta usage of the lines from GD patients and healthy controls. These results suggest that a limited pool of potentially autoreactive T cells survives clonal deletion. The pathogenic CD4+ cells involved in autoimmune diseases are likely recruited from that pool, since they have similar characteristics of epitope and TCR repertoire as the CD4+ cells specific for the same autoantigen in healthy subjects.

TSH receptor sequences recognized by CD4+ T cells in Graves' disease patients and healthy controls

Twenty-nine overlapping synthetic peptides, twenty residues long, representing the entire extracellular sequence of the human thyroid stimulating hormone receptor (hTSHr), were used to test the epitope repertoire of CD4+ T lymphocytes from patients with Graves' disease and from healthy subjects. The peptides were used to propagate and test short term CD4+ T cell lines specific for hTSHr epitopes, and to directly test CD8+ depleted, CD4+ enriched peripheral blood lymphocytes. Analysis of the response of short-term CD4+ T cells lines and CD8+ depleted peripheral blood lymphocytes to the individual peptides revealed that 14 of the 15 patients and nine of the ten controls responded to at least one hTSHr peptide. There was no common response pattern, nor any region of the hTSHr sequence that was predominantly recognized. Several peptides were recognized by both patients and controls. These results support the notion that immunological tolerance to hTSHr is due to peripheral tolerance of potentially autoreactive CD4+ T cells, not their clonal deletion. The presence of self-reactive, hTSHr-specific CD4+ T cells in healthy individuals implies that these cells are not permanently anergized, since they can be activated in vitro.

Inhibition of IL-10 expression by IFN-gamma up-regulates transcription of TNF-alpha in human monocytes

Stimulation of human monocytes with LPS induces expression of multiple cytokines, including TNF-alpha, IL-1 beta, IL-6, and IL-10, IL-10 expression is delayed relative to that of TNF-alpha, IL-1 beta, and IL-6. Furthermore, IL-10 feedback inhibits expression of TNF-alpha, IL-1 beta, and IL-6, thus providing an efficient autocrine mechanism for controlling proinflammatory cytokine production in monocytes. The Th1-type lymphokine, IFN-gamma, markedly up-regulates TNF-alpha production in monocytes. However, the precise mechanism by which IFN-gamma mediates this effect is unknown. We examined the effects of IFN-gamma on IL-10 expression in LPS-stimulated monocytes, and the relationship between IL-10 and TNF-alpha production in these cells. LPS stimulation induced rapid, ordered expression of multiple cytokines. Steady-state mRNA levels for TNF-alpha increased rapidly, reached maximal levels by 2 to 3 h poststimulation, and then declined sharply. IL-1 beta and IL-6 mRNA levels also increased markedly following stimulation with LPS, but decreased more slowly than did TNF-alpha. Down-regulation of mRNA for TNF-alpha, IL-1 beta, and IL-6 coincided with a delayed and more gradual increase in IL-10 mRNA levels. Furthermore, neutralization of IL-10 with anti-IL-10 Abs prolonged TNF-alpha mRNA expression, and significantly increased net TNF-alpha production. IFN-gamma suppressed expression of IL-10 mRNA and protein in a dose-dependent manner. Moreover, inhibition of IL-10 production correlated with a marked increase in both the magnitude and duration of TNF-alpha expression. Thus, potentiation of TNF-alpha production by IFN-gamma in monocytes is coupled to inhibition of endogenous IL-10 expression.

Inhibition of IL-10 expression by IFN-gamma up-regulates transcription of TNF-alpha in human monocytes

Stimulation of human monocytes with LPS induces expression of multiple cytokines, including TNF-alpha, IL-1 beta, IL-6, and IL-10, IL-10 expression is delayed relative to that of TNF-alpha, IL-1 beta, and IL-6. Furthermore, IL-10 feedback inhibits expression of TNF-alpha, IL-1 beta, and IL-6, thus providing an efficient autocrine mechanism for controlling proinflammatory cytokine production in monocytes. The Th1-type lymphokine, IFN-gamma, markedly up-regulates TNF-alpha production in monocytes. However, the precise mechanism by which IFN-gamma mediates this effect is unknown. We examined the effects of IFN-gamma on IL-10 expression in LPS-stimulated monocytes, and the relationship between IL-10 and TNF-alpha production in these cells. LPS stimulation induced rapid, ordered expression of multiple cytokines. Steady-state mRNA levels for TNF-alpha increased rapidly, reached maximal levels by 2 to 3 h poststimulation, and then declined sharply. IL-1 beta and IL-6 mRNA levels also increased markedly following stimulation with LPS, but decreased more slowly than did TNF-alpha. Down-regulation of mRNA for TNF-alpha, IL-1 beta, and IL-6 coincided with a delayed and more gradual increase in IL-10 mRNA levels. Furthermore, neutralization of IL-10 with anti-IL-10 Abs prolonged TNF-alpha mRNA expression, and significantly increased net TNF-alpha production. IFN-gamma suppressed expression of IL-10 mRNA and protein in a dose-dependent manner. Moreover, inhibition of IL-10 production correlated with a marked increase in both the magnitude and duration of TNF-alpha expression. Thus, potentiation of TNF-alpha production by IFN-gamma in monocytes is coupled to inhibition of endogenous IL-10 expression.

IFN-gamma priming of monocytes enhances LPS-induced TNF production by augmenting both transcription and MRNA stability

The induction of cytokine expression in monocytes/macrophages by bacterial endotoxin or lipopolysaccharide is a critical, highly regulated host defence response. The augmentation of LPS responses by interferon gamma (IFN-gamma), referred to as priming, is well established. However, the mechanism(s) by which priming occurs is poorly defined. Using tumour necrosis factor (TNF) induction as a model, experiments were designed to analyse in detail the priming effect on the LPS response in human monocytes. Priming by IFN-gamma was primarily manifested at the level of TNF mRNA accumulation. IFN-gamma pre-treatment affected the magnitude rather than the sensitivity of the LPS response. Priming occurred after several hours of treatment, and the primed state was induced by either IFN-gamma or GM-CSF, but not M-CSF. Primed monocytes transcribed TNF mRNA at a higher rate than freshly isolated monocytes upon activation with LPS. The increased transcriptional rate correlated with a marked increase in nuclear factor-kappa B activity in these cells as determined by electrophoretic mobility shift assay using a consensus NF-kappa B oligonucleotide. An additional significant finding was than TNF mRNA induced in primed cells was much more stable than in unprimed cells (T1/2 increased 6-8-fold). Consistent with the increased mRNA stability, the duration of mRNA accumulation was longer following LPS stimulation in primed monocytes, in addition to being of greater magnitude. Finally, primed and unprimed cells possessed a differential sensitivity to the kinase inhibitor H-89. H-89 substantially suppressed LPS-induced TNF mRNA accumulation in unprimed cells, but had no effect on primed monocytes following LPS stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)