Research Note: Rous sarcoma growth differs among congenic lines containing major histocompatibility (B) complex recombinants.

New arrangements of chicken major histocompatibility complex (MHC) class I BF and class IV BG genes are created through recombination. Characterizing the immune responses of such recombinants reveals genes or gene regions that contribute to immunity. Inbred Line UCD 003 (B17B17) served as the genetic background for congenic lines, each containing a unique MHC recombinant. After an initial cross to introduce a specific recombinant, 10 backcrosses to the inbred line produced lines with 99.9% genetic uniformity. The current study compared Rous sarcoma virus (RSV) tumor growth in 5 congenic lines homozygous for MHC recombinants (003.R1 = BF24-BG23, 003.R2 = BF2-BG23, 003.R4 = BF2-BG23, 003.R5 = BF21-BG19, and 003.R13 = BF17-BG23). Two experiments used a total of 70 birds from the 5 congenic lines inoculated with 20 pock forming units of RSV subgroup C at 6 wk of age. Tumor size was scored 6 times over 10 wk postinoculation followed by assignment of a tumor profile index (TPI) based on the tumor size scores. Tumor growth over time and rank transformed TPI values were analyzed by least squares ANOVA. Tumor size increased over the experimental period in all genotypes through 4 wk postinoculation. After this time, tumor size increased in Lines 003.R1, plateaued in Lines 003.R2, 003.R4, and 003.R13, and declined in 003.R5. Tumor growth over time was significantly lower in Line 003.R5 compared with all other genotypes. In addition, Line 003.R5 chickens had significantly lower TPI values compared with Lines 003.R2, 003.R4, and 003.R13. The TPI of Line 003.R1 did not differ significantly from any of the other genotypes. The BF21 in Line 003.R5 produced a greater response against subgroup C RSV tumors than did BF24, found in 003.R1; BF2 found in 003.R2 and R4 as well as BF17 found in 003.R13.

Major histocompatibility complex recombinant R13 antibody response against bovine red blood cells.

Recombination within the chicken major histocompatibility complex (MHC) has enabled more precise identification of genes controlling immune responses. Chicken MHC genes include BF, MHC class I; BL, MHC class II; and BG, MHC class IV that are closely linked on chromosome 16. A new recombination occurred during the 10th backcross generation to develop congenic lines on the inbred Line UCD 003 (B17B17) background. Recombinant R13 (BF17-BG23) was found in a single male chick from the Line 003.R1 (BF24-BG23) backcross. An additional backcross of this male to Line UCD 003 females increased the number of R13 individuals. Two trials tested this new recombinant for antibody production against the T cell-dependent antigen, bovine red blood cells. Fifty-one progeny segregating for R13R13 (n = 10), R13B17 (n = 26), and B17B17 (n = 15) genotypes were produced by a single R13B17 male mated to 5 R13B17 dams. One milliliter of 2.5% bovine red blood cell was injected intravenously into all genotypes at 4 and 11 wk of age to stimulate primary and secondary immune responses, respectively. Blood samples were collected 7 d after injection. Serum total and mercaptoethanol-resistant antibodies against bovine red blood cell were measured by microtiter methods. The least squares ANOVA used to evaluate all antibody titers included trial and B genotype as main effects. Significant means were separated by Fisher's protected least significant difference at P < 0.05. R13R13 chickens had significantly lower primary total and mercaptoethanol-resistant antibodies than did the R13B17 and B17B17 genotypes. Secondary total and mercaptoethanol-resistant antibodies were significantly lower in R13R13 chickens than in R13B17 but not B17B17 chickens. Gene differences generated through recombination impacted the antibody response of R13 compared with B17. Secondary antibody titers were not substantially higher than the primary titers suggesting that the memory response had waned in the 7-wk interval between injections. Overall, the results suggest that the lower antibody response in R13R13 homozygotes may be caused by recombination affecting a region that contributes to higher antibody response.

Clinical and laboratory characteristics in juvenile-onset systemic lupus erythematosus across age groups.

BACKGROUND: Systemic lupus erythematous (SLE) is a systemic autoimmune/inflammatory condition. Approximately 15-20% of patients develop symptoms before their 18th birthday and are diagnosed with juvenile-onset SLE (JSLE). Gender distribution, clinical presentation, disease courses and outcomes vary significantly between JSLE patients and individuals with adult-onset SLE. This study aimed to identify age-specific clinical and/or serological patterns in JSLE patients enrolled to the UK JSLE Cohort Study. METHODS: Patient records were accessed and grouped based on age at disease-onset: pre-pubertal (≤7 years), peri-pubertal (8-13 years) and adolescent (14-18 years). The presence of American College of Rheumatology (ACR) classification criteria, laboratory results, disease activity [British Isles Lupus Assessment Group (BILAG) and Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2 K) scores] and damage [Systemic Lupus International Collaborating Clinics (SLICC) damage index] were evaluated at diagnosis and last follow up. RESULTS: A total of 418 JSLE patients were included in this study: 43 (10.3%) with pre-pubertal disease onset; 240 (57.4%) with peri-pubertal onset and 135 (32.3%) were diagnosed during adolescence. At diagnosis, adolescent JSLE patients presented with a higher number of ACR criteria when compared with pre-pubertal and peri-pubertal patients [pBILAG2004 scores: 9(4-20] vs. 7(3-13] vs. 7(3-14], respectively, p = 0.015] with increased activity in the following BILAG domains: mucocutaneous (p = 0.025), musculoskeletal (p = 0.029), renal (p = 0.027) and cardiorespiratory (p = 0.001). Furthermore, adolescent JSLE patients were more frequently ANA-positive (p = 0.034) and exhibited higher anti-dsDNA titres (p = 0.001). Pre-pubertal individuals less frequently presented with leukopenia (p = 0.002), thrombocytopenia (p = 0.004) or low complement (p = 0.002) when compared with other age groups. No differences were identified in disease activity (pBILAG2004 score), damage (SLICC damage index) and the number of ACR criteria fulfilled at last follow up. CONCLUSIONS: Disease presentations and laboratory findings vary significantly between age groups within a national cohort of JSLE patients. Patients diagnosed during adolescence exhibit greater disease activity and "classic" autoantibody, immune cell and complement patterns when compared with younger patients. This supports the hypothesis that pathomechanisms may vary between patient age groups.

Outcomes following mycophenolate mofetil versus cyclophosphamide induction treatment for proliferative juvenile-onset lupus nephritis.

BACKGROUND: Juvenile-onset systemic lupus erythematosus (JSLE) is more severe than adult-onset disease, including more lupus nephritis (LN). Despite differences in phenotype/pathogenesis, treatment is based upon adult trials. This study aimed to compare treatment response, damage accrual, time to inactive LN and subsequent flare, in JSLE LN patients treated with mycophenolate mofetil (MMF) versus intravenous cyclophosphamide (IVCYC). METHODS: UK JSLE Cohort Study participants, ≤16 years at diagnosis, with ≥4 American College of Rheumatology criteria for SLE, with class III or IV LN, were eligible. Mann-Whitney U tests, Fisher's exact test and Chi-squared tests were utilized for statistical analysis. RESULTS: Of the patients, 34/51 (67%) received MMF, and 17/51 (33%) received IVCYC. No significant differences were identified at 4-8 and 10-14 months post-renal biopsy and last follow-up, in terms of renal British Isles Lupus Assessment Grade scores, urine albumin/creatinine ratio, serum creatinine, ESR, anti-dsDNA antibody, C3 levels and patient/physician global scores. Standardized Damage Index scores did not differ between groups at 13 months or at last follow-up. Inactive LN was attained 262 (141-390) days after MMF treatment, and 151 (117-305) days following IVCYC ( p = 0.17). Time to renal flare was 451 (157-1266) days for MMF, and 343 (198-635) days for IVCYC ( p = 0.47). CONCLUSION: This is the largest study to date investigating induction treatments for proliferative LN in children, demonstrating comparability of MMF and IVCYC.

Diffusion tensor imaging determines three-dimensional architecture of human cervix: a cross-sectional study.

OBJECTIVE: To determine the microarchitecture of the cervix using high-resolution diffusion tensor (DT) magnetic resonance imaging (MRI). DESIGN: Cross-sectional study. SETTING: Leeds, UK. SAMPLE: Women undergoing hysterectomy for benign pathology. METHODS: Ex-vivo DT-MRI measurements were obtained using a 9.4-T Bruker nuclear magnetic resonance (NMR) spectrometer on seven fixed human cervices obtained at hysterectomy. A deterministic fibre-tracking algorithm was used to indirectly visualise underlying fibre organisation. Inter-regional differences in tissue structure were sought using quantitative measurements of diffusion. MAIN OUTCOME MEASURE: The identification of an occlusive structure in the region corresponding to the internal cervical os. RESULTS: Fibre tracking demonstrated two regions: an outer circular and inner longitudinal layer. The total circumferential tract volume (TV) was greatest in the proximal region of the cervix (TV: proximal, 271 ± 198 mm3 ; middle, 186 ± 119 mm3 ; distal, 38 ± 36 mm3 ). Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) measurements were significantly different between regions in all samples (P < 0.0005), indicating greater tract density and organisation towards the internal os. CONCLUSION: Fibre tracking infers a system of dense, well-defined, encircling fibres in the proximal region of the cervix, corresponding to the location of the internal os. These findings may provide evidence of specific anatomic microarchitecture within the cervix able to resist intrauterine forces associated with pregnancy. TWEETABLE ABSTRACT: Diffusion-tensor MRI derived tractography identified well-defined encircling fibres at the internal os.

Evaluation of the ACR and SLICC classification criteria in juvenile-onset systemic lupus erythematosus: a longitudinal analysis.

Objectives The Systemic Lupus International Collaborating Clinics (SLICC) group proposed revised classification criteria for systemic lupus erythematosus (SLICC-2012 criteria). This study aimed to compare these criteria with the well-established American College of Rheumatology classification criteria (ACR-1997 criteria) in a national cohort of juvenile-onset systemic lupus erythematosus (JSLE) patients and evaluate how patients' classification criteria evolved over time. Methods Data from patients in the UK JSLE Cohort Study with a senior clinician diagnosis of probable evolving, or definite JSLE, were analyzed. Patients were assessed using both classification criteria within 1 year of diagnosis and at latest follow up (following a minimum 12-month follow-up period). Results A total of 226 patients were included. The SLICC-2012 was more sensitive than ACR-1997 at diagnosis (92.9% versus 84.1% p < 0.001) and after follow up (100% versus 92.0% p < 0.001). Most patients meeting the SLICC-2012 criteria and not the ACR-1997 met more than one additional criterion on the SLICC-2012. Conclusions The SLICC-2012 was better able to classify patients with JSLE than the ACR-1997 and did so at an earlier stage in their disease course. SLICC-2012 should be considered for classification of JSLE patients in observational studies and clinical trial eligibility.

The inter-relationship of symptom severity and quality of life in 2055 patients with primary biliary cholangitis.

BACKGROUND: Age at presentation with primary biliary cholangitis (PBC) is associated with differential response to ursodeoxycholic acid (UDCA) therapy. Younger-presenting patients are less likely to respond to treatment and more likely to need transplant or die from the disease. PBC has a complex impact on quality of life (QoL), with systemic symptoms often having significant impact. AIM: To explain the impact of age at presentation on perceived QoL and the inter-related symptoms which impact upon it. METHODS: Using the UK-PBC cohort, symptoms were assessed using the PBC-40 and other validated tools. Data were available on 2055 patients. RESULTS: Of the 1990 patients reporting a global PBC-QoL score, 66% reported good/neutral scores and 34% reported poor scores. Each 10-year increase in age at presentation was associated with a 14% decrease in risk of poor perceived QoL (OR = 0.86, 95% CI: 0.75-0.98, P < 0.05). All symptom domains were similarly age-associated (P < 0.01). Social dysfunction was the symptom factor with the greatest impact on QoL. Median (interquartile range) PBC-40 social scores for patients with good perceived QoL were 18 (14-23) compared with 34 (29-39) for those with poor QoL. CONCLUSION: The majority of patients with primary biliary cholangitis do not feel their QoL is impaired, although impairment is reported by a sizeable minority. Age at presentation is associated with impact on perceived QoL and the symptoms impairing it, with younger patients being more affected. Social dysfunction makes the greatest contribution to QoL impairment, and it should be targeted in trials aimed at improving life quality.

Transvaginal ultrasound (TVUS)-guided biopsy is safe and effective in diagnosing peritoneal carcinomatosis and recurrent pelvic malignancy.

AIM: To assess safety and accuracy of transvaginal ultrasound (TVUS)-guided biopsy in achieving a diagnosis of peritoneal carcinomatosis (PC). MATERIALS AND METHODS: This was a retrospective study comprising a cohort of 54 consecutive women aged 18-85 years referred from the gynaecological oncology multidisciplinary team meeting (MDTM) who attended for TVUS-guided biopsy procedures in a tertiary oncology centre over a 4-year period (2010-2014). Clinicopathological validation was assessed using online patient records and radiological information systems. An independent oncologist assessed patient outcomes. RESULTS: The procedure was successful in all 19 patients with suspected recurrent malignancy with diagnosis validated against previous histology. Successful histological confirmation was achieved in 31 of 35 patients with suspected PC, which was thereafter validated by histology from subsequent surgery and favourable response to site-specific therapies (n=22). In three patients with suspected PC, the procedure did not result in biopsy as a suitable target could not be identified. Another woman had two false-negative biopsies. Thus overall a site-specific and subtype cancer diagnosis was obtained for 50 women giving an overall patient success rate of 93% (50/54). There were no procedure-related complications. CONCLUSION: TVUS core biopsy is a safe, effective, well-tolerated, and valuable technique in modern oncological management of PC when other diagnostic options are unavailable.

Supercritical water oxidation of a model fecal sludge without the use of a co-fuel.

A continuous supercritical water oxidation reactor was designed and constructed to investigate the conversion of a feces simulant without the use of a co-fuel. The maximum reactor temperature and waste conversion was determined as a function of stoichiometric excess of oxygen in order to determine factor levels for subsequent investigation. 48% oxygen excess showed the highest temperature with full conversion. Factorial analysis was then used to determine the effects of feed concentration, oxygen excess, inlet temperature, and operating pressure on the increase in the temperature of the reacting fluid as well as a newly defined non-dimensional number, NJa representing heat transfer efficiency. Operating pressure and stoichiometric excess oxygen were found to have the most significant impacts on NJa. Feed concentration had a significant impact on fluid temperature increase showing an average difference of 46.4°C between the factorial levels.

Journeys of adjustment: the experiences of adolescents living with juvenile idiopathic arthritis.

BACKGROUND: Juvenile idiopathic arthritis (JIA) is one of the most common diseases of childhood causing pain, swelling of joints and reduced mobility. Previous research has focused on the challenges and psychosocial impact of JIA, but there has been limited attention given to how young people adjust and adapt to living with a long-term condition such as JIA. The aim of this qualitative study was therefore to explore adolescents' experiences of living with JIA, with particular focus on the process of adjustment. METHODS: Ten adolescents (7 female, 3 male) aged 13-17 years with good treatment adherence were recruited from an adolescent arthritis clinic. In-depth interviews were conducted, and data were analysed by two researchers independently using interpretative phenomenological analysis. RESULTS: These adolescents described the physical and psychosocial 'burden of living with JIA' and the challenges faced by an underlying preoccupation 'to be a normal teenager'. However, their accounts also revealed ways in which they regained agency and developed 'resilience through taking control' over their lives. This resilience helped the adolescents re-establish a sense of well-being through an ongoing process of 'acceptance and self-growth'. CONCLUSIONS: Although much research has adopted a deficit model that focuses on adjustment problems, the current study highlights the resourcefulness of young people in managing the challenges of living with a long-term condition. These experiences of successful adjustment can be used as the basis of positive, strength-based intervention approaches for adolescents with arthritis to enhance resilience and well-being.

ASPM and microcephalin expression in epithelial ovarian cancer correlates with tumour grade and survival.

BACKGROUND: The clinico-pathological and molecular heterogeneity of epithelial ovarian cancer (EOC) complicates its early diagnosis and successful treatment. Highly aneuploid tumours and the presence of ascitic fluids are hallmarks of EOC. Two microcephaly-associated proteins, abnormal spindle-like microcephaly-associated protein (ASPM) and microcephalin, are involved in mitosis and DNA damage repair. Their expression is deregulated at the RNA level in EOC. Here, ASPM and microcephalin protein expression in primary cultures established from the ascites of patients with EOC was determined and correlated with clinical data to assess their suitability as biomarkers. METHODS: Five established ovarian cancer cell lines, cells derived from two benign ovarian ascites samples and 40 primary cultures of EOC derived from ovarian ascites samples were analysed by protein slot blotting and/or immunofluorescence to determine ASPM and microcephalin protein levels and their cellular localisation. Results were correlated with clinico-pathological data. RESULTS: A statistically significant correlation was identified for ASPM localisation and tumour grade, with high levels of cytoplasmic ASPM correlating with grade 1 tumours. Conversely, cytoplasmic microcephalin was only identified in high-grade tumours. Furthermore, low levels of nuclear microcephalin correlated with reduced patient survival. CONCLUSION: Our results suggest that ASPM and microcephalin have the potential to be biomarkers in ovarian cancer.

Development of a method for detection of Giardia duodenalis cysts on lettuce and for simultaneous analysis of salad products for the presence of Giardia cysts and Cryptosporidium oocysts.

We report a method for detecting Giardia duodenalis cysts on lettuce, which we subsequently use to examine salad products for the presence of Giardia cysts and Cryptosporidium oocysts. The method is based on four basic steps: extraction of cysts from the foodstuffs, concentration of the extract and separation of the cysts from food materials, staining of the cysts to allow their visualization, and identification of cysts by microscopy. The concentration and separation steps are performed by centrifugation, followed by immunomagnetic separation using proprietary kits. Cyst staining is also performed using proprietary reagents. The method recovered 46.0% +/- 19.0% (n = 30) of artificially contaminating cysts in 30 g of lettuce. We tested the method on a variety of commercially available natural foods, which we also seeded with a commercially available internal control, immediately prior to concentration of the extract. Recoveries of the Texas Red-stained Giardia cyst and Cryptosporidium oocyst internal controls were 36.5% +/- 14.3% and 36.2% +/- 19.7% (n = 20), respectively. One natural food sample of organic watercress, spinach, and rocket salad contained one Giardia cyst 50 g(-1) of sample as an indigenous surface contaminant.

Women with peritoneal carcinomatosis of unknown origin: Efficacy of image-guided biopsy to determine site-specific diagnosis.

OBJECTIVES: To evaluate the use of image-guided biopsy (IGB) in routine clinical practice to obtain site-specific diagnoses in women presenting with peritoneal carcinomatosis (PC). STUDY DESIGN: Retrospective case study. SETTING: Tertiary referral centre. POPULATION: A total of 149 consecutive women with PC who underwent IGB. METHODS: Biopsy was performed in women considered unsuitable for primary surgery because of poor performance status or disease unlikely to be optimally debulked, with a prior history of malignancy or where there was clinicoradiological uncertainty about primary tumour site. Standard haematoxylin-eosin histological analysis was supplemented with immunohistochemistry. MAIN OUTCOME MEASURES: The rate of site-specific diagnosis. RESULTS: A total of 149 women underwent IGB using computed tomography or ultrasound over a 6-year period. The only complication was one rectus sheath haematoma. In 138 (93%) women, a site-specific cancer diagnosis was made on the IGB (including 111 müllerian tract, 8 gastrointestinal tract, 4 breast and 3 lymphoma); in ten women, a repeat biopsy was necessary, giving an overall failure rate of 7%. In a further six women, malignancy was confirmed but a site-specific diagnosis could not be made, and in four women, biopsy showed benign tissue. A site-specific diagnosis was obtained in 29 of the 32 women (94%) with previous malignancy, of which 18/32 (56%) showed a new primary cancer. CONCLUSIONS: IGB is a safe and accurate technique for providing site-specific diagnoses in women with PC in routine clinical practice, including those with a previous relevant malignancy. IGB can replace laparoscopic or open biopsy in defining primary therapeutic options. The data would suggest that the biopsy should be performed with ultrasound where feasible.

Bioavailability of vitamin A sources for cattle.

An experiment was conducted to evaluate the bioavailability of 5 sources of vitamin A. It was hypothesized that some vitamin A products have protective coatings that are more resistant than others to rumen destruction and that such protection would result in greater tissue concentrations of vitamin A. Fifty-three yearling Angus x Brahman cattle, consisting of 39 steers and 14 heifers, were stratified by BW and sex and randomly assigned to 6 high-concentrate diet groups receiving no vitamin A supplementation (control) or vitamin A supplemented from the following sources: Microvit A (Adisseo, Acworth, GA), Rovamix A (DSM, Parsippany, NJ), Sunvit A, Lutavit A, and Microvit A DLC (Adisseo). The vitamin A treatment groups were fed daily 80,000 IU of retinol/animal in a low-retinol concentrate diet (78.5% oats, 10% cottonseed hulls, 8% molasses, and 2% cottonseed meal; DM basis) and a free-choice, poor quality (low carotene) hay for 84 d. Every 28 d, BW was determined and liver biopsies and plasma were collected and analyzed for retinol concentrations. All retinol treatments showed significant increases in liver retinol concentrations compared with control animals (P < 0.0001), which steadily decreased over time. At all collection times, Microvit A led to numerically, but not significantly, greater concentrations of retinol in liver than did all other treatments. However, at the end of the experiment, there was no significant difference in liver retinol concentration among Microvit A, Rovamix A, Lutavit A, and Microvit A DLC diets. When liver retinol concentrations at all collection times were considered, Microvit A and Rovamix A appeared to provide the most bioavailable vitamin A.

Towards standard methods for the detection of Cryptosporidium parvum on lettuce and raspberries. Part 2: validation.

We report the results of interlaboratory collaborative trials of methods to detect oocysts of the protozoan parasite Cryptosporidium parvum on lettuce and raspberries. The trials involved eight expert laboratories in the United Kingdom. Samples comprised 30 g lettuce, and 60 g raspberries. Lettuce samples were artificially contaminated at three levels: low (8.5-14.2 oocysts), medium (53.5-62.6 oocysts), and high (111.3-135.0 oocysts). Non-contaminated lettuce samples were also tested. The method had an overall sensitivity (correct identification of all artificially contaminated lettuce samples) of 89.6%, and a specificity (correct identification of non-contaminated samples) of 85.4%. The total median percentage recovery (from all artificially contaminated samples) produced by the method was 30.4%. The method was just as reproducible between laboratories, as repeatable within a laboratory. Raspberry samples were artificially contaminated at three levels: low (8.5-26.8 oocysts), medium (29.7-65.7 oocysts), and high (53.9-131.3 oocysts). Non-contaminated raspberry samples were also tested. The method had an overall sensitivity (correct identification of all artificially contaminated raspberry samples) of 95.8%, and a specificity (correct identification of non-contaminated samples) of 83.3%. The total median percentage recovery (from all artificially contaminated samples) produced by the method was 44.3%. The method was just as reproducible between laboratories, as repeatable within a laboratory. The results of the collaborative trial indicate that these assays can be used effectively in analytical microbiological laboratories.

Image-guided biopsy in women with breast cancer presenting with peritoneal carcinomatosis.

When women with a history of breast cancer present with peritoneal carcinomatosis, the differential diagnosis lies between recurrent breast cancer or a new primary tumor. This scenario is of particular relevance to women with a BRCA gene mutation, who have a genetic predisposition to develop second primary tumors of the ovary, fallopian tube, and peritoneum. We describe the use of image-guided core biopsy as an alternative to laparoscopy or exploratory laparotomy in providing minimally invasive diagnosis in this increasingly common clinical dilemma.

Towards standard methods for the detection of Cryptosporidium parvum on lettuce and raspberries. Part 1: development and optimization of methods.

No standard method is available for detecting protozoan parasites on foods such as soft fruit and salad vegetables. We report on optimizing methods for detecting Cryptosporidium parvum on lettuce and raspberries. These methods are based on four basic stages: extraction of oocysts from the foodstuffs, concentration of the extract and separation of the oocysts from food materials, staining of the oocysts to allow their visualization, and identification of oocysts by microscopy. The concentration and separation steps are performed by centrifugation, followed by immunomagnetic separation using proprietary kits. Oocyst staining is also performed using proprietary reagents. The performance parameters of the extraction steps were extensively optimized, using artificially contaminated samples. The fully developed methods were tested several times to determine their reliability. The method to detect C. parvum on lettuce recovered 59.0+/-12.0% (n=30) of artificially contaminated oocysts. The method to detect C. parvum on raspberries recovered 41.0+/-13.0% (n=30) of artificially contaminated oocysts.

Tolerance of inorganic selenium by range-type ewes during gestation and lactation.

The objectives of this 72-wk study were to evaluate and compare the effects of 6 dietary levels of inorganic Se on serum, whole blood, wool, and tissue Se concentrations and to determine the maximum tolerable level of Se for mature ewes during lamb production. Forty-one, 4-yr-old, range-type ewes (57.4 +/- 5.7 kg) were used in a completely randomized design with 6 dietary treatments. Sodium selenite was added to a corn and soybean meal-based diet to provide 0.2 (control), 4, 8, 12, 16, or 20 mg of dietary Se/kg to ewes during lamb production. Serum Se and ewe BW were measured at 4-wk intervals; whole blood Se and wool Se were measured every 12 wk; and samples of brain, diaphragm, heart, hoof, kidney, liver, and psoas major were collected at the termination of the experiment. Dietary Se did not affect ewe BW during the study (P = 0.69), and there was no treatment x time interaction. Serum Se increased linearly as dietary Se level increased (P < 0.001) and responded cubically (P = 0.02) over time. Selenium in whole blood increased linearly (P < 0.001) as supplemental Se increased. Wool Se increased linearly (P < 0.001) as dietary Se increased, and the response over time was quadratic (P < 0.001). Brain, diaphragm, heart, and psoas major Se increased (P < 0.05) linearly as dietary Se increased, liver Se responded quadratically (P < 0.05), and hoof and kidney Se increased cubicically (P < 0.05) as supplemental Se increased. In general, serum, whole blood, and tissue Se concentrations of ewes receiving 12, 16, or 20 mg of dietary Se/kg were greater (P < 0.05) than those of controls and ewes receiving less dietary Se. Although they were elevated in ewes receiving increased dietary Se, at no time did serum, whole blood, or wool Se concentrations reach levels previously reported as toxic, nor were clinical signs of Se toxicosis observed. Histopathological evaluation of liver, kidney, diaphragm, heart, and psoas major did not reveal evidence of Se toxicosis in ewes at any dietary Se level. Ewes under our experimental conditions and during the stresses of production were able to tolerate up to 20 mg of dietary Se/kg as sodium selenite for 72 wk. These findings suggest that the maximum tolerable level of inorganic Se for sheep is much greater than 2 mg/kg as was suggested previously. Experiments of longer duration and utilizing greater dietary Se concentrations are necessary to clearly define the maximum tolerable level.