p38 MAP kinase interacts with and stabilizes pancreatic and duodenal homeobox-1

Pancreatic and duodenal homeobox-1 (PDX-1) is a homeodomain-containing transcription factor that plays a critical role in pancreatic development, β-cell differentiation, maintenance of normal β-cell function and tumorigenesis. PDX-1 is subjected to extensive post-translational modifications for its stability, subcellular location and transactivity. We report here that PDX-1 expression is up-regulated by p38 MAP kinase. Antibody array screen identified p38 as a candidate PDX-1-interacting protein in GFP-PDX-1 stable HEK293 cells. The p38-PDX-1 interaction was confirmed by immunoprecipitation/Western blotting analysis in both transient transfection system of HEK293 cells and endogenous system of β-TC-6 cells stimulated by glucagon-like peptide 1 (GLP-1). Co-transfection of p38 with PDX-1 resulted in increased PDX-1 expression in HEK293 cells, which was accompanied by a decreased PDX-1 ubiquitination. Mass spectrometry analysis showed that Ser 268 of human PDX-1 was phosphorylated in GFP-PDX-1 stable HEK293 cells. Functional mutagenesis analysis showed that mutation of Ser 269 of mouse PDX-1 (corresponding to Ser 268 of human PDX-1) into nonphosphorylatable alanine abolished the stabilizing effect of p38 on PDX-1, which was in line with enhanced PDX-1 ubiquitination and shortened half-life of PDX-1. p38 showed kinase activity towards PDX-1 in vitro, suggesting that Ser 269 is a potential p38-regulated phosphorylation site within PDX-1. GLP-1-stimulated PDX-1 expression was accompanied by p38 kinase activation in mouse insulinoma β-TC-6 cells and p38 inhibitor SB202190 inhibited GLP-1-stimulated PDX-1 expression with accompanied inhibition of p38 kinase activation. Taken together, our studies indicated that p38 MAP kinase is a positive regulator of PDX-1 stability and that p38 exerts its stabilizing effect on PDX-1 through a phosphorylation-dependent inhibition of PDX-1 ubiquitination.

Molecular cloning and functional characterization of a glutathione S-transferase involved in both anthocyanin and proanthocyanidin accumulation in Camelina sativa (Brassicaceae)

Recently, we found that the Arabidopsis TT19 protein, a glutathione S-transferase, has two functional domains that influence both anthocyanin and proanthocyanidin accumulation. To further understand the function of this protein in the other species, we cloned a cDNA encoding a glutathione S-transferase (namely CMGSTF12) from Camelina sativa, an oil crop that has received renewed interest due to its biofuel value and high omega-3 levels. Southern blot analysis demonstrated one copy of CMGSTF12 in C. sativa. Transformation of the Arabidopsis loss-of-function tt19-1 mutant with CMGSTF12 cDNA complemented accumulation of anthocyanin in vegetative tissues and resulted in the wild-type level of proanthocyanidin (both extractable and unextractable) in seeds. No obvious flavonoid accumulation changes were detected in the transgenic seeds, indicating that CMGSTF12 may only involve the lower flavonoid pathway, further proving that the TT19 protein controls accumulation of unextractable proanthocyanidin.

Abstract P4-09-09: Circulating HER2 extracellular domain (ECD) levels are associated with progression-free survival in metastatic breast cancer patients

Background: The human epidermal growth factor (HER2/neu) oncoprotein is composed of an intracellular tyrosine kinase portion, a short transmembrane section, and an extracellular ligand-binding domain (ECD). The latter is frequently cleaved from the surface of breast cancer cells and the serum HER2 ECD levels can be detected by enzyme-linked immunosorbent assay (ELISA). Consistent with majority of reports, our prior study showed that high circulating levels of the HER2 ECD indicates poor prognosis in 207 patients with metastatic breast cancer. In the present study, we aimed to elucidate whether serum HER2 ECD levels would predict the clinical outcome of metastatic breast cancer patients.

Methods: Till May 19, 2012, one hundred ninty metastatic breast cancer patients were followed up. Serum was available from 190 patients at baseline, 46 patients in the assessment of time. Serum HER2 ECD levels were measured by ELISA. Disease state was assessed using Response Evaluation Criteria in Solid Tumors (RECIST). Progression-free survival (PFS) was defined as the interval from the time of randomization until the first documentation of disease progression or death due to any cause. PFS and median PFS were generated by Kaplan-Meier spots.

Results: Elevated baseline HER2 ECD levels (bECD) (≥15 ng/ml) were observed in 40% (40/100) of patients with HER2-amplified tumors and 21.8% (19/87) of patients with HER2-negative tumors. Patients with bECD-elevated disease had a median PFS of 356 days compared with 229 days for patients with bECD-low disease(P = 0.001). In HER2-amplified cohort, median PFS for patients with low bECD levels was longer than those with bECD-elevated disease (391 days v 226 days, P = 0.005). And patients with low bECD levels treated with Herceptin-based regimen (n = 36) had a trend of longer PFS than patients(n = 24) treated with non-Herceptin regimen(447 days v 298 days, P = 0.227). Moreover, bECD-low patients (n = 36) showed a significantly longer median PFS than bECD-elevated patients(n = 22) when treated with Herceptin-based scheme (447 days v 229 days, P = 0.004). While, in patients with increased bECD levels, there was no statistical difference between Herceptin-treated groups (n = 22) and non-Herceptin-treated groups (n = 14) (229 days v 173 days, P = 0.761). In the HER2-negative group, patients with bECD-low disease had a median PFS of 313 days compared with 206 days for patients with bECD-elevated disease (P = 0.02). In a cohort of 46 patients whose HER2 ECD levels were monitored during treatment, 29 patients remains low ECD levels, 12 patients convert from elevated to low, 2 patients convert from low to high, and 3 patients remains elevated HER2 ECD levels. The patients who remained low ECD levels or achieved low ECD leves have significantly longer PFS than those whose levels remained above 15ng/mL or converted from low to high regardless of treatment given (440 days v 192days, P = 0.019).

Conclusion: Elevated HER2 bECD predicts poor median PFS irrespective of HER2 status. HER2-amplified patients with low-HER2 ECD levels may get more benefit from Herceptin-based scheme. Remained low-HER2 ECD levels or decreases in serum HER2 ECD levels during treatment were associated with longer median PFS in metastatic breast cancer.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-09-09.

CHK2 kinase promotes pre-mRNA splicing via phosphorylating CDK11(p110)

Checkpoint kinase 2 (CHK2) kinase is a key mediator in many cellular responses to genotoxic stresses, including ionizing radiation (IR) and topoisomerase inhibitors. Upon IR, CHK2 is activated by ataxia telangiectasia mutated kinase and regulates the S-phase and G1-S checkpoints, apoptosis and DNA repair by phosphorylating downstream target proteins, such as p53 and Brca1. In addition, CHK2 is thought to be a multi-organ cancer susceptibility gene. In this study, we used a tandem affinity purification strategy to identify proteins that interact with CHK2 kinase. Cyclin-dependent kinase 11 (CDK11)(p110) kinase, implicated in pre-mRNA splicing and transcription, was identified as a CHK2-interacting protein. CHK2 kinase phosphorylated CDK11(p110) on serine 737 in vitro. Unexpectedly, CHK2 kinase constitutively phosphorylated CDK11(p110) in a DNA damage-independent manner. At a molecular level, CDK11(p110) phosphorylation was required for homodimerization without affecting its kinase activity. Overexpression of CHK2 promoted pre-mRNA splicing. Conversely, CHK2 depletion decreased endogenous splicing activity. Mutation of the phosphorylation site in CDK11(p110) to alanine abrogated its splicing-activating activity. These results provide the first evidence that CHK2 kinase promotes pre-mRNA splicing via phosphorylating CDK11(p110).

Microbial diversity in the oral cavity of healthy Chinese Han children

OBJECTIVE

This study aimed to identify the oral microbial diversity of healthy Chinese Han children.

METHODS

Dental plaques were sampled from the oral cavity of ten healthy Chinese Han children. The oral microbiome was examined using the 16S rRNA-based Human Oral Microbe Identification Microarray. The microbial diversity and similarity were analyzed using the Chao-Jaccard similarity index.

RESULTS

A total of 112 species, which belonged to nine bacterial phyla and 41 genera, were detected. Each individual harbored an average of 54.1 microbial species (ranging from 37 to 69) and 26.2 genera (ranging from 21 to 31), with interindividual variations both at the species and genus level. Thirteen genera were conserved among all individuals. The Chao-Jaccard similarity index averages, at the genus and species level, were 0.642 (ranging from 0.485 to 0.871) and 0.506 (ranging from 0.338 to 0.676), respectively, suggesting that the healthy oral community was more conserved at the genus level than at the species level.

CONCLUSION

Although there was interindividual variation in the oral microflora, some bacterial genera were conserved among individuals, supporting the existence of a core microbiome in the oral cavity of healthy Chinese Han children.

[A randomized clinical trial of preoperative neoadjuvant chemotherapy followed by surgery in the treatment of stage III non-small cell lung cancer]

BACKGROUND

To explore the feasibility and toxicity of preoperative neoadjuvant chemotherapy followed by surgery in the treatment of stage III NSCLC and to evaluate its effects on tumor response, resection rate, tumor downstaging, and survival rate.

METHODS

From Jan. 1990 to Jan. 2001, 624 patients were randomly devided into group A ( preoperative neoadjuvant chemotherapy group) and group B ( control group, without neoadjuvant chemotherapy) . Group A had 314 patients and group B had 310 cases. The patients in group A were give 2 cycles of neoadjuvant chemotherapy, and operations were performed in 4 weeks after finishing the last chemotherapy. Twenty-one patients were given bronchial artery intervensional chemotherapy. The other 293 cases were given intravenous chemotherapy. The regimens included MVP in 68 cases, CAP in 36 cases, EP in 67 cases, VIP in 20 cases, Gem+ DDP in 30 cases, NVB+ DDP in 32 cases, Taxol+ NVB in 30 cases, and Taxol+ DDP in 10 cases. The patients in group B were firstly operated. Thoracic radiation therapy of 50-55 Gy was g iven in the patients with N1 and N2 disease both in group A and group B.

RESULTS

The tumor response to induction chemotherapy was 73. 57%( 231/ 314) in group A. The tumor downstaging was 43. 63%( 137/ 314) . The histological complete response was 15. 92%( 50/ 314) . The resection rate was 97. 69% in group A, and 91. 94% in group B. No significant differences of blood loss, operative complications and mortality were observed between the group A and group B. The 1-, 3-, 5- and 10-year survival rates were 89. 35%, 67. 46% , 34. 39% and 29. 34% in group A, and 87. 53%, 51. 54%, 24. 19% and 21. 64% in group B respectively. The long-term survival rate in group A was remarkably higher than that in group B ( P < 0. 01) .

CONCLUSIONS

The results demonstrate that the preoperative neoadjuvant chemotherapy is safe and effective. It is helpful to decrease the tumor staging , to increase the resection rate of the tumor, and to improve the long-term survival rate and life qualities of patients with stage III NSCLC.

[Lobectomy or pneumonectomy combined with extended resection of the heart, great vessels in the treatment of locally advanced lung cancer]

BACKGROUND

To summarize the results of extended resection of the heart, great vessels, or both in the treatment of 349 patients with locally advanced lung cancer.

METHODS

From February , 1983 to December, 2000, lobectomy or pneumonectomy combined with extended resection of the heart, great vessels or both were carried out in 349 patients with locally advanced lung cancer. The operations included bronchoplastic procedures and pulmonary artery reconstruction in 205 cases, extended resection of left atrium in 75 cases, superior vena cava resection and reconstruction in 65 cases ( 3 patients had carina resection and reconstruction simultaneously) , and aorta resection and reconstruction in 4 cases respectively.

RESULTS

There were two operative death. The operative mortality was 0. 6% in the series. Fifty-three patients had operative complications. The 1, 3, 5 and 10-year survival rates were 79. 36%, 59. 93%, 33. 14% and 23. 56% respectively.

CONCLUSIONS

Extended resection of the heart, great vessels or both can remarkably increase the long-term survival and improve the prognosis in patients with locally advanced lung cancer. Lobectomy or pneumonectomy combined with extended resection of the heart, great vessels in the treatment of locally advanced lung cancer.

High-resolution CT findings of pulmonary infections after orthotopic liver transplantation in 453 patients

OBJECTIVES

The objective of this study was to review the high-resolution CT (HRCT) findings in patients with pulmonary infection after orthotopic liver transplantation (OLT) and to determine distinguishing findings among the various types of infection.

METHODS

This study included 453 consecutive liver transplant recipients with pulmonary infection, on whom HRCT of the chest was performed within 24 h of the beginning of symptoms and for whom proven diagnosis had taken place within 1 week of the onset of symptoms. Two radiologists analysed the CT images; final decisions regarding the findings were reached by consensus.

RESULTS

Bacterial and viral pneumonia made up the bulk of infections (63.4% and 29.4%, respectively), followed by fungal infiltrates (24.5%). Large nodules were most common in patients with fungal pneumonia, having been seen in 38 (54%) of the 70 patients with fungal pneumonia, 22 (10%) of 220 with bacterial pneumonia (p=0.0059) and 6 (8%) of 78 with viral pneumonia (p=0.0011). The halo sign was also more frequent in patients with fungal pneumonia, having been seen in 38 (54%) of the 70 patients with fungal pneumonia, 17 (8%) of 220 with bacterial pneumonia (p=0.0026) and 7 (9%) of 78 with viral pneumonia (p=0.0015). There was no statistically significant difference in the prevalence of the other HRCT patterns including air-space consolidation, ground-glass attenuation and small nodules among bacterial, viral and fungal infections (all p>0.05).

CONCLUSION

The presence of large nodules with the halo sign is most suggestive of fungal infection after OLT. Other HRCT patterns are not helpful in distinguishing among the various types of infection seen in liver transplant recipients.

320-detector CT coronary angiography with prospective and retrospective electrocardiogram gating in a single heartbeat: comparison of image quality and radiation dose

OBJECTIVES

To compare the image quality, radiation dose and diagnostic accuracy of 320-detector CT coronary angiography with prospective and retrospective electrocardiogram (ECG) gating in a single heartbeat.

METHODS

Two independent reviewers separately scored image quality of coronary artery segment for 480 cardiac CT studies in a prospective group and a retrospective group (240 patients with a heart rate <65 beats per minute in each group). The two groups matched well for clinical characteristics and CT parameters. There was good agreement for image quality scores of coronary artery segment between the independent reviewers (κ=0.73). Of the 7023 coronary artery segments, the image quality scores of the prospective group and retrospective group were not significantly different (p>0.05). The mean radiation dose was 10.0 ± 3.5 mSv (range 6.2-21.6 mSv) for prospective ECG gating at 65-85% of R-R interval (the interval between the R-wave of one heartbeat to the R-wave of the next). The mean radiation dose for retrospective ECG-triggered modulated scans was 23.2 ± 3.4 mSv (range 17-27.4 mSv). The mean radiation dose was 57% lower for prospective gating than for retrospective gating (p<0.01).

RESULTS

Compared with coronary angiography, the results for prospective vs retrospective ECG gating were 92% vs 90% for sensitivity (p=0.23), 89% vs 91% for specificity (p=0.19), 90% vs 93% for positive predictive value (p=0.25) and 92% vs 95% for negative predictive value (p=0.21) for lesions with ≥50% stenosis, respectively.

CONCLUSION

320-detector CT coronary angiography performed with prospective ECG gating has similar subjective image quality scores, but a 57% lower radiation dose than retrospective ECG gating in a single heartbeat.

Remote Internet access to advanced analytical facilities: a new approach with Web-based services

Over the past decade, the increasing availability of the World Wide Web has held out the possibility that the efficiency of scientific measurements could be enhanced in cases where experiments were being conducted at distant facilities. Examples of early successes have included X-ray diffraction (XRD) experimental measurements of protein crystal structures at synchrotrons and access to scanning electron microscopy (SEM) and NMR facilities by users from institutions that do not possess such advanced capabilities. Experimental control, visual contact, and receipt of results has used some form of X forwarding and/or VNC (virtual network computing) software that transfers the screen image of a server at the experimental site to that of the users' home site. A more recent development is a web services platform called Science Studio that provides teams of scientists with secure links to experiments at one or more advanced research facilities. The software provides a widely distributed team with a set of controls and screens to operate, observe, and record essential parts of the experiment. As well, Science Studio provides high speed network access to computing resources to process the large data sets that are often involved in complex experiments. The simple web browser and the rapid transfer of experimental data to a processing site allow efficient use of the facility and assist decision making during the acquisition of the experimental results. The software provides users with a comprehensive overview and record of all parts of the experimental process. A prototype network is described involving X-ray beamlines at two different synchrotrons and an SEM facility. An online parallel processing facility has been developed that analyzes the data in near-real time using stream processing. Science Studio and can be expanded to include many other analytical applications, providing teams of users with rapid access to processed results along with the means for detailed discussion of their significance.

Cancer stem cell marker ALDH1 expression is associated with lymph node metastasis and poor survival in esophageal squamous cell carcinoma: a study from high incidence area of northern China

Tumor recurrence and metastasis is the leading cause of death in esophageal squamous cell carcinoma (ESCC). Cancer stem cell (CSC) may be responsible for tumor growth and maintenance of aggressive behavior. Aldehyde dehydrogenase 1 (ALDH1) has been proposed as one of the possible candidates for a CSC marker. The expression of ALDH1 may be correlated with the clinicopathologic factor and clinical outcome of patients with ESCC. The purpose of this study was to investigate the expression of ALDH1 protein in human ESCC tissues, and evaluated the clinical implication of ALDH1 expression for these patients. All 79 patients who underwent esophagectomy for ESCC between January 2005 and June 2006 were enrolled in this study. The expression of ALDH1 in ESCC and adjacent noncancerous tissues was analyzed by immunohistochemistry. ALDH1 was mainly expressed in ESCC cell nucleus. For the 79 ESCC patients, increased nuclear accumulation of ALDH1 was found in 12 (15.2%) specimens. ALDH1 expression was correlated with poor histological differentiation (P= 0.003), lymph node metastasis (P= 0.011), and late pathologic TNM classification (pTNM) staging (P= 0.003). Patients in ALDH1 positive group had a significantly poor 5-year overall survival than those in the negative group (8.3% vs. 52.2%, P= 0.025). We have demonstrated for the first time that the CSC marker, ALDH1, is expressed in human ESCC. The expression of ALDH1 protein in nucleus of the ESCC is significantly associated with lymph node metastasis and poor survival. Our results highly indicate the involvement of ALDH1 in the aggressive behavior of ESCC.

Radiological and clinical findings of 25 patients with invasive pulmonary aspergillosis: retrospective analysis of 2150 liver transplantation cases

OBJECTIVE

The purpose of this study was to evaluate the radiological and clinical findings of invasive pulmonary aspergillosis (IPA) after liver transplantation.

METHODS

This study included 25 consecutive liver transplant recipients with histologically confirmed IPA after liver transplantation. Radiological examinations performed for diagnosis were available in all patients. Clinical findings and changes in clinical response and radiological findings after treatment were also evaluated.

RESULTS

3 main radiological findings were identified: nodules, 64% (16/25); masses, 36% (9/25); and consolidations in a patchy pattern, 20% (5/25). A tree-in-bud pattern was found in 12% (3/25) of patients. In 8 (32%) of 25 patients, we found a combination of 2 or more of these signs: 5 (20%) patients presented with concurrent nodules accompanied by patchy consolidations and/or tree-in-bud, and 3 (12%) patients showed masses accompanied by large consolidations. A halo sign was observed in 20 (80%) of 25 patients. Hypodense sign and cavitary lesions were encountered in 17 (68%) of 25 patients. Follow-up radiological findings after treatment showed improvement in 18 patients, no change in 4 patients and progression in 3 patients. There were three aspergillosis-associated deaths during the follow-up period. The onset time of IPA was a median of 31 days after transplantation. The most common symptom at diagnosis was fever (n=15). None of the 25 patients had leukopaenia at the time of the diagnosis of IPA.

CONCLUSIONS

The most common radiological findings of IPA after liver transplantation are multiple nodules with or without halo sign, masses and consolidations, which usually appear about 1 month after transplantation.

Microbial profiles in saliva from children with and without caries in mixed dentition

OBJECTIVE

The purpose of this study was to determine the bacterial profiles in saliva of the isolated children for studying caries etiology.

MATERIALS AND METHODS

  Samples were collected from isolated children from 6 to 8years old including 20 caries-free (dmfs=0) (healthy) and 30 caries-active individuals (dmfs>8) (patients). 16S rRNA genes were amplified by PCR from bacterial DNA of saliva sample and labeled via incorporation of Cy3-dCTP in second nested PCR. After hybridization of labeled amplicons on HOMIM, the microarray slides were scanned and original data acquired from professional software.

RESULTS

Collectively, 94 bacterial species or clusters representing six bacterial phyla and 30 genera were detected. A higher bacterial diversity was observed in patients than in healthy samples. Statistical analyses revealed eight species or clusters were detected more frequently in diseased patients than in healthy samples, while six different species were detected more frequently in healthy as compared to diseased patients.

CONCLUSION

The diversity of microbe within saliva derived from isolated population increased in caries-active status, and there are some bacteria in salivary flora can be as candidate biomarkers for caries prognosis in mixed dentition. The imbalances in the resident microflora may be the ultimate mechanism of dental caries.

Value of three-dimensional power Doppler to predict clinical and histological response to neoadjuvant chemotherapy in locally advanced cervical carcinoma

OBJECTIVE

Platinum-based neoadjuvant chemotherapy followed by radical hysterectomy is an alternative therapeutic strategy for locally advanced cervical carcinoma but variables used to predict chemotherapy response are not well defined. We investigated the potential of three-dimensional (3D) power Doppler in predicting response to neoadjuvant chemotherapy.

METHODS

We enrolled 61 eligible patients with locally advanced cervical carcinoma who underwent neoadjuvant chemotherapy followed by surgery or radiation. Before the initial chemotherapy, we measured 3D power Doppler vascular indices, including vascularization index (VI), flow index (FI) and vascularization flow index (VFI), of the whole cervical carcinoma. We also measured two-dimensional (2D) hemodynamic parameters, such as resistance index and pulsatility index, at three random spots inside the tumor. The associations of all parameters with clinical and histological responses to chemotherapy were evaluated through univariable and multiple logistic regression analysis.

RESULTS

The clinical and histological response rates to chemotherapy were 70.5% and 70.7%, respectively. Univariable logistic regression analysis showed that VI, FI and VFI were significantly higher in clinical responders than in non-responders (P < 0.05), and that FI was significantly higher in histological responders (P = 0.012). Multiple logistic regression analysis showed that FI was the only significant factor associated with both clinical and histological responses. The best FI cut-off values were 35.3 and 37.3 for clinical response and histological response, respectively (with sensitivity 86.0% and 73.2%, and specificity 72.2% and 64.7%). Interestingly, none of the 2D hemodynamic parameters was significantly correlated with either response.

CONCLUSION

FI is a potential marker for predicting both clinical and histological responses to chemotherapy in patients with locally advanced cervical carcinoma.

Biomarker responses in fish exposed to sediments from northern Taihu Lake

Our study investigated multiple biomarker responses of goldfish exposed to sediments collected from northern Taihu Lake. The activities of acetylcholinesterase, 7-ethoxyresorufin-O-deethylase, glutathione-S-transferase and superoxide dismutase did not differ significantly from controls following exposure to sediment from the center of the lake. However, sediment collected from the northern bays did significantly alter enzymatic activities. An integrated biomarker response (IBR) was calculated and used to evaluate the impact of pollutants from different stations. The results indicated that Mashan in Meiliang Bay and Xiaogongshan in Gong Bay were the most stressful places for fish. Sediment polychlorinated biphenyl and polybrominated diphenyl ether concentrations were associated with IBR variation.

Conserved haplotype blocks within the sheep MHC and low SNP heterozygosity in the Class IIa subregion

This report describes single-nucleotide polymorphisms (SNPs) in the sheep major histocompatibility complex (MHC) class II and class III regions and provides insights into the internal structure of this important genomic complex. MHC haplotypes were deduced from sheep family trios based on genotypes from 20 novel SNPs representative of the class II region and 10 previously described SNPs spanning the class III region. All 30 SNPs exhibited Hardy-Weinberg proportions in the sheep population studied. Recombination within an extended sire haplotype was observed within the class II region for 4 of 20 sheep chromosomes, thereby supporting the presence of separated IIa and IIb subregions similar to those present in cattle. SNP heterozygosity varied across the class II and III regions. One segment of the class IIa subregion manifested very low heterozygosity for several SNPs spanning approximately 120 Kbp. This feature corresponds to a subregion within the human MHC class II region previously described as a 'SNP desert' because of its paucity of SNPs. Linkage disequilibrium (LD) was reduced at the junction separating the putative class IIb and IIa subregions and also between the class IIa and the class III subregions. The latter observation is consistent with either an unmapped physical separation at this location or more likely a boundary characterized by more frequent recombination between two conserved subregions, each manifesting high within-block LD. These results identify internal blocks of loci in the sheep MHC, within which recombination is relatively rare.