Optical coherence tomography.

Optical coherence tomography (OCT) is a non-contact method for imaging the topological and internal microstructure of samples in three dimensions. OCT can be configured as a conventional microscope, as an ophthalmic scanner, or using endoscopes and small diameter catheters for accessing internal biological organs. In this Primer, we describe the principles underpinning the different instrument configurations that are tailored to distinct imaging applications and explain the origin of signal, based on light scattering and propagation. Although OCT has been used for imaging inanimate objects, we focus our discussion on biological and medical imaging. We examine the signal processing methods and algorithms that make OCT exquisitely sensitive to reflections as weak as just a few photons and that reveal functional information in addition to structure. Image processing, display and interpretation, which are all critical for effective biomedical imaging, are discussed in the context of specific applications. Finally, we consider image artifacts and limitations that commonly arise and reflect on future advances and opportunities.

Biolayer interferometry predicts ELISA performance of monoclonal antibody pairs for Plasmodium falciparum histidine-rich protein 2.

Predicting antibody pair performance in a sandwich format streamlines development of antibody-based diagnostics and laboratory research tools, such as enzyme-linked immunosorbent assays (ELISAs) and lateral flow immunoassays (LFAs). We have evaluated panels of monoclonal antibodies against the malarial parasite biomarker Plasmodium falciparum histidine rich protein 2 (HRP2), including 9 new monoclonal antibodies, using biolayer interferometry (BLI) and screened antibody pairs in a checkerboard ELISA. This study showed BLI predicts antibody pair ELISA performance for HRP2. Pairs that included capture antibodies with low off-rate constants and detection antibodies with high on-rate constants performed best in an ELISA format.

Suppression of T-cell proliferation by and B7-H1 expression on human liver-derived stem cells.

BACKGROUND: Many types of stem cells have been widely used for the treatment of liver diseases. The therapeutic effect of stem cells is predominantly based on the immune regulatory properties of these cells. METHODS: We isolated human liver stem cells (HLSCs), which are considered intrahepatic stem cells, and examined their suppression of T-cell proliferation induced by phytohemagglutinin. RESULTS: HLSCs inhibited phytohemagglutinin-induced T-cell proliferation not only in direct co-culture but also in indirect co-culture in a cell number-dependent manner. That is, T-cell proliferation was substantially inhibited by cell-to-cell contact regardless of soluble factor(s). B7-H1, a co-inhibitory molecule that relies on cell-to-cell contact, was found to be constitutively expressed at low levels on HLSCs. Furthermore, its expression was upregulated moderately by tumor necrosis factor-α and dramatically by interferon-γ. CONCLUSIONS: These results suggest that HLSCs would have therapeutic effects through T-cell suppression in acute liver diseases.

In vitro differentiation of human liver-derived stem cells with mesenchymal characteristics into immature hepatocyte-like cells.

Liver transplantation is severely limited by donor shortage although it is the only effective treatment for end-stage liver disease. So the best alternative is hepatocyte transplantation. For obtaining human hepatocytes, some stem cells originating from extrahepatic or intraheptic tissues have been isolated and characterized. Previously we have reported that human liver-derived stem cells (HLSCs) could be isolated and expanded from donated livers unsuitable for transplantation; they expressed some markers of mesenchymal stem cells but neither hematopoietic nor oval cells. In this study, we isolated and expanded HLSCs with mesenchymal characteristics from another adult human liver. They showed mesenchymal morphology and grew well under serum condition similar to our previous reports. Also, they expressed some markers of mesenchymal stem cells, such as CD44, CD73, CD90, and CD105, through fluorescence-activated cell sorting analysis. When HLSCs were sequentially exposed to fibroblast growth factor-1 (FGF-1), FGF-4, and hepatocyte growth factor (HGF) followed by FGF-4, HGF, oncostatin M, and dexamethasone, they became round or polygonal, and expressed some hepatic markers such as albumin and α1-antitrypsin in the gene or protein level. Also, they showed urea synthesis activity 7 days after treatment of FGF-4, HGF, oncostatin M, and dexamethasone. These results provided that HLSCs would be a useful cell source in the field of regenerative medicine as well as liver cell biology.

B7-H1 inhibits T cell proliferation through MHC class II in human mesenchymal stem cells.

B7-H1 on mesenchymal stem cells (MSCs) is known to modulate immune response. However, its expression pattern and exact immunomodulatory mechanism are unclear. In this study, we examined the immunomodulatory mechanism through the expression pattern of B7-H1 and major histocompatibility complex class II in various MSCs. Human bone marrow, adipose tissue, and cord blood MSCs were isolated and cultured. B7-H1, HLA-ABC, and HLA-DR expression on MSCs by interferon-γ (IFN-γ) was detected time-dependently by flow cytometry. The inhibitory effect of MSCs on T lymphocytes was observed in phytohemagglutinin antigen-induced T cell proliferation assay. The expression of B7-H1 was rapidly induced, but the expression of HLA-DR was induced at 48 hours after IFN-γ treatment. The inhibitory effect of MSCs on T cell proliferation could be restored when the anti-B7-H1 monoclonal antibody was used to block the B7-H1, or when the HLA-DRα small interfering RNA was used to interfere with its expression. These results show that MSCs could inhibit the T cell proliferation and activation by B7-H1 depending on the presence of HLA-DR. Therefore, MSCs would have a strong effect on immune diseases such as graft-versus-host disease and autoimmune diseases when MSCs are primed with IFN-γ 48 hours before transplantation.

Effect of multiple infections with white spot syndrome virus and Vibrio anguillarum on Pacific white shrimp Litopenaeus vannamei (L.): mortality and viral replication.

Multiple infections are commonly found in practical shrimp culture and may cause more serious consequences than infections by one pathogen only. Therefore, this study was conducted to evaluate the effect of multiple infections with white spot syndrome virus (WSSV) and Vibrio anguillarum on Pacific white shrimp Litopenaeus vannamei (L.), mortality, WSSV replication in vivo and host immune response. In the WSSV single-infection group (WSSV load, 2 × 10(2) copies µL(-1)), mean cumulative mortality was 29.2%. In the V. anguillarum single-infection group, cumulative mortality was 12.5% when shrimp were challenged by 10(5) CFU mL(-1) of bacteria. In the co- and super-infection groups, 37.5% and 50% cumulative mortalities, respectively, were observed at a lower bacterial concentration of 10(3) CFU mL(-1), suggesting that shrimp with multiple infections died earlier and more frequently than singly infected shrimp. WSSV load after injection was tracked over time by TaqMan quantitative PCR. WSSV load increased more rapidly in the multiple-infection groups than in the single-infection group. Additionally, mRNA expression of the genes encoding prophenoloxidase 1 and 2, which are closely involved in innate immunity in shrimp, was down-regulated more extensively in multiple-infection groups than in single-infection groups, as indicated by quantitative reverse-transcription PCR.

Assessment of pulmonary artery morphology by optical coherence tomography.

Since its invention, optical coherence tomography (OCT) has been primarily used for the diagnosis of coronary artery disease. A few feasibility studies of OCT to visualise the pulmonary arteries were reported. However, OCT findings in the pulmonary arteries have not been validated using histology as the gold standard. To validate OCT findings for pulmonary arterial imaging, we selected 27 pulmonary arteries from 11 cadavers (6 males, 5 females, mean age 39.6 ± 21.3 years). Comparison of OCT images and histology was performed. Each histological sample was examined using three types of stains, and the quantified results were analysed by statistics. In conclusion, there was a strong correlation between histology and OCT measurements of the pulmonary arterial wall thickness, the pulmonary arterial wall has a single-layered structure with an average thickness of 0.162 mm. We propose that OCT is probably a useful tool of diagnosing pulmonary artery hypertension and may provide a means to study the pulmonary remodelling process.

In vitro evaluation of migratory capacity of human liver stem cells influenced by soluble factors.

Although several studies have addressed the engraftment of stem cells into the liver, the exact mechanisms in vivo remain unclear. In this study, we investigated the effects of soluble factors on cell migration using purified, expanded human liver stem cells (HLSCs) obtained from a pediatric liver resection. Using a in vitro transwell migration assay, we evaluated the migratory capacity of HLSCs under the influence of the cytokines tumor necross factor- [TNF]-α, interleukin [IL]-6, and interferon (IFN)-γ or the growth factors vascular endothelial growth factor [VEGF], basic fibroblast growth factor [bFGF], and hepatocyte growth factor [HGF], which are known to be highly secreted during liver injury. We also evaluated the migratory capacity indirectly influenced by cryopreserved human hepatocytes. The migration across the transwell membrane was promoted by VEGF, bFGF, TNF-α, IFN-γ, or hepatocytes. The cryopreserved human hepatocytes especially induced significant migration. These results suggested the presence of unidentified soluble factors from hepatocytes. This experiment described a reliable system for quantitative migration studies to broaden our understanding of the directional nature of cell migration.

Multipotent progenitor cells derived from human umbilical cord blood can differentiate into hepatocyte-like cells in a liver injury rat model.

Umbilical cord blood (UCB), a rich source of hematopoietic stem cells, offers practical and ethical advantages. It has been reported that various adult stem cells transplanted into a damaged liver show characteristics of a hepatic lineage. In a previous study, we reported on novel UCB-derived adult stem cells, termed umbilical cord blood-derived multipotent progenitor cells (UCB-MPCs). We demonstrated that these cells were capable of differentiating into hepatocyte- like cells in vitro. To assess the hepatic differentiation capacity of UCB-MPCs, rat models of hepatic injury were generated using carbon tetra-chloride (CCl(4)) with transplantation of cells into the liver. The transplanted cells successfully incorporated into the liver of the recipient animal differentiated into functional hepatocyte-like cells that expressed hepatocyte-specific markers, such as CK-18 and albumin. Moreover, human albumin was detected in the serum of the recipient rat model. These data indicated that UCB-MPCs were capable of displaying similar characteristics to those of functional hepatocytes in a recipient liver. UCB-MPCs may prove to be a useful, transplantable alternative for hepatic progenitor cells in both experimental and therapeutic applications.

Optical coherence tomography evaluation of zotarolimus-eluting stents at 9-month follow-up: comparison with sirolimus-eluting stents.

OBJECTIVE: To evaluate the vascular response at 9 months after zotarolimus-eluting stent (ZES; Endeavor) implantation using optical coherence tomography (OCT). These findings were compared with those after implantation of a sirolimus-eluting stent (SES; Cypher Select). DESIGN: Cross-sectional observational study with prospective OCT registry. SETTING: Nine months after ZES or SES implantation. PATIENTS AND METHODS: A total of 68 patients (32 ZES and 36 SES) underwent OCT at 9 months after stent implantation. The neointima hyperplasia (NIH) thickness inside each strut and percentage of NIH area at every 1 mm cross section were measured. MAIN OUTCOME MEASUREMENT: The degree of neointimal coverage and the prevalence of malapposition at 9 months after ZES and SES implantation using OCT. RESULTS: The mean (SD) NIH thickness (251.2 (110.0) mum vs 85.5 (53.3) mum, p<0.001) and percentage of NIH area (27.9 (9.1)% vs 11.2 (7.1)%, p<0.001) were significantly greater in ZES than in SES. The prevalence of uncovered strut as well as malapposed strut was significantly lower in ZES than in SES (0.3% vs 12.3%, p<0.001 and 0.08% vs 2.6%, p<0.001). Thrombus was not observed in ZES (0.0% in ZES vs 27.8% in SES, p = 0.001). CONCLUSIONS: Neointimal coverage in ZES was almost complete and malapposition was very rare at 9-months' follow-up.

Pathological effects of alcohol septal ablation for hypertrophic obstructive cardiomyopathy.

BACKGROUND: The pathological effects and the mechanisms of action of intracoronary administration of ethanol for alcohol septal ablation (ASA) for the management of hypertrophic obstructive cardiomyopathy (HOCM) are unknown. METHODS: We examined surgical specimens and, in one case, autopsy specimens from four patients who underwent surgical septal myectomy 2 days to 14 months after unsuccessful ASA. RESULTS: Pathological examination early after ASA showed coagulative necrosis of both the myocardium and the septal perforator arteries. Affected arteries were distended and occluded by necrotic intraluminal debris, without platelet-fibrin thrombi. Late after unsuccessful ASA, excised septal tissue was heterogeneous, containing a region of dense scar, and adjacent tissue containing viable myocytes and interspersed scar. CONCLUSIONS: Intracoronary administration of ethanol in patients with HOCM causes acute myocardial infarction with vascular necrosis. The coagulative necrosis of the arteries, their distension by necrotic debris and the absence of platelet-fibrin thrombi distinguish ethanol-induced infarction from that caused by atherosclerotic coronary artery disease. The direct vascular toxicity of ethanol may be an important aspect of the mechanism of successful ASA.

Disagreement between formal and medical record criteria for the diagnosis of acute coronary syndrome.

OBJECTIVES: To measure agreement between formal and medical record criteria for the diagnosis of acute coronary syndrome (ACS) among patients undergoing an emergency department evaluation for potential acute coronary symptoms. METHODS: Cases of ACS were determined by both formal (World Health Organization 1984 criteria for acute myocardial infarction [AMI], Braunwald criteria for unstable angina pectoris [UAP]) and medical record criteria. In the latter, a diagnosis was made if providers indicated AMI or UAP anywhere in the medical record. All information included in formal criteria was available to clinicians establishing the medical record diagnosis. The two criteria for diagnosis were compared, and a kappa value was recorded. Two blinded observers adjudicated discordant cases, with a kappa value recorded. Disagreements between these two coinvestigators were resolved by a Delphi technique. RESULTS: A total of 375 eligible subjects were enrolled, of whom 65 (17%; 45 AMI, 20 UAP) had ACS by both sets of criteria. Formal and medical record criteria disagreed in 32 subjects. This represented 9% (95% confidence interval = 6% to 12%) of the overall study population but 33% (95% confidence interval = 23% to 43%) of subjects with possible ACS. Coinvestigators acting as judges and blinded to each other's determinations agreed that 25 of these subjects had ACS and three did not; they disagreed on four subjects (kappa = 0.54). Among these four subjects, a Delphi consensus technique determined that two subjects had AMI and two had no ACS. CONCLUSIONS: In a single-site study, among subjects who have possible ACS as determined by either or both formal and medical record criteria, these two sets of criteria disagree in almost one third of cases. Among discordant cases, even two expert judges frequently disagreed on the final diagnosis. A modified Delphi technique to address these disagreements is described.

Evaluation of intracoronary stenting by intravascular optical coherence tomography.

BACKGROUND: Conventional contrast cineangiography and intravascular ultrasound (IVUS) provide a limited definition of vessel microstructure and are unable to evaluate dissection, tissue prolapse, and stent apposition on a size scale less than 100 micro m. OBJECTIVE: To evaluate the use of intravascular optical coherence tomography (OCT) to assess the coronary arteries in patients undergoing coronary stenting. METHODS: OCT was employed in patients having percutaneous coronary interventions. Images were obtained before initial balloon dilatation and following stent deployment, and were evaluated for vessel dissection, tissue prolapse, stent apposition, and stent asymmetry. IVUS images were obtained before OCT, using an automatic pull back device. RESULTS: 42 stents were imaged in 39 patients without complications. Dissection, prolapse, and incomplete stent apposition were observed more often with OCT than with IVUS. Vessel dissection was identified in eight stents by OCT and two by IVUS. Tissue prolapse was identified in 29 stents by OCT and 12 by IVUS; the extent of the prolapse (mean (SD)) was 242 (156) microm by OCT and 400 (100) microm by IVUS. Incomplete stent apposition was observed in seven stents by OCT and three by IVUS. Irregular strut separation was identified in 18 stents by both OCT and IVUS. CONCLUSIONS: Intracoronary OCT for monitoring stent deployment is feasible and provides superior contrast and resolution of arterial pathology than IVUS.

The comparison between optical coherence tomography and intravascular ultrasound.

Coronary angiography, despite its long history, has well recognized limitations, arising in part from the inability to image a three dimensional structure in a single plane. Furthermore the angiographic image of the arterial lumen conceals atherosclerotic processes that occur within the arterial wall. Alternative imaging techniques have evolved as an adjunct to angiography in an attempt to overcome these limitations. Two such invasive techniques are intravascular ultrasound and optical coherence tomography. Intravascular ultrasound allows tomographic imaging of long segments of the coronary tree, highlighting the arterial lumen as well as the arterial wall. Over the last 13 years intravascular ultrasound has enhanced our understanding of the pathophysiology of atherosclerosis, and the mechanisms involved in coronary intervention. Optical coherence tomography is an optical analogue of intravascular ultrasound that has recently reached coronary application. Its superior resolution results in improved diagnostic potential, particularly for vulnerable plaque in which the thin fibrous cap often measures 10-50 mm. The similarities, contrasts and applications of these two imaging techniques in terms of design, image interpretation, and future directions forms the subject of this review.