Computational fluid dynamics modelling of perfusion measurements in dynamic contrast-enhanced computed tomography: development, validation and clinical applications.

Dynamic contrast-enhanced computed tomography (DCE-CT) is an imaging tool that aids in evaluating functional characteristics of tissue at different stages of disease management: diagnostic, radiation treatment planning, treatment effectiveness, and monitoring. Clinical validation of DCE-derived perfusion parameters remains an outstanding problem to address prior to perfusion imaging becoming a widespread standard as a non-invasive quantitative measurement tool. One approach to this validation process has been the development of quality assurance phantoms in order to facilitate controlled perfusion ex vivo. However, most of these systems fail to establish and accurately replicate physiologically relevant capillary permeability and exchange performance. The current work presents the first step in the development of a prospective suite of physics-based perfusion simulations based on coupled fluid flow and particle transport phenomena with the goal of enhancing the understanding of clinical contrast agent kinetics. Existing knowledge about a controllable, two-compartmental fluid exchange phantom was used to validate the computational fluid dynamics (CFD) simulation model presented herein. The sensitivity of CFD-derived contrast uptake curves to contrast injection parameters, including injection duration and flow rate, were quantified and found to be within 10% accuracy. The CFD model was employed to evaluate two commonly used clinical kinetic algorithms used to derive perfusion parameters: Fick's principle and the modified Tofts model. Neither kinetic model was able to capture the true transport phenomena it aimed to represent but if the overall contrast concentration after injection remained identical, then successive DCE-CT evaluations could be compared and could indeed reflect differences in regional tissue flow. This study sets the groundwork for future explorations in phantom development and pharmaco-kinetic modelling, as well as the development of novel contrast agents for DCE imaging.

[Prescription of cholinesterase inhibitors in Alzheimer's disease in France in 2000-2001: an assessment of compliance with national guidelines for diagnosis and follow-up]. / Prescription des anticholinestérasiques dans la maladie d'Alzheimer en France en 2000-2001: évaluation du respect des procédures diagnostiques et de suivi.

INTRODUCTION: Alzheimer's disease (AD) became a treatable disease about ten years ago when cholinesterase inhibitors (CI) became available. We conducted a national population-based study in France in order to describe patients taking CI in 2001, to compare the diagnostic procedures of AD and the drug prescriptions with the French National guidelines, and to analyze the follow-up procedures of the patients. METHODS: The study was carried out in nine regions of France between December 1st 2000 and February 28th 2001 and included 3510 patients with CI treatment prescribed by the physicians affiliated with the National Social Security Health Care Fund. RESULTS: We found that the diagnostic procedures and the prescriptions were in compliance with the national guidelines with more than 90 percent of patients referred to a specialist, brain imaging in 85 percent and a MMSE scored between 10 and 26 in more than 90 percent. However, patient follow-up was in compliance with the guidelines in only 50 percent of patients. CONCLUSION: Diagnostic procedures of AD and first prescription of CI seem to be adequate in France, but patient follow-up needs to be improved.

Lung function in workers refining phosphorus rock to obtain elementary phosphorus.

Elevated levels of phosphoric acid, phosphorus pentoxide, fluorides and coal tar pitch volatiles were present in workplace air of a two-oven industrial refinery. One hundred thirty-one workers prospectively underwent annual pulmonary function testing (forced vital capacity, forced expiratory volume in 1 second, and forced expiratory flow). Regression of these spirometric data, analyzed longitudinally over 3 to 7 years and also cross-sectionally reveals no residual significant effect of industrial exposure after adjusting for the effect of age and smoking. This industrial exposure contributes only weakly and inconsistently to the well-documented reduction of spirometric lung function that occurs from smoking alone. No significant reductions of spirometry occurred in exposed nonsmokers or former smokers.

A method for production of antibodies to human T-cell receptor beta-chain variable regions.

Mouse T-cell hybridomas bearing human V beta elements were produced by transfection of human/mouse hybrid T-cell receptor beta-chain genes into a mouse T-cell hybridoma lacking an endogenous beta-chain gene. These hybridomas were entirely mouse in origin except for the human V beta region. These cells were used to immunize mice against human V beta elements. Mouse monoclonal antibodies have thus been generated against human V beta 13.1 and -13.2. We expect that the method outlined in this paper will be useful in the production of monoclonal antibodies specific for other human V beta or V alpha elements.

Characterization of a monoclonal antibody which detects all murine alpha beta T cell receptors.

Research on the specificities, functions, and maturation of T cells would be greatly aided by a collection of monoclonal antibodies which distinguishes different types of TCR. With this end in mind hamsters were immunized and tested for production of pan-reactive anti-mouse alpha beta TCR antibodies. In this report we describe the properties and uses of a mAb, H57-597, produced from one of these animals. The mAb reacts with surface receptors on all alpha beta TCR-bearing cells and does not react with receptors on gamma delta+ T cells. In an immobilized form, this antibody can directly activate T cells bearing alpha beta TCR. It can be used in immunoprecipitation reactions to precipitate receptor from the appropriate cell types. In combination with anti-CD3, the antibody can be used in cytofluorographic analyses to measure numbers of CD3+, alpha beta+, and CD3+, gamma delta+ cells in the thymus and periphery.

Raman spectroscopy of cytoplasmic muscle fiber proteins. Orientational order.

The polarized Raman spectra of glycerinated and intact single muscle fibers of the giant barnacle were obtained. These spectra show that the conformation-sensitive amide I, amide III, and C-C stretching vibrations give Raman bands that are stronger when the electric field of both the incident and scattered radiation is parallel to the fiber axis (Izz). The detailed analysis of the amide I band by curve fitting shows that approximately 50% of the alpha-helical segments of the contractile proteins are oriented along the fiber axis, which is in good agreement with the conformation and composition of muscle fiber proteins. Difference Raman spectroscopy was also used to highlight the Raman bands attributed to the oriented segments of the alpha-helical proteins. The difference spectrum, which is very similar to the spectrum of tropomyosin, displays amide I and amide III bands at 1,645 and 1,310 cm-1, respectively, the bandwidth of the amide I line being characteristic of a highly alpha-helical biopolymer with a small dispersion of dihedral angles. A small dichroic effect was also observed for the band due to the CH2 bending mode at 1,450 cm-1 and on the 1,340 cm-1 band. In the C-C stretching mode region, two bands were detected at 902 and 938 cm-1 and are both assigned to the alpha-helical conformation.

A study of the structure of polymyxin B-dipalmitoylphosphatidylglycerol complexes by vibrational spectroscopy.

The effect of the antibiotic polymyxin B on dipalmitoylphosphatidylglycerol (DPPG) bilayers has been studied by Raman and infrared spectroscopies and small-angle X-ray diffraction. Each polymyxin B molecule binds five DPPG molecules at physiological pH and induces a macroscopic phase separation of the complex rather than a lateral phase separation. Below the phase transition of DPPG/polymyxin B bilayers, the results obtained show that the intermolecular vibrational coupling is high and suggest that the acyl chains of the bound lipid are interdigitated and that the hydrophobic tail of the antibiotic does not penetrate this tight assembly. On the other hand, the phase transition of DPPG is shifted down from 41 degrees C to 37 degrees C in the complexes and remains highly cooperative. Above the phase transition of the complexes, the conformation of the acyl chains of DPPG is slightly more disordered as a result of the penetration of the polymyxin chain, but the structure of the glycerol backbone of the lipid does not seem to be affected. However, the rotational rate of the lipid appears to be restricted by the peptide.

Study of the effect of melittin on the thermotropism of dipalmitoylphosphatidylcholine by Raman spectroscopy.

The effect of amphiphilic toxin melittin (Mel) on the thermotropic behavior of dipalmitoylphosphatidylcholine (DPPC) has been studied by Raman spectroscopy. The spectra show that for complexes that were incubated above 40 degrees C, melittin does not penetrate DPPC bilayers in the gel state as an intrinsic protein since the conformation of the lipid acyl chains is just slightly perturbed by the toxin. Instead, at the DPPC/Mel molar ratios investigated (Ri = 5 and 15), Raman results suggest the formation of discoidal particles as complexes of apolipoproteins with phosphatidylcholines. These lipid/protein assemblies are characterized by a high conformational order, low intermolecular chain-chain interactions due to the size of the particles, and a low cooperativity of the gel to liquid-crystalline transition. The latter is biphasic for samples studied. It is believed that aggregation of these particles into larger ones occurs when the bilayers become less stable at higher temperature and that melittin is partially embedded into the hydrophobic core of the larger lipid/protein units. The freezing of the dispersion at approximately 0 degrees C also causes a reversible aggregation of the particles that leads to the formation of domains in which the interchain interactions are very similar to that of the pure lipid. The small particles of DPPC/Mel are also metastable, and with time, they form larger aggregates from which melittin is expulsed.

The major histocompatibility complex-restricted antigen receptor on T cells in mouse and man: identification of constant and variable peptides.

The variability of the MHC restricted receptor on murine T cells was examined by comparing tryptic peptide fingerprints of the receptor isolated fom three T cell hybridomas and a T cell tumor. Both variable and constant peptides were seen. Constant peptides were most apparent when comparing receptors from the same mouse strain. Peptide fingerprints of receptors from two independent T cell hybridomas with the same idiotype and specificity were identical. We also describe a molecule detected on the surface of a human T cell leukemia whose properties were identical to those reported for the MHC receptor on normal human T cells. The molecule was a dimer of 85,000-90,000 MW containing a 46,000 MW acidic alpha-chain and an unrelated 40,000 MW neutral beta-chain.

The major histocompatibility complex-restricted antigen receptor on T cells. I. Isolation with a monoclonal antibody.

An antibody-secreting B cell hybridoma, KJ1-26.1, has been prepared from mice immunized with the T cell hybridoma DO-11.10, which recognizes chicken ovalbumin in association with I-Ad (cOVA/I-Ad). KJ1-26.1 blocks I-restricted antigen recognition by DO-11.10 and a subclone of this T cell hybridoma, DO-11.10.24, which has the same specificity for cOVA/I-Ad as its parent. KJ1-26.1 does not block I-restricted antigen recognition by any other T cell hybridoma tested, including a number of T cell hybridomas closely related to DO-11.10, with similar, but not identical, specificities for antigen/I. Moreover, KJ1-26.1 binds to DO-11.10 and DO-11.10.24, but not to any other T cell hybridomas tested, including three subclones of DO-11.10 that have lost the ability to recognize cOVA/I-Ad. Thus, in every regard KJ1-26.1 appears to be binding to all or part of the receptors for antigen/I on the T cell hybridoma DO-11.10. KJ1-26.1 appears to bind to approximately 15,000 molecules/cell on the surface of DO-11.10. The antibody precipitates an 80,000 dimer from the cells, which on reduction migrates as 40-44,000 monomers. The receptor(s) for antigen/I on DO-11.10 therefore includes molecules with these properties.

Expression of membrane IGM by a human B lymphoblastoid cell line in the presence of monensin.

The effect of the carboxylic ionophore, monensin, on the synthesis and expression of membrane IgM in the human lymphoblastoid cell line, Daudi, was investigated. The normal processing events in the maturation of mu chains and k chains were altered in monensin treated Daudi cells; the immunoglobulin chains did not appear to undergo complete terminal glycosylation modifications. Transport of the glycoprotein to the plasma membrane could be demonstrated indicating that the interference of intracellular processing of the IgM by monensin did not significantly influence the membrane expression of the IgM.

Antigen-specific, major histocompatibility complex-restricted T cell receptors.

In this paper we have summarized our work on the structure of the receptor for Ag/MHC on 3 T cell hybridomas. In each case, these receptors have been identified by their reaction with antibodies, thought to be directed against Ag/MHC receptors because of their clone-specificity, and their ability to interfere with Ag/MHC recognition by the relevant hybridoma. The antibodies precipitate approximately 85 kd molecular weight heterodimeric glycoproteins from these cells. These reduce to 2 chains of 40-43 kd, one of acidic and the other of basic pI. These bulk characteristics apply to receptors from Class II-restricted, as well as Class I-specific T cells. There is evidence of molecular weight heterogeneity for both alpha and beta-chains in the mouse, both having 40 and 43 kd forms. Isoelectric focussing patterns suggest that both chains vary in amino acid sequence between clones. Peptide maps show that the receptor varies in amino acid sequence between clones, but that some peptides appear common, i.e., the receptor seems to have both variable and constant amino acid sequences. It is even possible that allotypic differences between the peptide maps of BALB/c and C57BL/6-derived receptors have been identified, though more data will be needed to confirm this. Finally we have recently shown that reaction with an anti-idiotype predicts both the Ag and MHC specificity of the T cell hybridoma bearing it, suggesting that a single receptor, responsible for binding both Ag and MHC, is identified by the anti-idiotypic antibody. The similarities between these T cell-bourne molecules, and immunoglobulin are inescapable. Both are disulphide-linked glycoproteins made up of 2 chains, both of which may vary in amino acid sequence. Secreted immunoglobulin is, of course, polyvalent, being composed of two or more of each type of chain, this contributes to the efficiency with which the molecule can bind polyvalent antigen or build precipitable lattices. Similar constraints do not apply to T cell-bound receptors, which do not seem to have a secreted form.