Effect of Latent Heat Phenomena on Thermal Insulation and Inside Climate of Greenhouses

By means of a dynamic greenhouse climate model, it was shown that condensation highly alters the thermal insulation properties (from +25% to -17%) of greenhouse cladding materials, depending on the far-infrared radiation transmittance of the dry material. Neglect of condensation and evaporation gave rise to an overestimation of the yearly mean inside air relative humidity of about 10% for most materials and to overestimates or underestimates of the vegetation temperature, according to the cladding's far-infrared radiation transmittance. The relative contri bution of condensation to the nighttime water vapor removal from the inside air was found to range from 79 to 89%.

The HMI™ module: a new tool to study the Host-Microbiota Interaction in the human gastrointestinal tract in vitro

Background

Recent scientific developments have shed more light on the importance of the host-microbe interaction, particularly in the gut. However, the mechanistic study of the host-microbe interplay is complicated by the intrinsic limitations in reaching the different areas of the gastrointestinal tract (GIT) in vivo. In this paper, we present the technical validation of a new device - the Host-Microbiota Interaction (HMI) module - and the evidence that it can be used in combination with a gut dynamic simulator to evaluate the effect of a specific treatment at the level of the luminal microbial community and of the host surface colonization and signaling.

Results

The HMI module recreates conditions that are physiologically relevant for the GIT: i) a mucosal area to which bacteria can adhere under relevant shear stress (3 dynes cm⁻²); ii) the bilateral transport of low molecular weight metabolites (4 to 150 kDa) with permeation coefficients ranging from 2.4 × 10⁻⁶ to 7.1 × 10⁻⁹ cm sec⁻¹; and iii) microaerophilic conditions at the bottom of the growing biofilm (PmO₂ = 2.5 × 10⁻⁴ cm sec⁻¹). In a long-term study, the host’s cells in the HMI module were still viable after a 48-hour exposure to a complex microbial community. The dominant mucus-associated microbiota differed from the luminal one and its composition was influenced by the treatment with a dried product derived from yeast fermentation. The latter - with known anti-inflammatory properties - induced a decrease of pro-inflammatory IL-8 production between 24 and 48 h.

Conclusions

The study of the in vivo functionality of adhering bacterial communities in the human GIT and of the localized effect on the host is frequently hindered by the complexity of reaching particular areas of the GIT. The HMI module offers the possibility of co-culturing a gut representative microbial community with enterocyte-like cells up to 48 h and may therefore contribute to the mechanistic understanding of host-microbiome interactions.

Stimulation of methanogenesis in a laboratory scale UASB reactor treating domestic sewage by Fe(0) application

The effects of application of zero valence Fe (Fe(0)) on the anaerobic digestion of sewage was investigated using two laboratory scale UASB reactors. One reactor had Fe(0) addition in a container found midway along the recycling loop. The other one was a control reactor. In a test run period of 76 days, the Fe(0) application significantly increased the CH, yield by 8.7% and decreased the effluent COD concentration by 21.0% relative to the control reactor. A decrease of the H, concentration of biogas and the CODs/CODt ratio in effluent by Fe(0) application were observed. The obtained results imply that the methanogenesis and COD removal efficiency of the UASB reactor were stimulated by Fe(0) application. The higher performance of the reactor with Fe(0) application arises from the integrated functions of Fe(0) or its ionic state as donor of H2, macronutrient, and flocculant. This study showed that the supply of Fe(0) to a UASB can improve the methanogenesis and the overall COD removal of a UASB reactor treating low-strength domestic waste water.

Entry and survival of pathogenic mycobacteriain macrophages

Pathogenic mycobacteria, including Mycobacterium tuberculosis, are phagocytosed by macrophages but manage to survive within the mycobacterial phagosome. Recent work has shed some more light on the mechanisms of mycobacterial entry and survival inside macrophages. Two host cell components, the steroid cholesterol and a phagosomal coat protein termed TACO were found to play crucial roles in the establishment of an intracellular infection. This review describes how these findings may help to understand the circumvention of the normal trafficking routes inside host cells by mycobacteria.

Evasion of host cell defense mechanisms by pathogenic bacteria

From an immunological viewpoint, invasion of pathogenic bacteria into a susceptible host poses a potential life-threatening situation and thus has to be met with all weapons that are available. A crucial component of host defense mechanisms is the macrophage. The scavenger activity of this cell ensures the uptake and destruction of bacteria in phagolysosomes, on the one hand, and activation of the adaptive component of the immune system through presentation of bacterial antigens, on the other hand. From the bacterial perspective, entry into a phagolysosome is usually fatal and many pathogens have developed strategies that circumvent the destructive environment of this organelle. Such evasion strategies often exploit normal host cell function. Understanding these survival strategies will deepen our insight of the pathogenesis of infection as well as host cell biology.

Association of distinct tetraspanins with MHC class II molecules at different subcellular locations in human immature dendritic cells

Dendritic cells have the capacity to trigger T cell responses in lymphoid organs against antigens captured in the periphery. T cell stimulation depends on the ability of MHC class II molecules to present peptides at the cell surface that are acquired in MHC class II compartments. The high capacity of dendritic cells to stimulate T lymphocytes is related to their ability to regulate the distribution of MHC class II molecules intracellularly. To analyze the molecular components involved in the generation of MHC class II-peptide complexes in human immature dendritic cells, mAb were raised against purified MHC class II compartments. One of the antigens turned out to be CD63, a member of the tetraspanin superfamily. CD63 localized exclusively intracellularly where it associated with peptide-loaded class II molecules. In contrast, the tetraspanins CD9, CD53 and CD81 associated with class II molecules at the plasma membrane. Selective association of distinct tetraspanins may be involved in the regulation of MHC class II distribution in human dendritic cells.

Individual wastewater treatment in Flanders (Belgium)

In Flanders, it is not possible to centralise the infrastructure for handling all wastewater. Decentralised treatment should be considered an essential part of an overall regional policy. Decentralised wastewater treatment can be small-scale (20 to 2,200 Inhabitant Equivalent (IE)) or individual (less than 20 IE). This paper deals with the operation, performances, technological aspects and costs of Individual Wastewater Treatment Plants (IWTPs) in Flanders. Different treatment systems are described and tentatively evaluated. The total costs (capital and operation) can be of the same order of those of centralised systems, i.e. 100 EURO/IE.year. In terms of overall performance, most of the systems tested in Flanders, i.e. aerobic biological filter, activated sludge system, submerged aerated filter, biorotor and percolation reed bed, appear capable to perform well in principle. However, there remain problems to be solved. The effluent quality differs 'in situ' considerably, depending on the care and attention given by the owner. Hence, the legislator should not only focus on certification of installations as such, but foremost give attention to regular validation of the performance at the household. In this respect, there is an urgent need for the design and the logistic management of proper performance control systems.

Essential role for cholesterol in entry of mycobacteria into macrophages

Mycobacteria are intracellular pathogens that can invade and survive within host macrophages, thereby creating a major health problem worldwide. The molecular mechanisms involved in mycobacterial entry are still poorly characterized. Here we report that cholesterol is essential for uptake of mycobacteria by macrophages. Cholesterol accumulated at the site of mycobacterial entry, and depleting plasma membrane cholesterol specifically inhibited mycobacterial uptake. Cholesterol also mediated the phagosomal association of TACO, a coat protein that prevents degradation of mycobacteria in lysosomes. Thus, by entering host cells at cholesterol-rich domains of the plasma membrane, mycobacteria may ensure their subsequent intracellular survival in TACO-coated phagosomes.

A secreted form of the major histocompatibility complex class II-associated invariant chain inhibiting T cell activation

Major histocompatibility complex (MHC) class II molecules function at the cell surface to present antigenic peptides to T helper cells. Intracellularly, MHC class II molecules are associated with the invariant chain (Ii). Ii can modulate MHC class II-dependent T cell activation through (i) assistance in the export of MHC class II molecules from the endoplasmic reticulum, (ii) providing a targeting signal for endosomal/lysosomal compartments, and (iii) preventing peptides from associating prematurely with MHC class II molecules. Here we describe the generation and subsequent secretion of a lumenal form of Ii, IiP25. IiP25 lacked the targeting sequences for transport to MHC class II compartments but contained part of the CLIP region that is known to compete with antigenic peptides for binding to MHC class II molecules. When added to an antigenic peptide presentation model system, IiP25 inhibited T cell activation by competing for the CLIP binding site at the plasma membrane. Secretion of a lumenal Ii fragment may represent an additional mechanism to modulate T cell activation by MHC class II molecules.

A coat protein on phagosomes involved in the intracellular survival of mycobacteria

Mycobacteria are intracellular pathogens that can survive within macrophage phagosomes, thereby evading host defense strategies by largely unknown mechanisms. We have identified a WD repeat host protein that was recruited to and actively retained on phagosomes by living, but not dead, mycobacteria. This protein, termed TACO, represents a component of the phagosome coat that is normally released prior to phagosome fusion with or maturation into lysosomes. In macrophages lacking TACO, mycobacteria were readily transported to lysosomes followed by their degradation. Expression of TACO in nonmacrophages prevented lysosomal delivery of mycobacteria and prolonged their intracellular survival. Active retention of TACO on phagosomes by living mycobacteria thus represents a mechanism preventing cargo delivery to lysosomes, allowing mycobacteria to survive within macrophages.

MHC class II and invariant chain biosynthesis and transport during maturation of human precursor dendritic cells

Dendritic cells (DC) are highly potent activators of the immune response. The precise mechanisms that give rise to the DC phenotype are not known. To investigate the mechanisms that contribute to the generation of the DC phenotype, precursor DC were freshly isolated from human blood and allowed to mature in vitro. These matured DC showed the phenotypical and functional characteristics of DC. Analysis of the MHC class II and invariant chain (li) biosynthesis revealed that upon maturation, class II synthesis was induced whereas li synthesis was significantly up-regulated. In mature DC, despite the presence of large amounts of li, export of MHC class II molecules from the endoplasmic reticulum was incomplete, up to 4 h after biosynthesis. Thus, MHC class II-li synthesis and transport in DC is highly regulated during maturation of DC. Analysis of the regulatory mechanisms may contribute to a better understanding of antigen-presenting capacities during the differentiation of DC.

Subcellular fractionation by organelle electrophoresis: separation of phagosomes containing heat-killed yeast particles

Uptake of foreign material and its subsequent lysosomal degradation is an important function of macrophages. The mechanisms involved in the binding, uptake and delivery of such material to lysosomal organelles, are, however, poorly understood. Here we describe a method using organelle electrophoresis to study the uptake and trafficking of heat-killed yeast particles within murine macrophages. Such yeast particles, which were fluorescently labeled, could be readily detected in intact cells as well as in subcellular fractions. Organelle electrophoresis of a homogenate from macrophages that had internalized yeast particles resulted in the separation of yeast-containing organelles from most other subcellular membranes. In addition, this method was used to follow the kinetics of yeast particle transport within macrophages could be followed readily. Organelle electrophoresis may be a valuable tool for the analysis of phagocytosis.

Distinct intracellular compartments involved in invariant chain degradation and antigenic peptide loading of major histocompatibility complex (MHC) class II molecules

Major histocompatibility complex (MHC) class II molecules are transported to intracellular MHC class II compartments via a transient association with the invariant chain (Ii). After removal of the invariant chain, peptides can be loaded onto class II molecules, a process catalyzed by human leukocyte antigen-DM (HLA-DM) molecules. Here we show that MHC class II compartments consist of two physically and functionally distinct organelles. Newly synthesized MHC class II/Ii complexes were targeted to endocytic organelles lacking HLA-DM molecules, where Ii degradation occurred. From these organelles, class II molecules were transported to a distinct organelle containing HLA-DM, in which peptides were loaded onto class II molecules. This latter organelle was not directly accessible via fluid phase endocytosis, suggesting that it is not part of the endosomal pathway. Uptake via antigen-specific membrane immunoglobulin resulted however in small amounts of antigen in the HLA-DM positive organelles. From this peptide-loading compartment, class II-peptide complexes were transported to the plasma membrane, in part after transit through endocytic organelles. The existence of two separate compartments, one involved in Ii removal and the other functioning in HLA-DM-dependent peptide loading of class II molecules, may contribute to the efficiency of antigen presentation by the selective recruitment of peptide-receptive MHC class II molecules and HLA-DM to the same subcellular location.

Analysis of subcellular organelles involved in major histocompatibility complex (MHC) class II-restricted antigen presentation by electrophoresis

Presentation of material derived from pathogenic organisms to the immune system requires uptake of antigens into antigen presenting cells, processing into peptide fragments and loading of the resulting fragments onto major histocompatibility complex (MHC) class II molecules. MHC class II-restricted antigen presentation involves both the biosynthetic as well as the endocytic pathway of antigen-presenting cells. In recent years, the general mechanisms that govern these processes have been delineated, and specialized organelles have been characterized in which processing and loading of antigens takes place. Here, we review the work that has led to the characterization of these MHC class II compartments, and describe the use of organelle electrophoresis and two-dimensional gel electrophoresis to analyze the molecular composition of the different subcellular organelles involved in MHC class II-restricted antigen presentation as well as in antigen uptake.

The mannose receptor functions as a high capacity and broad specificity antigen receptor in human dendritic cells

Dendritic cells, in contrast to B lymphocytes, must be able to efficiently internalize a diverse array of antigens for processing and loading onto major histocompatibility complex (MHC) class II molecules. Here we characterize the mannose receptor pathway in dendritic cells and show that mannose receptor-mediated uptake of antigens results in a approximately 100-fold more efficient presentation to T cells, as compared to antigens internalized via fluid phase. Immunocytochemistry as well as subcellular fractionation revealed the localization of the mannose receptor and MHC class II molecules in distinct subcellular compartments. The mannose receptor thus functions in rapid internalization and concentration of a variety of glycosylated antigens that become available for processing and presentation. This may contribute to the unique capacity of dendritic cells to generate primary T cell responses against infectious agents.

Inflammatory stimuli induce accumulation of MHC class II complexes on dendritic cells

Dendritic cells have the remarkable property of presenting any incoming antigen. To do so they must not only capture antigens with high efficiency and broad specificity, but must also maximize their capacity to load class II molecules of the major histocompatibility complex (MHC) with antigenic peptides in order to present a large array of epitopes from different proteins, each at a sufficient copy number. Here we show that formation of peptide-MHC class II complexes is boosted by inflammatory stimuli that induce maturation of dendritic cells. In immature dendritic cells, class II molecules are rapidly internalized and recycled, turning over with a half-life of about 10 hours. Inflammatory stimuli induce a rapid and transient boost of class II synthesis, while the half-life of class II molecules increases to over 100 hours. These coordinated changes result in the rapid accumulation of a large number of long-lived peptide-loaded MHC class II molecules capable of stimulating T cells even after several days. The capacity of dendritic cells to load many antigenic peptides over a short period of initial exposure to inflammatory stimuli could favour presentation of infectious antigens.

MHC class II compartments: specialized organelles of the endocytic pathway in antigen presenting cells

Mounting an immune response against foreign, extracellular material requires that this material be internalized by antigen presenting cells, processed to peptide fragments and then displayed on the cell surface for recognition by the T cell receptor on T helper cells. Such peptides, derived from internalized antigens are generally presented to T cells in association with Major Histocompatibility Complex (MHC) class II molecules. Recent work has identified subcompartments of the endosomal/lysosomal system that appear to be important sites for the generation of peptide-MHC class II complexes. These so-called MHC class II compartments receive antigenic fragments from endosomes and lysosomes and load them onto class II molecules. From these compartments, peptide-loaded class II molecules are transported to the plasma membrane, where they can trigger T cells bearing appropriate receptors. This review summarizes recent work characterizing MHC class II compartments as specialized organelles of the endosomal/lysosomal pathway. Interestingly, MHC class II compartments share many features common to organelles present in a wide variety of specialized cells with quite different functions. Modifying the endocytic pathway to serve the needs of specialized cells may be a common mechanism which allows very different cell types to carry out their disparate functions.

Isolation and characterization of the mycobacterial phagosome: segregation from the endosomal/lysosomal pathway

Mycobacteria have the ability to persist within host phagocytes, and their success as intracellular pathogens is thought to be related to the ability to modify their intracellular environment. After entry into phagocytes, mycobacteria-containing phagosomes acquire markers for the endosomal pathway, but do not fuse with lysosomes. The molecular machinery that is involved in the entry and survival of mycobacteria in host cells is poorly characterized. Here we describe the use of organelle electrophoresis to study the uptake of Mycobacterium bovis bacille Calmette Guerin (BCG) into murine macrophages. We demonstrate that live, but not dead, mycobacteria occupy a phagosome that can be physically separated from endosomal/lysosomal compartments. Biochemical analysis of purified mycobacterial phagosomes revealed the absence of endosomal/lysosomal markers LAMP-1 and beta-hexosaminidase. Combining subcellular fractionation with two-dimensional gel electrophoresis, we found that a set of host proteins was present in phagosomes that were absent from endosomal/lysosomal compartments. The residence of mycobacteria in compartments outside the endosomal/lysosomal system may explain their persistence inside host cells and their sequestration from immune recognition. Furthermore, the approach described here may contribute to an improved understanding of the molecular mechanisms that determine the intracellular fate of mycobacteria during infection.

MHC class II restricted antigen presentation

Presentation of antigenic peptides by MHC class II molecules to CD4(+) T cells requires many events in both the biosynthetic and endocytic pathways that must all occur in a controlled and coordinated fashion. In recent years the roles of two important chaperones, the invariant chain and the HLA-DM dimer, in promoting the acquisition of peptides by MHC class II molecules have largely been elucidated. The different compartments within the endosomal/lysosomal pathway that are involved in peptide loading are now being characterized. In addition to the specialized MHC class II compartments that exist in antigen-presenting cells, other intracellular compartments may also be involved in peptide loading. The precise mechanisms and intracellular sites of MHC class II peptide loading appear to dictate the nature of the T-cell epitopes presented by the antigen-presenting cell.

Mannose receptor mediated antigen uptake and presentation in human dendritic cells

In an immature state, dendritic cells (DC) can capture antigen via at least two mechanisms. First, DC use macropinocytosis for continuous uptake of large amounts of soluble antigens. Second, they express high levels of mannose receptor that can mediate internalization of glycosylated ligands. We found that dendritic cells can present mannosylated antigen 100-1000 fold more efficiently than non-mannosylated antigen. Immunocytochemistry as well as subcellular fractionation demonstrated that the mannose receptor and MHC class II molecules were located in distinct subcellular compartments. These results demonstrate that the mannose receptor endows DC with a high capacity to present glycosylated antigens at very low concentrations.

Isolation and characterization of the intracellular MHC class II compartment

An intracellular compartment has been isolated to which MHC class II molecules are transported on their way to the plasma membrane. They arrive with an associated invariant chain which is then proteolytically processed while MHC class II molecules acquire antigenic peptide. These loaded class II molecules then leave the compartment devoid of invariant chain and bound for the plasma membrane. This compartment represents a new stage in the endocytic/lysosomal pathway.

Application of an improved density gradient electrophoresis apparatus to the separation of proteins, cells and subcellular organelles

A DGE apparatus, made of Perspex, consisting of a separation column (5 x 2.2 cm) and containing a 0-4% linear Ficoll density gradient, was constructed. Only 2.5 cm of the column were used for high resolution separations. A specially designed removable top cone permitted precise gradient introduction, thin sample layering (0.3-1 mm) and precise fractionation after electrophoresis. A bottom circular palladium anode (nongassing) was separated hydrodynamically but not electrically from the density gradient by a cation-permeable membrane. A top circular platinum cathode caused negatively charged particles to migrate upwards (levitation). Thin sample layering permitted short separation times (30-60 min) at only 3 V/cm (10 mA). As for proteins, glycoforms of a1-antitrypsin were separated as well as isoenzymes of beta-hexoseaminidase. Furthermore, separation of transferrin (Tf) from the putative Tf-receptor complex was effectuated. The device was equally suitable for the separation of Megadalton proteins (mucins). Artificial mixtures of intact erythrocytes (rat, rabbit, human) were separated with high resolution. About 10(7) cells (of 100 microns3 cell volume) could be loaded onto the device. Crude microsomes from the human melanoma cell line Mel JuSo were separated after brief trypsin treatment within 38 min at 10 mA. Ratios of the migration velocities of the constituent organelles were: late endosomes (LE):lysosomes (L):Golgi (G):early endosomes (EE) = 1:0.94:0.77:0.55 and under slightly different conditions LE:L:G:endoplasmatic reticulum (ER):plasma membrane (PM) = 1:0.87:0.64:0.58:0.49.

The MHC class II-associated invariant chain contains two endosomal targeting signals within its cytoplasmic tail

The oligomeric complex formed by major histocompatibility complex (MHC) class II alpha and beta chains and invariant chain (Ii) assembles in the endoplasmic reticulum and is then transported via the Golgi complex to compartments of the endocytic pathway. When Ii alone is expressed in CV1 cells it is sorted to endosomes. The Ii cytoplasmic tail has been found to be essential for targeting to these compartments. In order to characterize further the signals responsible for endosomal targeting, we have deleted various segments of the cytoplasmic tail. The Ii mutants were transiently expressed and the cellular location of the proteins was analyzed biochemically and morphologically. The cytoplasmic tail of Ii was found to contain two endosomal targeting sequences within its cytoplasmic tail; one targeting sequence was present within amino acid residues 12–29 and deletion of this segment revealed the presence of a second endosomal targeting sequence, located within the first 11 amino acid residues. The presence of a leucine-isoleucine pair at positions 7 and 8 within this sequence was found to be essential for endosomal targeting. In addition, the presence of this L-I motif lead to accumulation of Ii molecules in large endosomal vacuoles containing lysosomal marker proteins. Both wild type Ii and Ii mutant molecules containing only one endosomal targeting sequence were rapidly internalized from the plasma membrane. When the Ii cytoplasmic tail was fused to the membrane-spanning region of neuraminidase, a resident plasma membrane protein, the resulting chimera (INA) was found in endocytic compartments containing lysosomal marker proteins. Thus the cytoplasmic tail of Ii is sufficient for targeting to the endocytic/lysosomal pathway.

Intracellular transport and localization of major histocompatibility complex class II molecules and associated invariant chain

The intracellular transport and location of major histocompatibility complex (MHC) class II molecules and associated invariant chain (Ii) were investigated in a human melanoma cell line. In contrast to the class II molecules, which remain stable for greater than 4 h after synthesis, the associated Ii is proteolytically processed within 2 h. During or shortly after synthesis the NH2-terminal cytoplasmic and membrane-spanning segment is in some of the Ii molecules cleaved off; during intracellular transport, class II associated and membrane integrated Ii is processed from its COOH terminus in distinct steps in endocytic compartments. Immunocytochemical studies at the light and electron microscopic level revealed the presence of class II molecules, but not of Ii on the cell surface. Intracellularly both Ii and class II molecules were localized in three morphologically and kinetically distinct compartments, early endosomes, multivesicular bodies, and prelysosomes. This localization in several distinct endosomal compartments contrasts with the localization of class II molecules in mainly one endocytic compartment in B lymphoblastoid cell lines. As in these lymphoblastoid cell lines Ii is known to be rapidly degraded it is conceivable that the rate of proteolysis of the class II associated Ii and its dissociation from class II molecules modulates the retention of the oligomeric complex in endocytic compartments, and as a consequence the steady-state distribution of these molecules within the endosomal system.

Heparin-stimulated inhibition of factor IXa generation and factor IXa neutralization in plasma

Generation and inhibition of activated factor IXa was studied in factor XIa-activated plasma containing 4 mmol/L free calcium ions and 20 mumol/L phospholipid (25 mol% phosphatidylserine/75 mol% phosphatidylcholine). Interference of other (activated) clotting factors with the factor IXa activity measurements could be avoided by using a highly specific and sensitive bioassay. Factor IXa generation curves were analyzed according to a model that assumed Michaelis-Menten kinetics of factor XIa-catalyzed factor IXa formation and pseudo first order kinetics of inhibition of factor XIa and factor IXa. In the absence of heparin, factor IXa activity in plasma reached final levels that were found to increase with increasing amounts of factor XIa used to activate the plasma. When the model was fitted to this set of factor IXa generation curves, the analysis yielded a rate constant of inhibition of factor XIa of 0.7 +/- 0.1 min-1 and a kcat/Km ratio of 0.29 +/- 0.01 (nmol/L)-1 min-1. No neutralization of factor IXa activity was observed (the estimated rate constant of inhibition of factor IXa was 0). Thus, in the absence of heparin, the final level of factor IXa in plasma is only dependent on the initial factor XIa concentration. While neutralization of in situ generated factor IXa in normal plasma was negligible, unfractionated heparin dramatically enhanced the rate of inactivation of factor IXa (apparent second order rate constant of inhibition of 5.2 min-1/per microgram heparin/mL). The synthetic pentasaccharide heparin, the smallest heparin chain capable of binding antithrombin III, stimulated the inhibition of in situ generated factor IXa, but sevenfold less than unfractionated heparin (k = 0.76 min-1 per microgram pentasaccharide/mL). We found that free calcium ions were absolutely required to observe an unfractionated heparin and pentasaccharide-stimulated neutralization of factor IXa activity. Factor XIa inhibition (psuedo first order rate constant of 0.7 min-1) was not affected by unfractionated heparin or pentasaccharide in the range of heparin concentrations studied.

In situ-generated thrombin is the only enzyme that effectively activates factor VIII and factor V in thromboplastin-activated plasma

We investigated the activation of the nonenzymatic protein cofactors factor VIII and factor V in plasma when coagulation was initiated by thromboplastin. With sensitive bioassays, we were able to measure specifically the generation of activated factor VIII and activated factor V in plasma. Our results showed that when plasma was triggered with a relatively high concentration of thromboplastin, factor VIII and factor V were completely activated at the clotting time of plasma. However, when the generation of thrombin, but not that of factor Xa, was delayed by addition of hirudin to the plasma, factor Va was generated only at the time thrombin generation overcame the hirudin inhibition. In addition, generation of factor VIIIa correlated with thrombin generation and not with factor Xa generation. Furthermore, addition of large amounts of factor Xa to hirudinized plasma did not show detectable factor VIII or factor V activation. We concluded that in plasma activated with thromboplastin the enzyme responsible for activation of factor V and factor VIII is thrombin, not factor Xa.

The limited importance of factor Xa inhibition to the anticoagulant property of heparin in thromboplastin-activated plasma

The antifactor Xa activities of heparin fractions are widely used as an ex vivo index of their antithrombotic efficacy. Its clinical meaning, however, remains speculative. In the study reported, we measured the effects of standard heparin, a synthetic pentasaccharide heparin (antifactor Xa activity only), and a low molecular weight heparin (LMWH) on factor Xa, factor Va, and thrombin generation in thromboplastin-activated plasma. We clearly demonstrated that the antifactor Xa activity of heparin contributed little in its anticoagulant activity. The inhibition of factor Va generation, dependent on the heparin antithrombin activity only, is of prime importance to the inhibition of thrombin generation in plasma. The inhibition of thrombin generation by the LMWH was comparable with that of standard heparin on the basis of their respective antithrombin specific activities, but not on the basis of their antifactor Xa activities.

Inhibition of factor IXa and factor Xa by antithrombin III/heparin during factor X activation

We investigated the kinetics of the inhibitory action of antithrombin III and antithrombin III plus heparin during the activation of factor X by factor IXa. Generation and inactivation curves were fitted to a three-parameter two-exponentional model to determine the pseudo first-order rate constants of inhibition of factor IXa and factor Xa by antithrombin III/heparin. In the absence of heparin, the second-order rate constant of inhibition of factor Xa generated by factor IXa was 2.5-fold lower than the rate constant of inhibition of exogenous factor Xa. It appeared that phospholipid-bound factor X protected factor Xa from inactivation by antithrombin III. It is, as yet, unclear whether an active site or a nonactive site interaction between factor Xa and factor X at the phospholipid surface is involved. The inactivation of factor IXa by antithrombin III was found to be very slow and was not affected by phospholipid, calcium, and/or factor X. With unfractionated heparin above 40 ng/ml and antithrombin III at 200 nM, the apparent second-order rate constant of inhibition of exogenous and generated factor Xa were the same. Thus, in this case phospholipid-bound factor X did not protect factor Xa from inhibition. In the presence of synthetic pentasaccharide heparin, however, phospholipid-bound factor X reduced the rate constant about 5-fold. Pentasaccharide had no effect on the factor IXa/antithrombin III reaction. Unfractionated heparin (1 micrograms/ml) stimulated the antithrombin III-dependent inhibition of factor IXa during factor X activation 400-fold. In the absence of reaction components this stimulated was 65-fold. We established that calcium stimulated the heparin-dependent inhibition of factor IXa.

Cloning and expression of cDNA for human vascular anticoagulant, a Ca2+-dependent phospholipid-binding protein

Based on sequence information from tryptic peptides an almost full-size cDNA coding for the human vascular anticoagulant was isolated from a placental cDNA library and sequenced. The coding region was cloned into an Escherichia coli expression vector and the protein expressed at high levels. The recombinant protein was purified and found to be indistinguishable from its natural counterpart in several biological assays.

Neutralization of heparin by prothrombin activation products

The neutralization of heparin by active site blocked meizothrombin and thrombin, prothrombin fragment 1.2, fragment 1 and fragment 2 was probed by the heparin-dependent factor Xa inactivation by antithrombin III (AT III). Meizothrombin had no effect on the inactivation of factor Xa, whereas thrombin had an inhibitory effect (IC50 = 700 nM). After factor Xa catalyzed cleavage of meizothrombin, the resulting products, prothrombin fragment 1.2 plus thrombin, did not show any heparin neutralizing properties. However, after isolation of the reaction products, both thrombin and prothrombin fragment 1.2 exhibited heparin neutralizing properties in the factor Xa inactivation reaction. The IC50-values were 700 nM and 100 nM, respectively. Prothrombin fragment 1, when present at 125 nM, caused a 50% reduction of the heparin-dependent rate of inactivation of factor Xa and prothrombin fragment 2 had no effect at all. From this we conclude that, in addition to the thrombin part of the prothrombin molecule, the fragment 1 region also exhibits a rather high affinity for heparin.

Synthesis and polymorphic phase behaviour of polyunsaturated phosphatidylcholines and phosphatidylethanolamines

A series of phosphatidylcholines and phosphatidylethanolamines was synthesized containing two acyl chains of the following polyunsaturated fatty acids: linoleic acid (18:2), linolenic acid (18:3), arachidonic acid (20:4) and docosahexaenoic acid (22:6). In addition two phospholipids with mixed acid composition were synthesized: 16:0/18:1c phosphatidylcholine and 16:0/18:1c phosphatidylethanolamine. The structural properties of these lipids in aqueous dispersions in the absence and in the presence of equimolar cholesterol were studied using 31P-NMR, freeze fracturing and differential scanning calorimetry (DSC). The phosphatidylcholines adopt a bilayer configuration above 0 degrees C. Incorporation of 50 mol% of cholesterol in polyunsaturated species induces a transition at elevated temperatures into structures with 31P-NMR characteristics typical of non-bilayer organizations. When the acyl chains contain three or more double bonds, this non-bilayer organization is most likely the hexagonal HII phase. 16:0/18:1c phosphatidylethanolamine shows a bilayer to hexagonal transition temperature of 75 degrees C. The polyunsaturated phosphatidylethanolamines exhibit a bilayer to hexagonal transition temperature below 0 degrees C which decreases with increasing unsaturation and which is lowered by approximately 10 degrees C upon incorporation of 50 mol% of cholesterol. Finally, it was found that small amounts of polyunsaturated fatty acyl chains in a phosphatidylethanolamine disproportionally lower its bilayer to hexagonal transition temperature.

Determination and calibration of crystal lattice images of biological apatites

Lattice imaging provides detailed information on the mineral phase of calcified tissues. The lattice space distances dhk1 depend directly on the accuracy of the magnification. Using synthetic apatite, K2PtCl6, graphitized C and crocidolite as calibration material the lattice parameters of human enamel have been determined. The relative errors in the mineral dhk1 values using crocidolite, K2PtCl6 and C are 0.6, 1.0 and 3.9 % resp. If hydroxyapatite is employed on the same grid as the enamel specimen, the d-values obtained are very close to the X-ray diffraction data; a reproducibility of 0.8% in a and c lattice parameter determination can be obtained on selected crystallites.