Impaired primary immune response in type-1 diabetes. Functional impairment at the level of APCs and T-cells

We have recently described an impaired proliferative response of CD4(+) T-cells to primary antigens in patients with insulin-dependent diabetes mellitus (IDDM) [Clin. Immunol. 103 (2002) 249]. In order to further investigate possible mechanisms underlying this impairment, several factors known to be involved in the down-regulation of the immune response both at the level of APCs and CD4(+) T-cells were investigated: Monocyte-derived dendritic cells (MDDC) from IDDM patients were shown to express elevated amounts of CD86 (B7.2) (p=0.003) and reduced amounts of the adhesion molecule CD54 (ICAM-1) (p=0.03) on their cell surface compared to age-matched healthy controls and patients with non-insulin-dependent diabetes mellitus (NIDDM) as well as decreased SDS-PAGE stability of HLA-DQ and -DR peptide complexes directly isolated from the IDDM patients' peripheral blood mononuclear cells (PBMCs). Expression of CTLA-4 (CD152), known to be involved in the down-regulation of the immune response, was shown to be increased on CD4(+) T-cells from IDDM patients after exposure to the primary antigen KLH (keyhole limpet hemocyanin) presented by MDDC (p=0.0047). Likewise, purified CD4(+) T-cells from IDDM patients produced elevated levels of the cytokine TGF-beta1 after stimulation with immobilized monoclonal antibodies directed against CD3 and CD28 (p=0.014). When monocytes from IDDM patients were stimulated with lipopolysaccharide (LPS), an increased tendency to produce the inhibitory cytokine interleukin (IL)-10 (p=0.007) and the acute phase cytokine IL-6 (p=0.044) was observed, whereas the concentrations of tumor necrosis factor (TNF)-alpha, IL-1beta, and IL-12 were comparable to controls. Taken together, our data suggest that a deviation in the expression of certain molecules known to be involved in the peripheral control of the immune response is present in IDDM patients and is underlying the observed impairment of the primary immune response.     

Oscillations of plants' stems and their damping: theory and experimentation

Free oscillations of upright plants' stems, or in technical terms slender tapered rods with one end free, can be modelled by considering the equilibrium between bending moments and moments resulting from inertia. For stems with apical loads and negligible mass of the stem and for stems with finite mass but without top loading, analytical solutions of the differential equations with appropriate boundary conditions are available for a finite number of cases. For other cases approximations leading to an upper and a lower estimate of the frequency of oscillation omega can be derived. For the limiting case of omega = 0, the differential equations are identical with Greenhill's equations for the stability against Euler buckling of slender poles. To illustrate, the oscillation frequencies of 25 spruce trees (Picea sitchensis (Bong.) Carr.) were compared with those calculated on the basis of their morphology, their density and their static elasticity modulus. For Arundo donax L. and Cyperus alternifolius L. the observed oscillation frequency was used in turn to calculate the dynamic elasticity modulus, which was compared with that determined in three-point bending. Oscillation damping was observed for A. donax and C. alternifolius for plants' stems with and without leaves or inflorescence. In C. alternifolius the difference can be attributed to the aerodynamic resistance of the leaves, whereas in A. donax structural damping in addition plays a major role.     

Sphingosylphosphorylcholine regulates keratin network architecture and visco-elastic properties of human cancer cells

Sphingosylphosphorylcholine (SPC) is a naturally occurring bioactive lipid that is present in high density lipoproteins (HDL) particles and found at increased levels in blood and malignant ascites of patients with ovarian cancer. Here, we show that incubation of human epithelial tumour cells with SPC induces a perinuclear reorganization of intact keratin 8-18 filaments. This effect is specific for SPC, largely independent of F-actin and microtubules, and is accompanied by keratin phosphorylation. In vivo visco-elastic probing of single cancer cells demonstrates that SPC increases cellular elasticity. Accordingly, SPC stimulates migration of cells through size-limited pores in a more potent manner than lysophosphatidic acid (LPA). LPA induces actin stress fibre formation, but does not reorganize keratins in cancer cells and hence increases cellular stiffness. We propose that reorganization of keratin by SPC may facilitate biological phenomena that require a high degree of elasticity, such as squeezing of cells through membranous pores during metastasis.     

A prion protein epitope selective for the pathologically misfolded conformation

Conformational conversion of proteins in disease is likely to be accompanied by molecular surface exposure of previously sequestered amino-acid side chains. We found that induction of beta-sheet structures in recombinant prion proteins is associated with increased solvent accessibility of tyrosine. Antibodies directed against the prion protein repeat motif, tyrosine-tyrosine-arginine, recognize the pathological isoform of the prion protein but not the normal cellular isoform, as assessed by immunoprecipitation, plate capture immunoassay and flow cytometry. Antibody binding to the pathological epitope is saturable and specific, and can be created in vitro by partial denaturation of normal brain prion protein. Conformation-selective exposure of Tyr-Tyr-Arg provides a probe for the distribution and structure of pathologically misfolded prion protein, and may lead to new diagnostics and therapeutics for prion diseases.     

Biomechanics and Functional Anatomy of Hollow Stemmed Sphenopsids: III. Equisetum hyemale

As in Equisetum giganteum, the hollow stem of Equisetum hyemale owes the mechanical stability of the internodes to an outer ring of strengthening tissue (hypodermal sterome) which provides stiffness and strength in the longitudinal direction. In contrast to hollow-stemmed grasses, the hypodermal sterome consists of living cells. The compound inner tissue of the overwintering aerial stem of Equisetum hyemale includes a continuous inner and outer endodermis layer of vital thick-walled cells that have slightly lignified Casparian thickenings. The two endodermis layers provide an inner tension and compression bracing which lend resistance to local buckling. The stress-strain relation in longitudinal tension is biphasic with remarkably high critical strains especially in the upper parts of the stem. Scraping off part of the epidermis with the built-in silicate does not change this behaviour, except in the initial steep part of the curve where the Young's modulus is reduced by 20%. No contribution of the endodermis and the parenchyma could be detected in tension tests of longitudinally-oriented strips. Relaxation experiments reveal viscoelastic behaviour. As with the biphasic stress-strain relation and the critical strains, the viscoelastic properties have largely to be ascribed to the hypodermal sterome.     

Hydrodynamics and Biomechanics of the Submerged Water Moss Fontinalis antipyretica - a Comparison of Specimens from Habitats with Different Flow Velocities

Flow velocity has an influence on the hydrodynamic and biomechanical properties, as well as on the morphology and the anatomy of the submerged water moss Fontinalis antipyretica Hedw. Cross-sections of the plant stems show two main types of tissues. The strengthening tissue in the outer part is characterized by thick-walled cells with a small lumen, the parenchyma in the centre by thin-walled cells with a large lumen. The specimens from habitats of different flow velocities differ in the proportions of the strengthening tissue and the branching angle of the leaves. A flow tank with a special sensitive two-component balance inserted into the bottom of the flume was used to measure the hydrodynamic drag, which acts on the plant stems at different flow velocities. The drag forces increase with the length of the plant. Mechanical properties such as elasticity and ultimate strength of the plant stems were tested in tension. Relating the data to the relative proportions of the strengthening tissue results in different estimates of Young's moduli for the strengthening tissue of plants from the different sites. The critical strains to which the stems can be extended are remarkably high. Loading and unloading cycles reveal viscoelastic behaviour of the stem tissues. In the first cycle plastic deformation is also observed, but only to a lesser degree in subsequent cycles.     

‘Therapeutic window’ for multiple drug treatment of experimental cerebral ischemia in gerbils

The effects of the following drugs: nimodipine (1 mg/kg b. w., i. p.), 2-amino-5-phosphonovaleric acid (4mg/kg b.w., i.p.) and propentofylline (25mg/kg b.w., i.p.), administered (alone or in combination) at the end of 15 min bilateral ischemia in gerbils were evaluated on mitochondrial superoxide dismutase (SOD), glutathione reductase (GR), glucose-6 phosphate dehydrogenase (G6PD), monoamine oxidase (MAO) activities, and thiobarbituric acid reactive material (TBARM), and brain water content at 1 hour of reperfusion. The combined treatment virtually abolished early postischemic brain edema (4.1% v.s. 0.6%) and efficiently counteracted ischemia-induced changes [decreased SOD (79% v.s. 98%), GR (52% v.s. 105%) and MAO (25% v.s. 79%), and increased TBARM (198% v.s. 108%)]. The same combination of drugs administered 15 min before ischemia had a similar effect (e.g., reduced brain swelling and lipid peroxidation) as when given at the end of ischemia, whereas a limited or absent impact was seen when the drugs were given 15 min or 1 hour after ischemia, respectively. The data suggest that (post)ischemic brain swelling and mitochondrial dysfunction can be reduced by drugs which synchronously prevent processes induced in the early stages of reperfusion.     

The functional morphology of the petioles of the banana, Musa textilis

Bananas are among the largest herbs in the world and their lightweight petioles hold up huge leaves. This study examined how the petioles manage to achieve adequate rigidity to do this, while allowing extensive and reversible reconfiguration in high winds. Morphological and anatomical examination of the petioles and leaves of Musa textilis suggested how these two apparently incompatible abilities are achieved. The hollow U-shaped section of the petiole and the longitudinal strengthening elements in its outer skin give it adequate rigidity, while its ventral curvature help support the leaf without the need for thick lateral veins. These features, however, also allow the petiole to reconfigure by twisting away from the wind, while the leaf can fold away. In addition, two sets of internal structures, longitudinal partitions and transverse stellate parenchyma plates, help prevent dorsoventral flattening, allowing the petiole to flex further away from the wind without buckling. These ideas were tested and verified by a range of mechanical tests. Simple four-point-bending and torsion tests showed that the petioles are indeed far more compliant in torsion than in bending. Axial bending tests and crushing tests showed that petioles could be flexed twice as far and were four times as resistant to dorsoventral flattening when intact than when the internal tissue is removed. The banana petiole, therefore, seems to be an excellent example of natural integrated mechanical design.     

Efficient plant regeneration of Mesembryanthemum crystallinum via somatic embryogenesis

 An efficient plant regeneration procedure has been established from hypocotyl explants of the common ice plant, Mesembryanthemum crystallinum L, a halophytic leaf succulent that exhibits a stress-induced switch from C3 photosynthesis to crassulacean acid metabolism (CAM). Somatic embryos were initiated and developed up to globular and heart stages in Murashige and Skoog (MS) media supplemented with 3% sucrose, 0.6% bacto-agar, 80 mM NaCl, 5 μM 2,4-D and 1 μM kinetin. High frequency regeneration occurred when somatic embryos were germinated on media that lacked 2,4-D. High cytokinin treatment suppressed normal growth of embryos and favored abnormal embryo proliferation. Without growth regulators, regenerated plants rooted on MS medium with 100% efficiency. Mature, regenerated plants were fertile and morphologically identical to seed-derived plants. Received: 29 April 1999 / Revision received: 2 July 1999 · Accepted: 12 July 1999