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K Clay

Publications and source records attributed to K Clay.

18 recordsLinked to original sources
PubMed2001

Evidence for the involvement of the NADPH oxidase enzyme complex in the optimal accumulation of Platelet-activating factor in the human cell line PLB-985.

Platelet-activating factor (PAF) is an early product of the inflammatory environment, influencing development and resolution of inflammation. Its production is greater in neutrophils and macrophages, which predominantly synthesize 1-alkyl sn-2 acetyl glycerophosphocholine (GPC) than in nongranulocytes (B cells and endothelial cells), which lack a respiratory burst and synthesize 1-acyl sn-2 acetyl GPC as their major PAF species. This study investigated whether the respiratory burst was responsible for the quantitative and qualitative differences in sn-2 acetyl GPC species generation by neutrophils and macrophages versus those cells lacking the NADPH oxidase complex. The myeloid cell line PLB-985 (capable of differentiation into neutrophils) was used to test this hypothesis, since these cells had previously been generated with a non-functional respiratory burst (X-CGD PLB-985). Differentiated PLB-985 cells underwent a large respiratory burst in response to PMA (phorbol ester), and smaller respiratory bursts in response to A23187 (calcium ionophore), and the bacterial polypeptide fMLP (receptor mediated activation). Concurrently, treated cells were assessed for production of 1-hexadecyl and 1-palmitoyl sn-2 acetyl GPC species by gas chromatography/mass spectrometry. Neither cell type generated these lipid species in response to PMA, but both cell types generated equal levels of sn-2 acetyl GPC in response to A23187, with five times more 1-hexadecyl than 1-palmitoyl species. Upon fMLP activation, X-CGD PLB-985 cells produced significantly less 1-hexadecyl and 1-palmitoyl sn-2 acetyl GPC in comparison to the wild-type PLB-985 cells. These findings suggest phagocytic oxidant production by NADPH oxidase is not essential for sn-2 acetyl GPC generation, but appears important for optimal production of PAF in response to some stimuli.

Calcimycin↗
PubMed2000

Soil pathogens and spatial patterns of seedling mortality in a temperate tree.

The Janzen-Connell hypothesis proposes that host-specific, distance- and/or density-dependent predators and herbivores maintain high tree diversity in tropical forests. Negative feedback between plant and soil communities could be a more effective mechanism promoting species coexistence because soil pathogens can increase rapidly in the presence of their host, causing conditions unfavourable for local conspecific recruitment. Here we show that a soil pathogen leads to patterns of seedling mortality in a temperate tree (Prunus serotina) as predicted by the Janzen-Connell hypothesis. In the field, the mean distance to parent of seedling cohorts shifted away from maternal trees over a period of 3 years. Seedlings were grown in soil collected 0-5 m or 25-30 m from Prunus trees. Sterilization of soil collected beneath trees improved seedling survival relative to unsterilized soil, whereas sterilization of distant soil did not affect survival. Pythium spp., isolated from roots of dying seedlings and used to inoculate healthy seedlings, decreased survival by 65% relative to controls. Our results provide the most complete evidence that native pathogens influence tree distributions, as predicted by the Janzen-Connell hypothesis, and suggest that similar ecological mechanisms operate in tropical and temperate forests.

Biological Evolution↗
PubMed1999

Fungal endophyte symbiosis and plant diversity in successional fields

Increasing evidence suggests that microbial interactions are important determinants of plant biodiversity. The hypothesis that fungal endophyte symbiosis reduces diversity in successional fields was tested by manipulating infection of tall fescue, the most abundant perennial grass in the eastern United States. Over a 4-year period, species richness declined and tall fescue dominance increased in infected plots relative to uninfected plots without differences in total productivity. A host-specific endophyte, with negligible biomass, altered plant community structure in this long-term field experiment and may be reducing plant diversity throughout its expanding range.

Journal Article↗
PubMed1996

The Red Queen Hypothesis and plant/pathogen interactions.

The Red Queen Hypothesis (RQH) explains how pathogens may maintain sexual reproduction in hosts. It assumes that parasites become specialized on common host genotypes, reducing their fitness. Such frequency-dependent selection favors sexual reproduction in host populations. Necessary conditions are that resistance and virulence are genotype specific so that host genotype frequencies respond to changes in pathogen genotype frequencies, and vice versa. Empirical evidence on the genetic basis of disease, variation in resistance and virulence, and patterns of infection in sexual and asexual plants support certain features of the hypothesis. However, gene-for-gene interactions are generally not consistent with the RQH because they do not result in cycling of gene frequencies, unlike a matching allele mechanism. A conclusion of whether the RQH can explain the maintenance of sexual reproduction cannot be reached at present. Nevertheless, the RQH theory has shed light on many aspects of plant/pathogen interactions important for reducing pathogen damage in agricultural systems.

Journal Article↗
PubMed1993

Suppressive effects of a novel antioxidant compound on human T cell functions in vitro.

The use of antioxidant compounds with differing modes of action has clearly demonstrated involvement of oxidative processes in the activation of T lymphocytes. In this paper, we show that a novel antioxidant (lazaroid U75412E, a free radical scavenger) suppressed mitogen-induced T cell proliferation in vitro. Similar results were obtained with diphenylene iodonium (DPI), a known inhibitor of NADPH oxidase. The lazaroid was further shown to inhibit IL 2 production but to be less potent in suppressing IL 2 receptor expression. Thus, scavenger-type antioxidants act on T cells primarily by blocking a signal necessary for the induction of IL 2 synthesis such as the activation of NF kappa B. Furthermore, the potent inhibition of lymphocyte responses caused by the specific enzyme inhibitor DPI provides direct proof of the source of the oxidants involved in these processes.

Antioxidants↗
PubMed1992

Alkaloids of Stipa robusta (sleepygrass) infected with an Acremonium endophyte.

Stipa robusta (= Stipa vaseyi) is a perennial grass found in certain areas of the southwestern United States. It is commonly known as sleepygrass, as horses that ingest this grass may become profoundly somnolent or stuporous for periods of time lasting up to several days. In an attempt to determine the active principle(s), fractionation of a methanolic extract of sleepygrass infected with an Acremonium endophyte has yielded lysergic acid amide (20 micrograms/g dry wt), isolysergic amide (8), 8-hydroxylsergic acid amide (0.3), ergonovine (7), chanoclavine-I (15), and N-formylloline (18). Related alkaloids have been found in many endophyte-infected grasses. The dominant alkaloid constituent in sleepygrass, lysergic acid amide, has not previously been identified in a grass in such high concentration. Lysergic acid amide is likely to be the basis for the extreme sedative effects on animals, given past pharmacological work on the compound from the ergot fungus Claviceps paspali.

Acremonium↗
PubMed1991

The protein kinase C inhibitor, K252a, inhibits superoxide production in human neutrophils activated by both PIP2-dependent and -independent mechanisms.

We report that the putative protein kinase C inhibitor, K252a, at concentrations of 0.2 and 1 microM, inhibited the respiratory burst induced by fluoride and formyl-methionyl-leucyl-phenyl-alanine respectively, both in human neutrophils primed with a subthreshold dose of phorbol myristate acetate and in non-primed neutrophils. In addition, K252a effectively inhibited ConA-zymosan-mediated superoxide generation in Ca2(+)-depleted neutrophils, with virtually maximal inhibition seen at 1 microM. These results suggest that protein kinase C is involved in the putative phosphatidylinositol bisphosphate-independent signal transduction mechanism of the respiratory burst as well as the pathway dependent on phosphatidylinositol bisphosphate hydrolysis.

Calcium↗
PubMed1989

Angiotensin II causes formation of platelet activating factor in cultured rat mesangial cells.

Angiotensin II may contribute to the progression of renal glomerular diseases. Beneficial effects of converting enzyme inhibition in models of renal disease are, however, not always explicable by hemodynamic consequences of angiotensin II inhibition. Angiotensin increases intracellular calcium in glomerular mesangial cells and activates phospholipase A2, factors required for the formation of the lipid mediator of inflammation platelet activating factor (PAF). We therefore examined whether angiotensin II could stimulate PAF production in cultured rat mesangial cells. During a 15-minute incubation angiotensin II caused formation of PAF in a dose-dependent manner with a threshold around 10(-9) M. In four experiments PAF formation in response to angiotensin II (10(-8) M) occurred within 5 minutes and was 29 +/- 8 pmol PAF/mg protein. The amount of PAF detected then declined to 9 +/- 2 and 13 +/- 3 pmol after 15 and 30 minutes of incubation with angiotensin II. More than 90% of the PAF remained cell-associated. The PAF formation was confirmed by negative ion chemical ionization mode of mass spectrometry. A single species of PAF was detected and identified as hexadecyl PAF. We speculate that part of the detrimental effects of angiotensin II in progressive renal disease may relate to PAF formation. The PAF generated may in turn influence glomerular function, platelets, and eicosanoid synthesis, all factors implicated in renal disease. Furthermore, we speculate that angiotensin II-induced PAF formation may contribute to microvasculature pathology in general.

Angiotensin II↗
PubMed1988

Evidence for immunoglobulin Fc receptor-mediated prostaglandin2 and platelet-activating factor formation by cultured rat mesangial cells.

The possibility of Fc-dependent uptake of IgG immune complexes was examined in subcultured rat mesangial cells free of monocytes. 195Au-labeled colloidal gold particles were coated either with BSA only or with BSA followed by rabbit anti-BSA-IgG or the F(ab')2 fragment of the IgG. Mesangial cells preferentially took up 195Au particles covered with BSA-anti-BSA-IgG over those covered with BSA or the F(ab')2 fragment. This uptake was a time-dependent and saturable process inhibitable by sodium azide or cytochalasin B. Using phase-contrast microscopy in the light reflectance mode, it was established that essentially all mesangial cells took up IgG-coated gold particles. By electron microscopy the process was shown to consist of vesicular uptake with delivery to endosomes. Mesangial binding-uptake of the IgG-covered particles was associated with stimulation of PGE2 synthesis and production of platelet-activating factor, a lipid mediator of inflammation. To characterize the potential Fc receptor for IgG we used the rosetting technique with sheep red blood cells coated with IgG subclass-specific mouse monoclonal antibodies. 50% of mesangial cells exhibited rosetting with red cells coated with mouse IgG2a, whereas negligible rosetting was observed with IgG2b or IgG1. Competition experiments confirmed the specificity of IgG2a binding. We conclude that cultured rat mesangial cells exhibit specific receptors for IgG and that occupancy of Fc receptors results in endocytosis and is associated with generation of PGE2 and platelet-activating factor. These observations may be of significance for immune-mediated glomerular diseases.

Animals↗
PubMed1986

Organic acids in ethylene glycol intoxication.

Ethylene glycol intoxication produces a severe metabolic acidosis with an increased anion gap. We examined three patients with this intoxication to identify the organic acids that cause acidemia in humans and to determine how effectively these acids can be removed during dialysis. All patients had markedly elevated glycolic acid levels of more than 7 meq/L and two patients had lactic acidosis, with lactic acid levels of greater than 5.0 meq/L. Hemodialysis clearance of glycolic acid was 105 mL/min, and 159 meq was removed in 3 hours. After hemodialysis using a bicarbonate dialysate, the mean anion gap decreased from 34 to 23 meq/L; the mean serum bicarbonate concentration increased from 5.5 to 20 meq/L. Therefore, glycolic and lactic acids are important in the acidosis caused by ethylene glycol intoxication in humans. Hemodialysis treatment with a bicarbonate dialysate is an efficient method for removing glycolic acid and resolving acidemia.

Acidosis↗
PubMed1983

Trehalose-containing lipooligosaccharides. A new class of species-specific antigens from Mycobacterium.

Mycobacterium kansasii is characterized by the presence of seven species-specific neutral lipooligosaccharide antigens. All react with hyperimmune anti-M. kansasii serum in enzyme-linked immunosorbent assays, and the more glycosylated members also react by gel diffusion. Both the native glycolipids and their inherent oligosaccharides were purified and the major features of their unique structures determined by acetolysis, partial acid cleavage, 1H-NMR and 13C-NMR, and chemical ionization and electron impact mass spectrometry of the permethylated products. They have in common a tetraglucose "core," beta-D-Glcp-(1 leads to 3)-beta-D-Glcp-(1 leads to 4)- alpha-D-Glcp(1 leads to 1)-alpha-D-Glcp where Glcp is glucopyranose, distinguished by the presence of an alpha,alpha-trehalose substituent. Variable residues of xylose, 3-O-methylrhamnose, fucose, and a novel N-acyl aminosugar, (4,6-dideoxy-2-O-methyl-3-C-methyl-4-(2'-methoxypropionamido)hexose; proof of this structure is not given) are linked to the core and the resulting oligosaccharides are acylated with 2,4-dimethyltetradecanoyl and acetyl functions to present a familial arrangement. Related but species-specific lipooligosaccharides typify Mycobacterium szulgai and apparently a host of other atypical mycobacteria. Thus, the antigenicity, and perhaps other features such as pathogenesis and drug resistance, of most atypical mycobacteria may be rationalized in terms of these new found cell wall lipooligosaccharides and the previously described glycopeptidolipids.

Antigens, Bacterial↗
PubMed1983

Partial resolution of tardive dyskinesia with treatment of co-existing thyrotoxicosis.

Neuroleptic-induced tardive dyskinesia improved after treatment of thyrotoxicosis. Neuroleptic blood levels indicated that the improvement was not caused by masking of the symptoms by rising drug levels. Dopamine metabolite measurements suggested that the thyrotoxicosis caused an increase in the sensitivity of caudate neurons to dopamine, rather than a change in release of dopamine.

Dopamine↗