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R W Leid

Publications and source records attributed to R W Leid.

At least 37 records · Page 2Linked to original sources
PubMed1989

Oxygen detoxifying enzymes in parasites: a review.

This review focuses on parasite enzymes which are involved in the detoxification of oxygen radicals, and covers the following enzymes: superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferase and glutathione reductase. These enzymes are crucial for parasites to evade oxygen-mediated attack by host leukocytes, both intracellularly and extracellularly. In addition, the newly defined parasite system involving trypanothione, trypanothione peroxidase and trypanothione reductase is discussed.

Animals↗
PubMed1989

In vivo chemotaxis of bovine neutrophils induced by 5-lipoxygenase metabolites of arachidonic and eicosapentaenoic acid.

The 5-lipoxygenase metabolites of arachidonic (AA) and eicosapentaenoic acid (EPA), 5S,12R-dihydroxy-6,8,10,14-eicosatetraenoic acid (LTB4), 5-hydroxyeicosatetraenoic acid (5-HETE), 5S,12R-dihydroxy-6,8,10,14,17-eicosapentaenoic acid (LTB5), and 5-hydroxyeicosapentaenoic acid (5-HEPE), were injected intradermally into the ear skin of steers to assess their in vivo potency as chemotactic factors for bovine neutrophils. A dose of 30 picomoles of LTB4 was required to elicit a significant extravascular dermal accumulation of neutrophils (P less than 0.05). In contrast, 1.0 nanomole of LTB5 was required to achieve a cellular influx equivalent to that elicited by 30 picomoles of LTB4. Nearly five times as many neutrophils were present in the bovine dermis injected with 1.0 nanomole of LTB4 compared with sites given the equivalent dose of LTB5 (245 cells/sq mm vs. 52 cells/sq mm). Six nanomoles of either 5-HETE or 5-HEPE were required before a significant neutrophil accumulation occurred. These results show clearly that 5-lipoxygenase metabolites can initiate the extravascular accumulation of bovine neutrophils in vivo. However, the chemotactic potency of the EPA metabolites is much reduced when compared with that of the homologous AA lipids. The results obtained support the premise that modification of the inflammatory response, including control of cellular influxes, by dietary supplementation with EPA is feasible.

Animals↗
PubMed1988

Production of lipoxygenase metabolites of eicosapentaenoic acid by bovine alveolar macrophages in vitro.

Lipoxygenase metabolites of arachidonic acid (AA), the leukotrienes (LTs), and hydroxyeicosatetraenoic acids (HETEs) are potent proinflammatory mediators. Release of LTs and HETEs by bovine alveolar macrophages (BAMs) was measured by reverse-phase high performance liquid chromatography. LTB4 (1.1 +/- 0.2 ng/10(6) cells) and 5-HETE (2.2 +/- 0.2 ng/10(6) cells) were the major metabolites calcium ionophore A23187-stimulated BAMs produced from endogenous AA. The tritiated forms of these compounds and their precursor fatty acids were produced following incorporation of [3H]AA into the cells and stimulation by calcium ionophore A23187. Incorporation of an alternative substrate, [3H]eicosapentaenoic acid [( 3H]EPA) into BAMs incubated in parallel resulted in production of [3H]LTB5 and [3H]5-hydroxyeicosapentaenoic acid (5-HEPE). Equivalent amounts of [3H]AA and [3H]EPA and of [3H]LTB4 and homologous [3H]LTB5 were released. BAM produced significantly greater amounts of [3H]5-HEPE than [3H]5-HETE, however. These findings indicate that the BAM 5-lipoxygenase is capable of metabolizing EPA to LTB5 and 5-HEPE, with the production of 5-HEPE preferred over 5-HETE.

Animals↗
PubMed1987

Arachidonic and eicosapentaenoic acid metabolism in bovine neutrophils and platelets: effect of calcium ionophore.

Substitution of dietary fatty acids has potential for altering the inflammatory response. The purpose of the present study was to define the metabolites of arachidonic acid (AA) and eicosapentaenoic acid (EPA) secreted by bovine peripheral blood neutrophils and platelets. High performance liquid chromatography was used to characterize cyclooxygenase and lipoxygenase metabolites secreted in response to the calcium ionophore A23187. Cells were prelabelled with 3H-AA or 3H-EPA prior to challenge with the calcium ionophore. Bovine neutrophils secreted leukotriene B4 (LTB4) and 5-hydroxyeicosatetraenoic acid (5-HETE) as the major metabolites of AA, as well as the corresponding leukotriene B5 (LTB5) and 5-hydroxyeicosapentaenoic acid (5-HEPE) metabolites of EPA. Peptidoleukotrienes derived from 3H-AA or 3H-EPA were not detected under these conditions. The major tritiated metabolites secreted from bovine platelets were: thromboxane A2, measured as the stable metabolite thromboxane B2 (TXB2); hydroxyheptadecatrienoic acid (HHT) and 12-HETE derived from 3H-AA; and the omega-3 analogs TXB3 and 12-HEPE, derived from 3H-EPA. Preferred substrate specificities existed amongst the AA- and EPA-derived metabolites for the intermediary enzymes involved in the arachidonic acid cascade. These findings support the hypothesis that substitution of membrane-bound AA by EPA has potential for modulation of the host inflammatory response following cellular phospholipid mobilization.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1987

Parasite defense mechanisms for evasion of host attack; a review.

This review covers some of the basic mechanisms whereby parasites evade host responses. These mechanisms include; antigenic variation, repeated antigenic determinants, induction of suppressor cells, acquisition of host proteins or molecular mimicry, proteinase destruction of host effector molecules, proteinase inhibitor-mediated inhibition of humoral and cellular immune effector arms and immunosuppressive products of parasite arachidonic acid metabolism. Vet. Parasitol.

Animals↗
PubMed1987

Inhibition of equine neutrophil chemotaxis and chemokinesis by a Taenia taeniaeformis proteinase inhibitor, taeniaestatin.

Taeniaestatin, a recently isolated Taenia taeniaeformis proteinase inhibitor, was used to inhibit equine neutrophil migration. Taeniaestatin itself was not chemotactic when used as a chemotactic factor but taeniaestatin did inhibit neutrophil chemokinesis when tested in a Zigmond-Hirsch checkerboard assay. A dose-dependent inhibition of both chemokinesis and chemotaxis was observed when zymosan activated bovine sera (ZABS) was used as the chemotactic factor. This inhibition was greater than 95% when 5 mu of taeniaestatin was present on both the cell and chemotactic factor side of the chambers. Equine neutrophils gave dose- and time-dependent migration responses to purified bovine C5a with an ED50 of 1.04 X 10(-7)M. Taeniaestatin inhibited the C5a-mediated chemotactic and chemokinetic neutrophil responses (51% using 1 mu and greater than 95% with 5 mu of taeniaestatin). The inhibition of leucocyte motility by taeniaestatin was reversible and without cytotoxicity at the highest doses of taeniaestatin tested.

Animals↗
PubMed1986

Interleukin inhibition by a parasite proteinase inhibitor, taeniaestatin.

A proteinase inhibitor, taeniaestatin, isolated from the larval stage of the cestode Taenia taeniaeformis inhibits endogenous IL 2 generation in murine lymphocytes and IL 1 induced proliferation of murine thymocytes in a dose-dependent manner. However, taeniaestatin does not inhibit exogenous IL 2-induced proliferation of an IL 2-dependent cell line at any dose tested. These data indicate that the lack of IL 2 generation may be due in part to inhibition of a crucial cell-associated proteinase subsequent to cellular activation, or the lack of an effective IL 2 signal for differentiation. Our results are novel findings concerning molecular pathways for parasite inhibition of host immune responses, and suggest that selected proteinase inhibitors may be useful in clinical situations in which IL 1 or IL 2 are elevated.

Animals↗
PubMed1986

Isolation and partial characterization of an eosinophil chemotactic factor from metacestodes of Taenia taeniaeformis (ECF-Tt).

Eosinophil chemotactic activity associated with protein extracts of Taenia taeniaeformis metacestodes was investigated. Chemotactic activity was associated with the nonbound protein after QAE cellulose chromatography of a 3 M KCl extract of homogenized larvae. When this material was precipitated with ammonium sulfate, activity was present in the 40 to 80% precipitate. Upon rechromatography on QAE cellulose equilibrated in a low ionic strength buffer, eosinophil chemotactic activity was retained by the gel and eluted after application of the NaCl gradient. Gel filtration of Sephacryl S-300 yielded an estimated m.w. of 91,000. Chromatofocusing revealed a broad peak of activity with a pI of 4.5 to 5.0. SDS-PAGE showed the active fraction migrated as a protein with a m.w. of 10,400. ECF-Tt had chemotactic and chemokinetic activity for equine eosinophils and murine eosinophils, but not for equine and murine neutrophils.

Ammonium Sulfate↗
PubMed1986

Arachidonic acid metabolism in bovine alveolar macrophages. Effect of calcium ionophore on lipoxygenase products.

The production of lipoxygenase metabolites of arachidonic acid was studied in bovine alveolar macrophages (BAM). Unstimulated macrophages produced small amounts of LTB4 (0.2 +/- 0.2 ng/10(6) BAM) but monohydroxyeicosatetraenoic acids (5-, 12-, and 15-HETE) usually were not detectable. Both exogenous arachidonic acid and the calcium ionophore A23187 induced production of LTB4, 5-, 12-, and 15-HETE, of which 60-80% was 5-HETE. Combined challenge of BAM with both exogenous arachidonic acid and A23187 was more effective in the production of these metabolites than with either stimulus alone. The generation of the peptidoleukotrienes LTC4, LTD4, and LTE4 by BAM could not be detected under these in vitro conditions. Our results demonstrate that bovine alveolar macrophages produce similar lipoxygenase metabolites of arachidonic acid in response to A23187, as do human alveolar macrophages stimulated with the same agonist.

Animals↗
PubMed1986

A superoxide dismutase of metacestodes of Taenia taeniaeformis.

Superoxide dismutase was purified from Taenia taeniaeformis metacestodes by sequential ion exchange chromatography on quaternary-amino-ethyl-cellulose, gel filtration chromatography on ACA 44 and ion exchange chromatography on DEAE-cellulose, followed by chromatofocusing on polybuffer exchanger 94. This isolation procedure resulted in the detection of a single protein-staining band on alkaline gels, coincident with enzyme activity. We have, however, detected what appear to be two peaks of enzyme activity within this single protein-staining band. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis using gradient slab gels and analysis under reducing conditions, resulted in the detection of only one protein at an apparent Mr of 16,600, while analysis under non-reducing conditions, gave a single protein of an apparent Mr of 64,000. The isoelectric point of the purified protein is 6.6. Boiling for 3 min completely destroyed the enzyme, whereas incubation for 2 h at 37 degrees C resulted in the loss of 56% of the enzymic activity. Incubation with 10 mM KCN resulted in 83% inhibition of the enzyme. We have detected up to 168 U ml-1 of enzyme activity in the cyst fluid surrounding the parasite in situ. This is the first instance in which any parasite superoxide dismutase has been purified to apparent homogeneity. Parasite-mediated enzymic destruction of superoxide anion can not only protect against oxygen toxicity as a result of normal parasite respiratory processes but also may serve as yet another mechanism used by tissue-dwelling parasites to evade host immunologic attack.

Animals↗
PubMed1986

Interaction of bovine complement with Fasciola hepatica.

The host-parasite relationship of Fasciola hepatica in cattle was characterized by determining the effects of the parasite on the bovine complement system. Phosphosaline extracts of F. hepatica adults inhibited both the classical and alternative pathways of complement activation in normal bovine and human sera in a protein dose-dependent manner. The in vitro reaction of viable newly excysted juveniles (NEJ) with bovine serum (NBS) and with bovine serum containing antibodies specific to F. hepatica (IBS) resulted in no detectable changes in serum hemolytic complement activity for either pathway. This lack of complement consumption occurred even though these same flukes incubated in IBS for at least 24 h developed a precipitate that adhered to the parasite tegument, a feature that may reflect antibody--antigen reactions.

Animals↗
PubMed1986

The susceptibility of the goat to Fasciola hepatica infections.

Mixed breed goats were infected with metacercariae of Fasciola hepatica and the resulting worm burdens were quantitated after primary and secondary exposure of the goats to the parasite. Mean length and width of the parasite recovered after all primary exposures were 1.91 +/- 0.2 cm and 0.91 +/- 0.2 cm, respectively. A mean of 71.8 +/- 5.9% of the flukes were recovered from all of the primary infections. In the secondary infections, the mean length and width of the flukes from the physically smaller population was 0.88 +/- 0.27 cm and 0.53 +/- 0.19 cm, respectively. A mean of 67 +/- 6.7% of the flukes were recovered from this secondary infection. It appears that the goat is susceptible to challenge infections with F. hepatica and that its response to this infection is much like that of sheep.

Animals↗
PubMed1986

A review of eosinophil chemotaxis and function in Taenia taeniaeformis infections in the laboratory rat.

The eosinophil has long been associated with diseases of acute hypersensitivity and with parasite infections, but its exact role in the pathogenesis of these conditions remains uncertain. Characterization of factors associated with migration of eosinophils into tissues has helped to elucidate eosinophil function. Eosinophil chemotactic factors associated with acute hypersensitivity reactions include the eosinophil chemotactic factors of anaphylaxis, histamine, and arachidonic acid metabolites, all of which are released from mast cells, and the lymphokine eosinophil stimulation promoter (ESP). Eosinophilotaxins associated with parasitic diseases include the lymphokine ESP and the low molecular weight factor ECF-G, both associated with schistosome infection in mice. In addition, in several parasite infections parasite-derived protein eosinophil chemotactic factors have been identified and characterized. The proteins associated with Ascaris, Anisakis, and Schistosoma infections appear to be distinct from one another. We have recently partially characterized a protein from Taenia taeniaeformis larvae which has marked chemotactic activity for eosinophils. In addition we have demonstrated eosinophil chemotactic activity associated with metabolism of arachidonic acid by T. taeniaeformis metacestodes. The results of studies in taeniasis and other parasite infections, therefore, indicate that parasite-derived factors may directly influence migration of eosinophils.

Animals↗
PubMed1985

Equine alternative pathway activation by unsensitized rabbit red blood cells.

The equine alternative complement pathway has been partially characterized and compared to the equine classical activation pathway. A dose-dependent lysis of RbRBC was observed with peak lytic values noted within 10 minutes at 37 degrees C when rabbit red blood cells (RbRBC) were used as an alternative pathway activator. Sheep red blood cells (SRBC) sensitized with rabbit hemolysin or partially purified equine IgM antibodies were equally sensitive to lysis. Dilution of the commercial hemolysin by 1/5 reduced lysis from 90% to 38% in the presence of constant cell numbers. Hemolysis of SRBC peaked at 10 minutes and the majority of lysis occurred within 10 minutes. Dilution of equine sera by as little as 1/5 decreased hemolytic activity for SRBC to 21.5% from greater than 90% with undiluted sera. The alternative pathway protein, equine factor B, was tested using RbRBC and monitored by its differential susceptibility to heat treatment at 50 degrees C. This treatment led to almost complete inactivation after a 15-minute incubation. An apparent heat-dependent decay of certain classical pathway components was also observed after 50 degrees C treatment. This sensitivity was indicated by a reduction in the lytic activity for sensitized SRBC. Treatment for 15 minutes at 56 degrees C with either RbRBC or SRBC was sufficient to abolish hemolytic activity in all equine sera tested. Chelation of cations with 0.04 M EDTA blocked expression of alternative and classical pathway activation; however, chelation of Ca++ ions with 10 mM EGTA containing 1 mM Mg++ ions permitted lysis of the RbRBC but not the SRBC. A dose-related Mg++-ion dependence for RbRBC hemolytic activity was observed as the concentration of Mg++ was increased to 1.0 mM. In addition, our results obtained with pre-colostral foal serum strongly suggest that natural antibody to RbRBC was of little importance in the lysis observed with these cells. These results also show that the equine alternative pathway activation may require Ca++ ions. If Ca++ ions are required, the equine alternative pathway is quite different from any other mammalian complement system so far described. Our results suggest that the alternative pathway of activation is of major importance in the equine complement system. Confirmation of this hypothesis requires both purification of the components involved as well as further characterization.

Animals↗
PubMed1985

Isolation of Fasciola hepatica metacercariae by density gradients.

Fasciola hepatica metacercariae were purified in high yield, removing contaminating cyst walls and plant material by step gradients consisting of 10 ml of 60% Percoll (density = 1.08 g ml-1) and 10 ml of 50% Metrizamide (density = 1.25 g ml-1). Greater than 90% of the metacercariae applied to the density gradients were recovered. These isolated metacercariae had an in vitro excystment rate of greater than 80%, which was the same excystment rate as metacercariae not subjected to density gradient centrifugation.

Animals↗
PubMed1985

Inflammation and mediators of lung injury.

This article covers the major pathways involved in acute inflammation in mammals with a particular emphasis on their relevance to the bovine species. It focuses on the potential and proven contributions of these systems to pulmonary defense mechanisms and lung pathology. The article also points out what is known and where gaps in our information exist as well as promising areas for research in the coming years.

Animals↗