A possible role for PAF in allergen-induced late responses: modification by a selective antagonist

We determined whether platelet-activating factor (PAF) plays a role in allergen-induced airway responses by studying the effects of a selective PAF antagonist WEB-2086 on antigen-induced early and late airway responses in allergic sheep. In seven sheep, inhaled Ascaris suum produced significant early (282%) and late (176%) increases in specific lung resistance (sRL). WEB-2086 (1 mg/kg iv) given 20 min before antigen challenge did not affect the early response, but the peak late increase in sRL was only 37% over base line (P less than 0.05 vs. control). To study the mechanism by which PAF contributes to antigen-induced responses, we evaluated the effects of pharmacological probes on PAF-induced bronchoconstriction. Inhaled PAF (dose range 75-700 micrograms) caused reproducible (r = 0.781, P less than 0.05) increases in sRL in eight sheep. The PAF-induced bronchoconstriction was blocked by WEB-2086 (1 mg/kg iv) and by the leukotriene antagonist FPL-55712 (30 mg by aerosol); however, neither the cyclooxygenase blocker indomethacin (2 mg/kg iv) nor the histamine H1-antagonist chlorpheniramine (2 mg/kg iv) blocked the PAF response. WEB-2086, however, did not block bronchoconstriction induced by aerosol leukotriene D4, indicating that PAF acts indirectly through leukotrienes. Finally, we determined whether PAF could induce late airway responses. Inhaled PAF produced an immediate increase in sRL in all seven sheep tested, but late airway responses were observed in only three of the seven sheep.(ABSTRACT TRUNCATED AT 250 WORDS)     

Conformational analysis of thioredoxin using organoarsenical reagents as probes. A time-resolved fluorescence anisotropy and size exclusion chromatography study

Reduced thioredoxin was subjected to chemical modification studies employing organoarsenical reagents specific for "spatially close" thiols. Modification was monitored by the loss in the free thiol content, by the percent incorporation of radiolabelled organoarsenical reagents, and by observing the changes in the amounts of the various thioredoxins by size exclusion chromatography. The rate of modification depends upon the polarity, rigidity, and size of the reagents. Small nonpolar organoarsenical reagents readily modified reduced thioredoxin, whereas polar and large reagents do not. Modifications resulted in the formation of stable 15-membered cyclodithioarsenite ring structures with no apparent changes in the secondary structure of the protein. Modification was reversed by the extrusion of the arsenical moiety by addition of 2,3-dimercaptopropanol. We have further characterized the oxidized, reduced, and modified thioredoxins by size exclusion chromatography and fluorescence anisotropy decay measurements. Both techniques show an increase in the hydrated volume of the protein upon reduction. Upon modification, the hydrodynamic volume of the protein further swells. Fluorescence anisotropy decay reveals that with modification there is loosening of the protein so that a "domain" containing the fluorophores can relax independently of the whole protein structure.     

Characterization of the Renibacterium salmoninarum haemagglutinin

Water-extracted proteins from nine geographically diverse strains of Renibacterium salmoninarum, all of which agglutinated rabbit erythrocytes and rainbow trout spermatozoa, were compared by SDS-PAGE. Extracts from eight strains, including the type strain, ATCC 33209, were similar, containing a major protein of 57 kDa and a minor protein of 58 kDa. The SDS-PAGE protein profile of the Char strain did not contain the 58 kDa protein. A non-agglutinating strain, MT-239, which was also non-hydrophobic, did not produce any water-extractable protein. Immunoblot reactions with rabbit antiserum prepared against whole cells of the type strain demonstrated that the water-extracted haemagglutinins from the various strains were antigenically related. When purified by polyacrylamide gel zone electrophoresis, the haemagglutinin from R. salmoninarum ATCC 33209 formed a doublet band with molecular masses of 57 and 58 kDa, similar to the previously described F antigen. The water-extracted haemagglutinin agglutinated salmonid spermatozoa, was degraded by protease K and trypsin, and was shown to self-assemble onto the cell surface.     

Integration is not necessary for expression of human immunodeficiency virus type 1 protein products.

A common feature in the life cycle of cytocidal retroviruses, including human immunodeficiency virus type 1 (HIV-1), is the accumulation of large amounts of unintegrated viral DNA. As yet, the role of unintegrated viral DNA in the cytopathogenesis of cytocidal retrovirus infections remains unresolved. HIV-1 mutants which were deleted in the integrase/endonuclease gene and which were unable to establish an integrated form of the virus were constructed. Despite an inability to integrate, these mutants were fully competent templates for HIV-1 core and envelope antigen production. HIV-1 antigen could be detected in the supernatants of lymphocyte cultures infected with HIV-1 integrase mutants. However, an inability to rescue infectious virus from these cultures indicated that HIV-1 integration was required for the production of infectious HIV-1. On the basis of the ability of unintegrated HIV-1 DNA to serve as a template for HIV-1 antigen production, it is plausible that unintegrated viral DNA can contribute to the HIV-1 antigen pool during HIV-1 replication.     

Cloning and characterization of human immunodeficiency virus type 1 variants diminished in the ability to induce syncytium-independent cytolysis.

The phenomenon of interference was exploited to isolate low-abundance noncytopathic human immunodeficiency virus type 1 (HIV-1) variants from a primary HIV-1 isolate from an asymptomatic HIV-1-seropositive hemophiliac. Successive rounds of virus infection of a cytolysis-susceptible CD4+ cell line and isolation of surviving cells resulted in selective amplification of an HIV-1 variant reduced in the ability to induce cytolysis. The presence of a PvuII polymorphism facilitated subsequent amplification and cloning of cytopathic and noncytopathic HIV-1 variants from the primary isolate. Cloned virus stocks from cytopathic and noncytopathic variants exhibited similar replication kinetics, infectivity, and syncytium induction in susceptible host cells. The noncytopathic HIV-1 variant was unable, however, to induce single-cell killing in susceptible host cells. Construction of viral hybrids in which regions of cytopathic and noncytopathic variants were exchanged indicated that determinants for the noncytopathic phenotype map to the envelope glycoprotein. Sequence analysis of the envelope coding regions indicated the absence of two highly conserved N-linked glycosylation sites in the noncytopathic HIV-1 variant, which accompanied differences in processing of precursor gp160 envelope glycoprotein. These results demonstrate that determinants for syncytium-independent single-cell killing are located within the envelope glycoprotein and suggest that single-cell killing is profoundly influenced by alterations in envelope sequence which affect posttranslational processing of HIV-1 envelope glycoprotein within the infected cell.     

Heat shock stimulates the release of arachidonic acid and the synthesis of prostaglandins and leukotriene B4 in mammalian cells

Heat shock has a profound influence on the metabolism and behavior of eukaryotic cells. We have examined the effects of heat shock on the release from cells of arachidonic acid and its bioactive eicosanoid metabolites, the prostaglandins and leukotrienes. Heat shock (42-45 degrees) increased the rate of arachidonic acid release from human, rat, murine, and hamster cells. Arachidonate accumulation appeared to be due, at least partially, to stimulation of a phospholipase A2 activity by heat shock and was accompanied by the accumulation of lysophosphatidyl-inositol and lysophosphatidylcholine in membranes. Induction of arachidonate release by heat did not appear to be mediated by an increase in cell Ca++. Stimulation of arachidonate release by heat shock in hamster fibroblasts was quantitatively similar to the receptor-mediated effects of alpha thrombin and bradykinin. The effects of heat shock and alpha thrombin on arachidonate release were inhibited by glucocorticoids. Increased arachidonate release in heat-shocked cells was accompanied by the accelerated accumulation of cyclooxygenase products prostaglandin E2 and prostaglandin F2 alpha and by 5-lipoxygenase metabolite leukotriene B4. Elevated concentrations of arachidonic acid and metabolites may be involved in the cytotoxic effects of hyperthermia, in homeostatic responses to heat shock, and in vascular and inflammatory reactions to stress.