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A Dulioust

Publications and source records attributed to A Dulioust.

11 recordsLinked to original sources
PubMed1992

Paf-acether acetylhydrolase activity is increased in patients with rheumatic diseases.

Paf-acether (platelet-activating factor) is a phospholipid described as a potent mediator of inflammatory response. We have recently shown that the level of paf bound to lipoproteins was significantly higher in the serum from patients with rheumatic diseases, compared to that of control subjects. In serum, paf is inactivated in part by a paf acetylhydrolase that catalyses the hydrolysis of the acetate residue. Acetylhydrolase activity was measured in the serum and synovial fluid of patients with rheumatoid arthritis and other arthritides, i.e. osteoarthritis and chondrocalcinosis. In serum, the activity of acetylhydrolase was significantly increased in patients with rheumatic diseases when compared with that in the control group. However, it was enhanced to a lesser degree in rheumatoid arthritis than in non inflammatory rheumatic diseases. These results suggest a role for acetylhydrolase in controlling paf levels in rheumatic diseases.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1990

Immunoregulatory functions of paf-acether. III. Down-regulation of CD4+ T cells high-affinity IL-2 receptor expression.

In the present report, we further explored the mechanisms by which 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (paf-acether), a phospholipid mediator of inflammation inhibited PHA-induced CD4+ cell proliferation. Evidence was obtained that CD4+ cells stimulated with either PHA or immobilized OKT3 in the presence of paf at concentrations that block CD4+ cell proliferation, exhibited a marked decrease in high affinity IL-2R expression. Importantly, paf did not prevent the binding of IL-2 to its receptor. Scatchard analysis of the binding data indicated that paf caused more than 50% decrease in the number of IL-2 high affinity sites per cell, whereas the receptor ligand affinity remained essentially constant. Moreover, the down-regulation of high affinity IL-2R was also accompanied by a loss of IL-2-dependent proliferative capacity. Together these data suggest that decreased expression of high affinity IL-2R may contribute to the diminished proliferative activity observed in CD4+ cells stimulated with PHA or immobilized OKT3 in the presence of paf. They further emphasize the potential role of lipid proinflammatory mediators such as paf in the regulation of T cell activation.

Antigens, CD↗
PubMed1990

Immunoregulatory functions of paf-acether. IV. Enhancement of IL-1 production by muramyl dipeptide-stimulated monocytes.

paf-Acether (paf) is a phospholipid mediator of inflammation released from monocytes along with IL-1. In this study, we have examined the role of paf on IL-1 production by human monocytes. When paf from 1 nM to 5 microM, but not its precursor lyso paf, was added to monocytes in the presence of muramyl dipeptide (MDP) or LPS, a marked increase in IL-1 activity over the value with MDP alone was observed. In contrast, paf alone had minimal activity over the same dose range. Antibodies against rHu IL-1 alpha and rHu IL-1 beta neutralized the increased IL-1 activity. Interestingly, MDP that prompts monocytes to synthesize IL-1, induced the synthesis of paf, as well. Most of the paf produced remained cell-associated and always preceded IL-1 synthesis. When the paf receptor antagonist, L-652,731 was added to monocytes, it prevented the enhancement of IL-1 activity induced by exogenous paf. In contrast, L-652,731 had little effect on MDP-induced IL-1 synthesis in the absence of exogenous paf. This may indicate that there are alternative mechanisms involved in the sequences of events leading to IL-1 production. It is also conceivable that the paf receptor antagonist is not able to compete or inhibit endogenous paf as well as it does for exogenous paf. Nevertheless, exogenous paf in association with a second signal, modulates IL-1 production from human monocytes in a positive manner. This may constitute another means through which paf can modulate inflammatory and immune reactions.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1989

Presence of paf-acether in human thymus.

Paf-acether (paf) is a phospholipid mediator of inflammation endowed with major immunoregulatory properties. The present study demonstrates that human thymus contains large amounts of paf, as well as paf precursors. In addition, isolated thymic cells produced paf under ionophore stimulation. Paf from thymus exhibited the same biological and physiochemical properties as synthetic paf. The purity and molecular structure of paf from thymus were further characterized by reverse-phase HPLC and gas chromatography with electron-capture detection. These findings may have important implications since thymus microenvironment is essential in the proper development of bone marrow progenitors committed to the T cell lineage into thymocytes capable of emigrating to the periphery as functional T lymphocytes.

Animals↗
PubMed1989

Biosynthesis of paf-acether. Paf-acether but not leukotriene C4 production is impaired in cultured macrophages.

After adherence for 24 or 48 h mouse peritoneal macrophages, upon a zymosan challenge, synthesized 114 +/- 55 and 82 +/- 31 pmol of paf-acether (paf)/mg of protein respectively, as compared with 513 +/- 195 pmol of paf/mg of protein in 2 h-adherent macrophages (means +/- S.D., n = 10). By contrast, 24 h- and 48 h-adherent macrophages exposed to zymosan produced more leukotriene C4 (2.7 +/- 1.1 and 1.4 +/- 0.2 nmol/mg of protein respectively, n = 5) than did 2 h-adherent macrophages (0.5 +/- 0.2 nmol/mg of protein, n = 5). Paf production was not altered when 2 h- and 24 h-adherent cells were cultured and/or stimulated in the presence of 5 microM-indomethacin, 10 microM-nordihydroguaiaretic acid or 100 microM-BW755C as compared with untreated cells. These results indirectly exclude the regulation of paf production by arachidonic acid metabolites. We investigated the efficiency of the enzymic steps which govern paf synthesis. We showed that the anabolic process was not impaired since (1) the amounts of alkylacylglycerophosphocholine and lyso-paf were similar in 2 h-, 24 h- and 48 h-adherent macrophages; (2) adding synthetic lyso-paf or acetyl-CoA to intact cells did not increase paf production in zymosan-stimulated 24 h- and 48 h-adherent macrophages; (3) the basal level of acetyltransferase was comparable in 2 h-, 24 h- and 48 h-adherent macrophages and in all cases was increased by 2-3 times upon zymosan challenge. We also showed that impaired paf production in 24 h- and 48 h-cultured macrophages was not due to the nature of the stimulus used to induce its synthesis.

Acetyltransferases↗
PubMed1989

Biosynthesis of paf-acether. XIV. Paf-acether output in murine peritoneal macrophages is regulated by the level of acetylhydrolase.

Paf-acether (paf) synthesis was previously shown to be impaired in 24 hr-adherent and Bacillus Calmette-Guérin-activated murine peritoneal macrophages as compared to resident macrophages. We report here that the induction of acetylhydrolase was responsible for the decreased paf output in 24 hr-adherent macrophages. The kinetic analysis of the enzymes derived from 2 hr-, 24 hr- and BCG-activated adherent macrophages and from plasma revealed that the Km for paf was similar whatever the source of the acetylhydrolase whereas the Vmax was five-fold increased in 24 hr-cultured macrophages. The acetylhydrolase activity was Ca2+-independent and was not inhibited by addition of alkyl-acyl (long chain)-glycero-phosphocholine suggesting that the enzyme was not a phospholipase A2.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1988

Immunoregulatory functions of paf-acether. I. Effect of paf-acether on CD4+ cell proliferation.

Paf-acether or platelet-activating factor (1-0-alkyl-2-acetyl-sn-glycero-3-phosphocholine) is a phospholipid mediator of inflammation initially described as a potent platelet-aggregating compound. It is newly formed by a variety of cells including monocytes and is now recognized as a major mediator of cell-cell interactions. The present studies were undertaken to determine whether paf-acether could modulate T cell function. We found that addition of paf-acether to CD4+ cells cultured with phytohemagglutinin markedly inhibited the proliferative response in a dose-dependent manner. Maximal inhibition occurred when paf-acether was present during the first 24 hr of cell culture and the presence of paf-acether did not alter the kinetics of CD4+ cell proliferation. Importantly, the mechanism by which paf-acether inhibited the proliferative response was not related to inhibition of interleukin 2 (IL-2) secretion since the amount of IL-2 in cultures was not altered and addition of exogenous IL-2 failed to restore the CD4+ cell proliferative response. Further, as judged by indirect immunofluorescence, paf-acether did not inhibit IL-2 receptor expression. Taken together, these data indicate that paf-acether interferes with some processes leading to CD4+ cell proliferation. This new role for the chemically defined monokine paf-acether emphasizes the potential role of inflammatory lipid mediators in the regulation of T cell response.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1988

Immunoregulatory functions of paf-acether. II. Decrease of CD2 and CD3 antigen expression.

Paf-acether (platelet-activating factor) is a phospholipid initially described as a potent platelet-aggregating compound. It is produced by numerous cell types and is now considered as an important mediator of cell-cell interactions. The effect of paf-acether on the expression of CD2 and CD3, two human T cell surface glycoproteins, was investigated by indirect immunofluorescence and flow cytometry. Paf-acether partially down-regulated, in a time- and dose-dependent manner, CD2 and CD3 but not HLA class I antigen expression on peripheral human T cells and Jurkat cells. Lysophosphatidylcholine, a phospholipid closely related to paf-acether, had no detectable modulatory effect on CD2 and CD3 expression. In addition to CD2/CD3 modulation, paf-acether markedly inhibited T cell proliferative response not only to phytohemagglutinin or concanavalin A but also to anti-CD3 or a stimulatory combination of anti-CD2 monoclonal antibodies. These data demonstrate for the first time that lipid mediators such as paf-acether might be involved in the regulation of the expression of cell surface glycoproteins that are essential in the execution of T cell function.

Antibodies, Monoclonal↗
PubMed1986

Biosynthesis of paf-acether: VIII: Impairment of paf-acether production in activated macrophages does not depend upon acetyltransferase activity.

Activated peritoneal macrophages (M phi) from mice injected with Bacilli Calmette-Guérin, trehalose dimycolate, a defined immunostimulant derived from Mycobacterium tuberculosis, or streptococci C74 (St), synthesized two to three times less paf-acether (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) in response to a zymosan challenge than did (0.7 +/- 0.2 nmol/mg protein) resident-M phi (R-M phi). To assess at which step the paf-acether biosynthetic pathway was impaired, the content in phospholipid paf-acether precursors was evaluated. The alkyl-acyl-glycerophosphocholine content was comparable in R-M phi (50.4 +/- 18.6 nmol/mg protein) and activated-M phi (40.0 +/- 6.5 to 63.9 +/- 7.7 nmol/mg protein), as well as the lyso paf-acether content (0.85 +/- 0.18 nmol/mg protein for R-M phi vs 0.63 +/- 0.16 to 1.23 +/- 0.21 nmol/mg protein for activated macrophages). The nonlimiting rate of the phospholipid substrate was strengthened by experiments showing that incubation of the various populations with lyso paf-acether did not yield increased amounts of paf-acether. Similarly, incubation of R-M phi or St-M phi with sodium acetate increased paf-acether production to the same extent in both populations, ruling out the acetate substrate deficiency as the cause of the impaired production. The level of acetyltransferase activity, the enzyme that transfers an acetate moiety of acetyl coenzyme A (acetyl-CoA) onto lyso paf-acether, was very low in thioglycolate (TG)-elicited M phi but high in R-M phi and activated ones. In all cases, it was increased by two to three times upon zymosan challenge. This suggested that increased paf-acether catabolism and not impaired anabolism could be responsible for the marked reduced formation noted in activated macrophages. The addition of acetyl-CoA (200 microM) to the various macrophage monolayers restored paf-acether formation by activated cells to R-M phi values but with delayed kinetics as compared with paf-acether formation induced by zymosan. The enhancing effect of acetyl-CoA on paf-acether production was inhibited upon oleyl-CoA addition, suggesting that acetyl-CoA may increase paf-acether production by preventing the reacylation of lyso paf-acether resulting from paf-acether degradation. In conclusion, the paf-acether output in some inflammatory macrophages may be regulated by the level of acetyltransferase activity, because it is observed in TG-M phi. However, we present the first evidence for another mechanism of regulation, most probably related to the deacylation/reacylation of paf-acether precursors and metabolites.

Acetates↗