Biomedical subjects

M Taplits

Publications and source records attributed to M Taplits.

7 recordsLinked to original sources

PubMed1992

Inhibition of release of arachidonic acid, superoxide, and IL-1 from human monocytes by monoclonal anti-HLA class II antibodies: effects at proximal and distal points of inositol phospholipid hydrolysis pathway.

Incubation of human elutriator-purified monocytes with anti-HLA-DR or DQ antibody inhibited the release of arachidonic acid induced by serum-treated zymosan (STZ), a phagocytic stimulus that is known to induce inositol phospholipid hydrolysis and Ca2+ influx. However, only anti-HLA-DR antibody partially inhibited STZ-induced inositol phospholipid hydrolysis and concanavalin-A-induced Ca2+ influx. Incubation with anti-HLA-DR or -DQ antibody inhibited phorbol ester-induced AA release as well as superoxide production and IL-1 release. Inhibition of monocyte function by anti-class II antibodies was not accompanied by cAMP elevation. Furthermore, addition of exogenous db-cAMP and other agents (forskolin, cholera toxin, or 3-isobutyl-1-methyl-xanthine) that increase cAMP levels through different mechanisms, alone or in combination with anti-HLA antibodies, had no inhibitory effect on factor release. Our results demonstrate that perturbation of class II molecules down-modulates cell activation at more than one point of the signal transduction pathway with dominant inhibition distal to inositol phospholipid hydrolysis. They also suggest that the inhibition by anti-HLA class II antibody is probably not mediated via cAMP elevation.

Antibodies, Monoclonal↗

PubMed1991

Down-regulation of surface FcRI and decrease in antibody-dependent cellular cytotoxicity of cultured monocytes. Reversal by monensin or cytochalasin-D.

To investigate the mechanisms involved in regulation of antibody-dependent cellular cytotoxicity (ADCC) mediated by human monocytes, 51Cr-labeled sheep red blood cells (RBC) were used as target cells in vitro. Monocytes incubated overnight at 37 degrees C before addition of SRBC and antibody exhibited a significant decrease in ADCC activity compared with freshly isolated cells. This pattern was observed with monocytes from all donors tested, regardless of the media used for culture. Supernatants from monocyte cultures did not inhibit the cytotoxic ability of fresh monocytes and cycloheximide, a protein synthesis inhibitor, could not reverse ADCC suppression in cultured monocytes, indicating that the alteration in ADCC is probably not due to inhibitory molecules secreted or synthesized during incubation. A correlation between the decrease in the number of surface FcRI and loss in ADCC ability of cultured monocytes was found. One mechanism for the reduced FcRI expression of 1-day-old monocytes may be rapid internalization that exceeds the rate of reexpression, because cytochalasin-D or monensin, each of which inhibits receptor internalization, maintained FcR expression as well as ADCC ability of cultured monocytes. These data illustrate mechanisms whereby alteration in the number of receptors may underlie loss of receptor-mediated functions, or be involved in augmentation of their biologic activity. The findings that important monocyte functions change under conditions of storage or culture have relevance to in vitro testing of various immune functions of monocytes performed clinically to monitor or guide therapy.

Animals↗

PubMed1991

Calcium-dependent eicosanoid metabolism by concanavalin A-stimulated human monocytes in vitro. Synergism with phorbol ester indicates separate regulation of leukotriene B4 synthesis and release.

Human monocytes obtained by counter-current centrifugal elutriation released arachidonic acid when challenged in vitro with Con A, as well as with other soluble (PMA or ionomycin) or particulate stimuli (serum-treated zymosan). Cyclo-oxygenase metabolites were the principal eicosanoids detected in the supernatants of Con A-stimulated, [3H]arachidonate-labeled monocytes, 5-Lipoxygenase (5-LO) products, such as leukotriene B4 (LTB4), were conspicuously absent. Release of arachidonate and its metabolites in response to Con A was dependent on the presence of extracellular Ca2+, but not Mg2+. In contrast to serum-treated zymosan challenge, which resulted in increased inositol trisphosphate and LTB4 release, Con A-induced inositol phospholipid hydrolysis in monocytes was limited to phosphatidylinositol or phosphatidylinositol monophosphate. Despite an inability to augment LTB4 release, Con A or PMA induced a loss of 5-lipoxygenase from a cytosolic compartment that was similar to that achieved with a calcium ionophore (ionomycin), a potent stimulus for LTB4 generation. When cell-associated LTB4 was evaluated, evidence for increased LTB4 production was obtained in response to either stimulus (PMA greater than Con A). In combination, however, PMA and Con A treatment resulted in monocyte LTB4 release comparable with that observed with the calcium ionophore or STZ. LTB4 release in response to all stimuli tested was inhibited by MK-886, a drug that binds to 5-lipoxygenase-activating protein. These results indicate the following: 1) Phospholipase A2 activation and attendant arachidonic acid release induced by agents that increase intracellular Ca2+ and/or generate diacylglycerol results in increased synthesis and release of PG and increased synthesis of leukotrienes, but not necessarily leukotriene release. 2) 5-LO translocation, which may occur independently of increased intracellular Ca2+, may be necessary for LTB4 generation but is insufficient for its release. 3) 5-Lipoxygenase-activating protein activity is necessary for 5-LO activation and LTB4 release in response to all stimuli investigated here. 4) Phorbol ester, an activator of protein kinase C, may synergize with agents such as Con A (which by themselves induce a minimal intracellular Ca2+ rise), so as to result in the release of LTB4. Thus, Con A may represent a class of surface receptor-aggregating agents that initiates inflammatory changes or immunomodulation associated with liberation of PG and might predispose to release of other inflammatory mediators, such as leukotrienes, in the presence of additional signals including protein kinase activation.

Arachidonate 5-Lipoxygenase↗

PubMed1991

Augmentation of monocyte-mediated antibody-dependent cellular cytotoxicity by protein synthesis inhibitors: evidence for an endogenous regulatory mechanism.

Protein synthesis inhibitors, cycloheximide and puromycin, were used in cytotoxic assays employing human peripheral blood monocytes as effectors and sheep erythrocytes as target cells. ADCC could be initiated and could also achieve its full lytic activity in the absence of new protein synthesis. Furthermore, an augmentation of ADCC was observed in the presence of protein synthesis inhibitors. This augmentation was due to an increase in the cytotoxic ability of effector cells rather than a change in the lytic susceptibility of the target. Enhanced cytotoxic potential could not be attributed to an increase in the expression of FcRI but could be due to increased availability of antibody for mediating ADCC as a result of reduced numbers of FcRII. Suppression of prostaglandin-E2 release by monocytes was noted in the presence of cycloheximide, possibly as a result of inhibition of synthesis of cyclooxygenase. However, prostaglandin-E2 and other arachidonic acid metabolites did not appear likely to play a role in negatively regulating human monocyte ADCC since neither cytotoxicity nor cycloheximide-induced augmentation was affected by the presence of exogenous prostaglandin-E2 or arachidonic acid. Cycloheximide was found to induce the secretion of superoxide anions by monocytes, but a role for reactive oxygen species in cycloheximide-induced augmentation of ADCC could not be established by experiments involving the use of catalase or superoxide dismutase. These results raise the possibility that a rapidly turning over protein which negatively regulates monocyte-mediated ADCC exists.

Antibody-Dependent Cell Cytotoxicity↗

PubMed1991

Absence of modulation of monokine production via endogenous cyclooxygenase or 5-lipoxygenase metabolites: MK-886 (3-[1-(4-chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl]-2,2- dimethylpropanoic acid), indomethacin, or arachidonate fail to alter immunoreactive interleukin-1 beta, or TNF-alpha production by human monocytes in vitro.

Human peripheral blood monocytes exposed to MK-886 (3-[1-(4-chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl]-2,2- dimethylpropanoic acid) at doses which abolish formation of 5-lipoxygenase metabolites showed unaltered interleukin-1 beta (IL-1 beta) or tumor necrosis factor-alpha (TNF-alpha) levels in response to phorbol ester, concanavalin A, serum-treated zymosan, or lipopolysaccharide. Indomethacin (10 microM), alone or in combination with MK-886, also failed to modulate monokine production in response to any stimulus. Exogenous arachidonate (3-30 microM) which augmented the formation of PGE2 and LTB4 in the absence of stimulation, also had no effect on monokine production. LPS-induced IL-1 and TNF production occurred despite stimulation of PGE2 synthesis. The results make a role for endogenous prostaglandins and leukotrienes in the regulation of monocyte IL-1 beta and TNF-alpha production unlikely. These data also indicate that MK-886, a novel inhibitor of 5-lipoxygenase product formation, is a potentially useful leukotriene inhibitor which does not affect monokine production.

Analysis of Variance↗

PubMed1987

Secretory processes in lymphocyte function.

The secretion of immunoglobulin by plasma cells has been considered a classical example of the "non-regulated" pathway of protein secretion, in which newly synthesized protein is processed by the Golgi, packaged into small vesicles, and immediately secreted without intracellular storage. In the case of lymphokine secretion by T lymphocytes, it is generally not clear whether this non-regulated pathway is also being used, as opposed to the "regulated" pathway which has been proposed to operate in the cytotoxic lymphocyte mechanism. In this case, as in mast cells and endocrine cells, proteins are synthesized and then stored in cytoplasmic granules. The secretion is triggered (regulated) by a membrane receptor-ligand interaction, which for the cytotoxic lymphocytes is part of the target cell binding process. In cytotoxic T lymphocytes, this secretion process can be measured by following the appearance of a granule serine protease in the medium, and it has been shown to be triggered by target cells or by immobilized antibodies which bind the T cell receptor complex. In addition to cytotoxic lymphocytes, cloned T helper cells contain this serine protease in cytoplasmic granules with a low internal pH. Helper lymphocytes secrete this enzyme in response to (1) soluble antigen which has been processed by cells bearing the appropriate MHC antigens; (2) immobilized antibodies against the T cell receptor complex; (3) a combination of phorbol ester and calcium ionophore. Thus in both helper and cytotoxic lymphocytes, the regulated pathway of protein secretion clearly operates after triggering by the T cell antigen receptor.

Animals↗

PubMed1979

Immune response to Escherichia coli B surface antigens.

The cell surface antigens of Escherichia coli B were investigated. We found that mice immunized with live bacteria responded with an immune response directed mainly against the protein structure of the cell surface. The lipopolysaccharide component of the bacterium was immunogenic, but its contribution to the overall response was only secondary. It is suggested that when considering the immune response to gram-negative bacteria, more attention should be given to the protein antigens.

Animals↗