Cooperation of chloroquine and blood platelets in inhibition of polymorphonuclear leukocyte chemiluminescence

The Effects of Serotonin in Immune Cells

Serotonin [5-hydroxytryptamine (5-HT)] plays an important role in many organs as a peripheral hormone. Most of the body’s serotonin is circulating in the bloodstream, transported by blood platelets and is released upon activation. The functions of serotonin are mediated by members of the 7 known mammalian serotonin receptor subtype classes (15 known subtypes), the serotonin transporter (SERT), and by covalent binding of serotonin to different effector proteins. Almost all immune cells express at least one serotonin component. In recent years, a number of immunoregulatory functions have been ascribed to serotonin. In monocytes/macrophages, for example, serotonin modulates cytokine secretion. Serotonin can also suppress the release of tumor necrosis factor-α and interleukin-1β by activating serotonin receptors. Furthermore, neutrophil recruitment and T-cell activation can both be mediated by serotonin. These are only a few of the known immunomodulatory roles of serotonin that we will review here.

Naturally appearing N-feruloylserotonin isomers suppress oxidative burst of human neutrophils at the protein kinase C level

N-feruloylserotonin (N-f-5HT) isomers, isolated from seeds of Leuzea carthamoides (Wild) DC, inhibited dose-dependent oxidative burst in human whole blood and isolated neutrophils in vitro, which were measured by luminol- and/or isoluminol-enhanced chemiluminescence in the following rank order of stimuli: PMA > OpZ > calcium ionophore A23187. In isolated neutrophils that were stimulated with PMA, N-f-5HT isomers were effective against extracellular and intracellular reactive oxygen species. Liberation of ATP, analysis of apoptosis, and recombinant caspase-3 activity revealed that N-f-5HT isomers, used in concentrations up to 100 μM, did not alter the viability and integrity of isolated neutrophils. Western blot analysis documented that in concentrations of 10 and 100 μM, N-f-5HT isomers significantly decreased PMA-induced phosphorylation of PKC α/β II. The results suggest that N-f-5HT isomers are an effective, naturally occurring substance with a potent pharmacological effect on the oxidative burst of human neutrophils. It should be further investigated for its pharmacological activity against oxidative stress in ischemia-reperfusion, inflammation and other pathological conditions.

Inhibitory effect of stobadine on FMLP-induced chemiluminescence in human whole blood and isolated polymorphonuclear leukocytes

The chemiluminescence (CL) technique with luminol and isoluminol was used to characterize the effect of stobadine on reactive oxygen metabolites (ROM) generation in human whole blood and in isolated polymorphonuclear leukocytes (PMNL) stimulated with N-formyl-methionyl-leucyl-phenyl-alanine (FMLP). In whole blood and in isolated PMNL, stobadine in the concentrations of 1, 10 and 100 micromol/L significantly inhibited the CL signal after FMLP, which activated predominantly extracellular generation of ROM. The same concentrations of stobadine were effective on CL in a cell-free system. On the other hand, myeloperoxidase (MPO) liberation was decreased by stobadine only in the concentration of 100 micromol/L. The results showed stobadine to act as a potent inhibitor/scavenger of extracellularly produced ROM in human PMNL and indicated interference of stobadine with ROM as well as with signalling events resulting in NADPH-oxidase activation and MPO liberation.

The combined luminol/isoluminol chemiluminescence method for differentiating between extracellular and intracellular oxidant production by neutrophils

To address the question why isoluminol, but not luminol, failed to detect oxidants produced intracellularly, differences between these luminophores were investigated with respect to physicochemical parameters and the character of chemiluminescence signal. Our results showed the isoluminol molecule to be more polar, more hydrophilic and possessing lower ability to form intramolecular bonds than the luminol molecule. Therefore, isoluminol: (i) only slightly pervaded biological membranes; (ii) depended essentially on extracellular peroxidase; (iii) did not produce chemiluminescence in the presence of extracellular scavengers; and (iv) it could be considered a specific detector of extracellular radicals. On the other hand, the physicochemical parameters of luminol and partial resistance of its chemiluminescence to the effect of extracellular inhibitors proved the lipo/hydrophilic character of this luminophore and thus its ability to interact with radicals both outside and inside of cells. The luminol chemiluminescence measured in the presence of extracellular scavengers and the isoluminol chemiluminescence were used with the intention to differentiate the effects of two antihistamine drugs on intra- and extracellular radical formation. In activated human neutrophils, brompheniramine inhibited the extracellular and potentiated the intracellular part of chemiluminescence signal, whereas a reducing effect of loratadine was observed in both compartments.

Chemiluminescence response of beta-glucan stimulated leukocytes isolated from different tissues and peritoneal cavity of Dicentrarchus labrax

The respiratory burst of leukocytes isolated from sea bass (Dicentrarchus labrax) pronephros, peritoneal cavity (P.C.), spleen and blood, was measured by a chemiluminescence (CL) assay after stimulation with beta-glucan. The CL response by P.C. and pronephros leukocytes was significantly higher than that expressed by a similar number of cells separated from spleen and blood. This probably reflects the observation that the proportion of macrophages and neutrophils was highest in the populations of leukocytes from peritoneal cavity and pronephros. Comparative observations showed a higher degree of yeast phagocytosis by leukocytes taken from peritoneal cavity than the pronephros. Moreover phagocytic index evaluated by microscopical observations, indicated that peritoneal macrophages internalised more yeast cells than neutrophils (identified by the peroxidase reaction). Scanning electron microscopy observations were also carried out. Inhibition experiments by a myeloperoxidase inhibitor sodium azide, iodonium-diphenyl-chloride which inhibits NADPH-oxidase, and exogenous superoxide dismutase, which catalyses O-2 dismutation to H(2)O(2), supported the correlation between CL and respiratory burst. Treatment with ouabain and DNP suggested that in this response, Ca(++) pump channels and calmodulin are involved in a metabolic energy-dependent pathway.