Impaired G-proteins and cyclic nucleotide phosphodiesterase activity in T-lymphocytes from patients with sarcoidosis.

Among the various immune abnormalities which characterize active sarcoidosis, a low proliferative response of peripheral blood lymphocytes to mitogenic lectins has long been observed. Since membrane-associated G-proteins are very likely to be crucial elements in lectin signal transduction, we investigated the binding of 5'-guanylylimidodiphosphate (GppNHp), a non hydrolyzable GTP analogue, to blood total lymphocyte membranes and to blood T-lymphocyte membranes from patients with active sarcoidosis, and from healthy control subjects. GppNHp binding was markedly decreased in peripheral cells from patients with sarcoidosis as compared to controls, suggesting the occurrence of a defect at the level of G-protein(s). A further characterization of G-proteins in these cells by means of ADP-ribose-labelling in the presence of bacterial toxins brought forward a significant decrease in the labelling of a 40 kDa protein, the major pertussis toxin substrate, in membranes from sarcoid patients, while the labelling of the major 44 kDa cholera toxin substrate proved to be unchanged with respect to control membranes. It is hypothesized that, in sarcoid lymphocytes, a defect in the negative control of adenylate cyclase mediated by the inhibitory G-protein Gi, prevents the lowering of cAMP necessary to normal mitogenic response of blood lymphocytes to stimulation. cAMP degradation by the specialized enzyme phosphodiesterase constitutes another critical step in the control of cAMP levels. Both cAMP and cGMP phosphodiesterase activities were found decreased in blood total lymphocyte preparations from sarcoid patients. With purified T-cells, although the mean cAMP and cGMP phosphodiesterase activities from sarcoid patients were found more markedly decreased with respect to healthy donors, only the decrease in cGMP phosphodiesterase was found statistically significant. The role these defects in cyclic nucleotide degradation potentially play in the disturbance of blood lymphocytes response associated with sarcoidosis is discussed.

Cyclic nucleotide phosphodiesterases and methyltransferases in purified lymphocytes, monocytes and polymorphonuclear leucocytes from healthy donors and asthmatic patients.

Cyclic nucleotide phosphodiesterase and phospholipid N-methyl-transferase activities were simultaneously measured in purified polymorphonuclear cell-, mononuclear cell-, lymphocyte- and monocyte-homogenates from control subjects, from patients with atopic asthma and from patients with non-atopic asthma. Whereas cyclic AMP and cyclic GMP phosphodiesterase activities were found to be about 10-fold lower in polymorphonuclear than in mononuclear cells, phospholipid N-methyltransferase proved to be rather similar in each cell type from control donors. Cyclic AMP phosphodiesterase and phospholipid N-methyltransferase were significantly decreased in polymorphonuclear cells and monocytes from asthmatic patients compared with the control group while cyclic GMP phosphodiesterase was significantly impaired only in the monocyte subpopulation.

Phosphatidylethanolamine methyltransferase and cAMP, cGMP phosphodiesterases in lymphocytes and monocytes in sarcoidosis.

Among the various hypotheses proposed to explain immune cell defect in sarcoidosis, we examined thoroughly that of Faguet who described abnormalities of signal transmission at lymphocyte membrane level. Phosphatidylethanolamine methyltransferase and cAMP cGMP phosphodiesterases were studied in blood lymphocytes and monocytes from 8 subjects with sarcoidosis disease. Phosphatidylethanolamine methyltransferase (PMT1) plays an important regulatory role in membrane signal transmission. cAMP and cGMP phosphodiesterases (PDE) regulate cytoplasmic cyclic nucleotide levels and so participate in the modulation of the cell cycle. We observed a decreased PMT1 activity in lymphocytes and monocytes and a decreased cAMP and cGMP PDE activities in monocytes. It is not now possible to say if these abnormalities are primary or secondary. Whatever the origin of this dysfunctioning, these results evoke simultaneous disturbances of membrane signal transmission and cell cycle in monocytes and membrane abnormalities in lymphocytes. These abnormalities could explain some immune cell defects in sarcoidosis disease.

[Methylation of membrane phospholipids of alveolar macrophages in pulmonary sarcoidosis and diffuse interstitial pulmonary fibrosis]. / La méthylation des phospholipides membranaires du macrophage alvéolaire dans la sarcoïdose pulmonaire et les fibroses pulmonaires interstitielles diffuses.

Alveolar macrophage plays an important role in alveolitis pathogenesis and lung fibrosis process. Macrophages exhibit plasmic membrane biochemical modifications during cell activation. Phospholipid methylation is involved during plasmic membrane stimulation. Phosphatidylethanolamine methyltransferase I was measured in alveolar macrophage membrane from normal subjects and patients presenting with pulmonary sarcoidosis or interstitial lung fibrosis. We observed increased enzyme activity among sarcoidosis subjects with high intensity lung alveolitis and normal subjects receiving immunostimulating treatment (RU 41740). The role of membrane phospholipidic modifications in granulomatous process is discussed.

Alveolar macrophage membrane phospholipid methylation in sarcoidosis and hypersensitivity pneumonitis.

Methylation of phospholipids seems to be an essential step in the recognition and transduction of regulatory signals by eukaryotic cells. Phosphatidylethanolamine methylation was compared in alveolar macrophage membrane from patients presenting with pulmonary sarcoidosis or hypersensitivity pneumonitis and control subjects. Phosphatidylethanolamine methyltransferase (PMT1) activity was determined by various measures of incorporation of tritiated methyl group from (3H) S-adenosyl-L-methionine in membrane phospholipids. Tritiated methyl group incorporation in macrophage membrane was higher in some patients presenting with sarcoidosis or hypersensitivity pneumonitis, than in controls. PMT1 activity was found to be higher in sarcoidosis patients with a positive gallium lung scan. As lipids play an important role during macrophage activation and cell interaction, although a wide heterogeneity was observed in PMT1 activity, increased membrane phospholipid methylation seems to be an important feature in pulmonary diseases where macrophages are involved.

[Membrane phosphatidylethanolamine methylase in blood leukocytes and alveolar macrophages of asthmatic patients]. / Etude de la phosphatidyl ethanolamine méthylase (PEMT) membranaire sur les leucocytes sanguins et les macrophages alvéolaires chez le sujet asthmatique.

Phosphatidyl ethanolamine methylase (PEMT) is an enzyme involved in the methylation of membrane phospholipids which plays a very important role in the modulation of the activity of the beta-receptors and the production of phosphatidylcholine, substrate of phospholipase A2. This report describes a study of PEMT on the membranes of blood leucocytes and alveolar macrophages obtained by bronchoalveolar washings in different types of asthma: allergic, intrinsic and occupational. This was accompanied by parallel study of respiratory function tests and the level of bronchial reactivity to carbachol in asthma sufferers as well as other alveolar biological parameters: phospholipid fractions of surfactant, angiotensin conversion enzyme and protein/albumin ratio. The authors found a significant increase (in comparison with controls) in PEMT activity both in macrophages and leucocytes in cases of intrinsic asthma. However, there was no correlation between the level of activity of the enzyme and the degree of bronchial hyper-reactivity. There was no change in alveolar phospholipid environment. In the light of these findings, the role of membrane activation of the alveolar macrophage is discussed in the physiopathology of intrinsic asthma.

Activity of cyclic AMP phosphodiesterase and methyltransferases in leukocyte membranes from allergic patients.

Cyclic AMP metabolism and methylation of phospholipids are central events which occur at the membrane level. Since a dysfunction of cell membranes seems to characterize some allergic diseases, we investigated cyclic AMP phosphodiesterase and methyltransferase activities in leukocyte membrane fractions obtained from healthy volunteers and from allergic patients. The allergic group presented a significantly decreased methyltransferase activity compared with a control group, whereas cyclic AMP phosphodiesterase and noradrenaline (NA)-stimulated methyltransferase were found to be increased with respect to the control group. A significant correlation has been found between cyclic AMP phosphodiesterase and NA-stimulated methyltransferase with both control and allergic subjects, which suggests close relationships between these two enzymes within the cell membrane.

Phosphatidylethanolamine methylation in leukocyte membrane preparations from allergic subjects: an unexpected result.

We studied the incorporation of [3H]methyl from [3H]methyl-S-adenosylmethionine into leukocyte phospholipids. A higher incorporation in leukocytes from control subjects than from allergic subjects was noticed.

Modulation by S-adenosyl-methionine and S-adenosyl-homocysteine of the human leucocytes histamine release.

Methylation of membrane phospholipids is an important stage in the process of histamine release. This methylation reaction can be modulated by S-adenosyl-methionine (SAM) as well as by S-adenosyl-homocysteine (SAH). The influence of SAM and of SAH upon the histamine release of leucocytes from asthmatic and normal subjects were compared. In concentration of 10(-4) M, SAM enhanced spontaneous and the specifically induced histamine release. In concentration of 10(-5) M SAM enhanced the histamine release only in normals. This phenomenon could indicate a deficit in methyl-transferase activity in the asthamatics. In concentration of 10(-4) M, SAH reduced spontaneous and specifically induced histamine release, having an effect comparable to that of 10(-4) M Theophylline.

[Changes in leukocyte phospholipid-N-methyltransferase activity after chronic treatment of allergic patients with mequitazine]. / Modification de l'activité phospholipide-N-méthyltransferase leucocytaire aprés traitement chronique de sujets allergiques par la méquitazine.

Phospholipid methyltransferase activity was lower in leukocyte preparations from allergic subjects than from control subjects. After chronic treatment by mequitazine, values from allergic subjects were increased to values near those of control subjects.

Phosphatidyl ethanolamine methylation in membrane from bronchoalveolar lavage mononuclear cells, in asthmatic patients: a new marker of macrophage activity.

Phosphatidyl ethanolamine methylation was compared in alveolar macrophage membrane from asthmatic and control subjects. Phosphatidyl ethanolamine methylase activity was determined by measuring the incorporation of (3H) methyl group from (3H) adenosyl methionine into membrane phospholipids. (3H) methyl group incorporation was significantly higher in macrophages from asthmatic patients. This result is consistent with macrophage membrane activation and could signify: a membrane phospholipid pool regeneration after allergenic or toxic disturbance or an enzymatic activation by inflammatory mediators.