María Elena Sales

Role of arachidonic acid metabolites in the action of a β adrenergic agonist on human monocyte phagocytosis

The mechanisms by which beta adrenergic stimulation regulates phagocytosis of Candida albicans by human peripheral monocytes (HPM) are characterized. Isoproterenol (ISO) inhibits phagocytosis in a concentration-dependent manner. This effect was blunted by propranolol, inhibitors of phospholipase A2 (PLA2), cyclooxygenase and verapamil, pointing to a participation of arachidonic acid (AA) metabolites and calcium in the phenomenon. Prostaglandin E2 (PGE2) and dibutyryl cyclic AMP (db-cAMP) also exerted the same inhibitory effect on phagocytosis. ISO interacts with beta adrenergic receptors of HPM increasing PGE2 and cAMP. We conclude that the mechanisms by which beta adrenergic stimulation regulates phagocytosis of Candida albicans by HPM appear to be secondary to beta adrenoceptor-mediated hydrolysis of AA accompanied by an increase in PGE2 generation and cAMP production. Both PGE2 and cAMP could act as mediators of the inhibitory action of beta agonists on the HPM-phagocytosis process.

Treatment in vitro with PPARα and PPARγ ligands drives M1-to-M2 polarization of macrophages from T. cruzi-infected mice.

Trypanosoma cruzi, the etiological agent of Chagas disease, induces a persistent inflammatory response. Macrophages are a first line cell phenotype involved in the clearance of infection. Upon parasite uptake, these cells increase inflammatory mediators like NO, TNF-α, IL-1β and IL-6, leading to parasite killing. Although desired, inflammatory response perpetuation and exacerbation may lead to tissue damage. Peroxisome proliferator-activated receptors (PPARs) are ligand-dependent nuclear transcription factors that, besides regulating lipid and carbohydrate metabolism, have a significant anti-inflammatory effect. This is mediated through the interaction of the receptors with their ligands. PPARγ, one of the PPAR isoforms, has been implicated in macrophage polarization from M1, the classically activated phenotype, to M2, the alternatively activated phenotype, in different models of metabolic disorders and infection. In this study, we show for the first time that, besides PPARγ, PPARα is also involved in the in vitro polarization of macrophages isolated from T. cruzi-infected mice. Polarization was evidenced by a decrease in the expression of NOS2 and proinflammatory cytokines and the increase in M2 markers like Arginase I, Ym1, mannose receptor and TGF-β. Besides, macrophage phagocytic activity was significantly enhanced, leading to increased parasite load. We suggest that modulation of the inflammatory response by both PPARs might be due, at least in part, to a change in the profile of inflammatory macrophages. The potential use of PPAR agonists as modulators of overt inflammatory response during the course of Chagas disease deserves further investigation.

Sympathetic control of specific and non-specific immune response

Following antigenic stimulation with specific (alloantigen) and non-specific (sheep red blood cells (SRBC) and lipopolysaccharide (LPS] antigens the expression of beta-adrenergic receptors and the interference of immune sera IgG, on uterine smooth muscle beta-adrenoceptor-specific ligands were studied. The binding of alloimmune IgG to beta-adrenoceptors appeared to be specific, because immunization with SRBC and LPS did not induce anti-beta-adrenoceptors antibodies. On the contrary, the decrease in beta-adrenergic receptor expression was observed even with alloantigens and with the conventional antigenic challenge, suggesting that this phenomenon could be a non-specific immunoregulatory mechanism.

Positive inotropic and chronotropic effect of alloimmune sera on isolated mouse atria.

The effects of alloimmune sera on the contractile tension and frequency of spontaneously beating isolated mouse atria were explored. Immune sera enhanced frequency as well as tension; both effects were blocked by the presence of propranolol. In contrast, pretreatment with 6-OH dopamine potentiated the stimulatory action of immune sera.

Major histocompatibility complex modulation of β-adrenoceptor function

Abstract Reciprocal interaction between β-adrenoceptor specific ligand occupancy and alloantibody binding to specific antigens of cardiac and smooth muscle tissues was observed. Interference of alloimmune antibody fixation to both cardiac and oviductal tract preparations by β 1 or β 2 selective blockers, respectively, was obtained by means of indirect immunofluorescence assays. Reciprocally, alloimmune IgG and monoclonal antibodies directed to class I H-2 antigens, behaving as β-adrenoceptor agonists, modified the contractility of both tissues, increasing intracellular levels of cyclic AMP (cAMP). Additionally, alloantibodies were also capable of inhibiting specific β-adrenoceptor radioligand binding to purified cardiac and smooth muscle membranes. These data suggested a modulation of β-adrenoceptor function by antibodies directed against H-2 class I histocompatibility molecules, probably through molecular interactions between both structures.

Variable inotropic effect of immune cells on mice atria — Participation of metabolic products of arachidonic acid

The effect of BALB/c anti CF1 lymph node cells and thymocytes on the spontaneous activity of isolated CF1 mouse atria was studied. Immune lymph node cells induced opposite effects depending on the number of immunizations. Immune lymph node cells from mice which received two immunizations decreased the contractile tension of the atrium, whereas, cells from mice exposed to three and five immunizations strongly increased the tension. Immune thymocytes induced only negative inotropic action and this effect did not depend on the number of immunizations. Indeed, it was similar after two, three or five immunizations. Control normal lymph node cells or thymocytes from BALB/c or CF1 mice had no effect on CF1 atria. Furthermore, BALB/c anti CF1 cells had no effect on BALB/c atria. Inhibitors of cyclooxygenase activity prevented the negative inotropic influence of immune thymocytes and lymph node cells seen after two immunizations. In contrast, inhibitors of the lipoxygenase pathway abolished the positive inotropic action induced by lymph node cells obtained after three and five immunizations. Cell-free supernatants of lymph node cells from animals receiving five immunizations, stimulated the contractile activity of atrium, while those from thymocytes inhibited it, indicating that soluble factors are generated by contact of immune cells with the myocardium. It is proposed that upon recognition of alloantigens expressed by atrial cells, lymph node cells and thymocytes are activated and release either arachidonic acid metabolites or some factor(s) that induces this release by other cells, which in turn triggers different effects in myocardial tissue depending on the set of cells involved in the primary immune response.

β-Adrenergic inhibitory effect of alloimmune antibody on isolated oviductal tract of mice

The effects of IgG purified from BALB/c anti CF1 sera on the spontaneous contractions of isolated oviductal tract from CF1 mice were explored. Cumulative dose-response curves were constructed for the effect of immune IgG on nice oviductal tracts from proestrus, estrus, metestrus and diestrus, comparing them with those obtained with norepinephrine. Both the adrenergic agonist and the immune IgG produced a sustained inhibition of spontaneous motility during the whole sex cycle. Normal IgG was virtually devoid of activity. The sensitivity of CF1 mouse oviducts to the inhibitory actions of immune IgG and norepinephrine varied depending on the hormonal stage, i.e. it was higher in natural diestrus than in metestrus; it became smaller in proestrus and was minimal during estrus. The mechanism triggered involved a beta-adrenergic reaction that could be blocked by 10(-7) M (-)-propranolol and 10(-6) M butoxamine and potentiated by chemical sympathectomy of the mice with 6-hydroxydopamine. It is concluded that: (a) alloimmune antibody reacts with isolated oviductal tract of mice inducing functional changes; (b) this action could be associated with an activation of postsynaptic beta-adrenergic sites of the plasma membrane and (c) the different effectiveness of the immune IgG observed during the sex cycle appears to depend on the affinity of beta-adrenoreceptors to react with it.

Endogenous lysophosphatidic acid participates in vascularisation and decidualisation at the maternal–fetal interface in the rat

Lysophosphatidic acid (LPA) affects several female reproductive functions through G-protein-coupled receptors. LPA contributes to embryo implantation via the lysophospholipid LPA3 receptor. In the present study we investigated the participation of endogenous LPA signalling through the LPA3 receptor in vascularisation and decidualisation, two crucial events at the maternal-fetal interface. Pregnant rats were treated with diacylglycerol pyrophosphate (DGPP), a highly selective antagonist of LPA3 receptors, on Day 5 of gestation. Pregnant rats received intrauterine (i.u.) injections of single doses of DGPP (0.1mgkg-1) in a total volume of 2μL in the left horn (treated horn) in the morning of GD5. DGPP treatment produced aberrant embryo spacing and increased embryo resorption. The LPA3 receptor antagonist decreased the cross-sectional length of the uterine and arcuate arteries and induced histological anomalies in the decidua and placentas. Marked haemorrhagic processes, infiltration of immune cells and tissue disorganisation were observed in decidual and placental tissues from sites of resorption. The mRNA expression of three vascularisation markers, namely interleukin 10 (Il10), vascular endothelial growth factor (Vegfa) and vascular endothelial growth factor receptor 1 (Vegfr1), was reduced at sites of resorption from Day 8. The results show that the disruption of endogenous LPA signalling by blocking the LPA3 receptor modified the development of uterine vessels with consequences in the formation of the decidua and placenta and in the growth of embryos.

Effect of alloimmunized thymic cells on isolated mouse atria: participation of prostaglandins

The effects of thymic cells from alloimmunized mice on the mechanical activity of isolated mouse atria were explored. Immune cells decreased the tension without changing the rate of beating of the atrium. After inhibition of prostaglandin synthesis with indomethacin and acetylsalicylic acid, the negative inotropic action of alloimmunized thymic cells was blocked.