Biomedical subjects

Irene Gramaglia

Publications and source records attributed to Irene Gramaglia.

8 recordsLinked to original sources

PubMed2006

Low nitric oxide bioavailability contributes to the genesis of experimental cerebral malaria.

The role of nitric oxide (NO) in the genesis of cerebral malaria is controversial. Most investigators propose that the unfortunate consequence of the high concentrations of NO produced to kill the parasite is the development of cerebral malaria. Here we have tested this high NO bioavailability hypothesis in the setting of experimental cerebral malaria (ECM), but find instead that low NO bioavailability contributes to the genesis of ECM. Specifically, mice deficient in vascular NO synthase showed parasitemia and mortality similar to that observed in control mice. Exogenous NO did not affect parasitemia but provided marked protection against ECM; in fact, mice treated with exogenous NO were clinically indistinguishable from uninfected mice at a stage when control infected mice were moribund. Administration of exogenous NO restored NO-mediated signaling in the brain, decreased proinflammatory biomarkers in the blood, and markedly reduced vascular leak and petechial hemorrhage into the brain. Low NO bioavailability in the vasculature during ECM was caused in part by an increase in NO-scavenging free hemoglobin in the blood, by hypoargininemia, and by low blood and erythrocyte nitrite concentrations. Exogenous NO inactivated NO-scavenging free hemoglobin in the plasma and restored nitrite to concentrations observed in uninfected mice. We therefore conclude that low rather than high NO bioavailability contributes to the genesis of ECM.

Alkenes↗

PubMed2006

A unified hypothesis for the genesis of cerebral malaria: sequestration, inflammation and hemostasis leading to microcirculatory dysfunction.

A unifying hypothesis for the genesis of cerebral malaria proposes that parasite antigens (released by replication in blood, surface molecules on parasitized erythrocytes, or merozoites) activate platelets that, in turn, contribute to the activation of the inflammatory response and increased levels of endothelial cell adhesion molecules (eCAMs). Increased levels of eCAMs result in further parasitized-erythrocyte sequestration and marked local inflammation that might disrupt the brain microvasculature, which cannot be repaired by the hemostasis system because of its procoagulant state. Disruption of the brain microvasculature can result in vascular leak and/or hemorrhaging into the brain; similar processes can occur in other vascular beds, including the lung. The blockage of functional capillaries by parasitized and/or unparasitized erythrocytes with decreased deformability or rosettes is also a key interaction between hemostasis and mechanical obstruction leading to pathogenesis. The events resulting in the development of cerebral malaria complications are multi-factorial, encompassing a dynamic interaction between three processes, thereby explaining the complexity of this deadly syndrome.

Animals↗

PubMed2005

Cell- rather than antibody-mediated immunity leads to the development of profound thrombocytopenia during experimental Plasmodium berghei malaria.

Experimental malarial thrombocytopenia can reach life-threatening levels and is believed to be due to Abs targeting platelets for destruction by the reticuloendothelial system. However, we report that Abs account for at most 15% of platelet destruction as Plasmodium berghei-infected B cell-deficient mice exhibited profound thrombocytopenia (83%) as did C57BL/6 controls (98%). Further, no significant increase in Abs bound to intact platelets was observed during infection. P. berghei infection can enhance the activity of anti-platelet Abs as indicated by a significantly (p < 0.005) increased thrombocytopenia on day 4 of infection in mice that were administered a low dose anti-CD41 mAb compared with rat IgG1-injected controls. RAG1-/- and CD4- plus CD8-deficient mice were markedly protected from thrombocytopenia (p < 0.005) and malarial pathogenesis. CD8- or TCRgammadelta-deficient mice were not protected from thrombocytopenia and CD4-deficient mice were modestly protected. RAG1-/- mice exhibited significantly (p < 0.05) lower levels of plasma TNF, IFN-gamma, and IL-12 during infection. IFNgamma-/- and IL-12-/- mice exhibited increased survival but similar thrombocytopenia to C57BL/6 controls. Collectively, these data indicate that thrombocytopenia is necessary but not sufficient for malarial pathogenesis and Abs are not the major contributors to malarial thrombocytopenia. Rather, we propose that both CD4+ and CD8+ T cell populations play key roles in malarial thrombocytopenia; a complex bidirectional interaction between cell-mediated immunity and platelets exists during experimental severe malaria that regulates both responses.

Animals↗

PubMed2005

Nitric oxide bioavailability in malaria.

Rational development of adjunct or anti-disease therapy for severe Plasmodium falciparum malaria requires cellular and molecular definition of malarial pathogenesis. Nitric oxide (NO) is a potential target for such therapy but its role during malaria is controversial. It has been proposed that NO is produced at high levels to kill Plasmodium parasites, although the unfortunate consequence of elevated NO levels might be impaired neuronal signaling, oxidant damage and red blood cell damage that leads to anemia. In this case, inhibitors of NO production or NO scavengers might be an effective adjunct therapy. However, increasing amounts of evidence support the alternate hypothesis that NO production is limited during malaria. Furthermore, the well-documented NO scavenging by cell-free plasma hemoglobin and superoxide, the levels of which are elevated during malaria, has not been considered. Low NO bioavailability in the vasculature during malaria might contribute to pathologic activation of the immune system, the endothelium and the coagulation system: factors required for malarial pathogenesis. Therefore, restoring NO bioavailability might represent an effective anti-disease therapy.

Anemia↗

PubMed2005

Plasmodium berghei resists killing by reactive oxygen species.

Reactive oxygen species (ROS) are widely believed to kill malarial parasites. C57BL/6 mice injected with P. berghei inocula incubated with supraphysiological doses of NO (< or =150 microM) or with peroxynitrite (220 microM), however, exhibited parasitemia similar to that seen with those given control inocula, and there was no difference in disease development. Only treatment of inocula with NO doses nearing saturation (> or =1.2 mM) resulted in no detectable parasitemia in the recipients; flow cytometric analysis with a vital dye (hydroethidine) indicated that 1.5 mM NO lysed the erythrocytes rather than killing the parasites. The hemoglobin level in the inocula was about 8 muM; the hemoglobin was mainly oxyhemoglobin (oxyHb) (96%), which was converted to methemoglobin (>95%) after treatment with 150 microM NO. The concentrations of 150 microM of NO and 220 microM of peroxynitrite were far in excess of the hemoglobin concentration (approximately 8 microM), and yet no parasite killing was detected. We therefore conclude that hemoglobin protects Plasmodium parasites from ROS, but the parasite likely possesses intrinsic defense mechanisms against ROS.

Animals↗

PubMed2005

Hemoglobin serves to protect Plasmodium parasites from nitric oxide and reactive oxygen species.

Our understanding of how the host immune response kills Plasmodium, the causative agent of malaria, is limited and controversial. One widely held belief is that reactive oxygen species are crucial for controlling parasite replication. One of the hallmarks of blood-stage malaria is the cyclic rupture of erythrocytes by the parasite, which releases free hemoglobin into the circulation. We propose that this free hemoglobin, as well as the hemoglobin within the erythrocyte and surrounding the parasite, effectively shields Plasmodium from reactive oxygen species well in excess of those achievable in vivo.

Animals↗

PubMed2004

Platelet depletion by anti-CD41 (alphaIIb) mAb injection early but not late in the course of disease protects against Plasmodium berghei pathogenesis by altering the levels of pathogenic cytokines.

Accumulating evidence indicates that platelets play a critical role in the pathogenesis of experimental severe malaria (ESM) elicited by infection with Plasmodium berghei. Mice injected on day 1 of P berghei infection (early) with either anti-CD41 or anti-CD61 monoclonal antibodies (mAbs) exhibited significantly (P<.001) increased survival from ESM compared with infection controls, indicating that platelets function early in the disease. In contrast, groups of mice treated on days 4, 5, and 6 (late) with anti-CD41 mAb exhibited similar mortality as controls. Because platelet depletion by anti-CD41 mAb on day 4 of infection did not protect mice, and platelet adherence occurs on day 6, platelet adherence to endothelium is not required to mediate malarial pathogenesis. Few platelet microparticles were detected in the blood during the course of malaria, but large numbers of erythrocyte vesicles, microparticles, and debris were detected. The protective effect of early anti-CD41 mAb treatment was independent of the number of platelets, platelet microparticles, erythrocyte-platelet conjugates, and erythrocyte vesicles. Mice treated early with anti-CD41 mAb exhibited markedly altered cytokine production on day 4 of P berghei infection (increased interleukin 10 [IL-10], IL-1alpha, IL-6, interferon-gamma [IFN-gamma], and tumor necrosis factor alpha [TNF-alpha]; decreased IL-2) but no decline in coagulation factors compared with rat immunoglobulin G (IgG)-treated controls, indicating that platelets regulate the levels of pathogenic cytokines.

Animals↗

PubMed2003

IL-10 and TGF-beta induce alloreactive CD4+CD25- T cells to acquire regulatory cell function.

We previously reported that interleukin-10 (IL-10) and transforming growth factor (TGF)-beta treatment of primary mixed lymphocyte reaction (MLR) cultures resulted in secondary alloantigen-specific hyporesponsiveness and protection from graft-versus-host disease (GVHD) lethality. Here, we report that CD4+ T cells recovered from the IL-10- and TGF-beta-treated primary MLR cultures have immunoregulatory function. Tolerized cells significantly inhibited proliferation of naive alloreactive CD4+ T cells in a primary MLR. Inhibition of the naive alloresponse was observed with as few as 1 tolerized cell to 10 naive responder cells. Tolerized cells were able to significantly reduce GVHD lethality when injected with naive alloreactive CD4+ T cells into major histocombatibility class (MHC) II disparate recipients. Rigorous CD25 depletion of the primary MLR had no effect on generation of a regulatory capacity, suggesting that the regulatory cells likely originated from CD4+CD25- T cells. Immune suppression was mediated independently of IL-10 and TGF-beta production, as neutralizing antibodies for IL-10, IL-10R, and TGF-beta were unable to revert suppression, and IL-10- deficient CD4+ T cells were able to mediate in vitro and in vivo suppression. The generation of immunoregulatory cells from a CD4+CD25- population during tolerization with IL-10 and TGF-beta provides an additional mechanism to prevent GVHD lethality by T cells that may escape full tolerance induction.

Animals↗