UV004 Modulation of interferon-regulated host cell functions by Toxoplasma gondii facilitates intracellular parasite survival

Wissenschaftliches Programm 55. DGHM-Tagung 29. September-1. Oktober 2003 in Dresden Abstracts - Kurzvortr~ge

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C, pneumoniae infection induces the release of prostaglandin E 2 in human blood monocytes via Cox-2 activation

Rupp, j.1; L0demann, T.~; Solbach, W}; Maass, M}

~University of LObeck; Institute of Medical Microbiology and Hygiene Introduction: Chlamydia pneumoniae (Cp) infection of PBMC has been detected in 20-30% of patients with atherosclerosis, appears refractory to treatment, and may modify cardiovascular risk by promoting vascular inflammation. As the cyclooxygenase-2 (Cox-2) mediated secretion of prostaglandin E2 (PGE2) has been accused to be involved in atherosclerotic lesion formation we analyzed the expression of those factors and their regulation by MAPkinase signaling cascades in Cp-infected human PBMC. Methods and Data: The expression of Cox-2 and subsequently PGE2 in Cpinfected PBMC was determined on mRNA (RT-PCR) and protein level (ELISA). MAPkinase signaling cascades were analysed by specific inhibition of the ERK1/2(UO126) and p38(SB203580) pathway and measurement of the activated phospho-ERK1/2 and phospho-p38 (Western blot). Infection of PBMC with Cp resulted in a rapid (13-fold, l h , n=4) and sustained (5fold, 24h) enhancement of Cox-2 mRNA expression. Subsequently, the expression of PGE2 was significantly induced in Cp-infected PBMC on mRNA (6-fold) and protein (1689 vs. 650 pg/ml) level after 24h. Inhibition of Cox-2 activation in Cp-infected PBMC significantly diminished PGE2 m R N A expression and protein secretion (765 vs. 1343 pg/ml). Cp-induced secretion of PGE2 in PBMC via Cox-2 activation was partially inhibited by blocking the p38-MAP kinase pathway, whereas inhibition of the ERK1/2-MAP kinase pathway had no influence on Cp-induced PGE2 secretion from human PBMC. Conclusions: C. pneumoniae infection in human PBMC results in the expression of the proatherosclerotic mediator PGE2 via sustained Cox-2 activation, which may provide a further link between infection and atherogenesis in humans. Selective Cox-2 inhibitors, which are currently under development for cardiovascular risk reduction, may thus represent a particular therapeutic option for patients with Cpinfected PBMC as they target the pathological signal transduction cascades.

Modulation of interferon-regulated host cell functions by Toxoplasma gondii facilitates intracellular parasite survival Lang, C.1; Gerdes, j.1; AIgner, M.1; Gross, U.1; L0der, C. 1

iUniversity of GOttingen; Department of Bacteriology Introduction Interferon (IFN)-v plays a critical role in immunity against the obligat intracellular protozoan Toxoplasma gondii. However, we have shown previously that 7-. gondii interferes with the IFN-y-induced JAK/STAT signaling cascade in murine macrophages. As a

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Wissenschaftliches Programm 55. DGHM-Tagung 29. September-1. Oktober 2003 in Dresden Abstracts - Kurzvortr~ge

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consequence expression of MHC class II genes and antigen presentation to CD4+ T cells is considerably impaired. Methods and Data We now investigated the impact of the impaired JAK/STAT signaling after Toxoplasma infection on IFN-v-regulated gene expression in general. Infection of murine macrophages by 7-. gondii differentially altered expression of a variety of IFN-y-regulated genes, depending on the gene under investigation. Alterations of the IFN-y-regulated gene expression was not cell type-specific since it was also observed in murine fibroblasts. Among the genes being considerably down-regulated by parasitic infection was that encoding the inducible NO synthase (iNOS), a potentially important effector molecule against intracellular T. gondii. Consequently, protein levels of iNOS as well as NO production was also significantly decreased. Such down-regulation was observed irrespective whether iNOS activity had been induced by IFN-¥, LPS, or both stimuli. Importantly, inhibition of NO production by 7-. gondii enabled considerable parasite replication in macrophages activated with IFN-y alone or LPS alone while the magnitude of inhibition did not suffice to allow parasite propagation in macrophages synergistically activated by IFN-¥ plus LPS. Conclusions Interference of T. gondii with the JAK/STAT signaling pathway considerably alters IFN-y-regulated gene expression of its host cell. The balanced interaction of host cell activation by IFN-¥ and possible other activating molecules and its partial inhibition by the parasite may represent an important mechanism of the parasite-host-equilibrium.

Helicobacter pylori mediated Src inactivation impairs functions of gastric epithelial cells Selbach, M. 1, Moese, S.1; Backert, S.2; Meyer, T.F} ~MPI for Infection Biology; Molecular Biology 2Institut fuer Medizinische Mikrobiologie; Medizinische Mikrobiologie

Helicobacter pylori is a gastric pathogen that resides in the stomach of half of the worlds population. Chronic infection leads to diseases like gastritis, gastric ulcer or even gastric cancer. Virulent H. pylori strains harbour a pathogenicity island (cagPAI) that encodes a type IV secretion system which translocates the bacterial CagA protein into the cytoplasm of gastric epithelial cells. Within the host cell CagA is phosphorylated on tyrosine residues by Src family kinases. At later time points, the accumulation of phosphorylated CagA inactivates the catalytic activity of Src family kinases and induces rearrangements of the host cell actin cytoskeleton. We have investigated the cellular effects of H. pylori induced Src inactivation. AGS gastric epithelial cells were infected with wild-type H. pylori and isogenic knock-out mutants. Cellular responses to CagA translocation and Src inactivation

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