Andreas Meryk

Tissue macrophages suppress viral replication and prevent severe immunopathology in an interferon-I-dependent manner in mice

The innate immune response plays an essential role in the prevention of early viral dissemination. We used the lymphocytic choriomeningitis virus model system to analyze the role of tissue macrophages/Kupffer cells in this process. Our findings demonstrated that Kupffer cells are essential for the efficient capture of infectious virus and for preventing viral replication. The latter process involved activation of Kupffer cells by interferon (IFN)‐I and prevented viral spread to neighboring hepatocytes. In the absence of Kupffer cells, hepatocytes were not able to suppress virus replication, even in the presence of IFN‐I, leading to prolonged viral replication and severe T cell‐dependent immunopathology. Conclusion: Tissue‐resident macrophages play a crucial role in early viral capture and represent the major liver cell type exhibiting responsiveness to IFN‐I and providing control of viral replication. (HEPATOLOGY 2010)

Involvement of Toso in activation of monocytes, macrophages, and granulocytes

Rapid activation of immune responses is necessary for antibacterial defense, but excessive immune activation can result in life-threatening septic shock. Understanding how these processes are balanced may provide novel therapeutic potential in treating inflammatory disease. Fc receptors are crucial for innate immune activation. However, the role of the putative Fc receptor for IgM, known as Toso/Faim3, has to this point been unclear. In this study, we generated Toso-deficient mice and used them to uncover a critical regulatory function of Toso in innate immune activation. Development of innate immune cells was intact in the absence of Toso, but Toso-deficient neutrophils exhibited more reactive oxygen species production and reduced phagocytosis of pathogens compared with controls. Cytokine production was also decreased in Toso−/− mice compared with WT animals, rendering them resistant to septic shock induced by lipopolysaccharide. However, Toso−/− mice also displayed limited cytokine production after infection with the bacterium Listeria monocytogenes that was correlated with elevated presence of Listeria throughout the body. Accordingly, Toso−/− mice succumbed to infections of L. monocytogenes, whereas WT mice successfully eliminated the infection. Taken together, our data reveal Toso to be a unique regulator of innate immune responses during bacterial infection and septic shock.

Interferon-alpha Subtype 11 Activates NK Cells and Enables Control of Retroviral Infection

The innate immune response mediated by cells such as natural killer (NK) cells is critical for the rapid containment of virus replication and spread during acute infection. Here, we show that subtype 11 of the type I interferon (IFN) family greatly potentiates the antiviral activity of NK cells during retroviral infection. Treatment of mice with IFN-α11 during Friend retrovirus infection (FV) significantly reduced viral loads and resulted in long-term protection from virus-induced leukemia. The effect of IFN-α11 on NK cells was direct and signaled through the type I IFN receptor. Furthermore, IFN-α11-mediated activation of NK cells enabled cytolytic killing of FV-infected target cells via the exocytosis pathway. Depletion and adoptive transfer experiments illustrated that NK cells played a major role in successful IFN-α11 therapy. Additional experiments with Mouse Cytomegalovirus infections demonstrated that the therapeutic effect of IFN-α11 is not restricted to retroviruses. The type I IFN subtypes 2 and 5, which bind the same receptor as IFN-α11, did not elicit similar antiviral effects. These results demonstrate a unique and subtype-specific activation of NK cells by IFN-α11.

Oxidized ATP inhibits T‐cell‐mediated autoimmunity

T cells directed against self antigens play an important role in several autoimmune diseases. The available immunosuppressive compounds used to treat autoimmune diseases are limited, and often they have side effects that limit their application. T cells express ATP receptors, which could be new target molecules to treat autoimmune disease. Here we analyzed the effect of oxidized ATP (oxATP), an inhibitor of the ATP receptor P2rx7, in different murine models of T‐cell‐mediated autoimmune diseases. Treatment with oxATP inhibited proliferation and effector function of T cells. In the systems we used, oxATP did not obviously interfere with the innate immune response, but strongly reduced antigen‐specific T‐cell responses. This treatment ameliorated T‐cell‐mediated autoimmune type I diabetes and autoimmune encephalitis in mice. In conclusion, oxATP was found to strongly inhibit activated T cells and could thus be used to target T‐cell‐mediated autoimmune disease.

Reduced type I interferon production by dendritic cells and weakened antiviral immunity in patients with Wiskott-Aldrich syndrome protein deficiency.

Background Wiskott-Aldrich syndrome (WAS) is a rare X-linked primary immunodeficiency caused by absence of Wiskott-Aldrich syndrome protein (WASP) expression, resulting in defective function of many immune cell lineages and susceptibility to severe bacterial, viral, and fungal infections. Despite a significant proportion of patients with WAS having recurrent viral infections, surprisingly little is known about the effects of WASP deficiency on antiviral immunity. Objective We sought to evaluate the antiviral immune response in patients with WASP deficiency in vivo. Methods Viral clearance and associated immunopathology were measured after infection of WASP-deficient (WAS KO) mice with lymphocytic choriomeningitis virus (LCMV). Induction of antiviral CD8+ T-cell immunity and cytotoxicity was documented in WAS KO mice by means of temporal enumeration of total and antigen-specific T-cell numbers. Type I interferon (IFN-I) production was measured in serum in response to LCMV challenge and characterized in vivo by using IFN-I reporter mice crossed with WAS KO mice. Results WAS KO mice showed reduced viral clearance and enhanced immunopathology during LCMV infection. This was attributed to both an intrinsic CD8+ T-cell defect and defective priming of CD8+ T cells by dendritic cells (DCs). IFN-I production by WAS KO DCs was reduced both in vivo and in vitro. Conclusions These studies use a well-characterized model of persistence-prone viral infection to reveal a critical deficiency of CD8+ T-cell responses in murine WASP deficiency, in which abrogated production of IFN-I by DCs might play an important contributory role. These findings might help us to understand the immunodeficiency of WAS.

Reply to Honjo et al.: Functional relevant expression of Toso on granulocytes

Functional relevant expression of Toso on granulocytes. (A) Toso expression. Splenocytes from WT and Toso−/− mice were immunostained with anti-CD19 (B cells) and anti-Gr1 (granulocytes) antibody in combination with DAPI and anti-Toso antibody after pretreatment with Fc receptor block. One representative staining of cells gated on Gr1hi DAPI− cells (Left) or CD19+ DAPI− cells is shown (Right). (B) Quantification of FACS stainings derived from A (n = 4/group). (C–E) WT recipient mice were irradiated and reconstituted with BM from WT mice (CD45.1; group 1), Toso−/− mice (CD45.2; group 2), or a 1:1 mixture of WT and Toso−/− BM (group 3). At 30 d posttransplantation, peripheral blood cells were stimulated with different concentrations of fMLP (Formyl-Methionyl-Leucyl-Phenylalanine) and granulocytes (Gr1+ cells) were analyzed after 30 min for CD45.1 expression (anti-CD45.1), CD45.2 expression (anti-CD45.2), reactive oxygen species production (dihydrorhodamine staining), and degranulation (side scatter). Representative FACS …

Toso regulates differentiation and activation of inflammatory dendritic cells during persistence-prone virus infection.

During virus infection and autoimmune disease, inflammatory dendritic cells (iDCs) differentiate from blood monocytes and infiltrate infected tissue. Following acute infection with hepatotropic viruses, iDCs are essential for re-stimulating virus-specific CD8+ T cells and therefore contribute to virus control. Here we used the lymphocytic choriomeningitis virus (LCMV) model system to identify novel signals, which influence the recruitment and activation of iDCs in the liver. We observed that intrinsic expression of Toso (Faim3, FcμR) influenced the differentiation and activation of iDCs in vivo and DCs in vitro. Lack of iDCs in Toso-deficient (Toso–/–) mice reduced CD8+ T-cell function in the liver and resulted in virus persistence. Furthermore, Toso–/– DCs failed to induce autoimmune diabetes in the rat insulin promoter-glycoprotein (RIP-GP) autoimmune diabetes model. In conclusion, we found that Toso has an essential role in the differentiation and maturation of iDCs, a process that is required for the control of persistence-prone virus infection.

O003 Interferon alpha subtype 11 activates NK cells and enables control of retroviral infection

Introduction Type I Interferons (IFNs) are a multigene family with up to 14 different IFNα subtypes. IFNs have direct anti-viral activity mediated by the induction of anti-viral enzymes, but they also stimulate cells of the innate and adaptive immune system. Various studies demonstrated distinct anti-viral activities of specific IFNα subtypes but their immunomodulatory properties during viral infections have not been investigated. The innate immune response mediated by cells such as natural killer (NK) cells is critical for the rapid containment of virus replication and spread during acute infection. In this study we are interested on the specific immunomodulatory effects of various IFNα subtypes on NK cell functions during retroviral infections. Methods We used different IFNα subtypes for immunotherapy of acute Friend retrovirus (FV) infection in mice to study their immunomodulatory effects in vivo . For that purpose, we did FACS analysis of different lymphocyte populations, analysis of viral loads, cell depletion experiments, adoptive transfer and in vitro cytotoxicity assays. Result Treatment of mice with IFNα11 during FV infection significantly reduced viral loads and resulted in long-term protection from virus-induced leukemia. The effect of IFNα11 on NK cells was direct and signaled through the type I IFN receptor. Furthermore, IFNα11-mediated activation of NK cells enabled cytolytic killing of FV-infected target cells via the exocytosis pathway. Depletion and adoptive transfer experiments illustrated that NK cells played a major role in successful IFNα11 therapy. Additional experiments with Mouse Cytomegalovirus infections demonstrated that the therapeutic effect of IFNα11 is not restricted to retroviruses. The type I IFN subtypes 2 and 5, which bind the same receptor as IFNα11, did not elicit similar antiviral effects. These results demonstrate a unique and subtype-specific activation of NK cells by IFNα11.