Branka Popović

IL-1R8 is a checkpoint in NK cells regulating anti-tumour and anti-viral activity

Interleukin-1 receptor 8 (IL-1R8, also known as single immunoglobulin IL-1R-related receptor, SIGIRR, or TIR8) is a member of the IL-1 receptor (ILR) family with distinct structural and functional characteristics, acting as a negative regulator of ILR and Toll-like receptor (TLR) downstream signalling pathways and inflammation. Natural killer (NK) cells are innate lymphoid cells which mediate resistance against pathogens and contribute to the activation and orientation of adaptive immune responses. NK cells mediate resistance against haematopoietic neoplasms but are generally considered to play a minor role in solid tumour carcinogenesis. Here we report that IL-1R8 serves as a checkpoint for NK cell maturation and effector function. Its genetic blockade unleashes NK-cell-mediated resistance to hepatic carcinogenesis, haematogenous liver and lung metastasis, and cytomegalovirus infection.

Viral inhibition of BAK promotes murine cytomegalovirus dissemination to salivary glands

ABSTRACT Apoptosis induction is an important host defense mechanism to control viral infection, which is antagonized by viral proteins. Murine cytomegalovirus m41.1 encodes a viral inhibitor of BAK oligomerization (vIBO) that blocks the mitochondrial apoptosis mediator BAK. However, its importance for viral fitness in vivo has not been investigated. Here, we show that an m41.1-deficient virus attains reduced titers in salivary glands of wild-type but not Bak1 −/− mice, indicating a requirement of BAK inhibition for optimal dissemination in vivo.

IL-33/ST2 pathway drives regulatory T cell dependent suppression of liver damage upon cytomegalovirus infection.

Regulatory T (Treg) cells dampen an exaggerated immune response to viral infections in order to avoid immunopathology. Cytomegaloviruses (CMVs) are herpesviruses usually causing asymptomatic infection in immunocompetent hosts and induce strong cellular immunity which provides protection against CMV disease. It remains unclear how these persistent viruses manage to avoid induction of immunopathology not only during the acute infection but also during life-long persistence and virus reactivation. This may be due to numerous viral immunoevasion strategies used to specifically modulate immune responses but also induction of Treg cells by CMV infection. Here we demonstrate that liver Treg cells are strongly induced in mice infected with murine CMV (MCMV). The depletion of Treg cells results in severe hepatitis and liver damage without alterations in the virus load. Moreover, liver Treg cells show a high expression of ST2, a cellular receptor for tissue alarmin IL-33, which is strongly upregulated in the liver of infected mice. We demonstrated that IL-33 signaling is crucial for Treg cell accumulation after MCMV infection and ST2-deficient mice show a more pronounced liver pathology and higher mortality compared to infected control mice. These results illustrate the importance of IL-33 in the suppressive function of liver Treg cells during CMV infection.

Murine Cytomegalovirus Infection Induces Susceptibility to EAE in Resistant BALB/c Mice

In contrast to C57BL/6 mice, BALB/c mice are relatively resistant to the induction of experimental autoimmune encephalomyelitis (EAE) after challenge with MOG35–55 peptide. Here, we provide the first evidence that infection with murine cytomegalovirus (MCMV) in adulthood abrogates this resistance. Infected BALB/c mice developed clinical and histological signs similar to those seen in susceptible C57BL/6 mice. In addition to CD4+ cells, large proportion of cells in the infiltrate of diseased BALB/c mice was CD8+, similar with findings in multiple sclerosis. CD8+ cells that responded to ex vivo restimulation with MOG35–55 were not specific for viral epitopes pp89 and m164. MCMV infection favors proinflammatory type of dendritic cells (CD86+CD40+CD11c+) in the peripheral lymph organs, M1 type of microglia in central nervous system, and increases development of Th1/Th17 encephalitogenic cells. This study indicates that MCMV may enhance autoimmune neuropathology and abrogate inherent resistance to EAE in mouse strain by enhancing proinflammatory phenotype of antigen-presenting cells, Th1/Th17, and CD8 response to MOG35–55.

NCR1‐deficiency diminishes the generation of protective murine cytomegalovirus antibodies by limiting follicular helper T‐cell maturation

NKp46/NCR1 is an activating NK‐cell receptor implicated in the control of various viral and bacterial infections. Recent findings also suggest that it plays a role in shaping the adaptive immune response to pathogens. Using NCR1‐deficient (NCR1gfp/gfp) mice, we provide evidence for the role of NCR1 in antibody response to mouse cytomegalovirus infection (MCMV). The absence of NCR1 resulted in impaired maturation, function and NK‐cell migration to regional lymph nodes. In addition, CD4+ T‐cell activation and follicular helper T‐cell (Tfh) generation were reduced, leading to inferior germinal center (GC) B‐cell maturation. As a consequence, NCR1gfp/gfp mice produced lower amounts of MCMV‐specific antibodies upon infection, which correlated with lower number of virus‐specific antibody secreting cells in analyzed lymph nodes.

Latent Murine Cytomegalovirus Infection Contributes to EAE Pathogenesis / Latentna Infekcija Mišjim Citomegalovirusom Ima Ulogu U Patogenezi Eksperimentalnog Autoimunskog Encefalomijelitisa

ABSTRACT Viral infection has been identified as the most likely environmental trigger of multiple sclerosis (MS). There are conflicting data regarding the role of cytomegalovirus (CMV) in MS pathogenesis. We utilised experimental autoimmune encephalomyelitis (EAE)-resistant BALB/c mice and murine cytomegalovirus (MCMV), the murine homolog of CMV, to examine the mechanism by which viral infection enhances autoimmune neuroinflammation. Mice subjected to latent neonatal MCMV infection developed the typical characteristics of EAE. Similar to MS, the MCMV-infected EAE-induced mice developed infiltrates in the central nervous system (CNS) composed of similar percentages of CD4+ and CD8+ T cells. The influx of both Th 1 and Th 17 cells into the CNS of MCMV- infected EAE-induced mice was observed. Interestingly, the development of autoimmune neuroinflammation after latent MCMV infection was accompanied by a significant influx of Tc17 cells (CD8+IL-17+ and CD8+RoRγt+) but not Tc1, cells. Our results suggest that latent MCMV infection affects the development of inflammatory lymphocytes that exhibit encephalitogenic potential, thereby mediating increased CNS pathology following EAE induction, and that CMV represents a possible environmental factor in the pathogenesis of MS and other autoimmune diseases SAŽETAK Virusna infekcija se navodi kao najverovatniji faktor okoline koji utiče na razvoj multiple skleroze (MS). Postoje konfliktni podaci o ulozi infekcije citomegalovirusom (CMV) u patogenezi multiple skleroze. Koristili smo BALB/c miševe, rezistentne na indukciju eksperimentalnog autoimunskog encefalomijelitisa (EAE), i mišji citomegalovirus (MCMV), mišji homolog humanom citomegalovirusu da ispitamo kako virusna infekcija može da utiče na razvoj autoimunske neuroinflamacije. Miševi sa latentnom neonatalnom infekcijom mišjim citomegalovirusom su razvili tipičan EAE. Slično kao u MS, MCMV EAE miševi su razvili infiltrate u centralnom nervnom sistemu (CNS) sa sličnom zastupljenošću CD4+ i CD8+ T limfocita. Uočen je influks i Th 1 i Th 17 ćelija u CNS MCMV EAE miševa. Interesantno je da razvoj autoimunske inflamacije nakon latentne MCMV infekcije prati značajan influks samo Tc17 (CD8+IL-17+ i CD8+RoRγt+), a ne i Tc1 ćelija. Naši rezultati ukazuju da latentna MCMV infekcija verovatno utiče na razvoj inflamatornih limfocita koji mogu da indukuju autoimunski proces u CNS-u, direktno pojačava razvoj patoloških procesa u CNS-u nakon indukcije EAE i ukazuje na CMV kao na mogući faktor okoline koji utiče na razvoj multiple skleroze i drugih autoimunskih bolesti.

Mouse cytomegalovirus encoded immunoevasins and evolution of Ly49 receptors - sidekicks or enemies?

Cytomegaloviruses (CMVs) have dedicated a large portion of their genome towards immune evasion targeting many aspects of the host immune system, particularly NK cells. However, the host managed to cope with the infection by developing multiple mechanisms to recognize viral threat and counterattack it, thus illustrating never-ending evolutionary interplay between CMV and its host. In this review, we will focus on several mechanisms of NK cell evasion by mouse CMV (MCMV), the role of host inhibitory and activating Ly49 receptors involved in the virus control and acquisition of adaptive features by NK cells as a consequence of MCMV infection.

Intrinsic Contribution of Perforin to NK-Cell Homeostasis during Mouse Cytomegalovirus Infection

In addition to their role as effector cells in virus control, natural killer (NK) cells have an immunoregulatory function in shaping the antiviral T-cell response. This function is further pronounced in perforin-deficient mice that show the enhanced NK-cell proliferation and cytokine secretion upon mouse cytomegalovirus (MCMV) infection. Here, we confirmed that stronger activation and maturation of NK cells in perforin-deficient mice correlates with higher MCMV load. To further characterize the immunoregulatory potential of perforin, we compared the response of NK cells that express or do not express perforin using bone-marrow chimeras. Our results demonstrated that the enhanced proliferation and maturation of NK cells in MCMV-infected bone-marrow chimeras is an intrinsic property of perforin-deficient NK cells. Thus, in addition to confirming that NK-cell proliferation is virus load dependent, our data extend this notion demonstrating that perforin plays an intrinsic role as a feedback mechanism in the regulation of NK-cell proliferation during viral infections.

CMV infection facilitates EAE development in resistant BALB/c mice

regarded as an important pathogenetic factor that contributes to chronic neuroinflammation.We determined a relationship between EBV, HHV-6 and HHV-7 viral load in the saliva and serum levels of pro-inflammatory cytokines (IFNalpha, IFNgamma, IL-1, IL-2) in a group of ME patients. Materials: 32 ME patients (11 female, mean age 32 ± 5) were enrolled into the study. The patients were divided into groups based on viral load and on viruses detected. 30 volunteers (12 female, mean age 32.3 ± 4.7) were enrolled as controls. Real-time quantitative PCR was used to assess the viral load, and ELISA was used to assess serum cytokine levels. Mann–Whitney U-test was used for statistical analysis. Results: Mean cytokine levels were higher in ME patients than in controls. To study the impact of EBV on cytokine levels, EBV-positiveME patients (n = 19) were divided into group 1 (EBV b 4 lg copies/ml) and group 2 (EBV N 4 lg copies/ml). Mean IFNgamma level differed significantly (p b 0.01) between groups (121.26 ± 41.76 pg/ml and 13.15 ± 5.76 pg/ml), and mean IL-2 level differed (p= 0.05) between groups (33.3 ± 15.66 pg/ml and 17 ± 16.8 pg/ml). Also, in group 2 EBV load correlatedwell with IFNgamma (r =−0.5, p b 0.05) andwith IL-2 levels (r =−0.56, p b 0.025). Mean IFNgamma and IL-2 levels were lower in patientswith EBV/HHV-6 coinfection then in patientswith EBV and without HHV-6, but the difference was not significant. To study the role of HHV-7 inME, we determined HHV-7 load in 22 random patients from ME group. In these patients, HHV-7 load N 6 lg copies/ml was a good marker for EBV load N 4 lg copies/ml (sensitivity 70%, specificity 100%), and HHV-7 load correlated well with EBV load (r = 0.8524, p b 0.001). 2 groups were formed based on HHV-7 load: group 1b (HHV-7 b 6 lg c/ml), and group 2b (HHV-7 N 6 lg c/ml). Mean EBV load differed significantly (p b 0.05) between groups (3.3 ± 0.6 lg copies/ml and 5.49 ± 0.76 lg copies/ml). Conclusions: ME patients differ in Th1-cell cytokine levels (IFNgamma and IL-2) depending on EBV viral load in the saliva. This result supports the suppressive impact of EBV on IFNgamma secretion described in vitro. HHV-7 viral load has predictive value for EBV viral load in ME patients. We are planning to assess cytokines in saliva as well as in blood serum of ME patients.