Inhibition of major histocompatibility complex class II-dependent antigen presentation by neutralization of gamma interferon leads to breakdown of resistance against measles virus-induced encephalitis

Roles of IFN-γ in tumor progression and regression: a review

BACKGROUND

Interferon-γ (IFN-γ) plays a key role in activation of cellular immunity and subsequently, stimulation of antitumor immune-response. Based on its cytostatic, pro-apoptotic and antiproliferative functions, IFN-γ is considered potentially useful for adjuvant immunotherapy for different types of cancer. Moreover, it IFN-γ may inhibit angiogenesis in tumor tissue, induce regulatory T-cell apoptosis, and/or stimulate the activity of M1 proinflammatory macrophages to overcome tumor progression. However, the current understanding of the roles of IFN-γ in the tumor microenvironment (TME) may be misleading in terms of its clinical application.

MAIN BODY

Some researchers believe it has anti-tumorigenic properties, while others suggest that it contributes to tumor growth and progression. In our recent work, we have shown that concentration of IFN-γ in the TME determines its function. Further, it was reported that tumors treated with low-dose IFN-γ acquired metastatic properties while those infused with high dose led to tumor regression. Pro-tumorigenic role may be described through IFN-γ signaling insensitivity, downregulation of major histocompatibility complexes, upregulation of indoleamine 2,3-dioxygenase, and checkpoint inhibitors such as programmed cell death ligand 1.

CONCLUSION

Significant research efforts are required to decipher IFN-γ-dependent pro- and anti-tumorigenic effects. This review discusses the current knowledge concerning the roles of IFN-γ in the TME as a part of the complex immune response to cancer and highlights the importance of identifying IFN-γ responsive patients to improve their sensitivity to immuno-therapies.

Maternal antibodies: clinical significance, mechanism of interference with immune responses, and possible vaccination strategies

Neonates have an immature immune system, which cannot adequately protect against infectious diseases. Early in life, immune protection is accomplished by maternal antibodies transferred from mother to offspring. However, decaying maternal antibodies inhibit vaccination as is exemplified by the inhibition of seroconversion after measles vaccination. This phenomenon has been described in both human and veterinary medicine and is independent of the type of vaccine being used. This review will discuss the use of animal models for vaccine research. I will review clinical solutions for inhibition of vaccination by maternal antibodies, and the testing and development of potentially effective vaccines. These are based on new mechanistic insight about the inhibitory mechanism of maternal antibodies. Maternal antibodies inhibit the generation of antibodies whereas the T cell response is usually unaffected. B cell inhibition is mediated through a cross-link between B cell receptor (BCR) with the Fcγ-receptor IIB by a vaccine-antibody complex. In animal experiments, this inhibition can be partially overcome by injection of a vaccine-specific monoclonal IgM antibody. IgM stimulates the B cell directly through cross-linking the BCR via complement protein C3d and antigen to the complement receptor 2 (CR2) signaling complex. In addition, it was shown that interferon alpha binds to the CD21 chain of CR2 as well as the interferon receptor and that this dual receptor usage drives B cell responses in the presence of maternal antibodies. In lieu of immunizing the infant, the concept of maternal immunization as a strategy to protect neonates has been proposed. This approach would still not solve the question of how to immunize in the presence of maternal antibodies but would defer the time of infection to an age where infection might not have such a detrimental outcome as in neonates. I will review successful examples and potential challenges of implementing this concept.

Foxp3+ regulatory T cells control persistence of viral CNS infection

We earlier established a model of a persistent viral CNS infection using two week old immunologically normal (genetically unmodified) mice and recombinant measles virus (MV). Using this model infection we investigated the role of regulatory T cells (Tregs) as regulators of the immune response in the brain, and assessed whether the persistent CNS infection can be modulated by manipulation of Tregs in the periphery. CD4⁺ CD25⁺ Foxp3⁺ Tregs were expanded or depleted during the persistent phase of the CNS infection, and the consequences for the virus-specific immune response and the extent of persistent infection were analyzed. Virus-specific CD8⁺ T cells predominantly recognising the H-2D^b-presented viral hemagglutinin epitope MV-H_22–30 (RIVINREHL) were quantified in the brain by pentamer staining. Expansion of Tregs after intraperitoneal (i.p.) application of the superagonistic anti-CD28 antibody D665 inducing transient immunosuppression caused increased virus replication and spread in the CNS. In contrast, depletion of Tregs using diphtheria toxin (DT) in DEREG (depletion of regulatory T cells)-mice induced an increase of virus-specific CD8⁺ effector T cells in the brain and caused a reduction of the persistent infection. These data indicate that manipulation of Tregs in the periphery can be utilized to regulate virus persistence in the CNS.

Induction of type I interferon secretion through recombinant Newcastle disease virus expressing measles virus hemagglutinin stimulates antibody secretion in the presence of maternal antibodies

Measles virus (MV) vaccine effectively protects seronegative individuals against infection. However, inhibition of vaccine-induced seroconversion by maternal antibodies after vaccination remains a problem, as it leaves infants susceptible to MV infection. In cotton rats, passive transfer of MV-specific IgG mimics maternal antibodies and inhibits vaccine-induced seroconversion. Here, we report that immunization in the presence of passively transferred IgG inhibits the secretion of neutralizing antibodies but not the generation of MV-specific B cells. This finding suggested that MV-specific B cells require an additional stimulus to mature into antibody-secreting plasma cells. In order to provide such a stimulus, we generated a recombinant Newcastle disease virus (NDV) expressing the MV hemagglutinin (NDV-H). In contrast to MV, NDV-H induced high levels of type I interferon in plasmacytoid dendritic cells and in lung tissue. In cotton rats immunized with NDV-H, neutralizing antibodies were also generated in the presence of passively transferred antibodies. In the latter case, however, the level and kinetics of antibody generation were reduced. In vitro, alpha interferon stimulated the activation of MV-specific B cells from MV-immune spleen cells. NDV infection (which induces alpha interferon) had the same effect, and stimulation could be abrogated by antibodies neutralizing alpha interferon, but not interleukin 6 (IL-6). In vivo, coapplication of UV-inactivated MV with NDV led to increased MV-specific antibody production in the presence and absence of passively transferred antibodies. These data indicate that MV-specific B cells are being generated after immunization in the presence of maternal antibodies and that the provision of alpha interferon as an additional signal leads to antibody secretion.

Measles virus infection of the CNS: human disease, animal models, and approaches to therapy

Viral infections of the central nervous system(CNS) mostly represent clinically important, often life-threatening complications of systemic viral infections. After acute measles, CNS complications may occur early (acute postinfectious measles encephalitis, APME) or after years of viral persistence (subacute sclerosing panencephalitis, SSPE). In spite of a presumably functional cell-mediated immunity and high antiviral antibody titers, an immunological control of the CNS infection is not achieved in patients suffering from SSPE. There is still no specific therapy for acute complications and persistent MV infections of the CNS. Hamsters, rats, and (genetically unmodified and modified) mice have been used as model systems to study mechanisms of MV-induced CNS infections. Functional CD4+ and CD8+ T cells together with IFN-gamma are required to overcome the infection. With the help of recombinant measles viruses and mice expressing endogenous or transgenic receptors, interesting aspects such as receptor-dependent viral spread and viral determinants of virulence have been investigated. However, many questions concerning the lack of efficient immune control in the CNS are still open. Recent research opened new perspectives using specific antivirals such as short interfering RNA (siRNA) or small molecule inhibitors. Inspite of obvious hurdles, these treatments are the most promising approaches to future therapies.

Pathogenesis of acute and chronic central nervous system infection with variants of mouse hepatitis virus, strain JHM

Infection of mice with variants of mouse hepatitis virus, strain JHM (MHV-JHM), provide models of acute and chronic viral infection of the central nervous system (CNS). Through targeted recombination and reverse genetic manipulation, studies of infection with MHV-JHM variants have identified phenotypic differences and examined the effects of these differences on viral pathogenesis and anti-viral host immune responses. Studies employing recombinant viruses with a modified spike (S) glycoprotein of MHV-JHM have identified the S gene as a major determinant of neurovirulence. However, the association of S gene variation and neurovirulence with host ability to generate anti-viral CD8 T cell responses is not completely clear. Partially protective anti-viral immune responses may result in persistent infection and chronic demyelinating disease characterized by myelin removal from axons of the CNS and associated with dense macrophage/microglial infiltration. Demyelinating disease during MHV-JHM infection is immune-mediated, as mice that lack T lymphocytes fail to develop disease despite succumbing to encephalitis with high levels of infectious virus in the CNS. However, the presence of T lymphocytes or anti-viral antibody can induce disease in infected immunodeficient mice. The mechanisms by which these immune effectors induce demyelination share an ability to activate and recruit macrophages and microglia, thus increasing the putative role of these cells in myelin destruction.

A mouse model of persistent brain infection with recombinant Measles virus

Measles virus (MV) nucleocapsids are present abundantly in brain cells of patients with subacute sclerosing panencephalitis (SSPE). This invariably lethal brain disease develops years after acute measles as result of a persistent MV infection. Various rodent models for MV infection of the central nervous system (CNS) have been described in the past, in which the detection of viral antigens is based on histological staining procedures of paraffin embedded brains. Here, the usage of a recombinant MV (MV-EGFP-CAMH) expressing the haemagglutinin (H) of the rodent-adapted MV-strain CAM/RB and the enhanced green fluorescent protein (EGFP) is described. In newborn rodents the virus infects neurons and causes an acute lethal encephalitis. From 2 weeks on, when the immune system of the genetically unmodified animal is maturating, intracerebral (i.c.) infection is overcome subclinically, however, a focal persistent infection in groups of neurons remains. The complete brain can be analysed in 50 or 100 microm slices, and infected autofluorescent cells are readily detected. Seven and 28 days post-infection (p.i.) 86 and 81% of mice are infected, respectively, and virus persists for more than 50 days p.i. Intraperitoneal immunization with MV 1 week before infection, but not after infection, protects and prevents persistence. The high percentage of persistence demonstrates that this is a reliable and useful model of a persistent CNS infection in fully immunocompetent mice, which allows the investigation of determinants of the immune system.

Pathogenic role for virus-specific CD4 T cells in mice with coronavirus-induced acute encephalitis

Acute viral encephalitis is believed to result from direct virus destruction of infected cells and from virus-induced host immune response, but the relative contribution of each remains largely unknown. For example, C57BL/6 (B6) mice infected with mouse hepatitis virus (JHM strain, JHMV) develop severe encephalitis, with death occurring within 7 days. Here, we show that the host response to a single JHMV-specific immunodominant CD4 T-cell epitope is critical for severe disease. We engineered a recombinant JHMV with mutations in the immunodominant CD4 T-cell epitope (rJ.M(Y135Q)). Infection of naïve B6 mice with this virus resulted in mild disease with no mortality. However, introduction of a CD4 T-cell epitope from Listeria monocytogenes into rJ.M(Y135Q) generated a highly virulent virus. The decrease in disease severity was not due to a switch from Th1 to Th2 predominance in rJ.M(Y135Q)-infected mice, an effect on CD8 T-cell function, or differential expression of tumor necrosis factor-alpha by JHMV-specific CD4 T cells. These results show that the response to a single virus-specific CD4 T-cell epitope may contribute to a pathogenic host response in the setting of acute viral disease and that abrogation of this response ameliorates clinical disease without diminishing virus clearance.

CD8 T cells require gamma interferon to clear borna disease virus from the brain and prevent immune system-mediated neuronal damage

Borna disease virus (BDV) frequently causes meningoencephalitis and fatal neurological disease in young but not old mice of strain MRL. Disease does not result from the virus-induced destruction of infected neurons. Rather, it is mediated by H-2(k)-restricted antiviral CD8 T cells that recognize a peptide derived from the BDV nucleoprotein N. Persistent BDV infection in mice is not spontaneously cleared. We report here that N-specific vaccination can protect wild-type MRL mice but not mutant MRL mice lacking gamma interferon (IFN-gamma) from persistent infection with BDV. Furthermore, we observed a significant degree of resistance of old MRL mice to persistent BDV infection that depended on the presence of CD8 T cells. We found that virus initially infected hippocampal neurons around 2 weeks after intracerebral infection but was eventually cleared in most wild-type MRL mice. Unexpectedly, young as well as old IFN-gamma-deficient MRL mice were completely susceptible to infection with BDV. Moreover, neurons in the CA1 region of the hippocampus were severely damaged in most diseased IFN-gamma-deficient mice but not in wild-type mice. Furthermore, large numbers of eosinophils were present in the inflamed brains of IFN-gamma-deficient mice but not in those of wild-type mice, presumably because of increased intracerebral synthesis of interleukin-13 and the chemokines CCL1 and CCL11, which can attract eosinophils. These results demonstrate that IFN-gamma plays a central role in host resistance against infection of the central nervous system with BDV and in clearance of BDV from neurons. They further indicate that IFN-gamma may function as a neuroprotective factor that can limit the loss of neurons in the course of antiviral immune responses in the brain.

Astrocyte expression of a dominant-negative interferon-gamma receptor

Interferon-gamma (IFN-gamma) is a major proinflammatory cytokine, and binding to its nearly ubiquitous receptor induces a wide variety of biological functions. To explore the role(s) of IFN-gamma signaling in astrocytes, transgenic mice (GFAP/IFN-gammaR1DeltaIC) expressing a dominant-negative IFN-gamma receptor alpha chain under control of the astrocyte-specific glial fibrillary acid protein (GFAP) promoter were generated. Transgenic mice developed normally, had normal astrocyte numbers and distribution, and exhibited no clinically overt phenotype. Transgene mRNA expression was detected only in the CNS, and the transgene-encoded IFN-gamma receptor 1 colocalized with GFAP, which is consistent with astrocyte expression. Astrocytes from transgenic mice exhibited reduced IFN-gamma-induced signaling as measured by major histocompatibility class II induction. Neither CNS inflammation nor perforin-mediated clearance of a neurotropic mouse hepatitis virus from astrocytes was impaired following infection. Transgenic mice with impaired astrocyte responsiveness to IFN-gamma provide a model for studying the selective astrocyte-dependent effects of this critical cytokine in CNS immunopathology.

A novel intranasal Protollin-based measles vaccine induces mucosal and systemic neutralizing antibody responses and cell-mediated immunity in mice

Protollin-MV is a vaccine produced by mixing split measles virus (MV) antigen with the novel adjuvant Protollin (Neisseria meningitidis outer membrane proteins non-covalently complexed with Shigella flexneri 2a lipopolysaccharide). Intranasal immunization of mice with two or three doses of Protollin-MV induces both serum IgG and mucosal IgA with strong neutralizing activity. There is a dose-dependent shift towards lower IgG1:IgG2a ratios and MV-specific IFNgamma production in splenocytes. Intranasal Protollin-MV can therefore induce systemic and mucosal neutralizing antibody responses as well as elicit a balanced TH1/TH2-type response.

Indoleamine 2,3-dioxygenase mediates cell type-specific anti-measles virus activity of gamma interferon

Gamma interferon (IFN-gamma) has been shown to be increased in sera from patients with acute measles and after vaccination, to exhibit protective functions in brains of patients with subacute sclerosing panencephalitis, and to mediate a noncytolytic clearance of measles virus (MV) from rodent brains. In order to reveal a possible intracellular antiviral activity in the absence of antigen presentation and cytotoxic T cells, we investigated IFN-gamma-induced effects on MV replication in various tissue culture cells. While attenuated MV strains are more sensitive to IFN-alpha/beta than are wild-type strains, IFN-gamma inhibits the replication of all MV strains in epithelial, endothelial, and astroglial cells, but not in lymphoid and neuronal cell lines. The antiviral activity induced by IFN-gamma correlates with the induction of indoleamine 2,3-dioxygenase (IDO), an enzyme of the tryptophan degradation pathway known to mediate antiviral as well as antibacterial and antiparasitic effects. The IFN-gamma-induced antiviral activity can be overcome by the addition of excess amounts of l-tryptophan, which indicates a specific role of IDO in the anti-MV activity. Our data suggest that the IFN-gamma-induced enzyme IDO plays an important antiviral role in MV infections of epithelial, endothelial, and astroglial cells.

The role of IL-12, IL-23 and IFN-gamma in immunity to viruses

IL-12, IL-23 and IFN-γ form a loop and have been thought to play a crucial role against infectious viruses, which are the prototype of “intracellular” pathogens. In the last 10 years, the generation of knock-out (KO) mice for genes that control IL-12/IL-23-dependent IFN-γ-dependent mediated immunity (STAT1, IFN-γR1, IFNγR2, IL-12p40 and IL-12Rβ1) and the identification of patients with spontaneous germline mutations in these genes has led to a re-examination of the role of these cytokines in anti-viral immunity. We here review viral infections in mice and humans with genetic defects in the IL-12/IL-23-IFN-γ axis. A comparison of the phenotypes observed in KO mice and deficient patients suggests that the human IL-12/IL-23-IFN-γ axis plays a redundant role in immunity to most viruses, whereas its mouse counterparts play a more important role against several viruses.

Perforin and gamma interferon-mediated control of coronavirus central nervous system infection by CD8 T cells in the absence of CD4 T cells

Infection of the central nervous system (CNS) with the neurotropic JHM strain of mouse hepatitis virus produces acute and chronic demyelination. The contributions of perforin-mediated cytolysis and gamma interferon (IFN-gamma) secretion by CD8(+) T cells to the control of infection and the induction of demyelination were examined by adoptive transfer into infected SCID recipients. Untreated SCID mice exhibited uncontrolled virus replication in all CNS cell types but had little or no demyelination. Memory CD8(+) T cells from syngeneic wild-type (wt), perforin-deficient, or IFN-gamma-deficient (GKO) donors all trafficked into the infected CNS in the absence of CD4(+) T cells and localized to similar areas. Although CD8(+) T cells from all three donors suppressed virus replication in the CNS, GKO CD8(+) T cells expressed the least antiviral activity. A distinct viral antigen distribution in specific CNS cell types revealed different mechanisms of viral control. While wt CD8(+) T cells inhibited virus replication in all CNS cell types, cytolytic activity in the absence of IFN-gamma suppressed the infection of astrocytes, but not oligodendroglia. In contrast, cells that secreted IFN-gamma but lacked cytolytic activity inhibited replication in oligodendroglia, but not astrocytes. Demyelination was most severe following viral control by wt CD8(+) T cells but was independent of macrophage infiltration. These data demonstrate the effective control of virus replication by CD8(+) T cells in the absence of CD4(+) T cells and support the necessity for the expression of distinct effector mechanisms in the control of viral replication in distinct CNS glial cell types.

Measles Virus 1998–2002: Progress and Controversy

Despite the extensive media exposure that viruses such as West Nile, Norwalk, and Ebola have received lately, and the emerging threat that old pathogens may reappear as new agents of terrorism, measles virus (MV) persists as one of the leading causes of death by infectious agents worldwide, approaching the annual mortality rate of human immunodeficiency virus (HIV)-1. For most MV victims, fatality is indirect: Virus-induced transient immunosuppression predisposes the individual to opportunistic infections that, left untreated, can result in mortality. In rare cases, MV may also cause progressive neurodegenerative disease. During the past five years (1998-2002), development of animal models and the application of reverse genetics and immunological assays have collectively contributed to major progress in our understanding of MV biology and pathogenesis. Nevertheless, questions and controversies remain that are the basis for future research. In this review, major advances and current debates are discussed, including MV receptor usage, the cellular basis of immunosuppression, the suspected role of MV in "nonviral" diseases such as multiple sclerosis and Paget's disease, and the controversy surrounding MV vaccine safety.

T cell responses in acute measles

Immune containment of measles virus (MV) infection has long been a focus of interest for investigators. An emerging theme is that MV immunity is conferred by appropriately polarized antiviral CD4+ and CD8+ T cell populations. Recent technological advances permit the analysis of the composition and dynamics of these CD4+ and CD8+ T cell responses at the single cell level, and of the molecular events responsible for their induction. Novel insights into these issues for measles are discussed in the light of their importance for the development of an improved vaccine.

Measles virus-specific T-cell immunity in rodent models

Measles virus (MV) infection still belongs to the most important infectious diseases world wide. To identify the components of the immune system that combat MV infection, infection models in rodents have been established. In rats and mice, the immune response to experimental MV infection is governed by the major histocombatibility complex (MHC). According to the MHC haplotype, the functional composition of the T-cell subsets determines the degree of susceptibility to experimental measles virus infection. CD4+ T-cells are the most important T-cell subset in combating experimental MV infection in rodents. However, the mechanism of action still remains to be elucidated.

Oral immunization with recombinant Yersinia enterocolitica expressing a measles virus CD4 T cell epitope protects against measles virus-induced encephalitis

Immunization via the oral route with an attenuated Yersinia enterocolitica strain expressing a fragment of the measles virus nucleocapsid protein (aa 79-161) via its type III protein secretion system induced a T helper type 1 response in immunized C3H mice, which conferred protection against measles virus-induced encephalitis in a time- and dose-dependent manner.