Response to influenza infection in mice with a targeted disruption in the interferon gamma gene

Persistent high plasma levels of interleukins 18 and 4 in children with recurrent infections of the upper respiratory tract

The aim of this study was to examine whether children with recurrent infections of the upper respiratory tract might have alterations in the systemic immune response to viral infections as compared with healthy control children. We quantitated plasma levels of interferon-gamma, interleukin-12, interleukin-18, interleukin-4, lymphocyte subpopulations, serum immunoglobulins, and subclasses of immunoglobulin G in 30 children under the age of 6 years with recurrent infections of the upper respiratory tract, both during the acute phase of the infection and 4 weeks later, when clinical symptoms had resolved, as well as in 20 normal controls. We found elevated levels of immunoglobulin G primarily due to increased levels of immunoglobulin G(1). Moreover, significantly higher levels of interleukin-18 and interleukin-4 were noted during the acute phase of infection among children with an increased incidence of respiratory infections as compared with the controls (P =.022 and P =.0001, respectively), while plasma levels of interferon-gamma and interleukin-12 were significantly lower (P =.034 and P =.0001, respectively) than in controls. We suggest that an imbalance between T-cell helper type-1 and T-cell helper type-2 immune responses might be responsible for the perpetuation of recurrent infections of the upper respiratory tract.

IFNgamma deficient C57BL/6 (H-2b) mice develop collagen induced arthritis with predominant usage of T cell receptor Vbeta6 and Vbeta8 in arthritic joints

BACKGROUND

Transgenic deficiency in interferon gamma (IFNgamma) or IFNgamma receptor makes resistant strains of mice bearing H-2(b) or H-2(d) susceptible to collagen induced arthritis (CIA).

OBJECTIVE

To determine whether the escape from regulation of disease susceptibility at the major histocompatibility complex level involves a new use of autoimmune T cells expressing T cell receptor (TCR) Vbeta that vary from the cell populations previously identified within arthritic joints.

METHODS

Arthritis was induced by a standard protocol with type II bovine collagen (CII) in complete Freund's adjuvant. Clinical features, histopathology, immunological responses, and TCR profile in arthritic joints in IFNgamma knockout C57BL/6 (B6.IFNgamma KO) mice (H-2(b)) were compared directly with those in DBA/1 mice (H-2(q)).

RESULTS

60-80% of B6.IFNgamma KO mice developed a progressive arthritis with a similar clinical course to classical CIA in DBA/1 mice. The affected joints in B6.IFNgamma KO mice had an erosive form of arthritis with similar features to joint disease in DBA/1 mice. B6.IFNgamma KO mice produced significantly higher levels of IgG2b and IgG1 autoantibodies to murine CII and showed increased proliferative response to CII compared with B6 mice. Comparable levels of interleukin 1beta and tumour necrosis factor alpha expression were detected in arthritic joints from beta6.IFNgamma KO and DBA/1 mice. B6.IFNgammaKO mice used predominantly TCR Vbeta6 and Vbeta8 in arthritic joints. This TCR Vbeta profile is similar to that found in DBA/1 mice with CIA.

CONCLUSIONS

C57BL/6 mice deficient in IFNgamma production can develop arthritis that resembles classical CIA. These data suggest that IFNgamma is a key factor mediating susceptibility to CIA.

Vaccine immunity to pathogenic fungi overcomes the requirement for CD4 help in exogenous antigen presentation to CD8+ T cells: implications for vaccine development in immune-deficient hosts

Systemic fungal infections with primary and opportunistic pathogens have become increasingly common and represent a growing health menace in patients with AIDS and other immune deficiencies. T lymphocyte immunity, in particular the CD4+ Th 1 cells, is considered the main defense against these pathogens, and their absence is associated with increased susceptibility. It would seem illogical then to propose vaccinating these vulnerable patients against fungal infections. We report here that CD4+ T cells are dispensable for vaccine-induced resistance against experimental fungal pulmonary infections with two agents, Blastomyces dermatitidis an extracellular pathogen, and Histoplasma capsulatum a facultative intracellular pathogen. In the absence of T helper cells, exogenous fungal antigens activated memory CD8+ cells in a major histocompatibility complex class I-restricted manner and CD8+ T cell-derived cytokines tumor necrosis factor alpha, interferon gamma, and granulocyte/macrophage colony-stimulating factor-mediated durable vaccine immunity. CD8+ T cells could also rely on alternate mechanisms for robust vaccine immunity, in the absence of some of these factors. Our results demonstrate an unexpected plasticity of immunity in compromised hosts at both the cellular and molecular level and point to the feasibility of developing vaccines against invasive fungal infections in patients with severe immune deficiencies, including those with few or no CD4+ T cells.

Infection-triggered regulatory mechanisms override the role of STAT 4 in control of the immune response to influenza virus antigens

Accurate control of the balance of the T1 and T2 cells during antiviral immunity is essential for optimizing immune effector functions and for avoiding potentially severe immunopathology. We examined the in vivo role of the signal transducer and activator of transcription (STAT) 4 in regulating the T1/T2 balance during the response to live influenza virus and isolated viral proteins. We found that the differentiation of gamma interferon (IFN-gamma)-producing Th1 and Tc1 cells after inoculation of live virus occurred independently of STAT 4 expression. Influenza virus-specific T2 and Tc2 responses were well controlled in such STAT 4-deficient mice unless IFN-gamma was eliminated as well. In contrast, the STAT 4-dependent signaling pathway played a more essential role in regulating the T1/T2 balance after immunization with viral proteins and, in particular, inactivated nonreplicating virus. Pulmonary infection was cleared even in the absence of both functional STAT 4 genes and functional IFN-gamma genes because virus-neutralizing antibodies were still generated, consistent with a substantial redundancy in different antiviral effector pathways. Thus, replicating agents such as live influenza virus can elicit IFN-gamma and control T2 immunity independently of STAT 4, whereas the profile of immunity to isolated proteins is more reliant on an intact STAT 4 signaling pathway.

Single-cell perforin and granzyme expression reveals the anatomical localization of effector CD8+ T cells in influenza virus-infected mice

Influenza virus infection activates cytolytic T lymphocytes (CTL) that contribute to viral clearance by releasing perforin and granzymes from cytoplasmic granules. Virus-specific, perforin-dependent CD8(+) CTL were detected in freshly isolated cells from the mouse lung parenchyma but not from the mediastinal lymph nodes (MLN), where they are primed, or from the spleen during primary influenza virus infection. To determine whether this difference was due to the low frequency or incomplete maturation of effector CTL in MLN, we measured expression of perforin, granzymes A, B, and C, and IFN-gamma mRNAs in CD8(+) populations and single cells immediately after isolation from virus-infected mice. Quantitative PCR revealed significant expression of perforin, granzyme A, granzyme B, and IFN-gamma in activated CD8(+) cells from MLN, spleen, and lung parenchyma. Granzyme C expression was not detected. Individual activated or nucleoprotein peptide/class I tetramer-binding CD8(+) cells from the three tissues expressed diverse combinations of perforin, granzyme, and IFN-gamma mRNAs. Although cells from lung expressed granzymes A and B at higher frequency, each of the tissues contained cells that coexpressed perforin with granzymes A and/or B. The main difference between MLN and lung was the elevated frequency of activated CD8(+) T cells in the lung, rather than their perforin/granzyme expression profile. The data suggest that some CTL mature into perforin/granzyme-expressing effector cells in MLN but reach detectable frequencies only when they accumulate in the infected lung.

Cytokines and the immune-testicular axis

Cytokines are regulatory proteins involved in haematopoiesis, immune cell development, inflammation and immune responses. Several cytokines have direct effects on testicular cell functions, and a number of these are produced within the testis even in the absence of inflammation or immune activation events. There is compelling evidence that cytokines, in fact, play an important regulatory role in the development and normal function of the testis. Pro-inflammatory cytokines including interleukin-1 and interleukin-6 have direct effects on spermatogenic cell differentiation and testicular steroidogenesis. Stem cell factor and leukaemia inhibitory factor, cytokines normally involved in haematopoiesis, also play a role in spermatogenesis. Anti-inflammatory cytokines of the transforming growth factor-beta family are implicated in testicular development. Consequently, local or systemic up-regulation of cytokine expression during injury, illness or infection may contribute to the disruption of testicular function and fertility that frequently accompanies these conditions. The aim of this review is to provide a very brief summary of the extensive literature dealing with cytokines in testicular biology, and to follow this with some speculation concerning the significance of these molecules in interactions between the immune system and the testis.

Requisite elements in vaccine immunity to Blastomyces dermatitidis: plasticity uncovers vaccine potential in immune-deficient hosts

Understanding fundamental mechanisms of vaccine immunity will allow proper use and optimization of vaccines. Vaccination with a genetically engineered, live, attenuated strain of Blastomyces dermatitidis carrying a targeted deletion at the BAD1 locus confers sterilizing immunity against experimental lethal pulmonary infection. We found in this study that alphabeta T cells are requisite for durable vaccine immunity, whereas other T and B cells are dispensable. In immune-competent animals, CD4(+) T-cell derived cytokines TNF-alpha and IFN-gamma mediate vaccine immunity. Surprisingly, these factors are dispensable in immune-deficient animals, which rely on alternate mechanisms for robust vaccine immunity, yet still require O(2)(-) production rather than generation of NO. Our results clarify the cellular and molecular bases behind the first genetically engineered fungal vaccine. They also illustrate a sharp difference in vaccine mechanisms between immune-competent and immune-deficient hosts, which underscores the plasticity of residual immune elements in compromised hosts, and points to the feasibility of developing vaccines against invasive fungal infection in this fast growing patient population.

In vivo stimulation of CD137 broadens primary antiviral CD8+ T cell responses

Given the key role CD8+ T cells play in controlling viral infection, strategies to enhance these responses may have important clinical applications. We found that in vivo CD137 stimulation with an agonistic monoclonal antibody enhanced the primary CD8+ T cell response to influenza type A viral infection in mice. Stimulation of CD137 increased the absolute number of CD8+ T cells to influenza epitopes in the lungs of infected animals, preferentially expanded CD8+ T cells that recognized nondominant epitopes and greatly enhanced direct ex vivo cytotoxicity. CD137 stimulation also restored the CD8+ T cell response to the immunodominant influenza epitope in CD28-/- mice. Thus, in vivo CD137 stimulation enhances and broadens the CD8+ T cell response to influenza virus and can restore the CD8+ T cell response when CD28 costimulation is absent. This suggests that CD137 stimulation may be useful as a strategy to enhance the CD8+ T cell response to viruses.

The role of IFN in respiratory syncytial virus pathogenesis

Formalin-inactivated respiratory syncytial virus (RSV) vaccine preparations have been shown to cause enhanced disease in naive hosts following natural infection. In this study we demonstrate a similar pattern of enhanced disease severity following primary RSV infection of IFN-nonresponsive STAT1(-/-) mice. STAT1(-/-) mice showed markedly increased illness compared with wild-type BALB/c animals following RSV inoculation despite similar lung virus titers and rates of virus clearance. Histologically, STAT1(-/-) animals had eosinophilic and neutrophilic pulmonary infiltrates not present in wild-type or IFN-gamma(-/-)-infected mice. In cytokine analyses of infected lung tissue, IFN-gamma was induced in both STAT1(-/-) and wild-type mice, with preferential IL-4, IL-5, and IL-13 induction only in the STAT1(-/-) animals. Eotaxin was detected in the lungs of both wild-type and STAT1(-/-) mice following infection, with a 1.7-fold increase over wild-type in the STAT1(-/-) mice. Using a peptide epitope newly identified in the RSV fusion protein, we were able to demonstrate that wild-type memory CD4(+) T cells stimulated by this peptide produce primarily IFN-gamma, while STAT1(-/-)CD4(+) cells produce primarily IL-13. These findings suggest that STAT1 activation by both type I (alphabeta) and type II (gamma) IFNs plays an important role in establishing a protective, Th1 Ag-specific immune response to RSV infection.

Th1 and Th2 cytokines regulate proteoglycan-specific autoantibody isotypes and arthritis

BALB/c mice immunized with human cartilage proteoglycan (PG) develop arthritis accompanied by the production of autoantibodies to mouse cartilage PG. To determine whether the autoantibody isotype contributes to the onset and severity of arthritis, PG-specific serum IgG1 (Th2, IL-4-cytokine-supporting) and IgG2a (Th1, IFN-gamma-controlling) concentrations were monitored during immunization with PG in IL-4-deficient and IFN-gamma-deficient mice. Paradoxically, despite elevated IFN-gamma, the PG-specific IgG1 isotype was significantly higher than the PG-specific IgG2a response, and the PG-specific IgG1 isotype was independent of IL-4. In contrast, the serum concentration of PG-specific IgG2a isotype was six times higher in IL-4-deficient mice than in wild-type controls. Moreover, the high concentration of PG-specific IgG2a isotype in IL-4-deficient mice corresponded to an increased severity of arthritis. The concentration of PG-specific IgG2a isotype was lower in IFN-gamma-deficient mice than in wild-type mice, and the incidence and severity of arthritis also were significantly lower. Concentrations of PG-specific IgG2a isotype autoantibody correlated with the onset and severity of arthritis, suggesting a pathological role of this isotype, probably locally in the joint.

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

BALB/c mice are resistant to measles virus (MV)-induced encephalitis due to their strong MV-specific CD4(+) T-cell response. Resistance is broken by neutralization of gamma interferon with monoclonal antibodies, indicating an important role for this pleiotropic cytokine. Here, we demonstrate that mouse gamma interferon has no direct antiviral effect in vitro and in vivo. The breakdown of resistance is due neither to a switch in the T-helper response nor to an impaired migration of CD4(+) T cells. Neutralization of gamma interferon interferes with the major histocompatibility complex class II-dependent antigen presentation and subsequent proliferation of CD4(+) T cells in vitro and in vivo. In consequence, the reduction in numbers of CD4(+) T cells below a protective threshold leads to susceptibility to MV-induced encephalitis.

Cryptosporidium parvum-specific mucosal immune response in C57BL/6 neonatal and gamma interferon-deficient mice: role of tumor necrosis factor alpha in protection

Both neonatal and C57BL/6 gamma interferon (IFN-gamma) knockout (C57BL/6-GKO) mice are susceptible to Cryptosporidium parvum, but the course of infection is different. Neonatal mice are able to clear the parasite within 3 weeks, whereas C57BL/6-GKO mice, depending on age, die rapidly or remain chronically infected. The mechanism by which IFN-gamma leads to a protective immunity is yet poorly understood. In order to investigate the effect of IFN-gamma on other cytokines expressed in the intestinal mucosa during C. parvum infection, we studied cytokine mRNA expression in the neonates and GKO (neonatal and adult) mice by quantitative reverse transcription-PCR (RT-PCR) at 4 and 9 days after infection. IFN-gamma mRNA levels were quickly and strongly up-regulated in the mucosa of neonatal mice. In GKO mice, the Th1-type response was dramatically altered during the infection, whereas the mRNA expression levels of the Th2-type cytokines interleukin 4 (IL-4) and IL-10 were increased in both mouse models. In the absence of IFN-gamma, the adult knockout mice up-regulated the mRNA levels of inflammatory cytokines, such as IL-1beta, IL-6, and granulocyte-macrophage colony-stimulating factor, in the mucosa, but not tumor necrosis factor alpha (TNF-alpha), whereas all these cytokines were up-regulated in the infected neonatal mice. Further experiments indicated that injections of TNF-alpha into GKO adult mice significantly reduced oocyst shedding. The results of the present study indicate that the resolution of infection is dependent on the expression of Th1-type cytokines in the mucosa of C57BL/6 mice and that TNF-alpha may participate in the control of parasite development.

Role of free radicals in viral pathogenesis and mutation

Oxygen radicals and nitric oxide (NO) are generated in excess in a diverse array of microbial infections. Emerging concepts in free radical biology are now shedding light on the pathogenesis of various diseases. Free-radical induced pathogenicity in virus infections is of great importance, because evidence suggests that NO and oxygen radicals such as superoxide are key molecules in the pathogenesis of various infectious diseases. Although oxygen radicals and NO have an antimicrobial effect on bacteria and protozoa, they have opposing effects in virus infections such as influenza virus pneumonia and several other neurotropic virus infections. A high output of NO from inducible NO synthase, occurring in a variety of virus infections, produces highly reactive nitrogen oxide species, such as peroxynitrite, via interaction with oxygen radicals and reactive oxygen intermediates. The production of these various reactive species confers the diverse biological functions of NO. The reactive nitrogen species cause oxidative tissue injury and mutagenesis through oxidation and nitration of various biomolecules. The unique biological properties of free radicals are further illustrated by recent evidence showing accelerated viral mutation by NO-induced oxidative stress. NO appears to affect a host's immune response, with immunopathological consequences. For example, NO is reported to suppress type 1 helper T cell-dependent immune responses during infections, leading to type 2 helper T cell-biased immunological host responses. NO-induced immunosuppression may thus contribute to the pathogenesis of virus infections and help expansion of quasispecies population of viral pathogens. This review describes the pathophysiological roles of free radicals in the pathogenesis of viral disease and in viral mutation as related to both nonspecific inflammatory responses and immunological host reactions modulated by NO.

Nitric oxide and virus infection

Nitric oxide (NO) has complex and diverse functions in physiological and pathophysiological phenomena. The mechanisms of many events induced by NO are now well defined, so that a fundamental understanding of NO biology is almost established. Accumulated evidence suggests that NO and oxygen radicals such as superoxide are key molecules in the pathogenesis of various infectious diseases. NO biosynthesis, particularly through expression of an inducible NO synthase (iNOS), occurs in a variety of microbial infections. Although antimicrobial activity of NO is appreciated for bacteria and protozoa, NO has opposing effects in virus infections such as influenza virus pneumonia and certain other neurotropic virus infections. iNOS produces an excessive amount of NO for long periods, which allows generation of a highly reactive nitrogen oxide species, peroxynitrite, via a radical coupling reaction of NO with superoxide. Thus, peroxynitrite causes oxidative tissue injury through potent oxidation and nitration reactions of various biomolecules. NO also appears to affect a host's immune response, with immunopathological consequences. For example, overproduction of NO in virus infections in mice is reported to suppress type 1 helper T-cell-dependent immune responses, leading to type 2 helper T-cell-biased immunological host responses. Thus, NO may be a host response modulator rather than a simple antiviral agent. The unique biological properties of NO are further illustrated by our recent data suggesting that viral mutation and evolution may be accelerated by NO-induced oxidative stress. Here, we discuss these multiple roles of NO in pathogenesis of virus infections as related to both non-specific inflammatory responses and immunological host reactions modulated by NO during infections in vivo.

Contrasting effects of CCR5 and CCR2 deficiency in the pulmonary inflammatory response to influenza A virus

The immune response to influenza A virus is characterized by an influx of both macrophages and T lymphocytes into the lungs of the infected host, accompanied by induced expression of a number of CC chemokines. CC chemokine receptors CCR5 and CCR2 are both expressed on activated macrophages and T cells. We examined how the absence of these chemokine receptors would affect pulmonary chemokine expression and induced leukocyte recruitment by infecting CCR5-deficient mice and CCR2-deficient mice with a mouse-adapted strain of influenza A virus. CCR5(-/-) mice displayed increased mortality rates associated with acute, severe pneumonitis, whereas CCR2(-/-) mice were protected from the early pathological manifestations of influenza because of defective macrophage recruitment. This delay in macrophage accumulation in CCR2(-/-) mice caused a subsequent delay in T cell migration, which correlated with high pulmonary viral titers at early time points. Infected CCR5(-/-) mice and CCR2(-/-) mice both exhibited increased expression of the gene for MCP-1, the major ligand for CCR2(-/-) and a key regulator of induced macrophage migration. These studies illustrate the very different roles that CCR5 and CCR2 play in the macrophage response to influenza infection and demonstrate how defects in macrophage recruitment affect the normal development of the cell-mediated immune response.

Gamma interferon is not required for mucosal cytotoxic T-lymphocyte responses or heterosubtypic immunity to influenza A virus infection in mice

Heterosubtypic immunity (HSI) is defined as cross-protection against influenza virus of a different serotype than the virus initially encountered and is thought to be mediated by influenza virus-specific cytotoxic T lymphocytes (CTL). Since gamma interferon (IFN-gamma) stimulates cytotoxic cells, including antigen-specific CTL which may control virus replication by secretion of antiviral cytokines such as tumor necrosis factor alpha and IFN-gamma, we have investigated the mechanism of HSI by analyzing the role of IFN-gamma for HSI in IFN-gamma gene-deleted (IFN-gamma(-/-)) mice. It has been reported that IFN-gamma is not required for recovery from primary infection with influenza virus but is important for HSI. Here, we conclusively show that IFN-gamma is not required for induction of secondary influenza virus-specific CTL responses in mediastinal lymph nodes and HSI to lethal influenza A virus infection. Although T helper 2 (Th2)-type cytokines were upregulated in the lungs of IFN-gamma(-/-) mice after virus challenge, either Th1- or Th2-biased responses could provide heterosubtypic protection. Furthermore, titers of serum-neutralizing and cross-reactive antibodies to conserved nucleoprotein in IFN-gamma(-/-) mice did not differ significantly from those in immunocompetent mice. These results indicate that lack of IFN-gamma does not impair cross-reactive virus-specific immune responses and HSI to lethal infection with influenza virus. Our findings provide new insight for the mechanisms of HSI and should be valuable in the development of protective mucosal vaccines against variant virus strains, such as influenza and human immunodeficiency virus.

The role of alpha/beta and gamma interferons in development of immunity to influenza A virus in mice

During influenza virus infection innate and adaptive immune defenses are activated to eliminate the virus and thereby bring about recovery from illness. Both arms of the adaptive immune system, antibody neutralization of free virus and termination of intracellular virus replication by antiviral cytotoxic T cells (CTLs), play pivotal roles in virus elimination and protection from disease. Innate cytokine responses, such as alpha/beta interferon (IFN-alpha/beta) or IFN-gamma, can have roles in determining the rate of virus replication in the initial stages of infection and in shaping the initial inflammatory and downstream adaptive immune responses. The effect of these cytokines on the replication of pneumotropic influenza A virus in the respiratory tract and in the regulation of adaptive antiviral immunity was examined after intranasal infection of mice with null mutations in receptors for IFN-alpha/beta, IFN-gamma, and both IFNs. Virus titers in the lungs of mice unable to respond to IFNs were not significantly different from congenic controls for both primary and secondary infection. Likewise the mice were comparably susceptible to X31 (H3N2) influenza virus infection. No significant disruption to the development of normal antiviral CTL or antibody responses was observed. In contrast, mice bearing the disrupted IFN-alpha/beta receptor exhibited accelerated kinetics and significantly higher levels of neutralizing antibody activity during primary or secondary heterosubtypic influenza virus infection. Thus, these observations reveal no significant contribution for IFN-controlled pathways in shaping acute or memory T-cell responses to pneumotropic influenza virus infection but do indicate some role for IFN-alpha/beta in the regulation of antibody responses. Recognizing the pivotal role of CTLs and antibody in virus clearance, it is reasonable to assume a redundancy in IFN-mediated antiviral effects in pulmonary influenza. However, IFN-alpha/beta seems to be a valid factor in determining tissue tropism and replicative rates of highly virulent influenza virus strains as reported previously by others, and this aspect is discussed here.

High-level dietary vitamin A enhances T-helper type 2 cytokine production and secretory immunoglobulin A response to influenza A virus infection in BALB/c mice

Vitamin A supplementation during acute pneumonia has not improved recovery in most human clinical trials. We hypothesize that high vitamin A intake may decrease the production of T-helper type-1 (Th1) cytokines and thereby inhibit antiviral responses. Such decreases might impair recovery from viral respiratory infections. We thus examined the effect of three interventions on viral pneumonia: 1) a high level vitamin A [250,000 IU/kg diet or 75,000 retinol equivalents (RE)/kg], or 2) control diet (4000 IU/kg diet or 1200 RE/kg) given before and during infection, and 3) initiating the high level diet upon infection to simulate the adjuvant therapy used in clinical trials. No difference was seen among the interventions in severity of disease (weight loss, lung virus titers and survival). However, both the high level diet group and the group in which vitamin A was increased at the time of infection had greater salivary immunoglobulin (Ig)A responses (geometric means, 166 and 105 microg/L, respectively) than did the control group (59 microg/L) (P = 0.0019). In contrast, the serum IgG response was higher in the control group (324+/-158 mg/L) than in the high level group (225+/-95 mg/L) (P = 0.028), although it did not differ from the group in which the diet was changed upon infection (230+/-163 mg/L) (P = 0.084). The production of interferon-gamma (IFN-gamma), a Th1 cytokine, was lower in the high level diet group (median, 0.153 microg/L) compared with the control group (median, 0.839 microg/L) (P = 0.014), whereas the production of interleukin-10 (IL-10), a Th2 cytokine, was higher with the high level diet (median, 0.304 microg/L) than with the control (median, 0.126 microg/L) (P = 0.022). This change in the Th1/Th2 pattern was not sufficient to affect recovery from viral pneumonia but may account for the increased IgA and decreased IgG responses seen with high level dietary vitamin A in this study. These data reinforce the lack of utility of vitamin A in treating acute pneumonia in children and suggest that high dose vitamin A supplements may enhance Th2-mediated immune responses, which are particularly beneficial in the case of extracellular bacterial and parasitic infections and IgA-mediated responses to mucosal infections.

Type I IFN modulates innate and specific antiviral immunity

IFNs protect from virus infection by inducing an antiviral state and by modulating the immune response. Using mice deficient in multiple aspects of IFN signaling, we found that type I and type II IFN play distinct although complementing roles in the resolution of influenza viral disease. Both types of IFN influenced the profile of cytokines produced by T lymphocytes, with a significant bias toward Th2 differentiation occurring in the absence of responsiveness to either IFN. However, although a Th1 bias produced through inhibition of Th2 differentiation by IFN-gamma was not required to resolve infection, loss of type I IFN responsiveness led to exacerbated disease pathology characterized by granulocytic pulmonary inflammatory infiltrates. Responsiveness to type I IFN did not influence the generation of virus-specific cytotoxic lymphocytes or the rate of viral clearance, but induction of IL-10 and IL-15 in infected lungs through a type I IFN-dependent pathway correlated with a protective response to virus. Combined loss of both IFN pathways led to a severely polarized proinflammatory immune response and exacerbated disease. These results reveal an unexpected role for type I IFN in coordinating the host response to viral infection and controlling inflammation in the absence of a direct effect on virus replication.

Cytokine expression and specific lymphocyte proliferation in two strains of Cryptosporidium parvum-infected gamma-interferon knockout mice

Differences in the immune response between 2 strains of interferon-gamma knockout mice (BALB/c-GKO and C57BL/6-GKO) infected with Cryptosporidium parvum were examined because the course of infection among these 2 strains is markedly different. Infection of the BALB/c-GKO with C. parvum (2 X 10(6) oocysts/mouse) resulted in slight weight loss, oocyst shedding, and recovery from infection by 2 wk postinfection (PI). Infection with 100 oocysts in the C57BL/6-GKO mice resulted in significant weight loss, oocyst shedding, and death by day 10 PI. Splenocytes from infected mice were able to proliferate in a dose-dependent manner to soluble C. parvum-sporozoite antigen (SAg). In vitro stimulation with SAg resulted in an increase in interleukin (IL)-2, IL-4, IL-5, and tumor necrosis factor-alpha mRNA cytokine expression from splenocytes of infected BALB/cGKO mice. In contrast, only IL-5 mRNA expression was increased in the splenocytes from C. parvum-infected C57BL/6-GKO mice. Phenotypic analysis indicated no significant differences in the splenic cell populations. Previous studies indicated that susceptibility to C. parvum is dependent on CD4+ T cells and interferon-gamma production. The present study indicates that although both of these strains of knockout mice become infected with C. parvum, resolution of infection may be in part dependent on the expression of Th2 cytokines.

CD8(+) T-cell priming against a nonsecreted Listeria monocytogenes antigen is independent of the antimicrobial activities of gamma interferon

Sublethal infection of mice with recombinant Listeria monocytogenes expressing a model epitope in either secreted or nonsecreted form results in similar CD8(+) T-cell priming. Since nonsecreted bacterial proteins have no obvious access to the endogenous major histocompatibility complex (MHC) class I presentation pathway, presentation of these antigens requires destruction of the bacterium to reveal the nonsecreted molecules to an exogenous MHC class I presentation pathway. Gamma interferon (IFN-gamma), a cytokine made by multiple cell types in response to L. monocytogenes infection, could be required for exogenous presentation of nonsecreted bacterial antigens via its capacity to upregulate the expression of molecules involved in antigen presentation, its capacity to activate macrophages to kill bacteria to expose nonsecreted molecules or both. IFN-gamma knockout (KO) mice were used to address the requirement for IFN-gamma in CD8(+) T-cell priming against (i) a model exogenous antigen and (ii) secreted and nonsecreted L. monocytogenes antigens. We demonstrate that IFN-gamma KO mice are capable of cross-presenting the model exogenous antigen ovalbumin to prime CD8(+) T-cell responses that are only slightly weaker than that in wild-type (WT) mice. Despite their extreme susceptibility to primary L. monocytogenes infection, previously immunized and naive IFN-gamma KO mice were able to generate CD8(+) T-cell responses against both secreted and nonsecreted L. monocytogenes antigens which were similar to responses of WT mice. Interestingly, IFN-gamma KO mice were as capable as WT mice in mediating the characteristic drop in bacterial load in the liver at 4 h postinfection, although the IFN-gamma KO mice have exacerbated bacterial loads as early as 24 h postinfection. These results demonstrate that the regulatory functions of IFN-gamma are not required for priming of CD8(+) T cells by cross-presentation of a model exogenous antigen or in response to a nonsecreted L. monocytogenes antigen. In addition, the capacity of IFN-gamma to activate the microbicidal activities of macrophages is not required for the very early innate immune response to L. monocytogenes or priming of CD8(+) T cells against a nonsecreted bacterial antigen.

Th cell-deficient mice control influenza virus infection more effectively than Th- and B cell-deficient mice: evidence for a Th-independent contribution by B cells to virus clearance

The notion that MHC class I- restricted CD8+ T (Tc) cells are capable of resolving autonomously infections with influenza virus is based largely on studies testing virus strains of low pathogenicity in CD4+ T (Th) cell-deficient/depleted mice. To test whether this holds also for pathogenic strains and to exclude possible contributions by B cells, we analyzed PR8 infection in Th cell-depleted B cell-deficient (muMT) mice. These mice, termed muMT (-CD4), showed 80% mortality after infection with a small dose of PR8, which resulted in insignificant mortality in intact or Th cell-depleted BALB/c mice. Infection of muMT(-CD4) mice with a virus of low pathogenicity was resolved without mortality, but, compared with intact BALB/c mice, with delay of approximately 5 and approximately 20 days from lung and nose, respectively. The low mortality of Th cell-depleted BALB/c mice suggested that B cells contributed to recovery in a Th-independent manner. This was verified by showing that transfer of 8-10 million T cell-depleted naive spleen cells into muMT(-CD4) mice 1 day before infection reduced mortality to 0%. The mechanism by which B cells improved recovery was investigated. We found no evidence that they operated by improving the lung-associated Tc response. Treatment of infected muMT(-CD4) mice with normal mouse serum spiked with hemagglutinin-specific IgM did not reduce mortality. Taken together, the data show that 1) the Tc response is capable of resolving autonomously (in conjunction with innate defenses) influenza virus infections, although with substantial delay compared with intact mice, and 2) B cells can contribute to recovery by a Th-independent mechanism.

IFN-gamma-independent IgG2a production in mice infected with viruses and parasites

After infection with some viruses and intracellular parasites, antibody production is restricted to IgG2a. We first observed that, whereas live viruses such as lactate dehydrogenase-elevating virus (LDV) or mouse adenovirus induced mostly an IgG2a response, a large proportion of antibodies produced against killed viruses were IgG1. This IgG1 antiviral response was suppressed when live virions were added to inactivated viral particles. These results indicate that the IgG2a preponderance is related to the infectious process itself rather than to the type of antigen involved. Since IFN-gamma is known to stimulate IgG2a production by activated B lymphocytes and to be secreted after infection, we examined the role of this cytokine in the antibody isotypic distribution caused by LDV. Most IgG2a responses were relatively unaffected in mice deficient for the IFN-gamma receptor or treated with anti-IFN-gamma antibody. A similar IFN-gamma-independent IgG2a secretion was observed after infection with the parasites Toxoplasma gondii and Trypanosoma cruzi. However, the IFN-gamma-independent IgG2a production triggered by infection still required the presence of functional T(h) lymphocytes. Therefore, signal(s) other than IFN-gamma secretion may explain the T(h)-dependent isotypic bias in antibody secretion triggered by viruses and parasites.

Th1-biased immune responses induced by DNA-based immunizations are mediated via action on professional antigen-presenting cells to up-regulate IL-12 production

The efficacy of DNA-based immunization in conferring protective immunity against certain microbial pathogens including human immunodeficiency virus type 1 (HIV-1) has been described. The potential advantage of DNA-based immunization over the traditional vaccines largely results from its capacity to efficiently induce Th1-biased immune responses against an encoded antigen. We describe how Th1-biased immune responses are induced by DNA-based immunization, using a DNA vaccine construct encoding HIV-1 gp160 cDNA and an eukaryotic expression plasmid carrying murine IFN-gamma cDNA. Transfection of an eukaryotic expression plasmid carrying immunostimulatory sequences (ISS) as well as a gene of interest (DNA vaccine) into professional antigen presenting cells (APC) induced transactivation of IL-12 mRNA, which resulted in antigen-specific Th1-biased immune responses against the encoded antigen. Th1-biased immune responses induced by DNA-based immunization were substantially upregulated by a codelivery of an ectopic IFN-gamma expression system, and this augmentation was mediated via action on professional antigen presenting cells to upregulate IL-12 production. Taken together, it appears likely that Th1-biased immune responses induced by DNA-based immunization are mediated via action on professional antigen-presenting cells to produce IL-12. Interestingly, the model provided strikingly resembles that previously described in infection with Listeria monocytogenes, an intracellular Gram-positive bacterium that induces strong Th1-biased immune responses. The result suggests that DNA-based immunization mimics certain aspects of natural infection with microbial organisms like attenuated vaccines, which in turn provides a rationale to the question of why DNA-based immunization so efficiently induces protective immunity against these microbial pathogens.

IL-4 and IL-10 antagonize IL-12-mediated protection against acute vaccinia virus infection with a limited role of IFN-gamma and nitric oxide synthetase 2

Resistance or susceptibility to most infectious diseases is strongly determined by the balance of type 1 vs type 2 cytokines produced during infection. However, for viruses, this scheme may be applicable only to infections with some cytopathic viruses, where IFN-gamma is considered as mandatory for host defense with little if any participation of type 2 responses. We studied the role of signature Th1 (IL-12, IFN-gamma) and Th2 (IL-4, IL-10) cytokines for immune responses against vaccinia virus (VV). IL-12-/- mice were far more susceptible than IFN-gamma-/- mice, and primary CTL responses against VV were absent in IL-12-/- mice but remained intact in IFN-gamma-/- mice. Both CD4+ and CD8+ T cells from IL-12-/- mice were unimpaired in IFN-gamma production, although CD4+ T cells showed elevated Th2 cytokine responses. Virus replication was impaired in IL-4-/- mice and, even more strikingly, in IL-10-/- mice, which both produced elevated levels of the proinflammatory cytokines IL-1alpha and IL-6. Thus, IL-4 produced by Th2 cells and IL-10 produced by Th2 cells and probably also by macrophages counteract efficient anti-viral host defense. Surprisingly, NO production, which is considered as a major type 1 effector pathway inhibited by type 2 cytokines, appears to play a limited role against VV, because NO sythetase 2-deficient mice did not show increased viral replication. Thus, our results identify a new role for IL-12 in defense beyond the induction of IFN-gamma and show that IL-4 and IL-10 modulate host protective responses to VV.

MHC Class I-Restricted Cytotoxic Lymphocyte Responses Induced by Enterotoxin-Based Mucosal Adjuvants

The ability of enterotoxin-based mucosal adjuvants to induce CD8+ MHC class I-restricted CTL responses to a codelivered bystander Ag was examined. Escherichia coli heat-labile toxin (LT), or derivatives of LT carrying mutations in the A subunit (LTR72, LTK63), were tested in parallel with cholera toxin (CT) or a fusion protein consisting of the A1 subunit of CT fused to the Ig binding domain of Staphylococcus aureus protein A (called CTA1-DD). Intranasal (i.n.) immunization of C57BL/6 mice with CT, CTA1-DD, LT, LTR72, LTK63, but not rLT-B, elicited MHC class I-restricted CD8+ T cell responses to coadministered OVA or the OVA CTL peptide SIINFEKL (OVA257–264). CT, LT, and LTR72 also induced CTL responses to OVA after s.c. or oral coimmunization whereas LTK63 only activated responses after s.c. coimmunization. rLT-B was unable to adjuvant CTL responses to OVA or OVA257–264 administered by any route. Mice treated with an anti-CD4 mAb to deplete CD4+ T cells mounted significant OVA-specific CTL responses after i.n. coadministration of LT with OVA or OVA257–264. Both 51Cr release assays and IFN-γ enzyme-linked immunospot assays indicated that IFN-γ−/− and IL-12 p40−/− gene knockout mice developed CTL responses equivalent to those detected in normal C57BL/6 mice. The results highlight the versatility of toxin-based adjuvants and suggest that LT potentiates CTL responses independently of IL-12 and IFN-γ and probably by a mechanism unrelated to cross-priming.

Compromised Virus Control and Augmented Perforin-Mediated Immunopathology in IFN-γ-Deficient Mice Infected with Lymphocytic Choriomeningitis Virus

To define the role of IFN-γ in the control of acute infection with a noncytopathogenic virus, mice with targeted defects of the genes encoding IFN-γ, perforin, or both were infected i.v. with two strains of lymphocytic choriomeningitis virus differing markedly in their capacity to spread in wild-type mice. Our results reveal that IFN-γ is pivotal to T cell-mediated control of a rapidly invasive stain, whereas it is less important in the acute elimination of a slowly invasive strain. Moreover, the majority of mice infected with the rapidly invasive strain succumb to a wasting syndrome mediated by CD8+ effector cells. The primary effector mechanism underlying this disease is perforin-dependent lysis, but other mechanisms are also involved. Wasting disease can be prevented if naive CD8+ cells from mice transgenic for an MHC class I-restricted lymphocytic choriomeningitis virus-specific TCR are adoptively transferred before virus challenge, indicating that the disease is the result of an unfortunate balance between virus replication in internal organs, e.g., liver and spleen, and the host response; resetting this balance by increasing host responsiveness will again lead to a rapidly controlled infection and limited tissue damage. Thus, the presence or absence of IFN-γ determines whether CTLs will clear infection with this noncytopathogenic virus or induce severe immunopathology.

Naive, Effector, and Memory CD8 T Cells in Protection Against Pulmonary Influenza Virus Infection: Homing Properties Rather Than Initial Frequencies Are Crucial

The goal of adoptive immunotherapy is to target a high number of persisting effector cells to the site of a virus infection or tumor. In this study, we compared the protective value of hemagglutinin peptide-specific CD8 T cells generated from the clone-4 TCR-transgenic mice, defined by different stages of their differentiation, against lethal pulmonary influenza infection. We show that the adoptive transfer of high numbers of Ag-specific unprimed, naive CD8 T cells failed to clear the pulmonary virus titer and to promote host survival. The same numbers of in vitro generated primary Ag-specific Tc1 effector cells, producing high amounts of IFN-γ, or resting Tc1 memory cells, generated from these effectors, were protective. Highly activated CD62Llow Tc1 effectors accumulated in the lung with rapid kinetics and most efficiently reduced the pulmonary viral titer early during infection. The resting CD62Lhigh naive and memory populations first increased in cell numbers in the draining lymph nodes. Subsequently, memory cells accumulated more rapidly and to a greater extent in the lung lavage as compared with naive cells. Thus, effector cells are most effective against a localized virus infection, which correlates with their ability to rapidly distribute at the infected tissue site. The finding that similar numbers of naive Ag-specific CD8 T cells are not protective supports the view that qualitative differences between the two resting populations, the naive and the memory population, may play a major role in their protective value against disease.

Vitamin E and infectious diseases in the aged

The incidence of infectious diseases, particularly respiratory diseases, increases with age. Age-associated decline in immune function contributes to the increased susceptibility of the aged to infections. Vitamin E supplementation has been shown to improve some aspects of immune function in aged animals and human subjects. The protective effect of vitamin E against viral or bacterial infections in experimentally-challenged young animals has been reported. We investigated the effects of supplementation with vitamin E and other antioxidants on resistance to influenza infection in young and old animals. While vitamin E-supplemented young mice showed only a modest reduction in lung viral titre, vitamin E-supplemented old mice exhibited a highly significant (P < 0.05) reduction in viral lung titre. In subsequent studies, we focused on the mechanism of vitamin E-induced reduction of influenza viral titre. The results of these studies as well as those reported by other investigators on the relationship between vitamin E and infectious diseases will be reviewed.

IL-12 and NK Cells Are Required for Antigen-Specific Adaptive Immunity Against Malaria Initiated by CD8+ T Cells in the Plasmodium yoelii Model

CD8+ T cells have been implicated as critical effector cells in protection against preerythrocytic stage malaria, including the potent protective immunity of mice and humans induced by immunization with radiation-attenuated Plasmodium spp. sporozoites. This immunity is directed against the Plasmodium spp. parasite developing within the host hepatocyte and for a number of years has been presumed to be mediated directly by CD8+ CTL or indirectly by IFN-γ released from CD8+ T cells. In this paper, in BALB/c mice, we establish that after immunization with irradiated sporozoites or DNA vaccines parasite-specific CD8+ T cells trigger a novel mechanism of adaptive immunity that is dependent on T cell- and non-T cell-derived cytokines, in particular IFN-γ and IL-12, and requires NK cells but not CD4+ T cells. The absolute requirement for CD8+ T cells to initiate such an effector mechanism, and the requirement for IL-12 and NK cells in such vaccine-induced protective immunity, are unique and underscore the complexity of the immune responses that protect against malaria and other intracellular pathogens.

Analysis of the Th1/Th2 paradigm in transplantation: interferon-gamma deficiency converts Th1-type proislet allograft rejection to a Th2-type xenograft-like response

The rejection mechanisms for fetal proislet allografts and pig proislet xenografts in mice are characterized by different intragraft cytokine mRNA profiles and cellular responses. Allograft rejection is predominantly CD8 T-cell-dependent and is associated with a Th1-type cytokine pattern (i.e., IFN-gamma, IL-2 but no IL-4 or IL-5 mRNA). In contrast, xenograft rejection is CD4 T-cell-dependent and is accompanied by a strong Th2-type response (i.e., enhanced expression of IL-4 and IL-5 mRNA) and by marked eosinophil accumulation at the graft site. We have now examined and compared the regulatory role of IFN-gamma in both proislet allograft and xenograft rejection processes. The histopathology and intragraft cytokine mRNA profile of BALB/c (H-2d) proislet allografts were examined in IFN-gamma-deficient and wild-type C57BL/6J recipient mice. The survival of pig proislet xenografts was also assessed in IFN-gamma -/- and wild-type hosts. Both proislet allografts and xenografts were acutely rejected in IFN-gamma -/- and wild-type mice. Unlike the conventional allograft reaction, which lacks eosinophil infiltration, the rejection of proislet allografts in IFN-gamma-deficient hosts correlated with intragraft expression of IL-4 and IL-5 mRNA (i.e., a Th2-type response) and eosinophil recruitment. The rejection of proislet allografts and xenografts can therefore occur by IFN-gamma-independent pathways; IFN-gamma, however, regulates the pathology of the allograft reaction but not the xenograft response. The immune destruction of proislet allografts is not prevented by Th2 cytokine gene expression; instead, the latter correlated with the recruitment of unconventional inflammatory cells (eosinophils), which may play an accessory role in effecting graft injury. Significantly, the Th1-to-Th2-like switch resulted in the novel conversion of an allograft rejection reaction into a xenograft-like rejection process.

Natural killer cells in antiviral defense: function and regulation by innate cytokines

Natural killer (NK) cells are populations of lymphocytes that can be activated to mediate significant levels of cytotoxic activity and produce high levels of certain cytokines and chemokines. NK cells respond to and are important in defense against a number of different infectious agents. The first indications for this function came from the observations that virus-induced interferons alpha/beta (IFN-alpha and -beta) are potent inducers of NK cell-mediated cytotoxicity, and that NK cells are important contributors to innate defense against viral infections. In addition to IFN-alpha/beta, a wide range of other innate cytokines can mediate biological functions regulating the NK cell responses of cytotoxicity, proliferation, and gamma interferon (IFN-gamma) production. Certain, but not all, viral infections induce interleukin 12 (IL-12) to elicit NK cell IFN-gamma production and antiviral mechanisms. However, high levels of IFN-alpha/beta appear to be unique and/or uniquely dominant in the context of viral infections and act to regulate other innate responses, including induction of NK cell proliferation in vivo and overall negative regulation of IL-12 production. A detailed picture is developing of particular innate cytokines activating NK cell responses and their consorted effects in providing unique endogenous milieus promoting downstream adaptive responses, most beneficial in defense against viral infections.

Role of the individual interferon systems and specific immunity in mice in controlling systemic dissemination of attenuated pseudorabies virus infection

The importance of each of the two interferon (IFN) systems in impeding herpesvirus replication and in stimulating virus-specific lymphocytes to control an acute systemic infection is not completely understood. To further our knowledge, pseudorabies virus, attenuated by deletion of the glycoprotein E gene to impair its neurovirulence and by deletion of the thymidine kinase gene (gE-TK-PRV), was used to infect wild-type 129Sv/Ev and congenic mice with immune system-associated genetic deficiencies. Mice with mature B and T lymphocytes but lacking either one or both functional receptors for members of each of the two IFN families were infected with gE-TK-PRV. At 3 and 7 but not 14 days after infection, replicating gE-TK-PRV could be isolated only from livers or spleens of mice lacking the receptors for both IFN families, and these mice survived the infection. Therefore, functional IFN receptors were not required to induce a protective immune response against an acute infection with gE-TK-PRV. Furthermore, PRV-specific antibodies of all immunoglobulin G isotypes were produced in these mice. Mice without mature B and T lymphocytes and lacking either one or both functional receptors for members of each of the two IFN families were also infected with gE-TK-PRV. Three days after infection, replicating virus could be isolated only from mice lacking both mature B and T lymphocytes and functional IFN receptors, and these mice were not able to clear the virus. We present evidence that mice with an intact gamma IFN system but without mature B and T cells were able to prevent systemic dissemination of gE-TK-PRV.

Roles of TH1 and TH2 cytokines in a murine model of allergic dermatitis

Skin lesions in atopic dermatitis (AD) are characterized by hypertrophy of the dermis and epidermis, infiltration by T cells and eosinophils, and expression of the cytokines IL-4, IL-5, and IFN-gamma. The role of these cytokines in the pathogenesis of AD is not known. We took advantage of a recently described murine model of AD elicited by epicutaneous sensitization with ovalbumin (OVA) (1) and of the availability of mice with targeted deletions of the IL-4, IL-5, and IFN-gamma cytokine genes to assess the role of these cytokines in this model.OVA-sensitized skin from IL-5(-/-) mice had no detectable eosinophils and exhibited decreased epidermal and dermal thickening. Sensitized skin from IL-4(-/-) mice displayed normal thickening of the skin layers but had a drastic reduction in eosinophils and a significant increase in infiltrating T cells. These findings were associated with a reduction in eotaxin mRNA and an increase in mRNA for the T-cell chemokines macrophage inflammatory protein-2 (MIP-2), MIP-1beta, and RANTES. Sensitized skin from IFN-gamma-/- mice was characterized by reduced dermal thickening. These results suggest that both the TH2 cytokines IL-4 and IL-5 and the TH1 cytokine IFN-gamma play important roles in the inflammation and hypertrophy of the skin in AD.

Interferon gamma expressed by a recombinant respiratory syncytial virus attenuates virus replication in mice without compromising immunogenicity

Interferon gamma (IFN-gamma) has pleiotropic biological effects, including intrinsic antiviral activity as well as stimulation and regulation of immune responses. An infectious recombinant human respiratory syncytial virus (rRSV/mIFN-gamma) was constructed that encodes murine (m) IFN-gamma as a separate gene inserted into the G-F intergenic region. Cultured cells infected with rRSV/mIFN-gamma secreted 22 microg mIFN-gamma per 10(6) cells. The replication of rRSV/mIFN-gamma, but not that of a control chimeric rRSV containing the chloramphenicol acetyl transferase (CAT) gene as an additional gene, was 63- and 20-fold lower than that of wild-type (wt) RSV in the upper and lower respiratory tract, respectively, of mice. Thus, the attenuation of rRSV/mIFN-gamma in vivo could be attributed to the activity of mIFN-gamma and not to the presence of the additional gene per se. The mice were completely resistant to subsequent challenge with wt RSV. Despite its growth restriction, infection of mice with rRSV/mIFN-gamma induced a level of RSV-specific antibodies that, on day 56, was comparable to or greater than that induced by infection with wt RSV. Mice infected with rRSV/mIFN-gamma developed a high level of IFN-gamma mRNA and an increased amount of interleukin 12 p40 mRNA in their lungs, whereas other cytokine mRNAs tested were unchanged compared with those induced by wt RSV. Because attenuation of RSV typically is accompanied by a reduction in immunogenicity, expression of IFN-gamma by an rRSV represents a method of attenuation in which immunogenicity can be maintained rather than be reduced.

IFN-γ Is Required for Viral Clearance from Central Nervous System Oligodendroglia

Infection of the central nervous system (CNS) by the JHM strain of mouse hepatitis virus (JHMV) is a rodent model of the human demyelinating disease multiple sclerosis. The inability of effective host immune responses to eliminate virus from the CNS results in a chronic infection associated with ongoing recurrent demyelination. JHMV infects a variety of CNS cell types during the acute phase of infection including ependymal cells, astrocytes, microglia, oligodendroglia, and rarely in neurons. Replication within the majority of CNS cell types is controlled by perforin-dependent virus-specific CTL. However, inhibition of viral replication in oligodendroglia occurs via a perforin-independent mechanism(s). The potential role for IFN-γ as mediator controlling JHMV replication in oligodendroglia was examined in mice deficient in IFN-γ secretion (IFN-γ0/0 mice). IFN-γ0/0 mice exhibited increased clinical symptoms and mortality associated with persistent virus, demonstrating an inability to control replication. Neither antiviral Ab nor CTL responses were diminished in the absence of IFN-γ, although increased IgG1 was detected in IFN-γ0/0 mice. Increased virus Ag in the absence of IFN-γ localized almost exclusively to oligodendroglia and was associated with increased CD8+ T cells localized within white matter. These data suggest that although perforin-dependent CTL control virus replication within astrocytes and microglia, which constitute the majority of infected CNS cells, IFN-γ is critical for control of viral replication in oligodendroglia. Therefore, different mechanisms are used by the host defenses to control virus replication within the CNS, dependent upon the phenotype of the targets of virus replication.

Migration kinetics and final destination of type 1 and type 2 CD8 effector cells predict protection against pulmonary virus infection

The requirements for CD8 T cells to provide protection against a localized virus infection in models of adoptive immunotherapy are not well defined. Here we investigated the protective value of defined in vitro-generated hemagglutinin (HA) peptide-specific primary CD8 T cell effectors from the clone 4 T cell receptor transgenic mice, secreting type 1 or type 2 cytokines, against pulmonary infection with whole influenza virus. Cytotoxic T lymphocytes producing type 1 and type 2 cytokine (Tc1 and Tc2) populations were equally cytolytic, but Tc1 effectors and not Tc2 effectors reduced the pulmonary virus titer early during infection. Host recovery mediated by Tc1 effectors was found to be independent of interferon gamma production. Tc2 effectors entered the lung with delayed kinetics as compared with Tc1 effectors, and after lung entry Tc2 effector cells did not localize near the infected airway epithelium as did Tc1 effectors but were found within clusters of inflammatory cells distant from the epithelium. We also show that the expression of several chemokine receptors was selectively regulated in the Tc1 and Tc2 subsets. Thus, the protective value of a CD8 cell population against pulmonary influenza virus infection is strongly correlated with its ability to exert its effector potential at the site of virus infection.

Suppression of Host Immune Response by the Core Protein of Hepatitis C Virus: Possible Implications for Hepatitis C Virus Persistence

Hepatitis C virus (HCV) is a major human pathogen causing mild to severe liver disease worldwide. This positive strand RNA virus is remarkably efficient at establishing chronic infections. Although a high rate of genetic variability may facilitate viral escape and persistence in the face of Ag-specific immune responses, HCV may also encode proteins that facilitate evasion of immunological surveillance. To address the latter possibility, we examined the influence of specific HCV gene products on the host immune response to vaccinia virus in a murine model. Various vaccinia/HCV recombinants expressing different regions of the HCV polyprotein were used for i.p. inoculation of BALB/c mice. Surprisingly, a recombinant expressing the N-terminal half of the polyprotein (including the structural proteins, p7, NS2, and a portion of NS3; vHCV-S) led to a dose-dependent increase in mortality. Increased mortality was not observed for a recombinant expressing the majority of the nonstructural region or for a negative control virus expressing the β-galactosidase protein. Examination of T cell responses in these mice revealed a marked suppression of vaccinia-specific CTL responses and a depressed production of IFN-γ and IL-2. By using a series of vaccinia/HCV recombinants, we found that the HCV core protein was sufficient for immunosuppression, prolonged viremia, and increased mortality. These results suggest that the HCV core protein plays an important role in the establishment and maintenance of HCV infection by suppressing host immune responses, in particular the generation of virus-specific CTLs.

New mouse model for dengue virus vaccine testing

Several dengue (DEN) virus vaccines are in development; however, the lack of a reliable small animal model in which to test them is a major obstacle. Because evidence suggests that interferon (IFN) is involved in the human anti-DEN virus response, we tested mice deficient in their IFN functions as potential models. Intraperitoneally administered mouse-adapted DEN 2 virus was uniformly lethal in AG129 mice (which lack alpha/beta IFN and gamma IFN receptor genes), regardless of age. Immunized mice were protected from virus challenge, and survival times increased following passive transfer of anti-DEN polyclonal antibody. These results demonstrate that AG129 mice are a promising small animal model for DEN virus vaccine trials.

The influence of a targeted deletion of the IFNgamma gene on emotional behaviors

Evidence suggests that interferon-gamma (IFNgamma) plays an important role in CNS function and development. While the paucity of agents that selectively modify IFNgamma production or interaction with its receptors makes analyses of its potential behavioral relevance difficult, mice with null mutations of the IFNgamma gene have been used to investigate the potential role of IFNgamma in emotional behaviors. C57Bl/6 (B6) mice with null mutations of the IFNgamma gene (IFNgamma (-/-)) showed significantly increased emotionality compared to the wild-type (IFNgamma (+/+)) B6 mice. This was manifested in performance in the elevated plus maze as well as increased defecation scores and decreased locomotor activity both in novel environments and following a sonic stimulus. In contrast, the general level of emotionality of both IFNgamma (+/+) and (-/-) BALB/c (C) mice was substantially greater than that of either of the B6 mouse groups. While C IFNgamma (-/-) showed increased immobility in response to novelty, other indices of emotionality of C IFNgamma (-/-) mice were not significantly different from those of the C IFNgamma (+/+) mice. In summary, the lack of IFNgamma appears to contribute to increased emotionality, but the basal behaviors of the parental strain (e.g., BALBc) may overshadow the expression of this emotionality. While mice with null mutations of the IFNgamma gene may be useful tools for investigating the role of IFNgamma in brain function and behavior, the influence of the parent strain genome(s) on the behaviors in question must be taken into account.

Interferon gamma derived from CD4(+) T cells is sufficient to mediate T helper cell type 1 development

Interferon gamma (IFN-gamma) has been implicated in T helper type 1 (Th1) cell development through its ability to optimize interleukin 12 (IL-12) production from macrophages and IL-12 receptor expression on activated T cells. Various systems have suggested a role for IFN-gamma derived from the innate immune system, particularly natural killer (NK) cells, in mediating Th1 differentiation in vivo. We tested this requirement by reconstituting T cell and IFN-gamma doubly deficient mice with wild-type CD4(+) T cells and challenging the mice with pathogens that elicited either minimal or robust IL-12 in vivo (Leishmania major or Listeria monocytogenes, respectively). Th1 cells developed under both conditions, and this was unaffected by the presence or absence of IFN-gamma in non-T cells. Reconstitution with IFN-gamma-deficient CD4(+) T cells could not reestablish control over L. major, even in the presence of IFN-gamma from the NK compartment. These data demonstrate that activated T cells can maintain responsiveness to IL-12 through elaboration of endogenous IFN-gamma without requirement for an exogenous source of this cytokine.

Rapid interferon gamma-dependent clearance of influenza A virus and protection from consolidating pneumonitis in nitric oxide synthase 2-deficient mice

Viral infection often activates the interferon (IFN)-gamma-inducible gene, nitric oxide synthase 2 (NOS2). Expression of NOS2 can limit viral growth but may also suppress the immune system and damage tissue. This study assessed each of these effects in genetically deficient NOS2(-/-) mice after infection with influenza A, a virus against which IFN-gamma has no known activity. At inocula sufficient to cause consolidating pneumonitis and death in wild-type control mice, NOS2(-/-) hosts survived with little histopathologic evidence of pneumonitis. Moreover, they cleared influenza A virus from their lungs by an IFN-gamma-dependent mechanism that was not evident in wild-type mice. Even when the IFN-gamma-mediated antiviral activity was blocked in NOS2(-/-) mice with anti-IFN-gamma mAb, such mice failed to succumb to disease. Further evidence that this protection was independent of viral load was provided by treating NOS2(+/+) mice with the NOS inhibitor, Nomega-methyl-L-arginine (L-NMA). L-NMA prevented mortality without affecting viral growth. Thus, host NOS2 seems to contribute more significantly to the development of influenza pneumonitis in mice than the cytopathic effects of viral replication. Although NOS2 mediates some antiviral effects of IFN-gamma, during influenza infection it can suppress another IFN-gamma-dependent antiviral mechanism. This mechanism was observed only in the complete absence of NOS2 activity and appeared sufficient to control influenza A virus growth in the absence of changes in cytotoxic T lymphocyte activity.

IFN-γ Is Required for IL-12 Responsiveness in Mice with Candida albicans Infection

To elucidate the role of IFN-γ in antifungal CD4+ Th-dependent immunity, 129/Sv/Ev mice deficient for IFN-γ receptor (IFN-γR−/−) were assessed for susceptibility to gastrointestinal or systemic Candida albicans infection and for parameters of innate and adaptive T helper immunity. IFN-γR−/− mice failed to mount protective Th1-mediated acquired immunity upon mucosal immunization or in response to a live vaccine strain of the yeast. The impaired Th1-mediated resistance correlated with defective IL-12 responsiveness, but not IL-12 production, and occurred in the presence of an increased innate antifungal resistance. The development of nonprotective Th2 responses was observed in IFN-γR−/− mice upon mucosal infection and subsequent reinfection. However, under experimental conditions of Th2 cell activation, the occurrence of Th2 cell responses was similar in IFN-γR−/− and in IFN-γR+/+ mice. These results indicate the complex immunoregulatory role of IFN-γ in the induction of mucosal and nonmucosal anticandidal Th cell responses; IFN-γ is not essential for the occurrence of Th2 responses but is required for development of IL-12-dependent protective Th1-dependent immunity.

Immunomodulatory properties of interferon-gamma. An update

During the early aspecific phase of host defense, production of interferon (IFN)-gamma by natural killer cells plays an important role in bringing about acute inflammation, mainly because of the activating effects of IFN-gamma on adhesive properties of endothelial cells and on mediator production by mononuclear phagocytes (MPCs). In the subsequent antigen-specific phase of the immune response, IFN-gamma acts as a regulator of antigen presentation and of proliferation and differentiation of lymphocyte populations. Immunosuppressive as well as immunostimulatory effects may result from these actions. High-level production of IFN-gamma during this phase of host defense is now classically seen as a hallmark of a T-helper 1 (TH1)-type reaction, characterized by activation of antimicrobial activity of macrophages and by inflammatory reactions with a DTH character. Development of TH1-type lymphocyte populations producing IFN-gamma is regulated by other cytokines including interleukin (IL)-12. In many systems IL-12 and IFN-gamma act in a similar fashion, and a current subject of debate is the question of whether all activities of IL-12 are mediated by IFN-gamma. Another question is whether IFN-gamma, by its ability to potentiate MPCs' ability to produce IL-12, plays a role in bringing about or stabilizing TH1 type responses. In two model systems of autoimmune disease, experimental autoimmune encephalomyelitis and collagen-induced arthritis, IL-12 and IFN-gamma were found to act independently.

A role for persisting antigen, antigen presentation, and ICAM-1 in increased renal graft survival after oral or portal vein donor-specific immunization

BACKGROUND

We studied the mechanism behind increased renal allotransplant survival when C3H mice received donor-specific portal vein or oral immunization with C57BL/6 cells. Both regimens lead to donor-specific increased graft survival, in association with decreased production of cytotoxic T lymphocytes and altered cytokine production from host lymphocytes (decreased interleukin [IL]-2 production; increased IL-4, IL-10, and transforming growth factor-beta).

METHODS

We examined a role for persistent donor-derived antigen, in association with host dendritic cells, as well as a role for intercellular adhesion molecule-1 (ICAM-1), in the maintenance of unresponsiveness in host C3H spleen cells to donor antigen. We investigated whether there was a cooperative interaction between donor dendritic cells (DC) and host hepatic mononuclear cells in the induction of immunoregulation in C3H cells.

RESULTS

In mice with surviving renal grafts, donor antigen, in association with host DC, induced the recall of cytotoxicity from C57BL/6 immune C3H spleen cells and IL-4 but not IL-2 production, despite the decreased cytotoxicity seen in the renal transplant recipients themselves. Fresh donor DC induced IL-2 but not IL-4 production. Blocking expression of ICAM-1 on donor grafts, either with anti-ICAM-1 monoclonal antibodies after renal grafting or using grafts from ICAM-1 "knockout" mice, led to further increased survival. Cultured C3H responder spleen cells, incubated with C57BL/6 DC and C3H hepatic cells, transferred hyporesponsiveness to C57BL/6 cells in vitro and in vivo (as assayed by survival of C57BL/6 renal allografts).

CONCLUSIONS

Our data suggest a role for ICAM-1, persistent donor antigen (on host DC), and accessory hepatic monocytes in the induction and maintenance of tolerance after portal vein immunization.

IL-4 Protects Adult C57BL/6 Mice from Prolonged Cryptosporidium parvum Infection: Analysis of CD4+αβ+IFN-γ+ and CD4+αβ+IL-4+ Lymphocytes in Gut-Associated Lymphoid Tissue During Resolution of Infection

Resistance of adult C57BL/6 mice to severe Cryptosporidium parvum infection is dependent on CD4+αβ+ TCR lymphocytes. In this study, we demonstrated that treatment with anti-IFN-γ mAb extended oocyst excretion 18 days longer, and anti-IL-4 mAb extended oocyst excretion at least 11 days longer than isotype control mAb treatment. Analysis of the specific activity of anti-IFN-γ mAb present in treated mouse sera suggested that IFN-γ may have a limited role in the resolution phase of infection. Changes were also documented in numbers of CD4+αβ+IFN-γ+ and CD4+αβ+IL-4+ lymphocytes in Peyer’s patches and intraepithelium of adult C57BL/6 mice during resolution of C. parvum infection. Resistance to initial severe infection was associated with CD4+αβ+IFN-γ+ lymphocytes, and eventual resolution of infection was associated with CD4+αβ+IL-4+ lymphocytes. Analysis of cytokine expression following in vitro stimulation with C. parvum Ags during resolution of infection demonstrated consistent increases in CD4+αβ+IL-4+ lymphocytes, but not CD4+αβ+IFN-γ+ lymphocytes. The relevance of CD4+αβ+IL-4+ lymphocytes in protection against C. parvum was then evaluated in C57BL/6 IL-4 gene knockout mice (IL-4−/−). Adult IL-4−/− mice excreted oocysts in feces approximately 23 days longer than IL-4+/+ mice. Further, anti-IFN-γ mAb treatment increased the severity and the duration of infection in IL-4−/− mice compared with those in IL-4+/+ mice. Together, the data demonstrated that IFN-γ was important in the control of severity of infection, and either IFN-γ or IL-4 accelerated termination of infection. However, neither IL-4 nor IFN-γ was required for the final clearance of infection from the intestinal tract of adult mice.

Protective role of gamma interferon during the recall response to influenza virus

During secondary immune responses to influenza virus, virus-specific T memory cells are a major source of gamma interferon (IFN-gamma). We assessed the contribution of IFN-gamma to heterologous protection against the A/WSN/33 (H1N1) virus of wild-type and IFN-gamma-/- mice previously immunized with the A/HK/68 (H3N2) virus. The IFN-gamma-/- mice displayed significantly reduced survival rates subsequent to a challenge with various doses of the A/WSN/33 virus. This was associated with an impaired ability of the IFN-gamma-/- mice to completely clear the pulmonary virus by day 7 after the challenge, although significant reduction of the virus titers was noted. However, the IFN-gamma-/- mice developed type A influenza virus cross-reactive cytotoxic T lymphocytes (CTLs) similar to the wild-type mice, as demonstrated by both cytotoxicity and a limiting-dilution assay for the estimation of CTL precursor frequency. The pulmonary recruitment of T cells in IFN-gamma-/- mice was not dramatically affected, and the percentage of CD4(+) and CD8(+) T cells was similar to that of wild-type mice. The T cells from IFN-gamma-/- mice did not display a significant switch toward a Th2 profile. Furthermore, the IFN-gamma-/- mice retained the ability to mount significant titers of WSN and HK virus-specific hemagglutination-inhibiting antibodies. Together, these results are consistent with a protective role of IFN-gamma during the heterologous response against influenza virus independently of the generation and local recruitment of cross-reactive CTLs.