An alternate pathway for type 1 T cell differentiation

T cell-intrinsic Interferon Regulatory Factor-1 expression suppresses differentiation of CD4+ T cell populations that support chronic gammaherpesvirus infection

Gammaherpesviruses are ubiquitous pathogens that establish life-long infection and are associated with B cell lymphomas. To establish chronic infection, these viruses usurp B cell differentiation and drive a robust germinal center response to expand the latent viral reservoir and gain access to memory B cells. Germinal center B cells, while important for the establishment of latent infection, are also thought to be the target of viral transformation. The host and viral factors that impact the gammaherpesvirus-driven germinal center response are not clearly defined. We showed that global expression of the antiviral and tumor-suppressor interferon regulatory factor 1 (IRF-1) selectively attenuates the murine gammaherpesvirus 68 (MHV68)-driven germinal center response and restricts expansion of the latent viral reservoir. In this study we found that T cell intrinsic IRF-1 expression recapitulates some aspects of antiviral state imposed by IRF-1 during chronic MHV68 infection, including attenuation of the germinal center response and viral latency in the spleen. We also discovered that global and T cell-intrinsic IRF-1 deficiency leads to unhindered rise of IL-17A-expressing and follicular helper T cell populations, two CD4⁺ T cell subsets that support chronic MHV68 infection. Thus, this study unveils a novel aspect of antiviral activity of IRF-1 by demonstrating IRF-1-mediated suppression of specific CD4⁺ T cell subsets that support chronic gammaherpesvirus infection. Importance Gammaherpesviruses infect over 95% of the adult population, last the lifetime of the host, and are associated with multiple cancers. These viruses usurp the germinal center response to establish lifelong infection in memory B cells. This manipulation of B cell differentiation by the virus is thought to contribute to lymphomagenesis, though exactly how the virus precipitates malignant transformation in vivo is unclear. IRF-1, a host transcription factor and a known tumor suppressor, restricts the MHV68-driven germinal center response in a B cell-extrinsic manner. We found that T cell intrinsic IRF-1 expression attenuates the MHV68-driven germinal center response by restricting the CD4⁺ T follicular helper population. Further, our study identified IRF-1 as a novel negative regulator of IL-17-driven immune responses, highlighting the multifaceted role of IRF-1 in gammaherpesvirus infection.

Listeria arpJ gene modifies T helper type 2 subset differentiation

BACKGROUND

Although the T-cell subset differentiation pathway has been characterized extensively from the view of host gene regulation, the effects of genes of the pathogen on T-cell subset differentiation during infection have yet to be elucidated. Especially, the bacterial genes that are responsible for this shift have not yet been determined.

METHODS

Utilizing a single-gene-mutation Listeria panel, we investigated genes involved in the host-pathogen interaction that are required for the initiation of T-cell subset differentiation in the early phase of pathogen infection.

RESULTS

We demonstrate that the induction of T helper types 1 and 2 (Th1 and Th2) subsets are separate phenomena and are mediated by distinct Listeria genes. We identified several candidate Listeria genes that appear to be involved in the host-Listeria interaction. Among them, arpJ is the strongest candidate gene for inhibiting Th2 subset induction. Furthermore, the analysis utilizing arpJ-deficient Listeria monocytogenes (Lm) revealed that the tumor necrosis factor (TNF) superfamily (Tnfsf) 9-TNF receptor superfamily (Tnfrsf) 9 interaction inhibits the Th2 response during Lm infection.

CONCLUSIONS

arpJ is the candidate gene for inhibiting Th2 T-cell subset induction. The arpJ gene product influences the expression of Tnfsf/Tnfrsf on antigen-presenting cells and inhibits the Th2 T-cell subset differentiation during Listeria infection.

A novel function of interferon regulatory factor-1: inhibition of Th2 cells by down-regulating the Il4 gene during Listeria infection

Infection with certain pathogens induces a shift of the Th subset balance to a Th1 dominant state. This, in turn, results in the suppression of Th2 responses. We focused on the involvement of interferon regulatory factor-1 (IRF-1) in the suppression of Th2 cells during Listeria infection. We found that the inhibition of IL-4 production by Th2 cells is mediated by a soluble factor (LmSN) produced by Listeria-infected antigen-presenting cells. The inhibition is not observed with T cells from Irf1 gene-targeted mice. IRF-1 suppresses transcription of the Il4 gene in Th2 cells. Under the influence of the LmSN, IRF-1 binds to the 3' untranslated region (UTR) region of the Il4 gene and down-regulates Il4 gene transcription. Finally, we identified IL-1α and IL-1β as the mediator of the LmSN activity. Signaling through IL-1R induces the stabilization and/or nuclear translocation of IRF-1. We propose that IRF-1 functions to induce the T-cell subset shift via a novel mechanism. Under the influence of IL-1, IRF-1 translocates into the nucleus and acts on the 3'UTR region of the Il4 gene, thus inhibiting its transcription in Th2 cells. As a result, the immune system shifts predominantly to a Th1 response during Listeria infection, resulting in effective protection of the host.

Tonsil-derived mesenchymal stem cells alleviate concanavalin A-induced acute liver injury

Acute liver failure, the fatal deterioration of liver function, is the most common indication for emergency liver transplantation, and drug-induced liver injury and viral hepatitis are frequent in young adults. Stem cell therapy has come into the limelight as a potential therapeutic approach for various diseases, including liver failure and cirrhosis. In this study, we investigated therapeutic effects of tonsil-derived mesenchymal stem cells (T-MSCs) in concanavalin A (ConA)- and acetaminophen-induced acute liver injury. ConA-induced hepatitis resembles viral and immune-mediated hepatic injury, and acetaminophen overdose is the most frequent cause of acute liver failure in the United States and Europe. Intravenous administration of T-MSCs significantly reduced ConA-induced hepatic toxicity, but not acetaminophen-induced liver injury, affirming the immunoregulatory capacity of T-MSCs. T-MSCs were successfully recruited to damaged liver and suppressed inflammatory cytokine secretion. T-MSCs expressed high levels of galectin-1 and -3, and galectin-1 knockdown which partially diminished interleukin-2 and tumor necrosis factor α secretion from cultured T-cells. Galectin-1 knockdown in T-MSCs also reversed the protective effect of T-MSCs on ConA-induced hepatitis. These results suggest that galectin-1 plays an important role in immunoregulation of T-MSCs, which contributes to their protective effect in immune-mediated hepatitis. Further, suppression of T-cell activation by frozen and thawed T-MSCs implies great potential of T-MSC banking for clinical utilization in immune-mediated disease.

Human immune responses to Plasmodium falciparum infection: molecular evidence for a suboptimal THαβ and TH17 bias over ideal and effective traditional TH1 immune response

BACKGROUND

Using microarray analysis, this study showed up-regulation of toll-like receptors 1, 2, 4, 7, 8, NF-κB, TNF, p38-MAPK, and MHC molecules in human peripheral blood mononuclear cells following infection with Plasmodium falciparum.

METHODS

This analysis reports herein further studies based on time-course microarray analysis with focus on malaria-induced host immune response.

RESULTS

The results show that in early malaria, selected immune response-related genes were up-regulated including α β and γ interferon-related genes, as well as genes of IL-15, CD36, chemokines (CXCL10, CCL2, S100A8/9, CXCL9, and CXCL11), TRAIL and IgG Fc receptors. During acute febrile malaria, up-regulated genes included α β and γ interferon-related genes, IL-8, IL-1b IL-10 downstream genes, TGFB1, oncostatin-M, chemokines, IgG Fc receptors, ADCC signalling, complement-related genes, granzymes, NK cell killer/inhibitory receptors and Fas antigen. During recovery, genes for NK receptors and granzymes/perforin were up-regulated. When viewed in terms of immune response type, malaria infection appeared to induce a mixed TH1 response, in which α and β interferon-driven responses appear to predominate over the more classic IL-12 driven pathway. In addition, TH17 pathway also appears to play a significant role in the immune response to P. falciparum. Gene markers of TH17 (neutrophil-related genes, TGFB1 and IL-6 family (oncostatin-M)) and THαβ (IFN-γ and NK cytotoxicity and ADCC gene) immune response were up-regulated. Initiation of THαβ immune response was associated with an IFN-αβ response, which ultimately resulted in moderate-mild IFN-γ achieved via a pathway different from the more classic IL-12 TH1 pattern.

CONCLUSIONS

Based on these observations, this study speculates that in P. falciparum infection, THαβ/TH17 immune response may predominate over ideal TH1 response.

Sequential Plasmodium chabaudi and Plasmodium berghei infections provide a novel model of severe malarial anemia

Lack of an adequate animal model of Plasmodium falciparum severe malarial anemia (SMA) has hampered the understanding of this highly lethal condition. We developed a model of SMA by infecting C57BL/6 mice with P. chabaudi followed after recovery by P. berghei infection. P. chabaudi/P. berghei-infected mice had an initial 9- to 10-day phase of relatively low parasitemia and severe anemia, followed by a second phase of hyperparasitemia, more profound anemia, reticulocytosis, and death 14 to 21 days after infection. P. chabaudi/P. berghei-infected animals had more intense splenic hematopoiesis, higher interleukin-10 (IL-10)/tumor necrosis factor alpha and IL-12/gamma interferon (IFN-γ) ratios, and higher antibody levels against P. berghei and P. chabaudi antigens than P. berghei-infected or P. chabaudi-recovered animals. Early treatment with chloroquine or artesunate did not prevent the anemia, suggesting that the bulk of red cell destruction was not due to the parasite. Red cells from P. chabaudi/P. berghei-infected animals had increased surface IgG and C3 by flow cytometry. However, C3(-/-) mice still developed anemia. Tracking of red cells labeled ex vivo and in vivo and analysis of frozen tissue sections by immunofluorescence microscopy showed that red cells from P. chabaudi/P. berghei-infected animals were removed at an accelerated rate in the liver by erythrophagocytosis. This model is practical and reproducible, and its similarities with P. falciparum SMA in humans makes it an appealing system with which to study the pathogenesis of this condition and explore potential immunomodulatory interventions.

Interferon regulatory factor-1 (IRF-1) shapes both innate and CD8(+) T cell immune responses against West Nile virus infection

Interferon regulatory factor (IRF)-1 is an immunomodulatory transcription factor that functions downstream of pathogen recognition receptor signaling and has been implicated as a regulator of type I interferon (IFN)-αβ expression and the immune response to virus infections. However, this role for IRF-1 remains controversial because altered type I IFN responses have not been systemically observed in IRF-1^-/- mice. To evaluate the relationship of IRF-1 and immune regulation, we assessed West Nile virus (WNV) infectivity and the host response in IRF-1^-/- cells and mice. IRF-1^-/- mice were highly vulnerable to WNV infection with enhanced viral replication in peripheral tissues and rapid dissemination into the central nervous system. Ex vivo analysis revealed a cell-type specific antiviral role as IRF-1^-/- macrophages supported enhanced WNV replication but infection was unaltered in IRF-1^-/- fibroblasts. IRF-1 also had an independent and paradoxical effect on CD8⁺ T cell expansion. Although markedly fewer CD8⁺ T cells were observed in naïve animals as described previously, remarkably, IRF-1^-/- mice rapidly expanded their pool of WNV-specific cytolytic CD8⁺ T cells. Adoptive transfer and in vitro proliferation experiments established both cell-intrinsic and cell-extrinsic effects of IRF-1 on the expansion of CD8⁺ T cells. Thus, IRF-1 restricts WNV infection by modulating the expression of innate antiviral effector molecules while shaping the antigen-specific CD8⁺ T cell response.

Interferon regulatory factor (IRF)-1 is a transcription factor that has been implicated in immune regulation and induction of type I IFN gene expression. To better understand the contribution of IRF-1 to antiviral immunity, we infected cells and mice lacking IRF-1 with West Nile virus (WNV), an encephalitic flavivirus. IRF-1^-/- mice were uniformly vulnerable to WNV infection with enhanced viral replication and rapid dissemination into the brain and spinal cord. Studies in cell culture revealed a cell-type specific antiviral role as IRF-1^-/- macrophages but not fibroblasts supported enhanced WNV replication. IRF-1 also had an independent effect on CD8⁺ T cell responses. Although fewer CD8⁺ T cells were observed in naïve animals, WNV-specific CD8⁺ T cells rapidly expanded in IRF-1^-/- mice and retained the capacity to clear infection. Collectively, our studies define independent roles for IRF-1 in restricting WNV pathogenesis and modulating the protective CD8⁺ T cell response.

Differential effect of Listeria monocytogenes infection on cytokine production and cytotoxicity of CD8 T cells

Bacterial infection induces a shift to type 1 CD4 T cell subset in an infected host and this shift is important for protection of the host from disease development. Many researchers think that the shift is antigen-dependent, but we previously demonstrated an initial induction step for CD4 T cell subsets during Listeria monocytogenes (Lm) infection is antigen-independent. Although Listeria is a TLR2 ligand, the immune system of the Lm-infected host responded to the pathogen to induce expression of CD69 but not CD25 on CD4 T cells, CD8 T cells and B cells even in the absence of TLR2 or MyD88. The antigen-independent activation of type 1 CD4 T cells accelerate the clearance of pathogens by activating innate immune cells with type 1 cytokines. Type 1 CD4 T cells and CD8 T cells also collaborate to protect the host from intracellular Lm infection. Since CD8 T cells function mainly as cytotoxic T cells and CD69-positive CD8 T cells increase during Lm-infection, cytotoxic activity of CD8 T cells was evaluated during Lm-infection. Although CD8 T cells were activated to produce IFN-gamma, the cytotoxic function of CD8 T cells in Lymphocytic choriomeningitis virus (LCMV) p14 TCR-transgenic mouse was not augmented by Lm-infection. Therefore, Lm-infection differentially influences on cytokine production and cytotoxicity of CD8 T cells.

Immune-mediated neuroprotection of axotomized mouse facial motoneurons is dependent on the IL-4/STAT6 signaling pathway in CD4+ T cells

The CD4(+) T lymphocyte has recently been found to promote facial motoneuron (FMN) survival after nerve injury. Signal Transducer and Activator of Transcription (STAT)4 and STAT6 are key proteins involved in the CD4(+) T cell differentiation pathways leading to T helper type (Th)1 and Th2 cell development, respectively. To determine which CD4(+) T cell subset mediates FMN survival, the facial nerve axotomy paradigm was applied to STAT4-deficient (-/-) and STAT6-/- mice. A significant decrease in FMN survival 4 weeks after axotomy was observed in STAT6-/- mice compared to wild-type (WT) or STAT4-/- mice. Reconstituting STAT6-/- mice with CD4(+) T cells obtained from WT mice promoted WT levels of FMN survival after injury. Furthermore, rescue of FMN from axotomy-induced cell death in recombination activating gene (RAG)-2-/- mice (lacking T and B cells) could be achieved only by reconstitution with CD4(+) T cells expressing functional STAT6 protein. To determine if either the Th1 cytokine, interferon-gamma (IFN-gamma) or the Th2 cytokine IL-4 is involved in mediating FMN survival, facial nerve axotomy was applied to IFN-gamma-/- and IL-4-/- mice. A significant decrease in FMN survival after axotomy occurred in IL-4-/- but not in IFN-gamma-/- mice compared to WT mice, indicating that IL-4 but not IFN-gamma is important for FMN survival after nerve injury. In WT mice, intracellular IFN-gamma vs. IL-4 expression was examined in CD4(+) T cells from draining cervical lymph nodes 14 days after axotomy, and substantial increase in the production of both CD4(+) effector T cell subsets was found. Collectively, these data suggest that STAT6-mediated CD4(+) T cell differentiation into the Th2 subset is necessary for FMN survival. A hypothesis relevant to motoneuron disease progression is presented.

Modulation of the immune system by Listeria monocytogenes-mediated gene transfer into mammalian cells

In this study, we established a method for Listeria monocytogenes(Lm)-mediated gene transfer into mammalian cells to manipulate the immune response of the host during infection by pathogens. We used the Lm-mediated gene transfer method in an in vivo study to manipulate host immune responses against Leishmania major(L. major )-infection. The injection of Lm modulated the susceptible host into a resistant state against L. major-infection. A more efficient protective effect was obtained with the injection of IL-12-cDNA containing Lm, and the protective effect was stronger than that of the resistant strain. The protective mechanism of Lm-injection against L. major-infection observed here appeared to be a result of the activation of the local immune system by the Lm-mediated gene transfer method. The present study is the first demonstration that a gene introduced into a host by Lm works to modulate the murine host immune response against infections in vivo. Since this system strongly induces Th1 responses and suppresses Th2 responses in infected hosts, the system can be used for controlling infectious diseases and for protection against allergic responses in the future.

Leishmania donovani induces interferon regulatory factor in murine macrophages: a host defense response

Macrophages play a key role in directing the host immune response to infection. Interaction of Leishmania donovani with macrophages results in the antagonization of host defense mechanisms by interfering with a cascade of cell signaling processes in the macrophages. Macrophages secrete interferon (IFN), as well as other cytokines, following lipopolysaccharide (LPS) stimulation. The interferon regulatory factors (IRFs) comprise a family of DNA-binding proteins that have been implicated in the transcriptional regulation of IFN and certain IFN-inducible genes. IRF-1 is a transcription factor, which regulates induction of several macrophage effectors and is known to bind to IRF-E site in the inducible nitric oxide synthase (iNOS) promoter. We for the first time report that L. donovani and its surface molecule lipophosphoglycan (LPG) result in a dose- and time-dependent activation of IRF-DNA-binding activity in macrophages. The components of this novel LPG-stimulated IRF-like complex are unclear. The interaction of parasite with the macrophages and not the cellular uptake was important for IRF activation. The use of inhibitors selective for ERK (PD98059) and p38 (SB203580) mitogen-activated protein (MAP) kinase pathway showed that preincubation of cells with either SB203580 or PD98059 did not affect the binding activity of IRF-E, suggesting that both p38 and ERK MAP kinase activation are not necessary for IRF-E activation. It is likely that induction of IRF in response to infection by L. donovani represents a host defense mechanism.

Expression profiles of genes involved in the mouse nuclear factor-kappa B signal transduction pathway are modulated by mangiferin

The polyphenol mangiferin (MA) has been shown to have various effects on macrophage function, including inhibition of phagocytic activity and of free radical production. To further characterize the immunomodulatory activity of MA, this study investigated its effects on expression by activated mouse macrophages of diverse genes related to the NF-kappaB signaling pathway, using a DNA hybridization array containing 96 NF-kappaB-related genes and on cytokine levels using a cytokine protein array. MA at 10 microM significantly inhibited the expression of (a) two genes of the Rel/NF-kappaB/IkappaB family, RelA and RelB (=I-rel), indicating an inhibitory effect on NF-kappaB-mediated signal transduction; (b) TNF receptor-associated factor 6 (Traf6), indicating probable blockage of activation of the NF-kappaB pathway by lipopolysaccharide (LPS), tumor necrosis factor (TNF), and interleukin 1 (IL-1); (c) other proteins involved in responses to TNF and in apoptotic pathways triggered by DNA damage, including the TNF receptor (TNF-R), the TNF-receptor-associated death domain (TRADD), and the receptor interacting protein (RIP); (d) the extracellular ligand IL-1alpha, again indicating likely interference with responses to IL-1; (e) the pro-inflammatory cytokines IL-1, IL-6, IL-12, TNF-alpha and RANTES (CCL5), and cytokines produced by monocytes and macrophages, including granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), macrophage colony-stimulating factor (M-CSF); (f) other toll-like receptor proteins (in addition to Traf6), including JNK1, JNK2 and Tab1; (g) Scya2 (small inducible cytokine A2=monocyte chemoattractant protein 1); and (h) various intracellular adhesion molecules (ICAMs), and the vascular cell adhesion molecule VCAM-1, which is locally increased in atheromas. The inhibition of JNK1, together with stimulation of c-JUN (i.e. the Jun oncogene) and the previously reported superoxide-scavenging activity of MA, suggests that MA may protect cells against oxidative damage and mutagenesis. Taken together, these results indicate that MA modulates the expression of a large number of genes that are critical for the regulation of apoptosis, viral replication, tumorogenesis, inflammation and various autoimmune diseases, and raise the possibility that it may be of value in the treatment of inflammatory diseases and/or cancer.

Dendritic Cells from Malaria-Infected Mice Are Fully Functional APC

Malaria infection has long been associated with diminished T cell responses in vitro and more recently in experimental studies in vivo. Suppression of T cell-proliferative responses during malaria has been attributed to macrophages in a variety of murine and human systems. More recently, however, attention has been directed at the role of dendritic cells in this phenomenon, with several studies suggesting that maturation of dendritic cells is inhibited in vitro by the presence of malaria-infected E. In the studies reported here, we have examined the function of dendritic cells taken directly from infected mice. We found that they express high levels of costimulatory proteins and class II MHC, can activate naive T cells to produce IL-2 as efficiently as dendritic cells from uninfected mice, and support high levels of IFN-gamma production by naive T cells through an IL-12-dependent mechanism. Dendritic cells from infected mice also support higher levels of TNF-alpha production by naive T cells. These same dendritic cells present parasite Ag to a malaria-specific T cell hybridoma, a finding that demonstrates that dendritic cells participate in the generation of Ag-specific immunity during infection. Our findings challenge the contention that dendritic cell function is inhibited by malaria infection.

Identification of IFN regulatory factor-1 binding site in IL-12 p40 gene promoter

IL-12 is a heterodimer composed of p40 and p35 and is a key cytokine that functions to protect the host from viral and microbial infections. IL-12 links the innate immune system with the acquired immune system during infection, and induces differentiation of type 1 T cells that play an important role in the eradication of microbes. The induction of the IL-12 p40 gene is regulated by NF-kappaB in the presence of IFN-gamma. IFN-gamma induces IFN regulatory factor-1 (IRF-1), which in turn induces the transcription of the IL-12 p40 gene. However, the IRF-1 binding site in the promoter region of the IL-12 p40 gene has not yet been formally determined. In the present study, we demonstrated that IRF-1 directly binds to the IL-12 p40 gene promoter and identified its binding site. The IRF-1 binding site in the promoter region of the IL-12 p40 gene is shown to be in the -72 to -58 area of the 5'-upstream region. The -63 to -61 position is the critical site within this region for the binding of IRF-1 to the IL-12 p40 gene promoter. While IFN-gamma must be present for IL-12 p40 gene induction, the p35 gene is strongly induced by LPS, even in the absence of IFN-gamma, and therefore the induction of the p35 gene is IRF-1 independent.

A two-step model of T cell subset commitment: antigen-independent commitment of T cells before encountering nominal antigen during pathogenic infections

Pathogenic infections lead to activation of innate immunity followed by induction of a type 1 T cell subset and, therefore, provide a good model to evaluate when T cells commit to type 1 T cells. Here we show a two-step mechanism of T cell subset commitment during pathogenic infection. The first step is mediated by the basal function of macrophage/dendritic cells and is antigen independent. This step modulates the committed precursor frequency of T cell subsets and influences the expression of T-box expressed in T cells (T-bet) and GATA-3 genes. IL-12 and NK cells are not required for this step. The second step requires antigenic stimulation of T cells together with IL-12 or IL-4, and influences on the expression of T-bet and GATA-3. We propose a two-step T cell subset commitment pathway based on these observations. Therefore, pathogenic infections influence functional T cell commitment before T cells encounter nominal antigen.

Reduced expression of STAT4 and IFN-gamma in macrophages from BALB/c mice

BALB/c mice have been shown to easily induce Th2 type responses in several infection models. In this study, to examine the mechanisms of Th2 dominant responses in BALB/c mice, we assessed several macrophage functions using C3H/HeN, C57BL/6, and BALB/c mouse strains. Peritoneal macrophages from three strains of mice equally produced IL-12 by stimulation with LPS plus IFN-gamma. However, IFN-gamma production in response to IL-12 or IL-12 plus IL-18 was much lower in macrophages from BALB/c mice than other strains. IFN-gamma produced by activated macrophages induced IL-12R mRNA expression in T cells and macrophages themselves depending on their amount of IFN-gamma; namely, macrophages from BALB/c mice induced lower expression of IL-12R. Intracellular levels of STAT4 were much lower in macrophages from BALB/c mice. However, other STATs, such as STAT1 or STAT6, were expressed similarly in the three mouse strains. STAT4 and IFN-gamma production by other cell types such as T cells and B cells were equal in C3H/HeN and BALB/c mice. These results indicate that macrophages from Th2-dominant BALB/c mice have different functional characters compared with other mouse strains; that is, STAT4 expression and IFN-gamma production are reduced, which is one of the causes to shift to Th2-type responses.

Down-regulation of IL-12 p40 gene in Plasmodium berghei-infected mice

We analyzed the mechanism that causes suppression of IL-12 p40 gene induction during Plasmodium berghei infection. Although IL-12 together with IFN-gamma plays an important role in protection against pathogenic infection, the IL-12 p70 protein production of infected macrophages is lower than that by the uninfected macrophages. We showed in the present study that the induction of IL-12 p40 gene but not IL-12 p35 gene in macrophages of P. berghei-infected mice was profoundly inhibited. The inhibition was induced by interaction with macrophages that had contacted with P. berghei-infected erythrocytes and was mediated by a soluble factor, IL-10. There was comparable activation of NF-kappaB in uninfected and infected cells. The induction of IFN-regulatory factor-1 gene was comparable in transcription level in uninfected and infected cells, while the unidentified complex formation of IFN-regulatory factor-1 was observed in infected cells. Therefore, the inhibition of the IL-12 p40 gene induction appeared to be regulated at transcriptional regulation level of the gene.

Lack of gastritis and of an adaptive immune response in interferon regulatory factor-1-deficient mice infected with Helicobacter pylori

To study the role of T cell responses in Helicobacter pylori gastritis, C57BL/6 wild-type and interferon regulatory factor-1-deficient (IRF-1(-/-)) mice were infected with the mouse-adapted H. pylori Sydney strain. Mice lacking the transcription factor IRF-1 are defective in Th1 development and are therefore biased to mount a Th2-type response. After 4 months of infection, C57BL/6 mice developed severe gastritis and atrophy and mounted a Th1-type response towards H. pylori. The Th1 response was abrogated in IRF-1(-/-) mice. This defective Th1 response was associated with the total lack of gastritis and atrophy in IRF-1(-/-) mice despite severe colonization with H. pylori. In addition, IRF-1(-/-) mice did also not develop a Th2 reaction, since they failed to generate H. pylori-specific antibodies and to produce IL-4 in response to H. pylori antigens in vitro. Thus, the transcription factor IRF-1 is necessary for the development of gastritis and atrophy in H. pylori-infected wild-type mice, suggesting a role of Th1 cells in the pathogenesis of H. pylori-associated diseases.

Modulation of host responses to blood-stage malaria by interleukin-12: from therapy to adjuvant activity

This review focuses on the role of interleukin (IL)-12, a proinflammatory cytokine with pleiotropic effects as a potent immunoregulatory molecule and hematopoietic growth factor, in infection with Plasmodium parasites, the causative agents of malaria. IL-12 has been demonstrated to have profound effects on the immune response to blood-stage malaria, to induce protection, and to alleviate malarial anemia. In combination with an anti-malarial drug, IL-12 is effective in an established malaria infection. This cytokine also has potent immune effects as a malaria vaccine adjuvant. However, IL-12 can also mediate pathology during blood-stage malaria.

Differential interleukin-10 expression in interferon regulatory factor-1 deficient mice during Plasmodium berghei blood-stage infection

Mice deficient of functional interferon regulatory factor-1 (IRF-1-/-) by targeted gene disruption infected with a lethal murine malaria strain, Plasmodium berghei ANKA survived longer than its wild-type littermates despite the inability to induce appreciable amounts of interferon-gamma (IFN-gamma) and nitric oxide. In addition, infected IRF-1-/- mice displayed less organ injury with reduced necrosis and inflammation. Both wild-type and IRF-1-/- mice treated with exogenous interleukin-12 (IL-12) suffered extensive organ damage with corresponding up regulation of IFN-gamma, suggesting the pathogenic potential of IL-12 and IFN-gamma. IL-10 is a cytokine produced by CD4+ T lymphocytes belonging to the Th2 subset. Expression of IL-10 in the wild-type mice correlated with the severity of the infection, with higher mRNA expression towards the later stage of infection. In contrast to the wild-type mice, IL-10 levels in the IRF-1-/- mice were induced early in the infection and decreased gradually as the infection progressed. Both untreated and IL-12 treated wild-type mice appeared to follow a Th1-like immune response early in the infection and a Th2-like immune response later in the infection. However, the IRF-1-/- mice were able to launch an altered immune response with a Th2-like immune response early in the infection. These findings suggest that IL-10 expression in the IRF-1-/- mice during the early stage of P. berghei ANKA infection could play an important role in suppressing pathogenic effects of a cell mediated immune response and promoting protective immunity against the parasite.

Absence of CD40-CD40 ligand interactions in X-linked hyper-IgM syndrome does not affect differentiation of T helper cell subsets

The aim of this study was to investigate the effect of absent CD40-CD40 ligand interactions in patients with X-linked hyper-IgM syndrome (XHIGM) on the generation of Th1 and Th2 immunity. Whole blood from patients and sex- and age-matched controls was stimulated with phorbol myristate acetate (PMA) and calcium ionophore A23187 in the presence of Brefeldin A. After 5 h, cellular production of interferon-gamma, IL-4, tumour necrosis factor-alpha and IL-2 was measured by intracellular cytokine staining and flow cytometry. This method has been shown previously to preferentially activate memory T cells and in preliminary experiments cells making these cytokines were found to be predominantly CD45RO+. No differences in the proportion of T cells (CD3+) or T cell subsets (CD4+/CD8+) secreting these cytokines between XHIGM patients and age- and sex-matched controls were observed. In addition, production of IL-12 and IL-6 by monocytes in response to lipopolysaccharide and CD40 stimulation was equivalent in patients and controls. These results suggest that development of Th1 or Th2 memory cells in patients with XHIGM is unaffected by the absence of functional CD40 ligand. Rather, the susceptibility of these patients to intracellular pathogens, such as Pneumocystis carinii and Cryptosporidium parvum, is more likely to be due to an inability to activate the effector arm of the cellular immune response.

Factors that influence T helper cell response to infection

Many factors influence the decision of a precursor T helper cell to become either a type 1 or type 2 cell. These comprise pathogen-defined factors such as the nature and quantity of the pathogen, the route of infection, the influence of immunomodulatory components and of concomitant infections, as well as host-defined factors including genetic predisposition, the number of responding T cells, the major histocompatibility complex haplotype of the individual, the nature of the antigen presenting cells involved and the cytokine environment of the T cells during and following activation. Understanding how such factors influence immune class regulation is fundamental to understanding the pathology of infectious diseases.