CD40 ligand has potent antiviral activity.

For B cells to make antibodies against most antigens, they require help from T cells. T cell help is delivered as two signals to the B cell, one of which is via CD40 and the other can be through receptors for any of a variety of soluble cytokines. We have constructed recombinant vaccinia viruses that express the ligand for CD40 and have shown that the growth of these viruses is dramatically controlled in vivo, even in mice that lack T or B cells. In this paper, we also describe our attempts to analyse the CD40 ligand-mediated antiviral activity by studying the clearance of these viruses in mice that are deficient in important antiviral mechanisms. Thus, the antiviral activity of CD40L may represent a surprising and potent effector mechanism of T cells activated during a virus infection.

Purification of human gamma interferon receptors by sequential affinity chromatography on immobilized monoclonal antireceptor antibodies and human gamma interferon.

mAbs against human IFN-gamma (huIFN-gamma) receptors were obtained by immunizing a BALB/c mouse with eluates from immobilized recombinant huIFN-gamma (rhuIFN-gamma) on which lysates of enriched Raji cell membranes had been adsorbed. mAbs were selected for competitive inhibition of receptor binding of 125I-labeled rhuIFN-gamma. The following additional properties suggest that these antibodies are specific for huIFN-gamma receptors: they bind to the surface of human cells expressing IFN-gamma receptors but not to heterologous cells; this binding is inhibited competitively by addition of rhuIFN-gamma; the number of binding sites revealed by direct binding of 125I-labeled rhuIFN-gamma correlates with the amount of antigen recognized by the mAbs on different cell lines. A Triton X-100 extract of a membrane-enriched fraction of human Raji cells was affinity purified with these mAbs and the eluates from such columns were further purified on immobilized rhuIFN-gamma. As revealed by SDS-PAGE, the final eluate contained two major protein bands with approximate Mr of 90,000 (p90) and 50,000 (p50), respectively. Both proteins were able to specifically bind 125I-labeled rhuIFN-gamma upon electroblotting to nitrocellulose. This binding could be inhibited by the huIFN-gamma receptor mAbs, suggesting that the same epitopes are recognized on p90, p50, and on the cell surface. Therefore, these proteins most likely represent at least a part of huIFN-gamma receptors.

Notch1 deficiency dissociates the intrathymic development of dendritic cells and T cells.

Thymic dendritic cells (DCs) form a discrete subset of bone marrow (BM)-derived cells, the function of which is to mediate negative selection of autoreactive thymocytes. The developmental origin of thymic DCs remains controversial. Although cell transfer studies support a model in which T cells and thymic DCs develop from the same intrathymic pluripotential precursor, it remains possible that these two types of cells develop from independent intrathymic precursors. Notch proteins are cell surface receptors involved in the regulation of cell fate specification. We have recently reported that T cell development in inducible Notch1-deficient mice is severely impaired at an early stage, before the expression of T cell lineage markers. To investigate whether development of thymic DCs also depends on Notch1, we have constructed mixed BM chimeric mice. We report here that thymic DC development from Notch1(-/)- BM precursors is absolutely normal (in terms of absolute number and phenotype) in this competitive situation, despite the absence of Notch1(-/)- T cells. Furthermore, we find that peripheral DCs and Langerhans cells are also not affected by Notch1 deficiency. Our results demonstrate that the development of DCs is totally independent of Notch1 function, and strongly suggest a dissociation between intrathymic T cell and DC precursors.

Theiler's virus infection of 129Sv mice that lack the interferon alpha/beta or interferon gamma receptors.

The Daniels strain of Theiler's virus causes a persistent infection of the white matter of spinal cord of susceptible mice, with chronic inflammation and primary demyelination. Inbred 129Sv mice are resistant to this infection; they present with mild encephalomyelitis and clear the infection within a matter of days. A very different outcome was observed with inbred 129Sv mice whose receptors for interferon alpha/beta or interferon gamma had been inactivated by homologous recombination. The former presented severe encephalomyelitis with acute infection of neurons, particularly in brain and hippocampus, and extensive infection with necrosis of the choroid plexus. Most animals died of this acute disease. The latter, presented the same early encephalomyelitis as the control 129Sv mice. However, they remained persistently infected and developed a very severe late infection of the white matter with extensive primary demyelination. This late disease looked like an exacerbated form of the chronic demyelinating disease observed in susceptible inbred mice such as the SJL/J or FVB strains. Our results show that the two interferon systems play nonredundant roles in the resistance of the 129Sv mouse to the infection by Theiler's virus. They also lend support to the notion that the Ifg gene is involved in the resistance/susceptibility of inbred strains of mice to persistent infection by this picornavirus.

Induction of specific immune unresponsiveness using purified mixed leukocyte culture-activated T lymphoblasts as autoimmunogen. I. Demonstration of general validity as to species and histocompatibility barriers.

Normal immunocompetent T lymphocytes can be induced into specific proliferation if confronted with the relevant alloantigen in vitro. Such mixed leuko-cyteculture-activated T lymphoblasts carring idiotypic receptors on their surface can be purified using velocity sedimentation and serve as immunogen if administered in adjuvant to the autologous host. Autoblast immunization can be shown to lead to specific, long-lasting unresponsiveness against the relevant alloantigens, while leaving reactivity against third-party antigens intact. When tested as to general validity, it could be shown to function in all species analyzed (mouse, rat, and guinea pig) as well as across both major and minor histocompatibility barriers. No negative side effects have been noted so far. It would thus seem clear that autoblast immunization using the above described scheme may serve as a general tool in inducing long-lasting, specific unresponsiveness in any species and across any histocompatibility barrier.

Induction of specific immune unresponsiveness with purified mixed leukocyte culture-activated T lymphoblasts as autoimmunogen. II. An analysis of the effects measured at the cellular and serological levels.

T lymphoblasts specific for foreign histocompatibility antigens and purified via mixed leukocyte culture (MLC) and 1 g velocity sedimentation procedures can be used as autoimmunogen to produce specific immunological unresponsiveness in adult animals. This unresponsiveness is positively correlated to the production of autoanti-idiotypic antibodies in the blast immunized animals and no evidence of coexisting alloimmunity was found. We consider this autoanti-idiotypic immunity to be the specific inducing agent of the immune tolerance. The blast immunization procedure will lead to selective reduction in T-cell reactivity against the relevant alloantigens as measured by MLC, cell-mediated lympholysis, or graft-versus-host assays. However, in individual animals, dichtomy in suppression between two T-cell assays could sometimes be observed indicating elimination of only a select group of idiotypic functionally distinct population of T cells in these blast-immunized animals. Attempts to abrogate already immune animals by the autoblast procedure were successful, in part suggesting the use of the present procedure when trying to induce in accelerated reversion of such immunity.

Mice that lack the interferon-gamma receptor have profoundly altered responses to infection with Bacillus Calmette-Guérin and subsequent challenge with lipopolysaccharide.

Mice with a targeted disruption of the interferon gamma receptor gene (IFN-gamma R0/0 mice) and control wild-type mice were inoculated with the Bacillus Calmette-Guérin (BCG) strain of Mycobacterium bovis. BCG infection was not lethal for wild-type mice whereas all IFN-gamma R0/0 mice died approximately 7-9 wk after inoculation. Histological examination at 2 and 6 wk after BCG inoculation showed that livers of IFN-gamma R0/0 mice had higher numbers of acid-fast bacteria than wild-type mice, especially at 6 wk. In parallel, the livers of IFN-gamma R0/0 mice showed a reduction in the formation of characteristic granulomas at 2 wk after inoculation. Injection of lipopolysaccharide (LPS) 2 wk after BCG inoculation was significantly less lethal for IFN-gamma R0/0 mice than for wild-type mice. Reduced lethality of LPS correlated with a drastically reduced production of tumor necrosis factor alpha (TNF-alpha) in the IFN-gamma R0/0 mice. Interleukin 1 alpha (IL-1 alpha) and IL-6 levels in the serum were also significantly reduced in the IFN-gamma R0/0 mice after BCG infection and LPS challenge. The greatly reduced capacity of BCG-infected IFN-gamma R0/0 mice to produce TNF-alpha may be an important factor in their inability to resist BCG infection. These results show that the presence of a functional IFN-gamma receptor is essential for the recovery of mice from BCG infection, and that IFN-gamma is a key element in the complex process whereby BCG infection leads to the sensitization to endotoxin.

Interferon gamma receptor deficient mice are resistant to endotoxic shock.

Antibody neutralization studies have established interferon gamma (IFN-gamma) as a critical mediator of endotoxic shock. The advent of IFN-gamma receptor negative (IFN gamma R-/-) mutant mice has enabled a more direct assessment of the role of IFN-gamma in endotoxin (lipopolysaccharide [LPS]-induced shock. We report that IFN gamma R-/- mice have an increased resistance to LPS-induced toxicity, this resistance manifesting well before the synthesis and release of LPS-induced IFN-gamma. LPS-induced lymphopenia, thrombocytopenia, and weight loss seen in wild-type mice were attenuated in IFN gamma R-/- mice. IFN gamma R-/- mice tolerated 100-1,000 times more LPS than the minimum lethal dose for wild-type mice in a D-galactosamine (D-GalN)/LPS model. Serum tumor necrosis factor (TNF) levels were 10-fold reduced in mutant mice given LPS or LPS/D-GalN. Bone marrow and splenic macrophages from IFN gamma R-/- mice had a four- to sixfold decreased LPS-binding capacity which correlated with similar reduction in CD14. Serum from mutant mice reduced macrophage LPS binding by a further 50%, although LPS binding protein was only 10% reduced. The expression of TNF receptor I (p55) and II (p75) was identical between wild-type and mutant mice. Thus, depressed TNF synthesis, diminished expression of CD14, and low plasma LPS-binding capacity, in addition to blocked IFN-gamma signaling in the mutant mice, likely to combine to manifest in the resistant phenotype of IFN gamma R-/- mice to endotoxin.

Early interleukin 12 production by macrophages in response to mycobacterial infection depends on interferon gamma and tumor necrosis factor alpha.

Interleukin 12 (IL-12) produced by macrophages immediately after infection is considered essential for activation of a protective immune response against intracellular pathogens. In the murine Mycobacterium bovis Bacillus Calmette-Guérin (BCG) model we assessed whether early IL-12 production by macrophages depends on other cytokines. In vitro, murine bone marrow-derived macrophages produced IL-12 after infection with viable M. bovis BCG or stimulation with LPS, however, priming with recombinant interferon gamma (rIFN-gamma) was necessary. In addition, IL-12 production by these macrophages was blocked by specific anti-tumor necrosis factor alpha (TNF-alpha) antiserum. Macrophages from gene deletion mutant mice lacking either the IFN-gamma receptor or the TNF receptor 1 (p55) failed to produce IL-12 in vitro after stimulation with rIFN-gamma and mycobacterial infection. In vivo, IL-12 production was induced in spleens of immunocompetent mice early during M. bovis BCG infection but not in those of mutant mice lacking the receptors for IFN-gamma or TNF. Our results show that IL-12 production by macrophages in response to mycobacterial infection depends on IFN-gamma and TNF. Hence, IL-12 is not the first cytokine produced in mycobacterial infections.

Mice from a genetically resistant background lacking the interferon gamma receptor are susceptible to infection with Leishmania major but mount a polarized T helper cell 1-type CD4+ T cell response.

Mice with homologous disruption of the gene coding for the ligand-binding chain of the interferon (IFN) gamma receptor and derived from a strain genetically resistant to infection with Leishmania major have been used to study further the role of this cytokine in the differentiation of functional CD4+ T cell subsets in vivo and resistance to infection. Wild-type 129/Sv/Ev mice are resistant to infection with this parasite, developing only small lesions, which resolve spontaneously within 6 wk. In contrast, mice lacking the IFN-gamma receptor develop large, progressing lesions. After infection, lymph nodes (LN) and spleens from both wild-type and knockout mice showed an expansion of CD4+ cells producing IFN-gamma as revealed by measuring IFN-gamma in supernatants of specifically stimulated CD4+ T cells, by enumerating IFN-gamma-producing T cells, and by Northern blot analysis of IFN-gamma transcripts. No biologically active interleukin (IL) 4 was detected in supernatants of in vitro-stimulated LN or spleen cells from infected wild-type or deficient mice. Reverse transcription polymerase chain reaction analysis with primers specific for IL-4 showed similar IL-4 message levels in LN from both types of mice. The IL-4 message levels observed were comparable to those found in similarly infected C57BL/6 mice and significantly lower than the levels found in BALB/c mice. Anti-IFN-gamma treatment of both types of mice failed to alter the pattern of cytokines produced after infection. These data show that even in the absence of IFN-gamma receptors, T helper cell (Th) 1-type responses still develop in genetically resistant mice with no evidence for the expansion of Th2 cells.

The orphan receptor CRF2-4 is an essential subunit of the interleukin 10 receptor.

The orphan receptor CRF2-4 is a member of the class II cytokine receptor family (CRF2), which includes the interferon receptors, the interleukin (IL) 10 receptor, and tissue factor. CRFB4, the gene encoding CRF2-4, is located within a gene cluster on human chromosome 21 that comprises three interferon receptor subunits. To elucidate the role of CRF2-4, we disrupted the CRFB4 gene in mice by means of homologous recombination. Mice lacking CRF2-4 show no overt abnormalities, grow normally, and are fertile. CRF2-4 deficient cells are normally responsive to type I and type II interferons, but lack responsiveness to IL-10. By approximately 12 wk of age, the majority of mutant mice raised in a conventional facility developed a chronic colitis and splenomegaly. Thus, CRFB4 mutant mice recapitulate the phenotype of IL-10-deficient mice. These findings suggest that CRF2-4 is essential for IL-10-mediated effects and is a subunit of the IL-10 receptor.

The stimulatory effects of interleukin (IL)-12 on hematopoiesis are antagonized by IL-12-induced interferon gamma in vivo.

Interleukin (IL)-12 synergizes with other cytokines to stimulate the proliferation and differentiation of early hematopoietic progenitors in vitro. However, in vivo administration of IL-12 decreases peripheral blood counts and bone marrow hematopoiesis. Here, we used interferon (IFN) gamma receptor-deficient (IFN gamma R-/-) mice to investigate whether the in vivo inhibition of hematopoiesis by IL-12 is indirectly mediated by IL-12-induced IFN-gamma. IL-12 administered for 4 d (1 microgram/mouse per day) resulted in lower peripheral blood counts and a 2-fold decrease in bone marrow cellularity in wild-type mice, but not in IFN gamma R-/- mice. Bone marrow hematopoietic progenitors were decreased after IL-12 treatment in wild-type mice, but rather increased in IFN gamma R-/- mice. Splenic cellularity was 2.3-fold higher after IL-12 administration in wild-type mice, largely due to natural killer (NK) cell and macrophage infiltration together with some extramedullary hematopoiesis. In IFN gamma R-/- mice, spleen cellularity was less increased, there were fewer infiltrating NK cells, but a strong extramedullary hematopoiesis. Thus, alterations mediated by IL-12-induced IFN-gamma include reduction in bone marrow cellularity and hematopoietic progenitors, as well as pronounced splenomegaly, largely caused by NK cell infiltration. In the absence of IFN-gamma signaling, IL-12 promotes hematopoiesis, consistent with its in vitro activities.

Inducible gene targeting in mice.

A method of gene targeting that allows the inducible inactivation of a target gene in mice is presented. The method uses an interferon-responsive promoter to control the expression of Cre recombinase. Here, Cre was used to delete a segment of the DNA polymerase beta gene flanked by IoxP recombinase recognition sites. Deletion was complete in liver and nearly complete in lymphocytes within a few days, whereas partial deletion was obtained in other tissues. This method can be used for the inducible inactivation of any other gene in vivo.

Immune response in mice that lack the interferon-gamma receptor.

Interferon-gamma (IFN-gamma) exerts pleiotropic effects, including antiviral activity, stimulation of macrophages and natural killer cells, and increased expression of major histocompatibility complex antigens. Mice without the IFN-gamma receptor had no overt anomalies, and their immune system appeared to develop normally. However, mutant mice had a defective natural resistance, they had increased susceptibility to infection by Listeria monocytogenes and vaccinia virus despite normal cytotoxic and T helper cell responses. Immunoglobulin isotype analysis revealed that IFN-gamma is necessary for a normal antigen-specific immunoglobulin G2a response. These mutant mice offer the possibility for the further elucidation of IFN-gamma-mediated functions by transgenic cell- or tissue-specific reconstitution of a functional receptor.

Functional role of type I and type II interferons in antiviral defense.

Mice lacking the known subunit of the type I interferon (IFN) receptor were completely unresponsive to type I IFNs, suggesting that this receptor chain is essential for type I IFN-mediated signal transduction. These mice showed no overt anomalies but were unable to cope with viral infections, despite otherwise normal immune responses. Comparison of mice lacking either type I or type II IFN receptors showed that, at least in response to some viruses, both IFN systems are essential for antiviral defense and are functionally nonredundant.

The role of antibody concentration and avidity in antiviral protection.

Neutralizing antibodies are necessary and sufficient for protection against infection with vesicular stomatitis virus (VSV). The in vitro neutralization capacities and in vivo protective capacities of a panel of immunoglobulin G monoclonal antibodies to the glycoprotein of VSV were evaluated. In vitro, neutralizing activity correlated with avidity and with neutralization rate constant, a measure of on-rate. However, in vivo, protection was independent of immunoglobulin subclass, avidity, neutralization rate constant, and in vitro neutralizing activity; above a minimal avidity threshold, protection depended simply on a minimum serum concentration. These two biologically defined thresholds of antibody specificity offer hope for the development of adoptive therapy with neutralizing antibodies.

Ligand-induced autoregulation of IFN-gamma receptor beta chain expression in T helper cell subsets.

Interferon gamma (IFN-gamma) responsiveness in certain cells depends on the state of cellular differentiation or activation. Here an in vitro developmental system was used to show that IFN-gamma produced during generation of the CD4+ T helper cell type 1 (TH1) subset extinguishes expression of the IFN-gamma receptor beta subunit, resulting in TH1 cells that are unresponsive to IFN-gamma. This beta chain loss also occurred in IFN-gamma-treated TH2 cells and thus represents a specific response of CD4+ T cells to IFN-gamma rather than a TH1-specific differentiation event. These results define a mechanism of cellular desensitization where a cytokine down-regulates expression of a receptor subunit required primarily for signaling and not ligand binding.

Aggressive behavior and altered amounts of brain serotonin and norepinephrine in mice lacking MAOA.

Deficiency in monoamine oxidase A (MAOA), an enzyme that degrades serotonin and norepinephrine, has recently been shown to be associated with aggressive behavior in men of a Dutch family. A line of transgenic mice was isolated in which transgene integration caused a deletion in the gene encoding MAOA, providing an animal model of MAOA deficiency. In pup brains, serotonin concentrations were increased up to ninefold, and serotonin-like immunoreactivity was present in catecholaminergic neurons. In pup and adult brains, norepinephrine concentrations were increased up to twofold, and cytoarchitectural changes were observed in the somatosensory cortex. Pup behavioral alterations, including trembling, difficulty in righting, and fearfulness were reversed by the serotonin synthesis inhibitor parachlorophenylalanine. Adults manifested a distinct behavioral syndrome, including enhanced aggression in males.

Multiple roles of mouse Numb in tuning developmental cell fates.

BACKGROUND: Notch signaling regulates multiple differentiation processes and cell fate decisions during both invertebrate and vertebrate development. Numb encodes an intracellular protein that was shown in Drosophila to antagonize Notch signaling at binary cell fate decisions of certain cell lineages. Although overexpression experiments suggested that Numb might also antagonize some Notch activity in vertebrates, the developmental processes in which Numb is involved remained elusive. RESULTS: We generated mice with a homozygous inactivation of Numb. These mice died before embryonic day E11.5, probably because of defects in angiogenic remodeling and placental dysfunction. Mutant embryos had an open anterior neural tube and impaired neuronal differentiation within the developing cranial central nervous system (CNS). In the developing spinal cord, the number of differentiated motoneurons was reduced. Within the peripheral nervous system (PNS), ganglia of cranial sensory neurons were formed. Trunk neural crest cells migrated and differentiated into sympathetic neurons. In contrast, a selective differentiation anomaly was observed in dorsal root ganglia, where neural crest--derived progenitor cells had migrated normally to form ganglionic structures, but failed to differentiate into sensory neurons. CONCLUSIONS: Mouse Numb is involved in multiple developmental processes and required for cell fate tuning in a variety of lineages. In the nervous system, Numb is required for the generation of a large subset of neuronal lineages. The restricted requirement of Numb during neural development in the mouse suggests that in some neuronal lineages, Notch signaling may be regulated independently of Numb.

Ligand-induced assembly and activation of the gamma interferon receptor in intact cells.

Functionally active gamma interferon (IFN-gamma) receptors consist of an alpha subunit required for ligand binding and signal transduction and a beta subunit required primarily for signaling. Although the receptor alpha chain has been well characterized, little is known about the specific role of the receptor beta chain in IFN-gamma signaling. Expression of the wild-type human IFN-gamma receptor beta chain in murine L cells that stably express the human IFN-gamma receptor alpha chain (L.hgR) produced a murine cell line (L.hgR.myc beta) that responded to human IFN-gamma. Mutagenesis of the receptor beta-chain intracellular domain revealed that only two closely spaced, membrane-proximal sequences (P263PSIP267 and I270EEYL274) are required for function. Coprecipitation studies showed that these sequences are necessary for the specific and constitutive association of the receptor beta chain with the JAK-2 tyrosine kinase. These experiments also revealed that the IFN-gamma receptor alpha and beta chains are not preassociated on the surface of unstimulated cells but rather are induced to associate in an IFN-gamma-dependent fashion. A chimeric protein in which the intracellular domain of the beta chain was replaced by JAK-2 complemented human IFN-gamma signaling and biologic responsiveness in L.hgR. In contrast, a c-src-containing beta-chain chimera did not. These results indicate that the sole obligate role of the IFN-gamma receptor beta chain in signaling is to recruit JAK-2 into the ligand-assembled receptor complex.