Murine models for acquired immune deficiency syndrome

The mouse has been suggested as a host for comparative studies of several aspects of Human Acquired Immune Deficiency Syndrome (AIDS). Models include studies where part or all of the genome of Human Immunodeficiency Virus (HIV) has been incorporated into murine DNA in living mice. However, the most promising opportunities for study of immunological changes, vaccine development, cofactor involvement in disease, and anti-retroviral and immunostimulatory drug testing involve infection with murine retroviruses which cause many functional changes similar to AIDS. The viruses' effects on immune systems are reviewed with special emphasis. LP-BM5 murine leukemia virus which infects T and B cells, and macrophages. LP-BM5 infection suppresses cell functions while causing polyclonal lymphocyte activation. Murine immunological characterization, availability of inbred mouse strains, economy of using mice versus primates or humans models, and similarity of immune change caused by murine retroviruses compared to those seen in AIDS caused by HIV encourage rapid development of the LP-BM5 murine leukemia model.     

Abrogation of resistance to severe mousepox in C57BL/6 mice infected with LP-BM5 murine leukemia viruses.

Strain C57BL/6 (B6) mice infected with LP-BM5 murine leukemia virus (MuLV) develop a disease which combines abnormal lymphoproliferation with profound immunosuppression and has many features in common with human acquired immunodeficiency syndrome induced by HTLV-III/LAV retroviruses. To determine whether this LP-BM5 MuLV infection would affect the innate resistance of B6 mice to a naturally occurring, highly virulent murine pathogen, mice were exposed to ectromelia virus at various times after treatment with LP-BM5 viruses. At week 4 after infection with LP-BM5, mice challenged with ectromelia virus were unable to generate a humoral immune response to this virus, and between weeks 8 and 10 after infection, challenged mice lost the ability to generate an ectromelia virus-specific cytotoxic-T-cell response. Loss of the cellular immune responses to ectromelia virus was associated with an increased susceptibility to the lethal effects of the virus.     

Inhibition of Premature Death by Isothiocyanates through Immune Restoration in LP-BM5 Leukemia Retrovirus-Infected C57BL/6 Mice

The purpose of this study was to determine the effect of isothiocyanates (ITCs) in delaying the progression of the murine immunodeficiency virus to murine AIDS, resulting in increased life span. Furthermore, we investigated the role of ITCs in modulating immune dysfunction caused by LP-BM5 retrovirus infection. Among the tested ITCs, oral administration of sulforaphane (SUL), benzyl isothiocyante (BITC), and phenethyl isothiocyanate (PEITC) showed the inhibition of premature death caused by LP-BM5 retrovirus infection, while indolo[3,2-b] carbazole (ICZ) and indole-3-carbinol (I3C) did not delay the progress of the LP-BM5 retrovirus to murine AIDS. Inhibition of premature death by BITC, PEITC, and SUL could be explained by restoration of the immune system and down regulation of free radicals. Dysfunction of T and B cell mitogenesis caused by retrovirus infection in primary cultured splenocytes has been partially recovered with administration of BITC, PEITC, and SUL. There was a shift from imbalanced cytokine production (increased Th2 and decreased Th1 cell cytokine production) into balanced Th1/Th2 cell secretion of cytokines under administration of these ITCs during the development of murine AIDS. Hepatic vitamin E level was significantly restored by administration of these ITCs, in accordance with reduced hepatic lipid peroxidation levels. This study suggests that certain types of ITCs have beneficial effects in preventing premature death during progression to murine AIDS by restoration of immune dysfunction and removal of excessive free radicals, implying that selective usage of ITCs would be helpful in retarding the progression from HIV infection to AIDS.     

Analysis of role of CD8+ T cells in resistance to murine AIDS in A/J mice.

The mixture of retroviruses termed LP-BM5 murine leukemia virus (MuLV) contains a replication-defective genome (BM5def), the crucial element for induction of murine AIDS (MAIDS), as well as helper B-tropic ecotropic and mink cell focus-forming MuLV. Among Fv-1b mouse strains, C57BL mice are sensitive to infection by these viruses and to development of MAIDS, but A/J mice are highly resistant to all viral components and to induction of disease. Inasmuch as previous genetic studies indicated a major role in susceptibility for the H-2D locus within the MHC, the effect of CD8+ T cells in A/J resistance to MAIDS was analyzed by depletion of this subset using mAb. A/J mice treated with anti-CD8 mAb beginning soon after inoculation with LP-BM5 MuLV developed disease within 5 wk after virus inoculation. Histopathologic and flow cytometry alteration of tissues and cells from the mAb-treated mice were identical to those seen in virus-infected MAIDS-sensitive strains, and assays for MuLV demonstrated high-level expression of ecotropic MuLV and integration of BM5def. Parallel studies of A/J mice treated with anti-CD4 mAb after infection revealed enhanced expression of ecotropic MuLV but no integration of BM5def, and no signs of MAIDS were detected. These observations indicate that CD8+ T cells are critical in the resistance of A/J mice to LP-BM5 MuLV replication and development of disease and suggest that CD4+ T cells play a role in regulation of ecotropic virus replication.     

Inhibition of premature death by isothiocyanates through immune restoration in LP-BM5 leukemia retrovirus-infected C57BL/6 mice

The purpose of this study was to determine the effect of isothiocyanates (ITCs) in delaying the progression of the murine immunodeficiency virus to murine AIDS, resulting in increased life span. Furthermore, we investigated the role of ITCs in modulating immune dysfunction caused by LP-BM5 retrovirus infection. Among the tested ITCs, oral administration of sulforaphane (SUL), benzyl isothiocyante (BITC), and phenethyl isothiocyanate (PEITC) showed the inhibition of premature death caused by LP-BM5 retrovirus infection, while indolo[3,2-b] carbazole (ICZ) and indole-3-carbinol (I3C) did not delay the progress of the LP-BM5 retrovirus to murine AIDS. Inhibition of premature death by BITC, PEITC, and SUL could be explained by restoration of the immune system and down regulation of free radicals. Dysfunction of T and B cell mitogenesis caused by retrovirus infection in primary cultured splenocytes has been partially recovered with administration of BITC, PEITC, and SUL. There was a shift from imbalanced cytokine production (increased Th2 and decreased Th1 cell cytokine production) into balanced Th1/Th2 cell secretion of cytokines under administration of these ITCs during the development of murine AIDS. Hepatic vitamin E level was significantly restored by administration of these ITCs, in accordance with reduced hepatic lipid peroxidation levels. This study suggests that certain types of ITCs have beneficial effects in preventing premature death during progression to murine AIDS by restoration of immune dysfunction and removal of excessive free radicals, implying that selective usage of ITCs would be helpful in retarding the progression from HIV infection to AIDS.     

Characterization of the CD154-positive and CD40-positive cellular subsets required for pathogenesis in retrovirus-induced murine immunodeficiency

Genetically susceptible C57BL/6 (B6) mice that are infected with the LP-BM5 isolate of murine retroviruses develop profound splenomegaly, lymphadenopathy, hypergammaglobulinemia, terminal B-cell lymphomas, and an immunodeficiency state bearing many similarities to the pathologies seen in AIDS. Because of these similarities, this syndrome has been called murine AIDS (MAIDS). We have previously shown that CD154 (CD40 ligand)-CD40 molecular interactions are required both for the initiation and progression of MAIDS. Thus, in vivo anti-CD154 monoclonal antibody (MAb) treatment inhibited MAIDS symptoms in LP-BM5-infected wild-type mice when either a short course of anti-CD154 MAb treatment was started on the day of infection or a course was initiated 3 to 4 weeks after LP-BM5 administration, after disease was established. Here, we further characterize this required CD154-CD40 interaction by a series of adoptive transfer experiments designed to elucidate which cellular subsets must express CD154 or CD40 for LP-BM5 to induce MAIDS. Specifically with regard to CD154 expression, MAIDS-insusceptible B6 nude mice reconstituted with highly purified CD4+ T cells from wild-type, but not from CD154 knockout, B6 donors displayed clear MAIDS after LP-BM5 infection. In contrast, nude B6 recipients that received CD8+ T cells from wild-type B6 donors did not develop MAIDS after LP-BM5 infection. B6 CD40 knockout mice, which are also relatively resistant to LP-BM5-induced MAIDS, became susceptible to LP-BM5-induced disease after reconstitution with highly purified wild-type B cells but not after receiving purified wild-type dendritic cells (DC) or a combined CD40+ population composed of DC and macrophages obtained from B6 SCID mouse donors. Based on these and other experiments, we thus conclude that the cellular basis for the requirement for CD154-CD40 interactions for MAIDS induction and progression can be accounted for by CD154 expression on CD4+ T cells and CD40 expression on B cells.     

Striatal Met-Enkephalin and Substance P Levels Are Decreased in Mice Infected with the LP-BM5 Murine Leukemia Virus

Abstract: Mice infected with the LP-BM5 murine leukemia virus mixture develop severe immunosuppression and an encephalopathy characterized by spatial learning deficits. Twelve weeks after infection of C57BL/6J mice with LP-BM5, significant (50–60%) reductions in Met-enkephalin and substance P levels were observed in the striatum, whereas somatostatin levels were unchanged. In addition, a 39% decrease in hypothalamic substance P concentrations was observed, with no alteration in Met-enkephalin levels. The apparent selectivity of the decrease in neuropeptide concentrations indicates that a functional alteration of the primary striatal efferent neurons occurs in this infection, which may contribute to the impairment of spatial learning observed in these mice. Moreover, this decrease in striatal neuropeptide levels is similar to the neuropathological changes in basal ganglia observed in HIV-infected individuals and is consistent with previous studies suggesting that the LP-BM5-infected mouse may serve as a useful model of AIDS dementia.     

Antibody to the ligand for CD40 (gp39) inhibits murine AIDS-associated splenomegaly, hypergammaglobulinemia, and immunodeficiency in disease-susceptible C57BL/6 mice.

Infection of genetically susceptible C57BL/6 mice with the LP-BM5 isolate of murine retroviruses cause profound splenomegaly, hypergammaglobulinemia, lymphadenopathy, and an immunodeficiency syndrome which includes the development of terminal B-cell lymphomas. Because many of these and the other manifestations of LP-BM5 virus-induced disease are similar to those seen in AIDS, this syndrome has been named murine AIDS, or MAIDS. Previous reports have shown that the onset of MAIDS depends on the presence of both CD4+ T cells and B cells and have suggested that CD4+ T-cell-B-cell interactions are important to disease pathogenesis. Here, we assessed the possibility that interactions between CD40 and its ligand on activated CD4+ T cells, CD40 ligand/gp39, are involved in the development of MAIDS. To test this hypothesis, LP-BM5-infected B6 mice were treated in vivo with anti-gp39 monoclonal antibody. As a result, MAIDS-associated splenomegaly, hypergammaglobulinemia, germinal center formation, and the loss of in vitro responsiveness to the T- and B-cell mitogens concanavalin A and lipopolysaccharide were inhibited. Anti-gp39 monoclonal antibody-treated LP-BM5-infected mice were also able to mount essentially normal alloantigen-specific cytolytic T-lymphocyte responses. These results support the possibility that molecular interactions between CD40 and gp39 are critical to the development of MAIDS.     

Adoptive transfer of polyclonal and cloned cytolytic T lymphocytes (CTL) specific for mouse AIDS-associated tumors is effective in preserving CTL responses: a measure of protection against LP-BM5 retrovirus-induced immunodeficiency.

Cytolytic T lymphocytes (CTL) can be raised against C57BL/6 B-cell lymphomas from mice with LP-BM5 murine leukemia virus-induced AIDS (MAIDS). Adoptive transfer of polyclonal anti-MAIDS tumor CTL or two CTL clones specific for the B6-1710 MAIDS lymphoma caused preservation of major histocompatibility complex-restricted and allogeneic CTL responses, which may be interpreted as indices of protection from LP-BM5 murine leukemia virus-induced immunodeficiency.     

Cellular and molecular mechanisms of vaccine-induced protection against retroviral infections

More than 15 years after the discovery of human immunodeficiency virus (HIV), researchers are still struggling to design a protective AIDS vaccine. A remaining problem is a lack of basic knowledge about the immunological requirements for protection against retroviruses. Infection of macaque monkeys with simian immunodeficiency virus is still the best model for HIV vaccine research. However, in this model it remains difficult to determine protective immunological mechanisms because of limited numbers of experimental animals and their genetic heterogeneity. Thus, fundamental concepts in retroviral immunology have to be defined in other ways such as mouse models. This minireview summarizes new findings on cellular and molecular mechanisms in protection of mice against Friend murine retrovirus infection. It has been shown that complex immune responses, including B and T cell responses, are required for efficient protection in this model. Multiple viral antigens are necessary to elicit such broad immune reactivity. Efficacious vaccines must protect not only against acute disease, but also against the establishment of persistent infections or the host is at serious risk of virus reactivation. The minireview closes with a discussion on the relevance of findings from the mouse model on the design of a protective vaccine against HIV.     

Clonal expansion of superantigen-reactive T cells is resistant to FK506 in mice with AIDS.

Subcutaneous injection of FK506 (10 mg/kg of body weight) completely blocked the clonal expansion of staphylococcal enterotoxin A (SEA)-reactive T cells in healthy (control) mice after SEA injection but did not disturb it in mice with murine AIDS (MAIDS) caused by infection with LP-BM5 murine leukemia virus. MAIDS mice are characterized by utilization of a FK506-insensitive pathway for clonal expansion of superantigen-reactive T cells.     

Mice with disrupted type I protein kinase A anchoring in T cells resist retrovirus-induced immunodeficiency

Type I protein kinase A (PKA) is targeted to the TCR-proximal signaling machinery by the A-kinase anchoring protein ezrin and negatively regulates T cell immune function through activation of the C-terminal Src kinase. RI anchoring disruptor (RIAD) is a high-affinity competitor peptide that specifically displaces type I PKA from A-kinase anchoring proteins. In this study, we disrupted type I PKA anchoring in peripheral T cells by expressing a soluble ezrin fragment with RIAD inserted in place of the endogenous A-kinase binding domain under the lck distal promoter in mice. Peripheral T cells from mice expressing the RIAD fusion protein (RIAD-transgenic mice) displayed augmented basal and TCR-activated signaling, enhanced T cell responsiveness assessed as IL-2 secretion, and reduced sensitivity to PGE(2)- and cAMP-mediated inhibition of T cell function. Hyperactivation of the cAMP-type I PKA pathway is involved in the T cell dysfunction of HIV infection, as well as murine AIDS, a disease model induced by infection of C57BL/6 mice with LP-BM5, a mixture of attenuated murine leukemia viruses. LP-BM5-infected RIAD-transgenic mice resist progression of murine AIDS and have improved viral control. This underscores the cAMP-type I PKA pathway in T cells as a putative target for therapeutic intervention in immunodeficiency diseases.     

Impaired calcium mobilization in CD4+ and CD8+ T cells in a retrovirus-induced immunodeficiency syndrome, murine AIDS.

After infection with LP-BM5 murine leukemia viruses, susceptible strains of mice develop a severe and progressive immunodeficiency disease, termed murine AIDS (MAIDS), features of which include markedly impaired T cell response to mitogens or specific Ag stimulation and decreased production of IL-2. Since an elevation of intracellular calcium concentration resulting from binding of Ag to the TCR is associated with IL-2 production, T cells from mice either uninfected or infected with LP-BM5 murine leukemia viruses were examined by a calcium mobilization assay. Both CD4+ and CD8+ T cells from infected mice manifested impaired calcium mobilization responses upon in vitro stimulation with anti-CD3 mAb or Con A. The abnormalities appeared early after virus inoculation and showed no difference in time course between subsets of T cells. Frequencies of prestimulation calcium-positive cells among both CD4+ and CD8+ cells in mice with MAIDS were significantly higher than those for uninfected mice. These abnormalities were associated with presence of the MAIDS-inducing defective virus genome, but were not induced by infection of mice genetically resistant to development of MAIDS or with nonpathogenic helper murine leukemia virus, a virus component that induces high spontaneous proliferation of T cells, even in MAIDS-resistant mice.     

Murine acquired immunodeficiency syndrome (MAIDS): an animal model to study the AIDS pathogenesis

Murine AIDS (MAIDS) is a disease that shows many similarities with human AIDS. Several immunological parameters of the disease have been analyzed and genetic studies have mapped a gene (or genes) of resistance in the H-2 complex and shown that the genetic background of the mouse can significantly modify some features of the disease. The etiologic agent of MAIDS is a defective murine leukemia virus that seems able to induce disease in the absence of virus replication. This defective virus induces proliferation of its target cells and the cell expansion was found to be oligoclonal, thus suggesting that the immunodeficiency observed in these mice is a paraneoplastic syndrome. The excellent response of MAIDS mice to antineoplastic agents is consistent with this notion. This animal model has already been useful in stimulating the emergence of novel questions and the formulation of new hypotheses about human AIDS, namely about the role of defective HIV, the role of HIV replication in the progression of the disease, and the importance to identify the target cells of HIV in vivo. Although MAIDS and AIDS are not identical and are induced by retroviruses of different classes, the availability of such a model in an easily accessible small animal species, whose genetics is very sophisticated, may be instrumental in understanding the pathogenesis of AIDS if some of the cellular and molecular affected pathways are common in both diseases.     

Changes in hepatic lipid composition after infection by LP-BM5 murine leukemia virus causing murine AIDS.

The severe hepatic disorders in patients with acquired immune deficiency syndrome (AIDS) is often attributed to a variety of other factors which could affect hepatic function. To evaluate the mechanism of liver damage in murine AIDS-induced immune-suppressed animal, a murine model of AIDS (MAIDS), caused by infection with LP-BM5 murine leukemia virus was used at a late stage of the disease. Retroviral infection significantly increased hepatic cholesterol, triacylgycerol and the cholesterol/phospholipid ratio. Similarly, the proportions of palmitic, palmitoleic, linoleic, ratios of linoleic to arachidonic and saturated to unsaturated fatty acids were significantly lower while the proportion of oleic, docosatetraenoic and docosahexenoic fatty acids were significantly increased in the retrovirus infected mice. Hepatic dysfunction as evidence by increased serum transaminase levels were also observed in the retrovirus infected animals. The data suggest that the liver damage in murine AIDS is induced by retroviral infection and the desaturase enzymes system necessary to maintain regular balance of the fatty acids in the cells may be affected during retroviral infection.     

Aberrant expression of cytokine genes in peritoneal macrophages from mice infected with LP-BM5 MuLV, a murine model of AIDS.

Mice infected with LP-BM5 murine leukemia virus (MuLV) develop a syndrome denoted as murine AIDS. Macrophages harvested from the peritoneal cavities of these mice at 4 or 9 wk postinoculation with LP-BM5 MuLV were analyzed by Northern hybridization for the presence of the defective LP-BM5 virus and their ability to synthesize various cytokines upon induction with Newcastle disease virus (NDV) or (LPS). Neither IFN-alpha or IFN-beta was found to be constitutively expressed in LP-BM5-infected macrophages and in NDV induction studies, and the levels of biologically active IFN-alpha and its mRNA were found to be lower in LP-BM5 MuLV-infected macrophages than in the macrophages from uninfected controls. Similarly, after NDV or LPS induction, the levels of TNF mRNA and TNF protein were significantly lower in LP-BM5-infected macrophages than in macrophages from uninfected mice. The LP-BM5 MuLV-infected macrophages constitutively expressed low levels of IL-1 beta, and when induced with LPS, the relative levels of IL-1 beta were significantly higher in infected than in uninfected macrophages. Although no constitutive expression of IL-6 was detected, the levels of IL-6 mRNA induced with NDV were higher in LP-BM5 MuLV-infected macrophages than in controls. Thus, we found alterations in the expression of selected cytokines in macrophages from mice inoculated with LP-BM5 MuLV rather than a general deregulation of all cytokine expression. These results show that macrophages infected with the defective LP-BM5 virus respond differently to NDV- or LPS-stimulation and suggest that aberrant expression of certain cytokine genes may play a role in the immunopathologic condition in mice with murine AIDS.     

小鼠艾滋病模型的建立及用鹿肠道病毒治疗的实验研究

用小鼠白血病病毒ＬＰ－ＢＭ５ＭｕＬＶ接种新生ＢＡＬＢ／Ｃ小鼠,感染后４～６个月可出现与人类ＡＩＤＳ极为相似的病理变化和免疫缺陷的症状,包括血免疫球蛋白增高、淋巴结肿大、Ｔ辅助淋巴细胞减少和淋巴细胞转化功能降低等。通常作为小鼠获得性免疫缺陷综合症即小鼠艾滋病（ＭＡＩＤＳ）的模型使用。本实验采用已证实具有溶瘤作用的鹿肠道病毒ＥＣＣＯ－１８株对小鼠艾滋病进行实验性治疗,结果表明鹿肠道病毒ＥＣＣＯ－１８可明显缓解艾滋病小鼠的淋巴结肿大和延长艾滋病小鼠的生存时间。提示鹿肠道病毒ＥＣＣＯ－１８治疗小鼠艾滋病有效。     

The CD154/CD40 interaction required for retrovirus-induced murine immunodeficiency syndrome is not mediated by upregulation of the CD80/CD86 costimulatory molecules

C57BL/6 (B6) mice infected with LP-BM5 retroviruses develop disease, including an immunodeficiency similar to AIDS. This disease, murine AIDS (MAIDS), is inhibited by in vivo anti-CD154 monoclonal antibody treatment. The similar levels of insusceptibility of CD40(-/-) and CD154(-/-) B6 mice indicate that CD154/CD40 molecular interactions are required for MAIDS. CD4(+) T and B cells, respectively, provide the CD154 and CD40 expression needed for MAIDS induction. Here, the required CD154/CD40 interaction is shown to be independent of CD80 and CD86 expression: CD80/CD86(-/-) B6 mice develop MAIDS after LP-BM5 infection.     

Increased Brain Levels of Platelet-Activating Factor in a Murine Acquired Immune Deficiency Syndrome Are NMDA Receptor-Mediated

Abstract: Mice infected with the LP-BM5 murine leukemia virus (MuLV) develop an immunodeficiency syndrome (murine AIDS) and an encephalopathy characterized by impaired spatial learning and memory. Because platelet-activating factor (PAF) has been implicated in the pathogenesis of HIV-associated dementia complex, brain PAF levels were measured in LP-BM5 MuLV-infected mice. PAF levels in cerebral cortex and hippocampus were significantly increased at 6 and 12 weeks after LP-BM5 MuLV inoculation, whereas significant increases in striatal and cerebellar PAF levels were observed only at 12 weeks after inoculation. Administration of the NMDA antagonist MK-801 significantly reduced the increased PAF levels in the cerebral cortex and hippocampus of LP-BM5 MuLV-infected mice. These results indicate that the LP-BM5 MuLV-induced increases in brain PAF levels are the result of NMDA receptor activation and are consistent with the hypothesis that elevated CNS PAF levels contribute to the behavioral deficits observed in LP-BM5 MuLV-infected mice.