The majority of cells infected with the defective murine AIDS virus belong to the B-cell lineage

Sympathetic Nerves and Innate Immune System in the Spleen: Implications of Impairment in HIV-1 and Relevant Models

The immune and sympathetic nervous systems are major targets of human, murine and simian immunodeficiency viruses (HIV-1, MAIDS, and SIV, respectively). The spleen is a major reservoir for these retroviruses, providing a sanctuary for persistent infection of myeloid cells in the white and red pulps. This is despite the fact that circulating HIV-1 levels remain undetectable in infected patients receiving combined antiretroviral therapy. These viruses sequester in immune organs, preventing effective cures. The spleen remains understudied in its role in HIV-1 pathogenesis, despite it hosting a quarter of the body’s lymphocytes and diverse macrophage populations targeted by HIV-1. HIV-1 infection reduces the white pulp, and induces perivascular hyalinization, vascular dysfunction, tissue infarction, and chronic inflammation characterized by activated epithelial-like macrophages. LP-BM5, the retrovirus that induces MAIDS, is a well-established model of AIDS. Immune pathology in MAIDs is similar to SIV and HIV-1 infection. As in SIV and HIV, MAIDS markedly changes splenic architecture, and causes sympathetic dysfunction, contributing to inflammation and immune dysfunction. In MAIDs, SIV, and HIV, the viruses commandeer splenic macrophages for their replication, and shift macrophages to an M2 phenotype. Additionally, in plasmacytoid dendritic cells, HIV-1 blocks sympathetic augmentation of interferon-β (IFN-β) transcription, which promotes viral replication. Here, we review viral–sympathetic interactions in innate immunity and pathophysiology in the spleen in HIV-1 and relevant models. The situation remains that research in this area is still sparse and original hypotheses proposed largely remain unanswered.

Virus Infections Incite Pain Hypersensitivity by Inducing Indoleamine 2,3 Dioxygenase

Increased pain sensitivity is a comorbidity associated with many clinical diseases, though the underlying causes are poorly understood. Recently, chronic pain hypersensitivity in rodents treated to induce chronic inflammation in peripheral tissues was linked to enhanced tryptophan catabolism in brain mediated by indoleamine 2,3 dioxygenase (IDO). Here we show that acute influenza A virus (IAV) and chronic murine leukemia retrovirus (MuLV) infections, which stimulate robust IDO expression in lungs and lymphoid tissues, induced acute or chronic pain hypersensitivity, respectively. In contrast, virus-induced pain hypersensitivity did not manifest in mice lacking intact IDO1 genes. Spleen IDO activity increased markedly as MuLV infections progressed, while IDO1 expression was not elevated significantly in brain or spinal cord (CNS) tissues. Moreover, kynurenine (Kyn), a tryptophan catabolite made by cells expressing IDO, incited pain hypersensitivity in uninfected IDO1-deficient mice and Kyn potentiated pain hypersensitivity due to MuLV infection. MuLV infection stimulated selective IDO expression by a discreet population of spleen cells expressing both B cell (CD19) and dendritic cell (CD11c) markers (CD19+ DCs). CD19+ DCs were more susceptible to MuLV infection than B cells or conventional (CD19neg) DCs, proliferated faster than B cells from early stages of MuLV infection and exhibited mature antigen presenting cell (APC) phenotypes, unlike conventional (CD19neg) DCs. Moreover, interactions with CD4 T cells were necessary to sustain functional IDO expression by CD19+ DCs in vitro and in vivo. Splenocytes from MuLV-infected IDO1-sufficient mice induced pain hypersensitivity in uninfected IDO1-deficient recipient mice, while selective in vivo depletion of DCs alleviated pain hypersensitivity in MuLV-infected IDO1-sufficient mice and led to rapid reduction in splenomegaly, a hallmark of MuLV immune pathogenesis. These findings reveal critical roles for CD19+ DCs expressing IDO in host responses to MuLV infection that enhance pain hypersensitivity and cause immune pathology. Collectively, our findings support the hypothesis elevated IDO activity in non-CNS due to virus infections causes pain hypersensitivity mediated by Kyn. Previously unappreciated links between host immune responses to virus infections and pain sensitivity suggest that IDO inhibitors may alleviate heightened pain sensitivity during infections.

A novel role for APOBEC3: susceptibility to sexual transmission of murine acquired immunodeficiency virus (mAIDS) is aggravated in APOBEC3 deficient mice

Background

APOBEC3 proteins are host factors that restrict infection by retroviruses like HIV, MMTV, and MLV and are variably expressed in hematopoietic and non-hematopoietic cells, such as macrophages, lymphocytes, dendritic, and epithelia cells. Previously, we showed that APOBEC3 expressed in mammary epithelia cells function to limit milk-borne transmission of the beta-retrovirus, mouse mammary tumor virus. In this present study, we used APOBEC3 knockout mice and their wild type counterpart to query the role of APOBEC3 in sexual transmission of LP-BM5 MLV – the etiological agent of murine AIDs (mAIDs).

Results

We show that mouse APOBEC3 is expressed in murine genital tract tissues and gametes and that genital tract tissue of APOBEC3-deficient mice are more susceptible to infection by LP-BM5 virus. APOBEC3 expressed in genital tract tissues most likely plays a role in decreasing virus transmission via the sexual route, since mice deficient in APOBEC3 gene have higher genitalia and seminal plasma virus load and sexually transmit the virus more efficiently to their partners compared to APOBEC3+ mice. Moreover, we show that female mice sexually infected with LP-BM5 virus transmit the virus to their off-spring in APOBEC3-dependent manner.

Conclusion

Our data indicate that genital tissue intrinsic APOBEC3 restricts genital tract infection and limits sexual transmission of LP-BM5 virus.

Inhibition of murine AIDS by pro-glutathione (GSH) molecules

Antioxidant molecules can be used both to replenish the depletion of reduced glutathione (GSH) occurring during HIV infection, and to inhibit HIV replication. The purpose of this work was to assess the efficacy of two pro-GSH molecules able to cross the cell membrane more easily than GSH. We used an experimental animal model consisting of C57BL/6 mice infected with the LP-BM5 viral complex; the treatments were based on the intramuscular administration of I-152, a pro-drug of N-acetylcysteine and S-acetyl-beta-mercaptoethylamine, and S-acetylglutathione, an acetylated GSH derivative. The results show that I-152, at a concentration of 10.7 times lower than GSH, caused a reduction in lymph node and spleen weights of about 55% when compared to infected animals and an inhibition of about 66% in spleen and lymph node virus content. S-acetylglutathione, at half the concentration of GSH, caused a reduction in lymph node weight of about 17% and in spleen and lymph node virus content of about 70% and 30%, respectively. These results show that the administration of pro-GSH molecules may favorably substitute for the use of GSH as such.

Dysregulated expression of mitotic regulators is associated with B-cell lymphomagenesis in HOX11-transgenic mice

Dysregulated expression of the homeobox gene, HOX11 is a frequent etiologic event in T-cell acute lymphoblastic leukemias. HOX11-transgenic mice (IgHmu-HOX11Tg)-expressing HOX11 in the B-cell compartment develop B-cell lymphomas with extended latency. The latency suggests that additional genetic events are required prior to the onset of malignant lymphoma. We report the identification of 17 HOX11 collaborating genes, revealed through their propensity to be targeted in a proviral insertional mutagenesis screen. Seven integrations disrupted genes in mitotic spindle checkpoint control, suggesting that cells with elevated HOX11 expression are especially sensitive to dysregulation of chromosome segregation during mitosis. IgHmu-HOX11Tg primary B-lymphocyte cultures exposed to the aneugenic agents, colchicine and colcemid, exhibited increased incidences of chromosome missegregation as assessed by cytokinesis-block micronucleus assays. Additionally, IgHmu-HOX11Tg cultures were shown to exhibit aberrant bypass of spindle checkpoint arrest, as assessed by the increased presence of cycling cells determined by assessment of DNA content and by BrdU immunolabelling. Western immunoblotting revealed elevated expression of the mitotic effector molecules, cyclin A, cyclin B1 and cdc20 in IgHmu-HOX11Tg cultures. Moreover, spontaneously arising lymphoid neoplasms in IgHmu-HOX11Tg mice frequently exhibit aberrant expression of mitotic regulators, concomitant with increased development of micronuclei, abnormal mitotic checkpoint control and increased incidences of abnormal karyotypes when expanded in culture. Collectively, these findings indicate that abnormal regulation of spindle checkpoint control as a result of HOX11 overexpression leads to a heightened predisposition for development of aneuploidy, contributing to oncogenesis.

Combination of inhibitors of lymphocyte activation (hydroxyurea, trimidox, and didox) and reverse transcriptase (didanosine) suppresses development of murine retrovirus-induced lymphoproliferative disease

The ribonucleotide reductase inhibitor hydroxyurea (HU) has demonstrated some benefit as a component of drug cocktails for the treatment of HIV-1 infection. However, HU is notoriously myelosuppressive and often administered only as salvage therapy to patients with late-stage disease, potentially exacerbating the bone marrow toxicity of HU. In this report we have compared the antiviral effects of HU and two novel RR inhibitors trimidox (3,4,5-trihydroxybenzamidoxime) and didox (3,4-dihydroxybenzohydroxamic acid) in combination with didanosine (2,3-didoxyinosine; ddI) in the LPBM5 MuLV retrovirus model (murine AIDS). We also evaluated the effects of these drug combinations on the hematopoietic tissues of LPBM5 MuLV-infected animals. The combination of RR inhibitors and ddI was extremely effective (DX>TX>HU) in inhibiting development of retrovirus-induced disease (splenomegaly, hypergammaglobulinemia, activated B-splenocytes and loss of splenic architecture). In addition, relative levels of proviral DNA were significantly lower in combination drug-treated animals compared to infected controls. Evaluation of femur cellularity, numbers of marrow-derived myeloid progenitor cells (CFU-GM and BFU-E) and peripheral blood indices revealed that TX and DX in combination with ddI were well-tolerated. However, treatment with HU and ddI induced moderate myelosuppression. These data demonstrate that RR inhibitors in combination with ddI provide significant protection against retroviral disease in murine AIDS. Moreover, the novel RR inhibitors TX and DX appear to be more effective and less myelosuppressive than HU when administered with ddI in this model.

Protection against murine leukemia virus-induced spongiform myeloencephalopathy in mice overexpressing Bcl-2 but not in mice deficient for interleukin-6, inducible nitric oxide synthetase, ICE, Fas, Fas ligand, or TNF-R1 genes

Some murine leukemia viruses (MuLVs), among them Cas-Br-E and ts-1 MuLVs, are neurovirulent, inducing spongiform myeloencephalopathy and hind limb paralysis in susceptible mice. It has been shown that the env gene of these viruses harbors the determinant of neurovirulence. It appears that neuronal loss occurs by an indirect mechanism, since the target motor neurons have not been found to be infected. However, the pathogenesis of the disease remains unclear. Several lymphokines, cytokines, and other cellular effectors have been found to be aberrantly expressed in the brains of infected mice, but whether these are required for the development of the neurodegenerative lesions is not known. In an effort to identify the specific effectors which are indeed required for the initiation and/or development of spongiform myeloencephalopathy, we inoculated gene-deficient (knockout [KO]) mice with ts-1 MuLV. We show here that interleukin-6 (IL-6), inducible nitric oxide synthetase (iNOS), ICE, Fas, Fas ligand (FasL), and TNF-R1 KO mice still develop signs of disease. However, transgenic mice overexpressing Bcl-2 in neurons (NSE/Bcl-2) were largely protected from hind limb paralysis and had less-severe spongiform lesions. These results indicate that motor neuron death occurs in this disease at least in part by a Bcl-2-inhibitable pathway not requiring the ICE, iNOS, Fas/FasL, TNF-R1, and IL-6 gene products.

Quantitative analysis of LP-BM5 murine leukemia retrovirus RNA using real-time RT-PCR

Murine AIDS (MAIDS) develops in susceptible mouse strains after infection with the LP-BM5 murine leukemia virus (MuLV) complex that contains a mixture of defective (BM5def) and replication-competent viruses. While the BM5def virus is the causative agent in MAIDS, the replication-competent viruses in LP-BM5, including ecotropic MuLV (BM5eco), are required for BM5def propagation and thus function as helper viruses. We describe quantitative real-time RT-PCR assays for RNA encoded by the BM5def and BM5eco components of LP-BM5. The assays were used to standardize better the input doses of LP-BM5 viruses across viral preparations and to quantify BM5def and BM5eco gag RNA levels in spleen and blood cells from MAIDS-susceptible and -insusceptible infected mice. Spleens of MAIDS-susceptible infected mice harbored approximately similar levels of BM5def gag RNA as infected spleens of mice that are insusceptible to MAIDS due to lack of CD40. In contrast, the same infected spleens of CD40-deficient mice contained substantially higher (up to 10-fold) levels of BM5eco gag RNA compared with susceptible controls. Similar to that seen in spleen, infected blood of CD40-deficient mice contained similar levels of BM5def gag as susceptible strains, but increased levels (up to threefold) of BM5eco gag RNA. The assays described below can be used to characterize better the contributions of different functional viral components of the LP-BM5 mixture to the development of MAIDS.

CD19 signaling pathways play a major role for murine AIDS induction and progression

Infection of genetically susceptible mice with the LP-BM5 mixture of murine leukemia viruses including an etiologic defective virus (BM5def) causes an immunodeficiency syndrome called murine AIDS (MAIDS). The disease is characterized by interactions between B cells and CD4(+) T cells resulting in polyclonal activation of both cell types. It is known that BM5def is expressed at highest levels in B cells and that B cells serve as viral APC. The CD19-CD21 complex and CD22 on the surface of B cells play critical roles as regulators of B cell responses to a variety of stimuli, influencing cell activation, differentiation, and survival. CD19 integrates positive signals induced by B cell receptor ligation by interacting with the protooncogene Vav, which leads to subsequent tyrosine phosphorylation of this molecule. In contrast, CD22 negatively regulates Vav phosphorylation. To analyze the role of CD19, CD21, Vav, and CD22 in MAIDS, we infected mice deficient in CD19, CD21 (CR2), Vav-1, or CD22 with LP-BM5 murine leukemia viruses. Infected CR2(-/-) mice developed MAIDS with a time course and severity indistinguishable from that of wild-type mice. In contrast, CD19 as well as Vav-1 deficiency restricted viral replication and suppressed the development of typical signs of MAIDS including splenomegaly, lymphadenopathy, and hypergammaglobulinemia. Finally, CD22 deficiency was found to accelerate MAIDS development. These results provide novel insights into the B cell signaling pathways required for normal induction and progression of MAIDS.

Induction of CD4 T cell changes in murine AIDS is dependent on costimulation and involves a dysregulation of homeostasis

Strong CD4 T cell activation and proliferation are seen in susceptible mice infected with the murine retroviral inoculum, LP-BM5, which produces an immunodeficiency syndrome called murine AIDS (MAIDS). We developed a short term adoptive transfer model of MAIDS to examine the requirements for the CD4 T cell response. Naive CD4 T cells from uninfected donors responded quickly after adoptive transfer into MAIDS-infected hosts, becoming activated and proliferating within several days. Using blocking mAbs to costimulatory ligands and CD4 T cells deficient in expression of their receptors, we found that the CD4 T cell response requires CD28:B7.1/B7.2 interactions, but not CTLA4 or CD40-CD40 ligand interactions. Naive CD4 T cells did not respond in H-2M-deficient mice with MAIDS, suggesting that disease requires recognition of self peptide-MHC complexes. The self MHC-dependent division and accumulation of large numbers of CD4 T cells suggest that MAIDS involves a disruption of the balance of homeostatic signals. Supporting this hypothesis, CD4 T cells from mice with MAIDS failed to regulate the homeostatic division of naive CD4 T cells in a cotransfer model. Thus, a combination of up-regulation of costimulatory ligands and disruption of homeostatic control may be responsible for CD4 lymphoproliferation in MAIDS.

Induction of murine AIDS virus-related sequences after burn injury

To better understand the molecular signaling events leading to systemic inflammatory response syndrome (SIRS) and multiple organ failure (MOF), changes in gene expression profiles after burn injury were investigated by differential display. C57BLKS/J mice were subjected to 18% total body surface area (TBSA) full-thickness burn and various tissues were harvested at multiple time points after injury. Initial differential display revealed that retroviral transcripts similar to the envelope sequence of murine AIDS (MAIDS) virus were rapidly and transiently up-regulated after injury. Subsequent RT-PCR and DNA sequencing analyses confirmed the transient up-regulation of retroviral sequences similar to those of the MAIDS virus. In addition, the presence and induction of the subgenomic envelope transcripts of these MAIDS virus-related sequences, including a novel double spliced message, were identified after burn injury. These data suggest that the transcriptional efficiency of the integrated retroviral DNA and reactivation of defective MAIDS virus-related sequences may be affected by pathophysiological signals, such as burn injury. The elevated expression of these MAIDS virus-related retroviral sequences may affect the transcriptional activities of the flanking genes at the integration sites and may be a cause of altered local and systemic immune responses to burn-related stress.

B cell immunodeficiency fails to develop in CD4-deficient mice infected with BM5: murine AIDS as a multistep disease

The immunodeficiency syndrome murine AIDS (MAIDS), caused by the BM5 retrovirus preparation, involves the activation, division, and subsequent anergy of the entire CD4(+) T cell population as well as extensive B cell hyperproliferation and hypergammaglobulinemia, resulting in splenomegaly and lymphadenopathy, followed many weeks later by death. The development of MAIDS requires CD4(+) T cells and MHC class II expression by the infected host, supporting a role for T-B interaction in disease development or progression. To explore this possibility, we examined development of MAIDS in mice deficient in CD4 (CD4 knockout), in which T-B interactions are compromised. We find that in CD4 knockout hosts, BM5 causes T cell immunodeficiency in the remaining T cells but has only a limited ability to induce B cell phenotypic changes, hyperproliferation, hypergammaglobulinemia, or splenomegaly. There is also delayed death of infected mice. This implies that CD4 dependent T-B interaction is needed to induce the B cell aspects of disease and supports a multistep mechanism of disease in which B cell changes follow and are caused by CD4(+) T cell effects.

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.

Mice transgenic for a soluble form of murine cytotoxic T lymphocyte antigen 4 are refractory to murine acquired immune deficiency sydrome development

Interactions between B and CD4+ T cells are central to the pathogenesis of retrovirus-induced murine acquired immune deficiency virus (MAIDS). Prompted by previous work showing that treatment with cytotoxic T lymphocyte antigen 4 immunoglobulin (CTLA4Ig) partly inhibited the disease, we studied the course of infection in mice deficient for CD28-B7 interactions (mCTLA4-Hgamma1 transgenic mice). Despite a relative viral load identical to that of non-transgenic mice, the transgenic mice did not develop any of the major MAIDS symptoms (i.e. lymphoproliferation and immune anergy). The mCTLA4-Hgamma1 did not however, completely inhibit B-cell activation as indicated by a slight hypergammaglobulinaemia and microscopic blastic transformation. Absence of MAIDS in transgenic mice was associated with much lower levels of both interleukin-4 and interferon-gamma transcripts following viral infection. These results support the theory that the CD28/B7 costimulatory pathway is a critical determinant to MAIDS development.

Activation of the ubiquitin proteolytic system in murine acquired immunodeficiency syndrome affects IkappaBalpha turnover

Murine acquired immunodeficiency syndrome (MAIDS) is a complex immunopathology caused by a defective murine leukemia virus (LP-BM5) that mainly targets B-lymphocytes. Lymphadenophathy, splenomegaly, hypergammaglobulinemia and progressive immunodeficiency are prominent features of MAIDS. Previously, we showed that the ubiquitin proteolytic system was upregulated in infected lymph nodes [Crinelli, R., Fraternale, A., Casabianca, A. & Magnani, M. (1997) Eur. J. Biochem. 247, 91-97]. In this report, we demonstrate that increased 26S proteasome activity is responsible for accelerated turnover of the IkappaBalpha inhibitor in lymph node extracts derived from animals with MAIDS. The molecular mechanisms mediating IkappaBalpha proteolysis involved constitutive phosphorylation of IkappaBalpha at Ser32 and Ser36 and subsequent ubiquitination, suggesting persistent activation of an NF-kappaB inducing pathway. Interestingly, enhanced IkappaBalpha degradation did not result in enhanced NF-kappaB DNA binding activity, but rather in a different subunit composition. The modulation of NF-kappaB/IkappaB system may affect multiple immunoregulatory pathways and may in part explain the mechanisms leading to the profound immune dysregulation involved in MAIDS pathogenesis.

Cytotoxic T lymphocytes to endogenous mouse retroviruses and mechanisms of retroviral escape

Mouse retrovirus-induced lymphoma/leukemia and immunodeficiency are useful models for analogous human diseases. Both ecotropic (mouse tropic) and recombinant retroviruses, including the polytropic mink cytopathic focus-inducing type, have been studied for disease pathogenesis and as targets for humoral and cellular immunity, particularly cytotoxic T-lymphocyte (CTL) responses. For AKR/Gross murine leukemia viruses (MuLV) we have defined an immunodominant CTL epitope in the p 15E transmembrane anchor envelope protein and three minor/subdominant epitopes. Evidence is presented for retroviral escape from CTL by selection following genetic recombination and point mutation both within and outside CTL epitope sequences, and via endogenous retrovirus-infected cell downregulation of the generation of anti-AKR/Gross MuLV CTL. As demonstrated in vivo in naturally occurring non-responder strains by adoptive transfer, and in vitro by cell-mixing experiments, a central non-responsiveness mechanism appears to be peripheral inhibition mediated by infected cells expressing MHC-presented viral peptides. Such inhibition requires Fas expression by antiviral T cells; occurs upon TCR-mediated recognition of virus-infected, Fas ligand-expressing "veto" cells; and apparently leads to an antigen-specific form of activation-induced cell death of T cells. In the LP-BM5 MuLV isolate that causes murine AIDS (MAIDS) retroviral variation also leads to CTL escape--the BM5-helper virus has altered forms of the immunodominant and two minor/subdominant epitopes. In contrast, a novel immunodominant CTL epitope is recognized by MAIDS resistant, but not MAIDS-susceptible, strains. This epitope is uniquely encoded in an alternative translational reading frame of the viral gag gene. It also appears that the LP-BM5 MuLV have co-opted the cells of the immune system for retroviral pathogenesis--CD40/CD40L (CD154) interactions are required both for the initiation and progression of MAIDS.

Nef harbors a major determinant of pathogenicity for an AIDS-like disease induced by HIV-1 in transgenic mice

Transgenic (Tg) mice expressing the complete coding sequences of HIV-1 in CD4+ T cells and in cells of the macrophage/dendritic lineages develop severe AIDS-like pathologies: failure to thrive/weight loss, diarrhea, wasting, premature death, thymus atrophy, loss of CD4+ T cells, interstitial pneumonitis, and tubulo-interstitial nephritis. The generation of Tg mice expressing selected HIV-1 gene(s) revealed that nef harbors a major disease determinant. The latency and progression (fast/slow) of the disease were strongly correlated with the levels of Tg expression. Nef-expressing Tg thymocytes were activated and alpha-CD3 hyperresponsive with respect to tyrosine phosphorylation of several substrates, including LAT and MAPK. The similarity of this mouse model to human AIDS, particularly pediatric AIDS, suggests that Nef may play a critical role in human AIDS, independently of its role in virus replication.

Decreased protein levels of the c-Cbl protooncogene in murine AIDS

Murine acquired immunodeficiency syndrome (MAIDS) can be viewed as a lymphoproliferative disease which involves B cells as well as T cells from spleen and lymph nodes while thymus and Peyer's patches do not participate in the process. The 120-kDa protooncogene product c-Cbl was initially cloned from the murine Cas NS-1 B cell lymphoma. It is a main target of immunoreceptor (TCR and BCR)-mediated protein tyrosine kinase activity. Moreover, recent data suggest that c-Cbl might play a crucial role in the regulation of cell proliferation through regulation of GTP-binding proteins. Therefore, the involvement of c-Cbl was evaluated in the lymphoproliferative disease induced by the MAIDS virus. The expression of the c-Cbl protein was dramatically reduced in the lymph node of infected mice while it remained normal in the thymus. In contrast, the expression of actin, TCR-zeta chain, ZAP-70, and p59(fyn) remained similar in controls and infected mice. Identical results were obtained with sorted B cells and T cells. Surprisingly, a B cell lymphoma line derived from late stage MAIDS mice displayed a normal level of c-Cbl.

Prevention of murine AIDS development by (R)-9-(2-phosphonylmethoxypropyl)adenine

LP-BM5 murine leukemia virus (MuLV) infection causes severe immunodeficiency termed murine AIDS (MAIDS). The acyclic nucleoside phosphonates, (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) and 9-(2-phosphonylmethoxyethyl)adenine (PMEA) were examined, in comparison with zidovudine (AZT), for their inhibitory effect on the development of MAIDS. Although no significant difference in inhibition of LP-BM5 MuLV replication was identified between PMPA and PMEA in cell cultures, PMPA was obviously less cytotoxic to the host lymphocytes. None of the mice treated in vivo with 5 or 25 mg/kg of PMPA or 25 mg/kg of PMEA developed MAIDS at 5 weeks after viral infection. However at 9 weeks, none of the 25 mg/kg PMPA-treated mice progressed to MAIDS, except for one that developed mild MAIDS, whereas PMEA, even at 100 mg/kg, could not prevent disease progression. MAIDS-associated activation of lymphocytes and viral replication were drastically inhibited by PMPA treatment. These results indicate that PMPA is a highly effective antiretroviral agent in vivo.

CD28-B7 costimulatory blockade by CTLA4Ig delays the development of retrovirus-induced murine AIDS

Mouse AIDS (MAIDS) induced in C57BL/6 mice by infection with a replication-defective retrovirus (Du5H) combines extensive lymphoproliferation and profound immunodeficiency. Although B cells are the main target of viral infection, recent research has focused on CD4(+) T cells, the activation of which is a key event in MAIDS induction and progression. A preliminary observation of increased expression of B7 molecules on B cells in MAIDS prompted us to address the possible involvement of the CD28/B7 costimulatory pathway in MAIDS. Mice infected with the MAIDS-inducing viral preparation were treated with murine fusion protein CTLA4Ig (3 x 50 microg/week given intraperitoneally), a competitive inhibitor of physiological CD28-B7 interactions. In CTLA4Ig-treated animals, the onset of the disease was delayed, lymphoproliferation progressed at a much slower rate than in untreated mice, and the loss of in vitro responsiveness to mitogens was reduced. Relative expression of Du5H did not differ between treated and untreated animals. These results suggest that the CD28/B7 costimulatory pathway contributes to MAIDS development.

Establishment of MAIDS-defective virus-infected B cell lines and their characterization

Mice inoculated with the murine AIDS (MAIDS)-defective virus develop severe B and T cell dysfunctions. The primary event in the development of this disease is the infection and polyclonal expansion of the target cells of this defective virus, which have been reported to belong to the B cell lineage. To further study the central role that these cells play in the development of MAIDS, we attempted to establish MAIDS-defective virus-infected B cell lines in vitro. We succeeded in establishing two cell lines, SD1 and CSTB5, from the enlarged organs of C57BL/6 mice inoculated with helper-free stocks of the MAIDS-defective virus. Both cell lines are not transplantable in syngeneic C57BL/6 mice or in nude or CD8-/- mice and are apparently not malignant. They both belong to the B lineage, as their immunoglobulin (Ig) genes, but not the T cell receptor (TcR) beta locus, are rearranged, suggesting that they are relatively mature B cells. However, analysis of cell surface marker expression by FACS revealed a surface phenotype similar to that of pre-B cells (MHC I+, MHC II+, B7.2+, sIgM-, sIgG-, kappa-, B220-, CD5-, Thy1.2-, TcR-, CD3-, CD4-, CD8-, Mac-1-, 33D1-). Additionally, the CSTB5 cells express CD40 and the SD1 cells express CD43. Both cell lines contain the MAIDS-defective provirus and express the expected 4.2-kb viral RNA and the corresponding Pr60gag protein. The CSTB5 cells are nonproducer, while the SD1 cell line produces what appears to be an endogenous MuLV. The phenotype of these cell lines is very similar to what is known about the target B cells of this virus in vivo. These new established cell lines are likely to be useful in elucidating the mechanism(s) by which the MAIDS-defective virus causes its target B cells to proliferate and induce T cell anergy in infected animals.

Evidence for a continued requirement for CD40/CD40 ligand (CD154) interactions in the progression of LP-BM5 retrovirus-induced murine AIDS

In genetically susceptible C57BL/6 mice the LP-BM5 isolate of murine retroviruses causes profound splenomegaly, lymphadenopathy, hypergammaglobulinemia, and an immunodeficiency syndrome bearing many similarities to the pathologies seen in AIDS. Because of these similarities, which also include terminal B cell lymphoma formation, this syndrome has been called murine AIDS or MAIDS. Prompted by previous reports showing that the onset of MAIDS is dependent on the presence of both CD4+ T and B cells, we have previously shown that anti-gp39/CD40 ligand mAb (anti-CD40L mAb) treatment of LP-BM5-infected mice is effective in inhibiting the induction of MAIDS when a short course of anti-CD40L mAb treatment was started on the same day as LP-BM5 administration. The success of anti-CD40L mAb therapy, as indicated by a much reduced degree of splenomegaly, hypergammaglobulinemia, and mitogen and allogeneic CTL unresponsiveness, demonstrated that CD40L/CD40 interactions were critical to the establishment of MAIDS. Here we extend these findings through the use of delayed anti-CD40L mAb treatment of mice, beginning 3-4 weeks after LP-BM5 infection, by showing that interruption of CD40L/CD40 interactions also interferes with the progression of MAIDS. About 60% of LP-BM5-preinfected mice were affected by delayed anti-CD40L mAb treatment, with substantially reduced spleen weights and serum hypergammaglobulinemia and normal or greatly restored proliferative responses to Con A stimulation and CTL responses to allogeneic stimulation. The other LP-BM5-infected mice that did not respond to anti-CD40L therapy were found to have made antibodies to the anti-CD40L mAb. Thus, in a majority of mice anti-CD40L mAb therapy was very effective in interfering with MAIDS pathogenesis well after the establishment of the virus infection and MAIDS symptomatology, indicating that CD40L/CD40 interactions are crucial to the maintenance and progression of the disease, as well as its initiation.

Relationship of cytokines and cytokine signaling to immunodeficiency disorders in the mouse

The contributions of cytokines to the development and progression of disease in a mouse model of retrovirus-induced immunodeficiency (MAIDS) are controversial. Some studies have indicated at etiologic role for type 2 cytokines, while others have emphasized the importance of type 1 cytokines. We have used mice deficient in expression of IL-4, IL-10, IL-4 and IL-10, IFN-gamma, or ICSBP-a transcriptional protein involved in IFN signaling-to examine their contributions to this disorder. Our results demonstrate that expression of type 2 cytokines is an epiphenomenon of infection and that IFN-gamma is a driving force in disease progression. In addition, exogenously administered IL-12 prevents many manifestations of disease while blocking retrovirus expression. Interruption of the IFN signaling pathways in ICSBP-/- mice blocks induction of MAIDS. Predictably, ICSBP-deficient mice exhibit impaired responses to challenge with several other viruses. This immunodeficiency is associated with impaired production of IFN-gamma and IL-12. Unexpectedly, however, the ICSBP-/- mice also develop a syndrome with many similarities to chronic myelogenous leukemia in humans. The chronic phase of this disease is followed by a fatal blast crisis characterized by clonal expansions of undifferentiated cells. ICSBP is thus an important determinant of hematopoietic growth and differentiation as well as a prominent signaling molecule for IFNs.

Modulation of murine AIDS-related pathology by concurrent antibody treatment and coinfection with Leishmania major

Infection of C57BL/6 mice with a mixture of murine leukemia viruses (MuLVs) designated LP-BM5 MuLV leads to a disease characterized by progressive immunodeficiency and lymphoproliferation, known as murine AIDS (MAIDS). The development of MAIDS is associated with increased B-cell lymphoblast proliferation, but there is reason to believe that T-cell function and, particularly, T-cell-derived cytokines may also play a role. We have previously shown that concurrent infection with Leishmania major (which induces a strongly polarized Th1 response in C57BL/6 mice) and LP-BM5 MuLV modulates the disease induced by both infections. Here we show by treatment of mice with anticytokine antibodies that this modulation is largely exerted through the balance of Th1 and Th2 cytokines. Infected mice treated with antibodies to interleukin-4 and interleukin-10 exhibited a delayed development of MAIDS-related pathology and maintained T-cell responsiveness longer than mice treated with control antibody. Gamma interferon induced by coinfection with L. major synergized with anti-IL-4 treatment to inhibit the development of MAIDS pathology. Conversely, treatment with anti-gamma interferon led to a significant increase in splenomegaly and lymphadenopathy and slightly exacerbated loss of T-cell function. These data suggest that the production of Th2-associated cytokines may promote MAIDS pathology, while Th1-associated cytokines may help control the disease.

The murine AIDS virus Gag precursor protein binds to the SH3 domain of c-Abl

The Pr60gag protein of the murine AIDS (MAIDS) defective virus promotes the proliferation of the infected target B cells and is responsible for inducing a severe immunodeficiency disease. Using the yeast two-hybrid system, we identified the SH3 domain of c-Abl as interacting with the proline-rich p12 domain of Pr60gag. The two proteins were shown to associate in vitro and in vivo in MAIDS virus-infected B cells. Overexpression of Pr60(gag) in these cells led to a detectable increase of the levels of c-Abl protein and to its translocation at the membrane. These results suggest that this viral protein serves as a docking site for signaling molecules and that c-Abl may be involved in the proliferation of infected B cells.

Studies of the susceptibility of nude, CD4 knockout, and SCID mutant mice to the disease induced by the murine AIDS defective virus

Murine AIDS (MAIDS) is induced by a defective retrovirus that infects lymphocyte cells of the B lineage. To determine whether functional T cells are required for the infection of B cells, T-cell-deficient mice (nude, CD4 knockout, and SCII)) were infected with helper-free stocks of the MAIDS defective virus. Infection of B cells was monitored by Northern blot analysis and in situ hybridization. The C57BL/6 nude mice contained clusters of infected B cells, but less so than did the euthymic mice. In contrast, the (C57BL/6 x BALB/c)F1 nude mice harbored more infected B cells than did their euthymic littermates when maintained in a pathogen-free environment. Clusters of infected B cells were also detected in the MAIDS virus-infected CD4-/- knockout mice despite the total absence of CD4+ T cells in these mice. However, infected cells were not detected in SCID mice (deficient in mature T and B cells) inoculated with the same virus, indicating that precursor B cells are not a target of the virus in the absence of mature CD4+ T cells. These data confirm that the primary event in the development of MAIDS is the infection of relatively mature peripheral B cells and that CD4+ T cells are required to promote the expansion of these infected B cells.

Effect of hot water extract of Chlorella vulgaris on cytokine expression patterns in mice with murine acquired immunodeficiency syndrome after infection with Listeria monocytogenes

We have previously reported that oral administration of hot water extract of Chlorella vulgaris (CVE) enhances resistance to Listeria monocytogenes through augmentation of Listeria-specific cell-mediated immunity in normal mice and mice with murine acquired immunodeficiency syndrome (MAIDS) caused by murine leukemia virus (MuLV) LP-BM5. To elucidate the mechanisms whereby CVE augments the cell-mediated immunity, we examined the expression patterns of mRNA for cytokines in normal and MAIDS mice given CVE orally after L. monocytogenes infection. The expression levels of IL-1 alpha, IL-12, GM-CSF, MIP and TNF alpha genes were significantly augmented in the peritoneal adherent cells by oral administration of CVE for 2 weeks before Listeria infection. The expression levels of gamma IFN and IL-12 mRNA were significantly higher in the spleen after Listeria infection in CVE-treated mice than in normal mice, while the expression of IL-10 mRNA in the spleen was decreased by CVE administration. In MAIDS mice, oral administration of CVE also augmented the expression of gamma IFN and IL-12 mRNA in the spleen after Listeria infection, while it rather reduced the expression of IL-10 mRNA. These results suggest that CVE may preferentially augment THI responses against Listeria via activation of macrophages to produce IL-12 and enhance host defence against Listeria infection both in normal and MAIDS mice.

Recovery from retrovirus-induced immune suppression in BDP/J mice: dominance of the "regressor' phenotype

Murine acquired immune deficiency syndrome (MAIDS) is an immunosuppressive disease of mice induced by infection with the LP-BM5 murine leukemia virus (MuLV) retrovirus isolate. Certain inbred strains of mice are resistant to disease, but F1 crosses between sensitive and resistant strains are predominantly sensitive to MAIDS. One inbred strain, BDP, demonstrates a novel disease phenotype, recovery of immune function after a period of profound immune suppression. This trait is genetically dominant in crosses between BDP and either sensitive or resistant strains. The 'regressor' phenotype reveals the existence of a mechanism for recovery from immunosuppressive retrovirus infections, which may be of import in developing therapies for AIDS patients.

Induction of murine acquired immunodeficiency syndrome (MAIDS) in allophenic mice generated from strains susceptible and resistant to disease

To examine whether a retroviral disease can be controlled in animals in which cells from a resistant strain coexist in a state of immunological tolerance with cells from a susceptible strain, allophenic mice were constructed and infected with LP-BM5 murine leukemia viruses which induce a fatal disorder, termed murine acquired immunodeficiency syndrome (MAIDS), characterized by lymphoproliferation and immunodeficiency in susceptible inbred strains of mice. We found that in two different strain combinations, resistance to MAIDS was contingent on the presence in individual animals of >50% of lymphocytes of resistant strain origin and correlated with reduction or elimination of retrovirus. In contrast, animals harboring substantial, but less than predominant, numbers of genetically resistant lymphocytes developed disease and died within the same time frame as susceptible control mice with uncontained proliferation of retrovirus.

Apoptosis by CD95 (Fas)-dependent and -independent mechanisms in Peyer's patch lymphocytes in murine retrovirus-induced immunodeficiency syndrome

CD95 (Fas)/CD95 ligand (CD95 L)-mediated apoptosis is thought to be involved in the delayed progression of murine AIDS (MAIDS) induced by LP-BM5 murine leukemia virus (MuLV). We show evidence of apoptosis in lymphocytes of Peyer's patches (PP) at the early stage of MAIDS. Both T and B cells in PP expressed CD95 at the early stage of MAIDS and decreased in number thereafter. The decrease in T cells was not evident in CD95-mutated lpr mice with MAIDS, suggesting that CD95/CD95 L interaction is involved in the apoptosis of T cells in PP during the course of MAIDS. On the other hand, the number of B cells was also decreased in PP of lpr mice with MAIDS. The proliferative ability of B cells in PP of MAIDS mice in response to immunoglobulin M cross-linking or lipopolysaccharide was severely impaired, while the B cells normally proliferated in response to anti-CD40 monoclonal antibody. These findings imply that aberrantly activated B cells in PP undergo apoptosis independently of the CD95/CD95 L system during the course of infection with MAIDS virus.

Competitive reverse transcription-polymerase chain reaction for quantifying murine AIDS virus

The causative agent of murine AIDS (MAIDS) is the defective murine leukemia virus BM5d, that requires the replication-competent ecotropic MuLV (BM5e) helper virus. We developed a competitive quantitative PCR method including specific internal standards to quantify the expression of BM5d in the spleen of infected mice and to characterize BM5d expression kinetics following experimental infection. Specimen RNA was reverse-transcribed and co-amplified with a competitive template containing a gag sequence specific for BM5d that can be discriminated from that corresponding to wild-type cDNA by the presence of a unique restriction site, Bg/II. PCR products were quantified by means of densitometric analysis after ethidium bromide staining of gels. To standardise the RNA extraction and reverse transcription steps, the amount of defective-virus mRNA was compared to a constant copy number of murine beta actin mRNA. LP-BM5 production was measured in the spleen of infected mice. Defective gag mRNA production was compared to that of the ecotropic virus. The mRNA level of the defective virus and the titre of replicative virus increased with the duration of infection, and the amount of defective virus mRNA correlated with the titre of replicating virus.

Quantitative assessment of murine retrovirus LP-BM5 infection in MAIDS by PCR and anion exchange HPLC

In vitro amplification of DNA by PCR is a powerful tool to detect small amounts of DNA. It is now widely used for detection of pathogenic agents from extracellular fluids and organs. The use of anion exchange HPLC to quantify the PCR product resulting from the specific amplification of the DNA from the replicative-defective viral DNA responsible for MAIDS is described. This technique allows precise quantification of MAIDS virus DNA in different organs and circumvents the use of radioactivity and gel electrophoresis.

ts1-Induced spongiform encephalomyelopathy: physical forms of high-mobility DNA in spinal cord tissues of paralyzed mice are products of premature termination of reverse transcription

ts1 is a temperature-sensitive mutant of Moloney murine leukemia virus that causes hind-limb paralysis in mice. In tissues of the central nervous systems of paralyzed moribund FVB/N mice, a major component of the unintegrated viral DNA of ts1 consists of highly mobile physical forms of viral-specific DNA (HM DNA). Previous studies with ecotropic virus-specific polarity probes showed that the gp70-coding region of the env gene in the HM DNA was minus-sense single-stranded DNA. The physical forms of the HM DNA have now been characterized in more detail with additional ecotropic virus-specific probes that hybridized to the p15E-coding region of the env gene and two locations within the U3 region of the long terminal repeat. Two major classes of HM DNA were found: class I molecules consist of short minus-sense single-stranded DNA; class II molecules are partial DNA duplexes that are longer than the class I molecules. The two classes of HM DNA molecules are intermediate products of reverse transcription of the viral RNA of ts1. Since tissues that are infected with cytopathic retroviruses may contain high levels of unintegrated viral DNA, the HM DNA may have a role in inducing neurodegeneration in the central nervous systems of mice that are infected with ts1.

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.

Evidence that the murine AIDS defective virus does not encode a superantigen

The T-cell receptor repertoire was analyzed in C57BL/6 mice upon infection with helper-free stocks of the pathogenic murine AIDS (MAIDS) defective virus in order to demonstrate if, as previously reported, this virus encodes a superantigen. A polyclonal T-cell stimulation involving T cells expressing multiple V beta subsets occurred within the first week of infection, while late in the disease we could note only a 50% deletion of V beta 5 CD8+ cells. Transfection of the MAIDS virus genomic DNA into fibroblasts and B cells expressing major histocompatibility complex class II molecules failed to show any stimulation of cells expressing the specific V beta (V beta 5) previously reported to respond to MAIDS virus-infected cells. In addition, mice lacking V beta 5 cells did not show any significant decrease in susceptibility to the disease compared with mice expressing V beta 5 and bred on the same genetic background. Our in vivo and in vitro results fail to demonstrate a role for a superantigen encoded by the MAIDS defective viral genome in the pathogenesis of MAIDS.

Frequent disruption of the Nf1 gene by a novel murine AIDS virus-related provirus in BXH-2 murine myeloid lymphomas

Evi-2, a common site of viral integration in BXH-2 myeloid lymphomas, is located within a large intron of the Nf1 tumor suppressor gene. Viral integration at Evi-2 appears to induce disease by disrupting normal Nf1 expression. During our attempts to characterize the nature of the proviruses located at Evi-2, we found that approximately half of the proviruses were defective nonecotropic proviruses (A. M. Buchberg, H. G. Bedigian, N. A. Jenkins, and N. G. Copeland, Mol. Cell. Biol. 10:4658-4666, 1990). This was surprising, since most proviruses characterized at other BXH-2 common integration sites are full-length ecotropic viruses. In the studies described here, we found that this defective provirus carries two large deletions, one in pol and one in env, and is structurally related to another murine retrovirus, the murine AIDS retrovirus. By using oligonucleotide probes specific for this defective provirus, designated MRV, we showed that MRV-related proviruses are carried as endogenous germ line proviruses in most inbred strains. In addition, we identified the endogenous MRV provirus that gives rise to the defective proviruses identified at Evi-2. We present a model that accounts for the positive selection of MRV proviruses at Evi-2, which may allow selective identification of common viral integration sites harboring tumor suppressor genes.

Morphological changes of thymus in retrovirus-induced murine acquired immunodeficiency syndrome (MAIDS)

The possible contribution of the thymus in the setting of acquired immunodeficiencies is still questioned. Here we report some new findings regarding a potential involvement of the thymus in mice infected with RadLV-Rs, a viral mixture inducing murine acquired immunodeficiency syndrome (MAIDS). Thymi were sequentially removed, weighted and morphologically analyzed at different time intervals post-infection. Infection with RadLV-Rs led to a decrease in thymus weight mostly apparent from the fourth week. The first changes were seen at the third week as perivascular clusters of B-cells at the cortico-medullary junction. The ensuing process of atrophy mainly involved the cortex, while a mixed population of large T- and B-cells filled the medulla. These observations are discussed with regard to the pathological changes occurring in other lymphoid and non-lymphoid organs, in the context of the lymphoproliferation and immunodeficiency characterizing the disease, and by comparison with other models of retrovirus-induced immunodeficiencies.

The murine AIDS defective provirus acts as an insertional mutagen in its infected target B cells

In susceptible mice, the murine AIDS (MAIDS) defective virus can induce marked expansion of its target cells, the majority of which belong to the B-cell lineage. This expansion, which appears to be critical for the development of the immunodeficiency syndrome, is initially polyclonal but becomes oligoclonal late in the disease, suggesting the involvement of a secondary genetic event(s) during this proliferation. To determine whether integration of the MAIDS defective provirus into particular regions of the cellular genome contributes to this oligoclonal expansion, we searched for common provirus integration sites in enlarged lymphoid organs of MAIDS mice. We identified two common proviral integration sites, Dis-1 and Dis-2, which were occupied by a defective provirus at frequencies of 20 and 13%, respectively. Our analysis revealed that the Dis-1 region corresponds to the Sfpil1 (Spi-1, PU.1) locus, which maps on chromosome 2, and encodes a transcription factor. Insertion of the MAIDS defective provirus into this region led to a two- to threefold increase in the expression of Sfpi1 RNA. The Dis-2 locus was found to map to mouse chromosome 11, between Hox2 and Scya. It appears to be a novel locus probably harboring a gene involved in B-cell proliferation. The present study indicates that the MAIDS defective provirus can act as an insertional mutagen, thus contributing to the oligoclonal expansion of infected cells. The detection of two common proviral integration sites, each of which targetted at a low frequency in diseased organs, suggests that the deregulation of a unique gene through provirus insertion is essential for neither proliferation of infected B cells nor development of the immunodeficiency syndrome.

Establishment of leukemic T-cell lines from mice inoculated with the MAIDS defective virus

Mice inoculated with replication-competent stocks of the murine acquired immunodeficiency syndrome (MAIDS) virus are severely immunocompromised and proned to the development of T- and B-cell lymphomas. We have studied the development of T-cell lymphomas in C57BL/6 and RF/J mice inoculated with helper-free stocks of the MAIDS defective virus. We observed the expansion of T cell clones (detected by TCR gene rearrangements and by transplantation) only rarely in diseased C57BL/6 mice and slightly more frequently in RF/J mice. We succeeded in establishing four transplantable T cell tumors and malignant cell lines. The three cell lines from RF/J mice were immature T-cells (Thy-1+, CD3-, CD4+, CD8+, Mac-1+), while the line from the C57BL/6 mouse had the phenotype of mature T-cells (Thy-1+, CD3+, CD4+, CD8-). All lines were virus-producers despite the fact that helper-free stocks of the virus were inoculated. These helper MuLVs most likely originated from endogenous MuLV sequences. Also, the defective viral genome was clearly detectable in one cell line and was rearranged in two other lines. These established cell lines may be useful to determine whether they share some of the characteristics of the anergic T-cells in vivo and to study the role of the MAIDS defective virus in T cell transformation.

Mutational analysis of the murine AIDS-defective viral genome reveals a high reversion rate in vivo and a requirement for an intact Pr60gag protein for efficient induction of disease

Pr60gag appears to be the only protein encoded by the murine AIDS (MAIDS)-defective virus. To study the role of Pr60gag or some other sequences of the viral genome in the pathogenicity of the virus, we have generated mutants of the defective viral genome. These mutant defective viruses, prepared as helper-free stocks, were inoculated into susceptible C57BL/6 mice. Mutant Du5H-A virus, which had a stop codon within gag MA(p15), did not induce target cell proliferation or MAIDS. Mutants Du5H-B and -C encoded truncated Pr60gag proteins containing, respectively, MA(p15)-p12 or MA(p15)-p12 and part of CA(p30). These mutants showed a very limited capacity to induce early cell expansion and were poorly pathogenic. Only recombinant (revertant) viruses were recovered from organs of diseased mice inoculated with these two mutants. Mutant Du5H-D was generated by deleting 1.4 kbp of the 3'-end sequences, outside the gag coding region. The levels of RNA and proteins made by this mutant were low. This mutant also reverting frequently but was nevertheless able to induce MAIDS at a low efficiency without reverting. Our results indicate that the Pr60gag protein is necessary and sufficient to induce MAIDS. These data also suggest that the Pr60gag protein needs to be relatively intact to be fully pathogenic. In addition, our study shows a very high reversion rate of some mutants and emphasizes the need to check for the presence of revertant (recombinant) viruses in diseased organs when working with mutants of the MAIDS-defective virus.

In vivo treatment with interleukin 12 protects mice from immune abnormalities observed during murine acquired immunodeficiency syndrome (MAIDS)

Lymphoproliferation, chronic B cell activation resulting in hypergammaglobulinemia, and profound immunodeficiency are prominent features of a retrovirus-induced syndrome designated murine acquired immunodeficiency syndrome (MAIDS). In vivo treatment of infected mice with recombinant interleukin 12 (IL-12) beginning at the time of infection or up to 9 wk after virus inoculation markedly inhibited the development of splenomegaly and lymphadenopathy, as well as B cell activation and Ig secretion. Treatment with IL-12 also had major effects in preventing induction of several immune defects including impaired production of interferon gamma (IFN-gamma) and IL-2 and depressed proliferative responses to various stimuli. The therapeutic effects of IL-12 on the immune system of mice with MAIDS were also associated with reduced expression of the retrovirus that causes this disease (BM5def), with lesser effects on expression of ecotropic MuLV. IL-12 treatment was not effective in IFN-gamma knockout mice or in infected mice treated simultaneously with IL-12 and anti-IFN-gamma. These results demonstrate that induction and progression of MAIDS are antagonized by IL-12 through high-level expression of IFN-gamma and may provide an experimental basis for developing treatments of retrovirus-induced immune disorders with similar immunopathogenic mechanisms.

In murine AIDS, B cells are early targets of defective virus and are required for efficient infection and expression of defective virus in T cells and macrophages

Previous studies showed that B cells and CD4+ T cells are required for induction of a murine retrovirus-induced immunodeficiency syndrome, murine AIDS. Using B6 mice deficient in mature B cells as a result of a knockout of the transmembrane exon of the immunoglobulin M gene, we found that spleen and other tissues from murine AIDS virus-infected mice did not express the defective virus (BM5def) required for induction of disease, even though helper viruses were readily detectable and BM5def proviral DNA was present. This indicates that the B-lineage cells are the primary targets for infection and expression of the defective virus and that in the absence of mature B cells, there is inefficient infection of T cells and macrophages.

The p15gag and p12gag regions are both necessary for the pathogenicity of the murine AIDS virus

The defective murine AIDS (MAIDS) virus has unique sequences in its p15gag and p12gag regions. To clarify whether these sequences are responsible for the development of MAIDS, we constructed recombinant viruses by replacing various regions of the gag gene of the nonpathogenic replication-competent LP-BM5 ecotropic virus with those of the MAIDS virus. Recombinants containing both unique sequences of the MAIDS virus were replication defective and induced MAIDS. However, a recombinant containing either the p15gag or p12gag region of the MAIDS virus was also replication defective but nonpathogenic in mice. A recombinant virus containing only the p30gag region of the MAIDS virus was replication competent and nonpathogenic. These results indicate that the p15gag and p12gag regions of the MAIDS virus do not function like those of replication-competent viruses and that both of the unique sequences in the p15gag and p12gag regions are required to develop MAIDS.

Myristylation of Pr60gag of the murine AIDS-defective virus is required to induce disease and notably for the expansion of its target cells

Murine AIDS (MAIDS) is characterized by severe lymphadenopathy and splenomegaly. The proliferation of the infected target B cells is also an important manifestation of the disease (M. Huang, C. Simard, D. G. Kay, and P. Jolicoeur, J. Virol. 65:6562-6571, 1991). The etiologic agent of MAIDS is a defective murine leukemia virus that is deleted of most of its pol and env genes and appears to encode a single protein, the Gag precursor Pr60gag protein. Pr60gag is myristylated and attached to the plasma membrane. To study the role myristylation on the function of Pr60gag, we have generated a myristylation-negative (Myr-) mutant of the MAIDS defective virus. We found that Myr- Pr60gag interacted less tightly with the plasma membrane. In addition, the Myr- MAIDS defective virus mutant was unable to induce expansion of infected cells and was nonpathogenic. These results emphasize the essential role of Pr60gag in the disease process. Our data also suggest that Pr60gag, once recruited to the cell membrane through its myristylation, interacts with other membrane-bound effectors to send signals to induce proliferation of the infected cells and to initiate immune dysfunctions.

Murine AIDS protects mice against experimental cerebral malaria: down-regulation by interleukin 10 of a T-helper type 1 CD4+ cell-mediated pathology

The retrovirus LP-BM5 murine leukemia virus induces murine AIDS in C57BL/6 mice that has many similarities with human AIDS; Plasmodium berghei ANKA causes experimental cerebral malaria in the same strain of mice. The outcome of malaria infection was studied in mice concurrently infected with the two pathogens. The retrovirus significantly reduced the gravity of the neurological manifestations associated with Plasmodium berghei ANKA infection. The protection against experimental cerebral malaria induced by murine AIDS increased with duration of viral infection and, hence, with the severity of the immunodeficiency. Interleukin 10, principally from splenic T cells, was shown to play a crucial role in this protection.

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.