Murine AIDS is an antigen-driven disease: requirements for major histocompatibility complex class II expression and CD4+ T cells

Effects of Morphine on Gp120-induced Neuroinflammation Under Immunocompetent Vs. Immunodeficient Conditions

HIV-associated neurocognitive disorder (HAND) is a common complication of HIV infection, whose development is known to be facilitated by inflammation and exacerbated by morphine. Previously, using the gp120 transgenic (tg) mouse model in combination with LP-BM5 (a murine retrovirus that can cause systemic immunodeficiency in susceptible mouse strains) we demonstrated differential gp120-associated central nervous system (CNS) neuroinflammatory responses under immunocompetent (-LP-BM5) vs. immunocompromised (+LP-BM5) conditions. Here, we further investigated the effects of morphine on gp120-associated neuroinflammatory response within the hippocampus under differential immune status. First, we confirmed that morphine treatment (2 × 25 mg pellets) did not significantly affect the development of immunodeficiency induced by LP-BM5 and all brain regions examined (hippocampus, striatum, and frontal lobe) had detectable LP-BM5 viral gag genes. Morphine notably reduced the performance of gp120tg+ mice in the alteration T-maze assay when 2-minute retention was used, regardless of LP-BM5 treatment. Morphine further enhanced GFAP expression in gp120tg+ mice regardless of host immune status, while promoted CD11b expression only in immunocompetent mice, regardless of gp120tg expression. In immunocompetent gp120tg+ mice, morphine increased the RNA expression of CCL2, CCL5, CXCL10, IL-12p40, and IFNβ; while under the immunodeficient condition, morphine downregulated the expression of CCL2, CCL5, CXCL10, IL-12p40, and IL-1β. Further, expression of TNFα and IFNγ were enhanced by morphine regardless of host immune status. Altogether, our results suggest that the effects of morphine are complex and dependent on the immune status of the host, and host immune status-specific, targeted anti-neuroinflammatory strategies are required for effective treatment of HAND.

Effects of HIV gp120 on Neuroinflammation in Immunodeficient vs. Immunocompetent States

HIV affects 37 million people worldwide, 25-69% of which develop HIV-associated neurocognitive disorders (HAND) regardless of antiviral treatment. HIV infection of the brain decreases cognitive function, disrupts/impairs learning and memory, and reduces quality of life for those affected. HIV-induced neuroinflammation has been associated with viral proteins such as gp120 and Tat, which remain elevated in the CNS even in patients with low peripheral viremia counts. In this study, we examined the effects of gp120 on neuroinflammation in immunodeficient vs. immunocompetent states by examining neuroinflammatory markers in gp120tg mice with or without systemic immunodeficiency caused by murine retroviral administration (LP-BM5 murine AIDS). Changes in inflammatory cytokine/chemokine mRNA expression was complex and dependent upon expression of gp120 protein, immunodeficiency status, brain region (hippocampus, frontal lobe, or striatum), and age. Gp120 expression reduced hippocampal synaptophysin expression but did not affect animals' learning/memory on the spontaneous T-maze test in our experimental conditions. Our results emphasize the critical role of the neuroinflammatory micro-environment and the peripheral immune system context in which gp120 acts. Multiple factors, particularly system-level differences in the immune response of different brain regions, need to be considered when developing treatment for HAND. Graphical Abstract.

Microglial content-dependent inhibitory effects of calcitonin gene-related peptide (CGRP) on murine retroviral infection of glial cells

C57BL/6 (B6) mice develop peripheral neuropathy post-LP-BM5 infection, a murine model of HIV-1 infection, along with the up-regulation of select spinal cord cytokines. We investigated if calcitonin gene-related peptide (CGRP) contributed to the development of peripheral neuropathy by stimulating glial responses. An increased expression of lumbar spinal cord CGRP was observed in vivo, post-LP-BM5 infection. Consequently, in vitro CGRP co-treatments led to a microglial content-dependent attenuation of viral loads in spinal cord mixed glia infected with selected doses of LP-BM5. This inhibition was neither caused by the loss of glia nor induced via the direct inhibition of LP-BM5 by CGRP.

Involvement of microglial CD40 in murine retrovirus-induced peripheral neuropathy

B6 mice infected with LP-BM5 develop severe immunodeficiency (termed murine acquired immunodeficiency syndrome (MAIDS)) and peripheral neuropathy. To determine whether microglial CD40 is involved in LP-BM5-induced peripheral neuropathy, B6-CD40 knockout (KO) mice and B6-CD40 KO mice adoptively transferred either total leukocytes or B cells were examined for behavioral sensitivity, tissue viral loads, cytokine responses, and the development of MAIDS. All three CD40 KO groups developed MAIDS, the severity of which was correlated with peripheral cytokine responses. CD40 KO mice displayed significantly reduced mechanical hypersensitivity post-infection compared to wild-type mice regardless of cell transfer. These findings support microglial CD40 involvement in LP-BM5-induced peripheral neuropathy.

Murine immunodeficiency virus-induced peripheral neuropathy and the associated cytokine responses

Distal symmetrical polyneuropathy is the most common form of HIV infection-associated peripheral neuropathy and is often associated with pain. C57BL/6 (B6) mice infected with LP-BM5, a murine retroviral isolate, develop a severe immunodeficiency syndrome similar to that in humans infected with HIV-1, hence the term murine AIDS. We investigated the induction of peripheral neuropathy after LP-BM5 infection in B6 mice. Infected B6 mice, like HIV-infected humans, exhibited behavioral (increased sensitivity to mechanical and heat stimuli) and pathological (transient loss of intraepidermal nerve fibers) signs of peripheral neuropathy. The levels of viral gag RNA were significantly increased in all tissues tested, including spleen, paw skin, lumbar dorsal root ganglia, and lumbar spinal cord, postinfection (p.i.). Correlated with the development of peripheral neuropathy, the tissue levels of several cytokines, including IFN-γ, IL-1β, IL-6, and IL-12, were significantly elevated p.i. These increases had cytokine-specific and tissue-specific profiles and kinetics. Further, treatment with the antiretroviral agent zidovudine either significantly reduced or completely reversed the aforementioned behavioral, pathologic, and cytokine changes p.i. These data suggest that LP-BM5 infection is a potential mouse model of HIV-associated distal symmetrical polyneuropathy that can be used for investigating the roles of various cytokines in infection-induced neuropathic pain. Further investigation of this model could give a better understanding of, and lead to more effective treatments for, HIV infection-associated painful peripheral neuropathy.

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.

Dendritic cell mediated delivery of plasmid DNA encoding LAMP/HIV-1 Gag fusion immunogen enhances T cell epitope responses in HLA DR4 transgenic mice

This report describes the identification and bioinformatics analysis of HLA-DR4-restricted HIV-1 Gag epitope peptides, and the application of dendritic cell mediated immunization of DNA plasmid constructs. BALB/c (H-2d) and HLA-DR4 (DRA1*0101, DRB1*0401) transgenic mice were immunized with immature dendritic cells transfected by a recombinant DNA plasmid encoding the lysosome-associated membrane protein-1/HIV-1 Gag (pLAMP/gag) chimera antigen. Three immunization protocols were compared: 1) primary subcutaneous immunization with 1×10⁵ immature dendritic cells transfected by electroporation with the pLAMP/gag DNA plasmid, and a second subcutaneous immunization with the naked pLAMP/gag DNA plasmid; 2) primary immunization as above, and a second subcutaneous immunization with a pool of overlapping peptides spanning the HIV-1 Gag sequence; and 3) immunization twice by subcutaneous injection of the pLAMP/gag DNA plasmid. Primary immunization with pLAMP/gag-transfected dendritic cells elicited the greatest number of peptide specific T-cell responses, as measured by ex vivo IFN-γ ELISpot assay, both in BALB/c and HLA-DR4 transgenic mice. The pLAMP/gag-transfected dendritic cells prime and naked DNA boost immunization protocol also resulted in an increased apparent avidity of peptide in the ELISpot assay. Strikingly, 20 of 25 peptide-specific T-cell responses in the HLA-DR4 transgenic mice contained sequences that corresponded, entirely or partially to 18 of the 19 human HLA-DR4 epitopes listed in the HIV molecular immunology database. Selection of the most conserved epitope peptides as vaccine targets was facilitated by analysis of their representation and variability in all reported sequences. These data provide a model system that demonstrates a) the superiority of immunization with dendritic cells transfected with LAMP/gag plasmid DNA, as compared to naked DNA, b) the value of HLA transgenic mice as a model system for the identification and evaluation of epitope-based vaccine strategies, and c) the application of variability analysis across reported sequences in public databases for selection of historically conserved HIV epitopes as vaccine targets.

Murine AIDS requires CD154/CD40L expression by the CD4 T cells that mediate retrovirus-induced disease: Is CD4 T cell receptor ligation needed?

LP-BM5, a retroviral isolate, induces a disease featuring an acquired immunodeficiency syndrome termed murine AIDS (MAIDS). Many of the features of the LP-BM5-initiated disease are shared with HIV/AIDS. Our lab has shown that the interaction of B and CD4 T cells that is central to MAIDS pathogenesis requires ligation of CD40 on B cells by CD154 on CD4 T cells. Despite this strict requirement for CD154 expression, whether CD4 T cell receptor (TCR) occupancy is essential for the induction of MAIDS is unknown. To block TCR engagement, Tg mouse strains with monoclonal TCR of irrelevant peptide/MHC specificities, all on MAIDS-susceptible genetic backgrounds, were tested: the study of a panel of TCR Tg CD4 T cells controlled for the possibility of serendipitous crossreactive recognition of virus-associated or induced-self peptide, or superantigen, MHC complexes by a given TCR. The results argue that TCR engagement is not necessary for the induction of MAIDS.

The role of CD4 T cells in the pathogenesis of murine AIDS

LP-BM5, a retroviral isolate, induces a disease featuring retrovirus-induced immunodeficiency, designated murine AIDS (MAIDS). Many of the features of the LP-BM5-induced syndrome are shared with human immunodeficiency virus-induced disease. For example, CD4 T cells are critical to the development of MAIDS. In vivo depletion of CD4 T cells before LP-BM5 infection rendered genetically susceptible B6 mice MAIDS resistant. Similarly, MAIDS did not develop in B6.nude mice. However, if reconstituted with CD4 T cells, B6.nude mice develop full-blown MAIDS. Our laboratory has shown that the interaction of B and CD4 T cells that is central to MAIDS pathogenesis requires ligation of CD154 on CD4 T cells with CD40 on B cells. However, it is not clear which additional characteristics of the phenotypically and functionally heterogeneous CD4 T-cell compartment are required. Here, in vivo adoptive transfer experiments using B6.nude recipients are employed to compare the pathogenic abilities of CD4 T-cell subsets defined on the basis of cell surface phenotypic or functional differences. Th1 and Th2 CD4 T cells equally supported MAIDS induction. The rare Thy1.2(-) CD4 subset that expands upon LP-BM5 infection was not necessary for MAIDS. Interestingly, CD45RB(low) CD4 T cells supported significantly less disease than CD45RB(high) CD4 T cells. Because the decreased MAIDS pathogenesis could not be attributed to inhibition by CD45RB(low) CD25(+) natural T-regulatory cells, an intrinsic property of the CD45RB(low) cells appeared responsible. Similarly, there was no evidence that natural T-regulatory cells played a role in LP-BM5-induced pathogenesis in the context of the intact CD4 T-cell population.

Cyclo-oxygenase type 2-dependent prostaglandin E2 secretion is involved in retrovirus-induced T-cell dysfunction in mice

MAIDS (murine AIDS) is caused by infection with the murine leukaemia retrovirus RadLV-Rs and is characterized by a severe immunodeficiency and T-cell anergy combined with a lymphoproliferative disease affecting both B- and T-cells. Hyperactivation of the cAMP-protein kinase A pathway is involved in the T-cell dysfunction of MAIDS and HIV by inhibiting T-cell activation through the T-cell receptor. In the present study, we show that MAIDS involves a strong and selective up-regulation of cyclo-oxygenase type 2 in the CD11b+ subpopulation of T- and B-cells of the lymph nodes, leading to increased levels of PGE2 (prostaglandin E2). PGE2 activates the cAMP pathway through G-protein-coupled receptors. Treatment with cyclo-oxygenase type 2 inhibitors reduces the level of PGE2 and thereby reverses the T-cell anergy, restores the T-cell immune function and ameliorates the lymphoproliferative disease.

CD40-associated TRAF 6 signaling is required for disease induction in a retrovirus-induced murine immunodeficiency

LP-BM5 retrovirus-infected C57BL/6 mice develop splenomegaly, lymphadenopathy, hypergammaglobulinemia, and immunodeficiency; thus, this disease has been named mouse AIDS. In this syndrome, CD154/CD40 interactions are required for but do not mediate disease by upregulation of CD80 or CD86. We report here that there is nonetheless a necessity for CD40 signaling competence, specifically an intact tumor necrosis factor receptor-associated factor 6 (TRAF 6) binding site.

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.

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.

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.

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.

The autoimmune accelerating yaa mutation does not accelerate murine AIDS

Murine acquired immunodeficiency syndrome (MAIDS) is characterized by lymphoproliferation, polyclonal B cell activation resulting in the production of autoantibodies, and a progressive immunodeficiency. These are all hallmarks of some autoimmune diseases. Yaa is a Y-chromosome-linked gene that accelerates autoimmune diseases in some autoimmune-prone strains of mice. To further elucidate a possible relationship with autoimmunity, the effect of the Yaa gene on MAIDS was investigated. Analysis of phenotypic and functional disease parameters revealed that Yaa does not accelerate MAIDS disease. This is probably due to the generalized activation of most or all lymphoid cells in MAIDS, which cannot be enhanced by the Yaa gene. This result is in accordance with the selective enhancing effect of the Yaa gene on the immune response against self and foreign antigens in a specific genetic background. It suggests that the autoimmune response associated with MAIDS is a secondary phenomenon. Interestingly, even in wild-type C57BL/6 mice, autoantibody production may contribute overproportionally to the hypergammaglobulinemia associated with MAIDS.

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.

Differential regulation of germinal center genes, BCL6 and SWAP-70, during the course of MAIDS

Germinal centers (GC) are the sites of antigen-driven B cell switch recombination, V(D)J gene hypermutation, and selection to generate high-afinity CD38+ memory B cells. A marked expansion of GC associated with hypergammaglobulinemia followed by complete disruption of normal splenic architecture and a striking drop in immunoglobulin levels are prominent features of the murine retrovirus-induced immunodeficiency syndrome, MAIDS. B cell lymphomas are frequent in long-term infected mice. Normal GC formation is critically dependent on a number of genes including the transcription factor, Bcl6. Deregulated expression of BCL6 protein has been implicated in the development of human and mouse B cell lymphomas. Another nuclear protein, SWAP-70, has been identified as a subunit of the protein complex, SWAP, that recombines switch regions in vitro. To develop a fuller understanding of B cell biology in MAIDS, we examined the characteristics of BCL6, SWAP-70, CD38, and peanut agglutinin (PNA)-staining cells during the course of the disease. The levels of both nuclear proteins increased rapidly until 6-8 weeks after infection. During this time frame, BCL6 was expressed at highest levels in the usually rare CD4+ Thyl- T cell subset as well as in B cells. At later times. BCL6 levels dropped to undetectable levels while SWAP-70 levels continued to increase. Changes in the levels of either protein could not be ascribed to transcriptional regulation. PNA-reactive cells decreased in concert with BCL6 while CD38 staining increased with SWAP-70. These results demonstrate that progression of MAIDS results in the massive accumulation of B cells with the morphology of secretory cells that behave like post-GC cells for expression of BCL6 and CD38, and for PNA-staining but with abnormally high-level expression of SWAP-70.

STAT6-deficient mice exhibit normal induction of murine AIDS and expression of immunoglobulin E following infection with LP-BM5 murine leukemia viruses

The unique Gag polyprotein of the replication-defective virus responsible for murine AIDS (MAIDS) induces B-cell activation, proliferation, and differentiation, including immunoglobulin class switch-recombination to immunoglobulin E (IgE). Secretion of IgE normally requires the serial induction of interleukin 4 (IL-4), engagement of the IL-4 receptor, activation of signal transducer and activator of transcription (STAT) 6, and induction of Iepsilon germline transcripts as a prelude to switching. Remarkably, expression of IgE is equivalent in normal and IL-4-deficient mice with MAIDS (Morawetz et al., J. Exp. Med. 184:1651-1661, 1996). To understand this anomaly, we studied mice with a null mutation of STAT6. Lymphoproliferation and immunodeficiency, the hallmarks of MAIDS, developed with comparable kinetics and degree in normal and mutant mice. In addition, serum IgE levels were indistinguishable in mice of either genotype. We conclude that B cells from mice with MAIDS activate unique IL-4- and STAT6-independent signaling pathways for B-cell activation and differentiation.

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.

Induction of endogenous mammary tumor virus in lymphocytes infected with murine acquired immunodeficiency syndrome virus

Mice infected with murine acquired immunodeficiency syndrome (MAIDS) virus developed lymphoadenopathy and profound immunodeficiency. Concomitantly the expression of endogenous mammary tumor virus (MTV) mRNA increased significantly, especially for the 1.7-kb 3' open reading frame (ORF) mRNA encoding MTV superantigen. B cell lines that are established from MAIDS mice and exhibit superantigen activity also express a high level of 1.7-kb endogenous MTV and mRNA. Infection of a B cell tumor line in vitro with retrovirus containing the cloned MAIDS virus gene induced superantigen activity and this cell line also expressed the 1.7-kb superantigen coding MTV 3' ORF mRNA. These results strongly suggest a link between MAIDS virus infection and the induction of endogenous superantigen activity. This may play an important role in the pathogenesis of the MAIDS virus.

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.

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.

Control of immunodeficiency and lymphoproliferation in mouse AIDS: studies of mice deficient in CD8+ T cells or perforin

CD8+ T cells were previously shown to be important in preventing lymphoproliferation and immunodeficiency following infection of murine AIDS (MAIDS)-resistant mice with the LP-BM5 mixture of murine leukemia viruses. To further evaluate the mechanisms contributing to MAIDS resistance, we studied mice lacking CD8+ T cells or deficient in perforin due to knockout of the beta2-microglobulin (beta2M) or perforin gene, respectively. In contrast to wild-type, MAIDS-resistant controls, B10.A mice homozygous for the beta2M mutation and B10.D2 mice homozygous for the perforin mutation were diagnosed as having MAIDS by 5 to 8 weeks after infection by the criteria of lymphoproliferation, impaired proliferative responses to mitogens, and changes in cell populations as judged by histopathology and flow cytometry. Unexpectedly, there was no progression of lymphoproliferation through 24 weeks, even though immune functions were severely compromised. Expression of the defective virus responsible for MAIDS was enhanced in spleens of the knockouts in comparison with wild-type mice. These results demonstrate that perforin-dependent functions of CD8+ T cells contribute to MAIDS resistance but that other, non-CD8-dependent mechanisms are of equal or greater importance.

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.

Endogenous Mtv-encoded superantigens are not required for development of murine AIDS

Immune activation in murine AIDS (MAIDS) has been suggested to involve a superantigen (SAG). The possibility that SAGs encoded by mammary tumor virus (MTV) might be the source of stimulation was studied by using Mtv mice. Mtv- mice developed typical MAIDS, excluding a requirement for Mtv-encoded SAGs in the pathogenesis of this disorder.

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.

Impact of MHC class I gene on resistance to murine AIDS

Development of murine AIDS in mice following infection with LP-BM5 murine leukaemia virus (MuLV) is highly strain dependent, with strain differences determined by genes within and outside H-2. Among H-2 genes, the Dd gene is the most closely associated with resistance to LP-BM5 MuLV infection. However, the Dd-mediated resistance is highly influenced by outside H-2 genes, i.e. A lineage strains are more resistant than mice strains of B6/B10 lineage. In this study, the mice having BALB background were analysed and, similarly to A lineage mice, only Dd gene products were found to be required to provide resistance to LP-BM5 MuLV infection. Furthermore, BALB/c Kh mice bearing both Dd and Ld genes clearly showed obviously higher resistance than BALB/c-H-2dm2 mice solely having the Dd gene. In addition, in the long-term observation of the effect of the Dd gene on B6/B10 background mice, D8 mice having the Dd gene as a transgene and expressing a high level Dd gene product showed higher resistance than naturally recombinant B10.A(18R) mice. These results suggest that the MAIDS resistance associated with the D end loci is dependent on the level of expression of an MHC class I gene.