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

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

The MA (p15) and p12 regions of the gag gene are sufficient for the pathogenicity of the murine AIDS virus.

Inoculation of the replication-defective retrovirus DEF27 (BM5d), packaged as an amphotropic virus pseudotype, into C57BL/6J mice leads to development of murine AIDS. Disease development showed a long incubation period (20 to 24 weeks), was associated with amplification of the BM5d provirus in splenocytes and lymph nodes, and was independent of the presence of exogenous or endogenous replication-competent helper viruses. However, both the onset of disease and amplification of the defective provirus were significantly enhanced by coinfection with the replication-competent B-cell-tropic ecotropic helper virus BM5e. The part of the BM5d viral genome that was essential for the pathogenicity was determined by making precisely engineered alterations in the reading frame of the gag and pol genes of BM5d proviral DNA and examining the ability of the altered amphotropic BM5d pseudotypes to induce the disease in C57BL/6J mice. The results show that expression of the MA (p15) and p12 regions of the gag gene is sufficient for pathogenicity of the BM5d retrovirus.     

Expression of defective virus and cytokine genes in murine AIDS.

A syndrome characterized by severe immunodeficiency and lymphoproliferation develops in susceptible strains of mice infected with a mixture of murine leukemia viruses (MuLVs) designated LP-BM5 MuLV. The etiologic agent in this mixture has been shown to be a replication-defective virus (BM5d) with a 4.8-kb genome that required replication-competent helper viruses, primarily ecotropic (BM5e), for cell-to-cell spread in the host. In the present study, we studied the expression of BM5d and BM5e in tissues of infected mice at various times after inoculation in relation to the expression of cytokine genes that may contribute to the pathogenesis of this disorder. Northern (RNA) analysis of total RNA showed that BM5d was expressed at significant levels in lymphoid tissues within 1 week of infection and that the levels of expression increased with time after inoculation. By 16 weeks postinfection, BM5d was expressed in all tissues examined. Expression of BM5e was relatively more restricted to lymphoid tissues and was detected at lower levels than expression of BM5d at early times after infection, but this virus was expressed in all tissues by 16 weeks. Infection with the virus mixture was associated with constitutive expression of tumor necrosis factor in all tissues examined and of interleukin-1 (IL-1) in lymphoid tissues within 1 week of infection, and at later times with widespread expression of these cytokines and gamma interferon. Also, the levels of interferon regulatory factor 1 mRNA were significantly increased in all infected tissues during the infection. In contrast, expression of IL-3, IL-4, IL-5, and IL-6 was not detectable by Northern analysis of the respective mRNAs in any infected tissue at early or late times postinfection.     

Characteristics and contributions of defective, ecotropic, and mink cell focus-inducing viruses involved in a retrovirus-induced immunodeficiency syndrome of mice.

LP-BM5 murine leukemia virus, a derivative of Duplan-Laterjet virus, contains a mixture of replication-competent B-tropic ecotropic and mink cell focus-inducing (MCF) viruses and a defective genome that is the proximal cause of a syndrome, murine AIDS (MAIDS), characterized by lymphoproliferation and immunodeficiency. The defective (BM5d) and ecotropic components of this mixture were molecularly cloned, and complete (BM5d) or partial (ecotropic) nucleotide sequences were determined. BM5d closely resembled the Du5H genome cloned from the Duplan virus, featuring a highly divergent p12 sequence in the gag open reading frame. In MAIDS-sensitive C57BL/6 mice, BM5d was detected in tissues within 2 weeks of infection but was absent from tissues of the MAIDS-resistant strain, A/J, 12 weeks after infection. B-cell-lineage tumors from mice with MAIDS contained and expressed BM5d, and clonal integrations of this genome were variably associated with clonal expansions of B cells in infected mice. Finally, mRNA crosshybridizing with a probe for BM5d was present in spleen but not kidney cells of uninfected B6 mice.     

Role of mink cell focus-inducing virus in leukemias induced by Friend ecotropic virus

Recombinant viruses have been implicated in the pathogenesis of murine leukemias induced by a variety of long-latency retroviruses. Neonatal mice of several strains were inoculated with Friend ecotropic virus (F-Eco) and analyzed for the presence of mink cell focus-inducing (MCF) virus or DNA restriction enzyme fragments which were specific for Friend MCF virus (F-MCF). MCF virus was detected within 2 weeks of inoculation in NFS /N mice and at about 2 months after inoculation in BALB/c mice. Both of these strains developed erythroblastosis after inoculation with F-Eco. In contrast, MCF virus was not detected in F-Eco-inoculated C57BL mice. These mice were resistant to erythroblastosis but developed lymphoma or myelogenous leukemia or both at about 5 months after inoculation. Thus, although MCF viruses were associated with F-Eco erythroblastosis in NFS /N and BALB/c mice, they were not necessary for F-Eco-induced lymphoid or myeloid leukemias in C57BL mice. To investigate the association between resistance to erythroblastosis and absence of MCF virus, C57BL mice were inoculated with pseudotypic mixtures of F-Eco plus F-MCF; MCF virus replicated well in these mice, but the mice remained resistant to erythroblastosis. Furthermore, in genetic crosses between C57BL and NFS /N or BALB/c, some mice inherited resistance to F-Eco erythroblastosis without inheriting the C57BL resistance to the generation of MCF viruses. These results indicate that C57BL mice carry a gene for resistance to F-Eco erythroblastosis which is distinct from the C57BL genes which interfere with the generation of MCF viruses.     

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

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

High frequency of transmission of murine AIDS virus in C57BL/10 mice via mother''s milk.

Maternal transmission of a murine leukemia virus (MuLV) mixture named LP-BM5 MuLV, which is knwon to induce murine AIDS (MAIDS), was investigated. Adult female C57BL/10 mice were inoculated intraperitoneally with LP-BM5 MuLV. When the virus-inoculated female mice developed splenomegaly or lymphadenopathy, they were mated with normal C57BL/10 male mice. Of 56 offspring born to MAIDS mothers, 14 appeared to develop MAIDS, as assessed by the occurrence of splenomegaly or lymphadenopathy as well as the mitogen response of spleen cells. The occurrence of MAIDS in offspring was found to be accompanied by the maternal transmission and expansion of a defective virus genome from which almost the entire pol and env regions are deleted. On the other hand, the ecotropic helper virus genome was detected in all offspring regardless of the occurrence of MAIDS. To examine the mode of maternal transmission of LP-BM5 MuLV, foster-nursing experiments were conducted. The ecotropic helper viruses were found in all normal offspring nursed by a MAIDS mother, and some of them developed MAIDS. In contrast, none of offspring born to a MAIDS mother that were nursed by an uninfected foster mother either carried the LP-BM5 MuLV or developed MAIDS. Finally, both the defective and the ecotropic helper viruses were detected in LP-BM5 MuLV-infected mother's milk. These results indicated that maternal transmission of LP-BM5 MuLV occurs with a high frequency and is mediated by mother's milk.     

Retrovirus-induced murine acquired immunodeficiency syndrome: natural history of infection and differing susceptibility of inbred mouse strains.

C57BL mice (Fv-1b) develop a severe immunodeficiency disease following inoculation as adults with LP-BM5 murine leukemia virus (MuLV), a derivative of Duplan-Laterjet virus which contains B-tropic ecotropic and mink cell focus-inducing MuLVs and a putative defective genome which may be the proximal cause of disease. The stages of development of this disease were defined for C57BL mice on the basis of lymphadenopathy and splenomegaly; histopathological changes consistent with B-cell activation; and alterations in expression of cell surface antigens affected by proliferation of T cells, B cells, and macrophages. By using this disease profile as a standard, the response of adult mice of various inbred strains and selected F1 hybrids was compared. We show that although the strains which are highly sensitive are of the Fv-1b genotype (i.e., permissive for B-tropic MuLVs), certain Fv-1b strains, e.g., BALB/c and A/J, are resistant to murine acquired immunodeficiency syndrome, whereas certain Fv-1n strains (permissive for N-tropic MuLVs but restrictive for B-tropic MuLVs), notably P/N, BDP, and AKR, show moderate sensitivity and (C57BL/6 x CBA/N)F1 mice (Fv-1n/b and thus dually restrictive) are of relatively high susceptibility. The results of virus recovery tests suggest that apparently anomalous sensitivity, based on predicted Fv-1 restriction, may reflect MuLV induction and/or mutation to provide a helper virus for which the host is permissive.     

Cytolytic T lymphocytes specific for tumors and infected cells from mice with a retrovirus-induced immunodeficiency syndrome.

LP-BM5 retrovirus complex-infected C57BL/6 mice develop immunodeficiency, somewhat analogous to AIDS, termed murine AIDS (MAIDS). After secondary stimulation with syngeneic B-cell lymphomas from LP-BM5-infected mice, C57BL/6 mice produced vigorous CD8+ cytotoxic T lymphocytes specific for MAIDS-associated tumors. An anti-LP-BM5 specificity was suggested because spleen and lymph node cells from LP-BM5-infected mice served as target cells in competition assays, and cells from LP-BM5, but not ecotropic, virus-infected mice functioned as secondary in vitro stimulators to generate cytotoxic T lymphocytes to MAIDS tumors.     

Effects of non-MHC loci on resistance to retrovirus-induced immunodeficiency in mice

Mice of certain strains are highly sensitive to development of a severe immunodeficiency disease following inoculation as adults with LP-BM5 murine leukemia viruses (MuLV) whereas others are extremely resistant. These strain-dependent differences in response to infection have been shown to be genetically determined with resistance to disease being, in general, associated with homozygosity for Fv-1 ⁿand H-2 haplotypes a and d and sensitivity with homozygosity for Fv-1 ^band other H-2 haplotypes including b, s, and q. The Fv-1 ^b, H-2 ^rstrain RIIIS/J (RIIIS) was found to be highly resistant to disease even though B10.RIII(71NS)/J (B10.RIII), also H-2 ^r, was very sensitive, thus excluding a role for H-2 in the resistance of RIIIS. The characteristics of RIIIS resistance were evaluated in studies of infected (B10.RIII×RIIIS) F₁, F₂ and reciprocal backcross mice. Resistance to disease was shown to be semidominant and determined by more than one gene, although a preponderant influence of a single gene was suggested. Studies of segregating populations showed that resistance was not associated with or linked to polymorphisms of the V _\complex or genes in proximity to the Emv-2 locus on chromosome 8. However, there was almost complete concordance between absence of disease in infected mice and inhibition of ecotropic virus spread. These results demonstrate that genes other than Fv-1 or H-2 can profoundly influence the development of retrovirus-induced immunodeficiency and replication of ecotropic viruses.Abbreviations MuLV murine leukemia virus - MCF mink cell focus-inducing MuLV - B6 C57BL/6 - BM5d the defective virus in LP-BM5 MuLV - MAIDS murine acquired immunodeficiency syndrome - RIIIS RIIIS/J - B10.RIII B10.RIII (71NS)/J - MLR mixed lymphocyte reaction - FACS fluorescence activated cell sorter     

Role of a cytotoxic-T-lymphocyte epitope-defined, alternative gag open reading frame in the pathogenesis of a murine retrovirus-induced immunodeficiency syndrome

LP-BM5 murine leukemia virus-infected C57BL/6 mice develop profound immunodeficiency and B-cell lymphomas. The LP-BM5 complex contains a mixture of defective (BM5def) and replication-competent helper viruses among which BM5def is the primary causative agent of disease. The BM5def primary open reading frame (ORF1) encodes the single gag precursor protein (Pr60gag). Our lab has recently demonstrated that a novel immunodominant cytotoxic-T-lymphocyte (CTL) epitope (SYNTGRFPPL) is expressed from a +1-nucleotide translational open reading frame of BM5def during the course of normal retrovirus expression. The SYNTGRFPPL CTL epitope may be generated from either of two initiation methionines present, ORF2a or ORF2b, located downstream of the ORF1 initiation site. This study investigates the role(s) of the alternative ORF2-derived gag protein(s) of BM5def in viral pathogenesis. We have examined the disease-inducing capabilities of mutant viruses in which the translational potential of either the initiating ORF2a or ORF2b AUG has been disrupted. Although these mutated viruses are capable of wild-type ORF1 expression, they are unable to induce disease. Our data strongly suggest the existence of a novel ORF2 product(s) that is required for LP-BM5-induced pathogenesis and have potentially broad implications for other retroviral diseases.     

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

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

Mouse hepatitis virus 3 replication in T and B lymphocytes correlate with viral pathogenicity

Viral pathogenicity may be regulated by host defense mechanisms at the virus-immune cell interaction level. The immune system plays an important role in the outcome of acute disease induced by the mouse hepatitis virus type 3 (MHV3) virus. The lymphoid cells act as effectors in the virus elimination as well as targets for viral replication. In order to demonstrate a correlation between MHV3 pathogenicity and viral replication in lymphocytes, genetically-determined resistant A/J and susceptible C57BL/6 mice were infected with pathogenic (L2-MHV3) or nonpathogenic (YAC-MHV3) viral strains. Pathogenicity and histopathologic studies have revealed that lymphoid organs such as thymus and spleen, showed injuries or atrophy in susceptible mice infected with L2-MHV3. No histopathologic lesions in the lymphoid organs occurred in C57BL/6 mice infected with YAC-MHV3 or A/J mice infected with both viruses. The mechanisms involved in the lymphoid injuries were studied regarding viral replication in the lymphoid organs and cells in infected mice. Results indicate that cell depletion in lymphoid organs is caused by a complete viral replication in lymphoid cells. Thy1.2+ and surface IgM+ lymphoid cells from susceptible C57BL/6 mice infected with L2-MHV3 were permissive to viral replication and to subsequent cell lysis. No cell lysis, however, occurred in lymphoid cells from C57BL/6 mice infected with YAC-MHV3 and A/J mice infected with both virus strains. In vitro studies, with purified T and B cell populations were performed to determine the mechanism effecting susceptibility or resistance to viral-induced cell lysis occurring in such cells. A blockade, probably occurring at the viral RNA polymerase activity level, prevents viral replication in resistant cells between the stages of fixation of the virus at the cell-surface receptor and the viral protein translation. These experiments indicate that an intrinsic virus-specific resistant mechanism occurs in lymphoid cells that plays a major role in the viral pathogenicity.     

Kinetics of ectromelia virus (mousepox) transmission and clinical response in C57BL/6j, BALB/cByj and AKR/J inbred mice

Research was undertaken to answer basic questions on susceptibility, clinical response and transmission of ectromelia virus in selected strains of inbred mice. C57BL/6J and AKR/J were found to be markedly more resistant to a virulent strain of ectromelia virus (isolated during the 1979-80 outbreak at the National Institutes of Health) than C57LJ, BALB/cByJ, DBA/2J, A.By/SNJ and C3H/HeJ when infected by footpad inoculation. In C57BL/6J and AKR/J the LD50 was about 7 logs higher than the ID50. With one exception, C57LJ, the LD50 and ID50 titers in the other strains were about equal. In C57LJ the LD50 titer was intermediate. Following intragastric inoculation, virus was isolated from feces of C57BL/6J mice for as long as 46 days and up to 29 days from BALB/cByJ mice. Transmission to cage mates from intragastrically infected C57BL/6J and BALB/cByJ occurred up to 36 and 30 days respectively after infection. Virus was isolated from the spleen in 2 of 5 BALB/cByJ mice and 1 of 7 C57BL/6J mice tested 95 days after gastric inoculation. Following footpad inoculation, BALB/cByJ mice consistently transmitted virus to cage mates before death at 10-12 days. C57BL/6J mice transmitted between days 8 and 17, but not beyond. Virus was maintained in C57BL/6J mice by exposure to infected cage mates for seven passages, which was the most attempted. Clinical signs in infected C57BL/6J mice were usually subtle or inapparent.     

Linkage of the Fv-2 gene to a newly reinserted ecotropic retrovirus in Fv-2 congenic mice

Restriction enzyme and Southern gel analyses were used to determine the number and location of endogenous ecotropic retroviruses in the germ line of several mouse strains congenic at the Fv-2 gene locus. A new endogenous ecotropic provirus was observed in the germ line of B6.S (Fv-2ss) mice, in addition to the resident provirus found in its congenic partner C57BL/6 (Fv-2rr). This new provirus was similar in structure to the C57BL provirus. The SIM strain of mice, the donors of the Fv-2s allele in B6.S mice, does not contain ecotropic proviruses, suggesting that the new provirus in the B6.S mouse strain arose by germ-line reintegration during the construction of this strain. Mendelian segregation analysis indicated that this new provirus was linked to the Fv-2 gene locus on chromosome 9. In three other Fv-2s congenic mouse strains--B10.C (47N), B6.C (H-7b), and C57BL/6J Trfa, Bgsd--no additional ecotropic endogenous viruses were detected, suggesting that the reinsertion event that occurred during the construction of B6.S is not essential for the acquisition of the Fv-2s phenotype in the C57BL genetic background. Although numerous reports of germ-line reinsertions of ecotropic virus in high-virus mouse strains have been received, the present results provide definitive evidence that similar germ-line amplifications of endogenous ecotropic virus can occur in a low-virus mouse strain.     

Mouse hepatitis virus 3 pathogenicity expressed by a lytic viral infection in bone marrow 14.8+ mu+ B lymphocyte subpopulations

Mouse hepatitis virus type 3 (MHV3) provides an excellent model for studying viral-B lymphocyte interaction in the immune system, which plays an important role in the outcome of an acute disease. Bone marrow B lymphocyte subpopulations, at various times postinfection, were studied in genetically C57BL/6 and resistant A/J mice, infected with pathogenic L2-MHV3 and its nonpathogenic variant, YAC-MHV3. B lineage cell subpopulations were identified by double immunofluorescence assays using mAb of terminal deoxynucleotidyl transferase, 14.8 and cytoplasmic (cu) or surface (su) Ig mu-chains. Results revealed diminished percentage and absolute number in the bone marrow 14.8+ mu+ B lymphocyte subpopulations, including pre-B (cu+ su-) and B (cu+ su+) cells of L2-MHV3-infected susceptible C57BL/6 mice; whereas, slight or no increase was evident in the cell subpopulations of L2-MHV3 infected resistant A/J mice or in YAC-MHV3 infected in both strains of mice. Abnormal large-sized forms of the 14.8+ mu+ cells occurred, at 48-h postinfection, in L2-MHV3-infected susceptible C57BL/6 mice only. In contrast, no change in the percentage and absolute number of precursor cells (terminal deoxynucleotidyl transferase positive) and pre pre-B cells (14.8+ mu-) were detected in all infected mice. In vitro L2-MHV3 infection of C57BL/6 bone marrow purified B lineage cell subpopulations showed that pre-B (cu+ su-) and B (cu+ su+) cells became abnormally large in size and depleted in number as a result of a productive and lytic viral replication. Low L2-MHV3 viral replication occurred in these cell subpopulations of A/J mice but no YAC-MHV3 virus was produced in the cells of both strains of mice. Pre pre-B (14.8+ mu-) cells in both strains were not permissive to L2-MHV3 or YAC-MHV3 viral replication. These results are discussed with regard to the role of humoral immunodeficiency in the pathogenic process.     

Direct interactions of coxsackievirus B3 with immune cells in the splenic compartment of mice susceptible or resistant to myocarditis.

In vitro replication of coxsackievirus B3 (CVB3) in cells of the immune system derived from uninfected adolescent A/J and C57BL/6J mice and replication of CVB3 in and association with immune cells from spleens of infected animals in vivo were assessed. Nonstimulated or mitogen-stimulated spleen cells were minimally permissive for viral replication during an 8-h period. Three days postinfection (p.i.), CVB3 RNA was localized in vivo to B cells and follicular dendritic cells of germinal centers in both A/J and C57BL/6J mice; however, extrafollicular localization was greater in C57BL/6J mice (P = 0.0054). Although the pattern of CVB3 RNA localization was different, the total load of infections virus (PFU per milligram of tissue) was not different. Splenic CVB3 titers (PFU per milligram of tissue) in both strains were maximal at day 3 or 4 p.i. and were back to baseline by day 7 p.i., with most infectious virus being non-cell associated. CVB3 titers (PFU per milligram of tissue) correlated directly with in situ hybridization positivity in splenic follicles and extrafollicular regions in both murine strains; however, follicular hybridization intensity was greater in A/J mice at day 5 p.i. (P = 0.021). Flow cytometric analysis demonstrated that 50.4% of total spleen cells positive for CVB3 antigen were B cells and 69.6% of positive splenic lymphocytes were B cells. Myocardial virus load in C57BL/6J mice was significantly lower than that in A/J mice at days 4 and 5 p.i. These data indicate that CVB3 replicates in murine splenocytes in vitro and in B cells and extrafollicular cells in vivo.     

Quinolinic Acid Levels in a Murine Retrovirus-Induced Immunodeficiency Syndrome

Abstract: Mice infected with the retrovirus mixture designated LP-BM5 murine leukemia virus (MuLV) develop an immunosuppressive disease. Quinolinic acid (QUIN) is an endogenous neurotoxic N -methyl- d -aspartate agonist that may contribute to the pathogenesis of HIV-associated neurologic disease. In the present study, the levels of QUIN in brain and blood were measured in mice infected with LP-BM5 MuLV and compared with those in uninfected mice and mice infected with the nonpathogenic strain of ecotropic MuLV (helper component of LP-BM5 MuLV). Infection with LP-BM5 MuLV resulted in progressive increases in blood QUIN levels beginning 2 weeks after inoculation that peaked by 16 weeks postinfection. QUIN levels were also increased in cerebral cortex, hippocampus, and striatum. In systemic tissues, QUIN levels were increased in lung, liver, and spleen. In contrast, infection with the ecotropic viral component of the LP-BM5 MuLV mixture was not associated with any changes in brain, blood, or systemic tissue QUIN levels, even though helper virus burdens were comparable to those in mice infected with LP-BM5 MuLV. Treatment of LP-BM5 MuLV-infected mice with the antiretroviral agent zidovudine (azidothymidine) significantly reduced blood and brain QUIN levels in association with reductions in viral load in brain and spleen. These observations suggest that elevated QUIN production is not attributable to productive infection with retrovirus per se but occurs in response to an agent or agents, such as cytokines, that are produced by the host in response to virus infection.     

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

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

T-deficient transmembrane signaling in CD4+ T cells of retroviral-induced immune-deficient mice.

The defective virus found in the LP-BM5 mixture of murine leukemia viruses induces a severe immune deficiency disease in C57BL/6 mice that is characterized by the activation and expansion of T and B cells that become unresponsive to normal immune stimuli. The nature of the biochemical lesion in these defective lymphocyte populations remains unknown. Flow cytometric analysis of the T cell population in infected animals has demonstrated expansion of both CD4+ and CD8+ subsets. Despite chronic expansion in vivo, CD4+ T cells by wk 4 postinfection failed to up-regulate cell surface IL-2R expression, produced IL-2, or proliferate in vitro in response to either Con A, Staphylococcal enterotoxin super-antigens, or anti-CD3 stimulation. Exogenous IL-2 did not restore the proliferative response and also failed to up-regulate IL-R expression on CD4+ T cells from infected mice, even though basal IL-2R expression was initially elevated compared to normals. In contrast, CD4+ T cells from infected mice could be induced to proliferate by stimulation with PMA and ionomycin resulting in IL-2R up-regulation, IL-2 production, and proliferation. Moreover, proliferation could also be induced by anti-CD3 plus PMA, although anti-CD3 plus ionomycin was without effect. These studies suggest that chronic expansion of CD4+ T cells in infected mice is probably not maintained by normal TCR signaling, which appears defective in these cells. In addition, the lesion in biochemical signaling appears to result in defective activation of protein kinase C, which can be overcome by direct activation with PMA.