Murine AIDS is initiated in the lymph nodes draining the site of inoculation, and the infected B cells influence T cells located at distance, in noninfected organs

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.

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.

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.

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.

Time course of viremia and antibody seroconversion following human immunodeficiency virus exposure

Rational application of diagnostic assays in the management of healthcare workers (HCWs) following occupational exposure is needed to rule out pre-existing human immunodeficiency virus (HIV) infection, detect HIV infection or seroconversion as early as possible in the small proportion individuals who become infected, and to rule out infection in the high proportion of individuals who remain uninfected following occupational exposure to HIV. An understanding of the time course of viremia and seroconversion following HIV exposure is essential in developing recommendations for management of occupational exposure among HCWs. Several data sources that address the timing and dynamics of HIV viremia and seroconversion following primary infection are reviewed. The implications of each data source for management of occupational exposure among HCWs is assessed. Although the majority of infected HCWs seroconvert within 2 months of exposure, the possibility of delayed seroconversion is well established, with approximately 5% of infected HCWs estimated to seroconvert >6 months after exposure. In contrast, the period of viremia (detectable by p24 antigen or RNA assays) preceding antibody seroconversion is consistently brief (1-3 weeks). Animal inoculation studies indicate that a variable period of localized viral replication in lymphoid tissue draining inoculation sites exists prior to systemic viremia and subsequent seroconversion.

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.

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.

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.

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.

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.