Retrovirus-induced acquired immunodeficiencies

Construction of a transposase accessible chromatin landscape reveals chromatin state of repeat elements and potential causal variant for complex traits in pigs

Background

A comprehensive landscape of chromatin states for multiple mammalian tissues is essential for elucidating the molecular mechanism underlying regulatory variants on complex traits. However, the genome-wide chromatin accessibility has been only reported in limited tissue types in pigs.

Results

Here we report a genome-wide landscape of chromatin accessibility of 20 tissues in two female pigs at ages of 6 months using ATAC-seq, and identified 557,273 merged peaks, which greatly expanded the pig regulatory element repository. We revealed tissue-specific regulatory elements which were associated with tissue-relevant biological functions. We identified both positive and negative significant correlations between the regulatory elements and gene transcripts, which showed distinct distributions in terms of their strength and distances from corresponding genes. We investigated the presence of transposable elements (TEs) in open chromatin regions across all tissues, these included identifications of porcine endogenous retroviruses (PERVs) exhibiting high accessibility in liver and homology of porcine specific virus sequences to universally accessible transposable elements. Furthermore, we prioritized a potential causal variant for polyunsaturated fatty acid in the muscle.

Conclusions

Our data provides a novel multi-tissues accessible chromatin landscape that serve as an important resource for interpreting regulatory sequences in tissue-specific and conserved biological functions, as well as regulatory variants of loci associated with complex traits in pigs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00767-3.

Long-term efficacy and safety of porcine islet macrobeads in nonimmunosuppressed diabetic cynomolgus macaques

Although human islet transplantation has proven to provide clinical benefits, especially the near complete amelioration of hypoglycemia, the supply of human islets is limited and insufficient to meet the needs of all people that could benefit from islet transplantation. Porcine islets, secreting insulin nearly identical to that of human insulin, have been proposed as a viable supply of unlimited islets. Further, encapsulation of the porcine islets has been shown to reduce or eliminate the use of immunosuppressive therapy that would be required to prevent rejection of the foreign islet tissue. The goal of the current study was to determine the long-term safety and efficacy of agarose encapsulated porcine islets (macrobeads) in diabetic cynomolgus macaques, in a study emulating a proposed IND trial in which daily exogenous insulin therapy would be reduced by 50% with no loss of glucose regulation. Four of six animals implanted with macrobeads demonstrated ≥ 30% reduction in insulin requirements in year 1 of follow-up. Animals were followed for 2, 3.5, and 7.4 years with no serious adverse events, mortality or evidence of pathogen transmission. This study supports the continued pursuit of encapsulated porcine islet therapy as a promising treatment option for diabetes mellitus.

Toll-Like Receptor and Cytokine Responses to Infection with Endogenous and Exogenous Koala Retrovirus, and Vaccination as a Control Strategy

Koala populations are currently declining and under threat from koala retrovirus (KoRV) infection both in the wild and in captivity. KoRV is assumed to cause immunosuppression and neoplastic diseases, favoring chlamydiosis in koalas. Currently, 10 KoRV subtypes have been identified, including an endogenous subtype (KoRV-A) and nine exogenous subtypes (KoRV-B to KoRV-J). The host’s immune response acts as a safeguard against pathogens. Therefore, a proper understanding of the immune response mechanisms against infection is of great importance for the host’s survival, as well as for the development of therapeutic and prophylactic interventions. A vaccine is an important protective as well as being a therapeutic tool against infectious disease, and several studies have shown promise for the development of an effective vaccine against KoRV. Moreover, CRISPR/Cas9-based genome editing has opened a new window for gene therapy, and it appears to be a potential therapeutic tool in many viral infections, which could also be investigated for the treatment of KoRV infection. Here, we discuss the recent advances made in the understanding of the immune response in KoRV infection, as well as the progress towards vaccine development against KoRV infection in koalas.

Virome characterization in serum of healthy show pigs raised in Oklahoma demonstrated great diversity of ssDNA viruses

In the United States, show pigs are raised to compete in agricultural events. These animals are usually raised in small herds with extensive human, domestic, and wild animal contact. Therefore, pathogen monitoring in this animal category is critical for improved disease surveillance and preparedness. This study characterized the virome of healthy show pigs using high-throughput sequencing using pooled serum samples from 2018 or 2019 (200 samples each pool). Results demonstrated the presence of DNA viral families (Parvoviridae, Circoviridae, and Herpesviridae) and RNA families (Arteriviridae, Flaviviridae, and Retroviridae). Twenty-three viral species were identified, including the first detection of porcine bufavirus in the US. Moreover, important swine pathogens identified included porcine reproductive and respiratory syndrome virus, atypical porcine pestivirus, and porcine circovirus (PCV). Additionally, complete coding genomes of 17 viruses from the Parvoviridae, Anelloviridae, and Circoviridae families were retrieved and included the first near full-length genomes of US Ungulate bocaparvovirus 3 species.

Koala retrovirus epidemiology, transmission mode, pathogenesis, and host immune response in koalas (Phascolarctos cinereus): a review

Koala retrovirus (KoRV) is a major threat to koala health and conservation. It also represents a series of challenges across the fields of virology, immunology, and epidemiology that are of great potential interest to any researcher in the field of retroviral diseases. KoRV is a gammaretrovirus that is present in both endogenous and exogenous forms in koala populations, with a still-active endogenization process. KoRV may induce immunosuppression and neoplastic conditions such as lymphoma and leukemia and play a role in chlamydiosis and other diseases in koalas. KoRV transmission modes, pathogenesis, and host immune response still remain unclear, and a clear understanding of these areas is critical for devising effective preventative and therapeutic strategies. Research on KoRV is clearly critical for koala conservation. In this review, we provide an overview of the current understanding and future challenges related to KoRV epidemiology, transmission mode, pathogenesis, and host immune response and discuss prospects for therapeutic and preventive vaccines.

Inactivation of porcine endogenous retrovirus in pigs using CRISPR-Cas9

Xenotransplantation is a promising strategy to alleviate the shortage of organs for human transplantation. In addition to the concerns about pig-to-human immunological compatibility, the risk of cross-species transmission of porcine endogenous retroviruses (PERVs) has impeded the clinical application of this approach. We previously demonstrated the feasibility of inactivating PERV activity in an immortalized pig cell line. We now confirm that PERVs infect human cells, and we observe the horizontal transfer of PERVs among human cells. Using CRISPR-Cas9, we inactivated all of the PERVs in a porcine primary cell line and generated PERV-inactivated pigs via somatic cell nuclear transfer. Our study highlights the value of PERV inactivation to prevent cross-species viral transmission and demonstrates the successful production of PERV-inactivated animals to address the safety concern in clinical xenotransplantation.

Early dissemination rates of Friend murine leukaemia virus variants correlate with late pathogenesis

FIS-2, a less oncogenic, immunosuppressive variant of the Friend murine leukaemia virus (F-MuLV), was used to explore whether the differences in biological features were related to early virus dissemination rates or sites of replication. We found that erythroblasts were the primary target cells for both F-MuLV and FIS-2, while B- and T-cells were infected later in the infection. Although FIS-2 replicated to similar titres as F-MuLV, we observed a delay in peak viraemia titre and in the number of virus-positive cells in bone marrow and spleen. Studies including the chimeric viruses RE3 (FIS-2LTR with a F-MuLV background) and RE4 (F-MuLV LTR with a FIS-2 background) indicated that the delay in dissemination was due to mutations in FIS-2 LTR. The kinetics for early virus replication correlated with previously reported mean latency time for virus-induced erythroleukaemia in mice inoculated as newborns and with the onset of immunosuppression in adult mice. In addition, F-MuLV-induced late immunosuppression coincided with signs of erythroleukaemia and persistent viraemia. FIS-2 induced a more moderate late immunosuppression without persistent viraemia or signs of erythroleukaemia. Overall, our findings indicated that early viral replication is a prognostic factor in murine retrovirus-induced pathogenesis.

Identification of genetic determinants responsible for the rapid immunosuppressive activity and the low leukemogenic potential of a variant of Friend leukemia virus, FIS-2

An immunosuppressive variant of Friend murine leukemia virus (F-MuLV), FIS-2, induces suppression of the primary antibody response against sheep erythrocytes (SRBC) in adult NMRI mice more efficiently than the prototype F-MuLV clone 57 (cl.57). It is, however, less potent than F-MuLV cl.57 in inducing erythroleukemia upon inoculation into newborn NMRI mice. Nucleotide sequence analysis shows a high degree of homology between the two viruses. Single point mutations are scattered over both the gag and the env encoding regions. The most notable mutations are the deletion of one direct repeat and a few single point mutations occurring in the binding sites for cellular transcriptional factors in the FIS-2 long terminal repeat region (LTR). To define the genetic determinants responsible for the pathogenic properties of FIS-2, we constructed six chimeras between FIS-2 and F-MuLV cl.57. Adult mice were infected with the chimeras, and their primary antibody responses against SRBC were investigated. The results showed that the fragment encompassing the FIS-2 env encoding region SU is responsible for the increased immunosuppressive activity in adult mice. A leukemogenicity assay was also performed by infecting newborn mice with the chimeras. Consistent with the previous studies, it showed that the deletion of one direct repeat in the FIS-2 LTR is responsible for the long latent period of erythroleukemia induced by FIS-2 in newborn-inoculated mice. However, studies of cell type-specific transcriptional activities of FIS-2 and F-MuLV cl.57 LTRs using LTR-chloramphenicol acetyltransferase constructs showed that the deletion of one direct repeat does not reduce the transcriptional activity of the FIS-2 LTR. The activity is either comparable to or higher than the transcriptional activity of the F-MuLV cl.57 LTR in the different cell lines that we used, even in an erythroleukemia cell line. It seems that the high transcriptional strength of the FIS-2 LTR is not sufficient to give FIS-2 a high leukemogenic effect. This suggestion is inconsistent with the previous suggestion that the transcriptional strength of an LTR in a given cell type is correlated with the leukemogenic potential in the corresponding tissue. In other words, these data indicate that the direct repeats in the F-MuLV LTR may play other roles besides transcriptional enhancer in the leukemogenesis of F-MuLV.

Lymphoproliferation assays in cattle naturally infected with bovine leukaemia virus (BLV) and bovine immunodeficiency-like virus (BIV)

Experiments were designed to evaluate the effect of BLV on mitogen-stimulated peripheral blood mononuclear cells (PBMC) from naturally infected cattle. BIV was also taken into consideration due to a recent report showing that in Costa Rica, most of the BLV-infected animals are also seropositive for BIV. The methodology was based on a non-radioactive technique to determine lymphoproliferation. A colorimetric assay using XTT (formazan salt) to measure cell multiplication was adapted for bovine PBMC. ELISA and Western blotting were used to determine the serologic status of the cattle. PCR was only available for BIV detection. Our results show clearly that, dually-infected cattle (BIV-BLV) have reduced lymphoproliferative responses to the mitogen Con A. Haematological abnormalities associated with viral infections were also observed, specially leukocytosis and lymphocytosis. Cows with lymphosarcomas are severely affected. The specific antibody response to different viral proteins could not be associated with the suppressive status of the animals. Due to the high rate of dual infections observed in Costa Rica, these results are not sufficient to clarify which virus is responsible for the suppressive activity, if one or both viruses are necessary, or if they act synergistically.

An immunosuppressive murine leukaemia virus induces a Th1-->Th2 switch and abrogates the IgM antibody response to sheep erythrocytes by suppressing the production of IL-2

Many retroviruses have tropism for cells in the immune system and have a propensity to induce immunosuppression in the host. Some of the effects of retroviruses on immune cell function are thought to be mediated through cytokines. Friend ImmunoSuppressive virus-2 (FIS-2) is a low oncogenic murine leukaemia virus (MuLV) that induces lymphadenopathy and immunosuppression in NMRI mice. The role of T cell cytokines during the generation of a primary antibody response in healthy and FIS-2-infected mice was studied following the antibody response to sheep erythrocytes by an in vitro immunization (IVI) technique. In cultures from FIS-2-infected mice, the antibody response was reduced compared with cultures from uninfected mice and the production of the Th2 cytokines IL-4 and IL-6 was elevated, whereas the Th1 cytokines IL-2, interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha) were reduced. The suppressed anti-sheep erythrocyte antibody response in cultures from mice infected with FIS-2 seemed to be caused by an insufficient production of IL-2, since addition of recombinant IL-2 stimulated the antibody response. This effect was also observed in cultures depleted of T cells, indicating a direct effect of IL-2 on B cells. A switch to a Th2 cell response and suppression of IL-2 production might play a central role in the immune cell dysfunction induced by FIS-2.

Methionine enkephalin combined with AZT therapy reduce murine retrovirus-induced disease

AZT (7.5 or 15 mg/kg/dose) and the neuropeptide methionine enkephalin (Met-ENK, 1 or 3 mg/kg/dose) were used in a combined protocol for therapy of established murine retroviral infection. In both models used, Friend virus leukemia (FV) and BM5 complex (lymphadenopathy and immune deficiency), the drug combination was able to reduce mortality and splenomegaly. While increasing mean survival time of those animals that did not survive infection by FV, when compared to infected control mice or mice treated with AZT alone, Met-ENK used alone at 1 and 3 mg/kg/mouse had no effect in reducing morbidity or mortality due to either virus. This suggested that Met-ENK had no direct antiviral effect at the concentrations used. In fact, mice treated with either single drug therapy or the combination still yielded virus in their spleen, even when splenomegaly was absent. The data suggest that Met-ENK, which has been reported to be immunostimulatory, acts in combination to improve the efficacy of AZT in reducing progression of disease in murine retrovirus models for human AIDS.

Bone marrow transplantation therapy using resistant donors for retrovirus-induced leukaemia in mice

Infection with Rauscher leukaemia virus (RLV) causes erythroleukaemia, anaemia, viraemia, and splenomegaly, features which develop very quickly in mice of strains susceptible to RLV but more slowly or not at all in strains resistant to RLV. We compared the effects of bone marrow transplantation (BMT) of donor cells obtained from a mouse strain resistant to the virus with the effects of BMT of donor cells obtained from strains susceptible to the virus, in recipient virus-susceptible mice which had previously been inoculated with RLV. Our results indicated that bone marrow transplantation from a marrow-resistant donor, but not from a susceptible donor, delayed the expression of leukaemia and delayed death, although such treatment did not appear to inhibit viral infection in susceptible recipients.

Effects of murine leukemia viruses on the function of dendritic cells

In asymptomatic human immunodeficiency virus-1 infection T cells respond normally to allogeneic dendritic cells (DC), but DC show reduced stimulatory capacity. By contrast in HTLV-1 infection no significant changes in allogeneic stimulation were seen but DC-stimulated activity of autologous T cells. In seeking animal models relevant to these diseases the effects of two murine leukemia retroviruses, Rauscher leukemia virus (RLV) and Moloney leukemia virus (MLV) on the function of dendritic cells and T cells in a primary mixed leucocyte reaction have been tested. Treatment by RLV in vitro suppressed the ability of DC to stimulate allogeneic T cells from healthy animals. MLV at the same concentration did not significantly affect the ability of DC to stimulate allogeneic T cells, but provoked considerable enhancement of the low level stimulation by DC in the syngeneic system. Similar results were obtained following in vivo exposure to viruses. Two pieces of evidence suggested that these effects were due to impairment of DC function and were not operating through infection of T cells. Firstly, exposure of T cells directly to virus in vitro and in vivo before stimulation with untreated allogeneic DC caused no significant alteration in T cell activity. Secondly, the impact of murine leukemia virus on DC function was not abrogated when infected DC were added to normal T cells and cultured in the presence of zidovudine. Treatment of DC by RLV caused a decrease of cluster formation with allogeneic T cells. No statistically significant influence of MLV was observed on cluster formation after 3-h of incubation in the allogeneic system. However, after 18-h incubation MLV-treated DC formed fewer clusters with T cells than untreated DC. At the same time a stimulatory effect of MLV on DC cluster formation with syngeneic T cells was found. Considerable decrease was found in major histocompatibility complex class II antigen and LFA-1 receptor expression on the DC surface in mice infected by RLV. MLV induced no significant changes. These mouse retroviruses can therefore cause changes in DC function similar to those already reported using human retroviruses and may provide models for studying their effects.

Lipopolysaccharide restores anti-Candida albicans growth inhibition activity of polymorphonuclear neutrophils from retrovirus-immunosuppressed mice

It has been documented that the immune function of leukocytes may be markedly suppressed after infection of mice with the murine retrovirus Friend leukemia virus (FLV). Antimicrobial activity of polymorphonuclear neutrophils (PMNs) against Candida albicans is impaired after retrovirus infection of mice, and this occurs as early as 3 days after infection of genetically susceptible BALB/c mice. By 2 weeks after infection, there was essentially very little growth inhibition of C. albicans by PMNs from the FLV-infected mice. However, when bacterial lipopolysaccharide (LPS), a known activator of macrophages and PMNs, was added to PMNs from the FLV-infected mice, anti-C. albicans activity was restored to normal levels. This restoration of anti-C. albicans activity of FLV-infected mouse PMNs was observed after stimulation with as little as 0.01 micrograms of LPS per ml. The data obtained show that the impaired antimicrobial function of PMNs from retrovirus-infected mice can be readily restored by a biological response modifier such as bacterial LPS.

Effect of a human immunodeficiency virus protease inhibitor on human monocyte function

Human immunodeficiency virus (HIV) is the cause of acquired immunodeficiency syndrome (AIDS). Encoded by the HIV genome are several precursor proteins that undergo proteolytic cleavage to yield functional proteins. The env precursor protein is cleaved by a cellular protease. The gag precursor protein of HIV (p55), however, is cleaved by a virally encoded aspartate protease (HIV Protease). Cleavage of p55 is required for viral maturation and infectivity. There are also several host cell aspartate proteases that serve important homeostatic functions. Cathepsins D and E are lysosomal aspartate proteases which are believed to play an important role in macrophage function, and it has been suggested that inhibition of these enzymes by an HIV protease inhibitor may exacerbate immunosuppression in AIDS patients. We have studied the effect of SK&F 107461 (a hydroxyethylene dipeptide isostere inhibitor of HIV protease), on various host defense functions of human monocytes. Pepstatin A (an inhibitor of most aspartate proteases) and leupeptin (an inhibitor of serine and cysteine proteases) were included as controls. Although less potent than the prototypic aspartate protease inhibitor pepstatin, SK&F 107461 inhibited partially purified cathepsin D in vitro. However, in cell-based assays, SK&F 107461 had no effect on the degradation of hemoglobin, antigen processing of the protein antigen streptokinase, or secretion of 17-kD IL-1 beta by monocytes at concentrations which inhibit maturation of intracellular virus in HIV infected monocytes. Furthermore, SK&F 107461 had no effect on constitutive candidacidal activity. In contrast, leupeptin and pepstatin A partially inhibited accessory cell function of monocytes in the proliferative response to the recall antigen streptokinase. In addition, leupeptin partially inhibited degradation of hemoglobin.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Suppression of virus-specific antibody production by CD8+ class I-restricted antiviral cytotoxic T cells in vivo

The question of whether virus-induced immunosuppression includes the antibody response against the infecting virus itself was evaluated in a model situation. Transgenic mice expressing the T-cell receptor (TCR) specific for peptide 32-42 of lymphocytic choriomeningitis virus (LCMV) glycoprotein 1 presented by Db reacted with a strong transgenic cytotoxic T-lymphocyte (CTL) response starting on day 3 after infection with a high dose (10(6) PFU intravenously [i.v.]) of the WE strain of LCMV (LCMV-WE); LCMV-specific antibody production in the spleen was suppressed in these mice. Low-dose (10(2) PFU i.v.) infection resulted in an antiviral antibody response comparable to that of the transgene-negative littermates. The induction of suppression of LCMV-specific antibody responses was specifically mediated by CD8+ TCR transgenic CTLs, since the LCMV-8.7 variant virus (which is not recognized by transgenic TCR-expressing CTLs because of a point mutation) did not induce suppression. In addition, treatment with CD8 monoclonal antibody in vivo abrogated suppression. Once suppression had been established, it was found to be nonspecific. The abrogation of antibody responses depended on the relative kinetics of the antibody response involved and the kinetics of the anti-LCMV CTL response. Analysis of T- and B-cell subpopulations showed no significant changes, but immunohistochemical analysis of spleens revealed extensive destruction of follicular organization in lymphoid tissue by day 4 in transgenic mice infected with LCMV-WE but not in those infected with the CTL escape mutant LCMV-8.7. Impairment of antigen presentation rather than of T or B cells was also suggested by adoptive transfer experiments, showing that transferred infected macrophages may improve the anti-LCMV antibody response in LCMV-immunosuppressed transgenic recipients; also, T and B cells from suppressed transgenic mice did respond in irradiated and virus-infected nontransgenic mice with antibody formation to LCMV. Such virus-triggered, T-cell-mediated immunopathology causing the suppression of B cells and of protective antibody responses, including those against the infecting virus itself, may permit certain viruses to establish persistent infections.

Altered macrophage antigen-presenting cell function following Friend leukemia virus infection

To investigate the mechanism by which Friend leukemia virus (FV) causes immunosuppression, the ability of peritoneal macrophages to mediate antigen-specific T-cell activation following FV infection was examined. Decreased IL-2 production was observed when antigen-primed T cells were cultured with antigen-pulsed macrophages from mice infected with FV, compared to T cells cultured with macrophages from control mice. Macrophages from FV-infected mice demonstrated decreased phagocytic and pinocytic activity, suggesting that antigen uptake may be impaired in these cells. In addition, FV-infected mice had decreased numbers of MHC class II positive macrophages compared to uninfected controls, as measured by immunofluorescence. The alterations in antigen uptake and class II expression observed in macrophages from FV-infected mice may be the result of infection of these cells by FV, which was demonstrated by in situ hybridization using a FV-specific probe. The ability of FV to infect and modulate the functions of macrophages may account, at least in part, for the immunosuppression observed in FV-infected mice.

In vitro immunomodulation and in vivo immunotherapy of retrovirus-induced immunosuppression

Early studies with the Gross passage A leukemia virus demonstrated that retroviral infection suppresses cellular and humoral immune responses. In extensive studies of the feline leukemia (FeLV) virus, which can induce profound immunodeficiency disease, are generative anemia and lymphoid, myeloid and erythroid neoplasia, the immunosuppressive effects of this retrovirus could be attributed to the actions of the retroviral envelope protein p15E. We found that a highly conserved, synthetic 17 amino acid peptide synthesized by Cianciolo and co-workers that is homologous to the hydrophilic portion of the otherwise hydrophobic transmembrane envelope protein can suppress polyclonal activation of B-cells, impair production of gamma- and alpha-interferon, inhibit production of interleukin-2, inhibit expression of IL-2 receptors, and suppress responses of cytotoxic lymphocytes. In analyses with inactivated preparations of the human immunodeficiency virus, with Pahwa et al. we demonstrated that purified non-infectious retrovirus and also retroviral proteins, in particular gp120, appeared to produce some of the immunosuppressive properties of HIV, particularly suppression of B-cell activation in response to known B-cell stimulants irrespective of T-cell influence, suppression of T-helper cell functions essential to B-lymphocyte responsiveness, and impaired function of immunoglobulin-secreting cells. Other investigators have also reported strong immunosuppressive or immunostimulatory influences for components of the HIV retrovirus and also gp120 through yet poorly elucidated but certainly complex actions on both T- and B-lymphocyte-mediated immune functions.

Fr-MLV infection induces erythroleukaemia instead of lymphoid leukaemia in mice given pituitary grafts

Here we report that the slow-transforming helper component of Friend murine leukaemia virus (Fr-MLV), which produces lymphoid leukaemias in normal mice, induces erythroleukaemia in mice given syngeneic pituitary grafts (SPG). Newborn mice were infected with Fr-MLV and, at one month of age, were transplanted with two pituitary glands under the kidney capsule. Sham-operated infected mice and uninfected transplanted mice served as controls. SPG selectively reduced the mean survival times of infected mice. Histopathology showed that, while most infected non-transplanted mice developed lymphoid leukaemias, virtually all Fr-MLF-infected mice given SPG developed erythroleukaemias. Experiments in vitro showed that Fr-MLV infection markedly depressed concanavalin A induced DNA synthesis in cells from spleen, thymus and lymph nodes. Addition of prolactin or growth hormone further suppressed lectin-induced mitogenesis of lymphoid cells from infected mice, but failed to influence the response of uninfected controls. These experiments indicate that, in mice, pituitary hormones modulate the development and the histological features of Fr-MLV induced leukaemias, and suggest that endocrine-immunological interactions play a role in retrovirus induced tumorigenesis.

Replication of the bovine immunodeficiency-like virus in diploid and aneuploid cells: permanent, latent and virus-productive infections in vitro

Bovine immunodeficiency-like virus (BIV) is an infectious and leukotropic retrovirus, the sole lentivirus candidate which has been isolated from cattle. Although BIV has recently been shown to be related to the human immunodeficiency virus, there is very limited information on the replication and the pathogenesis of BIV. It is reported here that BIV can permanently infect diploid and aneuploid cells from four different species: bovine, canine, ferret and ovine. With the exceptions of a bovine diploid and a canine aneuploid cell line, all lines were virus non-productive. However, BIV was rescued by co-cultivation of virus non-productive cells with homologous BIV-free or canine cells (Cf2Th). A permanent and BIV-productive infection was established for 90-serial subcultures in a canine cell line. A BIV titre of 1 x 10(6)/0.1 ml was observed in stationary culture and 1 x 10(10)/0.1 ml in suspension culture. The canine cell line above was used for production of BIV antigens, whereas BIV-free canine cells were routinely used to isolate BIV from BIV non-productive cells infected in vitro and from blood from experimentally BIV-infected cattle. The different steps of virus maturation were similar by electron microscopy to those of lentiviruses. BIV results are compared to those of lentiviruses.

Enhancement and suppression of DTH reactivity to Rauscher murine leukaemia virus induced tumour cell lines

Delayed-type hypersensitivity (DTH) to Rauscher murine leukaemia virus (R-MuLV) encoded or induced determinants was induced in mice by three syngeneic R-MuLV-induced tumour cell lines, i.e. a myeloid tumour, RMB-1, an erythroid tumour, RED-1, and a lymphoid tumour, RLD-1. DTH to subcutaneously (s.c.) administered RMB-1 cells appeared on day 4, with a maximum DTH response on day 6 or 7. The induction of DTH could be prevented by intravenous (i.v.) pre-immunisation with R-MuLV-induced tumour cells several days before the s.c. immunisation. The three R-MuLV-induced tumour cell lines showed cross-reactivity in the DTH assay, whereas no cross-reactivity was found with syngeneic WEHI-3 cells. This indicates that the three R-MuLV-induced tumour cell lines share a virally encoded or induced antigenic determinant, which activates T-cells. When the RMB-1 cells used for immunisation had been cultured in medium supplemented with interferon-gamma (IFN-gamma), the subsequent DTH response was increased. This coincided with an increased expression of the R-MuLV-specific antigenic determinants on RMB-1 cells as demonstrated by Scatchard analysis. Furthermore, IFN-gamma increased the MHC class I antigen expression on RMB-1 cells, whereas the class II antigen expression remained undetectable.

ts1, a mutant of Moloney murine leukemia virus-TB, causes both immunodeficiency and neurologic disorders in BALB/c mice

BALB/c mice infected with ts1, a mutant of Moloney murine leukemia virus-TB, develop generalized body wasting, profound neurologic disorders, severe thymic atrophy and lymphopenia due to destruction of T lymphocytes and drastic immunodeficiency. ts1 was found not only able to infect T lymphocytes but also to impair their function. In addition, ts1 also infects and induces syncyntia formation in macrophages. The genetic determinant(s) responsible for ts1's ability to induce immunodeficiency has been localized to the env gene.

Friend leukemia complex infection of mice as an experimental model for AIDS studies

It is now clear that AIDS results from a complex pathogenesis where virus-induced cytopathology represents only one of the contributing factors, while the others remain elusive. For this and other reasons there is much interest in the mechanisms whereby other classically immunodepressive noncytocidal retroviruses, such as viruses of the murine Friend leukemia complex (FLC), affect the immune system. FLC-induced immunosuppression has already provided important leads to the understanding of the mechanisms whereby retroviruses immunosuppress their hosts. It is expected that further investigation of the model will prove useful in several areas of AIDS research, including the development of efficacious drug therapies.

Immunodeficiency in latent feline leukemia virus infections

Challenge of naive experimental animals with a retroviral inoculum may result in one of two broad sequelae. The first is the establishment of an appropriate humoral and cellular immune response leading to a condition of immunity to subsequent infection with the retrovirus. Alternatively, the host may fail to develop a successful immune response, resulting in a chronic viremia associated with immunosuppression and ultimately death due to secondary pathogens. An alternate disease course is the establishment of a latent infection characterized by the presence of neutralizing antibody and strong cellular immune reactivity. Recent data from the feline leukemia virus (FeLV) system suggest that cats infected with this virus may develop immunosuppression in the form of persistent neutrophil dysfunction. The potential effect of this cellular dysfunction is the possible susceptibility of the host to the same opportunistic pathogens which are responsible for the increased mortality noted in chronic FeLV infections. These data demonstrate that persistent retroviremia is not essential for the establishment of immunosuppression. This overview presents data accumulated from the feline model of the human acquired immunodeficiency syndrome (AIDS) and discusses its relationship to human retroviral infections.

Murine models for acquired immune deficiency syndrome

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

Peripheral blood mononuclear cells from AIDS patients release but do not respond to antigen-stimulated NK-activating lymphokines

We have previously shown that streptococcal product (SP) extracted from the culture supernatants of Streptococcus pyogenes ATCC 19615 augments NK activity, partly by inducing the release of soluble factors from mononuclear cells. In this study we use SP as an NK stimulant to investigate the mechanism of NK depression in AIDS. We demonstrate that the NK activity of AIDS patients is lower than normal controls and can be significantly enhanced with SP, although not to control levels. The decreased cytotoxicity in AIDS is not due to a depletion of NK cells, nor to the depletion of lymphokines from CD4 cells that are directly involved in NK cell activation. PBMCs from patients with AIDS respond to SP, producing normal levels of NK-enhancing substances in their supernatants. However, upon examining the ability of SP-induced supernatants from control cells to augment the NK activity of cells from AIDS patients, we find significantly less activity in AIDS cells than in control cells, suggesting an intrinsic effector dysfunction of NK cells in AIDS.

Low dose total body irradiation: a potent anti-retroviral agent in vivo

Immunosuppression characterizes many human diseases including leukemia and AIDS. Friend virus (FV)-induced murine leukemia is a useful model for studying both malignancy and immunosuppression. In a previous series of experiments, we have demonstrated that untreated FV-infected mice died within 40 days post-infection, whereas infected mice given 150 cGy total body irradiation (TBI) on days 5 and 12 exhibited long-term survival. In this report, we show that no leukemic cells or type C virus particles are found in the spleens of mice treated with TBI. In addition, both NK activity as well as bone marrow cell's proliferative responses to PHA and Con A were fully restored. This treatment produces long term control of FV-induced murine leukemia, and thus might have relevance for the treatment of a number of immunosuppressive diseases including AIDS.

Non-toxic endotoxin polysaccharide induces soluble mediators which potentiate antibody production by murine retrovirus-suppressed splenocytes

Mice infected with Friend leukemia virus show marked acquired immunodeficiency characterized by the impairment of immune function of spleen cells to various antigens, both in vivo and in vitro. The large mol. wt. endotoxin derived from Serratia marcescens, as well as a smaller non-toxic polysaccharide derivative, were found to augment the antibody responsiveness of spleen cells from normal as well as FLV-infected mice. In addition, serum from normal donor mice pretreated with BCG and injected either with endotoxin or the polysaccharide derivative potentiated the antibody response of spleen cells from both normal and FLV-infected mice. Similar enhancement was induced by "antibody response helper factor(s)" present in 3-5 day spleen culture supernatants from endotoxin or polysaccharide-treated spleen cells from normal mice. Enhancement of the antibody response of spleen cells from FLV-infected mice by the antibody helper activity was due to stimulation of B-lymphocytes and reversal of a defect in antibody helper factor(s) formation by macrophages. Similar antibody response enhancing activity was induced by both endotoxin and the non-toxic polysaccharide derivative in cultures of normal spleen cells, adherent spleen cell populations, peritoneal cells and the P388D1 macrophage cell line.

HIV-mediated immunodepression: in vitro inhibition of T-lymphocyte proliferative response by ultraviolet-inactivated virus

In order to assess whether the human retrovirus HIV, like other animal retroviruses, is endowed with intrinsic immunosuppressive activity, we studied the effects of noninfectious, uv-irradiated virus on in vitro lymphocyte function. uvHIV preparations inhibited T-cell proliferation to mitogens and alloantigens, as well as mitogen-driven IL-2 production. The inhibitory effect, which was not exerted by uv-irradiated HTLV-I, was apparently not due to a decrease in cell viability and was likely associated with thermoresistant viral component(s). The suppression proved to be selective for T-cell responses, while sparing other lymphocyte functions, such as the B-cell proliferative response to a selective B-cell mitogen. The inhibitory effect of uvHIV was not counteracted by a substantial reduction in the number of monocytes or by indomethacin. Moreover, IL-1 production by monocytes was not affected upon virus incubation. On the other hand, the proliferative response of both CD4+ and CD8+ T-cell clones was inhibited by uvHIV, suggesting that T cells represent the actual target for the inhibitory effect. Although a sizeable decrease in IL-2 production was observed following uvHIV incubation, exogenous IL-2 was not capable of reversing the virus-induced suppression of the proliferation. The possibility that the immunosuppressive activity of noninfectious HIV contributes to the T-cell defect in infected patients by mechanisms other than the cytopathic effect on CD4+ T lymphocytes is discussed.

Feline leukemia virus: current status of the feline induced immune depression and immunoprevention

This is a review of the current knowledge of feline leukemia virus (FeLV) associated with immune depression observed in cats. It will focus on the clinical and experimental observations associated with feline retroviral infection and presence in vivo and in vitro. We will briefly describe retroviral-associated acquired immune deficiency syndrome associated with FeLV infection in the cat and specific cellular pathology associated with FeLV latency. In addition, we will focus on the action of FeLV-p15E in vitro and describe possible mechanisms of the FeLV-associated immunosuppression observed both in vivo and in vitro. Lastly, we will evaluate the current status of immunoprevention of FeLV. We will not attempt an in-depth analysis of the current literature; our focus is to review current findings as they relate to feline AIDS and immunotherapy.