Patterns of lesion and local host cellular immune response in natural cases of ovine maedi-visna.

This study investigates the nervous form of ovine maedi-visna by histological and immunohistochemical techniques. The aim was to study the lesion types and the local cellular immune response related to each lesion type, and the possible relationship between these parameters. Thirty-four Assaf ewes were studied, 29 of which had shown nervous signs. Microscopical lesion patterns were described according to location, extent and predominance of inflammatory cell type. Immunohistochemical labelling of T cells (CD3(+), CD4(+), CD8(+) and cells expressing the γδ form of the T-cell receptor), B cells and macrophages revealed clear differences between the lesion patterns. Two main lesion types were described. Lymphocytic lesions had areas of mild-moderate injury characterized by a predominance of infiltrating T cells. Histiocytic lesions were more severe and had extensive areas of malacia and dominant infiltration by macrophages and B cells. Each animal had a unique lesion pattern and these differences could be due to individual resistance to the progression of infection. The lymphocytic lesions appear to represent initial or latent phases of slow progression, in which the animal presents some natural resistance to the infection. The histiocytic pattern may reflect a poor immune response or a greater virulence of the viral strain.

Identification of the ovine mannose receptor and its possible role in Visna/Maedi virus infection.

This study aims to characterize the mannose receptor (MR) gene in sheep and its role in ovine visna/maedi virus (VMV) infection. The deduced amino acid sequence of ovine MR was compatible with a transmembrane protein having a cysteine-rich ricin-type amino-terminal region, a fibronectin type II repeat, eight tandem C-type lectin carbohydrate-recognition domains (CRD), a transmembrane region, and a cytoplasmic carboxy-terminal tail. The ovine and bovine MR sequences were closer to each other compared to human or swine MR. Concanavalin A (ConA) inhibited VMV productive infection, which was restored by mannan totally in ovine skin fibroblasts (OSF) and partially in blood monocyte-derived macrophages (BMDM), suggesting the involvement of mannosylated residues of the VMV ENV protein in the process. ConA impaired also syncytium formation in OSF transfected with an ENV-encoding pN3-plasmid. MR transcripts were found in two common SRLV targets, BMDM and synovial membrane (GSM) cells, but not in OSF. Viral infection of BMDM and especially GSM cells was inhibited by mannan, strongly suggesting that in these cells the MR is an important route of infection involving VMV Env mannosylated residues. Thus, at least three patterns of viral entry into SRLV-target cells can be proposed, involving mainly MR in GSM cells (target in SRLV-induced arthritis), MR in addition to an alternative route in BMDM (target in SRLV infections), and an alternative route excluding MR in OSF (target in cell culture). Different routes of SRLV infection may thus coexist related to the involvement of MR differential expression.

Granulocyte macrophage colony stimulating factor is elevated in alveolar macrophages from sheep naturally infected with maedi-visna virus and stimulates maedi-visna virus replication in macrophages in vitro.

Infection by maedi-visna virus, a lentivirus of sheep, leads to chronic inflammatory reactions of various tissues. In this report we have analysed the role of specific cytokines in the disease process. A significant increase in expression of interleukin-6, interleukin-10, granulocyte macrophage-colony stimulating factor (GM-CSF) and transforming growth factor-beta1 mRNA was observed in alveolar macrophages isolated from the lungs of naturally infected animals when compared with lungs of seronegative controls. Levels of GM-CSF mRNA expression in alveolar macrophages correlated with the presence of lung lesions, but there was no correlation of interleukin-10, interleukin-6, tumour necrosis factor-alpha and transforming growth factor-beta1 mRNA levels in alveolar macrophages from animals with pulmonary lesions. In vitro investigation showed that GM-CSF in the range 0.1-10 ng/ml induced a significant increase in viral p25 production after 7 days in acutely infected blood monocyte-derived macrophages. The production of p25 peaked between 7 and 14 days exposure to 10 ng/ml of GM-CSF. Quantitative polymerase chain reaction showed that the level of viral DNA in monocyte-derived macrophages was dose-dependent following GM-CSF treatment in the range 0.1-100 ng/ml after 7 days. Viral mRNA expression was also enhanced. These findings indicate a role for GM-CSF in the pathogenesis of lymphoid interstitial pneumonia in infected animals.

Alveolar macrophages from sheep naturally infected by visna-maedi virus contribute to IL-8 production in the lung.

Sheep naturally infected by visna-maedi virus often develop a chronic interstitial lung disease characterized by an alveolitis comprising lymphocytes, neutrophils and macrophages. The alpha chemokine interleukin-8 (IL-8) was detected in cell free bronchoalveolar lavage fluid from naturally infected animals, confirmed by RT-PCR, presenting typical lesions of maedi and elevated total alveolar cell counts. No detectable IL-8 was found in the fluid obtained from uninfected animals. IL-8 concentration in alveolar fluid is correlated with alveolar neutrophil counts. Bronchoalveolar lavage cells from infected animals were found to contain a large amount of IL-8 mRNA and may contribute to IL-8 production. In situ hybridization showed that macrophages were the predominant cell type expressing IL-8 mRNA. Sustained production of IL-8 by alveolar macrophages during visna-maedi infection could suffice for neutrophil attraction to the alveoli, and may contribute to the development of lesions.

Oxidant-antioxidant imbalance in the experimental interstitial lung disease induced in sheep by visna-maedi virus.

Infection of sheep by visna-maedi virus causes an interstitial pneumonitis similar to that associated with human immunodeficiency virus type-1 (HIV-1). Visna-maedi virus infection of alveolar macrophages leads to their activation. In this study we determined whether an imbalance in oxidant-antioxidant activity may be involved in the pathogenesis of the disease. We investigated the spontaneous and phorbol myristate acetate (PMA)-induced release of hydrogen peroxide (H2O2), and the activities of superoxide dismutase and glutathione peroxidase in alveolar macrophages from lambs experimentally-infected with visna-maedi virus, and in ovine alveolar macrophages infected in vitro. Alveolar macrophages from lambs experimentally-infected in vivo exhibited normal spontaneous H2O2 release and had superoxide dismutase and glutathione peroxidase activities similar to those from control animals. In contrast, after in vitro stimulation with PMA the H2O2 production by macrophages from experimentally-infected lambs was significantly increased. Similarly, spontaneous and PMA-induced H2O2 production by in vitro infected macrophages was significantly increased as compared to controls. In conclusion, the increased capacity of alveolar macrophages infected with the human immunodeficiency virus type-1-related visna-maedi virus to release hydrogen peroxide on stimulation suggests an oxidant-antioxidant imbalance, which may contribute to the pathogenesis of the observed chronic interstitial pneumonitis.

Increased expression of tissue factor mRNA and procoagulant activity in ovine lentivirus-infected alveolar macrophages.

To link ovine lentivirus infection to lung tissue damage, we studied the procoagulant response in alveolar macrophages from experimentally infected lambs and in in vitro infected alveolar macrophages. We cloned ovine tissue factor cDNA and analysed its in vitro expression by Northern blotting. Visna-maedi virus induced tissue factor mRNA. In order to correlate this mRNA induction with its cellular function, we analysed macrophage procoagulant activity after in vitro and in vivo infection. The procoagulant activity was increased by interaction with the virus in both cases. Thus, visna-maedi virus-induced expression of tissue factor mRNA was associated with enhanced macrophage procoagulant activity. These findings indicate an active role of alveolar macrophages in the pathogenesis of these inflammatory lung lesions.

Spontaneous interferon production by pulmonary leukocytes is associated with lentivirus-induced lymphoid interstitial pneumonia.

Ovine lentiviruses share genome sequence, structural features, and replicative mechanisms with HIV, the etiologic agent of AIDS. A lamb model of lentivirus-induced lymphoid interstitial pneumonia, comparable to lymphoid interstitial pneumonia associated with pediatric AIDS, was used to investigate production of leukocyte-soluble mediators. Lentivirus-infected lambs and adult sheep with severe lymphoid interstitial pneumonia had significantly elevated levels of spontaneous interferon (IFN) production from pulmonary leukocytes compared with ovine lentiviruses-infected animals with mild or no lesions of lymphoid interstitial pneumonia or non-infected controls. However, peripheral blood mononuclear cells from lentivirus-infected lambs did not spontaneously release significant amounts of IFN. IFN production by pulmonary lymph node lymphocytes was enhanced in the presence of lentivirus-infected alveolar macrophages. Animals with lentivirus-induced disease and spontaneous IFN production had enhanced virus replication within tissues. The ovine lentiviruses-induced IFN had a m.w. of between 25,000 and 35,000 and was resistant to freeze/thawing procedures. The IFN activity was sensitive to trypsin and stable to low pH and heat. IFN with similar physical and biochemical properties was produced when ovine lentiviruses was added to control leukocyte cultures. IL-2 and PGE2 production and responses to mitogen by pulmonary lymph node lymphocytes of lentivirus-diseased lambs were not statistically different from control animals. Increased local production of IFN in lentivirus-infected host tissues may serve to accelerate the entry of leukocytes into virus-induced lesions promoting cell-mediated tissue damage and also provide increased numbers of cells for virus replication.

[Ultrastructural aspects of sheep choroid plexus cells during exogenous cell fusion induced by Visna virus in vitro]. / Aspects ultrastructuraux de cellules de plexus choroïdes de mouton en voie de fusion cellulaire exogène induite in vitro par le virus Visna.

During the first moments of the in vitro infection of Sheep choroid plexus cells with high multiplicities of infection of Visna virus, the authors observed: a strong development of GERL, some signs of an intensive protein synthesis and numerous filament bundles. This infection leads to an exogenous cell fusion.

Unique virus-related DNA sequences in sheep progressive pneumonia lung.

Hybridization studies with [3H]-cDNA of progressive pneumonia, maedi and visna viruses demonstrate that lung DNA from sheep afflicted with progressive interstitial pneumonia possesses virus-related sequences not present in normal sheep lung DNA.