Expression of TNF alpha in arthritis caused by caprine arthritis encephalitis virus

The expression of cytokines in the milk somatic cells, blood leukocytes and serum of goats infected with small ruminant lentivirus

Background

The present study aimed to determine the expression of cytokines, which is associated with the immunological response of dairy goats against small ruminant lentivirus (SRLV). The study was conducted on 26 dairy goats in their second to sixth lactation, which were divided by breed and parity into two groups: SRLV naturally infected (N = 13) and non-infected (N = 13) animals. All goats in the study were asymptomatic. The milk and blood samples, which served as studied material were taken on days 7, 30, 120 and 240 of the lactation. The gene and protein expression of several cytokines was studied using Real-Time PCR and ELISA methods.

Results

INF-β and INF-γ expression was down-regulated in the milk somatic cells (MSC) of SRLV-infected goats. However, an increased concentration of INF-β was observed in the MSC in SRLV-infected goats, while INF-γ expression was not observed in both SRLV-infected and non-infected animals The SRLV-infected goats also displayed decreased expression of IL-1α, IL-1β, IL-6 and INF-γ genes in the blood leukocytes,with IL-1α, IL-1β and IL-6 protein levels also being decreased in the sera. TNF-α was the only gene that demonstrated increased expression in both the MSC and the blood of infected animals; however, no such overexpression was observed at the protein level.

Conclusions

SRLV probably influences the immune system of infected animals by deregulating of the expression of cytokines. Further, epigenetic studies may clarify the mechanisms by which SRLV regulates the gene and protein expression of the host.

Expanding possibilities for intervention against small ruminant lentiviruses through genetic marker-assisted selective breeding

Small ruminant lentiviruses include members that infect sheep (ovine lentivirus [OvLV]; also known as ovine progressive pneumonia virus/maedi-visna virus) and goats (caprine arthritis encephalitis virus [CAEV]). Breed differences in seroprevalence and proviral concentration of OvLV had suggested a strong genetic component in susceptibility to infection by OvLV in sheep. A genetic marker test for susceptibility to OvLV has been developed recently based on the TMEM154 gene with validation data from over 2,800 sheep representing nine cohorts. While no single genotype has been shown to have complete resistance to OvLV, consistent association in thousands of sheep from multiple breeds and management conditions highlight a new strategy for intervention by selective breeding. This genetic marker-assisted selection (MAS) has the potential to be a useful addition to existing viral control measures. Further, the discovery of multiple additional genomic regions associated with susceptibility to or control of OvLV suggests that additional genetic marker tests may be developed to extend the reach of MAS in the future. This review will cover the strengths and limitations of existing data from host genetics as an intervention and outline additional questions for future genetic research in sheep, goats, small ruminant lentiviruses, and their host-pathogen interactions.

Immunological parameters in goats experimentally infected with SRLV genotype E, strain Roccaverano

Genotype E of small ruminant lentivirus has been recently described in goats from different breeds in Italy. Genotype E infection may differ from known genotypes since deletions of dUTPase and VPR proteins have been confirmed in different independent areas and goat breed, and play a key role on virus replication and pathogenesis. In particular, genotype E Roccaverano strain has been described as low pathogenic since does not lead to clinical symptoms in goats. In contrast, classical CAEV infected goats of the same area and breed presented arthritis. In this study, we have used intratracheal and intra-bone marrow routes to establish genotype E persistent infections. Humoral and cellular immune responses elicited in the host against genotype E and genotype B derived antigens were evaluated until 200 days post-inoculation. Compared to genotype B antigen, seroconversion against genotype E GAG P16-25 antigen was detected at 2-3 weeks after inoculation, significantly earlier and at higher titres. Interestingly, antibody avidity did not increase in the course of the experiment neither against P16-25 nor against SU5, both derived from genotype E. T cell proliferation against P25-GST fusion protein antigens derived from genotype E was firstly detected at 15 days post-inoculation and was maintained throughout time until week 20 post-infection, while T cell proliferation against the genotype B P25 was not produced by the end of the experiment at 20 weeks post-inoculation. The strength of reaction was also higher when using P25 E as stimulator antigen. In contrast with antibody and T cell proliferation, cytotoxic-T-lymphocyte (CTL) activity in the circulating lymphocytes (effector cells) using blood-derived macrophages (BDM) as target cells, was not strain specific being surprisingly higher against genotype B infected antigen presenting cells (APCs). This is the first study reporting experimentally induced immunological changes in SRLV genotype E infection and indicates that CTL activity may be the adaptive immune response able to induce protection against heterologous infection.

Localization of a TNF-activated transcription site and interactions with the gamma activated site within the CAEV U3 70 base pair repeat

The cytokines TNFalpha and IFNgamma have previously been shown to activate caprine arthritis encephalitis virus (CAEV) transcription. Increased viral titers correlate with increased lesion severity. Therefore, TNFalpha and IFNgamma may augment the caprine arthritis lesion by increasing viral titers. CAEV transcription is under the control of the viral promoter within the U3 region of the long terminal repeat. A set of U3 deletion mutants was generated and used to establish stably integrated, U937-based cell lines. These cell lines were utilized to define the required promoter sequences for cytokine-induced transcriptional activation. Here we have identified a novel 17 nucleotide TNF-activated site within the U3 region 70 bp repeat which is both required and sufficient in a minimal construct for TNFalpha-induced CAEV transcriptional activation. In contrast to the results of previous studies with IFNgamma, we found that multiple sequences within the U3 region 70 bp repeat were required for IFNgamma-activation of the CAEV promoter. The results identify previously unrecognized complexity in the CAEV promoter that may be relevant to viral replication and disease.

TNFα and GM-CSF-induced activation of the CAEV promoter is independent of AP-1

Caprine arthritis encephalitis virus transcription is under the control of the viral promoter within the long terminal repeat. Previous studies with the closely related maedi visna lentivirus have indicated that viral transcription is dependent upon the AP-1 transcription factor. Other studies have indicated a potential role for the cytokines TNFalpha and GM-CSF in CAEV pathogenesis by increasing viral loads in infected tissues. The hypotheses that AP-1 transcription factors are necessary for transcriptional activation of the CAEV promoter and that CAEV transcriptional activation results from treatment with the cytokines GM-CSF and TNFalpha were tested with a stably transduced U937 cell line. Here, we found that TNFalpha and GM-CSF activated CAEV transcription in U937 cells. However, this activation effect was not blocked by SP600125, an inhibitor of Jun N-terminal kinase. SP600125 effectively prevented Jun phosphorylation in cells subsequently treated with cytokines. The cytokines TNFalpha and GM-CSF therefore activate CAEV transcription, and this effect occurs independently of AP-1. A set of progressive deletion mutants was utilized to show that TNFalpha-induced expression depends on an element or elements within the U3 70-bp repeat.

Changes in macrophages in spleen and lymph nodes during acute African swine fever: expression of cytokines

To gain further insight into the pathogenesis of African swine fever (ASF), the cytokine expression by macrophages in spleen and lymph nodes were examined. Twenty-one piglets were inoculated with the highly virulent isolate Spain-70 of ASF virus and killed in groups at 1-7 post-inoculation days (pid). An increase in the immunohistochemical detection of proinflammatory monokines in spleen and renal and gastrohepatic lymph nodes is reported, along with an increase in the serum levels of TNF-alpha and IL-1 beta. The expression of these cytokines is detected simultaneously in time and space with the viral protein 73 (vp 73) of the ASF virus detection. Our results demonstrate that mononuclear phagocyte system cell activation results in the release of several cytokines that could induce apoptosis of lymphocytes and haemodynamic changes.

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.

Infection of dendritic cells by the Maedi-Visna lentivirus

The early stages of lentivirus infection of dendritic cells have been studied in an in vivo model. Maedi-visna virus (MVV) is a natural pathogen of sheep with a tropism for macrophages, but the infection of dendritic cells has not been proven, largely because of the difficulties of definitively distinguishing the two cell types. Afferent lymphatic dendritic cells from sheep have been phenotypically characterized and separated from macrophages. Dendritic cells purified from experimentally infected sheep have been demonstrated not only to carry infectious MVV but also to be hosts of the virus themselves. The results of the in vivo infection experiments are supported by infections of purified afferent lymph dendritic cells in vitro, in which late reverse transcriptase products are demonstrated by PCR. The significance of the infection of afferent lymph dendritic cells is discussed in relation to the initial spread of lentivirus infection and the requirement for CD4 T cells.

Inducible nitric oxide synthase is expressed in joints of goats in the late stage of infection with caprine arthritis encephalitis virus

We have studied the expression of the inducible form of nitric oxide synthase (iNOS) in joints of goats infected with the caprine arthritis encephalitis virus (CAEV). Nitric oxide generated by iNOS is thought to play an important role in the pathogenesis of various types of arthritis, especially rheumatoid arthritis (RA) in humans. Surprisingly, iNOS immunoreactivity was found only in joints of long-term infected goats with severe clinical arthritis, whereas-despite the presence of high numbers of inflammatory cells in the synovial tissue-no iNOS immunoreactivity was detected in mildly arthritic and in short-term experimentally infected goats. Most iNOS-positive cells expressed neither MHC class II nor CD68, which suggests that they were fibroblast-like synoviocytes. In situ hybridization studies showed that there was no correlation between iNOS immunoreactivity and detectable virus expression in the joint. In addition, infection of macrophages in vitro-the major host cells of CAEV in vivo-did not lead to increased iNOS mRNA expression. In response to stimulation, similar levels of iNOS expression were observed in infected and in uninfected macrophages. These findings suggest that the expression of iNOS is a feature of late-stage chronic arthritis and is not involved in the development of the inflammatory lesions. Both the lack of co-localization of iNOS protein and viral transcripts in the joint and the finding that CAEV does not stimulate the expression of iNOS in vitro further suggest that iNOS is not directly induced by the virus or the anti-viral immune response in the joint, that it may well, however, be involved in tissue remodelling or scar formation.

Immunohistology of the early course of lentivirus-induced arthritis

Caprine arthritis encephalitis (CAE) is a lentiviral infection of goats characterized by mononuclear cell infiltration of various tissues, most prominently the joints, mammary glands and, in young animals, the brain. We have investigated the early stages of arthritis induced by intracarpal and intravenous infection with molecularly cloned CAE virus. Analysis of the synovial membranes by immunohistological methods showed that the proportion of CD8+ T cells peaked around day 12 post-infection. CD4+ T cells increased to a lesser degree. The relative proportion of B cells rose steadily post-infection. At 33 days post-infection, plasma cells accounted for over one third of all inflammatory cells in the inflamed synovium. Histopathologically, the arthritic lesions in the synovial membranes closely resembled those in membranes of animals with a 2-year history of chronic arthritis. Our observations indicate that this type of short-term experimental infection is particularly suitable for studying the pathogenesis of goat lentiviral infection. In addition, our observations support the view that a predominantly humoral (type 2) immune response may contribute to the pathogenesis of CAE.

Caprine arthritis encephalitis virus dysregulates the expression of cytokines in macrophages

Caprine arthritis encephalitis virus (CAEV) is a lentivirus of goats that leads to chronic mononuclear infiltration of various tissues, in particular, the radiocarpal joints. Cells of the monocyte/macrophage lineage are the major host cells of CAEV in vivo. We have shown that infection of cultured goat macrophages with CAEV results in an alteration of cytokine expression in vitro. Constitutive expression of interleukin 8 (IL-8) and monocyte chemoattractant protein 1 (MCP-1) was increased in infected macrophages, whereas transforming growth factor beta1 (TGF-beta1) mRNA was down-regulated. When macrophages were infected with a CAEV clone lacking the trans-acting nuclear regulatory gene tat, IL-8 and MCP-1 were also increased. No significant differences from cells infected with the wild-type clone were observed, suggesting that Tat is not required for the increased expression of IL-8 and MCP-1 in infected macrophages. Furthermore, infection with CAEV led to an altered pattern of cytokine expression in response to lipopolysaccharide (LPS), heat-killed Listeria monocytogenes plus gamma interferon, or fixed cells of Staphylococcus aureus Cowan I. In infected macrophages, tumor necrosis factor alpha, IL-1beta, IL-6, and IL-12 p40 mRNA expression was reduced in response to all stimuli tested whereas changes in expression of granulocyte-macrophage colony-stimulating factor depended on the stimulating agent. Electrophoretic mobility shift assays demonstrated that, in contrast to effects of human immunodeficiency virus infection of macrophages, CAEV infection had no effect on the level of constitutive nuclear factor-kappaB (NF-kappaB) activity or on the level of LPS-stimulated NF-kappaB activity, suggesting that NF-kappaB is not involved in altered regulation of cytokine expression in CAEV-infected cells. In contrast, activator protein 1 (AP-1) binding activity was decreased in infected macrophages. These data show that CAEV infection may result in a dysregulation of expression of cytokines in macrophages. This finding suggests that CAEV may modulate the accessory functions of infected macrophages and the antiviral immune response in vivo.