Hepatic immune response in calves during acute subclinical infection with bovine viral diarrhoea virus type 1

Fetal Hepatic Response to Bovine Viral Diarrhea Virus Infection in Utero

Non-cytopathic bovine viral diarrhea virus (ncp BVDV) can cause persistent infection (PI) in animals infected in utero during early gestation. PI animals shed the virus for life and are the major source of the virus in herds. The mechanism responsible for BVDV immune tolerance in the PI fetus is unknown. We assessed the impact of BVDV infection on the fetal liver. Dams were inoculated with ncp BVDV at gestational day 75. Fetal liver samples were collected at necropsy, 7 and 14 days post-maternal-BVDV inoculation. BVDV antigen was not detected in the liver at gestational day 82 (7 days post-maternal inoculation). However, at 14 days post-maternal inoculation, BVDV was detected by immunohistochemistry in fetal Kupffer cells. Flow cytometry analysis showed a higher percentage of hepatic immune cells expressed MHC I and MHC II in BVDV-infected fetal liver (as compared to uninfected controls). Immunofluorescence was used to identify Kupffer cells, which were positive for BVDV antigen, near populations of CD3+ lymphocytes. The identification of BVDV in the fetal liver Kupffer cells at 14 days post inoculation is interesting in the context of establishment of tolerance in persistent infection. These data indicate the presence of a hepatic immune response to fetal infection.

Innate and adaptive immune responses to in utero infection with bovine viral diarrhea virus

Infection of pregnant cows with noncytopathic (ncp) bovine viral diarrhea virus (BVDV) induces rapid innate and adaptive immune responses, resulting in clearance of the virus in less than 3 weeks. Seven to 14 days after inoculation of the cow, ncpBVDV crosses the placenta and induces a fetal viremia. Establishment of persistent infection with ncpBVDV in the fetus has been attributed to the inability to mount an immune response before 90-150 days of gestational age. The result is 'immune tolerance', persistent viral replication and shedding of ncpBVDV. In contrast, we describe the chronic upregulation of fetal Type I interferon (IFN) pathway genes and the induction of IFN-γ pathways in fetuses of cows infected on day 75 of gestation. Persistently infected (PI) fetal IFN-γ concentrations also increased at day 97 at the peak of fetal viremia and IFN-γ mRNA was significantly elevated in fetal thymus, liver and spleen 14-22 days post maternal inoculation. PI fetuses respond to ncpBVDV infection through induction of Type I IFN and IFN-γ activated genes leading to a reduction in ncpBVDV titer. We hypothesize that fetal infection with BVDV persists because of impaired induction of IFN-γ in the face of activated Type I IFN responses. Clarification of the mechanisms involved in the IFN-associated pathways during BVDV fetal infection may lead to better detection methods, antiviral compounds and selection of genetically resistant breeding animals.

Immune response to bovine viral diarrhea virus--looking at newly defined targets

Bovine viral diarrhea virus (BVDV) has long been associated with a wide variety of clinical syndromes and immune dysregulation, many which result in secondary bacterial infections. Current understanding of immune cell interactions that result in activation and tolerance are explored in light of BVDV infection including: depletion of lymphocytes, effects on neutrophils, natural killer cells, and the role of receptors and cytokines. In addition, we review some new information on the effect of BVDV on immune development in the fetal liver, the role of resident macrophages, and greater implications for persistent infection.

Effects of Preinfection With Bovine Viral Diarrhea Virus on Immune Cells From the Lungs of Calves Inoculated With Bovine Herpesvirus 1.1

The aim of this work was to study the interstitial aggregates of immune cells observed in pulmonary parenchyma of calves preinfected with bovine viral diarrhea virus and challenged later with bovine herpesvirus 1. In addition, the intent of this research was to clarify the role of bovine viral diarrhea virus in local cell-mediated immunity and potentially in predisposing animals to bovine respiratory disease complex. Twelve Friesian calves, aged 8 to 9 months, were inoculated with noncytopathic bovine viral diarrhea virus genotype 1. Ten were subsequently challenged with bovine herpesvirus 1 and euthanized at 1, 2, 4, 7, or 14 days postinoculation. The other 2 calves were euthanized prior to the second inoculation. Another cohort of 10 calves was inoculated only with bovine herpesvirus 1 and then were euthanized at the same time points. Two calves were not inoculated with any agent and were used as negative controls. Pulmonary lesions were evaluated in all animals, while quantitative and biosynthetic changes in immune cells were concurrently examined immunohistochemically to compare coinfected calves and calves challenged only with bovine herpesvirus 1. Calves preinfected with bovine viral diarrhea virus demonstrated moderate respiratory clinical signs and histopathologic evidence of interstitial pneumonia with aggregates of mononuclear cells, which predominated at 4 days postinoculation. Furthermore, this group of animals was noted to have a suppression of interleukin-10 and associated alterations in the Th1-driven cytokine response in the lungs, as well as inhibition of the response of CD8+ and CD4+ T lymphocytes against bovine herpesvirus 1. These findings suggest that bovine viral diarrhea virus preinfection could affect the regulation of the immune response as modulated by regulatory T cells, as well as impair local cell-mediated immunity to secondary respiratory pathogens.

Pathogenic mechanisms implicated in the intravascular coagulation in the lungs of BVDV-infected calves challenged with BHV-1

Resistance to respiratory disease in cattle requires host defense mechanisms that protect against pathogens which have evolved sophisticated strategies to evade them, including an altered function of pulmonary macrophages (MΦs) or the induction of inflammatory responses that cause lung injury and sepsis. The aim of this study was to clarify the mechanisms responsible for vascular changes occurring in the lungs of calves infected with bovine viral diarrhea virus (BVDV) and challenged later with bovine herpesvirus type 1 (BHV-1), evaluating the role of MΦs in the development of pathological lesions in this organ. For this purpose, pulmonary lesions were compared between co-infected calves and healthy animals inoculated only with BHV-1 through immunohistochemical (MAC387, TNFα, IL-1α, iNOS, COX-2 and Factor-VIII) and ultrastructural studies. Both groups of calves presented important vascular alterations produced by fibrin microthrombi and platelet aggregations within the blood vessels. These findings were earlier and more severe in the co-infected group, indicating that the concomitance of BVDV and BHV-1 in the lungs disrupts the pulmonary homeostasis by facilitating the establishment of an inflammatory and procoagulant environment modulated by inflammatory mediators released by pulmonary MΦs. In this regard, the co-infected calves, in spite of presenting a greater number of IMΦs than single-infected group, show a significant decrease in iNOS expression coinciding with the presence of more coagulation lesions. Moreover, animals pre-inoculated with BVDV displayed an alteration in the response of pro-inflammatory cytokines (TNFα and IL-1), which play a key role in activating the immune response, as well as in the local cell-mediated response.

Pathology of African swine fever: the role of monocyte-macrophage

African swine fever (ASF) is a viral hemorrhagic disease with different clinical and lesional changes depending of virulence of strains/isolates and immunological status of pigs. In acute and subacute forms of ASF, severe vascular changes are present, with hemorrhages in different organs (mainly melena, epistaxis, erythema, renal petechiaes and diffuse hemorrhages in lymph nodes), pulmonary edema, disseminate intravascular coagulation and thrombocytopenia. Lymphopenia and monocytopenia are developed during acute and subacute ASF. Lymphopenia is associated with lymphoid depletion in primary and secondary lymphoid organs, which is caused by apoptosis. All these lesions are not related to viral replication in endothelial cells or lymphocytes. Monocytes-macrophages show viral replication and cytophatic effect, including hemadsorption. The more significant changes in these cells are increased number and secretory activation (increased levels of proinflammatory cytokines) in targets organs. Proinflammatory activation is the initial cause of clinical and lesional pictures in ASF, including fever and changes in levels of acute phase proteins. Levels of IFN-β and -γ are increased from initial phase of acute ASF. Anti-inflammatory response, represented by increased level of IL-10, is observed also, although in the final phase of acute ASF only.

Quantification and determination of spread mechanisms of bovine viral diarrhoea virus in blood and tissues from colostrum-deprived calves during an experimental acute infection induced by a non-cytopathic genotype 1 strain

To detect and monitor the sequential changes in virus levels, a reverse transcription quantitative real-time polymerase chain reaction assay using a TaqMan probe was carried out on frozen blood and tissues samples collected from calves experimentally infected with a non-cytopathic Bovine viral diarrhoea virus (BVDV) genotype 1 strain. Blood samples were collected among days 1-14 post-inoculation (p.i). On day 3 p.i, viral RNA was detected in blood samples from six of the eight inoculated animals. Viral RNA was detected in all remaining inoculated animals between 5 and 12 days p.i. The levels of viral RNA increased along the experiment, with a maximal peak between 6 and 9 days p.i. Analysis of virus load in tissues collected from calves euthanized on days 3, 6, 9 and 14 p.i displayed that BVDV was detected on day 3 p.i, being especially abundant in tonsils and ileocaecal valve, highlighting the role of tonsils as the main earliest viral replication sites as well as the principal source for virus spread to other lymphoid tissues and visceral organs. Coinciding with the highest viraemia levels, the highest viral loads were recorded at 9 days p.i. in tonsils, ileal lymph nodes, distal ileum and spleen, showing the main role of these secondary lymphoid organs in the pathogenic mechanisms of BVDV. However, virus levels in the liver and lung increased only towards the end of the infection. This fact could influence in the appearance of bovine respiratory diseases because of the capacity of BVDV for enhancing susceptibility to secondary infections.

Response of proinflammatory and anti-inflammatory cytokines in calves with subclinical bovine viral diarrhea challenged with bovine herpesvirus-1

The aim of this work was to investigate the susceptibility of calves infected with bovine viral diarrhea virus (BVDV) against secondary infections. For this purpose, the profile of cytokines implicated in the immune response of calves experimentally infected with a non-cytopathic strain of BVDV type-1 and challenged with bovine herpesvirus 1.1 (BHV-1.1) was evaluated in comparison with healthy animals challenged only with BHV-1.1. The immune response was measured by serum concentrations of cytokines (IL-1β, TNFα, IFNγ, IL-12, IL-4 and IL-10), acute phase proteins (haptoglobin, serum amyloid A and fibrinogen) and BVDV and BHV-1.1 specific antibodies. BVDV-infected calves displayed a great secretion of TNFα and reduced production of IL-10 following BHV-1 infection, leading to an exacerbation of the inflammatory response and to the development of more intense clinical symptoms and lesions than those observed in healthy animals BHV-1-inoculated. A Th1 immune response, based on IFNγ production and on the absence of significant changes in IL-4 production, was observed in both groups of BHV-1-infected calves. However, whereas the animals inoculated only with BHV-1 presented an IFNγ response from the start of the study and high expression of IL-12, the BVDV-infected calves showed a delay in the IFNγ production and low levels of IL-12. This alteration in the kinetic and magnitude of these cytokines, involved in cytotoxic mechanisms responsible for limiting the spread of secondary pathogens, facilitated the dissemination of BHV-1.1 in BVDV-infected calves.