Bluetongue virus - 23 stimulates inducible nitric oxide synthase expression and nitric oxide production in mononuclear cells of blood and/or regional lymphoid organs

An updated review on bluetongue virus: epidemiology, pathobiology, and advances in diagnosis and control with special reference to India

Bluetongue (BT) is an economically important, non-contagious viral disease of domestic and wild ruminants. BT is caused by BT virus (BTV) and it belongs to the genus Orbivirus and family Reoviridae. BTV is transmitted by Culicoides midges and causes clinical disease in sheep, white-tailed deer, pronghorn antelope, bighorn sheep, and subclinical manifestation in cattle, goats and camelids. BT is a World Organization for Animal Health (OIE) listed multispecies disease and causes great socio-economic losses. To date, 28 serotypes of BTV have been reported worldwide and 23 serotypes have been reported from India. Transplacental transmission (TPT) and fetal abnormalities in ruminants had been reported with cell culture adopted live-attenuated vaccine strains of BTV. However, emergence of BTV-8 in Europe during 2006, confirmed TPT of wild-type/field strains of BTV. Diagnosis of BT is more important for control of disease and to ensure BTV-free trade of animals and their products. Reverse transcription polymerase chain reaction, agar gel immunodiffusion assay and competitive enzyme-linked immunosorbent assay are found to be sensitive and OIE recommended tests for diagnosis of BTV for international trade. Control measures include mass vaccination (most effective method), serological and entomological surveillance, forming restriction zones and sentinel programs. Major hindrances with control of BT in India are the presence of multiple BTV serotypes, high density of ruminant and vector populations. A pentavalent inactivated, adjuvanted vaccine is administered currently in India to control BT. Recombinant vaccines with DIVA strategies are urgently needed to combat this disease. This review is the first to summarise the seroprevalence of BTV in India for 40 years, economic impact and pathobiology.

Inhibition of the IFN Response by Bluetongue Virus: The Story So Far

Bluetongue virus (BTV) is the prototypical orbivirus that belongs to the Reoviridae family. BTV infection produces a disease in ruminants, particularly in sheep, that results in economic losses through reduced productivity. BTV is transmitted by the bite of Culicoides spp. midges and is nowadays distributed globally throughout subtropical and even temperate regions. As most viruses, BTV is susceptible to the IFN response, the first line of defense employed by the immune system to combat viral infections. In turn, BTV has evolved strategies to counter the IFN response and promote its replication. The present review we will revise the works describing how BTV interferes with the IFN response.

Pathological and immunological characterization of bluetongue virus serotype 1 infection in type I interferons blocked immunocompetent adult mice

Introduction

Wild-type adult mice with intact interferon (IFN) system were neither susceptible to bluetongue virus (BTV) infection nor showed signs of morbidity/mortality. Establishment of immunologically competent wild-type adult mouse model with type I IFNs blockade is necessary to assess the pathogenesis, immune responses and testing of BTV vaccines.

Objectives

Present study aimed to establish and characterize BTV serotype 1 infection in immunocompetent adult mice with type I IFNs blockade at the time of infection by studying immune responses and sequential pathology.

Methods

Adult mice were administered with anti-mouse IFN-α/β receptor subunit-1 (IFNAR1) blocking antibody (Clone: MAR1-5A3) 24 h before and after BTV serotype 1 infection, and sacrificed at various time points. Sequential pathology, BTV localization by immunohistochemistry and quantification by qRT-PCR, immune cell kinetics and apoptosis by flow cytometry, and cytokines estimation by c-ELISA and qRT-PCR were studied.

Results

IFNAR blocked-infected mice developed clinical signs and typical lesions of BT; whereas, isotype-infected control mice did not develop any disease. The IFNAR blocked-infected mice showed enlarged, edematous, and congested lymph nodes (LNs) and spleen, and vascular (congestion and hemorrhage) and pneumonic lesions in lungs. Histopathologically, marked lymphoid depletion with “starry-sky pattern” due to lymphocytes apoptosis was noticed in the LNs and spleen. BTV antigen was detected and quantified in lymphoid organs, lungs, and other organs at various time points. Initial leukopenia (increased CD4⁺/CD8⁺ T cells ratio) followed by leukocytosis (decreased CD4⁺/CD8⁺ T cells ratio) and significantly increased biochemical values were noticed in IFNAR blocked-infected mice. Increased apoptotic cells in PBMCs and tissues coincided with viral load and levels of different cytokines in blood, spleen and draining LNs and notably varied between time points in IFNAR blocked-infected mice.

Conclusion

Present study is first to characterize BTV serotype 1 infection in immunocompetent adult mouse with type I IFNs blockade. The findings will be useful for studying pathogenesis and testing the efficacy of BTV vaccines.

Betulinic acid‑induced expression of nicotinamide adenine dinucleotide phosphate‑diaphorase in the immune organs of mice: A possible role of nitric oxide in immunomodulation

The aim of the present study was to investigate the effects of betulinic acid (BetA) on the expression and distribution pattern of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH‑d), an indirect indicator of nitric oxide (NO) synthase in the thymus and spleen of mice. Mice were randomly assigned to four main groups (n=48 per group): Experimental group (BetA), positive control group (goniothalamin), vehicle control group (dimethyl sulfoxide) and control group (without vehicle). Each group was further divided into three equal subgroups according to the treatment length (4, 8 and 12 days). BetA treatment induced the expression of NADPH‑d activity in the thymus and spleen without any significant changes in the morphology of the organs. Furthermore, the expression pattern of NADPH‑d in BetA‑treated animals was significantly increased compared with that in the control animals. NADPH‑d expression in the thymus and spleen suggests that NO signaling may be a potential mechanism underlying the BetA‑induced immunomodulation in these organs. These findings are of direct clinical relevance and may contribute to the further development of BetA as a therapeutic drug.

Pathological Characterization Of IFNAR(-/-) Mice Infected With Bluetongue Virus Serotype 4

Bluetongue virus (BTV) replicates in lymphoid tissues where infected mononuclear leukocytes secrete proinflammatory and vasoactive mediators that can contribute to bluetongue (BT) pathogenesis. Using the well-characterized IFNAR(-/-) mice animal model, we have now studied the histopathology and dynamics of leukocyte populations in different target tissues (spleen, thymus, and lung) during BTV-4 infection by histological and immunohistochemical techniques. The spleen and thymus of BTV-4 infected mice showed severe lymphoid depletion on H&E stained sections. This finding was confirmed by IHC, showing moderate decreased immunopositivity against CD3 in the thymus, and scarce immunoreactivity against CD3 and CD79 in the rest of the white pulp in the spleen, together with an increase in MAC387 immunostaining. BTV-4 infection also induced the expression of active caspase-3 in the spleen, where apoptotic debris was observed by H&E. A dramatic increase in iNOS immunoreactivity associated to necrotic areas of the white pulp was observed, being less noticeable in the thymus and the lung. The induction of pro-inflammatory cytokines in tissues where BTV replicates was evaluated by measuring transcript levels by RT-qPCR. BTV-4 infection led to enhance transcription of IFN-γ, TNF, IL-6, IL-12-p40, and IL-1β mRNA in the thymus, spleen and lung, correlating with the level of virus replication in these tissues. Disease progression and pathogenesis in IFNAR(-/-) mice closely mimics hallmarks of bluetongue disease in ruminants. IFNAR(-/-) mice are a good choice to facilitate a faster advance in the field of orbiviruses.