Virology
Ovine pulmonary adenocarcinoma
Dr. Christine Cousins
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Fig 1. Dolly the sheep photographed with her lamb, Bonny. Picture courtesy of Roslin Research Institute. |
Ovine pulmonary adenocarcinoma (OPA) (previously known as sheep pulmonary adenomatosis (SPA) or Jaagsiekte) is a disease of considerable importance in the British sheep industry. The most significant victim of this disease was Dolly , the first cloned mammal (Fig 1). This contagious lung tumour is caused by a retrovirus known as Jaagsiekte sheep retrovirus (JSRV). Although the virus is now well characterised at the molecular level, little is known about the epidemiology, pathogenesis and immunology of the disease. These are now areas of active research by the team at MRI.
EPIDEMIOLOGY: We have developed protocols for analysing greater numbers of sheep blood samples for the presence of JSRV infected cells. In particular, a real time PCR method that can detect as few as 5 copies of JSRV provirus has been developed. This technique has several advantages over traditional PCR methods; the results are collected as the PCR runs improving speed, analysis takes place in closed tubes reducing possible contamination problems and the technique has the potential to quantify the number of infected cells in blood. The first blood samples have been collected for a study to follow, over several years, infected and uninfected ewes and their offspring. This study should provide important information on levels of infection compared to levels of disease. It should also indicate at what age sheep/lambs are most likely to become infected.
IMMUNOLOGY: We have put considerable emphasis in the past year on production of new and/or improved virus components for use as antigens in immune assays and as potential vaccines. Development of these assays and development of methods to induce immune responses go hand in hand as the basis of potential vaccination strategies. Lymphocyte stimulation assays were developed to determine specific immune responses to JSRV and recombinant JSRV proteins. We have previously shown that antibodies can be raised in sheep to the CA capsid antigen of JSRV and this year we showed for the very first time that a cell mediated immune response can also be induced with the appropriate immunisation protocol.
RELATED VIRUSES: In collaboration with the University of Zaragoza, Spain, we have sequenced the complete genome of caprine nasal tumour virus. This virus is closely related to JSRV but causes an infectious nasal tumour of goats. This disease has never been reported in the UK but is of considerable agricultural importance in several EU countries.