Parasitology
Protective immunity against Neospora caninum
Innes, L
Neospora caninum is a protozoan parasite, closely related to Toxoplasma gondii, that has emerged as a major cause of reproductive failure in cattle worldwide. Cattle infected with the parasite are 3-7 times more likely to abort than uninfected cattle, with infected heifers at the highest risk. To enable the development of effective control strategies against bovine neosporosis there is a need to understand more about how the parasite causes disease and how the host immune system fights the infection.
Neospora caninum, in common with other obligate intracellular parasites, can only multiply within the cells of the host organism. Activated T-lymphocytes (T-cells) can recognise and respond to parasite-infected cells. Through direct action or the production of soluble factors (cytokines), such as interferon gamma (IFNγ), T-cells can significantly inhibit parasite multiplication, thus contributing to protection of the host. The pregnant adjusts its immune system to allow the mother to carry what is essentially a foreign tissue graft (the foetus) without immunological rejection taking place. Studies examining cytokine regulation in pregnancy have shown that the environment in the placenta favours more regulatory cytokines such as interleukin 10 (IL-10) and transforming growth factor beta (TGF-ß) whose role is to counteract the inflammatory cytokines such as IFNγ. In addition, inflammatory cytokines, known to be protective against N. caninum, can, when present in placental tissues, compromise the pregnancy resulting in foetal death.
Therefore N. caninum infection presents a dilemma for the pregnant cow since the natural immunomodulation occurring during pregnancy may alter her ability to effectively control the infection, while the immune response made to fight the infection may in itself compromise the pregnancy.
To help us understand why some infected cattle abort their foetuses while others do not, this project aims to compare maternal and foetal immune responses in N. caninum infected cattle where foetal death has occurred with those infected cattle carrying live foetuses. A further aim of the project is to examine whether control of the disease is possible through vaccination.