Investigating the Immune Response to Feline Coronavirus

What is feline coronavirus?

Feline coronavirus is a virus that is present in almost all cat populations worldwide. In the majority of cats, feline coronavirus causes only mild disease and the cat will go on to recover completely. However, in a small proportion of infected cats, a deadly disease known as ‘feline infectious peritonitis’ will develop. There is no cure for feline infectious peritonitis.

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Why is it important to know about the immune response to feline coronavirus?

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Figure 1. Diagram to show how an ELISpot assay works. A plate is coated with tiny ‘hooks’ that capture a protein of interest; in this case the protein secreted by stimulated immune cells. A second set of ‘hooks’ against this protein is then added. These hooks are bound to a substance that turns purple, allowing us to see if the protein is present and therefore if the cells were stimulated.

It is not completely known why some cats with feline coronavirus develop only mild disease and recover while others succumb to feline infectious peritonitis and die, but mutation of the virus and the immune response of the cat are understood to be important factors. Our hypothesis for this study was that a particular mutation in the virus makes the immune system less able to respond effectively to the virus, therefore making it more likely that the cat will develop feline infectious peritonitis.

How was the immune response investigated?

Surplus blood available from cats, undergoing blood testing for feline coronavirus antibodies or other medical reasons, was used. The immune cells were extracted from the blood and tested with molecules representing the mutated and non-mutated versions of the virus to see which was better at stimulating the immune cells. This was done using a technique known as ‘ELISpot’ (see Figure 1). If the mutated virus was worse at stimulating the immune cells, this would suggest that the mutation made the immune system less able to respond effectively to the virus and would prove our hypothesis correct.


What did we find?

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Figure 2. Bar chart to show the feline coronavirus antibody levels of the 109 cats involved in the study. The vast majority of cats were positive for antibodies, particularly those from breeder households. This shows that feline coronavirus is very common and widespread.

A total of 109 blood samples were available, of which three quarters came from breeder households. Overall, 72% of cats had antibodies against feline coronavirus, but those from breeder households were significantly more likely to have antibodies compared to other cats (see Figure 2). This demonstrates how common feline coronavirus infection is, particularly in cats in breeder households.
Figure 2. Bar chart to show the feline coronavirus antibody levels of the 109 cats involved in the study. The vast majority of cats were positive for antibodies, particularly those from breeder households. This shows that feline coronavirus is very common and widespread.
Immune cells from 51 of these cats were tested with molecules representing the mutated and non-mutated versions of the virus (the remainder having been used to develop and optimise the ELISpot assay). The response to the mutated version of the virus was slightly worse, but this was not found to be statistically significant.

What will we do next?

The next step for the study is to continue testing more immune cells with molecules representing the virus. This will increase the sample size, allowing us to find out whether the slight difference observed between mutated and non-mutated was a coincidence or a real effect.

Who was involved in the study?

The study was carried out at the University of Bristol by Samantha Saunders, supervised by Dr Séverine Tasker, Dr Andrew Davidson, Dr Linda Wooldridge and Dr Anya Lissina. Feline coronavirus antibody testing was carried out by Leigh Marshall and Dawn Dunbar of Veterinary Diagnostic Services, University of Glasgow. Results were analysed with the assistance of Sian Llewelyn Lacey at the University of Cardiff. Surplus blood samples were kindly provided by veterinary surgeons with the cooperation of the feline patients and the consent of their guardians. Funding was generously provided by BBSRC, The Petplan Charitable Trust and The Langford Trust. The Langford Trust is particularly thanked for their funding of the laboratory consumables used in this study.

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