Working towards identifying the receptor for Type 1 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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Feline coronavirus can be either ‘Type 1’ or ‘Type 2’. The difference between the two strains is in the type of ‘spike’ protein that sits on the surface of the virus. This spike determines what receptor the virus uses to enter a cell, and therefore what kind of cells it can enter. Type 1 feline coronavirus is much more common than Type 2 in the UK and other countries.

Why is it important to find the receptor for Type 1 feline coronavirus?

Despite being the more common strain, much less is known about Type 1 feline coronavirus than Type 2. This is because, at present, scientists are unable to effectively grow Type 1 feline coronavirus in the laboratory. To overcome this problem, we must identify (or even create) a type of cell that will support the growth of Type 1 feline coronavirus. To do this, we must find out what receptor Type 1 feline coronavirus uses to get into the cell in the first place. Unfortunately we cannot use the cells that are naturally infected by Type 1 feline coronavirus – the cells lining the cat’s intestine – because we are unable to grow these in the laboratory.

Figure 1. Diagram to show how the bait will be used to detect the Type 1 feline coronavirus receptor. We hypothesise that the bait will bind to the receptor, allowing us to use the detectable structure to isolate it and find out what it is.

How are we working towards identifying the receptor for Type 1 feline coronavirus?

Tiny ‘baits’ have been designed and produced. These baits are the spike protein of Type 1 feline coronavirus bound to a detectable structure. Our plan is to take cells lining the cat’s intestine and mix them with the baits (see Figure 1). We hypothesise that the baits will bind to the receptor for Type 1 feline coronavirus and, using the detectable structure, we will be able to isolate the receptor and find out what it is.

How far have we got, and what are the next steps?

Prior to this project, the baits for Type 1 feline coronavirus were designed and produced. Baits for Type 2 feline coronavirus were designed and produced at the same time because, although we already know what receptor Type 2 feline coronavirus uses to get into the cell, these baits can be used to make sure that our laboratory method works well. In this project, we have worked on producing the baits, showing that the Type 2 baits bind to their receptor on the surface of cells in the laboratory (see Figure 2), and worked on a method to extract cells from cat intestinal tissue.

Our immediate objectives are to improve the efficiency of the bait production process and to successfully extract cells from cat intestinal tissue.

By working towards identifying the receptor for Type 1 feline coronavirus, we are closer to being able to grow the virus in the laboratory. In turn, this will allow us to study the virus to learn more about its behaviour and develop new ways of preventing and treating feline infectious peritonitis.

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Figure 2. Image to show the binding of the Type 2 baits to their receptor on the surface of cells. Each blue dot represents one cell, and the green colouration represents the Type 2 bait.

Who was involved in the study?

The study was carried out at the University of Bristol by Samantha Saunders, supervised by Dr Andrew Davidson and Dr Séverine Tasker. The baits were designed and produced by Dr Stuart Siddell. Cat intestinal cells were obtained post-mortem from cats euthanased for medical reasons at The Feline Centre, Langford Veterinary Services, with the assistance of veterinary surgeons and veterinary pathologists and the consent of the owners. Funding was generously provided by BBSRC, The Petplan Charitable Trust and The Langford Trust for Animal Health & Welfare.

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