The innate immune system is our first line of defence and in evolutionary terms is much older than the acquired immune system.

It is less specific; it can only recognise a limited number of compounds - around a dozen or so - that commonly occur on the surface of bacteria and yeasts. Its key cellular components are macrophages, neutrophils and Natural Killer (NK) cells.

Broadly, these ‘front line defensive troops’ constantly patrol the body and look out for anything that doesn’t belong there. If macrophages spot a bacterium they swallow it and try to digest it.

If NK cells recognise a virally infected cell they will kill it to prevent further viral replication, and if they encounter a cancer cell (and recognise it as cancerous) they will kill it to prevent tumour growth and spread.

The innate system can be strengthened by improved diet generally. We have also recently discovered how to ‘prime’ or boost it at times of additional threat – for example, in the cold and flu season, and when faced with stress and infections.