THE GUARDIAN: How to boost your immune system to avoid colds and coronavirus

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Sheena Cruickshank, a professor of immunology at the University of Manchester, has a “shocking cold” when we speak at a safe distance, over the phone. To know how to take care of your immune system, she says, first you need to understand the weapons in your armoury – a cheeringly impressive collection, it turns out.

“When you come into contact with a germ you’ve never met before,” she says, “you’ve got various barriers to try to stop it getting into your body.” As well as skin, we have mucus – “snot is a really important barrier” – and a microbiome, the collective noun for the estimated 100tn microbes that live throughout our bodies, internally and externally. Some of these helpful bugs make antimicrobial chemicals and compete with pathogens for food and space.

Beneath these writhing swamps of mucus and microbes, our bodies are lined with epithelial cells which, says Cruickshank, “are really hard to get through. They make antimicrobial products including, most relevant to coronavirus, antiviral compounds that are quite hostile.”

If a pathogen breaches these defences, it has to deal with our white blood cells, or immune cells. One type, called macrophages, inhabit all our body tissue and, says Cruickshank, “have all these weapons ready to go, but they’re not terribly precise”. They report to the cleverer, adaptive white blood cells known as lymphocytes. They are the ones that remember germs, “so if you meet that germ again,” says Cruickshank, “they’ll just deal with it probably without you even knowing. That’s when you’ve got immunity and is the basis of vaccination. It’s trying to bypass all the early stuff and create the memory, so you don’t have to be sick.”

Our immune systems may have blind spots. “This might mean that our immune response doesn’t recognise certain bugs,” she says, “or the bugs have sneaky evasion strategies. Personally, my immune system is not necessarily very good at seeing colds.” But a healthy lifestyle will ensure your defences are as good as they get.