1005 GMT April 05, 2020
It’s been a long, wet winter. Everybody has got colds, and now we are braced for a coronavirus epidemic. Boosting our immune system has rarely felt more urgent, but, beyond eating more tangerines and hoping for the best, what else can we do?
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 said, first you need to understand the weapons in your armory — a cheeringly impressive collection, it turns out.
“When you come into contact with a germ you’ve never met before,” she said, “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, said 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 defenses, it has to deal with our white blood cells, or immune cells. One type, called macrophages, inhabit all our body tissue and, said 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,” said 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 recognize certain bugs,” she said, “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 defenses are as good as they get.
Seeing as our bodies contain more cells belonging to microbes, such as bacteria and yeasts, than human ones, let’s start with the microbiome. “We live in a symbiotic relationship with our gut bacteria,” said Prof Arne Akbar, the president of the British Society for Immunology and a professor at University College, London. “Having the right ones around, that we evolved with, is best for our health. Anything we do that alters that can be detrimental.”
Not only do our microbes form protective barriers, they also program our immune systems. Animals bred with no microbiome have less well developed immune responses. Older people, and those with diseases that are characterized by inflammation, such as allergies, asthma, rheumatoid arthritis and diabetes, tend to have less varied gut microbiomes.
To feed your gut flora, Cruickshank recommends “eating a more varied diet with lots of high-fiber foods”. Being vegetarian isn’t a prerequisite for microbiome health, but the more plant foods you consume, the better. “The microbiome really likes fiber, pulses and fermented foods,” she added.
Kefir yoghurt and pickles such as sauerkraut and kimchi are among the fermented delicacies now fashionable thanks to our increasing knowledge of the microbiome. But the evidence for taking probiotic supplements, she said, “is mixed”. It’s not a dead cert that they will survive the journey through your digestive tract, or that they will hang around long enough if they do. “It’s more effective to change your diet,” said Cruickshank.
The skin microbiome is important, too, but we know less about it. High doses of ultraviolet light (usually from the sun) can affect it negatively, weakening any protective functions (as well as triggering immune suppression in the skin itself). Overwashing with strong soaps and using antibacterial products is not friendly to our skin microbiomes. “Combinations of perfumes and moisturizers might well also have an effect,” said Cruickshank.
To be immunologically fit, you need to be physically fit. “White blood cells can be quite sedentary,” said Akbar. “Exercise mobilizes them by increasing your blood flow, so they can do their surveillance jobs and seek and destroy in other parts of the body.” The NHS said adults should be physically active in some way every day, and do at least 150 minutes a week of moderate aerobic activity (hiking, gardening, cycling) or 75 minutes of vigorous activity (running, swimming fast, an aerobics class).
*Amy Fleming is a freelance writer and former Guardian staff journalist.