Read more: “Immune retune: Recharging your body’s natural defences“
Like most parts of the body, the immune system weakens with age. That is why older people catch more infections, are more likely to get cancer, and are more prone to shingles, a painful rash caused by the chicken pox virus reactivating after lying dormant for years.
You can’t stop yourself from growing older but that doesn’t mean you have to just sit there and take it. At the moment the only option is to take a leaf out of the kids’ book and get fully vaccinated. As well as annual flu shots, older people can get a one-off vaccine for pneumococcal disease, which causes pneumonia and meningitis, and the “childhood” jab against diphtheria, tetanus and pertussis. A vaccine giving partial protection against shingles has also recently been developed.
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In future there may be more high-tech countermeasures, such as rejuvenating the thymus – a gland in the chest where an important class of immune cells called T-cells mature. From puberty onwards the thymus gradually shrinks and is taken over by fat, and then it is downhill all the way.
There may be ways to reverse this decline, though. One candidate is injections with growth hormone, which has shown promise in .
Visible ageing is also seen at the cellular level. Every time immune cells multiply in response to a bug they recognise, parts of their chromosomes called telomeres shorten until there are none left. At this point they lose the ability to divide and become useless. As people age, more and more of their circulating immune cells approach the end of their lifespan.
This is unavoidable, but there is one microbe it might be particularly helpful to steer clear of: cytomegalovirus (CMV). Most people have a long-standing dormant infection with CMV which reawakens every so often, perhaps due to stress. This causes unusually widespread activation of immune cells, so hastening their decline. One theory is that CMV plays a key role in immune ageing. If that’s true, then there is good news – a vaccine against CMV is on the cards ().