The innate and adaptive immune systems
The innate immune system
The innate immune system includes all your body's first-line defences such as the physical barriers lining the nose, throat, lungs and gut, as well as the skin. Innate immunity provides broad protection and is quick to react to any threat.1
One of the most important types of cell involved in innate immunity is a form of scavenger cell known as macrophages. These recognise common components on viruses and bacteria, and secrete chemicals called cytokines that alert the body to a threat. Macrophages can also 'eat' viruses and bacteria by absorbing and destroying them.1
Many other cells support the innate immune system, including mast cells, neutrophils and natural killer cells. These cells play many roles, including consuming invading microbes, destroying cells that have been infected with a virus or bacteria, and triggering inflammation as a first defence.1
In the short term, inflammation is beneficial as it increases blood flow and brings in more immune cells, nutrients and other factors needed to fight infection and promote healing.
The adaptive immune system
The adaptive immune system is a more specialised branch of immunity and is triggered by exposure to particular microbes such as bacteria or viruses. It then uses 'memory cells' to remember that particular microbe so it can respond more quickly the next time it is encountered. Unlike innate immunity, this more customised adaptive immune response is slow to respond to any threats, but it does prepare the body for a repeat attack.1 Adaptive immunity forms the basis for protective vaccinations against specific viral and bacterial infections.
When it comes to fighting off infections, the adaptive immune system responds to threats in two different ways. One of these responses, humoral immunity, involves B cells that produce specific antibodies to bind to invading microbes and neutralise them. The second type of response is cell-mediated immunity, in which T cells secrete chemical signals, called cytokines, that alert the immune system when a threat is present. These cytokines activate other immune cells, which will then consume or attack the microbes before they cause harm.1
How to optimise your immune system
There are plenty of ways to support a healthy immune system. Some are specific to the different branches of the immune system, and some will benefit both. These tips will get you started.
Eat a diet rich in wholefoods
When it comes to supporting immunity, food is a good starting point. Consuming a variety of wholefoods such as fruit, vegetables, nuts, seeds, eggs, seafood, quality meats, legumes and wholegrains helps to ensure you obtain the vitamins, minerals and other nutrients your immune system needs to function properly.
Exercise might not be the first thing that comes to mind for boosting immunity, but one study showed cyclists in their 50-70s have similar T cell counts to healthy young adults in their 20s and 30s.2
Exercise could also regulate the immune system. Another study found aerobic exercise reduced elevated white blood cells (WBCs) and neutrophils in women who were at high risk of developing heart disease. Elevated WBCs and neutrophils are signs of ongoing inflammation and may indicate an immune problem.3
Manage your stress
Stress isn't just bad for your brain function - it has negative effects on the immune system, too. Acute stress was found to suppress natural killer cells and monocytes (scavenger cells within the circulation) in students, leaving them more vulnerable to illness.4 Chronic stress can also impair the function of T-cells, which can affect adaptive immunity.5
Stress management needs to be tailored to what relaxes you. For some, it means going for a walk or a run. For others, meditation or keeping a journal could be most effective. If you feel overwhelmed by stress, speak to a GP, as professional help is available.
Getting enough high-quality sleep is essential for a healthy immune system, as sleep deprivation has numerous negative effects on both innate and adaptive immunity.
One research study found sleep deprivation reduced both natural killer cells and immune responses after just one night.6 Poor sleep can even alter immunity and inflammatory genes, leading to a suppression of the immune system's genetic programming.7
Everyone's sleep needs are different, but you should aim for at least 7 to 8 hours a night.
Consider if supplements are right for you
A number of nutrients and essential vitamins contribute to the normal functioning of the immune system. If your diet is lacking in these, a supplement might be a good option to bridge the gap.
Vitamin D regulates both the innate and adaptive immune systems, and can stimulate low immunity or help to calm overactive immune responses.8
Some studies suggest vitamin D may even prevent certain infections. A meta-analysis of 25 studies found that vitamin D supplements protect against respiratory infections, for example. The best results were seen in those who were vitamin D-deficient.9
Zinc is another nutrient that contributes to immune function. It's involved with innate immunity, supporting the function of white blood cells including neutrophils, natural killer cells and macrophages. Zinc can also influence the growth and function of B and T cells, supporting adaptive immunity.10
Not only is zinc essential for a healthy immune system, but research suggests it may shorten the duration of a cold. A systematic review showed that using zinc acetate lozenges could reduce the duration of a cold by up to 42%.11
If you're interested in learning more about how to keep your immune system healthy, please see our Immunity Advice Centre.