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Scanning electron micrograph of a human T cell. Image credit: NIAID

We all know that it’s important to eat our greens, but can any of us actually explain why? Vitamins are critical for the normal growth and function of our bodies, but not always in entirely expected ways. In this latest blog, Lauren Howson explains how a subset of white blood cells can use vitamins to detect and fight bacterial infections. Who knew?

When referring to healthy food, you often hear people say: “It’s good for you, it’s full of vitamins.” But why do we actually need to eat our vitamins?

It’s because, unlike some plants and bacteria, we are unable to make vitamins ourselves and so we have to source them from our diet.

Because we don’t have the ability to make vitamins, all the intermediate products (or metabolites) created during the process of making vitamins are not found in our body.

Whilst perhaps not particularly remarkable in its own right, this is in fact a trait that is exploited by our immune system in its fight against bacteria.

It was only in the last few years that scientists discovered that immune cells not only recognise proteins as indicators of infection, but that there are also a specialised group of immune cells called Mucosal-Associated Invariant T (MAIT) cells that are able to recognise vitamin metabolites from the vitamin B group.

So when you have an infection the bacteria can be detected because they can produce vitamin B themselves (unlike us) and therefore the presence of vitamin B metabolites by the bacteria is a sure sign of infection.

The vitamin B intermediates are taken up by immune cells and presented to MAIT cells, which then assist the rest of the immune system to mount an effective immune response against the bacteria and clear it from the body.

Studying these cells and how they behave in different disease settings is an exciting area of research, and current knowledge of what we know about how these cells work and what they do in different disease settings is explored in a recent review from the Cerundolo group.

What we know so far is that MAIT cells are actually abundant in the human body, and make up around 5% of the total T cells (a type of white blood cell) in the blood, and up to 40% of the T cells in the liver.

Not only are these cells able to communicate with other immune cells to encourage immune responses, but they can also directly kill cells that are infected with bacteria. This makes them a key player in mounting successful immune responses against bacterial infections.

What is surprising is that MAIT cells are also found in regions of the body that have been damaged by autoimmune diseases. These are diseases where the immune system attacks the body instead of protecting it. So MAIT cell responses are not only controlled by the presence of vitamins but may also contribute to immune responses even when no bacteria is present.

With a greater knowledge of how MAIT cells work in the future we may be able to target these cells using vitamin metabolites to stimulate better immune response both in bacterial and non-bacterial diseases.

Another reason to eat your vitamins…

Post edited by Bryony Graham and Enzo Cerundolo.