Question: how do your special white blood cells differ from others and why are they special

Matt Bilton answered on 12 Nov 2014:

I’m glad you asked this! There are lots of types of white blood cells, and they all have different and important jobs to do protecting us against pathogens. T cells and B cells are the white blood cells mainly responsible for remembering past infections – and so they are quite interesting for that reason.

Before you become infected with a bug for the first time, you will have tonnes of different types of T and B cells, with only very few that, by chance, will specifically recognise any given bad guy. During the immune response to infection, those few T and B cells that do recognise the invader will divide rapidly so that soon there will be enormous numbers of nearly identical T and B cells, clones of each other, ALL of which recognise the bad guy. After the infection has been cleared, some of those clones will remain so that in future they can much more quickly expand and help clear away the invader.

The white blood cells I research, MAIT cells, are unique for a few reasons. They are also a type of T cell – but unlike most other T cells, people generally have LOADS of them to begin with from a very young age. Some scientists in Australia recently discovered that MAIT cells can detect not just one type, but actually a large range of bacteria and even some types of fungi – so long as they make a small molecule called riboflavin, also known as Vitamin B2.

Because there are so many of them to begin with, MAIT cells may form an important part of how the immune system responds to bacterial infections. We know that they can make some powerful chemicals – called cytokines – and they can even target and kill human cells that have been infected by bacteria.

My research looks at what sort of role MAIT cells might play in the immune response against tuberculosis, which, without treatment, is a potentially deadly disease caused by bacteria. Many people around the world are infected with tuberculosis bacteria – over 2 billion people (1/3rd of the world’s population!) – but many will stay totally healthy and may never know what lurks inside them. Perhaps MAIT cells are playing some sort of role in helping to protect those people? Or maybe they are important for being able to attack the bacteria BEFORE the other T cells have had a chance to do anything. We don’t know for sure yet, but hopefully we’ll find out!