To be immune means to be protected, and in a healthy body, this is exactly what our immune system does for us every second of the day. It does this with the use of specialised cells, tissues and organs, both inside and outside the body, to help keep pathogens - bacteria, virus, fungi and parasites - at bay. However, before the immune system is fit for purpose, it is crucial that it can differentiate between cells that are 'self' and those which are 'non-self'. Self are our ow