How does your immune system know the difference between 'self' and 'other'?

Your immune system has a special detective team that tells the difference between things that belong to you and things that don’t.

Imagine you’re playing with your toys, and someone brings in a new toy from another kid’s bag. Your detective team checks every toy, if it looks like one of yours, they say “this is self,” but if it looks different, they shout “other! Alert!”

Your immune system works the same way. Special cells called T-cells are like the detectives. They look at all the cells in your body, these are like your toys, and know what they should look like.

When something new comes in, like a virus, it looks different from your cells. The T-cells notice this difference and say “other!” Then they call in help to fight off the virus.

Sometimes, if the detective team gets confused, they might think one of your own cells is other, and that’s why you get sick or have allergies, like when you sneeze because you’re allergic to pollen.

So your immune system knows what's self and what's other, just like you know which toys are yours and which ones belong to someone else.