Tonsils. Tonsils are lumps of soft tissue and are part of the immune system. You have two tonsils, one on either side at the back of the mouth. Tonsils vary in size from person to person. A main function of tonsils is to trap germs (bacteria and viruses) which you may breathe in. Proteins called antibodies produced by the immune cells in the tonsils help to kill germs and help to prevent throat and lung infections.