Which immune reactions are 'natural'?
When you are injured, or infected with germs, your body's first line of defence is often inflammation. Blood flow to the affected area increases, making it red, swollen and tender. The blood vessels become 'leaky', allowing defender cells to reach the injured or infected area. Some of the defender cells then produce chemicals that kill bacteria, or virus-infected cells. Others clear up the debris. Inflammation is triggered by special proteins, known as cytokines and complement proteins.